Juxtarenal/pararenal Wilms' tumour in a six-year-old Malay girl

We report a six-year-old Malay girl who presented with a right retroperitoneal tumour that measured 7.5 cm in diameter. A wide excision of the lesion was performed. The tumour was separated from a normal-appearing right kidney by a capsule. Microscopically, this well-encapsulated tumour was composed of classical triphasic components: epithelial, mesenchymal and blastemal areas. The immunohistochemical study showed WT1 expression in the blastemal area. Thus, a diagnosis of Wilms' tumour with favourable histology was made. The patient was well for 12 months. Extrarenal Wilms' tumour is uncommon, with the majority of cases occurring in the retroperitoneal and inguinal areas. Wilms' tumour that is not arising from the intrarenal area but shares a common capsule with the ipsilateral kidney, is even rarer. Indeed, our case would be more appropriately classified as juxtarenal/pararenal Wilms' tumour. Despite its rarity, an extrarenal or even juxtarenal/pararenal Wilms' tumour should be included in the differential diagnosis of retroperitoneal tumour.