Rhabdomyosarcoma in an adult presenting with nodal metastasis: a pitfall in fine-needle aspiration cytology of lymph nodes.

A 40-yr-old woman with an asymptomatic sinonasal rhabdomyosarcoma (RMS) initially presented with submental nodal metastasis. The fine-needle aspiration (FNA) and the subsequent biopsy of the nodal metastasis were misinterpreted as metastatic carcinoma because the primary tumor was occult, the tumor cells were exclusively round cells with a nested arrangement, and rhabdomyoblasts were absent. The correct diagnosis of metastatic RMS became apparent when the primary sinonasal tumor, detected in a CT, was biopsy proven to be an alveolar RMS. Retrospectively, there were helpful clues to the correct diagnosis in the nodal FNA and biopsy. When FNA cytology or biopsy histology of a lymph node suggests metastatic carcinoma but the tumor cells are nonimmunoreactive to carcinoma markers, the differential diagnosis should be expanded to include not only metastatic melanoma but also metastatic sarcoma and lymphoma. Cytologically, the presence of multinucleated giant tumor cells, including the rosette forms, in the FNA smears should alert the cytopathologist to the possibilities of sarcoma and anaplastic large cell lymphoma. Copyright 2005 Wiley-Liss, Inc.