Bile duct calibre: the discrepancy between ultrasonic and retrograde cholangiographic measurement in the post-cholecystectomy patient.

The discrepancy between bile duct measurements obtained by ultrasound and retrograde cholangiography in post-cholecystectomy patients was prospectively evaluated by performing real-time biliary tract sonography on 50 patients 2-3 h prior to endoscopic retrograde cholangiography (ERC). A significant discrepancy was detected (P less than 0.001) which was greatest in 14 patients shown by cholangiography to have duct dilatation without evidence of biliary tract disease (P much less than 0.001). Factors contributing to the discrepancy included: measurement of different regions of the duct by the two techniques, loss of duct wall elasticity producing a 'floppy duct' phenomenon, the capacity of the biliary tract for rapid spontaneous change in calibre, radiographic magnification and ultrasonic underestimation of duct diameter. The sonographic diameters were significantly correlated to the diameters measured by ERC (r = 0.73). Although ERC generally agreed with ultrasound in the diagnosis of duct dilatation (specificity 90%), there was significant disagreement between the two techniques in the detection of non-dilatation, dilated or 'dilatable' systems being missed by ultrasound in 11 out of 21 (52%) of cases in which they were found by ERC. Our results suggest that, in the investigation of the symptomatic post-cholecystectomy patient, direct comparison of bile duct size measured by ultrasound and ERC is of limited clinical value.