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Monophasic fibrous type is the most common pattern seen in synovial sarcomas. The sarcomatous areas are composed purely of monotonous fibroblast-like spindle cells with plump nuclei resembling fibrosarcoma. The tumor cells are arranged in whorls or intersecting fascicles and may show focal nuclear palisading. Hemangiopericytomatous vascular pattern (stag-horn vessels) and abundant mast cells are additional features that are frequently present.