When it is not sacroiliitis.

Magnetic resonance imaging of the sacroiliac joints (SIJ) is now frequently performed to detect subchondral inflammatory and structural changes in patients with early axial spondyloarthritis (SpA). However, similar changes can also occur in various other conditions, which may lead to the overdiagnosis of axial SpA. The aim of this article is to review the key imaging features of the most common disorders that may mimic inflammatory sacroiliitis, including mechanical changes and osteoarthritis, osteitis condensans ilii and pregnancy-related changes, other strain related changes, anatomical variants, pediatric SIJs, hyperostosis, infectious sacroiliitis, SAPHO syndrome, hyperparathyroidism, and sacral stress fractures.