Stroke is a general term used to describe any brain injury caused when blood supply to the brain is interrupted, resulting in tissue loss and temporary or permanent impairment of function. It is the third leading cause of death in developed countries, and may result from a variety of factors, including atherosclerosis, heart disease, connective-tissue diseases (lupus, arthritis, etc.), and drug use.
Ninety percent of all strokes are ischemic (dry). An ischemic stroke results when blood flow to the arteries that feed the brain is interrupted. This type of stroke may be caused by a clot that arises within the arteries of the brain itself (thrombus), or a blood clot, plaque, or other blood-borne material that travels from another part of the body into the brain (embolus). Thrombosis is generally attributed to atherosclerosis, while embolisms are linked to heart disease and arrhythmia.
Hemorrhagic strokes account for 10 percent of all strokes and are caused when arteries within the brain form a balloon (aneurysm) that then explodes, or by the rupture of a weakened blood vessel. Apoplexy, or bleeding within the brain, is caused by hemorrhagic stroke. This type of stroke is usually caused by a combination of atherosclerosis and hypertension.
The effect of any kind of stroke depends on what part of the brain is affected, how large a volume of brain tissue is involved, and the overall health of the brain at the time of the stroke. Not all strokes are clinically evident: silent strokes affect parts of the brain that do not produce paralysis or obvious cognitive problems. In fact, a person may suffer many silent strokes before neurological problems occur.
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