The proposed sequence of inflammation, repair, and new bone formation in axial spondyloarthritis

Inflammatory affection of the bone marrow in axSpA (bone marrow edema/osteitis on MRI [arrows]) is normally detected by an MRI-STIR sequence, but lower levels of inflammation might remain undetected by the currently available imaging techniques. This is usually followed by the repair process and bone marrow replacement by granulation repair tissue that might appear (but not always) as a fatty lesion on MRI (dashed arrows). Finally, the process of new bone formation starts in the areas of active repair that gives rise to syndesmophytes (circle). Under some circumstances (eg, early antiinflammatory treatment), resolution of inflammation is possible without subsequent new bone formation.