Symposium on Cerebrovascular Diseases
Evaluation and Management of Asymptomatic Carotid Artery Stenosis

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Internal carotid artery stenosis (ICAS) is responsible for approximately 30% of ischemic strokes. Internal carotid artery stenosis of greater than 50% is present in about 4% to 8% of the population aged 50 to 79 years. Natural history studies and clinical trials have shown a small increase in stroke risk in patients with increasing degrees of ICAS, especially in those with greater than 80% reduction in carotid artery diameter. Randomized, prospective multicenter trials have revealed the superiority of carotid endarterectomy (CEA) over medical therapy in recently symptomatic patients with severe ICAS. However, the evidence from several randomized controlled trials of CEA in asymptomatic patients does not support the use of CEA in most of these patients; also, the role of noninvasive screening in this patient population remains uncertain and controversial. Furthermore, there is considerable uncertainty about whether the statistical benefit of avoiding a nondisabling stroke is worth the overall cost and risk of the procedure. Clinicians continue to struggle with treatment decisions for patients with asymptomatic ICAS. Carotid endarterectomy for asymptomatic ICAS should be considered only for medically stable patients with 80% or greater stenosis who are expected to live at least 5 years, and only in centers with surgeons who have a demonstrated low (<3%) perioperative complication rate. We outline the prevalence and natural history of ICAS, the evidence for CEA in patients with asymptomatic ICAS, the roles of screening and monitoring for ICAS, the methods of evaluating ICAS, and the implications for practicing clinicians.

Section snippets

NATURAL HISTORY

Clearly, the baseline risk of stroke in patients with asymptomatic ICAS is one of the most important factors to consider when interpreting the relative reduction and absolute reduction in stroke risk for any intervention. It is especially important when helping patients decide whether to undergo CEA for asymptomatic ICAS. Most short-term (2-3 years) natural history studies of asymptomatic ICAS have reported an annual risk of unheralded ipsilateral stroke of approximately 1% to 3%, depending on

EVIDENCE FOR CEA FOR ASYMPTOMATIC ICAS

Carotid endarterectomy was evaluated in 6 prospective, randomized, controlled clinical trials.4, 5, 6, 7, 24, 27 One study involved 57 asymptomatic patients with cervical bruits and abnormal findings on ocular pneumoplethysmography, 29 of whom were randomized to aspirin or CEA.27 More unfavorable outcomes were noted in those patients who underwent CEA, and the investigators concluded that most asymptomatic patients with cervical bruits and abnormal findings on ocular pneumoplethysmography are

SCREENING AND MONITORING FOR ASYMPTOMATIC ICAS

Publication of the ACAS in 1995 was followed by a large increase in the number of CEAs performed in the United States.42 Since then, guidelines and position papers have recommended clinical implementation of this prophylactic surgery.14,43, 44, 45, 46 The patients discussed are, by definition, neurologically asymptomatic; therefore, patients can be identified only through some form of case-finding or screening strategy. When screening tests are applied to large unselected populations, the

EVALUATION OF ICAS

Digital subtraction angiography (DSA) was used to assess the degree of stenosis in the early endarterectomy trials and thus became the gold standard for selecting patients for CEA. In the most recent ACST, sonographic assessment was used. When compared with MRA and CTA, DSA has a comparatively small risk of morbidity: the risk of permanent neurologic deficit ranges from 0.7% to 1.2%.7, 65 Even patients with no apparent neurologic complications after DSA have developed minor asymptomatic

IMPLICATIONS FOR CLINICIANS

According to the evidence, CEA in asymptomatic patients with moderate to severe ICAS reduces the odds of stroke by about 30% over a 3-year period. However, although this relative risk reduction appears impressive, the absolute benefit is extremely small because the risk of stroke without surgery for asymptomatic stenosis is low. In addition, the clinician and patient must consider the fact that the risk of treatment (surgical stroke) is present for several weeks, whereas the benefit accrues

CONCLUSIONS

Internal carotid artery stenosis of greater than 50% is present in approximately 4% to 8% of the population aged 50 to 79 years. Natural history studies and clinical trials reveal a small increase in stroke risk in patients with increasing degrees of stenosis, especially in those with greater than 80% diameter reduction. Paradoxically, this correlation between stroke risk and degree of stenosis has not been demonstrated in the asymptomatic CEA trials. The evidence does not appear to support the

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