Finally, there is the problem of the asymptomatic bruit over a carotid artery or incidentally discovered carotid artery stenosis when ultrasound or another diagnostic procedure is performed. A bruit generally corresponds to the reduction in luminal diameter of the artery to 2 mm or less and, while found in a large proportion of patients with severe stenosis, it is not specific and is heard in up to 10 percent of older patients who have little or no stenosis. The population studies by Heyman and associates over 40 years ago shed some light on this. They found, not surprisingly, that cervical bruits in men constituted a risk for death from ischemic heart disease, and that the presence of asymptomatic bruits in men (but not in women) carried a slightly increased risk of stroke. Notably, the subsequent stroke often did not usually coincide in its angioanatomic locus and laterality with the cervical bruit so that asymptomatic stenosis is in the short term a general marker for atherosclerosis more so than for a proximate stroke. Other investigators have reported similar findings. On the other hand, Wiebers and colleagues (1990) found that patients with asymptomatic carotid bruits who were followed for 5 years were approximately three times more likely to have ischemic strokes than an ageand sex-matched population sample without carotid bruits. All of these cohorts were studied prior to the epoch of aggressive risk factor reduction, particularly with statin drugs.
The appropriate step when a carotid bruit is found during a routine examination is probably to obtain ultrasonography in order to quantify the presence of and degree of stenosis and to make subsequent decisions cautiously based on the studies discussed below. We usually also obtain imaging of the brain to determine if there has been a stroke on the side of the carotid disease—this aids in decisions regarding therapy.
A note is made here regarding the self-audible bruit, which occasionally indicates carotid stenosis, dissection, or fibromuscular dysplasia, but is usually of less consequence and in some instances is associated with an enlarged and superiorly located jugular bulb—a benign anatomic variant that can be discerned on CT (Adler and Ropper).
Many attempts have been made to clarify the role of correcting asymptomatic carotid stenosis by means of endarterectomy. The Asymptomatic Carotid Atherosclerotic Study (ACAS) found that the frequency of strokes could be reduced from 11 to 5 percent over 5 years by removing the plaque if there was a stenosis greater than 60 percent (in diameter). These conclusions have been tempered by a reanalysis of the ACAS data, in which almost half of the strokes were of lacunar or cardioembolic (Inzitari et al). Data from a European trial, encompassing 3,120 patients (MRC Asymptomatic Carotid Surgery Trial [ACST] Collaborative Group), have indicated that asymptomatic carotid stenosis of more than 70 percent carries a 2 percent annual risk of stroke over a 5-year period and that the risk is reduced to 1 percent with endarterectomy. It was concluded that endarterectomy may be justified for asymptomatic carotid stenosis of this degree in men (not so in women) but that an audited surgical risk below 3 percent was required to obtain favorable results (just as for symptomatic carotid stenosis). However, all of these trials were conducted before the ubiquitous use of statin drugs, which seemingly stabilize carotid plaques. Several trials comparing endarterectomy to stenting, some of which were commented on earlier, included asymptomatic patients but there were too few on which to base conclusions and, as for symptomatic cases, they were performed before the epoch of aggressive risk factor management. In a trial involving asymptomatic patients with severe carotid stenosis (mean stenosis by diameter of 74 percent) who were not at high risk for surgical complications, comparing endarterectomy to stenting with a device that captured embolic material, 5-year stroke rates were approximately 7 percent in both groups ACTI, reported by Rosenfield et al).