Contrast-Enhanced Magnetic Resonance Angiography of the Carotid Arteries: Utility in Routine Clinical Practice
Background: Contrast-enhanced magnetic resonance angiography (CEMRA) is a new technique that is being used with increasing frequency for the evaluation of carotid disease in endarterectomy (CEA) candidates. However, evidence supporting the clinical utility of this test is lacking. Methods: We reviewed the results of CEMRA in comparison to catheter angiography (ANGIO) in a consecutive series of 50 patients being evaluated for CEA who had both tests. Using a prespecified protocol and indications for CEA based on published recommendations, the rate of misclassification for surgery, sensitivity, specificity, positive and negative predictive values (PPV, NPV) were measured. Results: When compared to ANGIO, 24% (95%CI:12,36) of patients would have been misclassified for CEA based on CEMRA alone. The reasons for misclassification were overestimation of the degree of stenosis in 18% and underestimation in 4%. CEMRA failed to detect a complete carotid occlusion on one case. CEMRA correctly classified all patients with high-grade stenosis (defined as >70% in symptomatic patients and >80% in asymptomatic patients). CEMRA had a sensitivity of 92%, specificty of 62%, PPV of 78% and NPV of 89%. Duplex ultrasound (DUS) was performed in 72% of the patients and the results of all three tests were concordant in 67%. The misclassification rate for CEA in comparison to ANGIO for cases in which CEMRA and DUS were concordant decreased to 17% (95%CI: 2,32) with corresponding increases in the sensitivity (100%) and NPV (100%) but a similar a specificity (60%) and PPV (78%). Conclusion: This study provides the first formal analysis of the performance of CEMRA in comparison to ANGIO in selecting patients for CEA. Clinicians should be cautious when using CEMRA for decisions regarding CEA as a significant number of patients may be misclassified if this test is used alone. The rate of misclassification is reduced when the results of DUS and CEMRA are concordant.