Pearls and pitfalls in imaging of axial spondyloarthritis for rheumatologists.

This review provides key insights into sacroiliitis imaging, covering anatomy, imaging techniques, and interpretation. It focuses on normal physiological changes in young to middle-aged women, children, and the elderly that can resemble sacroiliitis. We emphasize the importance of distinguishing between active and structural lesions, as highlighted in the recent ASAS-SPARTAN standardized magnetic resonance imaging protocol. Physicians should be aware that bone marrow oedema signals on magnetic resonance imaging, a hallmark of active inflammation in axial spondyloarthritis, can also be observed in young to middle-aged women, especially postpartum, even without spondyloarthritis. Paediatric sacroiliac joints may show changes mimicking inflammation due to ongoing bone growth. Furthermore, degenerative changes in the sacroiliac joint are common with advancing age and can be mistaken for sacroiliitis or interpreted as structural changes. The presence of accessory sacroiliac joints, prone to degeneration, further complicates diagnosis. Accurate interpretation requires considering these normal variations to avoid misdiagnosing spondyloarthritis. Collaboration between clinicians and radiologists is crucial, especially when encountering atypical or clinically inconsistent findings.