Stroke - Causes

There are four main types of strokes. They are:

• Cerebral thrombosis
• Cerebral embolism
• Subarachnoid hemorrhage
• Intracerebral hemorrhage

Cerebral thrombosis and cerebral embolism account for about three-quarters of all strokes.

Cerebral thrombosis occurs when a blood clot forms inside the brain, stopping the flow of blood to or from the brain. The medical term for blood clot is thrombosis. The most common cause for the formation of a blood clot is the hardening of the arteries, or atherosclerosis (see atherosclerosis entry).

A cerebral thrombosis occurs most often at night or early in the morning. It is often preceded by a transient ischemic attack (TIA), which is also referred to as a mini-stroke. A TIA may act as a warning sign that a full stroke is likely to occur.

Cerebral embolism is also caused by a blood clot. The clot, however, forms elsewhere in the body then travels through the bloodstream to the brain. Once in the brain, it produces effects like those of cerebral thrombosis.

Subarachnoid hemorrhage and intracerebral hemorrhage are caused when blood vessels in the brain break. Blood vessels sometimes develop weak spots in their walls. These weak spots are called aneurysms (pronounced AN-yu-RIHZ-umz; see cerebral aneurysm entry). When an aneurysm breaks, blood flows out of the blood vessel into the surrounding tissue and brain cells begin to die rapidly. An intracerebral hemorrhage takes place inside the brain. A subarachnoid (pronounced sub-uh-RAK-noyd) hemorrhage occurs on the surface of the brain.