Synovial sarcoma with extended occult period treated as juvenile rheumatoid arthritis: a case report.

Synovial sarcoma is a clinically high-grade malignant soft-tissue tumor; however, it demonstrates slow growth on occasion. A 2-year-old girl presented with persistent pain of the left forearm and was diagnosed with juvenile rheumatoid arthritis (JRA) by a pediatrician. Almost 10 years after the initial complaint, at the age of 11 years, a tumor mass appeared in her left forearm near the wrist joint, and the pain became more severe. Magnetic resonance imaging (MRI) showed a sarcomatous lesion, circumscribed by extensor tendons. A biopsy specimen revealed synovial sarcoma. The tumor was resected widely. Reconstruction was effected via free vascularized fibula grafting. The patient is well 13 months after surgery, with neither recurrence nor distant metastases.