A diagnostic challenge: primary renal biphasic synovial sarcoma presenting Homer Wright-like rosettes

Abstract Synovial sarcoma is a mesenchymal neoplasia of uncertain differentiation that usually presents in the extremities of young patients. Primary renal synovial sarcomas are rare. We report the case of an 11-year-old female patient initially diagnosed with an infected renal cyst. Imaging studies showed a heterogenous lesion measuring 7.1 × 6.9 cm. The renal mass was partially resected. The specimen received was a multi-fragmented pseudocystic lesion. Microscopic examination showed a round blue cell tumour with formation of rosettes, within a myxoid background, as well as fascicles of fusiform cells with anisocytosis. The immunophenotype showed positivity to CD56, AE1/AE3, and vimentin, as well as weak positivity to TLE1, BCL2, EMA and, S100. Molecular assays were done to confirm the possibility of a synovial sarcoma. The result showed a SYT-SSX1 translocation. This case exemplifies the multifaceted histology of synovial sarcoma.