Identification of carotid 'vulnerable plaque' by contrast-enhanced ultrasonography: correlation with plaque histology, symptoms and cerebral computed tomography.

Abstract

Indication to carotid revascularisation is commonly determined by percent of stenosis as well as neurological symptoms and clinical conditions. High plaque embolic potential is defined as 'vulnerability'; however, its characterisation is not universally used for carotid revascularisation. We investigated the role of contrast-enhanced ultrasonography (CEUS) to identify carotid vulnerable plaque. Patients undergoing carotid endarterectomy were preoperatively evaluated by cerebral computed tomography (CT) scan and CEUS. Contrast microbubbles detected within the plaque indicated neovascularisation and were quantified by decibel enhancement (dB-E). Plaques were histologically evaluated for five features: (microvessel density, fibrous cap thickness, extension of calcification, inflammatory infiltrate and lipid core) and blindly scored 1-5 to assess plaque vulnerability. Analysis of variance (ANOVA), Fisher's and Student's t-test were used to correlate patients' characteristics, histological features and dB-E. In 22 patients, dB-E (range 2-7.8, mean 4.85 ± 1.9 SD) was significantly greater in symptomatic (7.40 ± 0.5) vs. asymptomatic (3.5 ± 1.4) patients (p = 0.002). A higher dB-E was significantly associated with thinner fibrous cap (<200 μm, 5.96 ± 1.5 vs. 3 ± 1, p = 0.01) and greater inflammatory infiltrate (3.2 ± 0.9 vs. 6.4 ± 1.2, p = 0.03). Plaques with vulnerability score of 5 had significantly higher dB-E compared with those with vulnerability score of 1 (7.6 ± 0.2 vs. 2.5 ± 0.6, respectively, p = 0.001). Preoperative ipsilateral embolic lesions at CT were correlated with higher dB-E (5.96 ± 1.5 vs. 3.0 ± 1.0, p = 0.01). CEUS with dB-E is indicative of the extent of plaque neovascularisation. It can be used therefore as a marker for vulnerable plaque.