Seronegative spondyloarthropathy-related sacroiliitis: CT, MRI features and differentials.

Seronegative spondyloarthropathy is a group of chronic inflammatory rheumatic diseases that predominantly affect the axial skeleton. Involvement of sacroiliac joint is considered a hallmark for diagnosis of seronegative spondyloarthropathy and is usually the first manifestation of this condition. It is essential for the radiologist to know the computed tomography (CT) and magnetic resonance imaging (MRI) features of spondyloarthropathy-related sacroiliitis as imaging plays an important role in diagnosis and evaluation of response to treatment. We present a pictorial essay of CT and MRI imaging findings in seronegative spondyloarthropathy-related sacroiliitis in various stages and highlight common differentials that need to be considered.