Approximately every 40 seconds, someone in the United States has a stroke. A stroke can happen when the following occurs:

• A blood vessel that supplies blood to the brain is blocked by a blood clot. This is called an ischemic stroke.
• A blood vessel breaks open, causing blood to leak into the brain. This is called a hemorrhagic stroke.

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.

ISCHEMIC STROKE

Ischemic stroke is the most common type of stroke. Usually this type of stroke results from clogged arteries, a condition called atherosclerosis. (See: Stroke secondary to atherosclerosis) 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. There are two types of clots:

• A clot that stays in place in the brain is called a cerebral thrombus.
• A clot that breaks loose and moves through the blood to the brain is called a cerebral embolism.

Other causes of ischemic stroke include:

• Abnormal heart valve
• Inflammation of the inside lining of the heart chambers and heart valves ( endocarditis)
• Mechanical heart valve

A clot can form on a heart valve, break off, and travel to the brain. For this reason, those with mechanical or abnormal heart valves often must take blood thinners.

HEMORRHAGIC STROKE

A second major cause of stroke is bleeding in the brain. This is called a hemorrhagic stroke. It can occur when small blood vessels in the brain become weak and burst. 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.

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