CIrcle of willis artery and location
- ACA
- MCA
- PCA
- ICA
- SCA
- ACA: anterior cerebral artery (pointing anteriorly from circel)
- Acom artery (anterior communicating artery ) - located between the two ACA
- MCA: middle cerebral artery - outer aspect of circle
- pcom artery (posterior communicating artery) - located between MCA and PCA
- PCA: posterior cerebral artery: posterolateral aspect of circle
- ICA: internal carotid artery: interior aspect of circle at level of the MCA
Subarachnoid haemorrhage
- (symptoms?)
- bleeding into the subarachnoid space
symptoms:
- sudden severe headache (thunderclap headache)
- photophobia
- vomiting
- drowsiness
can be a result of trauma but mainly vascular abnormalitiy
CT head pathology
- is there symmetry - has midline shift occured?
-
Infarct (tissue death)
- appears as hypodense (dark) on a ct due to the development of odema caused by breakdown of the blood brain barrier
- not much odema is seen during the hyhperacute phase
- A thrombolytic agent is used to break down clot (thrombus) - should be given within 4 1/2 hourse of admission
blood appearance on CT image
acute blood (1-2 days): appears as bright white - HYPERDENSE - as it contains highly dense globin
sub-actue (1-14 days): iso-dense - same colour as surroundings
chronic (>14 days): hypodense - black
what is the MCA sign?
- a hyperdensity in the middle cerebral artery on NON-CONTRAST ct head
- it is a visualisation of the clot/thrombus
- earliest sign of a MCA infarction (90 minutes after)
- the longitudinal equivalent of the MCA dot sign
what is the MCA sign?
- a hyperdensity in the middle cerebral artery on NON-CONTRAST ct head
- it is a visualisation of the clot/thrombus
- earliest sign of a MCA infarction (90 minutes after)
- the longitudinal equivalent of the MCA dot sign
How to describe a CT lesion
- hypo/iso/hyper dense?
- shape/size/symmetry?
- position
- contours - e.g. well defined, ill-defined
- time after the episode
Haemorrhage
- an acitve bleed
Haematoma
- blood clot or build up of blood
contusion
- bruising caused from brain hitting of inside of skull resulting in little bleeds at multiple sites of the brain
Describe an extradural haematoma vs a subdural haematoma
extradural: blood is above the dura. The dura links to the sutures of the skull. THe blood can only go in the space between the sutures. Bulges into the brain
subsural: blood is below the dura. The blood stretches along the line of the brain as it is not stopped by the sutures
Low grade tumour
- small amount of associated odema
- when given contrast, there is only minimal enhancement
e.g. low grade glioma
High grade tumour
- big area of odema
- large enhancement with contrast
- often has different densities within the tumour
Primary or metastatic lesion?
- primary lesions tend to be singular
- metastases tend to multiple
- metastases: odema is a lot bigger than the lesion
- metastases have peripheral/ring enhancement
what does the 4th ventricle look like and its location?
- looks like a mouth (sylvian fissures look like eyes) and it located posterior of the brain, in the midline (posterior of where the foramen magnum would be)
- sits behind the pons
What is the falx cerebri?
- crescent shaped dura that separates the two hemishperes. runs down the midline of the brain
what are the sylvian fissures?
- separate the temporal lobe (below) from the frontal and pratietal lobes (above)
- look like eyes of the face at the lateral aspects of the brain
what does the third ventricle look like?
- appears as a vertical line running up the midline of the brain - appears hypo dense as it is full of csf
lateral ventricles
- (what do they look like?)
- (any areas of hyper/hypodensity?)
- two lateral ventricles, left and right with anterior and posterior horns
- areas of hyperdensity at the posterior horn
- this hyperdensity is calcificaiton within the choroid plexus - the area where CSF is produced
what is cerebral vasospasm?
- blood vessels spasm causing vasoconstriction which can lead to tissue ischemia and necrosis
- typically appears 4-10 days after a SAH - patients need to be monitored for up to 21 days after SAH
- after a SAH,white blood cells enter teh subarachnoid space to try and clear the blood but they get stuck there. when they die they release endothelins which cauuse vasoconstriction and vasospasm
what is arteriovenous malformation?
- abnormal connection between arteries and veins - bbypasses teh capillary system
- asymptomatic
- thought to be hereditary
