Fig. 2

Samples of discordant radiograph and MRI overall impressions of presence/absence of sacroiliitis. a and b) 16-year-old HLA-B27+ male with 2 months of hamstring, gluteal, and low back pain. (a) Radiograph – normal (no sacroiliitis) by 5/5 raters; two raters noted sclerosis. (b) MRI STIR – abnormal (sacroiliitis present) rated by 5/5 raters; bilateral sacral subchondral bone marrow edema is clearly present. Two raters reported a positive erosion finding and 3 raters reported a positive sclerosis finding. (c and d) 13-year-old HLA-B27 negative female with lower and mid-back pain with accompanying morning stiffness, acute uveitis, and multiple tender entheses. (c) Radiograph – rated abnormal (sacroiliitis present) by 5/5 raters; two raters reported a positive finding for erosion, two reported a finding of joint space narrowing, and all five raters reported sclerosis. (d) MRI STIR – rated as normal (no sacroiliitis) by 5/5 raters; no abnormalities (erosion, sclerosis, fat metaplasia, ankylosis, or backfill) were reported on MRI. Radiologist raters were blinded to patient clinical details and are included here to provide the reader with relevant medical history