What is a Stroke?

A stroke involves a sudden interruption of blood supply to part of the brain, leading to permanent damage to the brain.

The most common type of stroke occurs when a blood clot blocks the blood flow in a blood vessel supplying oxygen and nutrients to the brain. This most often occurs in a part of the artery that is already affected by hardening of the arteries, or atherosclerosis. Less commonly, a blood vessel in the brain can suddenly rupture, allowing blood to leak into brain tissue. About 80% of strokes are due to blocked blood vessels and are called "ischemic" strokes. The other 20% are due to bleeding in or around the brain and are called "hemorrhagic" strokes.

Strokes are sudden events, occurring over seconds or minutes, and can cause a wide range of symptoms, depending on which part of the brain is damaged. The severity of the damage that results depends on how long the brain cells are deprived of blood. If they are deprived for only a brief time, they may recover. However, if they are deprived of blood for longer (even if only for several minutes), brain cells die and the functions done by that part of the brain may be lost.

A temporary kind of stroke can also happen, in which the blood flow to part of the brain is interrupted briefly but returns to normal in a few hours with no permanent damage. This is called a transient (short-lived) ischemic attack, or TIA. A TIA or "mini-stroke" is usually considered a warning that the person is at risk for a permanent stroke, and urgent medical care is required.