Imprint Cytology of Soft Tissue Myoepithelioma: A Case Study
An 18-year-old man presented with a soft tissue mass of five months' duration in the right forearm. There was no trauma history. Physical examination revealed a round, tender mass. On magnetic resonance scan of the right forearm, T1-weighted imaging revealed a circumscribed mass with intermediate signal intensity. T2-weighted imaging revealed high signal intensity within the mass (). Gadolinium-enhanced fat-suppressed T1-weighted imaging of the mass showed inhomogeneous enhancement. There was no bony involvement. The initial clinical impression was schwannoma. The mass was excised and imprint cytology of the mass was performed.\nThe obtained slides were stained with hematoxylin and eosin and Papanicolaou methods. On microscopic examination, the smears were moderately cellular. The smear revealed clusters, sheets, and isolated cells in the background of myxoid materials (). Tissue fragments were occasionally scattered. The cells were round to spindle and epithelioid-shaped. The nuclei were uniformly round to ovoid, with finely distributed chromatin and a small nucleolus. The nuclear membrane was smooth. The cytoplasmic borders were well-defined or indistinct. The tumor cells had abundant eosinophilic or pale cytoplasm. Some cells had eccentrically-located nuclei and lesser amount of basophilic cytoplasm, resulting in a plasmacytoid appearance. Long, tapering cytoplasmic processes were also seen. Cytoplasmic vacuolation was noted in some tumor cells. Cells with naked nuclei were also present. Fibrillary materials were occasionally seen in the background. No nuclear pleomorphism was present. Neither mitosis nor necrosis was found. On immunohistochemical staining for cytologic slides, the tumor cells were occasionally positive for cytokeratin (AE1/AE3) and S100 protein.\nThe excised tumor measured 3.0×1.8×1.5 cm. The tumor was well-demarcated, yellow solid, soft, and myxoid (). Histologically, the tumor showed multilobulated growth with myxoid and fibrous stroma. The tumor consisted of epithelioid, spindle and plasmacytoid cells (). The tumor cells were present in solid sheets or reticular pattern without ductal component or necrosis. The tumor cells showed immunostaining for cytokeratin (AE1/AE3), epithelial membrane antigen (EMA), S100 protein, and glial fibrillary acidic protein (GFAP) (). Electron microscopic examination showed intermediate filaments, desmosomes, and basal lamina (). The histologic features were consistent with soft tissue myoepithelioma. Neither recurrence nor metastasis was noted four year follow-up.