MR Imaging Knee Synovitis and Synovial Pathology.

Knee synovitis is a common, but nonspecific finding on MR imaging in patients with knee pain, with causes ranging from post-traumatic and osteoarthritis to inflammatory and infectious causes. Synovial thickening, joint effusion, and synovial enhancement are present across the spectrum of etiologies and do not allow differentiation between them in most instances. This article reviews synovial physiology and MR imaging of the normal synovium and synovitis, with discussion of specific pathologies and limited signs that suggest one diagnosis over another. Intravenous contrast is helpful across the spectrum of pathologies to distinguish joint fluid from synovial proliferation.