Brain Imaging Flashcards
Describe the two main imaging modalities used for the brain and when they are and are not used?
CT – first line, fast, well tolerated. With or without IV contrast, specialist investigations such as angiography, venography.
MRI – better soft tissue resolution, longer duration, contra-indicated for some, can be poorly tolerated. With or without IV contrast, specialist investigations
and sequences- second line imaging for most brain things but may be first line for viewing the spinal cord, better imaging but v time consuming and claustrophobic
What are subarachnoid cisterns?
areas where the arachnoid and pia are widely separated, they are all continuous with the subarachnoid space and ventricles but named simply according to what structures they are close to
Why are middle cerebral artery strokes bad?
They cover a very large area
Why are patients with an acute stroke imaged and what imaging modality is used?
Need to exclude stroke mimics and check there is no haemorrhage so can thrombolyse.
Non contrast CT scan is used.
What is the very earliest Ct sign visible of a ischaemic stroke?
hyperdense segment of a vessel with the thrombus or embolus in it
Within the first few hours what signs of ischaemic stroke are available on CT?
loss of grey -white matter differentiation, and
hypoattenuation of deep nuclei (Hypoattenuation means that it appears darker than it should be on the scan)
cortical hypodensity with
associated parenchymal swelling with resultant gyral effacement
Later signs of previous stroke on CT?
With more time, gliosis occurs
eventually appearing as a region of low density with volume loss
An acute bleed on CT always appears _____
white
What shape does an extradural haemorrhage appear on CT and why?
biconvex lens shape
bounded by the fissures because its above the dura
What shape does a subdural haemorrhage appear on CT and why?
semilunar shape, it crosses the sutures because it is below the dura
How does a sub acute and chronic subdural haemorrhage appear on CT?
sub acute appears isodense (so difficult to pick up)
chronic appears hypodense (so dark grey as opposed to acute which is white)
How does subarachnoid haemorrhage appear on CT?
large volume of blood within the subarachnoid space so hyperdense material in SA space, most commonly around the circle or willis
The higher the grade of tumour the more ________ on CT and MRI
oedema, mass effect and enhancement
Investigation for spinal cord pathology?
MRI
CT doesn’t let you see the spinal cord or conus because too similar to the density of surrounding CSF
On a T2 weighted image fluid is ________
bright white
