Two cases of extrarenal malignant rhabdoid tumors are presented in whi
ch diagnosis was suggested by fine-needle aspiration biopsy and confir
med by histologic and electron microscopic examination. Fine-needle as
piration smears in both cases revealed round to polygonal cells with v
esicular nuclei and prominent nucleoli. Several tumor cells contained
cytoplasmic inclusions composed of intermediate filaments A majority o
f the tumor cells stained strongly for vimentin and cytokeratin. Elect
ron 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 rh
abdoid rumor. The diagnosis may be further confirmed by immunohistoche
mistry and electron microscopy. (C) 1994 Wiley-Liss, Inc.