'Primary extrarenal Wilms' tumour': rare presentation of a common paediatric tumour.

Wilms' tumour (nephroblastoma), the most common abdominal malignancy of childhood, occurs primarily as a malignant renal tumour. Extrarenal Wilms' tumour is rare with occasional reports from the Indian subcontinent. The various locations of extrarenal Wilms' tumour include retroperitoneum, uterus, skin and thorax. In this report we will discuss the imaging features highlighting the imaging differential diagnosis in a case of retroperitoneal (extrarenal) primary Wilms' tumour.