Pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS), or tenosynovial giant cell tumor, is a rare benign synovial proliferation in childhood with locally aggressive behavior. We report the case of an 11-year-old girl with right knee pain and swelling lasting several weeks, initially interpreted as a self-limited inflammatory process. Due to persistence of symptoms, she was referred to Pediatric Rheumatology, where imaging, arthroscopy, and biopsy showed suggestive but inconclusive findings. Subsequent genetic testing confirmed the CSF1::FN1 fusion, diagnostic of PVNS. This case illustrates the challenge of recognizing this entity in children, given its clinical overlap with more common rheumatologic and infectious diseases. Magnetic resonance imaging is essential to guide suspicion, while molecular analysis may be decisive in uncertain cases. Complete synovectomy remains the treatment of choice, but the risk of recurrence requires close follow-up.