[Two cases of lower abdominal tumors difficult to differentiate from urachal tumors].

CASE 1: A 28-year-old woman visited a local medical doctor, complaining of abdominal pain, urinary frequency and a sense of residual urine. Magnetic resonance imaging revealed a lower abdominal extraperitoneal tumor, approximately 5 cm in diameter, adjacent to the bladder dome. It was thought to be a urachal tumor, and she was referred to our hospital. A hard hen's egg-sized mass was palpable in the lower abdomen. Urinary analysis was normal. Cytological examination was also negative. Cystoscopy revealed redness in the bladder dome mucosa. Although the preoperative diagnosis was a urachal cancer, the pathological diagnosis on surgery was desmoids, and tumor excision was performed. No recurrence has been seen for 7 years postoperatively.

CASE 2: A 71-year-old man complaining of swelling of the lower abdomen was referred to our department because he was suspected to have a urachal tumor, of about 15 cm in diameter, on computed tomography. A hard infant head-sized mass was palpable in the lower abdomen. Urinary analysis was normal. Cystoscopical examination showed a markedly compressed bladder dome, however, no abnormal findings were seen in the mucosa. Although the preoperative diagnosis was a urachal tumor, the intraoperative pathological diagnosis revealed no malignancy. The mass was connected to the bladder dome, and partial cystectomy was conducted. The final pathological diagnosis was a solitary fibrous tumor. No recurrence has been seen for 5 years postoperatively. Because a urachal tumor is highly malignant, radical cystectomy and urinary diversion might be planned preoperatively. However, care should be taken not to be too invasive, considering the possibility of a benign tumor.