Diagnosing Stroke

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Harvard Medical School
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Diagnosing Stroke

Diagnosing Stroke
Diagnosing Stroke
Diagnosing Stroke
Physicians have numerous diagnostic techniques and imaging tools to help pinpoint the location and cause of stroke quickly and accurately.
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Reviewed by the Faculty of Harvard Medical School

Diagnosing Stroke

For some strokes, every minute that passes without therapy may mean a worse outcome. So, the first priority in evaluating a stroke is to determine whether the person should be treated with a clot-buster, an anticoagulant and/or an anti-platelet drug such as aspirin. The next priority is to understand what caused the stroke so measures can be taken to limit the chance of a second stroke.

Imaging Tests

To diagnose your stroke — and classify the type of stroke — your doctor needs an image of your brain. The most widely used image comes from the computed tomography scan (CT scan). A CT (or cat) scan is usually the quickest way to determine if the stroke is caused by bleeding in the brain vs. a clot that has cut off blood flow to part of the brain.

A CT scan will not show dramatic changes in the first few hours after a stroke caused by a blood-vessel blockage (ischemic stroke). If a ruptured blood vessel (hemorrhagic stroke) caused the stroke, however, a CT scan will show bleeding into or around the brain.

If bleeding has occurred, your doctor will not prescribe any drugs that "thin" the blood because this can increase your bleeding and make your symptoms worse. "Blood-thinning" medicines to avoid include heparin, warfarin and thrombolytic (clot-dissolving) therapy such as tissue plasminogen activator (t-PA). (All these medicines are helpful for strokes that do not have bleeding.)

Another imaging tool is the magnetic resonance imaging scan. MRI uses magnetic fields to detect subtle changes in brain tissue. One effect of a stroke is an increase in water in the cells of the brain, a condition called edema. MRI can detect edema as soon as 30 minutes after a stroke begins. Certain types of MRI scans, such as an MRI angiogram, can highlight blood flow in the brain.

Cardiac Tests

When a blood clot forms inside the heart, breaks loose and travels through the bloodstream to the brain, it can block the flow of blood and cause a stroke. This type of free-roaming clot is called an embolism. A perfectly healthy heart does not ever form a clot. People with atrial fibrillation, (an irregular heart rhythm) and people with severe heart failure can form a clot in the heart. In these heart conditions, blood can flow so slowly through some areas of the heart that the blood may congeal or clot. People with these heart conditions are at risk for embolic strokes.

An electrocardiogram (ECG or EKG) test shows the electrical performance of the heart. It can detect an irregular heart rhythm, such as atrial fibrillation. The test takes only minutes and is painless. The test measures electrical activity through wires taped to the chest, arms and legs.

If your doctor suspects that you have atrial fibrillation episodes that come and go, a one-time electrocardiogram may not show this irregular heart rhythm. You may need to wear a Holter monitor, a lightweight, portable device that takes a continuous electrocardiogram over days or over several weeks. Short episodes of atrial fibrillation that come and go can lead to a stroke, just like atrial fibrillation that is continuous.

To check for heart failure, you'll need an echocardiogram, which produces an ultrasound picture showing the heart's movement with each beat.

If your doctor finds a heart problem that can lead to a stroke, treatment with "blood-thinning" medications can help prevent a future stroke.

Rarely, a stroke caused by an embolism can come from a clump of bacteria that formed on the surface of one of the valves of the heart, after bacteria infected the bloodstream. Such a clump of bacteria can fragment, and a fragment can drift to the brain. For more information, see endocarditis.

Tests of the Arteries

Blood clots can form inside large arteries just outside of the brain, if the wall of the artery is not smooth. These clots typically form near a cholesterol plaque, because the cholesterol causes an irregularity in the lining of one of your arteries. A clot that forms in an artery leading towards the brain can break away from the damaged artery wall and float into the brain where it will block the flow of blood, causing an embolic stroke. The arteries that lead to the brain and commonly collect cholesterol plaques include the carotid arteries in front of the neck, the vertebral and basilar arteries in the back of the neck, and the aorta. The aorta is the large artery that comes out of the left ventricle of the heart.

Imaging of the carotid arteries can be done using ultrasound or MR angiogram. The carotid ultrasound (also called the duplex, Doppler or ultrasound scan of the neck) uses sound waves to generate a picture of the carotid arteries in the neck. MR angiogram uses magnetic waves and a computer to create the pictures. A special dye is usually given to provide the best images. These painless tests show the doctor if there is narrowing of one or both of the neck arteries. Narrowing of the artery comes from a cholesterol plaque.

Another way to view the arteries is for a doctor to insert a thin, flexible tube, called a catheter, through your skin and into an artery, usually the large artery at the top of your leg. This long catheter can then be maneuvered along the inside of your artery until the tip of the catheter (still inside the artery) is within your neck. A radioactive dye is injected through the catheter. This dye appears as a highlighted area on an X-ray, showing the arteries in your neck and in your brain. This test is called a cerebral angiogram.

If a carotid ultrasound or an angiogram shows a major narrowing of one of the carotid arteries, protection against a future stroke may be improved by a surgery called carotid endarterectomy or a procedure called carotid stenting.

Endarterectomy removes bulky cholesterol plaques from a carotid artery, so that it is less likely that a clot will form in the artery. Carotid stenting does not require surgery. It is similar to angioplasty for blocked coronary arteries. The doctor first opens the carotid narrowing with a balloon covered by a wire-mesh tube (stent). The balloon pushes away the plaque. The balloon is deflated. But the stent stays expanded to hold the carotid artery open.

A cerebral angiogram can show narrowing of arteries in the back of the neck and skull. These arteries, near the spine, are known as the vertebral and basilar arteries. When they contain cholesterol plaque, they can cause an embolic stroke. If vertebral or basilar artery cholesterol deposits lead to a stroke, doctors usually prescribe the long-term and carefully monitored use of aspirin or blood-thinning (anticoagulant) medicine called warfarin (brand name: Coumadin), instead of recommending surgery. Surgery may be needed for people who have another stroke even after they start using blood thinners.

Other Causes of Strokes

The CT scan or MRI scan can sometimes show one or more tiny "lakes" (called lacunes) of fluid, deep within the brain. These small fluid-filled areas form after brain cells are damaged by a type of stroke called a lacunar stroke. High blood pressure is usually the cause of a lacunar stroke. High blood pressure gradually damages small arteries within the brain until the artery closes. Preventing additional lacunar strokes requires controlling high blood pressure.

If no sign of heart disease or artery disease is found, blood tests may check for a disease called antiphospholipid antibody syndrome. In this condition, an increased tendency to form blood clots can lead to a stroke. Treatment with anticoagulant medicines can provide protection.


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Last updated June 03, 2014

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