Fine-needle aspiration biopsy diagnosis of extrarenal malignant rhabdoid tumor

Two cases of extrarenal malignant rhabdoid tumors are presented in which diagnosis was suggested by fine‐needle aspiration biopsy and confirmed by histologic and electron microscopic examination. Fine‐needle aspiration smears in both cases revealed round to polygonal cells with vesicular nuclei and prominent nucleoli. Several tumor cells contained cytoplasmic inclusions composed of intermediate filaments. A majority of the tumor cells stained strongly for vimentin and cytokeratin. Electron microscopic examination revealed many cells with large aggregates of intermediate filaments corresponding to the cytoplasmic inclusions. Fine‐needle aspiration biopsy may be used for diagnosing malignant rhabdoid tumor. The diagnosis may be further confirmed by immunohistochemistry and electron microscopy. Diagn Cytopathol 1994;11:271–276. © 1994 Wiley‐Liss, Inc.