Figure 3: A case with changes from unilateral to bilateral sacroiliitis in a 25-year-old male with 1–3 years history of suspected spondyloarthropathy. (a) The initial CT shows unilateral sacroiliitis with subtle erosions in the left sacroiliac joint on the iliac side, with surrounding mild inflammatory sclerosis. On the right, there is poor definition of the subchondral cortical bone. (b) Seven years later, there is progression to definite bilateral sacroiliitis.