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What is a stroke?

Stroke is the number one cause of life changing disability and the third leading cause of death. Stroke affects one person every 3 seconds around the world.

penumbra and infarctStroke is the disruption of blood flow in arteries of the brain, without blood brain tissue cannot survive. Blood carries glucose and oxygen to brain cells so they can function. After four minutes with out this supply of nutrients and oxygen cells begin to die.

How does a stroke occur?

Stroke occurs two ways, the first type is caused from a blockage within a blood vessel and is called an ischemic stroke. The second is from a break or rupture of a blood vessel and this is called a hemorrhagic stroke.

Thrombotic Stroke Embolic Stroke

Ischemic Stroke:

Ischemic stroke can occur in a number of ways.

  • Small blood vessels deep in the brain can narrow to the point that oxygen carrying blood cells can no longer flow through the vessel. This is called a lacunar stroke.
  • A blood clot that forms in the heart travels to a smaller vessel in the head and blocks the blood flow is called a cardioembolic stroke.
  • Blockages in the neck can send debris to the brain or lead to complete occlusion of the artery. This is called atherothrombotic stroke.
  • Occasionally, even after extensive testing no cause can be found. This is referred to as a cryptogenic stroke.

lacunar strokeThe cells that die from the blocked vessel are part of the core of the stroke. The area surrounding this core is called the penumbra.

The penumbra is the area of the brain at risk of dying if treatment to unblock the blood vessel does not occur immediately.

This penumbra is variable in individual patients. Perfusion Imaging can help identify patients who have penumbra that can be saved.

Click to view the Explaining Stroke booklet from the National Stroke Association in PDF format.

Perfusion image
Example of a Perfusion Image

Hemorrhagic Stroke:

Hemorrhagic stroke accounts for about 17 percent of stroke cases.
Walls of arteries can become weakened or damaged from hypertension, plaque, diabetes, aneurysms and age. These weakened or damaged vessels may leak or burst causing bleeding (hemorrhage) into brain tissue (intracerebral), into the ventricles, or into one of the coverings surrounding the brain (subarachnoid hemorrhage). Parts of the brain affected by the bleeding can become damaged, and if enough blood accumulates, it can compress the surrounding brain tissue. The amount of bleeding determines the severity of the stroke.

Two types of weakened blood vessels usually cause hemorrhagic stroke: aneurysms and arteriovenous malformations (AVMs).

An aneurysm is a ballooning of a weakened region of a blood vessel. If left untreated, the aneurysm continues to weaken until it ruptures and bleeds into the brain.

An arteriovenous malformation (AVM) is a cluster of abnormally formed blood vessels. Any one of these vessels can rupture, also causing bleeding into the brain.

Intracerebral hemorrhage:

  • Occurs when a blood vessel bleeds into the tissue deep within the brain.
  • Chronically high blood pressure or aging blood vessels are the main causes of this type of stroke. In addition to high blood pressure, factors that increase the risk of hemorrhagic strokes include:
    1. cigarette smoking
    2. use of oral contraceptives (particularly those with high estrogen content)
    3. excessive alcohol intake
    4. use of illegal drugs

Because hemorrhages may be life-threatening, hospital care is required. Medication can control high blood pressure.

Other medicine may be prescribed to reduce the brain swelling that follows a stroke. Surgery may be needed depending on the cause of the hemorrhage.

Surgery could be done to repair an aneurysm or remove a blood clot.

drawing of a clot

Subarachnoid (sub-ah-RAK-noid) Hemorrhage:

  • Occurs when a blood vessel on the surface of the brain ruptures and bleeds into the space between the brain and the skull.
  • A ruptured aneurysm is often caused by high blood pressure. An aneurysm is a
    blood-filled pouch that balloons out from an artery wall.

Treatments for aneurysms - coiling (left) and clipping (right)