Diffuse-type giant cell tumor: Pigmented villonodular synovitis of patellar fat pad.

Pigmented villonodular synovitis (PVNS) is a rare, relatively benign intra-articular lesion characterized by slowly progressing proliferation of the synovial tissue. It is most commonly observed in the knee joint. Localized and diffuse types are two types of PVNS depending on the synovial involvement.