Types and descriptions of structural changes
| Type | Description | Technical facts |
|---|---|---|
| Fatty deposition (figure 8) | ▶Replacement of bone marrow by fatty tissue | T1w: high signal intensity |
| ▶Frequently seen at vertebral corners and vertebral endplates, sometimes also at other sites, for example, zygoapophyseal joints, costovertebral joints and spinous processes | STIR: 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.