Background: Atherosclerotic disease of the aortic arch has been suspected to be a potential source of cerebral emboli. We conducted a study to quantify the risk of ischemic stroke associated with atherosclerotic disease of the aortic arch. Methods: Using transesophageal echocardiography, we performed a prospective case-control study of the frequency and thickness of atherosclerotic plaques in the ascending aorta and proximal arch in 250 consecutive patients admitted to the hospital with ischemic stroke and 250 consecutive controls, all over the age of 60 years. Results: Atherosclerotic plaques ≥ 4 mm in thickness were found in 14.4 percent of the patients but in only 2 percent of the controls. After adjustment for atherosclerotic risk factors, the odds ratio for ischemic stroke among patients with such plaques was 9.1 (95 percent confidence interval, 3.3 to 25.2; P<0.001). Among the 78 patients who had brain infarcts with no obvious cause, 28.2 percent had plaques ≥ 4 mm in thickness, as compared with 8.1 percent of the 172 patients who had infarcts whose possible or likely causes were known (odds ratio, 4.7; 95 percent confidence interval, 2.2 to 10.1; P<0.001). Plaques of ≥ 4 mm in the aortic arch were not associated with the presence of atrial fibrillation or stenosis of the extracranial internal carotid artery. In contrast, plaques that were 1 to 3.9 mm thick were frequently associated with carotid stenosis of ≥ 70 percent. Conclusions: These results indicate a strong, independent association between atherosclerotic disease of the aortic arch and the risk of ischemic stroke. The association was particularly strong with thick plaques. Atherosclerotic disease of the aortic arch should be regarded as a risk factor for ischemic stroke and as a possible source of cerebral emboli., Until recently, atherosclerotic disease of the aortic arch was not regarded as a source of cerebral emboli1. We have reported on the basis of autopsy studies that the presence of ulcerated plaques in the aorta is an independent risk factor for ischemic stroke, particularly in patients with strokes of unknown cause, and that ulcerated plaques are predominantly found in patients who are 60 years of age or older2. The advent of transesophageal echocardiography has made it possible to detect protruding atherosclerotic plaques in the aortic arch and descending aorta3,4. Although a causal link between pedunculated and… © 1994, Massachusetts Medical Society. All rights reserved.