What Is a Stroke

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What Is a Stroke

Stroke Overview
What Is a Stroke
What Is a Stroke
What happens when a stroke occurs?
InteliHealth Medical Content

Reviewed by the Faculty of Harvard Medical School

What Is a Stroke?

A stroke is commonly known as a brain attack. In stroke, the blood supply to a part of the brain is suddenly diminished or cut off. The reason for this depends on the type of stroke you have. In about 15 percent to 20 percent of cases, the cause is unknown.

There are two major types of stroke:

  • Ischemic stroke is the most common type of stroke. A blood clot blocks the flow of blood to one area of the brain, depriving that area of oxygen.
  • Thrombotic stroke is a type of ischemic stroke. It accounts for 40% to 50% of all cases of stroke. A blood clot forms in one of the brain's arteries, blocking blood flow to the area of the brain that is "downstream" to this blood vessel. In most cases, the blood clot forms where the artery was already narrowed as a result of atherosclerosis (cholesterol plaque). A specific type of thrombotic stroke affects small blood vessels that deliver blood deep within the brain. When these small, deep vessels are involved, the stroke is named a lacunar stroke.
  • Embolic stroke is a type of ischemic stroke. It accounts for 20% of all cases of stroke. A blood clot begins in the heart or in a large artery in the neck or chest and travels in the blood until it lodges within one of the brain's arteries, obstructing the flow of blood.
  • Hemorrhagic stroke accounts for 10% to 15% of all cases of stroke. Bleeding occurs within the brain (intracerebral hemorrhage) or between the brain and the skull (subarachnoid hemorrhage). The leaking blood irritates surrounding tissues and causes arteries in the area to go into spasm. This sharply decreases blood delivery, and results in damage to the brain near the site of the bleeding. Bleeding usually occurs because of a rupture in arterial walls that are weakened by high blood pressure.

If the brain is deprived of blood and oxygen for approximately 2 hours or more, brain cells will die. These cells cannot be replaced, and the parts of the body controlled by the area of the brain affected by a stroke will suffer. This can lead to temporary or permanent damage depending upon the severity of the stroke.

Stroke is a medical emergency. Both ischemic and hemorrhagic strokes may have devastating consequences. However, of the two types, hemorrhagic stroke is more likely to be deadly.


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Last updated June 10, 2014

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