An 84-year-old woman was brought to our emergency outpatient clinic with fever, epigastralgia, and back pain. On blood analysis, mild anemia and leukocytosis were noted. Abdominal CT showed a diverticulum in the fourth portion of the duodenum and pneumoretroperitoneum around this site. We conducted an emergency operation with the diagnosis of a perforated duodenal diverticulum. On laparotomy, the Treitz ligament showed inflammatory thickening, incision of the ligament allowed the efflux of the pus from the retroperitoneal space, and a perforated diverticulum was observed in the 4th portion of the duodenum. The diverticulum was resected, the wall was closed by suturing, and the abscess was drained. Histologically, the diverticulum was found to be a psuedodiverticulum lacking the muscularis propria, and the tissue around the thinned perforation site was necrotized. The patient’s postoperative course was uneventful, and she was discharged on the 24th hospital day. Perforation in the diverticulum in the 4th portion of the duodenum is a rare but serious disorder, and early surgical treatment with a prompt and accurate diagnosis is important.
