Does it matter where you measure bile duct diameter at ERCP?

Bile duct diameter (BDD) is described in the literature to be an important variable when considering the risk for ERCP-related complications and the likelihood for having sphincter of Oddi dysfunction. There is no consensus, however, regarding where along its course the bile duct should be measured. Purpose: To determine if variation of bile duct measurements at ERCP differ between locations and/or observers. Methods: Bile duct diameter was measured by two observers (radiologist and endoscopist) at three locations (distal, middle, and maximum diameter) in 47 consecutive patients undergoing sphincter of Oddi manometry and ERCP. Distal bile duct diameter was measured at the widest location 2-3 cm above the papilla. Correlation between observers was evaluated by Pearson correlation coefficient. The effect of bile duct diameter location on the measurements provided by the two observers was evaluated by ANOVA. Results: The Pearson correlation coefficients between the two observers were: r=0.81 for Distal BDD, r=0.91 for middle BDD, and r=0.96 for maximum BDD (p<0.0001). Location Observer x̄ BDD (mm) Std error p (two-sided) Distal 1 7.5 0.4 0.09 2 6.7 0.3 Middle 1 8.7 0.6 0.56 2 8.2 0.6 Maximum 1 10.2 0.7 0.70 2 10.6 0.7 Bile duct diameter differed significantly by ocation (site effect: p<0.001), but was similar at each location for both observers (rater effect: p=0.16). Conclusions: Bile duct diameter varies depending on where it is measured. Because of this variation, clinician/investigators need to state clearly where ductal measurements are taken in patients undergoing ERCP for evaluation of biliary and pancreatic disorders. If bile duct location is fixed, interobserver variability of measurements is low.