Salivary gland myoepitheliomas: cytological, histological, immunohistochemical and electromicroscopical studies of four cases

The results of a multidisciplinary study conducted on four salivary gland myoepitheliomas diagnosed with fine needle aspiration biopsy (FAB) and treated using local excision are presented. Histologically, two cases were benign and two malignant. Smears of the benign varieties contained an uniform population of slightly spindled cells with bipolar cytoplasm and conspicuous cell membranes. The nuclei were small and oval with homogeneous chromatin. The cells were observed in groups or clusters over a proteinaceous background. There were adjacent isolated cells differing in shape with rounded eosinophilic cytoplasm, the cytoplasm was discretely granular and/or clear with round hyperchromatic centrally-located nuclei. One smear showed numerous capillaries with prominent endothelial cells on a background made up of a chondroid matrix. Two cases disclosed malignant cytological changes with a necrohemorrhagic background, discrete pleomorphism, prominent nucleoli, hyperchromatism and occasional atypical mitosis. Immunohistochemical staining was strongly positive for protein S-100 and vimentin, and focally for cytokeratin. Electron microscopy was basically composed of myoepithelial cells.