Urachal mucinous adenocarcinoma with pseudomyxoma peritonei

RATIONALE Pseudomyxoma peritonei is an unusual clinical condition, and the appendix and ovaries are reported as the primary sites. PATIENT CONCERNS A 44-year-old man who was reported a 3-month history of lower abdominal pain and distention, along with increased abdominal girth, was admitted with a palpable tender mass in the central lower abdomen. DIAGNOSIS Ultrasonography showed a large well-circumscribed cystic-solid mass with lobulated margin, extending from the anterosuperior dome of the urinary bladder to the anterior abdominal wall. A computed tomography (CT) scan revealed a midline heterogeneous, hypodense, irregular polycystic-solid mass adjacent to the anterior wall of the abdomen and anterior to the dome of the urinary bladder. fluorodeoxyglucose positron-emission tomography/CT showed intense fluorodeoxyglucose uptake in the thickened wall of the mass. Intraperitoneal laparoscopic exploration also revealed a midline abdominal mass adjacent to the dome of the urinary bladder. Laparotomy showed that the mass originated from the dome of the urinary bladder and was disconnected with the urinary bladder lumen. The final histopathological diagnosis was urachal mucinous adenocarcinoma associated with high-grade pseudomyxoma peritonei. INTERVENTIONS The patient underwent surgical cytoreductive procedure and the perioperative intraperitoneal chemotherapy. OUTCOMES The patient made an uneventful recovery, and 7 months later had no recurrence. LESSONS The urachus is a tubular structure, which extends medially from the apex of the bladder to the allantoid during fetal development, and it usually obliterates after birth. Urachal remnants can cause urachal carcinoma or bladder cancers. Pseudomyxoma peritonei originating from mucinous neoplasm of the urachus is extremely rare.