Bilateral diffuse pigmented villonodular synovitis of the knee.

Pigmented villonodular synovitis (PVNS) is a proliferative disease of synovial tissue characterized by lipid-laden macrophages, multinucleated giant cells, and hemosiderin deposits. PVNS presents either in a localized form with minimal rates of recurrence after surgical resection or in a diffuse form with an expansive growth pattern showing formation of osseous erosions and extra-articular manifestation. In the diffuse form high recurrence rates occur as a result of the challenge of achievement of total synovectomy. Typically only one single joint, being the knee in 80% of cases, is involved with diffuse PVNS. Reports of bi- or multiarticular manifestation are at best rare. Here, a case of a 16-year-old girl with bilateral diffuse PVNS of the knee allows discussion of diagnostic and treatment considerations.