A stroke is an interruption of the blood supply to any part of the brain. A stroke is sometimes called a "brain attack."

See also: Arteriovenous malformation (AVM)

A stroke happens when blood flow to a part of the brain is interrupted because a blood vessel in the brain is blocked or bursts open.

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

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 thrombus. If it completely blocks the artery, it is called a thrombotic stroke.
• A clot may break off from somewhere in the body and travel up to the brain to block a smaller artery. This is called an embolism. It causes an embolic stroke.

Ischemic strokes may result from clogged arteries, a condition called atherosclerosis. (See: Stroke secondary to atherosclerosis) This may affect the arteries within the brain or the arteries in the neck that carry blood to the brain. Fat, cholesterol, and other substances collect on the wall of the arteries, forming a sticky substance called plaque. Over time, the plaque builds up. This often makes it hard for blood to flow properly, which can cause the blood to clot.

Ischemic strokes may also be caused by blood clots that form in the heart. These clots travel through the blood and can get stuck in the small arteries of the brain. This is known as a cerebral embolism.

Certain drugs and medical conditions can make your blood more likely to clot and raise your risk for ischemic stroke. A common cause of ischemic stroke in people under age 40 is carotid dissection, or a tear in the lining of the carotid artery. The tear lets blood flow between the layers of the carotid artery. This causes narrowing of the carotid artery that is not due to plaque buildup.

HEMORRHAGIC STROKE

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. The flow of blood that occurs after the blood vessel ruptures damages brain cells.

For more information on this type of stroke, see: Hemorrhagic stroke

STROKE RISKS

High blood pressure is the number one risk factor for strokes. The following also increase your risk for stroke:

• Diabetes
• Family history of stroke
• Heart disease
• High cholesterol
• Increasing age

Certain medications make blood clots more likely, and therefore your chances for a stroke. Birth control pills can increase the chances blood clots, especially in woman who smoke and who are older than 35.

Men have more strokes than women. But, women have a risk of stroke during pregnancy and the weeks immediately after pregnancy.

The following can increase the risk of bleeding into the brain, which makes you more likely to have a stroke:

• Alcohol use
• Bleeding disorders
• Cocaine use
• Head injury

For more information see: Stroke risk factors and prevention