An unexpected mass of the urachus: a case report.

The urachus is a remnant of the urogenital sinus and allantois, which persists after antenatal involution. Despite its rudimentary postnatal presence, it can undergo metaplasia and tumor formation. Malignant transformation of the urachus is rare. However, these tumors can recur and develop pseudomyxoma peritonei. Thus, they should remain on the differential for any female patient with a pelvic mass. A 28-year old G9P2062 presented at 8 weeks' gestation requesting pregnancy termination. On ultrasound, a single live intrauterine pregnancy was visualized. Also identified was a left-sided 8- × 7- × 6-cm complex echogenic mass with thickened septations, heterogeneous appearance, and fluid-fluid levels suspicious for a mature cystic teratoma. Surgical termination of pregnancy and diagnostic laparoscopy was planned. Intraoperatively a multiloculated midline mass was identified and excised. Final pathology identified a mucinous urachal neoplasm of low malignant potential. The patient followed up with urology and underwent surgical staging. Midline location is a key feature that helps distinguish ovarian masses from urachal or bladder masses. Many urachal and bladder neoplasms are managed with complete surgical excision and staging, illustrating the importance of preoperative identification. If laterality of a mass is unclear, further imaging is recommended to characterize the mass preoperatively. This case also reveals the feasibility of a minimally invasive abdominal wall mass resection.