Stroke - Part 1

Definition:  A stroke is the sudden death of  brain cells in a localized area due to inadequate blood flow.

Description: A stroke occurs when blood flow is interrupted to part of the brain.  Without blood to supply oxygen and nutrients and to remove waste products, brain cells quickly begin to die.  Depending on the region of the brain affected, a stroke may cause paralysis, speech impairment, a loss of memory and reasoning ability, coma, or death.  A stroke is also sometimes called a brain attack or a cerebrovascular accident (CVA).

Some important stroke statistics include:

• More than half a million people in the United States experience a new or recurrent stroke each year.
• Stroke is the third leading cause of death in the United States and the leading cause of disability.
• Stroke kills about 150,000 Americans each year, or almost one out of three stroke victims.
• Three million Americans are currently permanently disabled from stroke.
• In the United States, stroke costs about $30 billion per year in direct costs and loss of productivity.
• Two-thirds of strokes occur in people over the age of 65.
• Strokes affect men more often than women, although women are more likely to die from a stroke.
• Strokes affect blacks more often than whites, and are more likely to be fatal among blacks.

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 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 10 people died from stroke, compared to slightly less than one in three today. 

Causes:  There are four main types of stroke.  Cerebral thrombosis and cerebral embolism are caused by blood clots that block an artery supplying the brain, either in the brain itself or in the neck.  These account for 70-80% of all strokes.  Subarachnoid hemorrhage and intracerebral hemorrhage occur when a blood vessel bursts around or in the brain.

Cerebral Thrombosis occurs when a blood clot, or thrombus, forms within the brain itself, blocking the flow of blood through the affected vessel.  Clots most often form due to "hardening" (atherosclerosis) of brain arteries.  Cerebral thrombosis occurs most often at night or early in the morning.  Cerebral thrombosis is often preceded by a transient ischemic attach (TIA), sometimes called a "mini-stroke".  In a TIA, blood flow is temporarily interrupted, causing short=lived stroke-like symptoms.  Recognizing the occurrence of a TIA and seeking immediate treatment are important steps in stroke prevention.

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, a disorder of the heartbeat.  In atrial fibrillation, the upper chambers of the heart (atria) beat weakly and rapidly, instead of slowly and steadily.  Blood within the atria is not completely emptied.  This stagnant blood may form clots within the atria, which can then break off and enter the circulation.  Atrial fibrillation is a factor in about 15% of all strokes.  The risk of a stroke from atrial fibrillation can be dramatically reduced with daily use of anticoagulant medication.

Hemorrhage, or bleeding occurs when a blood vessel breaks, either from trauma or excess internal pressure.  The vessels most likely to break are those with preexisting defects such as an aneurysm.  An aneurysm is a "pouching out" of a blood vessel caused by a weak arterial wall.  Brain aneurysms are surprisingly common.  According to autopsy studies, about 6% of all Americans have them.  Aneurysms rarely cause symptoms until they burst.  Aneurysms are most likely to burst when blood pressure is highest, and controlling blood pressure is an important preventive strategy.

Intracerebral hemorrhage affect vessels within the brain itself, while subarachnoid hemorrhage affects arteries at the brain's surface, just below the protective arachnoid membrane.  Intracerebral hemorrhages represent about 10% of all strokes, while subarachnoid hemorrhages account for about 7%.  In addition to depriving affected tissues of blood supply, the accumulation of fluid within the inflexible skull creates excess pressure on brain tissue, which can quickly lead to death.  Nonetheless, recovery may be more complete for a person who survives hemorrhage than for one who survives a clot, because the blood deprivation effects are usually not as severe. 

Death of brain cells triggers a chain reaction in which toxic chemicals created by cell death affect other nearby cells.  This is one reason why prompt treatment can have such a dramatic effect on final recovery.

Risk Factors:  Risk factors for stroke involve age, sex, heredity, predisposing diseases or other medical conditions, and lifestyle choices including:

• Age and sex.   The risk of stroke increases with increasing age, doubling for each decade after age 55.  Men are more likely to have a stroke than women.
• Heredity.  Blacks, Asians, and Hispanics all have higher rates of stroke than do whites, related partly to higher blood pressure.  People with a family history of stroke are at greater risk.
• Diseases.  Stroke risk is increased for people with diabetes, heart disease (especially atrial fibrillation) high blood pressure, prior stroke, or TIA.  Risk of stroke increases tenfold for someone with one or more TIAs.
• Other medical conditions.  Stroke risk increases with obesity, high blood cholesterol level, or high red blood cell count.

Symptoms:  Symptoms of an embolic stroke usually come on quite suddenly and are at their most intense right from the start, while symptoms of a thrombotic stroke come on more gradually.  Symptoms  may include:

• blurring or decreased vision in one or both eyes
• severe headache
• weakness, numbness, or paralysis of the face, arm, or leg, usually confined to one side of the body
• dizziness, loss of balance or coordination, especially when combine with other symptoms

Diagnosis:  The diagnosis of stroke is begun with a careful medical history, especially concerning the onset and distribution of symptoms, presence of risk factors, and the exclusion of other possible causes.  A brief neurological exam is performed to identify the degree and location of any deficits such as weakness, loss of coordination, or visual losses.

Once stroke is suspected, a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan is performed to distinguish a stroke caused by blood clot from one caused by hemorrhage, a critical distinction that guides therapy.  Blood and urine tests are done routinely to look for possible abnormalities.  Other investigations that may be performed to guide the treatment include an electrocardiogram, angiography, ultrasound, and electroencephalogram.