A Rare Case of Poorly Differentiated Synovial Sarcoma of the Superficial Neck: Diagnostic Approach in a Fine-Needle Aspiration Specimen.

Synovial sarcoma (SS) is a rare and aggressive soft tissue malignancy that is more common in the extremities and has an unusual occurrence in the head and neck region. SS has two main subtypes: biphasic and monophasic. Some rare subtypes include poorly differentiated (round cell), monophasic epithelial, calcifying/ossifying, and myxoid types. Here, we present a rare case of a 61-year-old male with two left-sided neck masses abutting the supraclavicular fossa. One of the masses was present for over a year and gradually increased in size. The second mass was noticed a week before he presented to our institution. The fine-needle aspiration (FNA) specimen consists of tight clusters of monotonous epithelioid cells with scant amphophilic cytoplasm, hyperchromatic ovoid nuclei, increased mitotic activity (up to 6 per 10 HPF), and scattered apoptotic bodies. The tumor cells showed patchy expression for cytokeratins and claudin-4 and demonstrated strong and diffuse expression for TLE and SS18-SSX, consistent with a diagnosis of synovial sarcoma. Deep morphological analysis and targeted immunohistochemical workup can aid in the diagnosis of this rare entity in the head and neck area.