Strokes that occur as a result of an obstruction within a blood vessel supplying blood to the brain. There are two types of ischemic stroke: cerebral thrombosis (or thrombotic strokes) and cerebral embolisms (embolic strokes). Thrombotic strokes occur when a blood clot (thrombus) forms, often in an artery affected by atherosclerosis, becomes trapped and blocks the flow of blood to parts of the brain. Atherosclerosis is a condition in which the artery lining becomes thickened and narrowed by the buildup of fatty deposits called plaque. As plaque builds up in arteries, blood flows more slowly leading to increased risk of clotting. Embolic strokes occur when a blood clot that forms at another location in the circulatory system, usually the heart and large arteries of the upper chest and neck. A portion of the blood clot breaks loose, enters the bloodstream and travels through the brain's blood vessels until it reaches vessels too small to let it pass. A second important cause of embolism is an irregular heartbeat, known as atrial fibrillation. It creates conditions where clots can form in the heart, dislodge and travel to the brain. Ischemic strokes are often more devastating than hemorrhagic ones because brain tissue dies when the supply of blood to the brain is cut off.
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