|A cerebrovascular accident, commonly known as a stroke, is sudden, localized damage in the brain that results in nervous system (neurologic) deficits. Stroke may result from either interrupted delivery of blood and oxygen to the brain (ischemic stroke) or abnormal bleeding in the brain (hemorrhagic stroke). |
The cause of ischemic stroke is blockage (occlusion) of arteries that carry blood and oxygen to the brain or within the brain. The source of the occlusion may be a clot (thrombus) attached to the wall of a blood vessel, the heart, or the valves of the heart. Thrombi are most likely to form in the blood vessels when narrowing of the arteries caused by fatty deposits in the vessel walls (atherosclerosis) leads to turbulent blood flow. Thrombi form along the walls of the heart when portions of the heart muscle are damaged or not able to contract normally (e.g., myocardial infarction, atrial fibrillation, severe congestive heart failure, cardiomyopathy). Thrombi form on valves when there is damage to the valve (endocarditis, mitral stenosis, artificial valves). Certain medical conditions can also cause platelets or red blood cells to become stickier or cause increased blood viscosity, leading to formation of a thrombus. These conditions include polycythemia, multiple myeloma, sickle cell anemia, protein C deficiency, and protein S deficiency.
Occlusion can also be caused by material (embolus) traveling through the blood stream. Examples of an embolus include a thrombus that has broken away from the wall of the blood vessel, heart, or valve; a piece of plaque; or a clump of bacteria.
Non-thrombotic occlusion of small arteries deep in the brain is the most common cause of ischemic stroke. Regardless of the cause of blockage, nerve cells (neurons) and brain tissue die when robbed of blood and oxygen supply. The size and location of the blockage and the extent of damage before blood flow is restored determined the effects of a stroke. Brief ischemic episodes (transient ischemic attacks or TIAs) can occur as warning signs of an impending larger stroke. TIAs occur before almost 30% of ischemic strokes. Symptoms of TIA usually pass quickly; a diagnosis of ischemic stroke is made when neurologic deficits persist for more than one hour.
Bleeding from a ruptured blood vessel causes hemorrhagic stroke. The blood vessel may rupture because of high blood pressure (hypertension), increased tendency toward bleeding, an abnormal weakness in the wall of a blood vessel (aneurysm), or abnormal communication between arteries and veins (arteriovenous malformation). For specific information concerning hemorrhagic stroke, see the topic titled Cerebral Hemorrhage.
Conditions that predispose individuals for stroke are hypertension, diabetes mellitus, heart disease, congestive heart failure, and atrial fibrillation, particularly if these conditions are untreated or are poorly controlled. Risk also is increased in individuals who have a history of transient ischemic attacks, cerebrovascular disease, or a family history of stroke.
Risk: Three-quarters of all strokes occur in adults over the age of 55 (Becker), and the risk of stroke increases with each decade after age 55. Lifestyle risk factors for stroke are high cholesterol, obesity, cigarette smoking, cocaine use (the most common cause of stroke in people under age 55), and heavy use of alcohol.
Men have a higher risk for stroke than women (Becker). The stroke risk for young women who smoke and also take birth control pills (high-estrogen oral contraceptives) is more than 20 times higher than for women who do not smoke and also do not use oral contraceptives. African-Americans have a higher prevalence of hypertension, diabetes, obesity, smoking, and sickle cell anemia, leading to a prevalence of stroke almost twice that in Caucasian populations. The incidence of stroke in African-American males is 93 per 100,000; incidence in African-American females is 79 per 100,000. The incidence of stroke in Caucasian males is 62.8 per 100,000; incidence in Caucasian females is 59 per 100,000 (Jauch). The risk of stroke is reduced by moderate alcohol consumption (6 to 8 oz. of wine daily) and exercise (Sacco).
Incidence and Prevalence: Ischemic strokes account for 85% of all strokes (Becker). Each year 160 out of every 100,000 Americans experience a stroke (Singh). In industrialized countries, stroke is the third leading cause of death and the leading cause of disability in adults (Jauch).