[Width of the lumen of the common bile duct: sonography compared with ERCP]

The diameter of the common bile duct can be easily determined by ultrasound and by ERCP (endoscopic retrograde cholangiography). The measured values differ by as much as 20% due to the technical features of both methods. A study with 100 patients showed that in 20% of the patients the diameter of the common bile duct determined by ERCP was twice that of the value determined by sonography. The difference can be definitely explained by the influence of butyl scopolamine and the high-pressure injection of the contrast medium into the bile duct system. The sonographic measured size of the common bile duct is correlated with the physiological value but a sure prediction of the expected value to be determined by ERCP is not possible.