Adenocarcinoma originating from a colonic duplication cyst: A case report.

Background: Gastrointestinal duplication is a rare congenital anomaly of the digestive tract, with colonic manifestations being particularly uncommon. Malignant transformation of colonic duplication cysts is rare, with adenocarcinoma being the most frequently reported type. Herein, we report a rare case of adenocarcinoma originating from a colonic duplication cyst.

Case summary: A 49-year-old woman was found to have an elevated cancer antigen 19-9 level during a routine checkup. Imaging revealed a well-defined abdominal cavity cystic mass, which was initially suspected to be an ovarian teratoma. Laparoscopic surgery revealed a duplication cyst, and pathological examination confirmed adenocarcinoma arising from the cyst. The mass within the transverse mesocolon was successfully excised by a colorectal surgeon. Immunohistochemical analysis confirmed adenocarcinoma with invasion into the muscularis propria. Postoperative endoscopy and positron emission computed tomography scan showed no signs of malignancy, except for an elevated cancer antigen 19-9 level. A multidisciplinary team recommended no further chemotherapy, advising routine follow-up for monitoring.

Conclusion: Colonic duplications, though rare, remain a differential diagnosis of unexplained abdominal masses, with complete resection being their primary treatment approach.