Localized pigmented villonodular synovitis of the knee.

Pigmented villonodular synovitis (PVNS) is a well-recognized lesion that may affect any joint but is frequently found in the knee. It is a rare condition, especially in the localized form, and is still cause for discussion regarding to its pathogenesis and treatment. We report four cases of localized PVNS each one presenting with different clinical signs and symptoms. In one of our cases, a pedunculated mass and villous-like projections of the surrounding synovium were associated. Each case was studied with magnetic resonance imaging, treated arthroscopically, and the diagnosis confirmed by histological examination. Arthroscopy is an effective tool for both diagnosis and treatment.