Neuroradiology Flashcards
what would indicate the need for brain imaging?
headache / raised ICP seizure weakness stroke trauma LOC / neurological deficit post op monitoring
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 (magnet)
not compatible with ICU / emergency equipments
not as quick as CT
patient co-operation 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 (eg 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?
3Fs and 4Ms
- fat
- slow flow (eg partially blocked vessel)
- fluid (containing protein)
- melanin
- methaemoglobin (blood)
- mineralisation (Ca / Mg etc)
- magnevist (gadolinium contrast)
what components of the brain appear as “hypointense” on T1-weighted MRI imaging?
water high flow (eg arteries)
what shows up as hyperintense on T2-weighted MRI imaging?
water or any fluid collections - oedema, demyelination, gliosis, some tumours
fat (this can be suppressed by design)
what shows up as hypointense on T2-weighted imaging?
some blood products (subacute haematoma)
mineral deposition
high flow (eg arteries)
what are some of the basic sequences used in MRI and why are they used?
spin echo: T1, T2, FLAIR (type of T2 where free water = suppressed eg 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 or false?
true
why is gadolinium used as MRI contrast?
patients not allergic to it like iodine CT contrast
has many unpaired electrons which cause an MRI signal to be picked up
what 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 intraparenchymal bleed can break through to the ventricles - true or false?
true
what is a susceptibility weighted imagine (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 haemorrhage?
aneurysm
how long after an IV injection of CT contrast does it show up in arteries?
8-10s
in what type of imaging is CT contrast used?
CT angiogram
why are arteries and veins easy to distinguish in the brain?
separated anatomically so are distinct from each other in imaging
what imaging modality is used for aneurysm follow up?
MRI
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 or false?
false - CT more sensitive due to use of contrast, MRI angiography often doesnt use contrast
x-rays are still routinely completed in trauma cases - true or false?
false
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 a brain contusion and where does it usually occur?
part of many traumatic brain injuries
bruise of the brain tissue
associated with multiple microhaemorrhages
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 parenchyma
intra-axial = within brain parenchyma
intra-axial neoplastic processes are more likely to be benign - true or false?
false
extra-axial = more often benign
intra-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 spinal canal
can put pressure on 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 developed 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, 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
what type of MRI imaging would you use to visualise demyelination of white matter?
T2 and FLAIR
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 and what are the symptoms?
spongiform encephalopathy of brain - degenerative
early symptoms = memory problems, behavioural changes, poor co-ordination, visual disturbances
later symptoms = dementia, involuntary movements, coma
