Botryoid Wilms' tumor: a report of two cases.

We report two rare cases of botryoid Wilms' tumor (BWT) occupying the renal collecting system with no macroscopic parenchymal mass. In case 1, a 3-year-old boy presented with a mass in the right flank, low-grade fever, abdominal pain, and macrohematuria. Radiology revealed an enlarged right kidney with a heterogeneous mass occupying a large part of the dilated renal calyx, pelvis, and ureter. Radical right nephroureterectomy was performed. The histopathologic diagnosis was nephroblastoma, and the pedicle of the tumor was attached to the renal parenchyma near the pelvic wall. In case 2, a 2-year-old boy presented with macrohematuria, and the clinical course was almost the same as in case 1. No local recurrence or metastatic spread has been detected for 4 years postoperatively in case 1 and for 9 months postoperatively in case 2.