Synovial Sarcoma Mimicking Pleomorphic Hyalinizing Angiectatic Tumor of Soft Parts: A Case Report.

Synovial sarcoma is a high-grade sarcoma commonly affecting young adults. The sites of involvement include soft tissue near joints, lung, pleura, mediastinum, larynx, kidney, and buttocks. Histologic types include monophasic, biphasic, and undifferentiated. We report a unique case of synovial sarcoma with low-grade histologic features mimicking pleomorphic hyalinizing angiectatic tumor (PHAT) with indolent behavior for a period of 10 years. The tumor showed angiectatic blood vessels with fibrinous cuffing, hypocellular and hypercellular spindle cell areas with rare mitoses, and focal atypia in a myxoid background. TLE1 was positive with SYT gene translocation detected on fluorescent in situ hybridization. Cases of myxoinflammatory fibroblastic sarcoma and myxofibrosarcoma have been reported as exhibiting histologic features of PHAT. However, to the best of our knowledge, cases of synovial sarcoma mimicking PHAT have not been reported.