Which of the following is the most common site of intestinal obstruction in a case of gallstone ileus?

Ileum is the most common site of intestinal obstruction in gallstone ileus. Gallstone ileus refers to mechanical obstruction resulting from passage of a large gallstone into the bowel lumen. Large gall stone >2.5cm in diameter, predispose to the formation a fistula and erosion through the gall bladder fundus into the duodenum. Small gallstones will not cause obstruction, and they normally enter the duodenum by passing down the cystic duct and then the common bile duct. From duodenum stone pass down the intestine and get impacted at about 2 feet proximal to the ileocecal valve. This is the narrowest pa of the intestine after gastroesophageal junction. Ref: Harrison Internal Medicine, 18th Edition, Page 2622; Surgical Talk: Revision in Surgery By Andrew Goldberg, 2nd Edition, Page 90; Acute Care Surgery: Principles and Practice By L. D. Brit, Page 486.