Contrast-enhanced subtraction CT accurately and reproducibly assesses fibrous cap status associated with symptomatic carotid stenosis

BACKGROUND: The fibrous cap (FC) status is a crucial determinant of plaque vulnerability in symptomatic carotid stenosis. While MR angiography is used to assess the FC status, its clinical utility is limited by low reproducibility. This study aimed to assess the diagnostic accuracy and reproducibility of contrast-enhanced subtraction CT (CES-CT) for detecting FC and to evaluate its association with symptomatic carotid stenosis. METHODS: We retrospectively analyzed 49 patients (21 symptomatic, 28 asymptomatic) who underwent CES-CT before carotid revascularization. CES-CT images were generated by subtracting arterial-phase images from delayed-phase images to suppress intraluminal contrast signals. The FC status was classified as thick or thin/ruptured based on imaging and histological findings. Symptomatic patients had amaurosis fugax, transient ischemic attack, or stroke in the vascular territory of the ipsilateral carotid artery within the past 6 months. RESULTS: CES-CT showed excellent diagnostic performance with an area under the curve of 0.82, a specificity of 98%, and almost perfect intra- and inter-observer agreements (κ=0.80 and κ=0.85, respectively). A thin/ruptured FC on CES-CT was more frequent in the symptomatic group than in the asymptomatic group (67% vs 14%, P<0.001). A multivariable analysis showed that a CES-CT-based thin/ruptured FC was independently associated with symptomatic carotid stenosis (RR 2.63, 95% CI 1.27 to 5.56; P=0.009). CONCLUSIONS: CES-CT had excellent diagnostic accuracy and reproducibility for FC assessment. Moreover, a thin/ruptured FC on CES-CT was significantly associated with symptomatic carotid stenosis.