MR imaging of pigmented villonodular synovitis of the knee.

Six cases of pigmented villonodular synovitis (PVNS) of the knee are presented. MR imaging and surgical proof were available in all cases. Three of the six cases showed the diffuse form, and the other three cases the localized form. The MR appearance of PVNS varied, presumably according to the relative proportion of pathological components. It most commonly consisted of scattered low signal intensity areas representing hemosiderin deposition in hypertrophied synovium on T2(*)-weighted images, and dotted areas of low signal intensity, presumably resulting from fibrous components of the lesion, on T1-weighted images. The latter finding is described for the first time in this report. Two cases were associated with osteoarthritis. In the remaining four cases, the osseous structures, cruciate ligaments, and menisci were normal. MR imaging was of great use in the detection of PVNS. For the first time, a preoperative diagnosis of PVNS of the knee joint could be made by MR imaging.