A rare case of giant extra-ovarian mucinous cystadenoma arising from sigmoid mesocolon

An 80-year-old female presented with one month history of acutely worsening abdominal distention and pain, without features of bowel obstruction. A giant intra-abdominal simple cyst, separate from the ovaries, was seen on imaging. Initial haematological and biochemical investigations, including tumour markers, were normal. At laparotomy, the cystic tumour was discovered to arise from the sigmoid mesocolon and was resected en bloc. Histopathology revealed the tumour to be a benign extra-ovarian mucinous cystadenoma, which is a neoplasm of ovarian origin that can arise from extra-ovarian sites, including the mesentery. Extra-ovarian mucinous cystadenoma arising specifically from the mesentery are very rare intra-abdominal neoplasms with malignant potential despite its benign appearance on investigations. This case aims to raise awareness of this condition and to highlight its diagnostic approach and surgical management.