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Brain Health > Stroke > Stroke: what is it and what causes it?
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Stroke: what is it and what causes it?

A stroke occurs when blood flow to the brain is disrupted, which may cause loss of consciousness, paralysis, or death. Stroke and other blood vessel diseases of the brain are the third leading cause of death in Canada and the leading cause of disability.

There are 3 main types of stroke:

  • ischemic stroke
  • transient ischemic attack (TIA)
  • hemorrhagic stroke

Ischemic stroke

An ischemic stroke is caused by lack of oxygen in the brain, usually due to a blockage of blood flow caused by a blood clot. Permanent damage of the part of the brain to which the blood vessel travels usually results.

Normally, the inside of a blood vessel is smooth, allowing blood to flow easily. Atherosclerosis, or hardening of the arteries, can roughen the wall of the blood vessel. A blood clot may then form on the irregular surface and block the blood vessel. Or, the clot may dislodge and travel towards the brain, blocking the vessel higher up.

In certain types of heart rhythm irregularities, blood clots may form in the heart and travel to the brain. The medical term for this is cardiac embolism.

A much less common cause of stroke occurs when a person's blood tends to clot more easily than average. In other cases, the cause is unknown.

About 80% of all strokes are ischemic.

Transient ischemic attack (TIA)

A transient ischemic attack (TIA), also referred to as a mini-stroke, is caused by a temporary blockage of blood flow to the brain. In a TIA, the symptoms, such as slurring of speech and paralysis, last for several minutes to hours. Even though the symptoms are temporary, a TIA is still an emergency because you are at a higher risk of having a stroke after a TIA.

Hemorrhagic stroke

A hemorrhagic stroke is caused by a rupture of a brain blood vessel which results in bleeding or hemorrhaging into the brain. About 20% of all strokes are hemorrhagic. The only reliable way to tell the difference between an ischemic stroke and a hemorrhagic stroke is by obtaining a CT or MRI brain scan.

The most common cause of this type of stroke is high blood pressure. Years of high blood pressure weaken the blood vessel wall, eventually causing it to rupture. In other cases, the blood vessel wall in the brain is abnormal. For example, aneurysms may balloon out from a blood vessel wall and can burst causing a brain hemorrhage. There are several other blood vessel wall abnormalities that cause some people to be more likely to have a brain hemorrhage.

Regardless of the type of stroke, it's critical to get treatment as soon as possible to help reduce damage to the brain.

Written and reviewed by the MediResource Clinical Team 


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