Clustered localized pigmented villonodular synovitis.

The localized form of pigmented villonodular synovitis (PVNS) is a rare pathologic entity characterized by limited involvement of the synovium. In the knee joint, which is the most commonly affected joint, the disorder generally presents as a single nodular lesion, or rarely as 2 or 3 multiple nodular lesions into the joint. We report 2 cases of localized PVNS in which multiple nodules were clustered in a limited patella fat pad area. Clustered, multiple nodular lesions in a limited area suggested to us to consider a variant of localized forms.