In middle-aged and elderly people—among whom there’s a higher incidence of atherosclerosis, diabetes, and hypertension—thrombosis is the most common cause of stroke. Obstruction of a blood vessel causes the stroke. Typically, the main site of the obstruction is the extracerebral vessels, but sometimes it’s the intracerebral vessels.

Thrombosis causes ischemia in brain tissue supplied by the affected vessel as well as congestion and edema. The latter may produce more symptoms than the thrombosis itself, but these subside with the edema.

Thrombosis may develop while the patient sleeps or shortly after he awakens; it can also occur during surgery or after a myocardial infarction. The risk increases with obesity, smoking, or the use of hormonal contraceptives. Cocaine-induced ischemic stroke is now seen in younger patients.

The second most common cause of stroke, embolism is an occlusion of a blood vessel caused by a fragmented clot, a tumor, fat, bacteria, or air. It can occur at any age, especially among patients with a history of rheumatic heart disease, endocarditis, posttraumatic valvular disease, or myocardial fibrillation and other cardiac arrhythmias or after open-heart surgery or placement of a mechanical heart valve.

The embolus usually develops rapidly—in 10 to 20 seconds—and without warning. When it reaches the cerebral vasculature, it cuts off circulation by lodging in a narrow portion of an artery, most commonly the middle cerebral artery, causing necrosis and edema.

If the embolus is septic and infection extends beyond the vessel wall, an abscess or encephalitis may develop. If the infection is within the vessel wall, an aneurysm may form, which could lead to cerebral hemorrhage.

The third most common cause of stroke is hemorrhage. Like an embolism, it may occur suddenly, at any age. Such hemorrhage results from chronic hypertension or aneurysms, which cause sudden rupture of a cerebral artery. The rupture diminishes blood supply to the area served by this artery. In addition, blood accumulates deep within the brain, further compressing neural tissue and causing even greater damage.

Strokes are classified according to their course of progression. The least severe is the TIA, or little stroke, which results from a temporary interruption of blood flow, usually in the carotid and vertebrobasilar arteries. A progressive stroke, or stroke-in-evolution (thrombus-in-evolution),
begins with slight neurologic deficit and worsens in a day or two. In a completed stroke, neurologic deficits are maximal at onset and don’t progress.