[Malignant rhabdoid tumor of the kidney. A poorly differentiated type with difficult diagnosis]

Rhabdoid tumour of the kidney is a rare, distinct clinico-pathological entity, mostly occurring in children, with an extremely aggressive behaviour. There is a wide range of histologic patterns. We report a case in which the classical "rhabdoid" cytology with eosinophilic cytoplasmic inclusions and macronucleoli was scanty and abundant cytoplasm was absent. Immunocytochemical and ultrastructural studies were essential. This poorly differentiated type of rhabdoid tumour must not be confused with Wilms' tumour because it requires an intensive chemotherapy regimen.