Anaplastic Wilms' tumor. Initial diagnosis by fine needle aspiration.

The diagnosis of a diffusely anaplastic Wilms' tumor in a ten-month-old child was first suggested by cytologic and histologic study of a fine needle aspirate. The mesenchymal component was predominant (75%) and exhibited some cells with hyaline, periodic acid-Schiff-positive, intracytoplasmic droplets. Foci of clear-cell carcinoma were also present. Only one case showing this histologic pattern in this unusual variant of Wilms' tumor has been reported previously.