What is a Stroke?

From the National Institute of Health:

A stroke happens when blood flow to a part of the brain is interrupted because a blood vessel in the brain is blocked or bursts open.

If blood flow is stopped for longer than a few seconds, the brain cannot get blood and oxygen. Brain cells can die, causing permanent damage.

There are two major types of stroke: ischemic stroke and hemorrhagic stroke.

ISCHEMIC STROKE

Ischemic stroke occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot. This may happen in two ways:

•A clot may form in an artery that is already very narrow. This is called a thrombus. If it completely blocks the artery, it is called a thrombotic stroke.

•A clot may break off from another place in the blood vessels of the brain, or some other part of the body, and travel up to the brain to block a smaller artery. This is called an embolism. It causes an embolic stroke.

Ischemic strokes may result from clogged arteries, a condition called atherosclerosis. This may affect the arteries within the brain or the arteries in the neck that carry blood to the brain. Fat, cholesterol, and other substances collect on the wall of the arteries, forming a sticky substance called plaque. Over time, the plaque builds up. This often makes it hard for blood to flow properly, which can cause the blood to clot.

Ischemic strokes may also be caused by blood clots that form in the heart or other parts of the body. These clots travel through the blood and can get stuck in the small arteries of the brain. This is known as a cerebral embolism.

Certain drugs and medical conditions can make your blood more likely to clot and raise your risk for ischemic stroke. A common cause of ischemic stroke in people under age 40 is carotid dissection, or a tear in the lining of the carotid artery. The tear lets blood flow between the layers of the carotid artery. This causes narrowing of the carotid artery that is not due to plaque buildup.

Some ischemic strokes start out without any bleeding, and then bleeding into the damaged area occurs.

HEMORRHAGIC STROKE

Hemorrhagic stroke occurs when a blood vessel in part of the brain becomes weak and bursts open, causing blood to leak into the brain. Some people have defects in the blood vessels of the brain that make this more likely. The flow of blood that occurs after the blood vessel ruptures damages brain cells.