Ischemic Strokes

The most common type of stroke is caused by an obstruction within a blood vessel that supplies blood to the brain. It is known as an ischemic stroke, accounting for about 83 percent of all of strokes.

When an artery is blocked, the brain cannot receive oxygen and nutrients and it cannot have carbon dioxide and cellular waste removed. Brain cells begin to die after only a few minutes of inadequate circulation.

Causes of Ischemic Strokes

The obstruction that causes an ischemic stroke is usually the result of a blood clot that may either form in the brain or form in another part of the body and travel to the brain. A clot that forms and stays in the brain is called a cerebral thrombus. A clot that forms in another part of the body, breaks loose and moves through the bloodstream to the brain is called a cerebral embolism.

There are several different causes of ischemic strokes. The most common cause is atherosclerosis (commonly known as “hardening of the arteries”). A blood clot can form in the diseased arteries, either in the brain (a cerebral thrombus) or in another part of the body (usually in the carotid artery), break off and travel in the bloodstream to the brain (a cerebral embolism).

Blood clots formed in the heart are another cause of ischemic strokes. Atrial fibrillation is an irregular heart rhythm where the atria of the heart (the heart's two small upper chambers) quiver instead of beating. The blood that travels through the atria can pool or clot because it is not pumped out completely. About 15 percent of strokes are in people with atrial fibrillation. Heart attacks, endocarditis, heart valve abnormalities and mechanical heart valves can also cause blood clots that may result in ischemic strokes.

While less common, other possible causes of ischemic stroke including:

• Traumatic injury to the blood vessels of the neck
• Blood clotting disorders
• Excess red blood cells can cause the blood to become thicker than normal, which is known as polycythemia.
• An excessive blood loss of low blood pressure can result in an inadequate blood flow to the brain
• Inadequate oxygen in the blood caused by severe anemia, suffocation and carbon monoxide poisoning. This usually results in widespread brain damage and may lead to coma and death.
• Inflammation or infection in the blood vessels that bring blood to the brain.
• Spasms of the arteries that supply the brain with blood, caused drugs such as cocaine and amphetamines.
• Fat Embolism Syndrome is a rare condition that occurs when a broken long bone (such as an arm or leg) causes small pieces of fat from the bone marrow to be released into the bloodstream.

Although rare, children can also have ischemic strokes. The most common causes of pediatric stroke are cardiac disorders, sickle cell disease, coagulation disorders, arterial dissection, moya moya, infection, and other rare genetic disorders.

_Sources:

"What Are the Types of Stroke?" American Stroke Association. 4 Apr 2007.

"Ischemic Stroke" The Internet Stroke Center. 4 Apr 2007.

"Ischemic Stroke." Merck Medical Online Medical Library. 4 Apr 2007.

"Conditions Associated with Stroke in Children." Kids Have Strokes. Pediatric Stroke Organization. 4 Apr 2007.