NeuroRadiology Flashcards
What are the advantages of CT scans?
Excellent bony details/spatial resolution
Fast
Compatible with emergency/ICU equipment
What are the disadvantages of CT scans?
- Only sensitive to blood EARLY in acute injury
- Poor soft tissue detail
- Grey and white matter show little difference in density
- High radiation dose
What shows up bright and what shows up dark on CT imaging?
Bright = More dense => bone, any metal implants
Dark = Less dense => air
What are the advantages of MRI scanning?
- Excellent contrast/soft tissue resolution
- Excellent depiction of anatomy
- Good for visualising marrow and cord pathologies
- Multiplanar
What are the disadvantages of MRI scanning?
- Less bony detail/spatial resolution
- Not compatible with pacemakers and many implants (due to magnet)
- Not compatible with ICU/emergency equipment
- Not as quick as CT
- Patient cooperation required
Why are different MRI sequences used and give some examples of commonly used sequences.
Multiple sets of MRI images are taken at the one time
(e.g. T1, T2 etc)
=> Different sequences use different combinations of technical parameters
=> Each sequence is unique and gives different information.
What components of the brain enhance as “hyperintense” on T1-weighted MRI imaging?
3 Fs and 4Ms F: fat F: slow flow (e.g. partially blocked vessel) F: fluid (containing protein) M: melanin M: methaemoglobin (blood) M: mineralisation (Ca/Mg etc) M: Magnevist (gadolinium contrast)
What components of the brain appear as “hypointense” on T1-weighted imaging?
Water High Flow (e.g. arteries)
What shows up as hyperintense on T2-weighted MRI imaging?
Water or any fluid collections
- oedema, demyelination, gliosis, some tumors
Fat (this can be suppressed by design)
What shows up as hypointense on T2-weighted imaging?
- Some blood products (subacute hematoma)
- Mineral deposition
- High flow (e.g. arteries)
What are some of the basic sequences used in MRI and why are they used?
T1, T2,
FLAIR (Type of T2 where free water = suppressed e.g. ventricles)
T2* (gradient echo) = highlights blood
T1 (3D): Volumetric
Contrast enhancement = increases density of objects needing to be visualised
Any structure within the blood-brain barrier resists contrast. TRUE/FALSE?
TRUE
Why is gadolinium used as MRI contrast?
- Patients are not allergic to it like iodine CT contrast
- Has many unpaired electrons which cause an MRI signal to be picked up
What vascular pathologies would you expect to see on brain imaging?
- Infarcts
- Haemorrhage
- Vascular anomalies
Describe how a thrombus in a blood vessel of the brain will appear on CT?
Bright
Why is MRI more sensitive to diagnosing stroke?
Grey and white matter differentiation on CT not good enough to outline small infarcts
Why is CT completed first over MRI on presentation of stroke?
Faster
Gives indication of infarct vs haemorrhage and whether pt should receive thrombolysis
An intreparenchymal bleed can break through to the ventricles. TRUE/FALSE?
TRUE
What is a Susceptibility weighted imaging (SWI) MRI sequence used to look for?
- sensitive to venous blood
- especially old venous blood that cannot be picked up on CT
=> looking for haemorrhage and iron storage
what usually causes a subarachnoid haemorrage?
Usually due to aneurysm
How long after an IV injection of CT contrast does it show up in arteries?
8-10s
Describe how a “cavernoma” (type of vascular anomaly) appears on imaging?
Popcorn appearance
Ca2+ present
MRI is more sensitive than CT for small aneurysms. TRUE/FALSE?
FALSE - CT more sensitive due to use of contrast, MRI angiography often doesnt use contrast
What modality of imaging is sensitive for bone injury and ACUTE bleeding in trauma?
CT
What structures in the brain are rather immobile if a bleed occurs and compresses them?
Falx Cerebri - quite stiff and wont initially move much with internal bleed
What is brain contusion, and where does it usually occur?
- Part of many traumatic brain injuries
- Bruise of the brain tissue
- associated with multiple microhemorrhages
- usually occurs on underside of frontal lobe
Describe the difference between the appearance of an extradural and subdural haematoma on imaging
Extradural - biconvex, lemon-shaped and do not cross sutures
Subdural - concave, banana-shaped, crescentic, can cross sutures
What is the difference in location between intra and extra-axial neoplastic processes?
Extra-axial - outwith brain parencyhma
Intra-axial - within brain parenchyma
Intra-axial neoplastic processes are more likely to be benign. TRUE/FALSE?
FALSE
extra-axial = more often benign
nitra-axial = mostly malignant
Give examples of benign extra-axial tumours
meningioma
pituitary adenoma
dermoid/epidermoid
acoustic schwannoma
Give examples of intra-axial tumours
Glioma
Glioblastoma
Metastases
What is a chiari malformation?
- Congenital problem
- lowest part of the back of the brain extends into the spinal canal
- Can put pressure on the brainstem, spinal cord, and obstruct the flow of fluid.
What is cortical dysplasia?
Migration of sensory and motor information to the outer cortex during development is impaired
- grey and white matter seem “blurred” in the dysplastic areas
What is polymicrogyria?
- the brain develops too many folds (gyri and sulci)
- the folds are unusually small.
What is schizencephaly? How does it look on radiology and what can this cause?
- slits across grey and white matter from outer cerebral cortex
- clefts in both hemispheres commonly have developmental delays, delays in speech and language skills, seizures, and problems with brain-spinal cord communication
How does demyelination usually affect the brain?
Occurs in white matter surrounding small veins
- demyelination occurs perpendicular to corpus callosum
Where in the brain does Herpes Encephalitis normally occur, and what does it cause in these areas?
- Temporal lobe and limbic system
- swollen neurones seen
What is CJD?
- spongiform encephalopathy of brain => degenerative
Early Symptoms:
- memory problems
- behavioural changes
- poor coordination
- visual disturbances
Later Symptoms:
- dementia
- involuntary movements
- coma
