Definition of Stroke:

A stroke happens when blood flow to a part of the brain stops. A stroke is sometimes called a "brain attack."

Causes, incidence, and risk factors:

If blood flow is stopped for longer than a few seconds, the brain cannot get blood and oxygen. Brain cells can die, causing permanent damage.

There are two major types of stroke: ischemic stroke and hemorrhagic stroke.

Ischemic stroke occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot. This may happen in two ways:

• A clot may form in an artery that is already very narrow. This is called a thrombotic stroke.
• A clot may break off from another place in the blood vessels of the brain, or from some other part of the body, and travel up to the brain. This is called cerebral embolism, or an embolic stroke.

Ischemic strokes may be caused by clogged arteries. Fat, cholesterol, and other substances collect on the artery walls, forming a sticky substance called plaque.

A hemorrhagic stroke occurs when a blood vessel in part of the brain becomes weak and bursts open, causing blood to leak into the brain. Some people have defects in the blood vessels of the brain that make this more likely.

See also:

• Aneurysm
• Arteriovenous malformation (AVM)

STROKE RISK FACTORS

High blood pressure is the number one risk factor for strokes. The other major risk factors are:

• Atrial fibrillation
• Diabetes
• Family history of stroke
• High cholesterol
• Increasing age, especially after age 55
• Race (black people are more likely to die of a stroke)

People who have heart disease or poor blood flow in their legs caused by narrowed arteries are also more likely to have a stroke.

The chance of stroke is higher in people who live an unhealthy lifestyle by:

• Being overweight or obese
• Drinking heavily
• Eating too much fat or salt
• Smoking
• Taking cocaine and other illegal drugs

Birth control pills can increase the chances of having blood clots. The risk is highest in woman who smoke and are older than 35.

For more information, see: Stroke risk factors