Imaging of enthesitis: a new field for the radiologist?

Entheses are sites where tendons, ligaments, joint capsules, or fasciae attach to bone. Their function is to provide a mechanism for reducing stress at the bony interface by dissipating the biomechanical load acting on the bone. Enthesitis may occur in traumatic, endocrinologic, metabolic, degenerative, or inflammatory conditions and is a major symptom in patients with seronegative spondyloarthritis (SpA). The increasing interest in inflammation of the entheses associated with rheumatoid diseases has fundamentally changed our understanding of the clinical presentation, pathogenesis, and therapy of enthesitis. Conventional radiographs and computed tomography (CT) allow good evaluation of chronic changes of the entheses, such as soft-tissue calcification, erosions, and new bone formation. The method of first choice to evaluate acute enthesitis is magnetic resonance imaging (MRI), which depicts both soft-tissue changes and intraosseous abnormalities. The purpose of this overview is to discuss the MRI appearance of enthesitis in patients with SpA and to provide a morphologic survey of the predominantly affected entheses. (orig.)