A stroke is a medical emergency caused either by obstruction of an artery carrying blood to the brain or by rupture of one of the cerebral arteries. Because brain cells cannot regenerate, lack of oxygen from blockage of the blood supply may quickly lead to cell death and permanent brain damage.

Strokes are more likely to occur when arteries have been substantially narrowed by atherosclerosis (a buildup of plaques in the walls of the arteries). Blood flow through narrow arteries is reduced, and blood clots are more likely to form along the uneven surface of the plaque. A clot formed in a carotid artery in the neck or a cerebral (brain) artery can block the artery at the site. Clots may also form elsewhere, become detached, and ultimately block a cerebral artery, causing a stroke.

About 80 percent of strokes are due to blockage in either an artery in the brain or in one of the carotid arteries in the neck. The remaining 20 percent result from a rupture of a brain artery. This type of stroke is generally the most life-threatening, primarily because of the excessive pressure the hemorrhage exerts on brain tissue.

Although incidence is highest among those over age 65, a stroke may afflict anyone at any age. Symptoms of stroke vary depending on the portion of the brain affected, but they often come on suddenly. Some patients will have temporary stroke-like episodes called transient ischemic attacks, or TIAs, prior to a stroke, which may resolve in minutes to a few hours. Strokes are the third leading cause of death in the United States, but the leading cause of disability. Prevention is key.

Symptoms of Stroke

• Sudden, severe headache. (Stroke symptoms usually come on suddenly.)

• Weakness or paralysis on one or both sides of the face or body.

• Numbness and tingling in one or both arms or legs.

• Speech difficulty or loss; slurred speech; nonsensical speech.

• Nausea and vomiting.

• Total blindness or partial loss of vision, double vision, dilated pupils, or crossed eyes due to partial inability to move the eye.

• Dizziness, mental confusion, or sudden loss of consciousness.

• Memory loss.

• Inability to walk or coordinate limbs.

• Coma.

What Causes Stroke?

• Blood clots that obstruct a carotid or cerebral artery are the most common cause of stroke.

• An embolus (a fragment of plaque, tissue, or blood clot) may develop in the heart and travel to the brain to cause a stroke. Emboli are most likely to develop in association with cardiac arrhythmias (especially atrial fibrillation), valvular heart disease, heart attack, or cardiomyopathy.

• An aneurysm (a balloonlike weak spot in an arterial wall) in a cerebral artery may burst or leak, resulting in a stroke.

• High blood pressure (hypertension) is a significant risk factor for stroke.

• Severely narrowed arteries due to atherosclerosis increase the risk of stroke.

• Use of cocaine or amphetamines may boost blood pressure dangerously high and cause a stroke.

• Risk is high among those who have experienced one or more transient ischemic attacks (TIAs)—a temporary blockage in an artery that lasts for less than 24 hours (usually only a few minutes) and causes no brain damage.

• A family history of stroke, early or premature heart attacks, atherosclerosis, or high blood pressure increases the risk of stroke.

• Smoking, alcohol abuse, high blood cholesterol levels, a diet high in fat (especially animal fat), obesity, lack of exercise, diabetes mellitus, and oral contraceptive use all may increase the risk of stroke.

• Risk increases with age.

Prevention of Stroke

• Don’t smoke.

• Eat a diet low in fat, cholesterol, and salt.

• Engage in moderate, regular exercise. Check with a doctor before beginning an exercise program.

• Lose weight if you are more than 20 percent overweight.

• Have no more than two alcoholic drinks a day.

• Low daily doses of aspirin or other antiplatelet drugs (such as ticlopidine, clopidogrel, and dipyridamole) may be prescribed to reduce the chances of blood clot formation in those who have had a TIA or are otherwise at high risk for stroke.

• Hypertension must be treated aggressively.

• The anticoagulant warfarin may be prescribed for those with atrial fibrillation and some other conditions to prevent blood clot formation.

• Patients who show evidence of substantial atherosclerotic narrowing in the carotid arteries (the two main blood vessels in the neck supplying the brain) may be good candidates for carotid endarterectomy, a surgical procedure to clear away plaque deposits in these arteries.

Diagnosis of Stroke

• Diagnosis is often made immediately upon examination by a doctor or emergency rescue technician.

• Blood tests are taken.

• CT (computed tomography) scans or MRI (magnetic resonance imaging) may be used to locate an abnormal blood vessel or an area of brain damage.

• Ultrasound scans of carotid arteries reveal narrowing due to atherosclerotic plaque.

• Angiography may be performed to locate the arterial blockage or aneurysm. In this procedure a tiny catheter is inserted into an artery in the groin (femoral artery) and threaded up to the carotid artery in the neck. A contrast material is injected to produce a clear x-ray image of the carotid and cerebral arteries.

• An electrocardiogram (ECG) is performed to detect a cardiac arrhythmia or heart damage from a myocardial infarction (heart attack).

• A cardiac ultrasound (echocardiography) may locate a source of blood clots in the heart.

How To Treat Stroke

• Emergency treatment and immediate hospitalization is necessary in the event of a stroke. Life support measures may be required.

• If a stroke is caused by arterial blockage due to a blood clot, thrombolytic (clot-dissolving) drugs, such as intravenous tPA, should be initiated within three hours of the onset of symptoms.

• If the stroke is the result of a cerebral hemorrhage, physicians will immediately take measures to reduce blood pressure of hypertensive patients in order to minimize flow of blood from the ruptured artery.

• Long-term therapy following a stroke may include antiplatelet medications, such as aspirin, or blood thinners, such as warfarin, to prevent future clots.

• Special railings, braces, canes, wheelchairs, or other devices may be necessary to help increase mobility for those with partial paralysis.

• Physical, speech, occupational, and emotional therapy helps patients and their families cope.

• Those with extensive disabilities may need a period of in-hospital rehabilitation or professional in-home medical care.

When To Call A Doctor

• Emergency: Call an ambulance immediately if you or someone in your presence exhibits stroke symptoms.

For more information on stroke and related conditions, click on this link -- Johns Hopkins Health Alerts: Hypertension and Stroke

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