The two main causes of strokes are termed ischemic and hemorrhagic and involve blood vessels in the brain. Ischemic strokes comprise about 80% to 85% of all strokes. With an ischemic stroke, a blood vessel in the brain becomes clogged with a clot just like the clogged arteries in the heart. With a hemorrhagic stroke, a blood vessel in the brain actually bursts or leaks. Hemorrhagic strokes tend to be more serious. The distinction between these two types of stroke can be critical in determining the treatment used to help the patient.
- Ischemic strokes occur when a blood vessel gets so narrow or clogged that not enough blood can get through to supply oxygen and keep the brain cells alive.
- Plaques (or buildup of cholesterol-containing fatty deposits called arteriosclerosis) in the blood vessel walls can narrow the blood vessels that supply the brain. These plaques build up until the center of the blood vessel is so narrow that little, if any, blood can get past. Many things including high cholesterol and high blood pressure cause plaques. The plaques may occur in small vessels that supply only a very tiny portion of the brain but may also occur in the big blood vessels in the neck (carotids) or in the large arteries to the brain (cerebral arteries).
- Ischemic strokes may also be caused by small blood clots or emboli that go through the bloodstream and then get clogged in an artery when the artery narrows. These clots can come from pieces of plaques in the bigger arteries that break off or from the heart.
- Treatment is designed to break up or get rid of the blockage (see treatment section below).
- Hemorrhagic strokes occur when the wall of a blood vessel becomes weak and blood leaks out into the brain.
- In addition to having decreased blood flow past the leak, the blood in the brain damages brain cells as it decomposes. If a lot of blood leaks out, it can cause a buildup of pressure in the brain because the brain is enclosed in the skull. There is no room for brain tissue to expand, and so the leaked blood can compress and kill important areas of the brain.
- Hemorrhagic strokes tend to be more serious than ischemic strokes. Death occurs in 30% to 50% of people with this type of stroke.
- Treatment is designed to stop or prevent bleeding into brain tissue (see treatment section below).
Treating a hemorrhagic stroke with treatment designed for an ischemic stroke will likely cause worsening of the stroke or death.
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