Pneumobilia is the presence of air within the biliary system. Most commonly due to iatrogenic causes — post-ERCP sphincterotomy, bilioenteric anastomosis (Whipple, hepaticojejunostomy), or biliary stent placement. Pathologic causes include bilioenteric fistula (especially cholecystoduodenal fistula → gallstone ileus), emphysematous cholecystitis, and biliary infections (gas-forming bacteria). Best visualized on CT — air accumulates in non-dependent position (anterior/central) within bile ducts. Differential from portal venous gas is critical — pneumobilia is central, portal gas is peripheral in distribution.
Age Range
30-85
Peak Age
60
Gender
Equal
Prevalence
Uncommon
Pneumobilia results from air entering the normally sterile and airless biliary system. The sphincter of Oddi normally prevents passage of duodenal contents (including gas) into bile ducts. Three fundamental mechanisms of pneumobilia: (1) Iatrogenic — sphincterotomy or stent removes sphincter barrier and duodenal gas freely passes; bilioenteric anastomosis (Roux-en-Y) creates direct bowel-bile duct connection. (2) Pathologic fistula — choledocholithiasis or peptic ulcer eroding gallbladder/CBD wall creating fistula with bowel; gas passes through fistula into bile duct. (3) Infection — gas-forming bacteria (Clostridium, E.coli) produce gas within bile duct. In imaging, air is the lowest density structure and accumulates opposite to gravity — in supine position accumulates in anterior/central intrahepatic ducts. In portal venous gas, air is carried peripherally by blood flow along portal vein branches and accumulates in peripheral 2 cm of liver — this distribution difference is the critical differential criterion.
In pneumobilia air accumulates in central intrahepatic ducts (gravity effect); in portal venous gas air accumulates in peripheral 2 cm (blood flow effect) — this distribution difference is a vital differential criterion because portal venous gas may indicate emergencies like intestinal ischemia/necrosis.
Air within intrahepatic bile ducts with central/anterior localization on non-contrast CT — air accumulates in non-dependent area (anterior) in supine position and follows anatomic distribution of bile ducts. Air is usually more prominent in left lobe and anterior segments of right lobe. Unlike air within portal vein branches, pneumobilia is recognized by air clusters following bile duct course. Air may also be seen within extrahepatic CBD.
Report Sentence
Air with central distribution within intrahepatic bile ducts noted, consistent with pneumobilia.
Bilioenteric fistula tract between gallbladder and duodenum with ectopic large gallstone in intestinal lumen (usually terminal ileum) combined with pneumobilia on portal venous phase — Rigler's triad (gallstone ileus). Focal defect in gallbladder wall with connection to first portion of duodenum is detected. Small bowel dilatation (mechanical obstruction) accompanies. This combination of findings is an emergency surgical indication.
Report Sentence
Pneumobilia + cholecystoduodenal fistula + ectopic gallstone in intestinal lumen with small bowel obstruction (Rigler's triad) consistent with gallstone ileus.
Bright echogenic foci within intrahepatic bile ducts with posterior 'dirty shadowing' (ring-down artifact) on US — representing intraluminal air. Air bubbles appear as irregular echogenic dots and may move with position change. Unlike 'clean shadow' of stones, air creates 'dirty shadow' — due to reverberation artifact. If air is seen within portal vein branches, peripheral distribution and hepatofugal direction of movement favors portal gas.
Report Sentence
Echogenic foci with dirty shadowing in intrahepatic bile ducts noted, consistent with pneumobilia.
Gas in gallbladder wall and/or lumen on non-contrast CT — emphysematous cholecystitis. Intramural gas shows intramural dissection pattern. Inflammatory changes around gallbladder (pericholecystic fluid, surrounding fat stranding) accompany. Air-fluid level may be seen in lumen. This finding is emergency surgical indication — risk of gangrenous cholecystitis and perforation is high.
Report Sentence
Gas in gallbladder wall and lumen noted, consistent with emphysematous cholecystitis; emergency surgical evaluation recommended.
Expected pneumobilia in bile ducts after ERCP/sphincterotomy or biliary stent — not pathologic. Air accumulates in central intrahepatic ducts. Stent (hyperdense tubular structure) may be detected within CBD. No inflammatory changes or collections. This finding is interpreted as normal postprocedural status and requires no additional intervention.
Report Sentence
Pneumobilia in bile ducts noted as expected postprocedural finding after ERCP/sphincterotomy/stent.
Criteria
After ERCP, sphincterotomy, stent, or bilioenteric anastomosis
Distinct Features
Most common type; not pathologic; no treatment needed
Criteria
Due to bilioenteric fistula (cholecystoduodenal, choledochoduodenal)
Distinct Features
Risk of gallstone ileus (Rigler's triad); fistula tract detectable on CT
Criteria
Gas-forming bacterial infection (emphysematous cholecystitis, pyogenic cholangitis)
Distinct Features
Emergency surgical indication; gas in gallbladder wall; septic presentation accompanies
Distinguishing Feature
Emphysematous cholecystitis shows gas in gallbladder wall + inflammatory changes; simple pneumobilia contains air only in duct lumen
Distinguishing Feature
Acute cholangitis shows duct wall enhancement + periportal edema; pneumobilia shows only intraluminal air
Distinguishing Feature
Gallbladder perforation shows pericholecystic fluid + wall defect; pneumobilia shows isolated air in ducts
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upClinical significance of pneumobilia depends on underlying cause. Iatrogenic pneumobilia (post-ERCP/stent) is normal finding requiring no treatment. Fistula-related pneumobilia should be evaluated for gallstone ileus (Rigler's triad). Emphysematous cholecystitis is surgical emergency. Differentiation from portal venous gas is vitally important — portal gas may indicate surgical emergencies like intestinal ischemia/necrosis.
Pneumobilia is normal if iatrogenic (post-ERCP/sphincterotomy, biliodigestive anastomosis) and requires no treatment. If spontaneous, underlying pathology must be investigated: biliary-enteric fistula (Rigler triad: pneumobilia + gallstone ileus + ectopic stone) requires emergency surgery. Differentiation from portal venous gas is vitally important — portal venous gas indicates bowel ischemia.