Botryoid Wilms' tumor of the renal pelvis extending into the bladder

We report a case of botryoid Wilms' tumor that occupied the renal pelvis and extended into the bladder. A 3-year-old boy was referred to us with a chief complaint of gross hematuria and micturition pain. Computed tomography showed tumor occupying the right renal pelvis and ureter and extending into the bladder. Right radical nephroureterectomy was performed. The resected specimen showed a botryoid sarcoma-like appearance, occupied the right renal pelvis and ureter, and protruded into the bladder. Histologic findings showed typical triphasic Wilms' tumor. Botryoid Wilms' tumor has been reported in only 16 cases in the literature and in only 3 cases extended into the bladder.