From Stone to Unknown: Incidental Discovery of Oral Synovial Sarcoma in a Patient With a Renal Staghorn Stone.

Synovial sarcoma (SS) of the oral cavity is an exceedingly rare malignancy, particularly when arising in the floor of the mouth. We report a case of a 66-year-old male patient who was incidentally found to have a painless mass in the floor of the mouth during a perioperative assessment for nephrolithiasis. Histological examination revealed a biphasic tumor composed of spindle-shaped cells and epithelial elements with neuroendocrine-like immunophenotypic features. Immunohistochemistry confirmed the diagnosis with strong positivity for TLE-1, EMA, and vimentin, and focal positivity for synaptophysin and CD56. Fluorescence in situ hybridization (FISH) confirmed SS18 gene rearrangement. This case contributes to the limited literature on oral SS, particularly involving the floor of the mouth, and highlights an unusual clinical presentation in an elderly patient with neuroendocrine differentiation. To our knowledge, this is the first reported case of oral SS in Saudi Arabia or the surrounding region. The report underscores the importance of multidisciplinary collaboration in identifying clinically silent yet aggressive tumors.