Complex mucinous cystadenoma of undetermined malignant potential of the urachus: a rare case with review of the literature.

Urachal carcinoma is an uncommon neoplasm. Benign urachal tumours are extremely rare. All urachal mucinous tumours, regardless of tumour type, have the potential to behave in an aggressive clinical manner that includes the development of pseudomyxoma peritonei. We report a 58-year-old man who presented with lower abdominal pain. Ultrasound and CT imaging defined a large lobulated cystic mass superior to the urinary bladder. At laparotomy, the multiloculated cystic mass, 10 x 8 x 6 cm, could be completely separated from the bladder and was excised. It was smooth-walled and filled with thick mucinous fluid. Histology revealed a complex mucinous cystadenoma of undetermined malignant potential of the urachus. The cystic spaces were lined by mucin-secreting columnar epithelium that showed focal areas of mild atypia. The epithelium lacked architectural features of villous adenoma. There was no stromal invasion to support an invasive neoplastic process. No pseudomyxoma peritonei was present. The patient was well, with no tumour recurrence, at 6 months follow-up.