Synovial Sarcoma, Thigh

45-year-old male with a proximal posteromedial right thigh mass. There is a heterogeneous solid and cystic T1 hyper- and isointense lesion arising in the proximal right thigh semitendinosis muscle. The lesion is STIR hyperintense with partially circumscribed margins. There is heterogeneous enhancement with a peripheral rind of viable tumor posteriorly. At resection, the lesion was found to be a synovial sarcoma. Synovial sarcomas are intermediate to high-grade malignant soft tissue tumors often with an indolent course. Typical presentation is in adolescents and young adults with a slight male to female predominance. Clinical features include a slowly enlarging soft tissue mass. The most common location for synovial sarcoma is within soft tissues adjacent to large joints such as the knee. Treatment is with a combination of surgery and adjuvant chemoradiation therapy.