Strokes can be classified into 2 main categories:
Ischemic strokes. These are strokes caused by blockage of an artery (or, in rare instances, a vein). About 87% of all strokes are ischemic.
Hemorrhagic stroke. These are strokes caused by bleeding. About 13% of all strokes are hemorrhagic.
An ischemic stroke occurs when a blood vessel that supplies the brain becomes blocked or "clogged" and impairs blood flow to part of the brain. The brain cells and tissues begin to die within minutes from lack of oxygen and nutrients. Ischemic strokes are further divided into 2 groups:
Thrombotic strokes. These are caused by a blood clot that develops in the blood vessels inside the brain.
Embolic strokes. These are caused by a blood clot or plaque debris that develops elsewhere in the body and then travels to one of the blood vessels in the brain through the bloodstream.
Thrombotic strokes are strokes caused by a thrombus (blood clot) that develops in the arteries supplying blood to the brain. This type of stroke is usually seen in older persons, especially those with high cholesterol and atherosclerosis (a buildup of fat and lipids inside the walls of blood vessels) or diabetes.
Sometimes, symptoms of a thrombotic stroke can occur suddenly and often during sleep or in the early morning. At other times, it may occur gradually over a period of hours or even days.
Thrombotic strokes may be preceded by one or more "mini-strokes," called transient ischemic attacks, or TIAs. TIAs may last for a few minutes or up to 24 hours, and are often a warning sign that a stroke may occur. Although usually mild and transient, the symptoms caused by a TIA are similar to those caused by a stroke.
Another type of stroke that occurs in the small blood vessels in the brain is called a lacunar infarct. The word lacunar comes from the Latin word meaning "hole" or "cavity." Lacunar infarctions are often found in people who have diabetes or high blood pressure.
Embolic strokes are usually caused by a blood clot that forms elsewhere in the body (embolus) and travels through the bloodstream to the brain. Embolic strokes often result from heart disease or heart surgery and occur rapidly and without any warning signs. About 15% of embolic strokes occur in people with atrial fibrillation, a type of abnormal heart rhythm in which the upper chambers of the heart do not beat effectively.
Hemorrhagic strokes occur when a blood vessel that supplies the brain ruptures and bleeds. When an artery bleeds into the brain, brain cells and tissues do not get oxygen and nutrients. In addition, pressure builds up in surrounding tissues and irritation and swelling occur, which can lead to further brain damage. Hemorrhagic strokes are divided into 2 main categories, including the following:
Intracerebral hemorrhage. Bleeding is from the blood vessels within the brain.
Subarachnoid hemorrhage. Bleeding is in the subarachnoid space (the space between the brain and the membranes that cover the brain).
Intracerebral hemorrhage is usually caused by high blood pressure. Bleeding occurs suddenly and rapidly. There are usually no warning signs and bleeding can be severe enough to cause coma or death.
Subarachnoid hemorrhage results when bleeding occurs between the brain and the membrane that covers the brain (meninges) in the subarachnoid space. This type of hemorrhage is often due to an aneurysm or an arteriovenous malformation (AVM). It can also be caused by trauma.
An aneurysm is a weakened, ballooned area on an artery wall and has a risk for rupturing. Aneurysms may be congenital (present at birth), or may develop later in life due to such factors as high blood pressure or atherosclerosis.
An AVM is a congenital disorder that consists of a disorderly tangled web of arteries and veins. The cause of AVM is unknown, but it is sometimes genetic or part of certain syndromes.
Recurrent strokes occur in about 1 in 4 people who have had a stroke within 5 years after a first stroke. The risk is greatest right after a stroke and decreases over time. The likelihood of severe disability and death increases with each recurrent stroke. About 3% of people who have had a stroke have a second stroke within 30 days of their first stroke, and about one-third have a second stroke within 2 years.
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