Duplex ultrasound may lead to misclassification of carotid artery stenosis

Carotid duplex ultrasonography (CDUS) is often the first-line imaging modality for clinical evaluation of carotid disease. Despite improved equipment and standardization of vascular imaging protocols, CDUS can be technician-dependent and unreliable in calcified blood vessels. The aim of this study was to assess variability in carotid stenosis severity measured using CDUS compared with reference high-resolution magnetic resonance imaging (MRI).

In this prospective cohort study designed to study long-term brain health outcomes, we enrolled 123 participants with a diagnosis of asymptomatic carotid disease and/or ≥2 cardiovascular risk factors between the ages of 50 to 85 years from vascular and cardiology clinics in Tucson, Arizona, for the ongoing Carotids and Minds (CAM) study. Using a specialized radiofrequency coil for carotid imaging, high-resolution time-of-flight (0.63 × 0.63 × 1.0 mm³) and T1-weighted (in plane resolution = 0.63 × 0.63 mm²; slice thickness = 2.0 mm) MRIs were acquired to evaluate carotid stenosis severity. A neuroradiologist, vascular surgeon, and MRI specialist utilized cross-sectional measurements of carotid images to adjudicate stenosis percentage based on NASCET criteria. Agreement between percent carotid stenosis categories (<50%, 50%-69%, 70%-99%, 100%) derived from MRI and clinical CDUS was assessed using Cohen's Kappa with linear weights (κ_w). Sensitivity and specificity were calculated to evaluate how well CDUS identifies clinically significant stenosis defined by MRI.

A total of 246 carotid arteries were evaluated for percent stenosis using both MRI and clinical CDUS imaging. Twenty-five percent of the carotid arteries with severe (70%-99%) stenosis based on MRI were misclassified as having mild (<50%) or moderate (50%-69%) stenosis based on CDUS. Conversely, 33% of arteries with mild disease were overestimated by CDUS into higher stenosis categories. For detecting ≥70% carotid stenosis, clinical CDUS had a sensitivity of 0.77 (95% confidence interval, 0.67-0.87) and specificity of 0.92 (95% confidence interval, 0.88- 0.96), indicating a false negative rate of 23%.

CDUS provides a rapid, noninvasive assessment of carotid disease in clinical settings, yet in this cohort, it misclassified carotid stenosis severity (both over and under) 32% of the time. Thus, reliance on CDUS alone could lead to inappropriate treatment decisions. High-resolution MR angiography or computed tomography angiography should be considered for more accurate stratification of disease severity in patients with asymptomatic carotid disease.