Clinics in diagnostic imaging (70). Bilateral sacroiliitis due to ankylosing spondylitis.

A 15-year-old boy was incidentally found to have bilateral sacroiliitis. Radiographs showed erosions and subchondral sclerosis of both sacroiliac joints. His ESR was raised and HLA-B27 was positive. Presumptive diagnosis was ankylosing spondylitis. The clinical and imaging features, including the radiographical classification, of sacroiliitis are discussed. Knowledge of the patterns of distribution and correlation with clinical manifestations aid in differentiating among the various causes of sacroiliitis.