stroke, destruction of brain tissue as a result of intracerebral hemorrhage or infarction caused by thrombosis (clotting) or embolus (obstruction in a blood vessel caused by clotted blood or other foreign matter circulating in the bloodstream); formerly called apoplexy. Cerebral hemorrhage or thrombosis occurs most often in elderly persons with constricted arteries (see arteriosclerosis), although either may also be caused by inflammatory or toxic damage to the cerebral blood vessels. Cerebral embolism may occur at any age, even in children.

Symptoms of stroke develop suddenly. In cases of severe brain damage there may be deep coma, paralysis of one side of the body, and loss of speech, followed by death or permanent neurological disturbances after recovery. If the brain damage sustained has been slight, there is usually complete recovery, but most survivors of stroke require extensive rehabilitation. Hypertension, which is a major cause of intracranial hemorrhage and stroke, can be treated by preventive measures using diet (e.g., increasing nutrients such as antioxidants and folate), drug therapy, and stress reduction techniques. Other preventive measures for people at high risk include daily aspirin to retard clot formation and surgical correction of the narrowed carotid artery. Sometimes surgical removal of the clot is possible on larger vessels, but it is usually pointless after the stroke or when blockage is widespread. The thrombolytic drug tissue plasminogen activator, widely used to treat heart attacks, has been approved for use within three hours of the onset of strokes caused by clots.

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