STROKE

also called apoplexy, or cerebrovascular accident (CVA) a sudden impairment of brain function resulting either from a substantial reduction in blood flow to some part of the brain or from intracranial bleeding. The consequences may include transient or lasting paralysis on one or both sides of the body, difficulties in using words or in eating, and a loss in muscular coordination. A stroke may cause cerebral infarctionsdead sections of brain tissue. Smoking, high cholesterol, diabetes, aging, and heritable defects are among the major factors making stroke more likely. Stroke occurs in conjunction with at least one of the following four events: 1. A blood clot forms within a blood vessel of the brain (thrombosis). This is the most common cause of strokes. 2. A blood clot lodges in an artery supplying brain tissue after originating in another portion of the body and traveling to the brain. This is known as an embolism. A heart attack, damage to a valve, and an irregular heartbeat called atrial fibrillation can cause blood clots that may reach the brain. Both the first and second types of clotting reduce or stop the flow of blood to brain cells. During the early stages of stroke from these two causes, the illness may be further complicated by the oozing of blood and fluid into the surrounding areas (edema). 3. An intermittent insufficiency in the flow of blood results temporarily from a spasm of the arteries or the sludging of the blood as it passes through segments of vessels that have been narrowed by arteriosclerosis (atherosclerosis). Arteriosclerosis commonly results from the buildup of fatty deposits on artery walls. 4. Hemorrhage occurs after an artery ruptures, usually as a result of a weakening of the arterial wall because of arteriosclerosis or because of a thinning of the wall along with bulging (an aneurysm), which may be congenital or develop later in life. The walls of arteries in the brain can become weakened by the assault of high blood pressure. (Hypertension, as this is called, can also accelerate arteriosclerosis.) So-called little strokes result when long, thin arteries penetrating deep into the brain become blocked by arteriosclerosis, causing areas of surrounding tissue to lose their blood supply. The tissue may then wither, creating minute holes, called lacunes. A succession of these little strokes over the years can riddle the brain, causing dementia similar to Alzheimer's disease.