Recurrent Wilms' tumour or retroperitoneal teratoma? A challenging case.

The clinical and pathological features of a left renal tumour and a subsequent retroperitoneal tumour in a 2-year-old boy are presented. The nephrectomy specimen showed typical features of a triphasic Wilms' tumour with focal heterologous elements and intralobar nephrogenic rests. The tumour was assessed as clinical stage III and post-operative chemotherapy and radiotherapy were administered. A retroperitoneal mass, detected following completion of postoperative therapy, was mainly made up of skeletal muscle and mature adipose tissue. Nests of epithelium resembling ameloblastic nests and a unique structure reminiscent of a developing tooth were present.