This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gall Bladder & Bile Ducts, Subject name: Surgery
A very old lady, air in biliary tree, colicky abdominal pain with distension and hyper peristaltic abdominal sounds diagnosis 
Select and explain. 
A. Gall stone ileus, B. Hemobilia, C. Cholangitis, D. Pneumobilia
A: Gall stone ileus
Answer: A: Gall stone ileus 
Explanation: Ans. (a) Gall stone ileusRef: Sabiston 20th edition Page 1506* This is due to Cholecysto duodenal fistula which results in Pneumobilia and Obstruction