Localized pigmented villonodular synovitis of the knee with bone involvement mimicking a benign bone tumor: CT and MR findings.

The localized form of pigmented villonodular synovitis is characterized by a limited involvement of synovium. Although the knee is the joint that is commonly affected, bone changes in this location are not usual. We report the case of a histologically proven localized form of this entity in the knee, which mimicked a benign bone tumor on the basis of an MR pattern, CT findings, and scintigraphic results. Bone changes which may cause a pitfall in the diagnosis of the disorder are discussed.