Table 3

Types and descriptions of structural changes

TypeDescriptionTechnical facts
Fatty deposition (figure 8)▶Replacement of bone marrow by fatty tissueT1w: high signal intensity
▶Frequently seen at vertebral corners and vertebral endplates, sometimes also at other sites, for example, zygoapophyseal joints, costovertebral joints and spinous processesSTIR: low signal intensity
▶Including aFAT* and pFAT*
Erosions (figure 8)▶Disruption of cortical line▶T1w: hypointense
▶Occur at endplates and vertebral corners, sometimes also at other sites such as zygoapophyseal joints, costovertebral joints and spinous processes▶STIR: hypointense
▶Including COBE*, NOBE* and FABE*
Syndesmophytes▶Bony outgrowth at anterior, posterior or lateral corners of vertebral bodies▶T1w: isointense to normal bone marrow or hyperintense (in case of fatty marrow degeneration)
▶Does not reach the adjacent vertebra▶STIR: isointense to normal bone marrow
▶Origin of growth at attachment site of annulus fibrosus
▶Including COS* and NOS*
Ankylosis (figure 9)▶Bony fusion through the disc or/and at the attachment sites of the annulus fibrosus (bridging syndesmophytes)
▶Bony fusion of apophyseal or costovertebral joints may occur
▶Including CANK*, NANK* and FANK*
  • Each of the structural lesions described must be visible in at least two or more consecutive sagittal slices.

  • * Abbreviations of the Canada–Denmark MRI in ankylosing spondylitis working group48 are given for reference.

  • aFAT, anterior corner fat infiltration; CANK, corner ankylosis; COBE, corner bone erosion; COS, corner spur; FABE, facet joint bone erosion; FANK, facet joint ankylosis; NANK, non-corner ankylosis; NOBE, non-corner bone erosion; NOS, non-corner spur; pFAT, posterior corner fat infiltration; STIR, short τ inversion recovery.