Inflammatory and chronic structural changes are objective signs of axial spondyloarthritis. In the sacroiliac joints (SIJs), inflammation (sacroiliitis) can be visualized as bone marrow edema, whereas chronic structural changes are visualized as fat metaplasia, erosions, sclerosis, or ankylosis in the area of the SIJ. In the spine, bone marrow edema in the vertebral bodies represents spondylitis but can also affect the facet and the costovertebral and costotransverse joints (arthritis), whereas structural changes are visualized as fat metaplasia, sclerosis or syndesmophytes and ankylosis at the vertebral edges.