Background: Synovial sarcoma (SS), a malignant mesenchymal tumor, has a biphasic growth pattern characteristically. Histologically and cytologically the tumor can pose diagnostic difficulty when the epithelial component is predominant.
Case report: A 22-year-old female presented with a rapidly enlarging mass on the lower left side of the neck. Fine needle aspiration of the tumor yielded abundant, discohesive round-oval cells mingled with amorphous hyaline material, raising a suspicion of medullary carcinoma of the thyroid. In addition, air-dried, Giemsa-stained smears demonstrated rosettelike structures with central magenta globular material, mimicking adenoid cystic carcinoma. However, histologic examination of the excised tumor, including immunohistochemical and ultrastructural studies, proved it to be a typical SS with copious basement membrane accumulations.
Conclusion: The cytologic appearance of SS can be confusing. However, a false diagnosis may be avoided if adequate needle sampling is ensured and clinical correlation considered.