Composition of the Stable Carotid Plaque: Insights From a Multidetector Computed Tomography Study of Plaque Volume

Background and Purpose— Calcification has been associated with carotid plaque stability; however, an acceptable in vivo method to define plaques based on this component remains to be developed. The purpose of our study was to compare calcified and noncalcified volumes of carotid artery culprit symptomatic plaques with asymptomatic plaques using multidetector computed tomography. Methods— We identified 102 patients with ≥50% stenosis using NASCET criteria by multidetector computed tomography angiography between January 2004 and May 2006, which included 35 symptomatic (stenosis: 82.0±11.9%) and 67 asymptomatic patients (stenosis: 79.4±10.8%). Total plaque volume, noncalcified plaque volume, calcified plaque volume, and calcified/total ratio were measured for the 102 index plaques causing stenosis. Results— In a model including age, stenosis, and cardiovascular risk factors, calcified plaque volume/total plaque volume was significantly inversely associated with the occurrence of symptoms (P=0.012; odds ratio, 0.047; 95% CI, 0.004 to 0.511). There was a notable overlap in the calcified plaque volume/total plaque volume ratio between 0% and 45% for symptomatic and asymptomatic plaques. However, calcification >45% of the total plaque was very specific: 97.1% (34/35) for absence of symptoms (sensitivity: 28.4% 19/67). No significant association between total plaque volume, noncalcified plaque volume, or calcified plaque volume and symptomatology was found. Conclusion— The proportion of carotid plaque calcification, rather than absolute volume, is associated with stability in patients with stenosis. Specifically, for a subset of patients, plaque calcification >45% of the total volume may represent a clinically useful cutoff. The carotid plaque calcium ratio, determined by multidetector computed tomography volume measurements, may help noninvasively risk stratify patients with asymptomatic stenosis.