Objective The aim of this study was to define characteristic MRI findings in the spine of patients with axial spondyloarthritis (SpA) and provide a definition of a positive spinal MRI for inflammation and structural changes.

Methods Technical details of spinal MRI and the description of spinal lesions of both inflammation and structural changes were discussed in consecutive meetings of 10 experts of the Assessment in SpondyloArthritis international Society (ASAS). The discussions aimed at a broad consensus on definitions of ‘a positive spinal MRI’ for both types of lesions and were backed up by a systematic literature search.

Results A total of six different types of lesions were described for inflammation—anterior/posterior spondylitis, spondylodiscitis, arthritis of costovertebral joints, arthritis of zygoapophyseal joints and enthesitis of spinal ligaments—and another four for structural changes—fatty deposition, erosions, syndesmophytes and ankylosis. In the literature review, four relevant papers were identified. Anterior/posterior spondylitis and fat depositions at vertebral edges were considered as the most typical findings in SpA. Based on expert consensus and taking the literature review into consideration, a positive spinal MRI for inflammation was defined as the presence of anterior/posterior spondylitis in ≥3 sites. Evidence of fatty deposition at several vertebral corners was found to be suggestive of axial SpA, especially in younger adults. ASAS members (n=56) approved these definitions by voting in January 2010.

Conclusions This consensus statement gives clear descriptions of disease-related spinal lesions and of definitions of a positive spinal MRI for inflammatory lesions (spondylitis) and structural changes (fat deposition). These definitions can be used to describe findings of spinal MRI in patients with SpA in daily practice and clinical studies.