MRI lesions in the sacroiliac joints of patients with spondyloarthritis: an update of definitions and validation by the ASAS MRI working group

Walter P. Maksymowych, Robert G.W. Lambert, Mikkel Østergaard, Susanne Juhl Pedersen, Pedro M. Machado, Ulrich Weber, Alexander N. Bennett, Juergen Braun, Ruben Burgos-Vargas, Manouk De Hooge, Atul A. Deodhar, Iris Eshed, Anne Grethe Jurik, Kay Geert Armin Hermann, Robert B.M. Landewé, Helena Marzo-Ortega, Victoria Navarro-Compán, Denis Poddubnyy, Monique Reijnierse, Martin RudwaleitJoachim Sieper, Filip E. Van Den Bosch, Désirée Van Der Heijde, Irene E. Van Der Horst-Bruinsma, Stephanie Wichuk, Xenofon Baraliakos

Research output: Contribution to journalArticlepeer-review

171 Scopus citations


Objectives The Assessment of SpondyloArthritis international Society (ASAS) MRI working group (WG) was convened to generate a consensus update on standardised definitions for MRI lesions in the sacroiliac joint (SIJ) of patients with spondyloarthritis (SpA), and to conduct preliminary validation. Methods The literature pertaining to these MRI lesion definitions was discussed at three meetings of the group. 25 investigators (20 rheumatologists, 5 radiologists) determined which definitions should be retained or required revision, and which required a new definition. Lesion definitions were assessed in a multi-reader validation exercise using 278 MRI scans from the ASAS classification cohort by global assessment (lesion present/absent) and detailed scoring (inflammation and structural). Reliability of detection of lesions was analysed using kappa statistics and the intraclass correlation coefficient (ICC). Results No revisions were made to the current ASAS definition of a positive SIJ MRI or definitions for subchondral inflammation and sclerosis. The following definitions were revised: capsulitis, enthesitis, fat lesion and erosion. New definitions were developed for joint space enhancement, joint space fluid, fat metaplasia in an erosion cavity, ankylosis and bone bud. The most frequently detected structural lesion, erosion, was detected almost as reliably as subchondral inflammation (κappa/ICC:0.61/0.54 and 0.60/0.83). Fat metaplasia in an erosion cavity and ankylosis were also reliably detected despite their low frequency (κappa/ICC:0.50/0.37 and 0.58/0.97). Conclusion The ASAS-MRI WG concluded that several definitions required revision and some new definitions were necessary. Multi-reader validation demonstrated substantial reliability for the most frequently detected lesions and comparable reliability between active and structural lesions.

Original languageEnglish (US)
Pages (from-to)1550-1558
Number of pages9
JournalAnnals of the rheumatic diseases
Issue number11
StatePublished - Nov 1 2019


  • definitions
  • lesions
  • magnetic resonance imaging
  • reliability
  • sacroiliac joint
  • spondyloarthritis

ASJC Scopus subject areas

  • Rheumatology
  • Immunology and Allergy
  • Immunology
  • Biochemistry, Genetics and Molecular Biology(all)


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