Pigmented villonodular synovitis of the flexor hallucis longus tendon: A rare cause of leg pain in a 12-year-old girl.

Pigmented villonodular synovitis is an uncommon benign neoplastic proliferation associated with the synovium, bursa, or tendon sheaths; most commonly occurring in the third to fourth decade of life. It is rare in children and may be painful or painless. Magnetic resonance imaging is the diagnostic study of choice. In this report, the radiologic, ultrasound, and magnetic resonance imaging findings of pigmented villonodular synovitis of the flexor hallucis longus in a 12-year-old girl are discussed. We briefly review the surgical findings as well. To our knowledge, this is the first case report that simultaneously synthesizes the imaging findings of 3 diagnostic imaging modalities for optimal visualization and is the youngest reported case of pigmented villonodular synovitis of the flexor hallucis longus tendon.