Primary primitive neuroectodermal tumour of the kidney in adults.

Primitive neuroectodermal tumour (PNET) is a neural crest tumour derived from neuroectoderm. Renal PNET is a very rare tumour occurring during childhood or adolescence. We report two cases of PNET involving kidney in adults. Presenting signs and symptoms include abdominal/flank pain and/or haematuria. Microscopy reveals the tumour consisted of small round cells with round nuclei and scant cytoplasm. Diagnosis was confirmed by immunohistochemistry with diffuse membranous positivity of tumour cells with CD99. As these tumours have an aggressive clinical course with rapid death in many reported cases, it is important to differentiate them from other small round-cell tumours.