RESUMEN
The purpose of this case report is to present a rare finding of synovial sarcoma in a 5-year-old child. Most soft-tissue masses of the foot are too often presumed to be small and benign; therefore, compared with soft-tissue sarcomas, they are difficult to clinically differentiate and treat. A 5-year-old girl presented with a painful lesion that was diagnosed as synovial sarcoma after an excisional biopsy was performed. This was an unexpected finding of synovial sarcoma involving the tibialis posterior tendon of her right foot. The patient presented with an 8-month history of tenderness and an antalgic gait. We would like to encourage that all soft-tissue tumors of the foot be preoperatively evaluated with the aid of diagnostic imaging so that a well-planned biopsy assessment can be performed, with adequate margins excised.