Pneumobilia

Pneumobilia is the presence of gas in the biliary system. It is typically detected on a radiographic imaging exam, such as ultrasound, CT, or MRI. It is a common finding in patients that have recently undergone biliary surgery or endoscopic biliary procedure. While the presence of air within biliary system is not harmful, this finding may alternatively suggest a pathological process, such as a biliary-enteric anastomosis, an infection of the biliary system, an incompetent sphincter of Oddi, or spontaneous biliary-enteric fistula.

In a healthy individual with normal anatomy, there is no air within the biliary tree. When this finding is present, it may be secondary to:

Other rare causes that have been reported include duodenal diverticulum, paraduodenal abscess, operative trauma, and carcinoma of the duodenum, stomach and bile duct.

...
Wikipedia