Pelvic MRI findings of juvenile-onset ankylosing spondylitis

Ankylosing spondylitis (AS) is the most common clinical subgroup of sero-negative spondyloarthropathies. Radiographic and clinical signs of bilateral inflammatory involvement of sacroiliac joints are the gold standard for the diagnosis of juvenile AS. Although radiographic evidence of sacroiliitis is included in the definition, it is not mandatory for the diagnosis of juvenile AS. The aim of this study is to describe pelvic enthesitis–osteitis MRI findings accompanying sacroiliitis in a group of juvenile AS. Eleven patients suffering from low back pain underwent MRI of the pelvis and were enrolled in this retrospective study. The mean duration of symptoms was 12 months. The mean age of the 11 cases in our study was 12.18 years (range, 6–19). There were eight boys and three girls. Anteroposterior radiographs of the pelvis were obtained in all patients. Sacroiliac joint involvement was detected in all of the cases by pelvic MRI. Pathologic signal changes were detected in the pubic symphisis (osteitis pubis) in ten cases, trochanteric bursitis in six cases, coxofemoral joint in five cases, crista iliaca in three cases, and ischion pubis in three cases. There was increased T2 signal intensity in eight of the 11 cases (72.7%) relevant with soft tissue edema/inflammation. This high correlation between sacroiliitis and enthesitis suggests that enthesitis could be an important finding in juvenile AS.