Overview & Symptoms

In an ischemic stroke, a blood clot forms inside an artery in the brain, blocking blood flow. Sometimes, the clot forms in one of the arteries in the neck that transport blood from the heart to the brain. Blood clots form most often in arteries that have rough, fatty deposits built up on the walls that project into the bloodstream (a disease called atherosclerosis). These deposits gradually narrow the passageway, causing the blood flow to slow down and sometimes block the artery.

Blood clots from elsewhere in the body can also cause an ischemic stroke. These strokes occur when a clot breaks loose and travels through the blood stream to the brain's arteries and then smaller blood vessels where it gets stuck and cuts off the blood supply. This blockage is called an embolism.

The term "cerebral infarction" is also used in connection with ischemic stroke. An infarct is an area of tissue that has died because the blood clot has stopped the blood supply to that area.

An hemorrhagic stroke occurs when a blood vessel in or around the brain ruptures and spills blood into the brain or the area surrounding the brain. When this happens, the cells around the artery fail to get their normal supply of nutrients and cease to function properly.

The accumulated blood from the ruptured artery clots, displacing normal brain tissue and disrupting brain function. Cerebral hemorrhage is most likely to occur in people who suffer from a combination of atherosclerosis and high blood pressure.

There are two main types of hemorrhagic strokes: subarachnoid hemorrhage and intracerebral hemorrhage, which refer to the parts of the brain affected by the bleeding.

In subarachnoid hemorrhage, the bleeding occurs in the space between the brain and the skull.

Intracerebral hemorrhage is caused when a defective artery within the brain bursts, flooding the surrounding brain tissue with blood.

Hemorrhagic strokes often occur when an aneurysm (an abnormal bulging of a blood vessel in the brain) or a cluster of abnormal blood vessels called an arteriovenous malformation (AVM) burst.

In the case of an aneurysm, the weak spot in the vessel wall can be stretched out over the years, often by high blood pressure, which ultimately causes it to rupture.

While aneurysms may not cause any symptoms until they burst, AVMs may have many associated symptoms, including seizures, progressive neurologic problems and severe headaches that are unresponsive even to strong medications.