Definition of MRI Spinal Lesions in Axial Spondyloarthritis Updated

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A working group reviewed the existing literature on axial spondyloarthritis (axSpA) to update and validate the definitions for inflammatory and structural spinal lesions.

In the evaluation of spinal magnetic resonance imaging (MRI), bone marrow edema (BMO), and fat lesions are important in identifying pathologic findings, but can also be used in ongoing efforts for reevaluating the definition of a “positive” MRI of the spine in the context of axial spondyloarthritis (axSpA) vs non-SpA, according to a review published in Annals of the Rheumatic Diseases.

The Assessment of Spondyloarthritis International Society (ASAS) MRI Working Group, which comprised 12 rheumatologists and 2 radiologists, reviewed the existing literature on possible types of spinal MRI pathologies in patients with axSpA and revised and validated the existing definitions of spinal MRI lesions where necessary.

They consented on the required revisions of lesion definitions compared with the 2012 nomenclature. A second step in the process used 62 MRI scans from the ASAS classification cohort that validated the proposed definitions in a multireader campaign by global (absent/present), and detailed (inflammation and structural) lesion evaluation at the vertebral corner (VC), vertebral endplate, facet joints, transverse processes, and lateral and posterior processes. Their report used a subdivision of lesion definitions according to central and lateral slice anatomical locations in the thoracic and lumbar spinal segments on a sagittal MRI. These lesions were divided into those involving or not involving the vertebral bodies.

For vertebral body lesions, active inflammatory lesions were present if BMO was located at the VCs or endplates. Inflammatory lesions were specified for the different anatomical localizations, such as the VCs. Inflammatory activity at the VCs was subdivided into 2 types. Additional lesions that affect the vertebral bodies were the vertebral endplate inflammatory lesions and the thoracic lateral inflammatory lesions. The group noted, “All definitions of inflammatory lesions [related] to their appearance on the water-sensitive sagittal T2-weighted fat-suppressed (T2FS) or sagittal short tau inversion recovery (STIR) images in the sagittal orientation.”

Structural lesions were characterized by the presence of typical findings, including fat lesions, erosions, sclerosis, syndesmophytes, or ankylosis located at the vertebrae. The various types of structural lesions may present either solely or can be accompanied/ surrounded by BMO. The appearance of all lesions (both inflammatory and structural) were highly suggestive of SpA.

The ASAS MRI Working Group made revisions for both inflammatory (BMO) and structural (fat, erosion, bone spur, and ankylosis) lesions, which included localization (central vs lateral), extension (VC vs vertebral endplate), and extent (ie, the number of slices needed), whereas the new definitions were suggested for type of lesion according to lesion maturity (ie, VC monomorphic vs VC dimorphic). Of the lesions, the most reliably assessed were VC fat lesion and VC monomorphic BMO (intraclass correlation coefficient [mean of all 36 readers pairs/overall 9 readers]: 0.91/0.92 and 0/70/0.67, respectively).

The group concluded that their work resulted in “a consensus-based update of the definitions for spinal MRI lesions of patients referred with undiagnosed back pain and with clinical suspicion of axSpA.”

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Baraliakos X, Østergaard M, Lambert RG, et al. MRI lesions of the spine in patients with axial spondyloarthritis: an update of lesion definitions and validation by the ASAS MRI working group. Ann Rheum Dis. Published online May 24, 2022. doi:10.1136/annrheumdis-2021-222081