The use of MRI to assist in diagnosis of pigmented villonodular synovitis of the knee joint.

Pigmented villonodular synovitis (PVNS) of the knee joint remains a difficult and elusive entity to define and characterize. This entity most often appears in the young adult knee with nonspecific clinical features, including a painful range of motion and perhaps a sensation of locking. Detection and diagnosis of this localized soft-tissue mass are difficult because plain roentgenograms may be totally within normal limits. The case of a 21-year-old woman illustrates the use of magnetic resonance imaging (MRI) as an effective technique to define and characterize PVNS. Advantages of MRI include high-resolution/high-contrast multiplanar sections that depict bone, marrow, ligaments and tendons, fat, menisci, and articular cartilage in one image. In addition, MRI is noninvasive and requires no ionized radiation. MRI is an excellent clinical tool for the evaluation of intraarticular tumors of the knee joint.