This case report presents a teenage patient who initially was thought to have a sports-related injury but ultimately was diagnosed with a primary soft tissue tumor. A previously healthy 16-year-old softball player presented with a history of left knee joint line pain, clicking, and swelling. The patient was presumed to have a lateral meniscus tear. However, magnetic resonance imaging demonstrated an intra-articular mass. Arthroscopy revealed a 2.5- × 1.5-cm firm pedicular mass in the lateral joint. Histological exam demonstrated localized pigmented villonodular synovitis. The patient healed uneventfully and returned to sporting activities. This report re-emphasizes the possibility that "sports tumors" can mimic symptoms of a meniscal tear in young athletes.
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