Table 1.

Imaging findings of active and chronic changes of the sacroiliac joint and spine in axial spondyloarthritis.

	Sacroiliac joint	Spine
Active changes	• Bone marrow edema/osteitis • Inflammation at the site of erosion • Synovitis and synovial proliferation • Intra-articular fluid collection • Capsulitis • Enthesitis	• Spondylitis (anterior or posterior corner inflammatory lesions) and enthesitis* • Asseptic spondylodiscitis (Andersson lesion) • Zygoaphophyseal/facet joint arthritis • Costovertebral and costo-transverse joint arthritis • Inflammation of other vertebral elements (e.g., pedicles and spinous processes) • Inflammation of spinal ligaments
Chronic changes	• Cortical bone erosions and pseudo-widening of joint space • Joint space narrowing • Subchondral sclerosis • Fat depositions/collections (including fat deposition in an erosion cavity, also known as “backfill”) • Ankylosis/bone bridging • Juxta-articular osteoporosis	• Syndesmophytes • Ankylosis/bone bridging • Ligament calcifications • Erosions • Sclerotic changes • Fat deposition on vertebral corners and other previously inflamed bone marrow • Osteopenia

^*The terms “Romanus spondylitis” and “shiny corners” have been used in the context of MRI assessment but should be avoided as they were initially described in plain radiographs: “Romanus spondylitis” appears as irregularity and erosion involving the anterior and posterior corners/edges of the vertebral endplates, while “shiny corners” represent reactive sclerosis secondary to inflammatory process.