The term “stroke” or “paralytic stroke” is commonly used to describe a sudden problem with the brain that is usually related to its blood supply. A “stroke,” therefore, can be due to ischemia (decreased blood supply), infarction (interrupted blood supply), or hemorrhage (severe bleeding), and usually means that there is some kind of permanent problem with the nervous system.(1) All three of these causes (ischemia, infarction, or hemorrhage) would be due to cerebrovascular disease (disease related to the blood supply to the brain).

Cerebrovascular disease can be described as any disease affecting the blood vessels, blood flow, or quality of the blood in the brain.(2) Other terms for this disease include apoplexy or cerebrovascular accident (CVA). In the United States, the term stroke is most often used. Most strokes are caused by ischemia and infarction because of diseases of the large, small, and medium-sized arteries in the brain. Cerebral embolism (blood clot in the brain) causes strokes about 20 percent of the time. Hemorrhage into the brain tissue account for about 15 percent of all strokes.

Cerebrovascular disease is divided into two broad categories: thrombotic and embolic. Thrombotic strokes occur without warning symptoms in 80-90 percent of patients. They often occur with symptoms that start and stop, and then worsen over several minutes or hours. Embolic strokes have symptoms that are at their maximum when the stroke occurs.(3)

Within 10 seconds after brain blood flow stops, the brain tissue begins to fail. The electrical activity of the brain slows down, and brain function begins to be affected. If the circulation is restored immediately, brain function recovers. If the problem continues for a few minutes, injury to the nerve cells result. When the blood flow returns, the brain's recovery may not be complete.(3) When the blood flow is interrupted for longer periods of time, the brain tissue will die.

Atherosclerosis (hardening) of the brain arteries occurs in the same way that atherosclerosis occurs anywhere else in the body. The atherosclerosis that occurs in the arteries of the brain might be affected slightly less than the aorta, arteries in the heart, and arteries of the limbs. The atherosclerosis that develops includes the formation of plaque, and the narrowing or blockage of arteries. Plaque formation also stimulates the formation of clots, increasing the risk of stroke.

The other broad category of cerebrovascular ischemia is a brain embolism. Approximately 20 percent of strokes are caused by emboli. While any region of the brain may be affected by embolism, the middle cerebral artery is usually involved. The most common types of embolism result from pieces or fragments of an arterial blood clot that have broken off. The embolus usually circulates until it is too large to move through the blood vessel. The blockage often occurs in a narrowed area, and both sides of the brain are affected the same way. Hemorrhage often occurs in this process, due to blood returning into ischemic tissues. The size of the embolus may vary from large to so small that it cannot be noticed.

The third most frequent cause, accounting for approximately 15 percent of strokes, is hemorrhage in the brain. Some causes of hemorrhage include increased blood pressure and rupture of an artery. This allows for movement of blood into the brain tissue, which forms a mass. As bleeding continues, the mass enlarges, pushing aside other tissue. As tissue is pushed and moved, brain function may be affected.

While many risk factors have been identified that increases a person's risk for stroke, hypertension (high blood pressure), is by far, the greatest. Hypertension has been identified as a factor in 70 percent of all strokes. A famous heart study, the Framingham study, reported that there is a dir