Stroke Health Article

Definition

A stroke, also called a cerebral vascular accident (CVA), is the sudden death of cells in a specific area of the braindue to inadequate blood flow.

Description

A stroke occurs when blood flow is interrupted to a part of the brain, either when an artery bursts or becomes closed when a blood clot lodges in it. Blood circulation to the area of the brain served by that artery stops at the point of disturbance, and the brain tissue beyond that is damaged or dies. (Brain cells need blood to supply oxygen and nutrients and to remove waste products.) Depending on the region of the brain affected, a stroke can cause paralysis, loss of vision, speech impairment, memory loss and reasoning ability, coma, or death. The effects of a stroke are determined by how much damage occurs, and which portion of the brain is affected.

About a third of all strokes are preceded by transient ischemic attacks (TIAs), or mini-strokes, that temporarily interrupt blood flow to the brain. While TIAs cause similar symptoms (such as sudden vision loss or temporary weakness in a limb), they abate much more quickly than full-fledged strokes, usually within a few hours— sometimes as quickly as a few minutes.

Stroke is a medical emergency requiring immediate treatment. Prompt treatment improves the chances of survival and increases the degree of recovery that may be expected. A person who may have suffered a stroke should be seen in a hospital emergency room without delay. Treatment to break up a blood clot, the major cause of stroke, must begin within three hours of the stroke to be most effective. Improved medical treatment of all types of stroke has resulted in a dramatic decline in death rates in recent decades. In 1950 nine in ten stroke victims died, compared to slightly less than one in three today.

Causes

There are four main types of stroke: cerebral thrombosis, cerebral embolism, subarachnoid hemorrhage, and intracerebral hemorrhage. Cerebral thrombosisand cerebral embolism,known as ischemic strokes,are caused by blood clots that block an artery supplying the brain, either in the brain itself or in the neck. They account for 70–80% of all strokes. Subarachnoid hemorrhageand intracerebral hemorrhageare hemorrhagic strokesthat occur when a blood vessel bursts around or in the brain, either from trauma or excess internal pressure. Hypertension (high blood pressure) and atherosclerosis are usually contributing factors in these types of strokes.

CEREBRAL THROMBOSIS.Cerebral thrombosis, the most common type of stroke, occurs when a blood clot, or thrombus, forms within the brain itself, blocking blood flow through the affected vessel. This is usually due to atherosclerosis (hardening) of brain arteries, caused by a buildup of fatty deposits inside the blood vessels. Cerebral thrombosis occurs most often at night or early in the morning, and is often preceded by a TIA. Recognizing the occurrence of a TIA, and seeking immediate treatment, is an important step in stroke prevention.

CEREBRAL EMBOLISM.Cerebral embolism occurs when a blood clot from elsewhere in the circulatory system breaks free. If it becomes lodged in an artery supplying the brain, either in the brain or in the neck, it can cause a stroke. The most common cause of cerebral embolism is atrial fibrillation, which occurs when the upper chambers (atria) of the heart beat weakly and rapidly, instead of slowly and steadily. Blood within the atria does not empty completely, and may form clots that can then break off and enter the circulation. Atrial fibrillation is a factor in about 15% of all strokes, but this risk can be dramatically reduced with daily use of anticoagulant medication (such as Heparin or Coumadin).

SUBARACHNOID HEMORRHAGE.In this type of stroke, blood spills into the subarachnoid space between the brain and cranium. As fluid builds up, pressure on the brain increases, impairing its function. Hypertension is a frequent cause of these types of stroke, but vessels with preexisting defects, such as an aneurysm, are also at risk for rupture. Aneurysms are most likely to burst when blood pressure is highest, and controlling blood pressure is an important preventive strategy. Subarachnoid hemorrhages account for about 7% of all strokes.

INTRACEREBRAL HEMORRHAGE.Representing about 10% of all strokes, intracerebral hemorrhage affects vessels and tissue within the brain itself. As with subarachnoid hemorrhage, bleeding deprives affected tissues of blood supply, and the accumulation of fluid within the inflexible skull creates pressure on the brain that can quickly become fatal. Despite this, recovery may be more complete for a person who survives hemorrhage than for one who survives a clot, because the effects of blood deprivation are usually not as severe.