Pneumobilia

The underlying causes of pneumobilia are typically the result of an abnormal communication between the biliary tract and the intestines or infection by gas-forming bacteria. The most common conditions associated with pneumobilia are biliary-enteric surgical anastomosis, incompetence of the sphincter of Oddi, spontaneous biliary-enteric fistula, recent biliary instrumentation, infections, and biliary-bronchopleural fistulas.

Biliary-enteric surgical anastomosis (i.e., the surgical connection between the biliary tree and GI tract) is a very common surgical procedure conducted during surgeries, like cholecystoenterostomy (i.e., a surgery in which the gallbladder is joined to the small intestine to relieve an extrahepatic biliary tract obstruction), and Whipple procedure, which is a procedure that removes the head of the pancreas, the first part of the small intestine, the gallbladder, and the bile duct. The Whipple procedure is usually used to treat pancreatic cancers and other pathologies at the head of the pancreas, the duodenum, or bile duct. While trying to create a permanent connection between the biliary and the GI system, air may accumulate in the biliary tree. 

Less invasive procedures that concern the biliary system can also result in pneumobilia. During an Endoscopic Retrograde CholangioPancreatography (ERCP) and a common bile duct stent placement, small amounts of air can get trapped within the biliary tree. During ERCPs, the endoscope enters through the esophagus, goes to the stomach, and into the duodenum where it releases air to secure a better view. Then, the ampulla of Vater (i.e., the opening where the bile and pancreatic ducts empty into the duodenum) is located, and a thin, flexible tube called a catheter slides through the sphincter of Oddi (which surrounds the ampulla of Vater) and into the bile ducts. A contrast medium is subsequently injected into the ducts through the catheter to make them more visible. This communication between the GI tract and the biliary system may lead to pneumobilia.

The incompetence of the sphincter of Oddi can also allow air to flow from the GI tract to the biliary tree. Usually, this is the result of sphincterotomy or the passage of a gallstone that injures the biliary tree, but it may also result from scarring, like in chronic pancreatitis; medications, like atropine; and less frequently, congenital incompetence of the sphincter. Similarly, pneumobilia can result from a spontaneous biliary-enteric fistula, resulting from a complication of chronic cholelithiasis, peptic ulcer disease, trauma, or neoplasms (e.g., cholangiocarcinoma). 

A detailed analysis of history and physical findings must be completed before proceeding with further diagnostic testing. Ultrasonography is very sensitive in detecting pneumobilia and will identify pneumobilia as multiple highly reflective areas in the liver, described as having a striped appearance. Pneumobilia may appear on plain supine abdominal X-ray with an air bubble accumulation in the intrahepatic bile ducts and the common bile duct, thereby creating the saber sign (i.e., sword-shaped lucency in the right paraspinal region present in about 50% of individuals with pneumobilia). 

On CT scans, pneumobilia is generally seen as a branching pattern of air. Additionally, the presence of oral contrast in the biliary duct may also support the diagnosis of pneumobilia. The use of IV contrast can assist in localizing the identified air bubbles. A CT scan can additionally suggest an etiology to the presence of pneumobilia. For example, it may identify biliary stents or the presence of dilated bile ducts, suggesting the possible diagnosis of cholangitis with inflammatory infiltration of the bile duct, or confirm post-surgical anastomosis. Once identified on imaging, pneumobilia must be differentiated from air in the portal vein as both conditions may have a similar appearance on ultrasonography, and therefore, a CT scan with contrast may be necessary to differentiate. 

Pneumobilia requires a varied approach depending on the underlying cause. In some cases, conservative management (e.g., watch and wait, treatment of underlying infection) of pneumobilia in hemodynamically stable individuals with isolated pneumobilia and without additional radiologic or clinical findings is an option. If an infection is the cause of pneumobilia (e.g., emphysematous cholecystitis), broad-spectrum antibiotics (e.g., metronidazole, clindamycin) are suggested as first line treatment. However, prompt surgical cholecystectomy with excision of the gallbladder is frequently necessary as pneumobilia can progress quickly to septic shock and death, particularly in the elderly and individuals with diabetes mellitus.