Monophasic Synovial Sarcoma: A Cytologic Spectrum

Synovial sarcoma (SS) is a high-grade sarcoma that can be diagnosed in cytology with certainty only when it presents with a biphasic pattern. Monophasic SS (MSS), however, is a diagnostic consideration when a uniform spindle cell population is present. The purpose of this study was to evaluate a series of cytologic cases of MSS and its cytologic presentation. Twenty-one FNAs of histologically confirmed MSS were reviewed. Specimens consisted of tissue fragments and single cells containing scant granular cytoplasm, medium-sized nuclei, and coarse chromatin. A monotonous spindle pattern with comma-shaped nuclei was present in 5 cases. Sixteen cases contained oval and spindled nuclei. Eight of these specimens contained round nuclei, and 5 of these cases showed prominent nucleoli and cohesive clusters, reminiscent of biphasic SS. We conclude that a spectrum of cytologic findings can be seen in MSS, including a secondary population of cells with morphology usually typical of biphasic SS.