The carotid (pronounced ka-RAH-ted) arteries in the neck are the main supply route for blood to get to the brain. But atherosclerotic plaque can gum them up, just as it does the coronary arteries that provision the heart. If that plaque ruptures, blood clots can form that block the carotids or other, smaller arteries, resulting in an ischemic stroke.
Narrowed carotid arteries can be identified with an ultrasound before a stroke occurs. The examinations are noninvasive and inexpensive. Some hospitals are charging the public as little as $45 for an ultrasound of their carotid arteries.
Yet for several good reasons, the U.S. Preventive Services Task Force discourages routine screening of the carotid arteries. First, only about 1% of the general population has significant narrowing, or stenosis, of the carotids, although the percentage does increase with age. Second, less than 10% of first-time ischemic strokes are associated with carotid stenosis, so stroke prevention efforts based on ultrasound screening can only go so far. Third, roughly eight in every 100 ultrasounds produce a false positive — a result that indicates the presence of significant stenosis that isn’t really there. False positives result in unnecessary tests and possibly unnecessary treatment.
The plaque in a carotid artery can be surgically removed, and carotid endarterectomy, as the procedure is called, does lower stroke risk in some groups. But the procedure itself causes some strokes and heart attacks, so some harm done has to be factored in as well. Based on various assumptions, the task force calculated that if 100,000 people were screened for carotid artery stenosis with ultrasound, 23 strokes would be prevented over a five-year period, but 10 nonfatal heart attacks would be caused.