Villonodular pigment synovitis (PVNS) is a proliferative type of synovial membrane that most commonly affects the knee joint. It is classified as a tumor with local malignancy because the proliferation of synovial and histiocytic cells leads to an accumulation and deposition of hemosiderin and cholesterol, causing osteolytic degeneration of the articular components that can sometimes invade the surrounding soft tissues.

Editor's note: Per the 2020 WHO Soft Tissue and Bone Tumors Classification (5th ed.), the recommended terminology is tenosynovial giant cell tumor with pigmented villonodular synovitis no longer recommended (although remains in common use).