A Rare Case of Synovial Sarcoma Arising in the Parotid Gland

Abstract

Synovial sarcoma is a rare high-grade soft-tissue sarcoma with slight male predominance and peak incidence among young adults. The most common sites of origin are the extremities, near large joints, especially the knee, but it can arise in the head and neck region as well as in solid organs such as the prostate. The exact cell of origin is not known. The diagnosis of synovial sarcoma can be made by cytology/histopathology, and confirmed with molecular studies that show X;18 translocation. We report a case of a 37-year-old woman who presented with the new onset of severe worsening left frontal headache, lightheadedness and paresthesia with tingling in the distribution of the maxillary and mandibular divisions of the left trigeminal nerve. She had a firm tender left preauricular swelling extending from the anterior preauricular region posteriorly to the tragus and inferiorly to the left ear lobe. She denied fever, discharge and history of facial trauma. Physical examination revealed no lymphadenopathy. The direct smears of fine needle aspiration (FNA) of the left parotid mass showed hypercellular aspirate composed of a monomorphic population of spindle cells with bland tapering nuclei. No significant nuclear atypia or mitosis was present. There was no evidence of matrix material in the background. The spindle cells showed considerable nuclear overlapping. The preliminary diagnosis of cellular spindle cell neoplasm was made. In the cell block, tumor cells were positive for epithelial membrane antigen (EMA) and CD99. Molecular studies were positive for synovial sarcoma fusion transcripts (SYT-SSX1) by fluorescence in situ hybridization (FISH). These findings are consistent with synovial sarcoma in an unusual location. The resulting fusion protein is central to the pathogenesis of synovial sarcoma through dysregulation of gene expression. The key treatment is excision by surgery with radical neck dissection followed by radiation and chemotherapy.