Pathophysiological aspects of brain edema.

Two mayor types of brain edema, related to two different pathomechanisms, can be recognized: 1) cytotoxic type-where the main feature is the swelling of cellular elements of brain parenchyma and 2) vasogenic type-where an increased vascular permeability leading to accumulation of edema fluid in the extracellular spaces plays the principal role. In this type of edema, there is a close interrelationship between extravasation of serum proteins and retention of water in the brain tissue. In the ischemic brain edema both cytotoxic and vasogenic mechanisms are involved. A biphasic opening of the blood-brain barrier, associated with vasogenic edema, is observed following release of major cerebral artery occlusion. The first opening of the barrier is related to a reactive hyperemia which follows promptly recirculation. The second opening, recognizable after a delay, is associated with a severe ischemic brain tissue injury.