Case 1: Discussion

The non contrast head CT is often negative (normal) with the first 4 hours of a stroke. It generally takes 4-6 hours for changes of ischemia to manifest on CT. In this patient, at 3 hours the head CT was normal. 1 day later you start to notice blurring of the gray-white differentiation within the anterior right MCA distribution consistent with cytotoxic edema. 3 months later these findings are much more obvious, now with areas of encephalomalacia or volume loss.

MR is much more sensitive in detecting early infarction than CT. Specifically the DWI sequence can be positive within minutes of infarction (not ischemia, but infarction). If MR is more sensitive than CT to detect infarction why is MRI not performed as the first test in patients presenting with stroke? Treatment (tPA) decisions are based on clinical symptoms (stroke scale) and a negative head CT. MRI is not available everywhere and takes more time to screen patients and acquire images. Time = brain, so every second counts.

There are 2 primary patterns of edema found in the brain: cytotoxic edema and vasogenic edema. Cytotoxic edema is found in the setting of stroke and vasogenic edema is found in response to trauma, tumors, inflammation etc. Cytotoxic edema involves both the gray matter and white matter (resulting in blurring of these 2 regions), whereas vasogenic edema involves the white matter and typically spares the gray matter. The result is accentuation of the difference between the gray and white matter. See slide below for example of stroke on the left and tumor on the right. Why is it important to know the difference? If a patient presents clinically with a suspicion of a stroke, but has a vasogenic pattern of edema on CT, the patient likely does not have a stroke, but rather a disease process like tumor, infection, trauma etc and different treatment is required.