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There are three types of cerebral edema:
• Cytotoxic (intracellular)
• Vasogenic (extracellular or interstitial)
• Hydrostatic/Hydrocephalic (extracellular)

Cytotoxic edema occurs when the cell-membrane pump fails and there is a net movement of water from the interstitial space into the cell. This most commonly occurs after cerebral ischemia - causing "red, dead, swollen neurons". The cell membrane may also fail with hypoxia, metabolic poisons, and hypoglycemia.

Vasogenic edema is, by definition, edema created by a breakdown in the blood-brain-barrier with leakage of water and solutes into the interstitial spaces of the brain. Therefore, we should expect to see a lesion with contrast enhancement as the cause of the edema. The edema itself is not observed to enhance on routine imaging.

"Ischemic edema" is actually a combination of both cytotoxic and vasogenic edema. Cytotoxic edema occurs rapidly after cerebral ischemia. With infarction, vasogenic edema can develop, and takes hours to days, typically reaching a peak at 3-7 days. This is also associated with the peak mass effect of the infarct.

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Hydrostatic edema results from increased intraventricular pressure, with rupture of the ependymal lining. This allows CSF to leak into the interstitium, and it then spreads through the periventricular white matter. This is usually most pronounced around the frontal horns and the trigone of the lateral ventricles.


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Brain Swelling, Herniation, and Edema:
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