European Radiology

, Volume 27, Issue 5, pp 2024–2030 | Cite as

MR signal in the sacroiliac joint space in spondyloarthritis: a new sign

  • Frederiek Laloo
  • N. Herregods
  • G. Varkas
  • J. L. Jaremko
  • X. Baraliakos
  • D. Elewaut
  • F. Van den Bosch
  • K. Verstraete
  • L. Jans



To determine the diagnostic value of MR signal within the sacroiliac (SI) joint space in spondyloarthritis (SpA).


A retrospective analysis of MRIs of SI joints was performed in 363 patients, aged 16-45 years, clinically suspected of sacroiliitis. Intra-articular SI joint MR signals were categorized as normal, high T1 signal, fluid signal, ankylosis or vacuum phenomenon (VP). These MRI findings were correlated with the final diagnosis, according to the ASAS criteria. Sensitivity, specificity, and positive and negative likelihood ratios (LR) and predictive values were calculated.


Presence of intra-articular high T1 signal, fluid signal and ankylosis had a specificity of 95.8 %, 95.3 % and 99.5 % for SpA. High T1 signal, fluid signal and ankylosis were present in 38.4 %, 19.2 % and 17.9 % of SpA patients and in 4.2 %, 4.7 % and 0.5 % of patients without SpA, resulting in LR+ of 9.0, 4.1 and 37.9, respectively. VP was present in 13.2 % of SpA patients and in 20.8 % of patients without SpA, resulting in an LR+ of 0.6.


Presence of high T1 signal, fluid signal and ankylosis within the SI joint on MRI have high specificity for SpA. High T1 signal is the most sensitive MRI feature within the SI joint for SpA.

Key Points

MRI of the SI joints is typically obtained for diagnosis of spondyloarthritis.

The MR signal within the SI joint itself reflects features of spondyloarthritis.

Intra-articular high T1 signal, fluid signal and ankylosis are seen in spondyloarthritis.

The vacuum phenomenon makes spondyloarthritis less likely.


MRI Spondyloarthritis Sacroiliac joint Sacroiliitis Ankylosis 



Vacuum phenomenon



The scientific guarantor of this publication is Lennart Jans. The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. No complex statistical methods were necessary for this paper. Institutional Review Board approval was obtained. Written informed consent was obtained from all patients in this study. Methodology: retrospective, diagnostic or prognostic study, performed at one institution.


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Copyright information

© European Society of Radiology 2016

Authors and Affiliations

  • Frederiek Laloo
    • 1
  • N. Herregods
    • 1
  • G. Varkas
    • 2
  • J. L. Jaremko
    • 3
  • X. Baraliakos
    • 4
  • D. Elewaut
    • 2
  • F. Van den Bosch
    • 2
  • K. Verstraete
    • 1
  • L. Jans
    • 1
  1. 1.Department of Radiology and Medical ImagingGhent University HospitalGentBelgium
  2. 2.Department of RheumatologyGhent University HospitalGentBelgium
  3. 3.Department of Radiology & Diagnostic ImagingUniversity of Alberta HospitalEdmontonCanada
  4. 4.Rheumazentrum RuhrgebietRuhr-University BochumHerneGermany

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