<prompt> Pneumobilia can be seen inMirizzis syndromeAcute pancreatitisGallstone ileusCarcinoma gallbladder  <response>: Gallstone ileus is a type of acute intestinal obstruction,often seen in elderly and is due to blockage by a bolus or mass of gallstones which commonly enter the intestine through cholecystoduodenal fistula75 or rarely through cholecystointestinal or gastric fistulas.Plain Xray abdomen in erect posture shows air in the biliary tractbranching gas pattern,pneumobilia and multiple air fluid levels.Pneumobilia along with an ectopic stone and intestinal obstruction together constitutes the Riglers triad. Reference:SRBs manual of surgery,5th edition,page no:648. 