[Reactive synovitis: MRI features with arthroscopic correlation]

To evaluate MR imaging in detecting and characterizing secondary reactive synovitis and correlate the results with arthroscopy.

Retrospective study of 10 patients referred for MR imaging and arthroscopy of the knee or shoulder. The diagnosis of reactive synovitis was confirmed by arthroscopy and pathological examination. Synovial thickening was graded at MRI as follows. Grade 0: normal; grade 1: diffuse synovial thickening; grade 2: nodular synovial hypertrophy; grade 3: pseudotumoral synovial mass.

Synovitis was described at MRI in 8 cases. There were 2 false negative results on MR imaging for the knee. Synovitis was secondary to knee trauma and rotator cuff tear or surgery of the shoulder. On arthroscopy, all synovial lesions were detected and confirmed at pathology. Synovitis was not detected at MRI (grade 0) in 20% of cases. Synovitis appeared diffuse (grade 1) in 30%, nodular (grade 2) in 30% and pseudotumoral (grade 3) in 20%. Bony erosions were adjacent to synovial thickening in 5 cases.

Reactive synovitis can occur after trauma. MR imaging is useful in detecting and evaluating secondary reactive synovitis. Arthroscopy and synovial biopsy are necessary to exclude infectious or tumoral synovitis.