Predictors of surface disruption with MR imaging in asymptomatic carotid artery stenosis

Abstract

Background and purpose: Surface disruption, either ulceration or fibrous cap rupture, has been identified as a key feature of the unstable atherosclerotic plaque. In this prospective observational study, we sought to determine the characteristics of the carotid lesion that predict the development of new surface disruption.

Materials and methods: One hundred eight asymptomatic individuals with 50%-79% carotid stenosis underwent carotid MR imaging at baseline and at 3 years. Multicontrast imaging criteria were used to determine the presence or absence of calcification, LRNC, intraplaque hemorrhage, and surface disruption. Volume measurements of plaque morphology and the LRNC and calcification, when present, were collected.

Results: At baseline, 21.3% (23/108) of participants were identified with a surface disruption. After 3 years, 9 (10.6%) of the remaining 85 individuals without disruption at baseline developed a new surface disruption during follow-up. Among all baseline variables associated with new surface disruption during regression analysis, the proportion of wall volume occupied by the LRNC (percentage LRNC volume; OR per 5% increase, 2.6; 95% CI, 1.5-4.6) was the strongest classifier (AUC = 0.95) during ROC analysis. New surface disruption was associated with a significant increase in percentage LRNC volume (1.7 +/- 2.0% per year, P = .035).

Conclusions: This prospective investigation of asymptomatic individuals with 50%-79% stenosis provides compelling evidence that LRNC size may govern the risk of future surface disruption. Identification of carotid plaques in danger of developing new surface disruption may prove clinically valuable for preventing the transition from stable to unstable atherosclerotic disease.

Fig 1.

Multicontrast images from the baseline examination of a 68-year-old man. The axial images are consecutive sections of the right internal carotid artery beginning at the flow divider (column A). There are substantial flow artifacts due to the proximity of the bifurcation. In column D, 2 separate lumens are developing in the internal carotid artery as indicated by 2 levels of intensity on TOF and a band of tissue (arrowheads) separating the true lumen from a penetrating ulcer (arrow). The ulceration extends into the adjacent more distal section (column E). There is no evidence of an LRNC in this artery. Asterisk indicates the lumen of the external carotid artery.

Fig 2.

Multicontrast images from the right carotid artery of a 78-year-old man. Baseline images (top panel) demonstrate the presence of a relatively small lesion and minimal lumen narrowing, but a large portion of the arterial wall is occupied by the LRNC. There is an identifiable band of tissue separating the LRNC (white arrowheads, hypointense signal intensity on T2) from the lumen on T2, which is consistent with the presence of a thick fibrous cap. At 3 years (bottom panel), there is an identifiable surface disruption (white arrow) on both axial images and the longitudinal scout image. The dashed line on the longitudinal image represents the imaging location of the axial image in column B. IPH is not present at baseline or at follow-up, but there is visual evidence of an increase in plaque burden and a reduction in lumen area, particularly in column D. The asterisk indicates the lumen of either the common carotid artery or the internal carotid artery; the black arrowhead, calcification.

Fig 3.

Plots from ROC analysis for development of a new surface disruption.