Magnetic resonance imaging‐determined synovial membrane and joint effusion volumes in rheumatoid arthritis and osteoarthritis. Comparison with the macroscopic and microscopic appearance of the synovium

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Abstract
Objective. To evaluate the relationship between synovial membrane and joint effusion volumes determined by magnetic resonance imaging (MRI) and macroscopic and microscopic synovial pathologic findings in patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Methods. Synovial biopsies were performed, and macroscopic grades of synovitis assigned, at preselected knee sites during arthroscopy or arthrotomy in 17 knees with RA and 25 with OA. Synovial inflammation and 9 separate tissue characteristics were graded histologically. Synovial membrane and joint effusion volumes were determined by preoperative MRI, enhanced with intravenous gadopentetate dimeglumine. Results. MRI-determined synovial membrane volumes were correlated with the overall histologic assessment of synovial inflammation (Spearman's σ = 0.55, P < 0.001), with fibrin deposition, with subsynovial mononuclear and polymorphonuclear leukocyte infiltration (σ = 0.51-0.59), and less significantly with macroscopic synovitis, vessel proliferation, and granulation tissue formation (σ = 0.40-0.42). No correlation with synovial lining multiplication, perivascular edema, villous formation, or fibrosis was found (σ < 0.30). Conclusion. MRI-determined synovial volumes are correlated with synovial inflammatory activity. Synovial volumes probably mainly reflect the mass of cell-infiltrated, vascularized subsynovial tissue, but may also be influenced by the cumulative synovial proliferative activity. MRI-determined synovial membrane and effusion volumes may be sensitive markers and/or predictors of disease activity and treatment outcome in RA.