This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Medicine
Most common site of Gallstone ileus: 
Select and explain. 
A. Caecum, B. 2nd pa of duodenum, C. Terminal ileum, D. Stomach
C: Terminal ileum
Answer: C: Terminal ileum 
Explanation: Gallstone ileus is an unusual complication of chronic cholecystitis due to impaction of gallstone in ileum after passing through a biliary-enteric fistula. Impacted gallstone usually in the terminal ileum at ileocecal valve Rigler's Triad: Pneumobilia Small bowel obstruction Gallstone at terminal ileum