A 54-year-old man was admitted to our hospital with abdominal pain and vomiting. Abdominal CT scan showed retroperitoneal air and a low density area between the duodenum and the pancreatic head. Perforation of the duodenal diverticulum was diagnosed, and an emergency operation was performed. Laparotomy with a Kocher maneuver disclosed a retroperitoneal abscess behind the 2nd to 3rd portion of the duodenum ; however, there was no clear evidence of a diverticulum.
Retroperitoneal drainage was performed. After surgery, upper gastrointestinal imaging revealed a diverticulum on the 2nd portion of the duodenum. We report a case of a perforated duodenal diverticulum diagnosed by CT scan before surgery.