Cerebral Oedema

This young patient was found belatedly after a collapse secondary to drug overdose. Note the extensive cerebral oedema with loss of normal grey-white matter differentiation.
The patient never regained consciousness and eventually died with increased intracranial pressure.
Cerebral oedema is divided into vasogenic oedema and cytotoxic oedema.
Vasogenic is due to disruption of the blood brain barrier with leakage of fluid out of capillaries, and is most frequently seen around brain tumours (both primary and secondary) and cerebral abscesses, although some vasogenic oedema is also seen around maturing cerebral contusions and cerebral haemorrhages.
Cytotoxic oedema, (as in this case) in contrast, is due to cellular swelling from lack of ATP, and is typically seen in an area of cerebral ischaemia or cerebral hypoxia.
Reference:
Primer of Diagnostic Imaging by Weissleder
Credit: Dr Frank Gaillard