[Localized pigmented villonodular synovitis: a primary overlooked diagnosis in a young female patient].

Localized pigmented villonodular synovitis is a rare condition of the knee that may present with symptoms suggesting internal derangement. We report a case of juvenile patient who presented with a 1-year history of signs and symptoms of a loose body in the knee. Radiographic examination and MRI were within normal limits. The lesion was treated arthroscopically by resection.