is an injury to the brain that occurs when the brain's blood supply is interrupted. Blood carries oxygen which is necessary for all cells in the body to survive. The brain has one of the highest demands for oxygen. In fact, cells in the brain start to die if they are without oxygen-rich blood for more than a few minutes. The death of these brain cells can result in permanent brain damage.
Other terms for stroke include cerebrovascular accident (CVA) or brain attack.
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Blood vessels that carry blood from the heart to the body are called arteries. Oxygen-rich blood is delivered to the brain through the carotid arteries along both sides of the neck. These arteries split into several smaller vessels that reach throughout the brain and skull. Damage or blockage to any of these arteries can slow or stop blood flow to the brain. The severity of brain damage will depend on the amount of brain tissue affected, the length of time the blood flow is impaired, and the area of the brain affected.
Blood Supply to the Brain
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Types and Causes of Stroke
An ischemic stroke occurs when a blood vessel of the brain becomes blocked. Nearly 90% of all strokes are ischemic. Blockage may be caused by:
Carotid artery stenosis
—Narrowing of the carotid arteries that supply blood to the brain. The narrowing occurs as a result of
, the build up of plaque (fat, cholesterol, and other substances) inside artery walls.
—A blood clot that forms in the arteries of the brain, often a result of atherosclerosis.
—A blood clot that travels from another part of the body. In many cases, the clot travels from the heart and gets trapped in the arteries that supply blood to the brain. A common cause of embolism is
, a type of
—Blood vessels have muscular walls that can tighten or loosen to help blood flow. Problems with nerves, blood vessel structure, injuries, or stimulants can cause these muscles to spasm and tighten, making it difficult for blood to flow through the blood vessel. Although spasms can cause problems on their own, they may be more likely to cause blockages in blood vessels with current atherosclerosis.
A stroke may also occur if a blood vessel breaks and bleeds into or around the brain. Hemorrhagic stroke is the most common type of stroke in young people. The leading causes of this type of stroke are:
—Blood pressure is the force of blood on arteries walls. Prolonged high blood pressure damages and weakens blood vessels.
—An aneurysm is an outpouching of a blood vessel wall in the brain that form in areas where the artery wall is weak or thin. The bulging, blood-filled pocket can put pressure on parts of the brain. Aneurysms that burst often have devastating consequences.
(AVM)—A rare condition marked by abnormal connections that occur between arteries and veins. Instead of an artery supplying an area of the brain with blood, it is connected directly to a vein that takes it away, bypassing the brain tissue that needs it. The blood vessels may be weakened over time. This, in turn, may cause widening of the vessels, which may eventually burst.
A silent stroke occurs without any typical signs or symptoms of a stroke. Despite this, silent strokes cause damage to brain tissue and increase the risk of a major stroke in the future. Silent strokes tend to occur in silent areas of the brain that are not obviously active in cognitive function or mobility. Brain tissue damage is usually found incidentally during imaging tests.
Strokes can also be classified according to their course in time:
- Completed stroke—Reaches its maximum extent immediately or over the course of a few hours.
Transient ischemic attack
(TIA)—A temporary loss of blood supply to the brain that resolves on its own, within 24 hours. It serves as a warning that a more severe stroke is likely.
- Stroke in progress—One that continues to worsen over time, possibly even days.
Multiple small strokes may occur over time, from days to years, and create effects similar to one big stroke.