Axial Spondyloarthritis: Updates in Concepts and Reporting in Radiology.

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease primarily affecting the axial skeleton, historically termed "human leukocyte antigen B27 positive spondyloarthropathy" or ankylosing spondylitis. Improved understanding of the underlying pathologic mechanisms has led to an ongoing redefinition of this disease state, a recognition of the substantial phenotypic and biological variation, and an emphasis on earlier detection. Magnetic resonance imaging has become central to identifying and confirming early axSpA, critical to fulfilling the promise of slowing disease progression and preventing irreversible structural abnormalities. We review the clinical background and current role of medical imaging in axSpA, with a focus on Assessment of SpondyloArthritis International Society consensus definitions, to improve radiology reporting and facilitate discussion between radiologists and other clinical experts in spondyloarthritis.