Open-Access 12-Minute MRI Screening for Acute Appendicitis: A Five-Year Retrospective Observational Study of Diagnostic Accuracy

Objective: This retrospective observational diagnostic accuracy study aims to demonstrate that open-access rapid-sequence non-contrast magnetic resonance imaging (MRI) is accurate for exclusion or confirmation of appendicitis. Methods: In 2017 a locally designed 12-minute MRI protocol was made available as a new open-access option (no booking needed) for any emergency department (ED) or acute surgical patient with any clinical presentation at the authors’ sites. Uninterrupted single radiologist reporting availability was provided. A 5-year consecutive report list from January 1, 2019 to December 31, 2023 was recorded in an activity log, from which 3,478 eligible reports were identified as ED-based referrals assessing for possible appendicitis. There was “appendicitis possibility” in 581/3,478 (17%) reports and “no evidence of appendicitis” in 2897/3,478 (83%). These were retrospectively reviewed and compared with medical record findings of 557/3,478 proven cases of appendicitis (16%). Report availability and reliability metrics have been assessed. Results: Overall, 2,583/3,478 reports (74%) were finalized within 2 hours of MRI study completion, 3,254/3,478 (94%) within 4 hours. The 3,478 reports combined had 98% sensitivity, 98% specificity, 98% accuracy, 94% positive predictive value, and 99% negative predictive value for appendicitis. The largest subgroup, 15–19-year-old females—with proven appendicitis in 66/440, had 98% accuracy. Pregnant women within this series, 21/171 with proven appendicitis, had 99% report accuracy. Conclusions: The described MRI protocol is accurate for appendicitis assessment and is a suitable first-imaging choice for children, young adults, and pregnant women. It does not require intravenous contrast and poses no radiation risk.