Sclerosing myoepithelial neoplasm: immunohistochemical and ultrastructural features in a unique case

Abstract

Background Histopathologic features of myoepithelial tumors may vary and include spindled, plasmacytoid, epithelioid, and clear cells as well as mucoid to hyalinized matrix. Objective We present a unique myoepithelial neoplasm with dense sclerosis. Case report A19-year-old male presented with a 2-year history of a right buccal lesion. A poorly circumscribed submucosal lesion without ulceration or tenderness was located near Stenson's duct. Contributor's impression was “lipoma.” Pathologic features The specimen was 2.1 × 1 × 1 cm, very firm, and varied in color from tan-brown to yellow. Microscopic examination revealed very dense fibrous stroma that infiltrated striated muscle, adipose tissue, and minor salivary gland lobules. Small strands and irregular islands of cells with poorly defined plasma membranes, abundant pale eosinophilic fibrillar to vacuolated cytoplasm, and oval to round nuclei were embedded in, and often compressed by, the dense stroma. Ductal structures and chondroid matrix were not present. Tortuous thin-walled vascular channels were common. The cellular strands and nests reacted with antibodies for S-100, pancytokeratin (AE1/AE3) and GFAP, but not for SMA, CD34, or CD68. There was mild expression of CD99 and Bcl-2. Electron microscopy revealed occasional intermediate filament aggregates, hemidesmosomes, rare structures representing myofilament attachment plaques, basement membranes, and basal lamina material. Neural processes, neurosecretory granules, neurofilaments, and glial differentiation were not identified. Myoepithelial origin was supported by the histopathologic, immunohistochemical, and ultrastructural findings. Conclusion Dense sclerosis may be associated with myoepithelial neoplasms, and both immunohistochemical and ultrastructural examination may help define the cell of origin.