Strokes are sudden losses of brain function due to the blockage or rupture of blood vessels. Image: Strokefig2.jpg
Ischemic strokes are the most common variety. They occur when a brain artery is blocked. Fatty deposits resulting from arteriosclerosis can clog arteries. If a clot forms where the fat has built up, the stroke is called a cerebral thrombosis. If a clot forms elsewhere in the body and makes its way to the brain, the stroke is called a cerebral embolism. Blood clots leading to embolism often originate in the lungs and neck. A type of impaired heart function known as atrial fibrillation can cause blood to pool and clot in the heart; if the clots break up and move into the blood stream, they can also cause cerebral embolisms.
Hemorrhagic strokes are less common than ischemic strokes. They occur when an artery bursts in the brain, often at a weak portion of a vessel where the vessel walls are abnormally thin. High blood pressure and high cholesterol may damage cerebral blood vessels and cause hemorrhagic strokes.
Stroke is the third leading cause of death, behind heart disease and cancer. It killed 283,000 people in the U.S. in 2000 and accounted for about 1 of almost 14 deaths. About 4.7 million U.S. stroke survivors (2.3 million men, 2.4 million women) are alive today.