Primary Extra-renal Wilms' Tumor in Urinary Bladder: Rare Presentation of a Common Pediatric Malignancy.

In pediatric population, the most common solid malignant tumor of the kidney is Wilms' tumor (WT). Incidence of Extra-Renal Wilms' Tumor (ERWT) is immensely unusual. Prognosis of ERWT is comparable to renal WT. Hence, diagnosis, staging workup and start of treatment in a timely manner is very essential. The most common location of ERWT is the retroperitoneum. The staging of ERWT is done according to National Wilms' Tumor Study group (NWTS). ERWT is considered as stage II or higher; because it is outside renal capsule. A 6-year boy presented with complaints of increased frequency of micturition and difficulty in urination for 15 months. Biopsy of bladder mass showed WT by immunohistochemistry stains such as WTI and Desmin. Cross-sectional imaging showed both kidneys clear of any tumor. Hence, the final diagnosis of ERWT was made.