Air in the Biliary System
Pneumobilia

General Considerations

• Air in the biliary tree, also known as pneumobilia
• Most frequently from the following causes
• Incompetent Sphincter of Oddi
• Recent instrumentation, as in ERCP, or surgery, as in spincterotomy
• Fistulous connection with the GI tract, as in gallstone ileus
• It is rarely due to gas-forming infection, as in cholangitis or emphysematous cholecystitis

Clinical Findings

• Usually benign or asymptomatic when caused by incompetent sphincter or surgery

Imaging Findings

• Several, air containing-tubular structures seen in the region of the hilus of the liver
• The common bile duct is frequently recognizable
• There may be other, left and right biliary radicals, filled with air
• Since air produces echogenic artifacts on ultrasound, pneumobilia is visible on US

Differential Diagnosis

• Portal venous gas
• Usually a more ominous finding than pneumobilia
• Can be differentiated by the peripheral nature of innumerable air-containing branching structures near the outer edge of the liver rather than centrally

 
Air in the Biliary System. Close-up of the right upper quadrant shows a tubular structure containing air (red arrow) representing the common bile duct and several air-containing biliary radicals (white arrows).

The air-filled left hepatic duct: the saber sign as an aid to the radiographic diagnosis of pneumobilia.BJ Lewandowski, C Withers, and F Winsberg. Radiology. 1984;153 (2): 329-32.