Stroke
Alternative names:
cerebrovascular accident; cerebrovascular disease; CVA
Definition:
A group of brain disorders involving loss of brain functions that occur when the blood supply to any part of the brain is interrupted.
Causes, incidence, and risk factors:
The brain requires about 20% of the circulation of blood in the body. The primary blood supply to the brain is through 2 arteries in the neck (the carotid arteries), which then branch off within the brain to multiple arteries that each supply a specific area of the brain. Even a brief interruption to the blood flow can cause decreases in brain function (neurologic deficit). The symptoms vary with the area of the brain affected and commonly include such problems as changes in vision, speech changes, decreased movement or sensation in a part of the body, or changes in the level of consciousness. If the blood flow is decreased for longer than a few seconds, brain cells in the area are destroyed (infarcted) causing permanent damage to that area of the brain or even death.
A stroke affects about 4 out of 1,000 people. It is the 3rd leading cause of death in most developed countries, including the U.S. The incidence of stroke rises dramatically with age, with the risk doubling with each decade after age 35. About 5% of people over age 65 have had at least one stroke. The disorder occurs in men more often than women.
A stroke involves loss of brain functions (neurologic deficits) caused by a loss of blood circulation to areas of the brain. The specific neurologic deficits may vary depending on the location, extent of the damage, and cause of the disorder. A stroke may be caused by reduced blood flow (ischemia) that results in deficient blood supply and death of tissues in that area (infarction). Causes of ischemic strokes are blood clots that form in the brain (thrombus) and blood clots or pieces of atherosclerotic plaque or other material that travel to the brain from another location (emboli). Bleeding (hemorrhage) within the brain can rarely cause symptoms that mimic stroke.
The most common cause of a stroke is stroke secondary to atherosclerosis (cerebral thrombosis). Atherosclerosis ("hardening of the arteries") is a condition in which fatty deposits occur on the inner lining of the arteries, and atherosclerotic plaque (a mass consisting of fatty deposits and blood platelets) develops. The occlusion of the artery develops slowly. Atherosclerotic plaque does not necessarily cause a stroke. There are many small connections between the various brain arteries. If the blood flow gradually decreases, these small connections will increase in size and "by-pass" the obstructed area (collateral circulation). If there is enough collateral circulation, even a totally blocked artery may not cause neurologic deficits. A second safety mechanism within the brain is that the arteries are large enough that 75% of the blood vessel can be occluded, and there will still be adequate blood flow to that area of the brain.
A thrombotic stroke (stroke caused by thrombosis) is most common in older people, and often there is underlying atherosclerotic heart disease or diabetes mellitus. This type of stroke may occur at any time, including at rest. The person may or may not lose consciousness.
Strokes caused by embolism (moving blood clot) are most commonly strokes secondary to a cardiogenic embolism, clots that develop because of heart disorders that then travel to the brain. An embolism may also originate in other areas, especially where there is atherosclerotic plaque. The embolus travels through the bloodstream and becomes stuck in a small artery in the brain. This stroke occurs suddenly with immediate maximum neurologic deficit. It is not associated with activity levels and can occur at any time. Arrhythmias of the heart are commonly seen with this disorder and often are the cause of the embolus. Damage to the brain is often more severe than with a stroke caused by cerebral thrombosis. Consciousness may or may not be lost.
The probable outcome is worsened if blood vessels damaged by stroke rupture and bleed (hemorrhagic stroke).
See also: The risks for a stroke include a history of high blood pressure (hypertension is present in about 70% of all victims of stroke), heart disease (especially with atrial fibrillation/flutter), smoking, transient ischemic attack (TIA), atherosclerosis or high blood lipids, diabetes, migraine headaches, or any of the other disorders that may cause a stroke. Gout and high red blood cell count have been associated with a stroke. Although young women generally have a fairly low risk for a stroke, use of birth control pills will increase their risk, and smoking combined with use of birth control pills makes the risk even higher.
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