An ischemic stroke is caused by a blood clot that blocks blood flow to the brain. A blood clot can develop in a narrowed artery that supplies the brain or can travel from the heart (or elsewhere in the body) to an artery that supplies the brain.

Blood clots are usually the result of other problems in the body that affect the normal flow of blood, such as:

Hardening of the arteries (atherosclerosis). This is caused by high blood pressure , diabetes, high cholesterol, and smoking.
Atrial fibrillation or other irregular heart rhythms.
Certain heart valve problems, including having an artificial heart valve, a repaired heart valve, heart valve disease such as mitral valve prolapse, or narrowing (stenosis) of a heart valve.
Infection of the heart valves (endocarditis).
A patent foramen ovale, which is a congenital heart defect.
Blood-clotting disorders.
Inflammation of blood vessels (vasculitis).
Heart attack.
Heart failure.

Low blood pressure (hypotension) may also cause an ischemic stroke, although less commonly. Low blood pressure results in reduced blood flow to the brain and may develop as a result of narrowed or diseased arteries, a heart attack, a large loss of blood, or a severe infection.

Some surgeries (such as endarterectomy) or other procedures (such as angioplasty) that are used to treat narrowed carotid arteries may cause a blood clot to break loose, resulting in a stroke.

Causes of hemorrhagic stroke

A hemorrhagic stroke is caused by bleeding inside the brain (called intracerebral hemorrhage) or bleeding in the space around the brain (called subarachnoid hemorrhage). Bleeding inside the brain may be a result of long-standing high blood pressure. Bleeding in the space around the brain may be caused by a ruptured aneurysm or uncontrolled high blood pressure.

Other causes of hemorrhagic stroke are less common but include:

Inflammation in the blood vessels, which may develop from conditions such as syphilis, Lyme disease, vasculitis, or tuberculosis.
Blood-clotting disorders, such as hemophilia.
Head or neck injuries that result in damage to blood vessels in the head or neck.
Radiation treatment for cancer in the neck or brain.
Cerebral amyloid angiopathy (a degenerative blood vessel disorder).

WebMD Medical Reference from Healthwise

Last Updated: March 06, 2007

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