The carotid arteries: Vital vessels to the brain
An important cause of stroke is the carotid arteries. Arising from the aorta and its branches (see figure 1), the carotid arteries serve as conduits for oxygenated blood to reach the brain. If atherosclerosis occurs in the carotid arteries, small emboli can dislodge and travel to the smaller brain arteries and clog blood flow, thereby resulting in a stroke. Severe narrowing (stenosis) can completely interrupt blood flow to the brain supplied by that artery.
An insidious danger
Narrowing in the carotid arteries generally occurs over many years without producing symptoms. Often, the first indication of a problem is a sudden neurologic event. This can be relatively mild with transient weakness, a vision or speech disturbance, or other motor or sensory abnormality. If the symptoms resolve over a few minutes to hours, the event is called a transient ischemic attack, or TIA. Unfortunately, the initial symptom of carotid disease can also be a devastating stroke, which results in major loss of function, paralysis or even death.
There is a clue to carotid narrowing that can be detected on physical examination. A carotid bruit is a "whooshing" sound, heard with the stethoscope placed over the neck. It is important to note that not everyone with a carotid bruit has significant disease. Similarly, not every patient with major carotid stenosis will have an audible bruit. Another clue to carotid disease may be detected during a funduscopic (eye) examination.
Finding the blockage
In order to detect the presence and extent of disease in the carotid arteries, imaging studies are performed. The most commonly available technique is duplex ultrasound sonography, which uses sound waves to create images of the arteries and measure the severity of stenosis. Other imaging modalities include MRA (magnetic resonance angiography), CTA (computerized tomographic angiography) and catheterization. The gold-standard test is angiography, in which catheters are inserted into the carotid artery and contrast is injected under x-ray guidance to determine the degree of blockage.
Stroke risk related to carotid narrowing and symptoms
The risk of stroke in patients with carotid stenosis is related both to the degree of narrowing and the presence of symptoms. In general, the risk of a stroke rises when the blockage is greater than 80%. If a patient has already suffered a stroke, even a 50% stenosis confers a significant risk of recurrent stroke with medical therapy alone.
Potential treatments to reduce the risk of stroke include medicines to control risk factors for atherosclerosis, blood thinners to prevent clots and mechanical means to restore blood flow (revascularization). Revascularization can either be performed surgically with carotid endarterectomy (CEA), or by insertion of a stent via a catheter.
This article first appeared in the January/February 2007 issue of Heart & Health Reports. For a subscription, call 1-877-HEART-12.
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