Extrarenal teratoid Wilms' tumour.

We report an unusual case of extrarenal teratoid Wilms' tumour in a 15-month-old male child. The tumour was retroperitoneal in location and consisted of triphasic Wilms' tumour elements, along with the presence of heterologous components. The heterologous teratoid elements were composed of predominantly glandular epithelium with the presence of focal skeletal muscle, adipose and neuroglial tissues. Although extrarenal Wilms' tumours have been documented in the literature, only a few cases have been noted to date. We present the relevant clinical, radiological, histomorphological, histochemical and immunohistochemical features of this rare tumour, and discuss the various theories of its histogenesis.