Pigmented Villonodular Synovitis
Pigmented villonodular synovitis is a benign proliferative process of the synovial lining of a joint, bursa, or tendon sheath. The cause of this lesion is unknown. Repeated trauma, repeated intra-articular hemorrhage, and inflammation have been suggested.
There is no sex predilection. The peak incidence is between 20 and 40 years of age.
Morphology and Location
There are two forms.
The focal form (also called giant cell tumor of the tendon sheath) is more common and usually involves the tendon sheaths of the hands.
The diffuse form involves large joints, especially the knee.
MRI characteristics are typical and often lead to the correct diagnosis. As a result of the deposition of hemosiderin within the tumor, the lesion has areas of low signal intensity on both TI-weighted and T2-weighted images. The presence of bone erosion on both sides of the joint also suggests the diagnosis. Joint effusion may be present.
On CT scans, bone erosions have well-defined sclerotic borders. On non-contrast-enhanced scans, the soft tissue component may contain areas of high attenuation; these correspond to deposits of hemsider