Fine needle aspiration biopsy of primary renal synovial sarcoma. A case report

Primary renal synovial sarcoma is a relatively recently described and characterized neoplasm, formerly designated embryonal sarcoma of the kidney, and has not been diagnosed before by fine needle aspiration biopsy cytology. We describe the cytologic features of a malignant biphasic neoplasm of the kidney that was subsequently diagnosed at nephrectomy and confirmed with molecular genetic analysis as a biphasic renal synovial sarcoma.

A 38-year-old male presented with acute abdominal pain. Computed tomography (CT) demonstrated a 4.7-cm mass in the left kidney. No soft tissue or extrarenal masses were identified. A CT-guided fine needle aspiration biopsy revealed a malignant biphasic tumor characterized by minimally atypical tubular epithelium, immature spindle cells and foci of coagulative tumor necrosis. At nephrectomy, a necrotic, pseudo-encapsulated synovial sarcoma of the upper pole of the left kidney was identified and was additionally evaluated with immunohistochemistry and molecular genetic studies. The case is unique since biphasic synovial sarcomas have yet to be reported to occur in the kidney and fine needle aspiration biopsy findings of this renal neoplasm have never been reported to our knowledge.

Synovial sarcoma should be a diagnostic consideration particularly in a young adult with a malignant spindle cell neoplasm of the kidney. The list of differential diagnoses should include sarcomatoid renal cell carcinoma, sarcomatoid transitional cell carcinoma of the renal pelvis, angiomyolipoma and monophasic or biphasic synovial sarcoma.