Retromolar monophasic synovial sarcoma: a rare entity in a rare location

Synovial sarcoma (SS) is a rare tumour that arises mainly in the peri articular tissues of the extremities. The majority of SS are biphasic on histology. Monophasic synovial sarcoma (MSS) of the mandible is a rare, aggressive malignancy having non-specific clinical and histological features with a tendency for distant metastasis. A 17- year-old girl presented to the surgical clinic with a gradually enlarging, painless ulcerated, right retro molar mass. Biopsy of the lesion revealed mitotically active, elongated, spindle cells arranged haphazardly and as fascicles with a hemangiopericytoma-like vascular pattern. The differential diagnosis included both odontogenic and non-odontogenic tumours. Immunohistochemistry showed positivity for AE1/AE3, CD99 and BCL2. CD34, CD31, SMA, CD117 and p63 were negative, thereby confirming a diagnosis of MSS. This case highlights key features of MSS and focuses on the importance of including it in the working differential diagnosis of malignant spindle cell tumours of the oral cavity.