Primary synovial sarcoma of the kidney.

Primary synovial sarcoma (SS) of the kidney is a very rare disease as well as a diagnostic dilemma. Here, we present a case of a 60-year-old male clinically diagnosed as renal cell carcinoma. The radical nephrectomy specimen showed a well-circumscribed renal mass of approximately 13 cm × 9 cm × 7 cm. The cut-surface of the mass was tawny and firm, with cystic areas, and also showed focal hemorrhage and necrosis. Histologically, the tumor was composed of spindle cells arranged in the intersecting fascicles, alternating with hypocellular areas suggestive of monophasic synovial sarcoma. Morphological and immunohistochemical features were compatible with the diagnosis of SS of the kidney.