Pigmented villonodular synovitis - knee
Knee pain and swelling associated with limitation in flexion
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There is diffuse irregular thickening and proliferation of the synovial lining of anterior and posterior recesses of knee joint forming nodular and villous projections associated with moderate joint effusion. These projections display low T1, intermediate T2 and bright STIR signal intensities with moderate enhancement after contrast administration. The synovial membrane as well as some of the nodular projections exhibit low T2 signal intensity suggesting possible hemosiderine deposition. Some of the synovial masses imprint the surface of adjacent bone causing erosion best seen at medial and lateral aspect of lateral femoral condyle, lateral aspect of lateral tibial condyle and tibial plateau beneath the spine.
PVNS is a chronic inflammatory lesion affecting the synovial membranes resulting in synovial hypertrophy, forming villous and nodular projections and causing pressure erosion of the adjacent bones. Although the appearance is radiologically classic for PVNS yet other differential diagnosis include siderotic synovitis, synovial osteochondromatosis and rheumatoid arthritis.