[A case of urachal abscess].

A 26-year-old male with urachal abscess was demonstrated. Ultrasonography, CT and MRI revealed that there was a mass at the supravesical region, which was connected to the umbilicus. However, a differential diagnosis as to whether the mass was a tumor or an abscess was difficult from these examinations. Thus we performed an open biopsy. A pathological examination revealed no malignant change in the biopsy specimen. On the other hand, the pathological diagnosis of a follicular tumor located at the roof of the urinary bladder was TCC G2, but we considered that, this change was a reactive hyperplasia with dysplasia resulting from chronic inflammation of urachal abscess. Thus, the complete excision of urachal abscess and partial cystectomy were performed. The serial sections of the bladder wall revealed no malignant changes. We reviewed similar cases reported in our country and discussed various factors causing urachal abscess, especially related to the infectious root.