Stroke secondary to atherosclerosis

Definition:

A group of brain disorders involving loss of brain functions, caused by complications of atherosclerosis.

Causes, incidence, and risk factors:

Stroke secondary to atherosclerosis affects about 2 out of 1,000 people, or approximately 50% of all those who have strokes. Strokes are the third leading cause of death in most developed countries, including the U.S. Stroke secondary to atherosclerosis is most common in people over 50 years old. The incidence of stroke rises dramatically with age, with the risk doubling with each decade after 35 years old. About 5% of people over 65 years old have had at least one stroke. The disorder occurs in men more often than women.

Atherosclerosis ("hardening of the arteries") is a condition where fatty deposits occur in the inner lining of the arteries, and atherosclerotic plaque (a mass consisting of fatty deposits and blood platelets) develops. The plaque may obstruct (occlude) the artery by itself, or may trigger a clot (thrombus) at that location, causing cerebral thrombosis (thrombotic stroke). The occlusion of the artery develops slowly.

Atherosclerotic plaque does not necessarily cause stroke. There are many small connections among the various brain arteries. If 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.

Atherosclerosis occludes the blood vessels, causing ischemia (reduced tissue oxygenation associated with insufficient blood flow) and infarction (tissue death associated with ischemia).

Pieces of atherosclerotic plaque or clot may travel in the bloodstream (embolism); however, strokes caused by embolism are most commonly strokes secondary to cardiogenic embolism (clots that develop because of heart disorders, which then travel to the brain). Whatever the source of the embolism, the clot travels through the bloodstream and becomes stuck in a small artery in the brain. This stroke occurs suddenly with immediate maximum neurologic deficit (loss of brain function).

Risks for stroke secondary to atherosclerosis include: a history of high blood pressure (hypertension is present in about 70% of all victims of stroke); peripheral vascular disease; smoking; transient ischemic attacks or other cerebrovascular disease; atherosclerosis or high blood lipids; diabetes mellitus; obesity; and kidney disease requiring dialysis.