Diagnostic Accuracy of EUS versus MRCP for Extrahepatic Biliary Tract Disorders: A Prospective Observational Study

Introduction: Accurate diagnosis of Extrahepatic Biliary Tract Disorders (EHBTDs) is essential for guiding appropriate management. Magnetic Resonance Cholangiopancreatography (MRCP) is a widely used non-invasive modality but may miss small calculi or early lesions. Endoscopic Ultrasound (EUS), with its superior spatial resolution and ability for tissue sampling, may provide enhanced diagnostic yield. Aim: To compare MRCP and EUS in EHBTDs, with special focus on obscure Common Bile Duct (CBD) dilatation. Materials and Methods: The present prospective observational study was carried in the Department of General Surgery at Dr DY Patil Medical College, Hospital and Research Centre, Pimpri, Pune, Maharashtra, India, from January 2024 to March 2025. It included 100 adults with suspected EHBTDs who underwent MRCP followed by EUS within one week. Final diagnoses were confirmed using Endoscopic Retrograde Cholangiopancreatography (ERCP), operative findings, histopathology, and structured follow-up. Diagnostic performance was assessed by sensitivity, specificity, predictive values, and area under the ROC curve (AUC). Subgroup analysis was performed for obscure CBD dilatation (n=9). Results: The EUS consistently outperformed MRCP across diagnostic categories. For choledocholithiasis, EUS achieved sensitivity and specificity of 97.2% and 95.4% (AUC 0.96), compared with 91.8% and 90.1% for MRCP (AUC 0.91). In benign biliary strictures, EUS reached 98.3% sensitivity and 96.2% specificity, surpassing MRCP (91.7% and 89.6%). For neoplastic lesions, EUS showed sensitivity of 96.8% and specificity of 95.0%, slightly higher than MRCP (95.0% each). The most striking difference was observed in obscure CBD dilatation: MRCP failed to reveal any aetiology, whereas EUS correctly identified the underlying pathology in six of nine patients. The remaining three cases required ERCP for definitive confirmation. Conclusion: These results reinforce the higher diagnostic accuracy of EUS in EHBTDs and emphasise its role when MRCP is inconclusive. In obscure CBD dilatation, EUS not only clarified the diagnosis in most patients but also reduced unnecessary reliance on diagnostic ERCP.