This patient had a CT scan of the abdomen where gas was noted in the intrahepatic bile ducts. Note the relatively central location of linear air density in the liver (contrast this with the peripheral linear air densities seen with portal venous gas). The causes of pneumobilia include an incompetent Sphincter of Oddi (e.g. post sphincterotomy, or following passage of a gallstone), gallstone ileus, trauma, a duodenal ulcer perforating into the common bile duct, and secondary to surgery (e.g. cholecystoenterostomy). Gas in the gallbladder is seen in emphysematous cholecystitis. In this case it was due to previous biliary surgery.
Reference: Dahnert W. Radiology Review Manual 5th ed. 2003. Lippincottt Williams & Wilkins.
Credit: Dr Bernard Ng