Respiratory variation of extrahepatic bile duct diameter during ultrasonography.

The attachments and adjacent structures of the extrahepatic bile duct may not move uniformly throughout the respiratory cycle, potentially affecting the diameter of the common bile duct. This study was performed to evaluate possible respiratory variation in extrahepatic bile duct diameter. Thirty consecutive subjects with maximal anteroposterior common bile duct diameter of 5 mm or greater were studied. Inspiratory increase in ductal diameter exceeding 1 mm was noted in 11 subjects (37%), eight without biliary obstruction. Awareness of this normal phenomenon may avert sonographic misdiagnosis of common bile duct obstruction, particularly during fatty-meal sonography.