Cytomorphology of metastatic mesothelioma in fine-needle aspiration specimens

The morphologic features of mesothelioma occurring in serous fluids, as wel l as fine-needle aspiration (FNA) of primary tumors, have been extensively described. Descriptions of the FNA findings in metastatic lesions of mesoth elioma, however, are limited to single cases. In this report, we illustrate the cytomorphologic features of four cases of metastatic mesothelioma whic h underwent FNA, and one additional cytologic preparation taken from a surg ically-excised metastatic lesion. The cytomorphologic features of metastati c mesothelioma varied greatly among individual cases with respect to the de gree of nuclear pleomorphism, amount of cytoplasm, and degree of cellular c ohesion. However, one feature which was consistently seen was the presence of numerous distinct, uniformly small intracytoplasmic vacuoles, believed t o represent intracellular fat and glycogen. These morphologic features are illustrated and the differential diagnosis of intracytoplasmic vacuoles wit hin epithelioid tumor cells in primary and metastatic lesions is discussed. (C) 1999 Wiley-Liss, Inc.