There are two major types of strokes: ischemic stroke and hemorrhagic stroke, and variations within both. A third type of stroke, called a transient ischemic attack, or TIA, is a minor stroke that serves as a warning sign that a more severe stroke may occur.

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Strokes: The Ischemic Stroke

Ischemic strokes are the most common, making up about 83 percent of all strokes. An ischemic stroke occurs when a blood vessel becomes blocked, usually by a blood clot. Clots can form when blood vessels become clogged with fat and cholesterol, a condition known as atherosclerosis. In an ischemic stroke, blood can’t reach the brain, and brain cells suffer from the lack of nutrients and oxygen that they would normally get.

There are actually two different types of ischemic stroke, depending on where the clots form. Clots that form inside a blocked blood vessel in the brain cause a thrombotic stroke. Embolic strokes result from clots that form elsewhere in the body and travel toward the brain until they become lodged in a narrow artery, causing a blockage.

Ischemic stroke may also be caused by a deformity in the valves of the heart or as a result of a condition called endocarditis, in which the lining inside the heart becomes inflamed. Clots can form on these abnormal surfaces and later travel to and lodge in a small artery in the brain.

Strokes: The Hemorrhagic Stroke

A hemorrhagic stroke occurs when a blood vessel in the brain bursts or breaks, causing bleeding in the brain.

Hemorrhagic stroke can most often be traced to high blood pressure, but it may also be caused by an aneurysm. This is when a weakened portion of a blood vessel balloons out, ruptures, and causes bleeding in the brain.

Another possible cause is an arteriovenous malformation, or AVM, a group of malformed blood vessels that can rupture, again resulting in bleeding in the brain.

The buildup of the protein amyloid inside the arteries is also a common cause of hemorrhagic stroke, especially in older individuals.

Strokes: A Word About TIAs

A transient ischemic attack (TIA) is a so-called pre-stroke, or a warning sign of an impending serious stroke that could cause damage. A TIA is minor, generally does no damage, and is usually caused by a blood clot. A TIA does produce temporary stroke symptoms that then subside. But a TIA means you should get checked out immediately by your doctor or in a hospital emergency department, and start making changes to prevent a more serious stroke.

Stroke: Understanding the Similarities

Although the two types of stroke occur differently, the risk factors and outcomes are often the same.

People who are at greater risk for developing blood clots, including women who take birth control pills, are over age 35, and smoke, are at a greater risk of ischemic stroke.

And some health habits and conditions that increase the risk of bleeding in the brain — including drinking too much alcohol or abusing drugs, having a bleeding condition (such as hemophilia or thrombocytopenia) or suffering a head injury — may up your risk of having a hemorrhagic stroke.

And keep in mind that smoking, obesity, and poor diet, along with health conditions such as heart disease, diabetes, high blood pressure, and high cholesterol, all contribute to your overall stroke risk.

No matter how the damage to the brain occurs when a person has a stroke, without quick and proper treatment the outcome may be the same. Understanding how strokes occur and how they can be prevented are important for everyone, but especially for those who are at increased risk. The more you know about stroke, the more you can keep yourself from having a stroke.