If blood flow in any of these arteries is interrrupted for longer than a few seconds, brain cells can die, causing permanent damage. The resulting stroke-related symptoms depend on the area of the brain affected, the extent of the damage, and the cause of the stroke.

Common symptoms include changes in vision, speech, and comprehension; weakness; vertigo; loss of sensation in a part of the body; or changes in the level of consciousness.

Stroke accounts for 1 out of every 15 deaths in the United States. It is the 3rd leading cause of death in most developed countries, and the leading cause of disability in adults. The risk doubles with each decade after age 35. Stroke occurs in men more often than women.

The risk of stroke is increased by smoking, hypertension, diabetes, hyperlipidemia, and heart disease. Rarely, strokes may happen in women on birth control pills -- the risk is increased if a woman also smokes and is older than 35. Women have a higher risk of stroke during pregnancy and the weeks immediately after pregnancy. Other illnesses such as vasculitis, lupus, or high blood viscosity may contribute to stroke.

The most common cause of stroke is atherosclerosis. (See stroke secondary to atherosclerosis.) Atherosclerosis is a condition in which fatty deposits and blood platelets collect on the wall of the arteries, forming plaques. Over time, the plaques slowly begin to block the flow of blood. A plaque may block the artery enough to cause a stroke, or it may trigger a blood clot that causes a stroke.

The formation of a plaque does not always lead to a stroke. The arteries are large enough that 75% of the blood vessel can be blocked, and there will still be adequate blood flow to that area of the brain. Furthermore, there are many small connections between the arteries in the brain. If the blood flow is gradually blocked in one artery, these small connections will increase in size and "by-pass" the obstructed area. Even a totally blocked artery may not cause a stroke.

A stroke may be caused by a blood clot that forms in the brain (a thrombus) or a blood clot, piece of plaque, or other material that travels to the brain from another location (an embolism). Bleeding (hemorrhage) within the brain can, on rare occassions, cause symptoms that mimic stroke.

A stroke caused by a blood clot in the brain (a thrombus) is most common in older people, and often there is underlying atherosclerosis or diabetes. This type of stroke may occur at any time, including at rest. The person may or may not lose consciousness.

Strokes caused by embolism (a blood clot that travels to the brain) are most commonly caused by heart disorders. An embolism may also originate in the aortic arch, especially where there is atherosclerotic plaque. The blood clot travels through the bloodstream and becomes stuck in a small artery in the brain. This stroke occurs suddenly with immediate, maximum damage to the brain. Consciousness may or may not be lost.

Embolic strokes are NOT associated with activity levels and can occur at any time. Arrhythmias of the heart, such as atrial fibrillation, are often seen with with this type of stroke and may be the cause of the clot. Other causes of embolic stroke include endocarditis (an infection of the heart valves), or a mechanical heart valve that may have a clot attached to it. A heart attack puts people at greater risk for having an embolic stroke.

The probable outcome is worsened if blood vessels damaged by stroke rupture and bleed (hemorrhagic stroke).

See also:

• Stroke secondary to carotid dissection (bleeding from the carotid arteries)
• Stroke secondary to carotid stenosis (narrowing of the carotid arteries)
• Stroke secondary to cocaine
• Stroke secondary to FMD (fibromuscular dysplasia)
• Stroke secondary to syphilis

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