A giant 31-cm pancreatic mucinous cystic neoplasm: a 4-year progression and surgical challenge.

Mucinous cystic neoplasms (MCNs) of the pancreas are slow-growing tumours but carry a risk of malignant transformation and massive enlargement if left untreated. We present a rare case of a 49-year-old female initially diagnosed in 2022 with a 14-cm pancreatic cyst. After declining surgery, she presented four years later with acute bowel obstruction and a distended abdomen. Imaging revealed dramatic progression to a giant 31 × 22.7 cm mass displacing most abdominal viscera. An emergency distal pancreatectomy and splenectomy were performed, followed by a staged second-look laparotomy to ensure colonic viability. Despite the massive size, tumour markers remained normal. Histopathology confirmed MCN with focal high-grade dysplasia but no invasive carcinoma. This case demonstrates that extreme mass effect from a giant MCN can cause acute intestinal obstruction and emphasizes that size alone, while increasing surgical complexity, is not an absolute predictor of invasive malignancy.