Unusual primary intracranial dural-based poorly differentiated synovial sarcoma with t(X; 18)(p11; q11)

Synovial sarcoma is a rare aggressive neoplasm occurring at any site of the body, mainly in young adults. It may also arise in the CNS but has seldom been reported. We report a case of unusual intracranial synovial sarcoma in a young male patient. Neuroimaging revealed a large gadolinium-enhancing mass was located at the right anterior cranial fossa and was associated with multiple cyst formation. The mass was dural-based and was observed to invade the right orbital apex and ethmoidal bulla. Histologically, the tumor was composed of uniform oval and round cells with scant cytoplasm and indistinct borders. The tumor cells were observed to form densely cellular sheets, but in some areas, the tumor showed hemangiopericytomatous vascular pattern consisting of tumor cells arranged around dilated, thin-walled blood vessels. By immunohistochemistry, vimentin, CD99 and Bcl-2 were diffusely positive in most cells, and a focally weak reactivity for S-100 protein was also observed. However, the tumor cells were negative for cytokeratin (AE1/AE3), CK7, CK8/18, CK19, epithelial membrane antigen, CD34, synaptophysin, GFAP, desmin, myogenin, and smooth muscle actin. Cytogenetic analysis using fluorescence in situ hybridization (FISH) demonstrated a translocation t(X;18)(p11;q11), an aberration specific for synovial sarcoma. A diagnosis of primary dural-based poorly differentiated synovial sarcoma was made. To our knowledge, this is the first report of a poorly differentiated variant of synovial sarcoma occurring in dura mater and confirmed by cytogenetic analysis. The present case indicates that appropriate immunohistochemical analysis, and in particular molecular analysis, are essential for accurately diagnosing small, round-cell neoplasms in unusual locations.