Causes and types of strokes

Your brain gets blood mainly through two arteries in your neck (carotid arteries) and two arteries near your spine (vertebral arteries). They branch into other blood vessels which supply your brain with blood carrying oxygen and nutrients.

A stroke results when blood flow to the brain is stopped or interrupted. This happens as a result of a ruptured or blocked blood vessel.

There are two types of stroke: ischemic and hemorrhagic.

Ischemic strokes

There are two main types of ischemic stroke:

• Thrombotic: This is the most common type. Over time, fatty deposits -- plaque -- attach inside the artery walls. The plaque may narrow or close the artery, preventing normal blood to flow to the brain.

  Another type of thrombotic stroke occurs deep in the brain, involving smaller vessels and causing damage to small areas of brain tissue. This type is called lacunar. The location of the lacunar stroke determines how extensive the stroke symptoms will be.

• Embolic: This occurs when a small blood clot breaks off from a blood vessel in the heart or one of the larger blood vessels leading to the brain. This small clot travels in the bloodstream to the brain until it becomes stuck and causes blockage of a blood vessel.

In more severe embolic and thrombotic strokes, the large cerebral blood vessels, the carotid arteries or the vertebral arteries can be blocked. This blockage may result in permanent injury to the large area of the brain.

A person who has this type of stroke often has more serious problems due to widespread brain damage. This damage can cause swelling in the brain, which may lead to more injury and, sometimes, death.

Hemorrhagic strokes

This type of stroke happens when a blood vessel in the brain ruptures and bleeds. It can be caused by a weakened area in the wall of a blood vessel called an aneurysm or by abnormal branching of blood vessels. This is knows as an arteriovenous malformation (AVM). It can also be caused by dangerously high blood pressure.

About 15 percent of all strokes are hemorrhagic. Also, bleeding can occur in the area of the brain already damaged by an ischemic stroke. (See treatment for more information.)