Abstract
Ankylosing spondylitis (AS) is a chronic inflammatory disease affecting the spine and the sacroiliac joints. AS occurs with the inflammation of the entheses and formation of syndesmophytes and finally sacral and spinal ankylosis. Imaging demonstrates both inflammatory and chronic lesions. Sacroiliitis is the hallmark of the disease. Spinal changes usually take place in advanced stages of the disease. 1984 The Modified New York criteria evaluated for the diagnosis of AS with definite radiological sacroiliitis (bilaterally grade 2 or unilateral grade 3/4 sacroiliitis) on imaging. The Modified New York criteria are well performed in diagnosing the established disease but its sensitivity is too low in early disease identification and leads to a diagnostic delay. So, in 2009 The Assessment in Spondyloarthritis International Society (ASAS) recommended classification criteria for axial spondyloarthritis (axSpA). Patients have sacroiliitis on imaging and ≥1 SpA features (imaging arm) or positive HLA B27 and ≥2 SpA features (clinical arm) are classified as axial SpA. On the imaging arm, either radiographic sacroiliitis according to Modified New York criteria or active inflammation on MRI is required. Imaging is also used for determining extent of disease, monitoring activity and progression of the disease, assessment of the treatment effect, and prognosis in AS patients.