We report a case of a 78-year-old woman with a urachal tumor of the bladder wall. We performed a biopsy and revealed the tumor as a villous adenoma. We excised the tumor by partial cystectomy together with the umbilical ligament, because it was possible there was a co-existing malignancy. The tumor turned out to be villous adenoma and a urachal adenocarcinoma. Because the superficial section of the tumor consisted only of adenoma, a biopsy could not identify the malignant component. Villous adenoma of the urinary tract or the urachus is very rare, and it is considered as an intestinal premalignancy.
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