Primary Orbital Synovial Sarcoma Mimicking a Periocular Cyst.

Synovial sarcoma (SS) is a high-grade soft-tissue sarcoma occurring predominantly in older children and young adults. Only approximately 7% occur in the head and neck region, with SS representing less than 0.1% of all head and neck cancers. Orbital location is exceedingly rare with only 8 cases reported so far in the literature. It is noted for its propensity for late local recurrences and metastases. Histologically, SS is monophasic, biphasic, or poorly differentiated and harbors a specific chromosomal translocation t(X;18)(p11.2;q11.2) in >95% of cases. In this article, we describe a case of monophasic SS primarily arising in the left supero-nasal orbital region in a 24-year-old woman, clinically mistaken for a periocular cyst. The case is peculiar for its highly unusual location and for its clinical deceptively benign appearance.