Introduction Magnetic resonance cholangiopancreatography (MRCP) is considered the first-line investigation in patients with suspected common bile duct stones after ultrasound scanning (USS). We conducted a study to determine whether MRCP is indeed useful prior to endoscopic retrograde cholangiopancreatography (ERCP) in the management of patients presenting with symptoms of biliary obstruction, abnormal liver function tests (LFTs) and gallstones evident on USS.

Methods We performed a retrospective casenote analysis for patients presenting with classical symptoms, abnormal LFTs and who had undergone each of the following investigations – USS, MRCP and ERCP – between January 2007 and June 2008. Patients were managed as an inpatient or outpatient depending on their clinical state.

Results A total of 43 patients (31 female, mean age 63.2 years, 19 as inpatients) were identified. LFTs were abnormal: median bilirubin 8 (3–246); alkaline phophatase 146 (69–1650); alanine transferase 52 (16–752). In 26 patients (group 1), cholelithiasis without extrahepatic duct (EHD) dilatation was evident on USS. Within this group, a subsequent MRCP confirmed EHD stones in 77% of patients, EHD dilatation without stones in 4% and a clear, non-dilated EHD in 19%. Complete correlation between ERCP and MRCP findings occurred in 81% of patients. Three out of 5 patients with clear, non-dilated EHDs on MRCP had EHD stones at ERCP. 17 of the 43 patients had evidence of cholelithiasis and EHD dilatation without EHD stones (group 2). Subsequent MRCP revealed EHD stones in 71% and only EHD dilatation in 29%. Complete correlation between ERCP and MRCP was evident in 52% of cases. In four cases in which only EHD dilatation was noted on MRCP, ERCP revealed EHD stones. In four patients, ERCP failed to identify EHD stones but the median time interval between MRCP and ERCP was 13 days during which time a stone may have passed. ERCP provided identical and additional information when compared to MRCP in 96% and 76% of cases in groups 1 and 2, respectively. 38 out of 43 (88%) patients required therapeutic intervention at ERCP. No complications arose as a result of ERCP.

Conclusion This observational study demonstrates that ERCP should remain the first-line imaging modality for the investigation and management of suspected EHD stones in the appropriate clinical setting. There is a strong correlation between ERCP and MRCP findings in patients with cholelithiasis, and in particular the cohort without EHD dilatation or stones. MRCP gave false reassurance that the duct was clear in 7 (16%) cases. In addition to therapeutic benefit, the sole use of ERCP will reduce cost by avoiding the need for an expensive investigation and reducing the length of hospital stay and follow-up.