1. Understanding Stroke Slideshow Pictures
2. Take the Stroke Quiz
3. Atrial Fibrillation Slideshow: Causes, Tests and Treatment

In this Article

• Introduction
• What is a Stroke?
• What are Warning Signs of a Stroke?
• What are Risk Factors for a Stroke?
• What Are the Treatable Risk Factors?
• Do You Know Your Stroke Risk?
• Stroke Prevention Index

A stroke, or "brain attack," occurs when blood circulation to the brain fails. Brain cells can die from decreased blood flow and the resulting lack of oxygen. There are two broad categories of stroke:

1. those caused by a blockage of blood flow and
   
   
2. those caused by bleeding.

Blockage of Blood Flow

While not usually fatal, a blockage of a blood vessel in the brain or neck, called an ischemic stroke, is the most frequent cause of stroke and is responsible for about 80 percent of strokes. These blockages stem from three conditions:

• the formation of a clot within a blood vessel of the brain or neck, called thrombosis;
  
  
• the movement of a clot from another part of the body such as the heart to the neck or brain, called embolism; or
  
  
• a severe narrowing of an artery in or leading to the brain, called stenosis.

Bleeding

Bleeding into the brain or the spaces surrounding the brain causes the second type of stroke, called hemorrhagic stroke.

Two key steps you can take will lower your risk of death or disability from stroke: know stroke's warning signs and control stroke's risk factors. Scientific research conducted by the NINDS has identified warning signs and a large number of risk factors.

Warning signs are clues your body sends that your brain is not receiving enough oxygen. If you observe one or more of these signs of a stroke or "brain attack," don't wait, call a doctor or 911 right away!

• Sudden numbness or weakness of face, arm or leg, especially on one side of the body
  
  
• Sudden confusion, trouble speaking or understanding
  
  
• Sudden trouble seeing in one or both eyes
  
  
• Sudden trouble walking, dizziness, loss of balance or coordination
  
  
• Sudden severe headache with no known cause

Other danger signs that may occur include double vision, drowsiness, and nausea or vomiting. Sometimes the warning signs may last only a few moments and then disappear. These brief episodes, known as transient ischemic attacks or TIAs, are sometimes called "mini-strokes." Although brief, they identify an underlying serious condition that isn't going away without medical help. Unfortunately, since they clear up, many people ignore them. Don't. Heeding them can save your life.