Small-cell variant of synovial sarcoma: fine-needle aspiration with ancillary features and potential diagnostic pitfalls.

We report a small-cell variant of synovial sarcoma examined by fine-needle aspiration (FNA) biopsy. The patient is a 23-yr-old female who had a synovial sarcoma involving the left infratemporal region, diagnosed at 7 yr of age, followed by a metastatic lesion involving the lung and chest wall 16 yr later. The chest wall metastases was sampled by FNA biopsy. The aspirate consisted of numerous, small, round cells with very high nuclear-to-cytoplasmic ratios. The cytomorphologic features could potentially be confused with other pediatric small round cell tumors. Ancillary studies demonstrated positive staining of the neoplastic cells for cytokeratin, epithelial membrane antigen (EMA), and CD99. The differential diagnosis of other small round cell tumors that may be mistaken for the small-cell variant of synovial sarcoma are presented. We believe that this is the first FNA report detailing the cytologic and ancillary features of the small-cell variant of synovial sarcoma.