Radiology Flashcards
What 2 changes occur to protons when RF pulse is applied?
- More protons flip from spin up to spin down (the result is that Mz component of M0 decreases)
- Protons precess in phase (the result is that transverse magnetization progressively increases)
** net result of these two is that the net magnetization vector will progressively tilt away from initial orientation with its tip describing a spiral motion from the north pole to its equator
Mai
What is longitudinal relaxation?
90 degree RF pulse –> net magnetization shifted into the transverse plane –> RF pulse stops –> longitudinal magnetization (z-axis) progressively grows back to its initial (maximum) value
AKA spin lattice relaxation
Mai
What is spin-spin relaxation?
90 degree RF pulse applied –> neg magnetization shifted into the transverse plane –> RF pulse stopped –> rapid DECREASE in the amplitude of transverse magnetization
AKA transverse relaxation
Results from progressive de-phasing of protons due to:
- brownian motion
- magnetic field inhomogeneities
- movement of spins
Mai
T/F: The rate of regrowth of longitudinal magnetization is the same as rate of decrease of transverse magnetization after the end of RF pulse
FALSE
- Regrowth of longitudinal magnetization and decrease in transverse magnetization are due to independent processes:
- energy exchange between protons and microenvironment
- rapid dephasing of the precession motion of the protons
- The decrease in transverse magnetization (T2) is much faster than the regrowth of longitudinal magnetization (T1)
Mai
What is free induction decay?
During relaxation, the tip of the transverse component of the net magnetization vector describes a spiral in the XY plane
This rotating magnetic field in the XY plane can generate an electrical signal in a receiving coil placed in the XY plane
Mai
How do magnetic field inhomogeneities infleunce T2 relaxation?
- Magnetic field inhomogeneities make dephasing of protons during relaxation much faster so that Mxy actually decreases at a much faster rate than expected
- The resulting decrease in transverse magnetization is characterized by T2* (which is significantly less than T2)
- T2* is heavily dependent on the strength of B0 (it is harder to obtain a homogeneous field in a high-field system)
- T2 is independent of B0
- Due to magnetic field inhomogeneities, the signal measured (FID) does not only reflect the magnetic properties of the tissue, but is compounded by extrinsic inhomogeneities of B0
Mai
Regarding spin echo sequence - what is the effect of the 180 degree pulse applied?
180 degree pulse cancels out onl the fixed magnetic field inhomogeneities (but not the intrinsic spin-spin interactions)
- t=0, 90 degree RF pulse applied –> all protons are in phase causing transverse magnetization to be maximum
- Rapidly, protons start to lose phase coherence
- At t=180 after the end of the RF pulse, a 180 degree pulse is applied –> spins move symmetrically across the y-axis
- after a time equal to 2x t180, the spins are again in phase and Mxy is maximal
- this is the ECHO
- occurs at time = TE
- The newly created Mxy (Mxy2) has LESS amplitude than the initial one
The longer one waits to apply the 180 pulse, the weaker the echo signal will be (more irreversible spin-spin relaxation will have occurred in the sample)
Mai
To obtain an echo at a specific TE, one needs to apply a 180 RF pulse at ________ seconds after the RF pulse
Why does the 180 RF pulse not affect T1 relaxation?
TE/2
180 degree pulse will influence longitudinal relaxation but is usually negligible because TE/2 is very short in comparison with T1
(There has been minimal regrowth of T1 by the time the 180 pulse is applied)
Mai
After initial 90 degree, then 180 degree RF pulse are applied, what needs to happen before the next 90 degree RF pulse can be applied?
Wait a sufficient amount of time for Mz to have regrown enough so that a 90 degree pulse will be able o shift that new magnetization into the XY plane again
This is called the REPETITION TIME = TR
Mai
How are FOV, matrix size, and spatial resolution related?
For a given FOV, if the matrix size increases, the size of each individual pixel decreases –> spatial resolution increases
Mai
Regarding fourier transformation, what is the significance of the high amplitude/low frequent components vs. the high frequenc/low amplitude components?
High amplitude, low frequency components –> general shape and contrast
High frequency, low amplitude –> detail and spatial resolution
Mai
What is spatial encoding?
MRI signal is detected - need a way to localize the spatial origin of that signal and attribute it to a specific voxel
Relies on:
- magnetic field gradients
- fourier transformation
Mai
How is a linear gradient created?
How is a slice selection gradietn created?
Gradient coils
- A gradietn is applied along the axis of the main magnetic field B0
- the gradient is centered at the isocenter of the bore
Slice selection gradient
- because of the linear gradient created by gradient coils, in a transverse plane perpendicular to B0 and located at some distance d from the isocenter, all protons will process at a unique frequency (that is dependent on the strength of the gradient and the distance)
- apply an RF pulse that is tuned to that specific frequency –> only the protons located n the specific slice will experience resonance and be excited
- the other protons in the volume of the bore are processing at different frequencies and thus will be insensitive to that RF pulse
Mai
What determines slice thickness?
- Transmit bandwidth
- in reality, the RF pulse contains a small range of frequencies called the transmit bandwidth
- it is a slab of a certain thickness, proportional to the frequency range, that gets excited by the RF pulse
- wider transmit bandwidth –> thicker slice (and shorter RF pulse frequency)
- Changing the strength of the slice selection gradient
Mai
4 radiographic changes of discospondylitis:
How do radiographic changes in young dogs vary from adults?
- osteolysis of vertebral end plates and vertebral bodies
- collapse of the intervertebral disc space
- variable sclerosis adjacent to the osteolytic regions
- variable osseous proliferation adjacent to the intervertebral disc spaces
Young dogs - intervertebral disc space narrowing without vertebral end plate osteolysis
- over time, majority developed osteolysis of vertebral metaphysis with appearance similar to adult dogs
- 8/10 had subluxation at initial diagnosis or follow up
Vet Clin N America
Vertebral physitis = osteolysis initially restricted to the _________ vertebral physis
Caudal vertebral physis
Eventually collapse of the caudal vertebral body, spondylosis of caudal vertebral body occurs
Acinetobacter and Enterococci species have been isolated from vertebral biopsy material
Vet Clin N America
CT abnormalities in patients with discospondylitis?
Same as radiography: osteolysis of adjacent vertebral end plates, with or without osteolysis of the underlying bone
Vet Clin N America
Radiographic evidence of healing discospondylitis? (2)
Replacement of lytic bone by osseous proliferation
Ankylosis of the vertebrae
Vet Clin N America
MRI characteristics of discospondylitis
- end plate changes
- cortical bone changes
- soft tissues
- intervertebral discs
- empyema
- spinal cord changes
- end plate changes - T1 hypointense (or mixed signal), T2 hypointense (or hyperintense), STIR hyperintense, contrast-enhancing
- cortical bone changes - cortical lysis and irregularity
- soft tissues - abnormal soft tissues adjacent to the affected vertebrae
- intervertebral discs - hyperintense on STIR and T2W, isointense on T1W, contrast enhancing
- empyema - T1 hypointense, T2 and STIR hyperintense, contrast enhancement (rim enhancement or diffuse enhancement)
- spinal cord changes - T2 hyperintensity of the spinal cord (no correlation with severity of signs)
Vet Clin N America
What sequences should be included in MRI for discospondylitis
- T1 pre and post contrast
- T2 fat sat?
- STIR
Vet Clin N America
Processes that affect the appearance of end plates on MRI (5)
- Reactive end plate changes
- Fatty infiltration of the body and end plates
- End plate sclerosis
- Osteochondrosis
- Schmorl nodes
Vet Clin N America
Rate of positive culture using fluoroscopically guided disc aspirates?
9/10
Vet Clin N America
Discospondylitis starts as an infection of that anatomic structure?
5 most common discospondylitis organisms?
4 Risk factors for discospondylitis?
Discospondylitis - infection of the cartilaginous end plates of the vertebral bodies –> secondary involvement of the intervertebral disc
Staphylococcus, then Strep, Brucella, E. coli, Enterobacter
Risk factors:
- lg breed
- intact male
- recent corticosteroid administration
- recent surgery
Vet Clin N America
What 3 parameters define the spatial resolution of an MR image?
- Dimensions of the FOV
- Slice thickness
- Size of the image matrix
For a given FOV: increasing the matrix size –> decreases pixel dimension –> increases resolution
Increasing slice thickness –> decreases resolution in the direction perpendicular to the image plane
Larger voxes lead to increased volume averaging
Mai
What is phase wrap around? How is it prevented?
MRI artifact that occurs when the dimensions of an object exceed the defined FOV
- A type of aliasing where large phase shifts in the periphery of an object are mismapped into lower phase shifts near the center
- More severe along the phase-encoding axis
Prevented:
- FOV in the PE direction needs to be larger than the area of anatomy being imaged
- Phase oversampling
MRI Q&A
How are gradient strength, bandwith, and FOV related?
For a given gradient strength: smaller bandwidth –> smaller FOV
Fixed bandwidth: increased gradient strength –> smaller FOV
** in practice the technician specifies the FOV desired in the frequenting encoding direction and has no access to gradient strength
Bandwitch can be modified at the control station in order to improve SNR (decreasing bandwitch)
The machine automatically adjusts the frequency encoding gradient strength to maintain the specified FOV
How can sampling frequency result in aliasing/wrap?
For a given sampling frequency, there is a risk that high frequencies may not be sampled and represented accurately in the MR signal leading to aliasing or wraparound artifact
Mai
For a standard spin-echo pulse sequence, when is the slice selection gradient applied in relation to the RF pulses?
When is the phase encoding gradient applied?
When are the frequency encoding gradients applied?
Slice selectin gradient is applied simultaneously with the RF pulses so that these pulses are selective of the slice of interest
Phase encoding gradient applied between the 90° and 180 degree pulses
Frequency encoding gradients applied during the application of phase-encoding gradients, and at the same time the echo is formed (during readout of the MRI signal)
Mai
What kind of TE and TR are required for T1W imaging?
What kind of TE and TR are required for T2W imaging?
PDW imaging?
T1W imaging: short TR, short TE
T2W imaging: long TR, long TE
PDW: long TR (minimizes T1 differences of various tissues); short TE (minimizes differences of T2 of various tissues) - only proton density determines the signal of the image
Mai
What are:
- MRI sources of noise? (2)
- Noncontrollable factors influencing SNR? (2)
- Controllable factors influencing SNR? (4)
MRI sources of noise:
- Patient’s body (emits RF energy due to thermal motion)
- Receiver chain (preamplifier, RF receive coil)
Noncontrollable factors influence SNR:
- Magnetic field strength (B0 increases, increase signal to read)
- Relaxation times of tissues (determines the amount of signal available for readout)
Controllable factors that influence SNR:
- Volume of voxels (larger voxels = more protons = more signal, less resolution)
- Receiver bandwidth
- Number of exitations
- Number of PE steps (number of pixels in the PE direction)
Mai
What are operator-controlled parameters that influence SNR? (4)
TR: longer TR –> more longitudinal magnetization has recovered –> more magnetization available for next pulse –> more signal
TE: Longer TE –> less transverse magnetization remains –> lower signal
Flip angle: Flip angle < 90, lower amplitude of transverse magnetization, less signal
Type of receiver coil
Mai
What factors control acquisition time?
Number of phase encoding steps = number of pixels in the phase encoding direction
NEX = number of excitations
TR = time to repetition
Mai
Series of events for spin echo sequence?
T0: 90 degree RF pulse (shifts net magnetization into the transverse plane)
TE/2: 180 degree RF pulse tuned to the slice of interest
TE: progressive rephasing of the protons, signal readout (while FE gradient is turned on for a period of time that depends on chosen rBW)
TR: after readout, new 90 degree RF pulse is applied
One echo is obtained per TR, filling 1 line of K space at a time
Mai
How does gadolinium affect T1 relaxation?
Shortens the T1 relaxation time of protons –> longitudinal magnetization recovers much faster –> more measurable transverse magnetization
Mai
How does fast spin echo differ from spin echo?
Fast spin-echo uses separate phase-encodings for each echo, allowing accelerated imaging
- in conventional spin echo, all echoes are recorded with the same TE
- in FSE, pulse sequences are collected at various TEs with 1 TR
- “if we use shallow gradients for the echoes within the echo train that occur at the desired TE, we maximize signal contrast for these echoes, and thus obtain an appropriately weighted image
- FAT tends to be BRIGHTER on TW FSE images
- Susceptibility artifacts (ex/ metal implants) are reduced with FSE
MRI Q&A
What MRI sequence is described by the following: Single 90° RF pulse –> little over half of the lines of K space acquired within 1 TR. The other half is synthesized using conjugate symmetry of k-space
Single-shot fast spin-echo
- short acquisition time = low SNR
- long echo train after single excitation –> severe T2 blurring artifacts in the PE direction –> significantly degrades image quality
- Clinical applications:
- used to image tissues with long T2 relaxation times
- myelogram effect on sagittal images of the spine - quick snapshot of the subarachnoid space in a short time, rapid detection of spinal cord compressive lesions and areas of dilation of the subarachnoid space
Mai
Which MRI sequence fits the following description:
Same principles as spin echo, except an additional 180° RF preparation pulse occurs at time T1, that is equal to the nulling time of the longitudinal magnetization of the tissue that is targeted
Inversion recovery
- STIR - TI is short (matching the nulling time of fat)
- Nulling of fat with STIR is more efficient than with the fat saturation techniques as STIR is not sensitive to magnetic field inhomogeneities
- Cannot be used with gadolinium contrast because the T1 of enhancing tissue is shortened, closer to that of fat –> enhancing tissues will be suppressed on STIR images
- FLAIR - TI is calculated so that signal from fluid is nulled
- relatively pure fluids (CSF) have long relaxation times
- FLAIR can be made with T1 or T2 images depending on TR and TE values
Mai
What MRI sequence describes the following:
- Strategy to generate an echo that does not rely on 180° RF pulse
- RF pulse generates a transverse magnetization –> dephasing gradient is applied in the frequency encoding direction, then the rephasing gradient is applied in the frequency encoding direction (opposite polarity, equal strength) –> progressive rephasing of protons and regrowth in transverse magnetization
Gradient echo imaging - reversal gradient
- Smaller flip angles
- Shorter TR and TE –> faster acquisition times
- Echo is created by biphasic gradient (dephasing/rephasing)
- Transverse magnetization decays according to T2* (does not compensate for dephasing of spins caused by tissue magnetic susceptibilities)
Mai
How does SNR of gradient echo sequence image compare with SNR of spin-echo sequence?
What factors control imaging weighting of gradient echo images?
SNR tends to be reduced compared with spin-echo sequences due to smaller flip angle and decreased TR
Image weighting of gradient echo: depends on TR, TE and flip angle
- TR is always short - main determinants are TE and flip angle
- A significant degree of T2* weighting is always present
- T1 weighting: flip angle > 70°, short TE
- T2* weighting: flip < 20°, long TE
- PDW: flip angle < 20°, short TE
Mai
Clinical applications for gradient echo pulse sequences:
- High sensitivity to magnetic susceptibility - used to identify hemorrhage (low flip angle, long TR, long TE)
- single slice breath hold image for abdominal scanning for dynamic contrast enhancement studies
- MR angiography
Mai
Which MRI sequence describes the following:
MRI signal made of 2 components:
- Classic echo from FID induced RF excitation, weighted in T1 or proton density
- Rephased (stimulated echo) from the residual transverse magnetization (transverse coherence) weighted more in T2*
Steady state gadient echo/rewound gradient echo/coherent gradient echo
- The signal is T2* and T1W because it is contributed to by transverse coherence and longitudinal magnetization tilted by the RF pulse
- Steady state gradient echo imaging, TR is very short, tissue with longer T2 do not loose their transverse magnetization between 2 excitation RF pulses. There is a permanent longitudinal and transverse magnetization
- Image contrast depends on the ratio of T2/T1
Mai
What MRI sequence describes the following:
Gradient echo imaging where the residual transverse magnetization following signal readout is altered so that only a longitudinal component contributes to the net magnetization vector
Spoiled gradient echo = incoherent gradient echo
- because transverse magnetization is spoiled, the residual signal depends less on T2/T2*, and more heavily on T1
- Spoiling done in 2 ways:
- Application of spoiled gradient –> dephases transverse magnetization
- Excitation RF pulses of variable phase in a pseudo random fashion (called RF spoiling)
- Excellent T1 contrast, fast imaging, sensitivity to flow make them suitable for MRI angiography
Mai
Which MRI sequence describes the following:
Gradient echo sequence that allows acquisition of more heavily T2W images by recording only the signal from the echoes from the residual transverse magnetization
Time reversed gradient echo
- Represents a T2 contrast enhanced approach
- Gradients are applied prior to the RF excitation pulses (as opposed to simultaneous to them) –> no gradient echo from the pure FID is recorded
- Signal is more T2W because it is generated in the form of a spin echo
Mai
What physiologic processes result in isotropic restriction of water motion?
Neoplasia with high cellular density - compresses the extracellular space and restricts free diffusion of water in the EC space
Cytotoxic edema - water molecules move in the intracellular compartment where their movement is impaired by cell membranes and intracellular organelles
Mai
What MRI sequence is described by the following:
2 diffusion gradients, either in slice selection, phase encoding, or frequency encoding direction are placed symmetrically on either side of the 180 RF pulse of the spin echo sequence
Classic DWI
- Duration and amplitude of the 2 gradients are identical
- First diffusion gradient –> phase to be acquired by protons in water molecules in the voxel
- If protons move out of the voxel prior to the application of the second diffusion gradient - that phase is not reversed by the second diffusion gradient –> drop in signal in the voxel
- If the water molecule has restricted motion and remains in the voxel between the 2 diffusion gradients, the phase acquired during the first diffusion gradient and inverted by 180 pulse is completely reversed by the second diffusion gradient –> high signal in the voxel
- Typically this is repeated 3x by applying the diffusion gradients in the slice selection, frequency encoding and phase encoding gradients - assessment of movement of restriction of water is performed in all 3 directions of space
Mai
What is used to model the amplitude of diffusion in diffusion weighted imaging?
B-value
- An image is obtained with a B value of 0 = no diffusion = T2W
- An image is obtained with a b value of > 0 (typically around 1000) = DWI
- From that information, an ADC can be determined within each voxel that measures the absolute diffusion of water between the 2 images
- This is displayed on an ADC map - restricted motion appears black and unrestricted motion has a brighter signal
Mai
______ vertebrae result from a failure of segmentation in the developing vertebrae
Block vertebrae result from a failure of segmentation in the developing vertebrae
- can involve fusion of the vertebral bodies, arches, or entire vertebrae
- Often incidental BUT there may be instability and an increased likelihood of intervertebral disc herniation at the site adjacent to block vertebrae
- Results from fusion of 2+ vertebral bodies +/- vertebral arches
- Disc space seen as radiolucent line
- Most common in the cervical region
- Fused sacral vertebrae = normal block vertebrae
(BSAVA Manual, Thrall)
Myelograph induced seizures have been reported to occur in _______% of patients and are more likely to occur in ______ patients
Why should CSF be collected prior to myelography?
Myelograph induced seizures have been reported to occur in 10-20% of patients and are more likely to occur in large patients
Myelograph contrast medium induces mild meningitis that makes csf interpretation within a WEEK of myelography difficult
(BSAVA Manual)
What type of compression?
Extradural - displacement of at least one contrast column is seen in at least one projection
Brain Camp
Sacral OCD
- Arrow - multiple small but highly attenuating osseous fragments are seen within the vertebral canal at the level of the lumbosacral junction
- large arrowhead - there is a defect of the craniodorsal margin of the first sacral body (angular flattening of the bone)
- small arrowhead - lumbosacral intervertebral disc space is widened and a soft tissue mass containing the fragmented bone protrudes into the vertebral canal, indicative of intervertebral disc herniation and possible dorsal ligamentous hypertrophy
(Atlas of Small Animal MRI and CT)
What were associated risk factors for seizures in dogs after iohexol for myelogram according to Barone et al?
What was the overall prevalence of seizures in the study?
Prevalence of seizures was 21.4% (dog had at least 1 generalized seizure during or after myelography)
Risk factors:
- injection site (cerebellomedullary injection 7x > lumbar)
- Mean total volume higher in dogs that developed seizures
- Dogs weighing > 20kg
*dogs that did NOT have surgery were more likely to have a seizure
Barone et al 1998
MRI characteristics of MLO according to Lipsitz et al?
T1W - hypointense as compared to brain, not as hypointense as CSF
PDW and T2 images - hypointense as compared to brain with central hyperintensities
T1WI+C - 2/3 dogs had rim of contrast enhancement, areas of uniform enhancement interspersed with nonenhancing regions
1/3 dog had uniform enhancement
Lipsitz et al 2001
T/F: Meningeal enhancement was consistently identified in dogs with intracranial extension of orbital infection? (according to Kneissl et al)
False - definite meningeal enhancement was not observed in any dog in this study
MRI features of intracranial extension or orbital disease:
- Structures within and in continuity with the skull foramina had increased T2, STIR, and FLAIR signal
- Contrast enhancement at the skull base in continuity with the orbital lesion
- Hyperintensity and thickening of the periorbita after contrast medium injection
Kneissl et al 2007
What is the sensitivity of MRI for detecting inflammatory CSF?
28%
Lamb 2005
MRI characteristics of trigeminal neuritis? (3)
- Diffuse enlargement of the trigeminal nerve within the calvarium and trigeminal canal
- Affected nerves are isointense on T1W, iso-to-hyperintense on T2W images, and have homogeneous or heterogeneous contrast enhancement after gadolinium injection
- +/- concurrent atrophy of the masticatory muscles
Mai
What are the contrast-enhancing characteristics of the NORMAL trigeminal nerve according to Pettigrew et al
Contrast enhancement of the entire trigeminal nerve in 39/42 dogs
Contrast enhancement in the region of the trigeminal ganglion in all 42 dogs
(Intensity of contrast enhancemet was subjectively less than or equal to that of the pituitary gland)
Retrospective - 42 dogs w/ normal MRI images, no trigeminal disease
T/F: The normal canine optic nerve is contrast enhancing?
False
(Boroffka et al 2008)
According to Bentley et al 2013, what 3 MRI characteristics of glioma are more common for grade III-IV tumors?
- Single cysts/ Intratumoral fluid accumulations
- Moderate or severe contrast-enhancement
- Some or all tumor situated in the diencephalon or any part of the internal capsule (deeper location)
Astrocytoma vs. oligodendroglioma:
- caudal fossa location more common?
- more likely to contact the surface?
- more likely to cause ventricular distortion?
- intraventricular location?
- caudal fossa location - astrocytoma
- contact surface - oligodendroglioma
- ventricular distortion - oligodendrogliomas have been reported to be more likely to cause ventricular than astrocytomas, however others found no difference between astrocytomas and oligodendrogliomas regarding relationship to the lateral ventricles
- Intraventricular location - oligodendrogliomas. CSF drop metastases have been reported
Mai
According to Bentley et al 2013, what 3 MRI characteristics were significantly associated with astrocytomas?
- Significantly associated with presence of moderate to extensive peri-tumoral edema
- Lack of ventricular distortion
- Isointense to hyperintense T1W signal
Glioblastoma multiforme is a high-grade _____ that is sporadically reported in dogs
astrocytoma
Mai
If glial tumor, what kind?
Glioblastoma multiforme
MRI findings:
- focal or multifocal ill-defined T2/FLAIR hyperintense areas associated with brain and/or spinal cord
- typically not contrast enhancing; however mild parenchymal enhancement and meningeal enhancement is possible
- several adjacent cerebral lobes are typically simultaneously affected
- Focal mass-like changes are possible in the midst of diffuse lesions, and concurrent astrocytoma or oligodendroglioma may be identified
- Normal MRI is possible (?)
Mai
How does MRI enhancement pattern correlate with histopathologic findings according to Brunner Singh et al?
in 73% of the lesions, the histomorphologic features explained the contrast enhancement pattern
- vascular proliferation and dilated vessels occurred significantly more often in areas with enhancement than in areas without enhancement
In 15/81 lesions, there was no association between MR images and histologic findings
- contrast enhancement was found within necrotic areas
- ring enhancement was seen in lesions w/o central necrosis
“These findings imply that necrosis cannot be differentiated reliably from viable tissue based on postcontrast images”
Brunner-Sing et al 2011
According to Sturges et al, the incidence of specific meningioma grades was ____% benign, ____% atypical, and ____% malignant
56% benign
43% atypical
1% malignant
Sturges 2008
injection into the central canal
Brain Camp
What % of French Bulldogs, English Bulldogs, and Pugs in retrospective study (Bertram et al) were found to have thoracic caudal articular process dysplasia?
70% of french bulldogs
84% of english bulldogs
97% of pugs
retrospective study of 271 dogs presenting for problems unrelated to spinal disease
Bertram et al 2017
2 headed arrow - foramen magnum is larger than normal and elongated in the dorsal-ventral axis
OAA malformation
arrowhead - the rostral margin of the dorsal arch of the atlas extends into the dorsal part of the foramen resulting in atlantooccipital overlapping
arrows/arrowheads - occipital condyles are hypoplastic but appear to articulate well with the articular fovea of the atlas
marked rotational subluxation of the atlantoaxial joint is evident. the odontoid process of the axis is hypoplastic
(Atlas of Small Animal MRI and CT)
Arrows - multiple T1 isointense and T2 hyperintense ovoid extradural masses that uniformly enhance following intraveneous contrast administration
Masses = confirmed extradural nephroblastoma presumably resulting from residual disease or surgical seeding
(Atlas of Small Animal MRI and CT)
Asterisk - A large, ovoid, T2 hyperintense, T1 isointense mass is present in the caudal cranial fossa, causing rostrodorsal displacement and compression of the cerebellum and dorsal compression of the brainstem
Arrow - There is a complex, sessile mixed‐intensity “cap” on the dorsal margin of the mass, best seen on T2 images
The mass nonuniformly and peripherally contrast enhances
*confirmed epidermoid cyst, ruptured causing lipogranulomatous encephalitis surrounding the cyst
(Atlas of Small Animal CT and MRI)
What imaging technieuq of the CNS produces planar images that aidentify areas where the blood-brain barrier has broken down and fails to exclude the injected radionucleotide?
Covnentional scintigraphy
(BSAVA Manual)
arrowheads (a) - comminuted fractures of the pedicles and the cranial body
white arrow - comminuted fractures of the cranial body of the 11th thoracic vertebra
Arrowhead (b) - T10-11 intervertebral disc space narrowing and subluxation
black arrow - contrast medium has absorbed into the spinal cord marenchyma indicative of myelomalacia
(Atlas of Small Animal MRI and CT)
A) 2y pug with dilation of the quadrigeminal cistern
B) 4y male chihuahua w/ moderate dorsocaudal dilation of the 3rd ventricle
C) 1y mix with large dorsocaudal expansion of the 3rd ventricle. Enlargement of the quadrigeminal cistern leads to the dorsoventral compression of the cerebellum
D) 11y shih tzu with dilation of the quadrigeminal cistern
E) 2y Chihuahua with dorsocaudal out pocketing of the 3rd ventricle
F) 8m Yorkie with supracollicular dilation of the 3rd ventricle and displacement of the quadrigeminal plate
*large dilations of quadrigeminal cistern and 3rd ventricle lead to displacement of the occipital lobes and interthalamic adhesion
Bertolini et al 2016
T4/5
A - anatomically correct articular process joint
ventral = cranial articular process
dorsal = caudal articular process
B - right-sided unilateral caudal articular process aplasia
Bertram et al 2017
arrow - Well-delineated, contrast-enhancing mass within the horizontal part of the right external ear canal
arrowhead - fluid is entrapped between the tympanic membrane and the mass in the proximal part of the canal
Thickening of the ipsilateral tympanic bulla and a small volume of exudate adherent to the bulla wall are suggestive of previous otitis media.
*biopsy = ceruminous adenoma of the external ear canal, chronic otitis externa
(Atlas of Small Animal MRI and CT)
well demarcated expansile mass emanating from the left tympanic bulla which has eroded the petrous temporal bone and adjacent occipital bone, extends into the cranial vault and has resulted in brainstem deformation.
Mass is heterogeneously but T1 hypointense, and moderately T2 hyperintense. There is irregular peripheral contrast enhancement (small arrows) and adjacent meningeal enhancement (large arrow)
Similar changes in the R tympanic bulla, confined within the bulla cavity
Pronounced left-sided temporal, masseter, and pterygoid muscle atrophy is evident
*biopsy = cholesteatoma
(Atlas of Small Animal MRI and CT)
MRI has a high sensitivity and specificity for detecting which 2 categories of brain disease?
It has a low sensitivity for detecting what category of brain disease?
High sensitivity (94%)/specificity (95%) for detecting neoplastic and inflammatory brain disease
Low sensitivity (38%) for detecting cerebrovascular disease
(Wolf et al 2012)
Contents of the cavernous sinus? (6)
Located on either side of the sella turcica
- internal carotid arteries
- sympathetic plexus associated w/ internal carotid artery
- CN 3, 4, 5, 6
(Atlas of Small Animal CT and MRI)
mild left-sided displacement of the spinal cord and a split contrast column on the right, indicative of an intradural-extramedullary mass
The mass homogeneously enhances following intraveneous contrast administration
*post-mortem confirmed meningioma
(Atlas of Small Animal MRI and CT)
A partially and diffusely mineralized mass arises from the right frontal bone and extends around the right zygomatic arch
The mineralized component of the mass has a coarse, granular appearance characteristic of MLO
Arrow - mass is osteodestructive and displaces normal soft tissue structures
Arrowhead - right globe
** approximately 50% of dogs experience local recurrence after treatment, approximately half develop metastatic disease
(Atlas of Small Animal MRI and CT)
What are the 2 patterns identified on MRI for brachial plexus nerve sheath tumors identified by Kraft et al?
Diffuse brachial plexus nerve thickening
Circumscribed brachial plexus mass +/- additional brachial plexus thickening
Kraft et al 2007
injection of gas
Brain Camp
arrowheads - multiple extradural T2 isointense, mildly T1 hyperintense masses are widely distributed within the vertebral canal and uniformly enhance following intraveneous contrast administration
*B-cell lymphoma
(Atlas of Small Animal MRI and CT)
Cerebellum is small and the surface contours appear unusually well defined because of increased CSF volume.
4th ventricle and cerebellomedullary cistern are larger than expected
3.5m MI Cocker Spaniel w/ presumptive cerebellar hypoplasia
(Atlas of Small Animal CT and MRI)
It has been suggested that only _____% of Pugs diagnosed with cauda articular process dysplasia will demonstrate neurological signs
4%
Bertram et al 2017
Most common MRI findings in cats with meningoencephalitis according to Negrin et al?
gadolinium contrast enhancement (71%)
T2 hyperintense foci (50%)
Negrin et al 2006
causes of intradural/extramedullary myelographic pattern (3)
arrowhead - a large mass of partially mineralized disc material has been extruded into the right side of the vertebral canal extradural space, causing lateralized spinal cord compression
some disc material has migrated cranially and can be seen within the mid body of T12
Arrow - the T12/13 intervertebral disc space contains residual mineralized disc material
(Atlas of Small Animal MRI and CT)
T2 shine through
(Brain Camp)
Arrowhead - dorsal subluxation of C7 relative to C6 and narrowing of the C6/7 intervertebral disc space
Arrow - highly comminuted and displaced fracture of the right cranial articular process of C7
(Atlas of Small Animal MRI and CT)
CT characteristics of masses of the brachial plexus according to Rudich et al
contrast enhancement 83% (20/24) - uniform or heterogeneous enhancement with hypoechoic central area
well defined margins (13/24)
muscle atrophy in 83% (20/24) - most apparent in the region of the scapula
Arrows - T2 hyperintensity in the caudal lumbar spinal cord and cauda equina that enhances following intraveneous contrast administration
the enhancement is plaque-like and appears to be contained by the dura matter
*postmortem confirmed widely disseminated intradural-extramedullary histiocytic sarcoma
(Atlas of Small Animal MRI and CT)
Uniformly contrast enhancing and symmetrical pituitary gland is evident
The gland is considered within normal limits for size, but the dorsal margin is convex and extends beyond the dorsal extend of the sella turcica
*pituitary macroadenoma
(Atlas of Small Animal CT and MRI)
Histologic lesions that result in low ADC values (indicating restricted diffusion) (4)
- acute nonhemorrhagic infarcts
- meningiomas
- glial cell tumor
- granulomatous meningoencephalitis
Sutherland-Smith et al 2011
R optic nerve is enlarged and has a nonuniform diameter
Meningeal sheath of R optic nerve intensely enhances. R orbital exenteration was performed and a R optic nerve meningioma was confirmed histologically
The dog returned 2y later with clinical signs referrable to intracranial dz - proximal remnant of the right optic nerve is enlarged, irregularly margined, and nonuniformly contrast enhances
(Atlas of Small Animal CT and MRI)
Arrowheads - Ill‐defined bilateral T1 hyperintensity in the lentiform nuclei is seen
There is no corresponding change on T2 images and no evidence of enhancement following contrast administration.
These lesions are consistent with those described in dogs with
liver insufficiency due to portosystemic shunting.
The T1 hyperintensity is due to manganese accumulation
(Atlas of Small Animal CT and MRI)
Arrow - ill-defined, ovoid mass within the left thalamic region which is heterogeneously T1 hypointense and heterogeneously FLAIR hyperintense
Arrow - similar but larger mass is seen in the right occipital lobe
Arrowheads - extensive, bihemispheric white matter edema associated with both masses
Arrow - masses markedly contrast enhance, revealing ill-defined and irregular margins
Arrowhead - excessive meningeal enhancement evident adjacent to the masses
*Post-mortem examination confirmed granulomatous encephalitis from systemic aspergillosis
(Atlas of Small Animal CT and MRI)
causes of extradural myelographic pattern (7)
Survey spinal radiographs - widespread focal and coalescing osteodestructive lesions involving the ribs, vertebrae and scapulae.
CT/myelogram - multifocal osteolytic lesions in the ribs and scapular cortices
the subarachnoid contrast column is circumferentially attenuated at the level of T5
Multiple myeloma confirmed on post mortem exam
(Atlas of Small Animal MRI and CT)
What are the three compartments of the three column classification model for thoracolumbar vertebral trauma?
Dorsal column = lamina, pedicles, and articular processes
Middle column = dorsal half of the vertebral body and intervertebral disc
ventral column = ventral half of the vertebral body
(Atlas of Small Animal MRI and CT)
What is wrap artifact? how is it mitigated?
artifact that occurs when the dimensions of an object exceed the field of view
Generally more severe along the phase-encode axis
mitigated by
- increase FOV
- phase oversampling
- applying saturation bands
Black arrow - hyperattenuating new bone of the lamina and articular processes (arrow heads) results in reduction of the vertebral canal cross-sectional area and change in shape
White arrow - osseous fragment associated with the distal margin of the right caudal aspect of the 4th cervical articular process - consistent with OSTEOCHONDROSIS
The spinal cord is grossly distorted by bilateral compression from hypertrophied articular facets.
(Atlas of Small Animal MRI and CT)
rads arrow - vertebral end plate osteolysis, surrounding bone sclerosis, and narrowing of the L3-4 intervertebral disc space
CT arrow - endplate destruction is more apparent
CT arrow - loss of normally fat attenuating ventral epidural space
CT arrowhead - regional enhancement adjacent to the vertebral column and within the ventral epidural space
(Atlas of Small Animal MRI and CT)
White arrow - right occipital condyle is axially subluxated in relation to the cranial articular fovea of C1
Asterisk - cranial articular fovea of C1
arrowhead - left occipital condyle is ventrally luxated
(Atlas of Small Animal MRI and CT)
small arrowhead - an in situ mineralized nucleus pulposus is present at the T11-12 intervertebral disc space
arrow - mineralized disc material from the T12-13 intervertebral disc space has herniated into the ventral subdural space of the spinal canal causing spinal cord compression with attenuation of the contrast columns.
large arrowhead - the T12/13 disc space is narrow and contains residual mineralized disc material
(Atlas of Small Animal MRI and CT)
arrow - hyperattenuating new bone of the lamina
arrow head - hyperattenuating new bone of the articular processes
reduction of vertebral canal cross‐sectional area and change in shape, with greatest narrowing occurring in the horizontal axis.
Remodeled articular facet margins impinge on the spinal cord to the greatest extent at C4–5, although a thin subarachnoid
contrast column is retained
(Atlas of Small Animal MRI and CT)
What is this myelogram artifact called?
The contrast medium has been injected into the epidural space, causing opacification of the intervertebral foramina (short arrow) and an undulating appearance to the contrast medium column due to opacification of the venous sinuses (long arrow).
(BSAVA Manual)
T/F: MRI has a low sensitivity for diagnosis of meningeal pathology in dogs.
TRUE
Especially for lesions of the leptomeninges
Keenihan et al 2013
There is ill‐defined, bihemispheric, white‐matter T2 hyperintensity and T1 hypointensity
There are multiple focal signal voids in the deep gray matter and at the cerebral cortical gray–white matter interface, best seen on T2* images
The residual pituitary tumor is best seen on the contrast‐enhanced T1 image
The signal voids represent susceptibility effect from multiple lacunar infarcts from the vascular effects of irradiation.
The white matter T2 hyperintensity is consistent with necrotizing leukoencephalopathy.
(Atlas of Small Animal CT and MRI)
regarding epidurography for LS compression: if the gontrast medium is deviated by > ___% of the diameter of the vertebral canal, there is significant neural compression
50%
(BSAVA Manual)
T/F: The imaging features of pituitary adenomas, invasive adenomas, and adenocarcinomas are not sufficiently different to reliably differentiate these entities
True
(Atlas of Small Animal CT and MRI)
Arrowheads - T1 and T2 hyperintense mass involving the entire right cerebral cortex, causing a pronounced midline shift
Arrowheads - the mass intensely and uniformly enhances following contrast administration
*confirmed granular cell tumor
(Atlas of Small Animal CT and MRI)
Arrow - large, well-defined mass present within the 3rd ventricle
arrowheads - generalized hydrocephalus
Solitary 3rd ventricle choroid plexus carcinoma was confirmed on post mortem examination w/o evidence of overt obstruction –> diagnosis of overproduction hydrocephalus
(Atlas of Small Animal MRI and CT)
There are focal regions of T2 and FLAIR hyperintensity involving the lateral geniculate nuclei, the caudal colliculi, and vestibular nuclei
Other thalamic nuclei were similarly affected (not shown). There is also ill‐defined T2 and FLAIR hyperintensity of the axial regions of the parietal and occipital cortex, which enhance following contrast administration.
These MR features are characteristic of multifocal polioencephalopathy due to thiamine deficiency. Further questioning of the owner revealed the cat had been fed an almost exclusively meat diet. Clinical signs resolved with dietary change and thiamine supplementation
(Atlas of Small Animal CT and MRI)
arrowhead - well-defined, uniformly enhancing caudal fossa mass
T2 hyperintense, variably contrast enhancing nodules widely distributed in the periphery of the spinal cord, intradural in location
*post mortem confirmed a choroid plexus carcinoma arising from the right lateral aperature with widespread CSF disseminated metastasis
(Atlas of Small Animal MRI and CT)
Asterisk - large, encapsulated soft tissue attenuating mass adjacent to the third lumbar vertebra. heterogeneously enhances following intraveneous contrast administration
arrowhead - tissue within the vertebral canal is uniformly soft tissue attenuating without evidence of epidural fat
arrowhead (c) - CT image cranial to the mass shows clearly defined spinal cord surrounded by lower attenuating epidural fat
*Postmortem - infiltrative left paralumbar myxosarcoma with invasion of the spinal cord
(Atlas of Small Animal MRI and CT)
The transverse plane image reveals a unilateral regional nasal turbinate destruction. The fluid-attenuating mass represents a combination of remaining turbinates, mucosa and accumulated exudate. The fragmented gas pattern suggests this is not a solid mass. A plant awn (foxtail foreign body) was removed via rhinoscopy.
(Atlas of Small Animal MRI and CT)
A well‐delineated, T1 isointense, T2 hypointense intraaxial cerebral mass is present in the region of the
right piriform lobe.
There is moderate edema surrounding the mass as well as a thin peripheral rim of contrast enhancement
There is uniform susceptibility effect within the lesion
Acute intracranial hemorrhage
(Atlas of Small Animal CT and MRI)
What is T2 “shine through”?
regions of hyperintensity on DWI images that conforms to regions of T2 hyperintensity on T2WI
does NOT indicate cytotoxic edema
(Brain Camp)
What is the sensitivity and specificity of MRI for detecting specific brain diseases, according to Wolf et al?
high sensitiity, low specificity for detecting specific brain diseases
(Wolf et al 2012)
T2W, T1W and T1W+C characteristics of brachial plexus NST?
T2W hyperintense (13/18)
T1WI isointense (14/18)
T1WI+C heterogeneously contrast enhancing (13/18), uniform (4/18)
Kraft et al 2007
Abnormalities identified on epidurograms fall into 3 major categories:
epidurogram with complete obstruction of cranial flow of contrast media over the LS junction
epidurogram with dorsal deviation of the ventral epidural space
epidurogram with epidural space deviation/attenuation recognized on dorsoventral views
(Roberts, Selcer 1993)
Black arrow - T1 and T2 hyperintense mass dorsal to the caudal thoracic vertebral column that has caused osteolysis of the vertebral lamina and pedicles
White arrow/arrowhead - the mass extends into the vertebral canal producing spinal cord compression. The mass is hypointense on a fat suppressed contrast-enhanced sequence and has minimal peripheral enhancement
CT - mass is predominantly fat attenuating
*confirmed liposarcoma
(Atlas of Small Animal MRI and CT)
highly aggressive mass extends from the ethmoid bone to the retropharyngeal region
Mass margins are ill defined on the contrast enhanced images with enhancement extending along fascial planes and invading temporal and pterygoid musculature
marked destruction of ethmoid, frontal, palatine, pterygoid, and sphenoidal bones is evident
The mass extends into the cranial vault
*cytology = aggressive, anaplastic adenocarcinoma
(Atlas of Small Animal MRI and CT)
rad arrowheads - ill defined new bone formation on the ventral aspect of the L1 and L2 vertebral bodies
arrow - right sublumbar musculature is focally enlarged at the level of the first lumbar vertebra, which is peripherally contrast enhancing following contrast administration
CT arrowhead - an additional tract is seen extending toward the right lateral paraspinal region
*migrating foxtail was removed
(Atlas of Small Animal MRI and CT)
Intradural - spinal cord enlargement and subsequent divergence and thinning of the contrast columns visible on all radiographic projections
Brain Camp
Causes of intramedullary myelographic pattern (4)
Arrowheads - Multiple foci of marked T2/FLAIR hyperintensity and T1 hypointensity involving the cerebral cortex
Arrow - Regional T2 hyperintensity of the white matter and caudate nucleus on the right
Arrowheads - mild amorphous contrast ehancement of the right caudate nucleus
Arrowheads - mild amorphous contrast enhancement of the meninges overlying the cerebral cortical lesions
*confirmed NME (extensive cortical necrosis and encephalomalacia)
(Atlas of Small Animal CT and MRI)
white arrowheads - complex tubular contrast-filling defect is seen within the cervical subarachnoid space
black arrowhead - A complex of dilated, coiled blood vessels is seen in the cervical region on a CT myelogram following intraveneous contrast administration
White arrow - postmortem examination documented the extent of vascular dilation and impingement on the cervical spinal cord
(Atlas of Small Animal MRI and CT)
Arrow - mineralized disc material from the C5/6 intervertebral disc space has herniated into the right ventral extradural space of the vertebral canal causing focal spinal cord impingement with attenuation of the contrast column
large arrowhead - part of the herniated disc material also extends into the right intevertebral foramen, potentially compressing the origin of the right 6th cervical spinal nerve
small arrowhead - the C5/6 disc space contains residual mineralized disc material
(Atlas of Small Animal MRI and CT)
Arrow - Communuted fracture of the right wing of the atlas with moderate displacement of fracture fragments
(Atlas of Small Animal MRI and CT)
Subdural injection of contrast
“Dural drape sign.”
Brain Camp
Transcranial doppler ultrasonography can be used to evaluate the blood flow in the ______ artery via the foramen magnum
basilar artery
the resistance index can be calculated for the basilar artery and has been shown to be related to intracranial pressure and neurological status (Fukushima, Saito et al)
(BSAVA Manual)
What is mean diffusivity?
measures the total diffusion within a voxel
the measurement that is used to produce DWI images
(Brain Camp)
There is diffuse T2/FLAIR white matter hyperintensity in both cerebral hemispheres, consistent with vasogenic edema.
Arrow - There is focal right hemispheric subcortical T2 hyperintensity, FLAIR mixed intensity, and T1 hypointensity consistent with a focal fluid collection
Arrow - an additional T2 hyperintense mass is present within the pons
Arrowhead - diffuse meningeal enhancement is also evident
*confirmed NLE (multifocal lymphohistiocytic leukencephalitis with cystic malacia and necrosis, consistent with necrotizing leukoencephalitis)
(Atlas of Small Animal CT and MRI)
Current neurologic signs include nystagmus and rolling. arrowheads - symmetrical T2 and FLAIR hyperintensity of the dentate nuclei is present
There is no visible abnormality on the unenhanced T1 image and no evidence of contrast enhancement
MR features are consistent with metronidazole neurotoxicity, and both serum and cerebrospinal fluid were positive for metronidazole on liquid chromatography/mass spectrometry analysis.
(Atlas of Small Animal CT and MRI)
Arrowheads - comminuted compression fracture of L3 that results in marked reduction of the vertebral canal diameter
arrow - sharp fracture margin from one of the larger fragments is displaced dorsally into the canal and impinges on the ventral margin of the spinal cord
(Atlas of Small Animal MRI and CT)
There is a mass in the left dorsal thalamic region causing a midline shift and compression o the third and left lateral ventricles
Arrow - The mass is characterized by T1 hypointensity with heterogeneous T2 intensity
arrowheads - extensive perilesional edema
*similar lesion also present in the L occipital lobe
Arrow - the mass intensely and heterogeneously enhances following contrast administration and mass margins are poorly defined and irregular
*Confirmed granulomatous encephalitis from systemic aspergillosis
(Atlas of Small Animal CT and MRI)
Marked expansion and osseous remodeling of the right tympanic bulla
Soft-tissue attenuating material fills the bulla and the horizontal ear canal
Bulla contents and soft tissues adjacent to the bulla are mildly contrast enhancing
Histologic features of biopsy material were consistent with cholesteatoma
(Atlas of Small Animal MRI and CT)
The external ear canals are occluded because of stenosis and exudates.
Contrast-enhanced images show marked enhancement and redundancy of the external ear canal walls
Gas and fluid within the canal lumen can be distinguished from adjacent enhancing epithelium
Biopsy revealed severe diffuse chronic lymphoplasmacytic otitis externa with epithelial hyperplasia and ceruminous and sebaceous gland hyperplasia
(Atlas of Small Animal MRI and CT)
arrow - reduced opacity of the body of C5 on survey radiographs
MR - osteodestructive soft tissue mass arising from the C5 vertebral body that is T2 hyperintense and mildly T1 hyperintense (compared to adjacent muscle) and also involves the right pedicle and invades the transverse foramen
lg arrowhead - the mass breaches the dorsal cortex and extends into the floor of the vertebral canal causing spinal cord compression
small arrowhead - mass involves the right pedicle and invades the transverse foramen
Arrowhead (g) - spinal cord compression
(Atlas of Small Animal MRI and CT)
How is inter-rater agreement for detecting detection of structural brain disease on MRI according to Wolf et al?
Inter-rater agreement was very good for overall detection of structural brain lesions and neoplastic lesions
MRI inter-rater agreement was only fair for cerebrovascular lesions
(Wolf et al 2012)
What MRI sequence a heavily T2W sequence that generates a high signal from CSF?
HASTE = half-Fourier-acquisition single-shot turbo spin-echo
Mankin et al 2012
There is generalized reduction in cerebral and cerebellar volume with concomitant generalized ventriculomegaly and prominence of the subarachnoid space due to gyral atrophy and sulcal widening
There is also loss of white and gray matter definition on the proton density image
Postmortem examination revealed neuronal accumulation of eosinophilic granular intracytoplasmic material. The material was autofluorescent and stained positive with PAS, LFB, and Sudan black B, all of which supported the diagnosis of neuronal ceroid lipofuscinosis
2y MC Border Collie cross with 4‐month history of progressive behavior changes, ataxia, and incoordination.
(Atlas of Small Animal CT and MRI)
Pituitary tumors on MRI:
- What 2 types of tumor are > 10mm in height and arise from the sellar region?
- Are invasive adenomas or noninvasive adenomas typically larger?
- How can smooth/irregular margins, cysts, hemorrhage and mineralization help differentiate the type of tumor
- Pituitary macroadenoms and adenocarcinomas are > 10mm in height and arise from the sellar region
- Invasive adenomas are on average, larger than noninvasive adenomas
- Both macroadenomas and adenocarcinomas can have smooth or irregular margins, can contain cysts or hemorrhage, and can occasionally be mineralized
(Atlas of Small Animal CT and MRI)
arrow - There is evidence of noncompressive increased spinal cord diameter and parenchymal update of contrast medium at T13/L1
arrowhead - the T13/L1 intervertebral disc width is also slightly narrower than those of the adjacent disc spaces
(Atlas of Small Animal MRI and CT)
L5/6 injection in which the contrast medium has entered the subdural space causing a characteristic spindle-shaped end to the contrast medium column caudally
(BSAVA Manual)
Smooth, dense production of bone centered on the parietal bone and expanding both intracranially and extracranially. The mass is hyperattenuating and uniform on CT images.
MR - mass effect compressing the brain, lateral ventricle and displacement of the falx cerebri to the right
T2 hyperintensity of white matter next to the mass - edema
OSTEOMA
(Atlas of Small Animal MRI and CT)
What biologic change is suspected to be responsible for change in signal intensity of denervated muscle?
water shift from intracellular to extracellular space with a consecutive widening of the extracellular space
Bendszus et al 2001 (human paper)
Well-demarcated ovoid mass within the 3rd ventricle which is predominantly T1, T2 and FLAIR hyperintense.
The mass deforms the lateral ventricles, but there is minimal hydrocephalus and no peritumoral edema
The mass intensely and nonuniformly enhances following contrast administration
Confirmed ependymoma within the 3rd ventricle post-mortem
*an unrelated diagnosis of lymphoplasmacytic meningitis explains the meningeal enhancement
(Atlas of Small Animal CT and MRI)
What condition has been associted with diagnosis of Rathke’s cleft cyst in dogs?
Hypopituitarism –> dwarfism
HASEGAWA et al 2008
Suspected to be the dorsal longitudinal ligament
Olby et al 2000
Location for epidural puncture when performing epidurography?
between 1st and 2nd caudal vertebrae or at the sacral-caudal vertebral junction
Roberts, Selcer 1993
Arrow - mixed pattern of osteoproduction and osteolysis of the first cervical vertebra
arrow - predominantly right-sided osteoproductive and destructive expansile mass that extends into the vertebral canal causing spinal cord compression
*confirmed osteosarcoma
(Atlas of Small Animal MRI and CT)
Bilateral tympanic bulla effusion is seen associated with mild bulla wall thickening
Arrow - large polyp completely occludes the naropharyngeal lumen.
The nasopharyngeal mass likely occludes the auditory canals resulting in obstructive bulla effusion
(Atlas of Small Animal MRI and CT)
The _____ spinal nerve wraps cranioventral and medial to the 1st rib.
T1 spinal nerve
Between French Bulldogs, English Bulldogs and Pugs, which breed has more severe caudal articular process disease?
Pugs
“When compared to French and English bulldogs, Pugs showed a significantly higher prevalence of caudal articular process dysplasia, a significantly higher number of affected vertebrae per dog, Pugs had significantly more often caudal articular process aplasia, significantly less often hypoplasia, demonstrated significantly more frequently a generalized spatial pattern, and vertebra being affected bilaterally. Furthermore, Pugs showed a significantly different anatomical distribution of caudal articular process dysplasia along the vertebral column, with a high prevalence of articular process aplasia between T10 and T13. This area was almost completely spared in the two other breeds”
Bertram et al 2017
R vestibular
noncontrast - right tympanic bulla is filled with fluid-attenuating material and there is partial osteolysis of the bulla wall laterally
contrast - enhancement of tissues surrounding the tympanic bulla consistent with a clinically confirmed abscess. There is also focal intracranial contrast enhancement in the location of the cochlear branch of the vestibulocochlear nerve suggesting extension of disease through the internal acoustic meatus.
(Atlas of Small Animal MRI and CT)
Arrow - displaced odontoid process fracture
arrowhead (a)- mildly displaced left C1 wing fracture
arrowhead (b) - focal region of T2 hyperintensity within the ventral aspect of the spinal cord immediately dorsal to the fractured odontoid process
(Atlas of Small Animal MRI and CT)
Arrowhead - apical fracture of the odontoid process is not seen on survey radiographs, but easily detected on CT
White/black arrowheads - transverse images through C1 ordered from cranial to caudal show the apical fracture fragment positioned on midline with the basilar part of the dens positioned to the left of midline - indicative of fracture displacement and atlantoaxial instability
(Atlas of Small Animal MRI and CT)
What is used to differentiate cytotoxic edema from T2 shine through?
ADC - calculated by the MRI system on a voxel-by-voxel basis from multiple diffusion weighted images.
Used to identify restricted diffusion and differentiate cytotoxic edema from T2 shine through
(Brain Camp)
intradural extramedullary - focal widening of the contrast column adjacent to the lesion = golf tee
Brain Camp
Arrowhead - Salter Harris type 1 fracture of the caudal body of physis of T5 with concurrent ventral displacement of T6 relative to T5
Arrow (a, c) - T5/6 vertebral articulations are subluxated
Arrow (b) - vertebral canal diameter is reduced
(Atlas of Small Animal MRI and CT)
Signs of epidural, subdural, and subarachnoid hemorrhage are evident.
Arrowheads - epidural hemorrhage is seen as a T1 isointense
and T2 hyperintense contrast‐enhancing crescent dissecting between the right hemispheric dura and parietal bone
Large arrow - Focal subdural hemorrhage is seen in the right dorsal parietal region and is T1 hyperintense and of mixed T2 intensity
Small arrows - There is T1 hyperintensity and prominence of the sulci margins indicative of subarachnoid hemorrhage.
(Atlas of Small Animal CT and MRI)
arrows - hyperattenuating hemorrhage in the lateral and 3rd ventricles.
Arrowheads - additional hyperattenuating parenchymal hemorrhage and associated hypoattenuating edema are seen in the right and left parietal lobes
(Atlas of Small Animal CT and MRI)
Bilateral lateral ventriculomegaly
CSF in the right lateral ventricle is moderately intense compared to the low-intensity signal within the left lateral ventricle on FLAIR
Thickening and intense enhancement of the right lateral ependymal lining is evident on the contrast enhanced T1 image
FIP
(Atlas of Small Animal MRI and CT)
Spina bifida
- Results from lack of development of the vertebral arch, may be associated neural tube defects too
- Cleft in the dorsal part of the vertebral arch, absence or splitting of the spinous process
- There is rarely a neural tube defect in dogs with spinal bifida occurring in the thoracic spine
- At the lumbosacral junction - more severe NTD
- Bulldogs + Manx cats
(Atlas of Small Animal MRI and CT, Thrall)
arrowheads (ABDE) - regional T2 hyperintensity and T1 hypointensity surrounding the spinal cord consistent with a fluid collection, causes cord deformation and compression. Appears to be both extradural and intradural
arrow/arrowhead (f) - extradural and extramedullary intradural enhancement on the transverse T1+C image
arrow (a) - diffuse parenchymal T2 hyperintensity with increased spinal cord diameter at the level of C2
Meningioma
(Atlas of Small Animal MRI and CT)
Arrowheads - FLAIR images reveal ill-defined areas of mildly increased signal intensity, primarily in the cerebrum and thalamic regions
Mild asymmetrical hyperintensity of the parietal and temporal lobes.
Arrowhead -These areas do not contrast enhance with the exception of one focal lesion in the right thalamic region.
*post-mortem: severe generalized neuronal loss, axonal necrosis, and demyelination
*immunohistochemical staining documented abundant intralesional CANINE DISTEMPER VIRUS antigen
*symmetrical parietal and temporal lobe changes were thought to be associated with recent seizures
(Atlas of Small Animal CT and MRI)
T/F: A quantative ADC evaluation at a single time point is of limited use as a predictor of the histologic type of canine intracranial disease
False
Sutherland-Smith et al 2011
AV = vestibular aqueduct (extension of the membranous labyrinth and connects with the meninges of the brain)
C = cochlea
I = incus, M = malleolus
TC = tympanic cavity. TB = tympanic bulla
(Atlas of Small Animal MRI and CT)
q - quadrigeminal cistern
tv - 3rd ventricle
short arrow - thin membrane isoattenuatting to the soft tissue separates the quadrigeminal cistern from the overlying 3rd ventricle
long arrow - on parasagittal image, the rostral extensions of the quadrigeminal cistern reach the middle-rostral part of the interthalamic adhesion
p - quadrigeminal plate
The quadrigeminal cistern is visible on mid sagittal image as a short linear cavity on the roof of the midbrain
Bertolini et al 2016
Large ovoid mass with mixed T1, T2 and FLAIR intensity in the left cerebrum. Mass margins are well-defined on T2 and FLAIR images, and the halo of hyperintensity surrounding the mass on these sequences is indicative of vasogenic edema
The mass nonuniformly enhances following contrast administration, with more intense enhancement peripherally
Post-mortem examination confirmed glioblastoma multiforme
There was extensive intratumoral hemorrhage consistent with the complex, mixed signal intensity seen on unenhanced images.
(Atlas of Small Animal CT and MRI)
5y MC DSH. Trauma of unknown cause
a - fracture-luxation involving the nasal and maxillary bones
b - mandibular symphyseal fracture
c - fractures of the perpendicular processes of the palatine bones and separation of the palating symphysis
d - fractures of the pterygoid bones
e - caudal luxation of the condyloid process (arrowhead) and fracture through the zygomatic process of the left temporal bone (arrow)
(Atlas of Small Animal MRI and CT)
Comminuted fracture of the sacrum with displacement of major fragments
large arrowhead - the fracture disrupts the ventral margin of the vertebral canal
small arrowheads - fracture fissures involve the drosal and pelvic sacral foramina
arrow - mildly displaced left sacroiliac luxation
(Atlas of Small Animal MRI and CT)
arrow - well-defined, bone-attenuating mass arising from the caudal lamina of T6 that appears continuous with more normal adjacent bone of the basilar part of the T6 spinous process
arrowhead - encroachment into the spinal canal implies spinal cord compression
*surgical excision confirmed solitary osteochondroma
(Atlas of Small Animal MRI and CT)
An open, comminuted depression fracture of the right frontal bone is evident on unenhanced, wide‐windowed images
Arrow - A focal hyperattenuating epidural hemorrhage is evident on the same unenhanced images (narrow window) adjacent to the internal surface of the largest fracture fragment
arrowhead - A smaller hyperattenuating lesion is present within the right frontal lobe, consistent with acute intraparenchymal hemorrhage
arrows - Regional hypoattenuation in the right frontal lobe is
consistent with parenchymal edema
(Atlas of Small Animal CT and MRI)
T/F: Discography in combination with epidurography is a nonsensitive and nonspecific means of evaluating the LS junction
False
Barthez et al 1994
(BSAVA Manual)
There is moderate ill‐defined T2 and FLAIR hyperintensity and T1 hypointensity involving both piriform lobes
No other abnormalities were seen on this examination, and the dog responded to medical management of seizures
(Atlas of Small Animal CT and MRI)
Arrowheads - regional marked T2/FLAIR hyperintensity and T1 hypointensity involving the frontoparietal cerebral cortex
Arrow - transtentorial herniation
Arrowhead - cerebellar herniation
Arrows - interstitial edema
Arrows - widespread meningeal enhancement is seen following contrast administration
*Confirmed NME (meningitis and necrotizing encephalitis of gray and white matter predominantly in the cerebral hemispheres)
(Atlas of Small Animal CT and MRI)
Nasopharyngeal stenosis
arrow - Focal occlusion of the nasopharyngeal lumen near the level of the pterygoid processes and 1cm caudal to the caudal margin of the hard palate
arrow - the pharyngeal lumen rostral and caudal to this focal lesion appears normal
The soft tissues associated with the occlusive lesion mildly contrast enhance
*biopsy - moderate chronic active neutrophilic eosinophilic and lymphoplasmacytic pharyngitis and rhinitis
(Atlas of Small Animal MRI and CT)
T11/12
A - anatomically correct articular process joint
cranial articular process (lateral)
caudal articular process (medial)
B - bilateral caudal articular process aplasia
Bertram et al 2017
Precontrast - fluid/soft tissue opacity withinthe right external ear canal and tympanic bulla is indicative of otitis externa and otitis media
Post contrast/arrow - well-delineated contrast enhancing mass is seen within the horizontal part of the right external ear canal and the bulla. The mass is distinguished from nonenhancing fluid in the bulla
Excisional bx revealed inflammatory polyp and suppurative otitis externa
(Atlas of Small Animal MRI and CT)
C2/3
marked hypertrophy and remodeling of the C2 and 3 articular processes is seen on the CT image
Arrowheads - subchondral bone defects
Arrows - encroachment of new bone into the vertebral canal
(Atlas of Small Animal MRI and CT)
Enhancement of dura was evident in multiple contiguous subtraction images (arrowheads), hence a pachymeningeal lesion was suspected. Leptomeningeal enhancement was considered within normal limits.
Histopathologically there is infiltration of the leptomeninges over the gyri and into the sulci with invasion of the brain by lymphoid cells
Keenihan et al 2013
Arrow - a crescent-shaped T1 hyperintense, right-sided subdural hematoma
arrow - the hemorrhage has central T2 hypointensity consistent with subacute hemorrhage
Arrowhead - A focal, nonenhancing, T1 hyperintense lesion is also present in the left pyriform lobe associated with regional edema and consistent with subacute parenchymal hemorrhage. Given the location of this second lesion in relation to the subdural hematoma, it is thought to represent a contrecoup brain contusion.
(Atlas of Small Animal CT and MRI)
What is the dose and type of contrast agent used for radiograph myelogram? How long should the injection be given over?
How should the dose be adjusted for CT myelogram?
Dose: 0.3 - 0.5mL/kg
Iohexol 240
Given over 1-2 minutes
HEAD ELEVATED
“When CT myelography is performed alone, one- fifth to one-third of the regular iohexol dose is injected at the cisterna manga” - RE CSM CT myelogram
(BSAVA Manual)
arrowheads - pronounced increase in spinal cord diameter centered at C6. The magnitude of the diameter change is abnormal, and causes annular attenuation of the subarachnoid contrast medium
FCE
(Atlas of Small Animal MRI and CT)
arrow - large, irregularly shaped osteodestructive and expansile mass arises from the left side of the second thoracic vertebra and rib head
arrow - mass is heterogeneous T1 and T2 hyperintensity compared to adjacent paraspinal muscle and intense and nonuniformly enhances following intraveneous contrast administration.
arrowhead - Axially, it extends into the vertebral canal causing right-sided spinal cord displacement and compression
The complex intensity pattern seen in all sequences suggests a hemorrhagic component
*confirmed hemangiosarcoma (along w/ splenic mass)
(Atlas of Small Animal MRI and CT)
Large arrow - large T1 and T2 hyperintense ovoid mass in the left lateral recess
Mass that encroaches on the 4th ventricle, distends the contralateral lateral recess, and displaces and compresses the brainstem and cerebellum
Smaller mass is seen ventral to the brainstem
Both masses intensely and uniformly enhance following contrast administration
Distention of the 3rd ventricle and infundibular recess is indicative of obstructive hydrocephalus
The large mass in the left lateral recess was confirmed to be a choroid plexus carcinoma and the small mass confirmed local metastatic lesion. the 4th ventricle and right lateral aperature were somewhat distended
(Atlas of Small Animal CT and MRI)
Expansile mass that is T1 and T2 hyperintense compared to adjacent muscle arises from the body of the 7th lumbar vertebra. There is extensive cortical osteolysis and the mass extends into the vertebral canal elevating and enveloping the cauda equina
The mass uniformly enhances following intraveneous contrast
biopsy - plasma cell neoplasia
(Atlas of Small Animal MRI and CT)
Large, well-defined T1 isointense, T2 hyperintense ovoid mass arising from the pituitary fossa
Carotid arteries are identified in cross-section and appear to be surrounded by the mass
Following administration of contrast, the mass uniformly and intensely enhances, and the basilar part of the mass can be seen to invade into the cavernous sinus bilaterally
Carotid arteries are confirmed to be incorporated into the mass bilaterally (arrowheads)
*cavernous sinus syndrome
(Atlas of Small Animal CT and MRI)
A lateral view of a myelogram in a dog with ascending myelomalacia precipitated by an
intervertebral disc herniation (arrowed). There is contrast medium in the subarachnoid space and within the spinal cord parenchyma.
(BSAVA Manual)
white arrow - dorsal deviation of the dural sac
white arrowhead - neural elements within the dural sac
black arrowhead - thin stalk extends from the dorsum of the myelomeningocele to the skin surface, which is dimpled.
(Atlas of Small Animal MRI and CT)
The pituitary gland has nonuniform mixed T1 intensity and T2 signal that is isointense
Hyperintense secretory granules within the neurohypophysis are displaced to the right
The pituitary enhances nonuniformly following contrast administration
Dorsal pituitary margin is irregular, convex, and extends beyond the dorsal extent of the sella turcica
*Consistent w/ Pituitary Microadenoma
(Atlas of Small Animal CT and MRI)
RE vessels in close proximity to the brachial plexus:
the _____ artery and vein lie ventromedial and caudal to the plexus
The ________ vein and ________ artery cross the ventral surfaces of the 7th and 8th cervical spinal nerves laterally
the axillary artery and vein lie ventromedial and caudal to the plexus
The external jugular vein and superficial cervical artery cross the ventral surfaces of the 7th and 8th cervical spinal nerves laterally
Kraft et al 2007
Epidural hemorrhage of the left parietal region
(Atlas of Small Animal CT and MRI)
What kind of MRI artifact is described:
moving protons develop different phase shifts from static tissue - incorrectly spatially located during phase encoding
Motion related artifacts (phase mismapping)
- most severe in PE direction
- Avoid by:
- Swap PE and FE
- Apply saturation bands over lg blood vessels/GI tract
- Gating
- Increase NEX
Mai
3 vascular flow-related artifacts
- Time of flight
- Entry slice phenomenon
- Intravoxel dephasing
Mai
What kind of MRI artifact:
Occurs when flow through a vessel is through the plane of the image, and some or all of the flow is replaced between radiofrequency pulses
Time of flight flow artifact
- Stationary fluid experience both 90 and 180 pulses (in spin echo sequence) –> generates a signal
- Faster fluids, either all or only part of the blood experiences both RF pulses so partial or no signal is generated
- Gradient echo: no flow-related loss of signal, instead show flow-related enhancement because whole body receives the refocusing gradient and flowing fluid is rephased irrespective of its slice position
Mai
What MRI artifact?:
Differing signal intensity of blood in different slices within a stack of slices
Entry slice phenomenon (vascular flow artifact)
- Nuclear spins of blood flowing perpendicularly become progressively more saturated as protons move through a stack of slices
- Nuclear spins of blood within the center will have experienced more excitation
- Blood within the entry slice may show greater signal than blood in the image slices further away from the entry slice
- Varies with TR, slice thickness, and direction/velocity of the flow
Mai
What MRI artifact:
Occurs when nuclei having different velocities are present in the same voxel, related to vascular flow
Flow-related intravoxel dephasing
- Occurs when nuclei having different velocities are present in the same voxel
- Due to their different velocities - these nuclei will have traveled different distances to reach that voxel between the 90RF pulse and signal readout - therefore will have accumulated variable amounts of phase during their travel
- When they arrive in the voxel, these differences in phase accrued will cause destructive interference in amplitude of the signal that is recorded from that voxel - signal drop in affected voxels
- This can be reduced using gradient moment rephasing (nulling) = flow compensation
Mai
What MRI artifact is due to altered magnetization of CSF as it moves?
CSF flow artifact
- Most commonly seen on T2 and T2W FLAIR
- T2 - signal drouput
- T2 FLAIR - failure of suppression of high CSF signal
Mai
What MRI artifact is the result of pulsing of larger blood vessels, and appear as multiple ghost images
Phase-encoded motion artifact (Pulsatility artifact)
- Usually associated with the pulsing of larger blood vessels –> ghost images in the PE direction
- They are only visible in one imaging plane and inconsistent
- Brighter moving structure –> brighter ghost images
- Usually more marked on post-contrast images - should not be mistaken for abnormal contrast enhancement
Mai
What MRI artifact appears as narrow linear band of image noise (alternating increase and decrease signal) which runs across the entire field of view
Zipper artifact
- caused by leakage of external RF signals into the MRI scanning room
- in the FREQUENCY ENCODING direction
Mai
What MRI artifact appears as multiple parallel dark stripes across the image occurring during certain sequences
Spike or Herringbone artifact
- Only occurs during certain sequences when there is a loose electrical connection - most likely to occur when the gradients are applied at a very high duty cycle
Mai
What MRI artifact appears as variation in signal intensity across the images, with the greatest signal intensity in the tissues closest to the coil
Coil artifact
- correction via filtering of the image
- correct FOV
Mai
What MRI artifact appears as loss of signal during slice selection due to excitation of a slice from adjacent slices resulting in partial saturation of spine
Cross excitation
- Occurs if there is no gap between slices
- Worst on inversion recovery sequences
- Can be avoided by having an interslice gap of at least 1/3 of the slice thickness, using an interleaved acquisition technique, or 3D acquisition
Mai
What MRI artifact occurs when slices overlap during multislice, multiangle acquisition, resulting in a focal band of loss of signal at the overlap point?
Slice overlap/cross talk
- results in dark bands across the images
Mai
What is phase oversampling?
Technique used to prevent phase wrap artifact
- FOV is enlarged in the PE direction in order to cover a wider area of anatomy and to preserve spatial resolution
- Results in longer acquisition time
Mai
What MRI artifact appears as a series of alternating dark and bright lines that occurs at high contrast boundaries and follow the contour of the boundary?
Gibb’s artifact
- occurs due to phase undersampling - causes high frequency signal from a high contrast sharp interface not to be represented accurately
- occurs most often in the PE direction
- Correction - increase size of image matrix and voxel size
Mai
What MRI artifact results in an artifactual line at fat/soft tissue interfaces due to the fact that the resonant frequency of spins varies across the image, due to varying magnetic gradients used in image acquisition
Chemical shift artifact - misregistration of signal
- Occurs in the FE direction
- Worsens at increasing magnetic field strength
Minimized by:
- Increase receiver bandwidth
- Fat suppression technique
Mai
What MRI artifact results from differences in the resonant frequencies of fat and water and results in black lines on the boundaries of tissues
Phase cancellation artifact (chemical shift)
- Differences in the resonant frequencies of fat and water –> phase cancellation or 2nd order chemical shift artifact
- Occurs on gradient echo sequences, not spin echo sequences
- results in black lines at the boundaries of tissues when voxels along the periphery of the object contain both water and fatty tissues
- At specific TEs when the spins of fat and water are exactly 180 out of phase, they cancel each other out –> signal loss
- Can be avoided by choosing a TE when fat and water are in phase
Mai
What MRI artifact occurs at boundaries between substances of different magnetic susceptibility
Susceptibility artifact
- at these boundaries, there is microscopic variation in local magnetic field –> focal distortion of the image
- largest around ferromagnetic objects - hemorrhage, suture material, foreign body, gas
- Larger with increasing field strength
- Causes spectral fat suppression not to be homogeneous
Mai
Techniques to reduce susceptibility artifacts (12)
- Avoid gradient echo pulse sequences
- Avoid parallel imaging if metal artifacts are present
- Parallel imaging reduces artifacts due to air in the sinuses and tympanic bullae
- Short-echo spacing – allows collection of more echoes during the echo-train before the signal decays, and less time for dephasing of spins
- Use longer echo train
- Shorter TE – less time for dephasing of spins
- High receiver bandwidth
- Thin slices
- Avoid spectral fat saturation – if suppression of fat signal is desired, use sequences that do not rely on frequency-specific fat saturation (STIR)
- Maintain adequate SNR
- Swap PE and FE directions
- Change alignment of metallic implants relative to B0 – change limb or body position
Mai
What MRI artifact is described by: If a voxel contains different tissues with different signal intensities, the brightness of the pixel on the image will be intermediate between the two
Partial volume averaging
- occurs with large voxels at the boundaries of different structures
- more severe with increasing slice thickness
Mai
What % of cat with focal rostro-tentorial lesion and secondary brain herniation have clinical signs of brainstem dysfunction?
66% of cats with focal rostro-tentorial lesions and concurrent brain herniation showed signs of brainstem dysfunction
48% of these cats presented with nystagmus
ACVIM Proceedings
Mean survival for nerve sheath tumor treated with palliation, surgery and SRT according to Dolera et al
Palliative: 97 days
Surgery: 144 days
SRT: 371 days
ACVIM Proceedings
Inheritance of NAD/EDM?
incompletely penetrant or polygenic trait
clinical findings - if a genetically susceptible horse receives enough dietary vitamin E during the first year of life, they are unlikely to develop a moderate to severe ataxia
Autosomal dominant mode of inheritance suggested in Morgan horses
ACVIM Proceedings
_____ vertebrae have characteristics of 2 different anatomic divisions
Transitional vertebrae
- Usually involve vertebral arch rather than body
- Occur at cervicothoracic, thoracolumbar and lumbosacra junctions
- Increased incidence of lumbosacral disc disease and nerve root compression occurs in dogs with a lumbosacral transitional malformation
(Thrall)
What radiographic projection should be made to determine if dens is present on cervical radiographs?
What is the most reliable radiographic sign of atlantoaxial subluxation?
Left 15 - 30 degree ventral/ right dorsal radiograph
- VD projections can be made, there is risk of exacerbating the spinal cord compression. VD is not necessary to confirm a diagnosis of AA subluxation
Normal linear relationship between dorsal lamina of atlas and axis - if this becomes angular luxation is present
(Thrall)
Radiographic changes in dogs with disc vs. osseous CSM?
Disc-associated
- Changes in shape of the vertebral body
- Narrowing of the intervertebral disc space
- Vertebral canal stenosis
- Approximately 20 - 25% of clinically normal dogs have radiographic changes comparable with those seen in dogs with CSM
- “cervical vertebral ratios may be useful as a screening test for dogs with CSM”
Osseous
- Osteoarthritis, sclerotic changes of articular facets
(DeCosta VCNASAP)
Diffuse brain atrophy resulting in enlargement of the ventricular system and subarachnoid space.
The pituitary fossa is filled and appears T1 hypointense and T2 hyperintense. This fluid accumulation appears to communicate with the 3rd ventricle by way of the infundibular recess (lg arrow)
The interpeduncular (small arrow) and chiasmic (arrowhead) cisterns are also prominent
*Empty sella syndrome
(Atlas of Small Animal CT and MRI
Large arrow - nonuniformly T1 hypointense, T2 mixed intensity mass that distends the 3rd ventricle and results in lateral ventriculomegaly (arrowheads)
Small arrows - mass has an extraventricular component involving the falx cerebri
CT - mass is mineralized
Post-contrast - marked nonuniform enhancement following contrast administration
Arrows - post-mortem examination confirmed the presence of a predominantly intraventricular psammomatous meningioma
(Atlas of Small Animal CT and MRI)
What is the ideal kVp and mA for spinal radiography?
Low kVp
High mA
Brain Camp
Prominent, well-delineated, T1 hypointense, T2 hyperintense extraaxial masses are present on either side of the brainstem, causing axial compression bilaterally
The masses are moderately and uniformly contrast enhancing
CSF/postmortem - lymphoma
(Atlas of Small Animal CT and MRI)
Arrow - elongated tear drop-shaped dilation of the dorsal subarachnoid space at the level of the 2nd cervical vertebra
arrowhead - pronounced spinal cord compression
(Atlas of Small Animal MRI and CT)
Arrowhead - meningeal lining of the pituitary fossa is T2 hyperintense
Arrrowhead - the meninges of the fossa and dural septum intensely contrast enhance
arrows - more diffuse meningeal enhancement is evident involving the meninges of the falx cerebri and the basilar regions of the piriform obes
*postmortem - diffuse meningoencephalitis with marked chronic granulomatous and lymphoplasmacytic hypophysitis
(Atlas of Small Animal CT and MRI)
Spinous processes and pedicle margins of the caudal-most lumbar vartebra are missing, consistent with spina bifida
(Atlas of Small Animal MRI and CT)
Radiographic (nonmyelographic) abnormalities of CSM? (6)
- Tilting of the craniodorsal edge of the vertebral body dorsally - site of spinal cord compression may NOT be related to the tilt
- Abnormal vertebral body shape (flattened cranioventral epiphysis, triangular shape)
- Spondylosis deformans ventral to the intervertebral space
- Stenosis of the vertebral canal - cranial orifice narrower than the caudal
- Suggested that - normal dobermans, difference between diameter of cranial orifice and caudal orifice is < 3mm
- Increased opacity, loss of joint space of articular processes +/- new bone
- Intervertebral disc space - narrowing, mineralization of the disc
Plain film changes do not always correlate with myelographic evidence of cord compression
Lewis et al 1991 - 28 dogs that had marked changes indicative of CCSM (stepping > 3mm, vertebral malformation, canal stenosis, ventral spondylosis) - 20 developed signs of CCSM
** Dogs without such changes did not go on to develop CCSM during the period of the study
(Sharp)
Myelographic abnormalities of CCSM? (3)
- Ventral extradural compression is the most common findings - usually related to the intervertebral disc. Splitting of the contrast column is seen if the compression is asymmetrical
- Dorsal extradural compression from ligamentum flavum or articular processes
- Articular process hypertrophy - best seen on VD
What are the CT HU values for:
- Brain/spinal cord
- CSF
- Recent hemorrhage (<24 hours)
- Fat
- Bone
- Recently herniated mineralized disc
- Chronically herniated mineralized disc material
What is the recommended CT windowing for CNS?
- Fat: -100 to -50
- CSF: 0-15
- Brain/spinal cord: 25 - 50
- Recent hemorrhage (<24 hours): 55 - 95
- Recently herniated mineralized disc: 100 - 500
- Chronically herniated mineralized disc material: 450 - 1000
- Bone: 600 - 1000
100 - 200HU (this is because differences in physical density and anatomic number are not markedly different)
(BSAVA Manual)
Imaging features to identify for Cervical spondylomyelopathy (8)
- Vertebral body malformation
- Stenosis
- Malalignment
- Vertebral tipping
- Articular process remodeling
- Disc degeneration/prolapse
- Spinal cord compression
- Ligamentum flavum hypertrophy, interarcuate ligament or joint capsule hypertrophy (can only be assessed with MRI)
(Thrall)
What is the sensitivity and specificity of radiography for identifying spinal fracture/luxation?
Sensitivity 72%, specificity 77%
CT is superior to radiography for identifying and characterizing vertebral fractures
(Thrall)
Radiographic signs consistent with intervertebral disc protrusion? (5)
- Narrowing of the intervertebral disc space
- Narrowing of the intervertebral articular process joint
- Small intervertebral foramen
- Increased opacity within the intervertebral foramen
- Mineralized disc material within the vertebral canal
(Thrall)
Causes of spondylitis? radiographic changes?
Spondylitis (nonspecific term referring to inflammation of the vertebrae)
- Microbial infection
- Plant awn migration
- Spirocerca lupi
- Paraspinal abscess
Radiographic changes:
- Increased opacity over the vertebral body
- Periosteal response of the vertebral body
- Osteomyelitis - aggressive bone response with patchy lysis of the vertebral bodies and irregular periosteal response
- S. lupi infection results in osseous proliferation of the ventral aspect of the vertebral bodies of T8-11
Metastatic neoplasia can cause similar periosteal lesions
How is the intervertebral disc attached to the vertebrae?
What is the proposed mechanism of development of spondylosis?
Sharpey fibers - connect annulus fibrosus to vertebral end plate
Annulus fibrosus is anchored to the dorsal longitudinal ligament by short fibers
Presently - accepted theory states that disruption of sharpeys fibers is the initiator –> radiographic evident osseous proliferation (or enthesopathy) of the margins of the end plate
- These enthesophytes are variably sized ventrolateral spurs that have been referred to as osteophytes incorrectly
- osteophytes occur at osteochondral junctions of synova joints
- Eventually, ventral vertebral enthesophytes can bridge the intervertebral disc space at single or multiple sites –> fusion
- When this occurs in the thoracolumbar junction, adjacent vertebral junctions are at risk for disc degeneration
- Other radiographic findings:
- End plate thickening
- Narrowing of the intervertebral disc space
- Whether or not disc degeneration is a factor in the development of spondylosis deformans is unclear
- In dogs, type II intervertebral disc disease may be part of the pathogenesis of spondylosis deformans
- Type II IVD is often seen in dogs at sites of spondylosis deformans, cause and effect are not clearly established
- Most agree that spondylosis deformans is insignificant clinically, unless a concurrent prolapsed disc is present or if there is bony impingement on the spinal cord or spinal nerve roots
- Nerve root compression from spondylosis is rare except in lumbosacral instability where foraminal impingement results from dorsal extension of enthesophytes
(Thrall)
Typical radiographic changes associated with osteoarthrosis of the dorsal intervertebral articular process joints?
- Remodeling of the articular processes
- Osteophytosis
- Thinning of the joint space
No clinical signs unless causing spinal cord compression
(Thrall)
Components of “cauda equina syndrome”
- Intervertebral disc disease
- Instability of the lumbosacrum
- Stenosis from remodeling changes associated with spondylosis deformans
- Impingement from osteoarthritis of the articular process joints
- Osteochondrosis-like lesion of the sacral end plate (GSD)
(Thrall)
Most common primary vertebral tumor in dogs and cats?
Most common site for canine vertebral tumors?
Which is more common - primary or metastatic vertebral neoplasia?
Sarcomas (osteosarcoma, chondrosarcoma, hemangiosarcoma, fibrosarcoma)
Other ddx: lymphoma, multiple myeloma
In 61 canine vertebral tumors, the most common site for primary neoplasia was the thoracic area
Most metastatic lesions were found in the lumbar area
Metastatic neoplasia is more common than primary vertebral neoplasia - carcinomas and sarcomas most common metastatic neoplasias
(Thrall)
______ frequently cause multiple focal osteolytic lesions in the vertebral processes that are easily recognized on radiographs
Multiple myeloma and lymphoma - these changes are not pathognomic
Textbook of veterinary diagnostic radiology
Radiographic findings of disseminated idiopathic skeletal hyperostosis? (7)
- Bridging ossification along ventral and lateral aspects of three contiguous vertebral bodies
- Relative preservation of disc space width within involved areas, absence of changes of degenerative disc disease
- Osteoarthritis of the dorsal intervertebral process joints
- Pseudoarthrosis of the spinous processes
- Enthesopathy of soft tissue attachments (axial and appendicular skeleton)
- Osteophytes, sclerosis and ankylosis of the sacroiliac joints
- Bony ankylosis of the symphysis pubis
Suggested that 4/7 criteria be present for confirmation of DISH in the dog
Likely a separate entity than spondylosis deformans - predominant excessive ventral distribution supports this
Radiographic vertebral column changes of mucopolysaccharidosis type VI in cats (3)
Skull abnormalities?
- Remodeling and shape change of the vertebra,
- Spondylosis deformans
- Abnormal development of the dens
These changes are primarily a manifestation of vertebral epiphyseal dysplasia
Skull
- Shortened nasal conchae
- Aplasia and hypoplasia of the frontal and sphenoid sinuses
- Shortened dimensions of the incisive and maxillary bones
Changes in appendicular skeleton
- Epiphyseal dysphasia of long bones
- Abnormal nasal choncal development
- Coxofemoral luxation
(Thrall)
(picture) severe degenerative shoulder changes (arrows), and short cervical vertebrae with irregular epiphysis
What are the 2 types of articular process cysts?
What are the 2 ages/locations of presentation
Cysts associated with the articular processes are extradural fluid-filled round or oval, well defined structures that develop as a result of degeneration of the articular process joint
- Synovial cysts - lined by synovium-like epithelial cells resulting from outpouching of synovial membrane through weakened capsular tissue
- Ganglion cysts - result of mucinous degeneration of periarticular connective tissue and which do not have a synovial lining
From clinical and imaging perspectives, the 2 entities are indistinguishable and can be grouped together
Giant breed dogs, cysts tend to be multiple and located in the cervical spine in young dogs
Large breed dogs, cysts more commonly found in the thoracolumbar or lumbosacral area in young adults and older dogs
(Thrall)
What are the most common extradural spinal cord tumors in dogs? cats?
Dogs: osteosarcoma, chondrosarcoma
- Solitary/disseminated histiocytic sarcoma
- Lymphosarcoma
- Multiple myeloma
- Metastatic vertebral tumors - prostatic carcinoma, transitional cell carcinoma
- Sarcoma
- Infiltrative lymphoma
Cats: lymphosarcoma
What are the MRI characteristics of infiltrative lipoma on CT and MRI?
CT - infiltrative lipomas characteristically hypoattenuating, similar to normal fat
MRI - infiltrating lipomas are T1 and T2 hyperintense, and suppress with fat suppression
(Thrall)
CT characteristics of nerve sheath tumor:
- Soft tissue asymmetry - tumor often has attenuating properties similar to muscle
- Unilateral muscle atrophy
- Soft tissue mass that is isoattenuating to surrounding muscles and contrast-enhancement that is uniform, patchy or rim-like
- Occasionally tracks in a linear fashion into a neighboring intervertebral foramen, can invade the vertebral canal
- Invasion into the thoracic cavity can also be seen
Approximately 45% are located in the nerve roots proximal to the spinal cord, while 55% are located in the plexus area or peripheral nerves
Masses as small as 1cm can be identified on CT
MRI features of nerve sheath tumor (5)
- Focal mass or diffuse thickening of affected nerves
- Proximal extension into the intervertebral foramen and vertebral canal is possible
- T2 hyperintense or mixed signal intensity, T1 isointense (or hyperintense/mixed)
- STIR and T1WI+C fat suppressed useful in increasing conspicuity of the tumor
- homogenous/inhomogenous contrast enhancement
- Ipsilateral muscle atrophy - T1 and T2 hyperintense and mildly contrast-enhancing (neurogenic atrophy, edema, fat infiltration, fibrosis)
(Thrall)
Where are the most common locations for spinal meningiomas (according to Thrall)
CT features of spinal cord meningioma
Occasionally frow in the epidural space, most lesions are intradural extramedullary
Usually single, multifocal meningiomas seen occasionally
CT - golf tee sign!! - best seen on sagittal and dorsal images
- May be IV contrast-enhancement of the mass
(Thrall)
MRI features of spinal cord meningioma (5)
- Focal masses
- T2 hyperintense
- T1 isointense/hypointense
- T2 hypointensity and T1 hyperintensity have also been reported
- T1WI+C - meningiomas usually have moderate to strong, well-defined contrast enhancement
- Dural tail often present
(Thrall)
CT findings of nephroblastoma (2)
MRI findings of nephroblastoma (3)
CT: swelling of the spinal cord with obliteration of the epidural fat observed in the affected area
- Intradural/extramedullary pattern with myelography
MRI:
- T2 isointense (may have heterogeneous signal), T1 isointense
- Widening of SAS cranial and caudal to the mass
(Thrall)
MRI features of myelomalacia (4)
- Spinal cord swelling (loss of SAS, loss of epidural fat
- Diffuse patchy T2 hyperintensity that extends over the length of several vertebral bodies
- Focal regions of T2 hypointensity - hemorrhagic foci
- T1 isointense to hypointense
- Regions of T2* hypointensity (presumed hemorrhage)
(Thrall)
Ischemic myelopathy -
Approximately what % of dogs have normal (according to Thrall)
A lesion-length-to-vertebral-length ratio > ____ has a sensitivity of 100% in predicting a poor clinical outcome
A % cross-sectional area of the lesion > _____ has a sensitivity of 100% in predicting poor clinical outcome
20% have normal MRI
- Usually happens when dogs are imaged < 72 hrs after onset of clinical signs
- Higher in ambulatory dogs
A lesion-length-to-vertebral-length ratio > 2.0 has a sensitivity of 100% in predicting a poor clinical outcome
- On average - length of the spinal cord T2 hyperintensity observed on sagittal MRI images in dogs with ischemic myelopathy is approximately 1.8 x length of C6 for cervical/cervicothoracic lesions
- 2.2 x length of L2 for thoracolumbar and lumbosacral lesions
A % cross-sectional area of the lesion > 67% has a sensitivity of 100% in predicting poor clinical outcome
(Thrall)
Spinal epidural empyema
CT findings (2)
MRI findings (6)
CT: epidural mass suspected based on lack of visualization of hypoattenuating epidural fat around the spinal cord. Epidural mass best identified with myelography.
MRI:
- Well defined epidural mass in the dorsal or ventral vertebral canal
- T2 hyperintense or mixed signal
- T1 hypointense
- Peripheral, rim-like contrast enhancement or a diffuse enhancement pattern
- T2* - focal hypointense areas in the epidural mass may be present
- T2 hyperintense gray matter lesions within the spinal cord - secondary to compression or vascular compromise
(Thrall)
Meningomyelitis
CT findings:
MRI findings:
CT:
- Spinal cord swelling
- Spinal cord hypoattenuation
- Occasionally intramedullary or meningeal contrast enhancement
MRI
- Irregular areas of T2 intramedullary hyperintensity
- Precontrast T1 weighted images - isointense or hypointense to the spinal cord, various contrast enhancement
** MRI findings are not specific for meningomyelitis - ddx myelomalacia or ischemic myelopathy
(Thrall)
CKCS with Chari and syringomyelia -
Maximum syrinx width is the strongest predictor of which 3 clinical signs?
Signs of pain
Scratching behavior
Scoliosis
95% of CKCS with max syrinx width of 0.64cm or more will have associated clinical signs
(Thrall)
Multilobular osteochondrosarcoma
MRI characteristics (2)
CT characteristics (3)
MRI:
- Heterogeneous signal intensity with large regions of contrast enhancement
- Well-delineated invasion of soft tissues and brain
CT:
- Well defined margins
- Limited lysis of bone
- Central cord of the tumor appears granular
(Thrall)
MRI and CT features of epidermoid cyst, dermoid cyst
MRI Epidermoid
- Hypointense on T1WI,
- Hyperintense on T2WI/FLAIR
- Peripherally enhancing
CT epidermoid
- Hypoattenuating on CT images
Dermoid cyst MRI
- Hyperintense on T1 and T2WI due to fat content
What techniques can increase the visibility of meningeal contrast-enhancement on MRI?
- Chemical fat suppression of T1W images
- Delayed acquisition time following gadolinium administration reported to provide marginal improvement of contrast enhancement
Subtraction images - Normal dogs have been shown to have consistently identifiable contrast enhancement of the meninges when dynamic subtraction is applied to the images, attributable mainly to the pachymeningeal vessels. In dogs with confirmed inflammatory conditions of the brain, dynamic subtraction does not appear to increase sensitivity of detection of meningeal enhancement (compared with standard pre post contrast images)
** Dynamic subtraction images appear to increase the sensitivity of MRI to detect intra-axial inflammatory lesions in dogs, therefore may still be recommended when meningoencephalitis is suspected
(Mai)
MRI changes associated with meningoencephalitis vs. neoplasia
In general, when compared with neoplasia, the MRI appearance of meningoencephalitis is more likely to:
- Be multifocal
- Involve both supratentorial and infratentorial regions of the brain
- Irregular lesion shape with ill-defined margins
- Uniform T2W and T2 FLAIR signal hyperintensity
- Meningeal contrast enhancement
In general, when compared with neoplasia, the MRI appearance of meningoencephalitis is LESS likely to
- Have strong contrast enhancement (contrast enhancement is still common)
- Have heterogeneous T2W or T2 FLAIR signal intensity
- Have mass effect (still frequently seen)
(Mai)
Brain MRI findings of:
- Multifocal lesions of the white and gray matter, can involve the forebrain, brainstem and cerebellum
- Irregular lesion margins, T2 and T2 FLAIR hyperintensity, T1 hypo or isointensity
- Variable contrast enhancement, can have ring-like pattern
- T2W perilesional hyperintensity (edema)
- Meningeal enhancement not typical but may be present
Most consistent with?
Diffuse GME
(Mai)
Brain MRI findings of:
- Single mass
- Mass with compression or displacement of the adjacent structures
- Variable, occasionally strong contrast enhancement
- T2W hypointense foci associated with hemorrhage
Most consistent with?
Focal GME vs. neoplasia
(Mai)
Brain MRI findings of:
- Multifocal, asymmetric lesions with ill-defined margins affecting cortical gray and subcortical white matter, causing loss of gray-white matter distinction
- Lesions found in the cerebral hemispheres, hippocampus, thalamus, caudal brainstem, and cerebellum
- Lesions are iso-or-mildly hypointense on T1W images and hyperintense on T2/T2FLAIR images
- Variable and mild contrast enhancement of parenchymal lesions
- Mild contrast enhancement of the leptomeninges
- Asymmetric lateral ventriculomegaly
- Mass effect causing falx cerebri shift
- Perilesional T2 and T2 FLAIR hyperintensity
- Occasional findings: cerebellar herniation through foramen magnum, sharply marginated cyst-like lesions characteristic of necrotic fluid, lesions confined to caudal brainstem
Necrotizing meningoencephalitis
(Mai)
Brain MRI findings of:
- Multifocal, asymmetric irregularly shaped lesions with ill-defined margins, predominantly affecting the subcortical white matter of the cerebral hemispheres (but also cortical gray matter, thalamus and brainstem)
- Lesions are hypointense on T1W images and hyperintense on T2W FLAIR images
- Variable contrast enhancement (can have ring pattern)
- Perilesional T2W hyperintensity (edema)
- Sharply delineated cyst-like lesions reported, uncommon
Most consistent with?
Necrotizing leukoencephalitis
(Mai)
Brain MRI characteristics of:
- Widening of the cerebral sulci (cortical atrophy)
- Patchy cerebral T2W hyperintensity
- Diffuse T1 hypointensity of the cerebral gray matter
- Patchy or diffuse contrast enhancement of the cerebral cortex/meninges
- Intra-axial mass lesions
Most consistent with?
Idiopathic eosinophilic meningoencephalitis
(Mai)
Brain MRI findings of:
- Thickening, increased T2 hyperintensity and increased contrast enhancement of the pachymeninges (limited to the dura without extension into the sulci), which can be severe
- In some cases, the enhanced dura has a layered pattern (2 enhancing layers surrounding an iso to hypointense central layer)
Most consistent with?
Idiopathic hypertrophic pachymeningitis
(Mai)
Brain MRI findings of:
- Large, ill-defined lesions affecting the cerebral gray matter that are T2W and T2 FLAIR hyperintense, T1 iso or hypointense. Seen most commonly in the temporal lobes
- T2W hyperintense, T1W hypointense lesions in the cerebellum and brainstem w/ loss of gray-white matter distinction, corresponding histopathological to areas of demyelination
- Variable contrast enhancement of these lesions
Acute distemper encephalitis
(Mai)
A ______ vertebrae has been defined as one in which a portion of the vertebra failed to form correctly, resulting in a wedge-shape to the vertebral body
What is the more appropriate name for a “butterfly” vertebrae?
Cuneiform vertebra
- The base of the wedge in most cases is oriented dorsally
- Incorrectly called hemivertebra
- A true hemivertebrae is one where half of the vertebra (centrum and neural arch) fails to form
- This would lead to scoliosis rather than kyphosis
Butterfly vertebra = Ventral and median aplasia of the vertebra
(Dewey et al)
How is the cobb angle measured? What is the cutoff for clinical signs associated with kyphosis?
Most dogs with neurologic dysfunction had a Cobb angle associated with the kyphotic vertebral segment > 35 degrees
(Vet Clin N America)
What MRI slice thickness, planes, and sequences are optimal for imaging cranial nerves?
2mm slice thickness
Transverse T2 best
T1 can be helpful for bony landmarks
(Mai)
Dogs:
What cranial nerves can be consistently visualized with MRI?
What cranial nerves are better visualized on thin slices?
Chat cranial nerves are poorly visualized or not visualized?
Cranial nerves 2. 3. 5 (and divisions), 8 - consistently visualized
Cranial nerves 4, 7, and group of 9, 10, and 11 - better visualized on thin slices
CN 6 and 12 - poorly visualized or not visualized
2mm thick slices allowed accurate visualization of most CN emergencies - 2, 3, 4, 5, 7, 8 and 9/10/11
Course of 2, 3, and 5 could be followed on several slices
Main branches of CN V seen well on thin-slice studies
(Couturier et al)
Cats:
What cranial nerves can be consistently visualized with MRI?
What cranial nerves are inconsistently visualized with MRI?
What cranial nerves cannot be visualized with MRI?
Cranial nerves II, V and its divisions, VII and VIII are typically visualized
The emergency of CN IX, X, XI, XII, and the common path of nerves IX, X, and XI through the TOF can be visualized as an ill-defined HYPERINTENSE structure
CN III - inconsistently visualized
CN IV and VI - not visualized
(Couturier et al)
A1 - Vermis
2 - Accessory n
3 - Basilar artery
B1 - Lateral recess of the 4th ventricle
2 - Caudal cerebellar peduncle
3 - Emergence of CN IX, X, XI
C1 - 4th ventricle
2 - paraflocculus of the cerebellum
3 - cochlear nucleus
D1 - Culmen
2 - Lingula
3 - Perilymph and endolymph (within vestibule of inner ear)
4 - CN VIII
Couturier et al.
k9 brain
E1 - culmen
2 - fourth ventricle
3 - middle cerebellar peduncle
4 - facial nerve
5 - perilymph and endolymph of the cochlea
F1 - facial canal
2 - rostral part of the cochlea
3 - tympanic bulla of the middle ear
G1 - rostral part of cerebellum
2 - caudal colliculus
3 - area of emergence of the trochlear nerve
4 - emergence of trigeminal nerve
H1 - optic chiasm
2 - orbital fissure
(Couturier et al)
k9 brain
G - 1 oculomotor nerve
2 - ophthalmic branch of trigeminal nerve
3 - maxillary branch of trigeminal nerve in round foramen
H1 - optic chiasm
2 - maxillary branch of trigeminal nerve in rostral alar foramen
I1 - optic nerves
2 - oculomotor, trochlear, and abducent nerves in orbital fissure
3 - ophthalmic branch of the trigeminal nerve in orbital fissure
4 - retractor bulbi muscle
(Couturier et al)
K9 brain
J - 1, optic nerves
2 - oculomotor nerve in orbital fissure
3 - ophthalmic branch of trigeminal nerve in orbital fissure
4 - maxillary artery
5 - maxillary branch of trigeminal nerve
K1 - optic nerve
2 - ophthalmic branch of the trigeminal nerve with associated vessels, oculomotor nerve, trochlear nerve, and abducent nerve. These structures cannot be differentiated here
L1 - optic nerve
Couturier et al
K9 brain
A1 - caudal colliculus
2 - mesencephalic aqueduct
3 - periaqueductal gray matter
4 - trigeminal nerve
B1 - rostral colliculus
2 - brachium (white matter) of the caudal colliculus
3 - mesencephalic aqueduct
4 - trigeminal nerve and ganglion
C1 - lateral geniculate nucleus
2 - medial geniculate nucleus
3 - area of oculomotor nucleus
4 - trigeminal nerve and ganglion
Couturier et al
K9 brain
D1 - thalamus
2 - trigeminal nerve
E1 - thalamus
2 - interthalamic adhesion
3 - third ventricle
4 - ophthalmic and maxillary branches of trigeminal nerve
F1 - thalamus
2 - interthalamic adhesion
3 - third ventricle
4 - pituitary gland
5 - ophthalmic and maxillary branches of trigeminal nerve
6 - mandibular branch of trigeminal nerve in the oval foramen.
(Couturier et al)
K9 brain
(A) Dorsal T1W image through the brain of a normal medium-sized dog showing the optic nerves (white arrow).
(B) Dorsal T2W image through the brain of a normal medium-sized dog showing the maxillary branch of the trigeminal nerve (small white arrow) and the zygomatic salivary gland (large white arrow)
Couturier et al
K9 brain
(A) Parasagittal T2W image through the brain of a normal Afghan hound showing the emergence of the trigeminal nerve (small white arrows)
Fel brain
A1 - vermis
2 - fourth ventricle
3 - hypoglossal nerve
4 - pyramid
B1 - vermis
2 - fourth ventricle
3 - CN IX, X, XI, and XII
4 - pyramid
C1 - occipital lobe of telencephalon
2 - rostral vermis of cerebellum
3 - cerebellar peduncle
4 - vestibulocochlear nerve
5 - fourth ventricle
6 - myelencephalon
D1 - occipital lobe of telencephalon
2 - rostral vermis of cerebellum
3 - caudal colliculus
4 - facial nerve
5 - cochlea
6 - transverse pontine fibers
E1 - longitudinal cerebral fissure
2 - hippocampus
3 - cerebral cortex
4 - periaqueducal gray matter
5 - mesencephalic aqueduct
6 - brachium of the caudal colliculus
7 - trigeminal nerve
F1 - rostral colliculus
2 - mesencephalic aqueduct
3 - medial geniculate body
4 - trigeminal nerve ganglion
(Gomes et al)
Fel Brain
G1 - temporal lobe of telencephalon
2 - third ventricle
3 - lateral geniculate body
4 - thalamus
5 - pituitary gland
6 - oval foramen with mandibular branch of trigeminal nerve
H1 - dorsal part of the third ventricle
2 - interthalamic adhesion
3 - pituitary gland
4 - oculomotor nerve
5 - round foramen with maxillary branch of trigeminal nerve
I1 - lateral ventricle
2 - interthalamic adhesion
3 - third ventricle
4 - orbital fissure nerve group (III, IV, VI, and ophthalmic branch of V)
J1 - longitudinal cerebral fissure
2 - lateral ventricle
3 - hypothalamus
4 - optic chiasm
5 - orbital fissure (CNIII, IV, V, and VI)
K1 - corpus callosum
2 - internal capsule
3 - caudate nucleus
4 - optic nerve
5 - sphenoid sinus
L1 - optic nerve
2 - ophthalmic branch (trigeminal nerve), oculomotor, abducent, and trochlear nerves. CN, cranial nerve.
(Gomes et al)
Fel Brain
(A): Thin copper wire in thehypoglossal canal (arrow)
(B) 1, hypoglossal canal and 2, tympano-occipital fissure
(C) internal acoustic meatus (arrow)
(D) facial canal (arrow)
(E) ovalforamen (arrow)
(F) round foramen (arrow)
(Gomes et al)
Fel brain
(A) through the optic nerve: 1, optic nerve, 2,optic chiasm
(B) through the vestibulocochlear nerve (arrow)
(Gomes et al)
The area of ischemic tissue within the lesion that is potentially salvageable with treatment is known as the __________
Ischemic penumbra
- Surrounding the penumbra, there is an area of tissue with mild reduction in blood flow, which is more likely to survive called the ‘oligemic region’
(Mai)
How does T2W imaging estimate the volume of an ischemic lesion?
Underestimates the size
DWI is significantly more sensitive, especially in peracute stage
(Mai)
What is the utility of expotential ADC maps in the diagnosis of acute ischemic infarct?
The exponential ADC map is calculated from the ADC values, leads to an inverted scale more similar to the DW images, where restricted diffusion appears bright, but again eliminating T2 shine-through effects like the regular ADC map
These exponential ADC maps may be more sensitive than ADC images for recognizing restricted diffusion in periventricular areas, as bright signal adjacent to the dark CSF
(Mai)
In experimental models, ADC values have a maximal decrease at approximately _______ hours after onset of ischemia
How does ADC change in chronic stroke
24 hours
Chronic stroke - ADC elevated (after 10d in human)
(Mai)
What are the sequences necessary to diagnose arterial infarction in small animals?
T2FLAIR
T1W post contrast
T2*W GRE (or other susceptibility weighted imaging)
DWI
(Mai)
Criteria for chronic infarct? (3)
- Resolution of edema
- Resorption of necrotic tissue
- Restoration of the BBB
Usually takes 6 weeks
Serial imaging of infarcts has shown that:
- Chronic infarcts are smaller and more sharply marginated than acute infarcts
- Often parenchymal volume loss
- Areas of cavitation
- Absence of parenchymal contrast enhancement
- Secondary changes (atrophy due to wallerian degeneration) may be seen downstream of the areas of infarction
(Mai)
What are the main perforating arteries of the brain in dogs?
- Medial striate arteries which arise form the circle of willie at the junction of the ethmoidal and middle cerebral artery
- Number varies, usually symmetric and there is no association between the number and the dog’s size
- Lateral striate arteries - arise from the middle cerebral artery
- The distribution and number of lateral striate arteries is more variable (usually 2 on each site)
- Origin of these arteries is variable - may arise from the communicating arteries, rostral or middle cerebral arteries
- Some anastomoses and small overlap of vascular territories occur
(Mai)
Ischemic arterial stroke with:
- No mass effect
- No contrast enhancement, or mild arterial enhancement
- Decreased ADC
Peracute
(Mai)
Ischemic arterial stroke with:
- Variable mass effect
- No contrast enhancement, or mild/moderate vascular and parenchymal enhancement
- Decreased ADC value
Acute
(Mai)
Ischemic infarct with:
- Variable mass effect
- Gyral or parenchymal contrast enhancement
- Normal ADC
Subacute
(Mai)
Ischemic arterial infarct with:
- No mass effect or atrophy
- No contrast enhancement
- Elevated ADC value
Chronic arterial infarct
(Mai)
What brain vessel supplies:
- Caudal crus of the internal capsule
- Caudal caudate nucleus
- Optic tract
- Putamen
- Globus pallidus
- Choroid plexus of the lateral ventricles
Rostral choroidal artery
Branch of middle cerebral artery or directly from arterial circle @ the level of MCA
(Mai)
What vessel supplies:
- Basal nuclei
- Medial part of the internal capsule
Medial striate arteries/lenticulostriate arteries
(arise from the circle of willis @ level of MCA)
(Mai)
What vessel supplies:
- Claustrum
- External capsule
- Insula
- Lateral part of the internal capsule
- Dorsal part of the caudate nucleus
Lateral striate arteries/lenticulostriate arteries
Branches of MCA
(Mai)
Vessel that supplies rostromedial thalamus?
Proximal perforating artery
Arises from the caudal communicating branch
(Mai)
What vessel supplies the caudolateral aspect of the thalamus and subthalamus?
Distal perforating artery
Arises from the caudolateral aspect of the thalamus and subthalamus
(Mai)
What vessel supplies the median and paramedian aspect of the caudal thalamus, rostral pons, and midbrain?
Caudal perforating artery arising from the basilar bifurcation
Paramedian branches arising from the proximal portion of the caudal cerebral artery
(Mai)
These images are examples of?
Acute lacunar infarcts
In dog 1 (a), the transverse T2-FLAIR image shows an infarct within the territory of the right striate arteries (solid arrow).
In dog 2 (b, c), transverse and dorsal T2W images show an infarct within the territories of the perforating arteries (dotted arrows).
In dog 3 (d), there is an infarct also in the territories of the perforating arteries (open arrow). Acute lacunar infarcts have variable shapes.
Often on one imaging plane lacunar infarcts have an angular appearance and are relatively sharply marginated with minimal or no mass effect. Note the difference in shape of the infarct on the transverse (b) and dorsal (c) images in dog 2. Small lacunar infarcts adjacent to the lateral ventricles are often best seen on dorsal plane T2W images.
Clinical history, CSF analysis, and DWI may be required to differentiate some lacunar infarcts from inflammatory disease.
The distribution of lacunar infarcts depends on which arteries are involved.
It is not uncommon for there to be multiple lacunar infarcts in different vascular territories, in contrast to large territorial infarcts, which are usually solitary
(Mai)
MRI brain lesion of:
- Small focal lesion that is irregular or angular in shape
- Located within territory of small vessels (thalamus, basal ganglia, internal capsule, brainstem)
- Mass effect usually absent/mild
- Hyperintense on T2W images
- Commonly solitary (may be multiple)
- Contrast enhancement is absent or mild
Lacunar infarct
- Multiple infarcts in differing vascular territories are suggestive of an embolic disease
- DWI pulse sequences may show restricted diffusion in the early stages, but due to small size lesions may not be visible
- In chronic stages, cavitation and loss of volume are common
- Hemorrhagic transformation is uncommon
(Mai)
Differential diagnosis for lesions appearing bright on DWI?
- Artifactual (T2 shine through)
- Lesions containing viscious/proteinaceous fluid (early abscessation)
- Cytotoxic edema
- Infarction/ischemia
- Post-ictal edema
- Some metabolic diseases and toxicosis
- Hypertensive encephalopathy
- Viral encephalitis/Encephalitis
- Leukodystrophy
- Densely cellular mass
- Lymphoma
- Some gliomas
- Granulomas
(Mai)
Features that may help differentiate infarct from glioma
Glioma:
- Not confined to vascular territory
- Tend to be larger
- More pronounced mass effect
- More pronounced perilesional edema
- More often bright on DWI and ADC
Infarct
- Confined to vascular territory
- Smaller
- Less mass effect, less perilesional edema
- Bright on DWI, dark on ADC
- Wedge-shaped
(Mai)
How does the perfusion of seizure-induced post-ictal changes differ from ischemic infarct?
Seizure induced post-ictal changes have hyperperfusion (acute infarcts are underperfused)
MRI findings suggestive of global brain ischemia?
- T2W, T2FLAIR hyperintensity within the cortical gray matter of the parieto-occipital lobes
- T2W and T2 FLAIR hyperintensity within the caudate nuclei
- Bilateral distribution, most commonly symmetric but may be asymmetric
- Mild or no involvement of subcortical white matter
- Mild diffuse cortical and caudate nucleus contrast enhancement in some cases
Follow up MRI - may show reduced size and severity of lesions, gray matter hyperintensities may persist permanently
(Mai)
Transverse T2W (a) and T2-FLAIR (b) images in an 8-year-old Maltese who had general anesthesia the day prior for a dental procedure. The dog was previously healthy but was slow to recover from anesthesia and then developed generalized tremor with altered mentation; he became stuporous and non-ambulatory tetraplegic. There is increased signal intensity in the gray matter of both frontoparietal lobes, symmetric but worse on the left. The changes together with the history are consistent with global brain ischemia.
(Mai)
Name the abbreviations
DSS = dorsal sagittal sinus
TR = transverse sinus
TE = temporal sinus
MV = maxillary vein
ST = straight sinus
SI = sigmoid sinus
DCV = dorsal cerebral vein
(Mai)
What are the MRI features of central venous thrombosis?
Abnormal signal within a sinus
Corresponding absence of flow on MRV
(Mai)
MRI findings associated with hypertensive encephalopathy
- T2 hyperintensities within the white matter (vasogenic edema)
- Isoitnense T2W, noncontrast-enhancing (or mild contrast enhancement)
- Lesions preferentially involve the mid-caudal cerebrum (parietal and occipital lobes), although lesions can be extensive within the cerebrum and involve the frontal regions
- Caudate nuclei/thalamus are less commonly affected
- Lesions may be bilaterally symmetric or asymmetric
- Clear differentiation between white and gray matter in affected areas
- DWI show increased signal on ADC maps - increased diffusion due to vasogenic edema
Diagnosis is based on documenting hypertension and resolution of the neurologic signs following control of the hypertension
(Mai)
Feline brain
Hypertensive encephalopathy
(Mai)
Vascular anomalies involving the brain and meninges: (7)
- Absence or hypoplasia of normal vessels
- Persistent transient embryonic vessels
- Vessels with abnormal morphology
- Arteriovenous malformations
- Dural arteriovenous fistulas
- Aneurysms
- Cavernous malformatin
(Mai)
What are the anatomic components of arteriovenous malformations?
- Feeding arteries
- Draining veins
- Nidus of abnormal vessels between the 2
- Differs histologically from capillaries
- Functions as an arteriovenous shunt
(Mai)
___________ is a vascular malformation composed of closely packed, thin walled vessels without norma interposed brain parenchyma
Cavernous malformations
- they may occur anywhere in the brain, most commonly found within the subcortical white matter (and may be multiple)
(Mai)
How do paramagnetic and superparamagnetic effects affect longitudinal and transverse relaxation?
How do Fe and heme affect longitudinal and transverse relaxation
Accelerate both longitudinal and transverse proton relaxation = decrease the T1 and T2 relaxation time
The effects are most obvious on T2W –> results in increased signal
For paramagnetic effects of Fe and heme to be recognized, water molecules must be in close proximity to the Fe atoms
Although the Fe in deoxyhemoglobin, and hemosiderin/ferritin is paramagnetic/superparamagnetic, the molecular configuration of these molecules shields the Fe from water molecules –> no or minimal effects on relativity (T1 signal) are seen on the image
(Mai)
How does hemorrhage affect the T2 relaxation of tissues, and how does it affect the neighboring protons?
Hemorrhage: Fe creates a local magnetic field distortion –> shortened T2 relaxation and rapid loss of neighboring protons’ phase coherence
Fe within cell (compartmentalization) –> local heterogeneity in magnetic field –> acceleration of spin dephasing
Weaker paramagnetic substances (methemoglobin) may not cause significant magnetic field heterogeneity
When noncompartmentalized, this will be even weaker
(Mai)
What form of hemoglobin is diamagnetic and T1 isointense?
Oxyhemoglobin
(Mai)
What form of hemoglobin is T1 isointense and paramagnetic?
Deoxyhemoglobin
(Mai)
What form of hemoglobin is T1 hyperintense and paramagnetic?
Methemoglobin
(Mai)
What form of hemoglobin is T1 isointense to slightly hyperintense, and superparamagnetic?
Ferritin and hemosiderin
(Mai)
Regarding intracranial hemorrhage relaxivity and susceptibility, which one affects T1 relaxation more, and which one affects T2 relaxation more?
Relaxivity effects are greatest on T1 relaxation
Susceptibility effects are greatest on T2 relaxation (especially T2*)
(Mai)
The appearance of hemorrhage on _____ images is useful in differentiating acute from subacute hemorrhage
T1W images
Acute - isointense
Subacute - hyperintense
(Mai)
The appearance of hemorrhage on ______ is useful in differentiating early subacute from late subacute stages
T2W in people (this may not apply to dogs)….
Early subacute - T2 hypointense
Late subacute - T2 hyperintense
(Mai)
Age of hemorrhage?
T1 and T2 hyperintensity suggests late subacute/chronic
(Mai)
T1 hyperintense lesions (8)
- Melanin (melanoma mets, melanosis)
- Flow artifacts
- Lipis (dermoid cyst, lipoma)
- Protein effects (colloid cysts, rathke’s cleft cyst, epidermoid cyst, laminar cortical necrosis)
- Magnanese/Fe/gadolinium/Cu deposition
- Calcification
- Vasopressin in the pituitary gland
- Hemorrhage (methemoglobin)
(Mai)
What MRI features of hemorrhage are suggestive of a neoplastic cause?
- MRI appearance is predominantly a solid mass
- Hemorrhagic tumors are often complex masses with solid, contrast-enhancing parts
- Lack of a distinct, complete T2/T2* hypointense rim
- Bleeding of different ages within the lesion
- Humans - there is a trend for tumors to have more severe perilesional edema (remains present on repeat imaging)
(Mai)
Age of the hemorrhage?
Early subacute hematoma
(Mai)
Age of the hemorrhage?
Hyperacute-acute lesion
The large amount of perilesional edema, absence of contrast enhancement, narrow complete hypointense rim of T2* - consistent with benign etiolog
(Mai)
Why is the MRI signal appearance of extra-axial hemorrhage different than intraparenchymal hemorrhage?
Higher oxygen tension in the dura/CSF/subarachnoid space - progression between stages is slower (especially for subarachnoid and intraventricular hemorrhage)
The appearance of very chronic hemorrhage in the extra-axial spaces differs due to the formation of non-paramagnetic hemichromes when methemoglobin undergoes oxidative denaturation (due to greater oxygen levels)
Chronic extra-axial hemorrhage - absence of a hemosiderin rim (unless there is repeated bleeding)
(Mai)
What type of intracranial has the following characteristics:
- Serpentine or linear in shape
- Follows adjacent sulci, resulting in displacement of cortical gray matter away from the adjacent bone
- Variable mass effect
- Variable signal intensity depending on age
Subarachnoid hemorrhage
- Focal/diffuse hemorrhage confined to the subarachnoid space within the basal cisternae and/or adjacent to the cerebral hemispheres
- Variable signal intensity dependent on age but T1 hyperintensity, T2 hypointensity, or T2* gradient echo hypointensity +/- susceptibility artifact is suggestive
- Chronic cases (in humans) - superficial siderosis (subpial accumulation of hemosiderin) is reported - appears as linear T2/T2* gradient echo hypointensity following the cortex and in later stages, cyst formation and brain atrophy
(Mai)
What type of intracranial hemorrhage has the following characteristics:
- Single or multiple cresent-shaped hemorrhages superficial to the brain
- signal intensity varies w/ chronicity
- May cross suture lines of the cranium, but does not cross midline or os-tentorium
- Significant mass effect
Subdural hemorrhage
- Signal intensity varies with chronicity - main component is usually hyperintense or of mixed signal intensity on T2W images, and low signal intensity on T1W images in the chronic stages
- Acutesubacute stages - similar to intraparenchymal hemorrhages
- In chronic cases, meninges may be markedly thickened and show diffuse increased contrast enhancement
- Repeated bleeding may result in low signal periphery due to hemosiderin deposits - overwhelm normal clearance mechanisms
(Mai)
Whats wrong
Fig. 5.7.16 Acute traumatic brain injury and extra-axial (probable subarachnoid) hemorrhage and small skull fracture in a 3-year-old Cavalier King Charles Spaniel hit by a car 3 days previously and showing signs of mild ataxia.
Dorsal (a) and transverse T2W (b), T2-FLAIR (c), and T2*W gradient echo (d) images showing a small fracture in the left temporal bone on the dorsal plane image (solid arrow, a) and linear T2 hyperintensity conforming to the surface of the left cerebrum consistent with an acute small subarachnoid hemorrhage (dotted arrows, a and c).
The fluid accumulation is best seen on the T2-FLAIR image (c).
The presence of corresponding reduced signal within the fluid on the T2*W image (d) is difficult to visualize due to the small size of the lesion and adjacent bone.
(Mai)
What type of intracranial hemorrhage has the following characteristics:
- Most commonly convex or biconvex (lenticular) in shape
- May cross dural folds, does not cross suture lines
Epidural hemorrhage
- Occurs within the space between the inner cortex of the cranium, and the dura mater
- Most commonly arterial in origin
- Rare
- Low signal from the fibrous dura may be visible between the hematoma and surface of the cerebral cortex
(Mai)
Where is the hemorrhage?
Acute epidural hematoma in a 1-year-old Labrador Retriever secondary to Angiostrongylus vasorum infection. Sagittal (to the left of midline, a) and transverse T2W (b), T2*W gradient echo (c), and T1W (d) images showing a
biconvex (‘lenticular’) extra-axial fluid accumulation, which does not cross the frontoparietal suture line (arrow, a).
Within the hematoma, there is dependent fluid-fluid level (arrow, b).
The presence of peripheral T1 hyperintensity (dotted arrow, d) and low signal on the T2*W (c) image is consistent with an acute hemorrhage
(Mai)
During what stage may ventricular hemorrhage be isointense to CSF?
Acute stage - isointense on T1 and T2 but will be hyperintense on FLAIR
(and can be noted on T2*)
(Mai)
____________ is defined as injury that results from rapid acceleration head trauma causing shearing injuries related to differences in elastic and inertial properties between different but adjacent brain tissue
Diffuse axonal injury
- This results in disruption of axons (especially at the gray-white matter junction of the cerebrum, corpus callosum, basal nuclei, and rostral aspect of the brainstem)
- DAI is poorly documented in animals
(Mai)
MRI findings associated with secondary traumatic brain injury (5)
- Diffuse cerebral swelling (effacement of cerebral sulci, ventricular compression, vasogenic edema ect.)
- Herniation
- Ischemia/infarct
- Infection
- Pneumocephalus
(Mai)
What are prognosic indicators on MRI in patients with head trauma?
- Degree of midline shift
- Extent of intraparenchymal lesions
- Brain herniation
- Skull fractures
- Injuries affecting the caudal fossa, or both rostral and caudal fossa
(Mai)
MRI findings of brain maturation in the dog:
- Expansion of the lateral ventricles?
- MRI maturation of the cerebellum and brainstem?
- MRI maturation of the corpus callosum?
- Maturation of cerebral gyri and sulci?
- Expansion of lateral ventricles - first detected at 3-4 weeks of age
- Changes in gray and white matter signal intensity due to progressive myelination of the brain
- Occur from caudal to rostral in the brainstem
- And from central to peripheral in the cerebellum
- MRI maturation of the cerebellum and brainstem reached at 4 weeks on T1W images, 6 weeks on T2W and STIR images, 12 weeks on FLAIR images
- MRI maturation of the corpus callosum is reached at 6 weeks on T1 images, 8 weeks on T2W and STIR images, and 12 weeks on FLAIR images
- Maturation of cerebral gyri and sulci continues after birth, complete by 14 days postpartum
- Sequence and time course of gyrification are identical for all breeds studied
- Symmetry of gyri is maintained during this development
(Mai)
Postnatal maturation of the cerebral hemispheres on T1W images? (1-3 weeks, 3-4 weeks, 16+ weeks)
1-3 weeks: white matter isointense or hyperintense to gray matter
3-4 weeks: Isointense transition
16+ weeks: White matter hypointense to gray matter (mature)
(Mai)
Postnatal maturation of canine cerebral hemispheres on T2W and STIR images?
- 1-4 weeks - juvenile, white matter isointense or hyperintense to gray matter
- 4-8 weeks - isointense transition
- 16+ weeks - white matter hypointense to gray matter (mature)
(Mai)
Postnatal maturation of the canine cerebrum on FLAIR images
- 1-2 weeks - White matter hypointense to gray matter (pseudomature)
- 3 weeks - 1st isointense transition
- 4-6 weeks - White matter hyperintense to gray matter (Juvenile)
- 6-12 weeks - 2nd isointense transition
- 36 weeks - white matter hypointense to gray matter (mature)
(Mai)
Brain age? (T2W sequences)
a) 1-4 weeks - subcortical white matter is T2 hyperintense to gray matter during the juvenile phase
b) 6 weeks - subcortical white matter is isointense during the transition phase
c) 8-36 weeks - subcortical white matter is hypointense during maturation phase and into adulthood
The relative decrease in white matter intensity is predominantly due to a decrease in water content during myelination
(Mai)
Variations in cerebral atrophy seen in brachycephalic/metasicephalic dogs, male vs. female dogs?
Male - larger loss of prefrontal cortex, reduction in white matter tract volume of the optic nerve bundle
Female - larger loss of temporal cortex, greater atrophy of hippocampal white matter
Male/female - equivalent atrophy of the internal capsule
Cerebral atrophy is most pronounced in mesaticephalic and brachycephalic breeds
(Mai)
What 3 factors are associated with decreased performance on cognitive tests?
- Smaller frontal lobe volume
- Larger A-beta load
- Smaller interthalamic adhesion
(Mai)
How does the size of the hippocampus change with age?
Unclear -
Hippocampal volume in dogs > 11 years was significantly smaller than younger animals (study of 66 beagles)
No correlation between hippocampus size and age was observed in a study of 19 beagles
(Mai)
Possible causes of periventricular white-matter changes in dogs?
- Chronic ischemia –> perivascular demyelination and axonal loss
- BBB compromise
- Amyloid angiopathy
These seem to correspond to age-related white matter changes and leukoariosis originally reported in elderly people, more recently in dogs
In people, they are known to contribute to dementia while their significance in dogs is undetermined to date
(Mai)
Age-related MRI changes reported in the cat
- Cerebral atrophy with increased ventricular size and widening of sulci (less marked than dog)
- Small multifocal T2 hypointensity, predominantly in the piriform lobes
(Mai)
What value can be increased in dogs with intracranial hypertension, related to the optic nerve?
Increased value of:
Intraorbital optic nerve sheath diamteer (measured on transverse T2W images) : body weight
(Mai)
Cause?
Idiopathic oculomotor neuropathy
Transverse MR images obtained at the level of the pituitary gland (asterisk, c) in a 6-year-old male neutered Beagle presented with internal ophthalmoplegia and external ophthalmoparesis of the right eye.
There is marked enlargement of the right oculomotor nerve with isointensity on T2W (arrow, a), hypointensity on T2-FLAIR (arrow, b), and isointensity on T1W pre-contrast (arrow, c) with marked focal homogeneous enhancement following contrast administration (arrow, d).
(Mai)
Causes of cavernous sinus sundrome
** most common ** Neoplastic: Meningioma, lymphoma, metastatic carcinoma, pituitary tumors, GCT, glial cell tumors, PNET< retropharyngeal neuroendocrine tumors
Trauma
Vascular anomalies
Infectious - cryptococcosis, FIP
(Mai)
Solid arrow?
Facial neuritis (secondary to otitis media/interna)
________ is CT artifact that occurs when a polyenergetic x-ray beam passes through regions of thick bone, increasing the average energy of the beam
Beam hardening artifact
After passing through a particularly dense bone (petrous temporal bone) from a variety of angles, the reconstruction algorithm does not allow for the unpredicted increase in energy –> formation of white and black lines superimposed on the image
The reconstruction algorithm falsely interprets the transmitted high energy beam as the result of low attenuation
(BSAVA)
What can be done to reduce beam hardening artifact?
- Shift highly attenuating structures (bones, metal) away from the area of interest (not feasible….)
- Change slice angle
- Use high kVp and high filtration to increase the average beam energy
(CT PPT)
What are the HU of hemorrhage following trauma?
Normal white matter 25 - 35, normal gray matter 35-50
Immediately: 40 - 60HU
(Hematoma forms heterogeneous mass of RBCs + WBCs + platelets + serum)
Early hours: 60 - 80HU
(Formation of meshwork of fibrin fibrils + globin molecules; clot retraction)
Days 80 - 100HU center, hypodense halo
(Further clot retraction, serum extrusion, vasogenic edema)
Weeks - density decreases 0.7 - 1.5HU/day from the periphery to the center
(Breakdown of globin molecules)
Weeks/months - Resolution of hematoma or persistence of hypodense area
(Digestion of blood degradation products by macrophages)
“Acute and subacute hemorrhage is hyperattenuating to the normal brain parenchyma (40 - 100HU) and is readily depicted on CT. Over time, density of intracranial hemorrhage decreases until it becomes hypoattenuating to brain parenchyma”
(Hecht)
Why is the lipid-rich myelin of white matter T2 hypointense?
Myelin = mostly phospholipids (as compared to triglycerides in adipose)
Phospholipids - very fast T2 relaxation = ~*MRI invisible*~
White matter contains 12% less water than grey matter which makes them T2 hypointense
Demyelinating lesions are T2 hyperintense due to increased water
(Tidwell)
What MRI artifact is depicted?
Time of flight vascular flow-related artifact
Transverse T2W (a) and T2*W gradient echo (b) images of the normal cervical spine in a dog. There is absence of signal within the carotid arteries (solid arrows) and jugular veins (dashed arrows) on the T2W image (a) but high signal on the T2*W image (b) due to ‘time of flight’ effects. Blood within the ventral vertebral venous sinuses
(Mai)
What MRI artifact is depicted?
Entry slice phenomenon - vascular flow-related artifact
Transverse T1W images of the cranial abdomen showing entry slice phenomenon. Blood flowing into the aorta (solid arrows) is highest in signal in the entry (cranial) slice (a) and is low signal at the exit (caudal) slice (b). The reverse is seen in the caudal vena cava (dashed arrows), where the entry slice is caudal and the exit slice is cranial.
(Mai)
What MRI artifact is depicted?
Intravoxel dephasing - vascular flow-related artifact
Transverse T2*W gradient-echo images with (a) and without (b) flow compensation of the cervical spine in a French Bulldog with syringomyelia. Without flow compensation (b) there is low signal within the carotid arteries (solid arrows, b) due to intravoxel dephasing. With flow compensation (a), the altered phase shifts of the flowing blood are corrected and the vessels appear higher in signal (solid arrows, a). In addition to correcting for signal changes due to intravoxel dephasing, flow compensation can reduce other flow-related artifacts (
(Mai)
What is the MRI artifact?
Pulsatility artifact (a type of flow-related artifact)
Matched post-contrast transverse T1W images of the canine brain at the level of the thalamus. (a) With the phaseencoding gradient applied in a ventral to dorsal direction, vascular pulsations (dashed arrows) create ghosts superimposed on brain parenchyma (solid arrows).
(b) When the phase-encoding direction is changed to a horizontal orientation (left to right), the artifact is no longer superimposed on the brain.
(Mai)
What is the MRI artifact?
Pulsatility artifact (a type of flow artifact)
Transverse T1W post-contrast (a), T2W (b), and dorsal T1W post-contrast images in a normal 10-year-old Boxer.
In (a) a pulsatility artifact originating from the venous sinuses (arrowhead) overlies the cerebellum and appears a curvilinear hyperintensity (solid arrow) on the transverse T1W post-contrast image. Smaller pulsatility artifacts (dashed arrows) are present overlying the digastricus muscles. Pulsatility artifacts occur in the phase-encoding direction, which in this case is right to left. The pseudolesion can be recognized as artifactual as it is not visible on other pulse sequences or imaging planes (b, c).
(Mai)
What type of MRI artifact is depicted?
Intensity nonuniformity
Transverse T2W image of the brain (a) and sagittal T2W image of the lumbar spine in a dog (b) obtained with a spine surface coil. There is variation in signal intensity across the images with greatest signal intensity in the tissues closest to the coil (circle in a; arrow in b). Filtering of the image (c) to correct for the non-uniformity of signal results in more uniform signal intensity across the image
(Mai)
What MRI artifact is depicted?
Gibbs artifact (truncation/ringing artifact)
Sagittal T2W images in a dog with C4-C5 disc extrusion with images acquired with 302 (a) and 476 (b) phase-encoding steps. The linear T2 hyperintensities (arrows) within the spinal cord, which mimic the central canal, are artifactual and occur due to truncation (Gibbs) artifact. The severity of the artifact can be reduced by increasing resolution in the phase encoding direction. Note that the artifact is reduced with an increased number of phase-encoding steps (b).
(Mai)
What MRI artifact is depicted?
B0-sensitive (‘off-resonance’) banding artifact
Transverse bFFE image of the cervical spine of a normal dog. The curved black bands (arrows) are due to B0-sensitive banding artifact
(Mai)
What MRI artifact is depicted?
Chemical shift - misregistration of signal
Dorsal T2W images of the normal lumbar spine in a dog showing the effect of frequency-encoding direction on chemical shift artifact. With frequency encoding right to left (a) the artifact is asymmetrical lateral to the spinal cord and lumbar nerves and results in apparent thickening of the meninges and lumbar nerves (arrows). When frequency encoding is craniocaudal, the fat/cord interface is parallel to the direction of frequency-encoding, and the dark bands from the chemical shift artifact are no longer visible, making interpretation easier.
(Mai)
What type of MRI artifact is depicted?
Chemical shift - phase cancellation
Transverse T2*W gradient echo images of the lumbar spine of a normal dog acquired in-phase with TE of 13.8 ms (a) and out-of-phase (b) with TE of 20.7 ms showing phase cancellation artifact. The black boundary (arrows, b) along the margins of the bladder and intestines is due to voxels containing fat and water and is most severe in the phase-encoding direction (right to left).
(Mai)
Young cat with:
- Progressive tremors, ataxia, dysmetria, and weakness
- Emaciation, skeletal abnormalities, hepatomegaly, thymic aplasia, gingival hyperplasia, ocular abnormalities, and polycystic kidney disease
- MRI abnormalities associated with this disease?
Alpha mannosidosis
- Reported in Persian, long-hair and shorthair cats
- Affected animals present as early as 8 weeks of age
- MRI - morphologic/signal intensity changes have not been reported
- DWI - increase in ADC values of white and gray matter
- T2 mapping - increase in T2 values of white matter - corresponds to neuronal swelling, abnormal myelin, astrogliosis
(Mai)
MRI findings of neuronal ceroid lipofuscinosis (3)
- Widening of cerebral sulci and cerebellar fissures
- Ventriculomegaly
- Abnormally small corpus callosum
- Less common MRI findings include:
- Enhancement and thickening of meninges
- Subdural hematoma formation
- Lack of gray and white distinction on T2W images
(Mai)
Degenerative brain disease described in:
- Staffordshire Bull Terriers
- West Highland White Terriers
- Yorkshire Terriers
Affected animals present between 6 mos and 1 year of age with progressive prosencephalic signs (seizures), muscle stiffness, cerebellar ataxia
What is the disease?
What are the MRI findings?
L-2-hydroxyglutaric aciduria
MRI
- Bilaterally symmetric gray matter abnormalities (polioencephalopathy) affecting the cerebrum, cerebellum, diencephalon, mesencephalon, and metencephalon
- T2 hyperintensity and T1 hypointensity of gray matter with no contrast enhancement
- Cerebral cortex, thalamus, caudal colliculi, and dorsomedian tegmentum commonly affected
- Symmetric changes to gray matter nuclei
- T2 hyperintensity of peripheral subcortical white matter
(Mai)
MRI findings of hereditary polioencephalomyelopathies? (mitochondrial encephalopathy)
- Bilaterally symmetric abnormalities (T2 hyperintensity, T1 iso-or-hypointensity) without evidence of contrast enhancement of various brain and brainstem nuclei
- Symmetric spinal cord lesions affecting gray matter (same signal characteristics as brain lesions)
(Mai)
What does magnetic resonance spectroscopy show for hepatic encephalopathy MRI
What are general MRI findings: (3)
Significantly higher concentration of glutamine-glutamate complex and significantly lower concentration of myoinositol on magnetic resonance spectroscopy
MRI findings:
- Brain atrophy
- Bilaterally symmetric T2 hyperintensity of the lentiform nuclei attributed to increased concentration of manganese
- This decreases with treatment of the underlying cause
- Bilaterally extensive T2 hyperintense lesions along the cerebral cortex
(Mai)
MRI findings of thiamine deficiency in dogs vs. cats
How do the MRI changes respond to supplementation with thiamine?
Dogs:
- T2/FLAIR hyperintensity and contrast-enhancement in:
- Red nuclei
- Caudal colliculi
- Vestibular nuclei of the brainstem
- Cerebellar nodulus
- T2 hyperintensity in the:
- Caudate nuclei
- Rostral colliculi
Cats:
- T2, FLAIR hyperintensity in the:
- Lateral geniculate nuclei
- Caudal colliculi
- Periaqueductal gray matter
- Medial vestibular nuclei
- Cerebellar nodulus
- Facial nuclei
- T1 hyperintensity of the:
- Caudal colliculi
- Medial vestibular nuclei
- Facial nucleus
Abnormalities improve with thiamine supplementation
(Mai)
MRI findings of myelinolysis/osmotic demyelination syndrome:
- Bilaterally symmetric, T2/FLAIR hyperintense, nonenhancing lesions of the:
- Thalamus
- Caudate nuclei
- Cerebrocortical gray-white matter junction
(Mai)
Brain MRI findings associated with hypoglycemia? (4)
Bilaterally symmetric lesions in the caudate nuclei
- Strongly hyperintense on T2W and T2 FLAIR images
- Hyperintense rim with a hypointense center on T2WI images
- No evidence of contrast enhancement
- Improvement of lesions after treatment
(Mai)
MRI findings of hypocobalaminemic encephalopathy?
- Bilaterally symmetric abnormalities mostly affecting gray matter
- T2 hyperintense lesions in the thalamus, mesencephalon, pons, caudal cerebellar peduncle, and interposital nuclei
Signs improvement with supplementation
(Mai)
MRI findings of Papillions with neuroaxonal dystrophy
- Normal MRI
- Progressive, generalized brain atrophy
(Mai)
MRI abnormalities associated with leukoencephalomyelopathy in Rottweilers?
- Bilaterally symmetric, T2/T2*/T2FLAIR hyperintense, T1 isointense, and nonenhancing intra-axial lesions in the pyramids and ventral aspect of the crus cerebri
(Mai)
