Histologic characterization of mobile and nonmobile carotid plaques detected with ultrasound imaging

Objectives: Although mobile plaques in the carotid arteries detected by duplex ultrasound imaging are considered to cause unstable neurologic symptoms such as crescendo transient ischemic attack or progressive stroke, the histology of mobile plaques has not been sufficiently documented. This study examined the histopathologic features of mobile plaques of the carotid artery and compared the histopathology between mobile and nonmobile plaques. Methods: Of 228 carotid plaques assessed by preoperative carotid ultrasound imaging, 21 (9.3%) were diagnosed as mobile symptomatic plaques. Of these, 18 were intact after excision by endarterectomy and enrolled for histologic examination. From the remaining 207 nonmobile plaque specimens, 17 nonmobile but symptomatic plaque specimens were extracted for histologic comparison. An investigator blinded to the ultrasound findings assessed both plaque specimens for fibrous cap thickness, fibrous cap rupture, fibrous cap area, necrotic core size, inflammatory cells, intraplaque hemorrhage, and mural thrombus. Clinical data, including progressive ischemic symptoms after admission, were also examined. Results: Progressive ischemic symptoms were more frequently seen in patients with mobile plaques than in those with nonmobile plaques (33.3% vs 0%, P = .02). The ratio of the cross-sectional area of the necrotic core to that of the entire plaque was significantly larger for mobile plaques than for nonmobile plaques (mean, 0.660 vs 0.417, P < .0001). Mural thrombus was more prevalent among mobile plaques (89%) than among nonmobile plaques (59%), but the difference was not significant (P = .06). The median minimum thickness of the fibrous cap was extremely small in both groups (80 mu m in mobile plaques and 100 mu m in nonmobile plaques, P = .33). Conclusions: The histologic characteristics of mobile carotid plaques are different from those of nonmobile symptomatic plaques, especially in the area of the necrotic core. This histologic difference may partly explain the unstable neurologic presentations of patients with mobile carotid plaques. (J Vasc Surg 2011;53:977-83.)