Hidden malignancy in an ileal duplication cyst: a rare adult case highlighting the practical challenges

Malignant transformation within an intestinal duplication cyst is uncommon and rarely detected preoperatively. Here, we report a 28-year-old man who presented with vomiting along with a progressively enlarging abdominal lump and weight loss. Imaging revealed a large cystic intra-abdominal lesion with a mural solid component and focal calcifications, but the diagnosis remained uncertain. Surgical excision was performed, and histopathological examination demonstrated a moderately differentiated adenocarcinoma arising within a non-communicating ileal duplication cyst. The patient remained clinically stable without evidence of recurrence at the six-month follow-up. This case highlights the diagnostic limitations of imaging and emphasizes the importance of complete excision and meticulous histopathological examination of adult duplication cysts, particularly when mural nodularity or other suspicious features are present.