[A case of urachal actinomycosis with bone formation].

We report a case of urachal actinomycosis with bone formation. A 76-year-old woman was admitted to our hospital with a complaint of gross hematuria. Cystoscopy revealed bleeding from the dome of the bladder wall. Magnetic resonance imaging revealed a mass extending from the dome of the bladder to just below the umbilicus. A urachal tumor was clinically suspected, and the mass was resected together with urachal remnant and part of the bladder wall. Pathological diagnosis of the specimen was actinomycosis. The bone tissue was found in the abcess. Actinomycosis is a chronic suppurative infection caused by Actinomyces israelii. Although urachal actinomycosis is a rare desease, it is important to recognize this uncommon intrapelvic infection as the differential diagnosis of any intrapelvic mass.