Magnetic resonance cholangiopancreatography versus endoscopic retrograde cholangiopancreatography in the diagnosis of choledocholithiasis

Objective Endoscopic retrograde cholangiopancreatography (ERCP) has become established as the gold standard in imaging of the biliary tree. Recently, magnetic resonance cholangiopancreatography (MRCP) has been introduced as a new, non-invasive imaging modality for the detection of bile-duct stones and other pathology related to the biliary tract and pancreas. The aim of this study was to determine how MRCP compared with ERCP in the diagnosis of choledocholithiasis. Design and methods A prospective study of 133 patients referred for either ERCP or MRCP was carried out to compare the results of both these methods in determining the presence of choledocholithiasis. Results 18 patients were excluded from the analysis: ERCP was unsuccessful in eight of these patients and MRCP was not possible in the remaining 10 patients. There were six false negative results with MRCP; in five of these the calculi were less than 5 mm in diameter. MRCP showed a sensitivity of 84%, specificity of 96%, positive predictive value of 91%, negative predictive value of 93% and diagnostic accuracy of 92% when compared to ERCP as the gold standard. Conclusions MRCP has high sensitivity and high specificity for stones greater than 5 mm in diameter and should be performed in preference to ERCP as the first-line investigation in patients with gallstones and abnormal liver function tests in the elective setting. Adoption of this guideline at our institution would result in a 9% reduction in the number of ERCPs performed.