摘要：Primary mediastinal synovial sarcoma is rare and poses a diagnostic challenge particularly when unusual histologic features are present and t (x;18) is negative. Five cases of primary mediastinal synovial sarcoma were evaluated to define clinicopathologic features including unusual histology that may result in misdiagnosis. Clinically, compared with pulmonary synovial sarcomas, mediastinal synovial sarcomas occurred in younger patients and showed male predominance. Radiology images were reviewed. Histologically, tumors showed many identical characteristics of typical pulmonary and soft tissue synovial sarcomas with dense cellularity, interlacing fascicles, hyalinized stroma, and mast cell influx with focal hemangiopericytoma-like vasculature and calcification. In contrast, they showed no myxoid change, more infiltrative growth, and focal unusual histology not usually seen with soft tissue synovial sarcoma but typical of other neoplasms. These included Verocay bodies [1], papillary structures with fibrovascular cores [1], and adenomatoid change [1]. Immunohistochemistry demonstrated expected expression of focal cytokeratins, CD99, Bcl-2, and smooth muscle actin. Three of 5 tumors were positive for t (x;18), with one having no tissue remaining for testing. In conclusion, this small case series of mediastinal synovial sarcomas occurred in younger patients with male predominance compared with pulmonary synovial sarcoma, and had more infiltrative growth, less myxoid change and focal histology typical of other neoplasms. Awareness of focal unusual histology can prevent misdiagnosis particularly in t (x;18) negative tumors.
