<p><strong>OBJECTIVE: </strong>Magnetic resonance imaging (MRI) is pivotal in the assessment of early sacroiliitis in children. We aimed to evaluate the agreement between local radiology reports and central imaging reviewers for active inflammation and structural damage at the sacroiliac joints (SIJs).</p>

<p><strong>METHODS: </strong>Eight hospitals each contributed up to 20 cases of consecutively imaged children and adolescents with juvenile idiopathic arthritis and suspected sacroiliitis. Studies were independently reviewed by 3 experienced musculoskeletal pediatric radiologists. Local assessments of global impression and lesions were coded from the local radiology reports by two study team members. Test properties of local reports were calculated using the central imaging team's majority as the reference standard.</p>

<p><strong>RESULTS: </strong>For 120 evaluable subjects, median age was 14 years, half of cases were male, and median disease duration at time of imaging was 0.8 years (IQR: 0-2). Sensitivity, 93.5% (95% CI: 78.6-99.2%), and specificity, 69.7% (95% CI: 59.0-79.0%), of local reports for inflammation were high and moderate, respectively, but positive predictive value (PPV) was low 51.8% (95% CI: 38.0-65.3%). Twenty-seven (23%) cases had active inflammation reported locally but rated normal centrally, nineteen (70%) with subsequent medication changes. Sensitivity of local reports detecting structural damage was low, 45.7% (95% CI: 28.8-63.4%), and specificity, 88.2% (95% CI: 79.4-94.2%), was high; PPV was low 61.5% (95% CI: 40.6-79.8%).</p>

<p><strong>CONCLUSION: </strong>Substantial variation exists in the interpretation of inflammatory and structural lesions at the SIJs in children. In order to reliably identify pathology, additional training in the MR appearance of the maturing SIJ is greatly needed.</p>