Ankylosing Spondylitis (Radiographic Axial Spondyloarthritis)

Ankylosing spondylitis (AS) is a chronic seronegative spondyloarthropathy primarily affecting the axial skeleton, characterized by progressive inflammation, ossification, and eventual fusion of the spine and sacroiliac joints. This chapter provides a comprehensive overview of the radiological imaging modalities essential for the diagnosis, staging, and management of AS in musculoskeletal radiology. Beginning with radiography, which remains the cornerstone for detecting classic findings such as sacroiliitis, syndesmophytes, and bamboo spine, the discussion extends to advanced techniques including magnetic resonance imaging (MRI) for early detection of inflammatory changes like bone marrow edema and enthesitis. Computed tomography (CT) is explored for its role in assessing erosions, sclerosis, and ossification. Key imaging criteria from classification systems are reviewed, alongside pitfalls in interpretation and differential diagnoses.