Health

The brain relies on a steady supply of oxygenated blood to perform its myriad tasks — everything from coordinating your arm and leg movements as you walk down a street to allowing you to appreciate the complexity of language in a favorite novel. Because maintaining a steady blood supply is so important, multiple blood vessels snake into and around the brain, ensuring that even if one blood vessel becomes narrowed or damaged, alternate delivery routes still exist (see Figure 1).

A stroke occurs when an injury to a blood vessel supplying the brain causes it to burst, resulting in a hemorrhagic stroke, or becomes blocked, resulting in an ischemic stroke. In both cases, the injury deprives the brain of a constant blood supply carrying oxygen and nutrients; some of the cells of the brain die, possibly taking with them the ability to move, speak, feel, think, or even recognize people. In this way, a stroke threatens the very core of one's humanity.

Recovery after a stroke depends on how well healthy areas of the brain take over duties that had been performed by the damaged brain tissue. To some extent, especially in children and young adults, recovery is possible because of the brain's ability to compensate for damage in one area by working harder in another — by relying on alternate wiring for some functions or by rewiring around the injured site. In some cases, rehabilitation techniques can also facilitate functional recovery.

Major types of stroke

The two major types of stroke have different causes. Ischemic strokes account for more than 80% of strokes and result from an interruption in blood flow through a specific artery supplying a specific area of the brain. Four basic types of arterial pathologies can cause a blockage that interferes with blood flow (see "Subtypes and causes of strokes"). When brain cells die as a result of ischemic stroke, the resulting injury to the brain is called a cerebral infarction.

Hemorrhagic strokes account for slightly less than 20% of strokes and are caused by rupture of a blood vessel either inside the skull, but outside the brain (known as an extracerebral hemorrhage) or inside the brain (intracerebral hemorrhage). Once a blood vessel ruptures, the resulting heavy bleeding (hemorrhage) tears through the brain. This results in a mass of accumulated blood known as a hematoma, which compresses nearby brain tissue and interferes with its blood supply. The initial arterial rupture has a specific pathological cause that must be determined before treatment can begin (see "Subtypes and causes of strokes").

Whether a stroke is hemorrhagic or ischemic, immediate treatment is crucial in limiting brain damage. Starting treatment within minutes to several hours can often limit the disability caused by the stroke. As doctors often say, "Time is brain."

Updated thinking about TIAs

Transient ischemic attacks (TIAs) were once considered less dangerous than full-blown strokes because symptoms tend to disappear within 24 hours, and in most cases no permanent disability remains. However the thinking about TIAs has changed considerably, as evidenced by stroke guidelines updated in 2006 by the American Heart Association and the American Stroke Association.

The consensus now is that a TIA should be regarded, and treated, every bit as seriously as a full-blown stroke. TIAs usually last several minutes to hours and are caused by partial or temporary obstruction of an artery by the same pathological process that causes an ischemic stroke. For this reason, although the symptoms of a TIA may disappear, take it as a warning of an impending serious ischemic stroke.

But TIAs may also last longer, and in such cases the potential for brain damage is significant even if the TIA never progresses to a full-blown stroke. If the TIA lasts as long as 24 hours (at which point a TIA technically becomes a full-blown stroke) it is likely that it has caused some type of brain infarction, or tissue death. Advances in brain imaging have revealed that brain infarction may occur even in TIAs that end much earlier — and even if symptoms have abated. Here the infarcted tissue is in a "silent" area of the brain, one not currently being used, and so there are no symptoms. Or the damaged area may be adjacent to a part of the brain that produced symptoms following the initial injury, but then recovered, so that the symptoms disappeared.

What's more, as many as 10% of people who have a TIA will suffer a full-blown stroke within 90 days, with the greatest risk in the first week. That's why it's so important to seek medical help promptly: The fact that symptoms have disappeared does not mean that the danger is over.

Who is at risk?

Stroke is the third leading cause of death in the United States and other industrial countries, trailing only heart disease and cancer. In the United States, about 700,000 people have a stroke each year. If you have a stroke, the risk of dying from it increases with age: 88% of deaths from stroke are in people 65 and older. About two-thirds of people who have a stroke have some resulting disability and require rehabilitation.

The odds of having a stroke more than double for each decade after age 55. Two-thirds of strokes involve people over 65. Men and women are about equally likely to have a stroke, but women have a greater risk of dying from one. Race is another risk factor. African Americans, for example, are almost twice as likely to suffer a stroke as are whites.

Although you can't change your age or race, you can take steps to reduce other risk factors for stroke, especially ischemic stroke. The most common risk factors for both ischemic stroke and TIAs are high blood pressure (hypertension), diabetes, unhealthy cholesterol levels, and obesity. All of these factors affect the health of your blood vessels — increasing the risk not only of stroke, but also of heart disease. That's why medications and other steps you take to reduce the risk of an ischemic stroke will also benefit your heart (see "Treating ischemic stroke").

Some types of hemorrhagic strokes are more likely to occur in people with chronic high blood pressure (see "Deep hypertensive hemorrhages"). But other types of hemorrhagic strokes seemingly strike out of the blue. Although abnormal blood vessel conditions such as an aneurysm (a bubble in the blood vessel wall that could rupture) or an arteriovenous malformation (an abnormal tangle of blood vessels) increase the risk, these conditions may only be discovered inadvertently while you are undergoing testing for something else — or may not be discovered until a stroke occurs.

How to tell if you're having a stroke

When stroke symptoms occur, quick action is vital. Warning signs can begin anywhere from a few minutes to days before a stroke. If you think you or someone with you is having a stroke or a transient ischemic attack (TIA), seek immediate medical attention (see "Stroke warning signs and symptoms"). If you can't reach your doctor by telephone, go to a hospital emergency room, preferably one that specializes in treating stroke as it occurs (called acute stroke). If you know you are at risk for stroke, find out ahead of time the name and location of the nearest hospital that specializes in treating acute stroke.

In a Gallup survey, 97% of people over age 50 did not recognize the warning signs of a stroke. Everyone, especially those who are at increased risk for strokes, should learn these warning signs and know what to do if they occur.

Seek help early. Since the 1980s, researchers have developed rapid, safe, and effective diagnostic techniques that accurately identify the extent and location of a stroke and the nature of the blood vessel (vascular) problem causing it. The goal of treatment is to restore blood circulation before brain tissue dies. The time frame for reaching this goal is frighteningly slim. Treatment usually has to begin within 60 minutes of a stroke to prevent brain cell death that is significant enough to cause disability.

One of the main clot-dissolving drugs, recombinant tissue plasminogen activator (tPA), is best given early. People treated with tPA one hour after the onset of a stroke were more than three times as likely to survive with few disabilities compared with those treated two hours after stroke onset, according to two trials sponsored by the National Institute of Neurological Disorders and Stroke. An important goal of research is to find treatments that can buy time by protecting the patient's brain until blood circulation is restored, thus improving the odds of survival and decreasing disability.

Prepare for an emergency. If you are at risk of having a stroke, prepare for an emergency by displaying important phone numbers prominently next to the telephone, such as the numbers of your doctor and a relative or close friend who should be contacted. It's also a good idea to keep on hand a current list of prescription medications and other drugs you use and a brief medical history to take to the hospital in the event of a stroke.

Source: from Harvard Health Publications, Copyright © 2008 Harvard University. All rights reserved. Harvard Medical School does not endorse products.
Used with permission of StayWell.
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