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.
The urachus is a fibrous remnant of the urogenital sinus and allantois, a structure connecting the urinary bladder to the umbilicus during embryogenesis. The involution of the urachus usually transpires antenatally, and it subsequently becomes a vestigial remnant that can undergo metaplasia and subsequent tumor formation. A patent urachus is found in 1 in 200,000 live births and 1 in 5000 adults have an urachal cyst at autopsy. Malignant transformation of the urachus to urachal adenocarcinoma is rare, represents <1% of all bladder tumors, and occurs annually in 20 per 100,000 women and men. Primary mucinous urachal neoplasms of low malignant potential are exceedingly rare, and are subject to recurrence and pseudomyxoma peritonei. These neoplasms are often managed with complete surgical excision, making preoperative identification important to facilitate proper surgical management. Consequently, urachal tumors should be considered for any female patient with a pelvic mass.
Case Report
A 28-year old G9P2062 presented requesting pregnancy termination. On transvaginal ultrasound, a single live 8-week size intrauterine pregnancy was visualized. Additionally, an 8- × 7- × 6-cm complex echogenic mass, thought to arise from the left adnexa, was visualized superior to the bladder. The mass demonstrated thickened septations, heterogenous appearance, and fluid-fluid levels, findings suspicious for a mature cystic teratoma (MCT) ( Figure 1 ). Surgical termination of pregnancy, intrauterine device placement, and diagnostic laparoscopy was planned. Intraoperatively, a multiloculated, cystic, midline mass was noted arising from the anterior abdominal wall in close proximity to the bladder ( Figure 2 ). Surgical consultation with general surgery and gynecology oncology was obtained. The peritoneum was undermined and omentum was dissected from the mass. The mass was noted to be independent of bladder, ureters, and surrounding vasculature, and was dissected away from the peritoneum and excised with at least 1-cm margins. The appendix appeared normal and no gastrointestinal tract involvement was identified. The remainder of the pelvis including the adnexa appeared normal. A 6-cm posterior colpotomy was made under direct and laparoscopic visualization. The mass was removed en-bloc through the colpotomy, which was closed in a running locked fashion with 2-0 polyglactin suture. While urachal mass was now part of the differential diagnosis, the patient was not preoperatively consented for staging. Therefore, no further investigation, including frozen section, was performed. Postoperatively the patient did well and was discharged on postoperative day 1.
Pathology revealed a mucin-filled cyst ( Figure 3 ) lined by intestinal-type mucinous epithelium with mild cytological atypia and areas of villous and undulating epithelial proliferation. Significant mucin extravasation with focal clusters of tumor cells into the cyst wall and surrounding fibroadipose tissue and smooth muscle were present. The tumor cells were diffusely positive for CDX2 and CK20. Immunostain was negative for CK7. Final pathologic diagnosis was mucinous urachal neoplasm of low malignant potential.
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