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 supplyoxygen and nutrients and to remove waste products, brain cells quickly begin to die. Dependingon the region of the brain affected, a stroke may cause paralysis, speech impairment, loss ofmemory and reasoning ability, coma, or death. A stroke also is sometimes called a brain attackor a cerebrovascular accident (CVA).
Stroke is a medical emergency requiring immediate treatment. Prompt treatment improves thechances of survival and increases the degree of recovery that may be expected. A person whomay 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 ofthe stroke to be effective. Improved medical treatment of all types of stroke has resulted in adramatic decline in death rates in recent decades. In 1950, nine in ten died from stroke,compared to slightly less than one in three in the twenty-first century. However, about two-thirdsof stroke survivors will have disabilities ranging from moderate to severe.
Causes and symptoms
Causes
There are four main types of stroke. Cerebral thrombosis and cerebral embolism are caused byblood 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 intracerebralhemorrhage 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 themorning. Cerebral thrombosis is often preceded by a transient ischemic attack, or 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 immediatetreatment, is an important step in stroke prevention.
Cerebral embolism occurs when a blood clot from elsewhere in the circulatory system breaksfree. If it becomes lodged in an artery supplying the brain, either in the brain or in the neck, it cancause a stroke. The most common cause of cerebral embolism is atrial fibrillation, a disorder ofthe heart beat. In atrial fibrillation, the upper chambers (atria) of the heart beat weakly andrapidly, instead of slowly and steadily. Blood within the atria is not completely emptied. Thisstagnant 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 fibrillationcan be dramatically reduced with daily use of anticoagulant medication.
Hemorrhage, or bleeding, occurs when a blood vessel breaks, either from trauma or excessinternal pressure. The vessels most likely to break are those with preexisting defects such as ananeurysm. 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 allAmericans have them. Aneurysms rarely cause symptoms until they burst. Aneurysms are mostlikely to burst when blood pressure is highest, and controlling blood pressure is an importantpreventive strategy.
Intracerebral hemorrhage affects vessels within the brain itself, while subarachnoid hemorrhageaffects arteries at the brain's surface, just below the protective arachnoid membrane.Intracerebral hemorrhages represent about 10% of all strokes, while subarachnoid hemorrhagesaccount for about 7%.
In addition to depriving affected tissues of blood supply, the accumulation of fluid within theinflexible skull creates excess pressure on brain tissue, which can quickly become fatal.Nonetheless, recovery may be more complete for a person who survives hemorrhage than for onewho survives a clot, because the blood deprivation effects usually are not as severe.
Death of brain cells triggers a chain reaction in which toxic chemicals created by cell deathaffect other nearby cells. This is one reason why prompt treatment can have such a dramaticeffect on final recovery.
Risk factors
Risk factors for stroke involve age, sex, heredity, predisposing diseases or other medicalconditions, use of certain medications, and lifestyle choices:
- Age and sex. The risk of stroke increases with age, doubling for each decade after age 55.Men are more likely to have a stroke than women.
- Heredity. Blacks, Asians, and Hispanics have higher rates of stroke than do whites, relatedpartly 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 atrialfibrillation), high blood pressure, prior stroke, or TIA. Risk of stroke increases tenfold forsomeone with one or more TIAs.
- Other medical conditions. Stroke risk increases with obesity, high blood cholesterol level, orhigh red blood cell count.
- Hormone replacement therapy. In mid-2003, a large clinical trial called the Women'sHealth Initiative was halted when researchers discovered several potentially dangerous effectsof combined hormone replacement therapy on postmenopausal women. In addition toincreasing the risk of some cancers and dementia, combined estrogen and progesteronetherapy increased risk of ischemic stroke by 31% among study participants.
- Lifestyle choices. Stroke risk increases with cigarette smoking (especially if combined withthe use of oral contraceptives), low level of physical activity, alcohol consumption abovetwo drinks per day, or use of cocaine or intravenous drugs.
Symptoms
Symptoms of an embolic stroke usually come on quite suddenly and are at their most intenseright from the start, while symptoms of a thrombotic stroke come on more gradually. Symptomsmay include:
- blurring or decreased vision in one or both eyes
- severe headache, often described as "the worst headache of my life"
- weakness, numbness, or paralysis of the face, arm, or leg, usually confined to one side ofthe body
- dizziness, loss of balance or coordination, especially when combined with other symptoms
Diagnosis
The diagnosis of stroke is begun with a careful medical history, especially concerning the onsetand distribution of symptoms, presence of risk factors, and the exclusion of other possiblecauses. A brief neurological exam is performed to identify the degree and location of any deficits,such as weakness, incoordination, or visual losses.
Once stroke is suspected, a computed tomography scan (CT scan) or magnetic resonance imaging (MRI) scan is performed to distinguish a stroke caused by blood clot from one causedby hemorrhage, a critical distinction that guides therapy. Blood and urine tests are doneroutinely to look for possible abnormalities.
1. A sudden loss of neurological function,caused by vascular injury (loss of bloodflow) to an area of the brain. Stroke isboth common and deadly: about 700,000strokes occur in the U.S. each year.Stroke is the third leading cause of deathin the U.S. Because of the long-termdisability it often produces, stroke is thedisease most feared by older Americans.In the U.S., 80% of strokes are causedby cerebral infarction (i.e., blockage of thecarotid or intracerebral arteries by clot oratherosclerosis); intracranial hemorrhageand cerebral emboli are responsible formost other strokes. Innovations in themanagement of stroke (e.g., inprevention, the early use of thrombolyticdrugs, vascular ultrasonography, andendarterectomy) have revolutionized theacute and follow-up care of the strokepatient. Synonym: apoplexy; attack, brain; cerebrovascular accident See:carotid endarterectomy; intracranial hemorrhage; transient ischemic attack; illustration; table
Etiology
Risk factors for stroke include advancedage (esp. older than 65 years),atherosclerosis of the aortic arch, atrialfibrillation, carotid artery disease,cigarette use, excessive alcohol use(more than 5 drinks daily), heart failure,hyperlipidemia, hypertension, a history ofmyocardial infarction, diabetes mellitus,male gender, close relation of someonewho has had a stroke, nonwhite race,peripheral vascular disease, physicalinactivity, obesity, using combinationhormonal contraception (the pill, ring,patch), being pregnant or immediatelypostpartum, or a recent transientischemic attack.
