a 53-years - old iraqi immigrant with longstanding ulcer history complained of severe epigastric pain . minimal biliary dilatation was identified , with normal gallbladder , intrahepatic ductal air [ figure 1a ] , adhesion between the ventral pancreatic head and posterior proximal duodenum [ figure 1b ] , thin fluid - like track suggesting choledocho - duodenal fistula ( cdf ) [ figure 1c ] . unenhanced images detect peripheral intrahepatic pneumobilia ( arrowhead in a ) , overdistended stomach , and focal adhesion between posterior wall of the proximal duodenum and ventral aspect of the pancreatic head ( thick arrow in b ) . after intravenous contrast administration , detailed oblique - reformatted image ( c ) shows thin fluid - like communication consistent with choledocho - duodenal fistula ( arrow ) . three days later , during acute pancreatitis repeat ct ( d ) detects appearance of peripancreatic effusion , confirms fluid - containing fistulous track between the posterior duodenal bulb and the distal common bile duct ( thin arrow ) endoscopy revealed chronic peptic duodenal bulb deformation without active ulcers and fistulous orifices . after unsuccessful endoscopic retrograde cholangiopancreatography ( ercp ) , clinical conditions worsened with acute pancreatitis . repeat ct detected peripancreatic fluid , increasing pneumobilia , persistent cdf [ figure 1d ] . spontaneous pneumobilia suggests bilioenteric communication , most usually cholelithiasis - related gallbladder perforation into normal duodenum . conversely , the uncommon ( 3.5 - 10% of cases ) cdf results from bulb ulcer penetrating the choledochus.[15 ] reflecting distribution of peptic disease , cdf manifests with pain , malaise or hematemesis in middle - aged men ; jaundice or cholangitis are exceptional . historically , duodenal deformity and biliary opacification during gastrointestinal barium studies identified cdf . conversely , gallbladder mural thickening and intraluminal air shift the diagnosis toward cholecysto - duodenal fistulization . often impossible because of duodenal narrowing