neuroimaging for stroke Flashcards
what is fogging and why does it occur
temporary loss of visibility of a cerebral infarction on noncontrast brain computed tomography (CT) scan - often occurs subacutely post ischaemic stroke; As time goes on, the swelling starts to subside and the cortex begins to increase in attenuation. Occurs as the result of a number of processes occurring simultaneously including the migration of lipid-laden macrophages and leucocytes into the infarcted tissue, proliferation of capillaries, extravasation of red blood cells out of damaged capillaries and a decrease in oedema; At 2 to 3 weeks following an infarct, the cortex regains near-normal density and imaging at this time can lead to confusion or missed diagnosis
what are the 3 main reasons for a CT in acute stroke
- check for signs of hemorrhage
- look for early ischaemic changes
- look for any other potential causes of symptoms (e.g. brain tumour)
what substances are hyperdense in CT (appear bright - 3)
blood (acute haematoma); calcium; metal
what substances appear hypodense in CT (darker -3)
water; air
what is the dense MCA sign
an early sign of acute infarction - the acute thrombus is bright due to the density of methaemoglobin
after performing thrombolysis what should be done?
repeat CT 24hrs after to check for complications
what happens to brain parenchyma during early ischaemia and how does this appear on a CT
it becomes oedematous - quite subtle, look for sucli effacement (low attenuation and loss of gyri)
when is an acute infarction most visible on CT
24 hrs-1 week
when do micro haemorrhages occur and what do they contribute to (on CT)
occur when the oedema from ischaemia resides; contributes to fogging as hey average out the density over the less dense area
what is mass effect
a lesion within the skull that will compress and/or displace adjacent structures; may be caused by tumours, haemorrhages, oedema etc.
what is encephalomalacia and when does it occur
an area of cerebral parenchymal loss with or without surrounding gliosis (tissue remaining present), i.e. liquefactive necrosis; it occurs >3 weeks post-infarction as the cells in the affected area die and the remaining area is filled by CSF
when is CT angiography useful (stroke)
if there is a dense MCA sign and the patient is being considered for mechanical thrombectomy; can be used to identify the location of the clot and how much blood is getting around it
how is catheter angiography performed
invasively - catheter inserted in radial or femoral artery; contrast is injected which allows for imaging of the brain arteries, meaning that on-table assessment can be done
risks of catheter angiography (3)
psuedo-aneurysm; vessel rupture; thrombus; prophylaxis to the contrast
what is a thrombectomy
removal of blood clot using suction or breaking it up; done via catheter insertion
