This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Most common site of gall stone impaction is 
Select and explain. 
A. Duodeno-jejunal junction, B. Proximal to ileocaecal junction, C. Distal to ileocaecal junction, D. Colon
B: Proximal to ileocaecal junction
Answer: B: Proximal to ileocaecal junction 
Explanation: Gall stone ileus It is an acute intestinal obstruction, often seen in elderly and is due to Blockage be a bolus or mass of gallstones which commonly enter the intestines through cholecystoduodenal fistula (75%) or rarely through cholecystointestinal or gastric fistula MC site : Between gallbladder and duodenum 2nd MC site : Between gallbladder and transverse colon Obstruction is seen in Distal ileum or proximal to ileocaecal junction Ref: SRB's Manual of Surgery 5th edition Pgno : 648