Sacroiliitis in Axial Spondyloarthritis: Assessing Morphology and Activity.

Objective:  To review the strengths, limitations, and new insights in the anatomy and magnetic resonance imaging (MRI) features of active and structural lesions of sacroiliitis in spondyloarthritis.

Discussion:  MRI plays a key role in the diagnosis and follow-up of sacroiliitis in spondyloarthritis. MRI of the sacroiliac joints in affected patients may show active lesions such as bone marrow edema, capsulitis, enthesitis, or synovitis as well as structural changes such as erosion, fat infiltration, sclerosis, backfill, and ankylosis. Active lesions of sacroiliitis on MRI are particularly important for the diagnosis and assessment of ongoing active inflammation. Structural lesions increasingly gain importance for diagnosis and follow-up.

Conclusion:  Active lesions remain the hallmark for assessment of inflammation in sacroiliitis. Structural lesions increasingly play a role in the diagnosis of spondyloarthritis.