What is a Stroke?

A stroke occurs when a blood vessel that brings oxygen and nutrients to the brain bursts or is clogged by a blood clot or some other particle. Because of this rupture or blockage, part of the brain does not get the blood and oxygen it needs to survive.

Deprived of oxygen, nerve cells in the affected area of the brain cannot work and die within minutes. When nerve cells cannot work, the part of the body they control cannot work then either.

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The effects of stroke from the damaged brain cells are often permanent, because brain cells cannot be replaced. There are two types of strokes, hemorrhagic (bleeding or blood vessel rupture) and ischemic (from blockage).

An ischemic stroke, or blockage, can be caused by a thrombosis or embolism, which is a clot or particle that can plug an artery. These account for most strokes, about 75-80 percent.

Cerebral thrombosis is the most common cause of stroke. A thrombus, or blood clot, forms in arteries damaged by fatty buildups, called atherosclerosis. The clot may eventually block blood flow in the artery, preventing blood from flowing to that part of the brain.

Cerebral embolism occurs when a clot or some other particle forms in the body, usually the heart, and travels through the bloodstream to an artery going to or in the brain. Most emboli are blood clots that form during an irregular heart beat, atrial fibrillation. Blood pools in the upper chamber of the heart that does not beat effectively. It can then enter the circulation and travel to the brain, causing a stroke.

Hemorrhagic strokes are caused by ruptured or damaged blood vessels and account for approximately 15-20 percent of strokes. These types of stroke may have a much higher fatality rate than strokes caused by clots. There are several causes for hemorrhagic strokes; one of which can be from a subarachnoid hemorrhage (SAH), which occurs when a blood vessel ruptures on the brain’s surface and bleeds around, but not into, the brain itself.

A cerebral hemorrhage is another cause for hemorrhagic strokes. They occur when a defective or damaged artery in the brain bursts, flooding the brain’s tissue with blood. Bleeding from an artery in the brain can be caused by a head injury or a defective artery (aneurysm). Aneurysms are weakened, blood filled pouches in an artery that can rupture. High blood pressure will weaken the aneurysm or can rupture fragile vessels in the brain. If the person survives, the pressure will eventually decrease and the brain may regain some of its former functioning.