Synovial sarcoma- A potential diagnostic pitfall on FNAC

Synovial sarcoma is a malignant mesenchymal tumour with an uncertain origin. It is most commonly seen in the extremities, particularly lower extremities. The diagnosis of synovial sarcoma can be challenging due to its morphological diversity. Histologically, it can be of three subtypes: Monophasic, Biphasic and Poorly differentiated. The transcriptional corepressor, Transducin-Like Enhancer 1(TLE1) is a sensitive and specific marker for synovial sarcoma which helps in distinguishing it from histologic mimics. This case report presents a 48 year old female with swelling over right forearm since 1 year which was misdiagnosed on FNAC as Benign spindle cell lesion, probably Schwannoma. Surgery was done and on histopathological examination, it was diagnosed as Biphasic synovial sarcoma. It was confirmed by TLE1 immunohistochemistry which showed diffuse strong nuclear positivity. FNAC can sometimes fails to sample the epithelial component in biphasic synovial sarcoma, which complicates accurate diagnosis. The exact subtyping of spindle cell tumours is difficult on cytology owing to their complex heterogeneity. Though, Synovial sarcoma is an aggressive tumour, it responds well to treatment including surgery and chemotherapy. Therefore, correct and early diagnosis of synovial sarcoma is vital.