RESUMO
INTRODUCTION: Synovial cyst is composed by a fibrous wall; lining by a thin layer of synovial cells containing synovial fluid, the prototype of these, in the knee is the Baker's cyst, which is located abnormally in the gastrocnemius semimembranous bursa. Baker's cyst prevalence ranges from 5 - 38%. Clinical diagnosis is supported by the presence of increased volume of soft tissues located in the popliteal region. CLINICAL CASE: A 74 year-old woman with longstanding active rheumatoid arthritis who developed a large, recurrent Baker's cyst. The Baker's cyst had two flare-ups of pain and soft tissue swelling which eventually limited knee movements; was treated with needle aspiration guided by ultrasound and synovectomy with methotrexate twice. At 18-months follow-up, the patient remains without evidence of recurrence. CONCLUSIONS: Local infiltration of methotrexate represents an alternative therapy for those refractory Baker's cyst with partial response to conventional treatment, where the surgical procedure carries a high risk.