Stroke occurs when the blood supply to a part of the brain is suddenly blocked or diminished, which alters the body function controlled by that area of the brain. If any part of the body - including the brain - is without a source of fresh blood and oxygen, the cells will be injured or may die. Although some cell injury is reversible, the death of brain cells is permanent, usually leaving lasting disability.

There are three main types of stroke:

1. Thrombotic – the most common, caused by a clot that is not able to pass through an artery that may already be obstructed by a buildup of plaque (fat) in the blood vessels (usually in the neck) and block the flow of blood.
2. Embolic – caused by a circulating piece of a clot that lodges in a blood vessel in the brain. The clot forms elsewhere in the body, usually in the heart, and moves freely until it reaches the small vessels in the brain and cannot move further.
3. Hemorrhagic – may be caused by the rupture of a blood vessel, causing blood to accumulate in the brain. They can occur from the inside by aneurysms - weak spots on the artery wall - or from the outside from head injury. Aneurysms are often caused by congenital defects or high blood pressure. Hemorrhagic strokes are the most severe and are often fatal. The chance of a full recovery is less than that for the other two types.

There are many risk factors for stroke. These include:

Major risk factors:

Other risk factors include:

Most strokes are preceded by one or more mini-strokes (called transient ischemic attacks or TIAs) that should act as a warning to seek medical attention immediately. The most common symptoms of a stroke are:

• sudden numbness, weakness, or paralysis of the face, arm, or leg – usually on one side of the body;
• loss of speech or trouble talking or understanding what is said; and
• sudden blurred vision, dizziness, loss of balance, or severe, unexplained headache.

Diagnosis of a stroke is currently based mostly on non-laboratory testing, but specific laboratory tests are in development.

Treatment of stroke depends on the areas affected and the damage done. With strokes caused by blood clots, use of “clot busting” drugs (as used in treating heart attacks) can be helpful in the early stages of a stroke. Often, anticonvulsant drugs are used in conjunction with other therapies. It is important that anyone with sudden onset of symptoms suggestive of a stroke seek medical attention as soon as possible.