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

: 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 acute appendicitis (AA). : In 2017, a locally designed 12 min 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 1 January 2019 to 31 December 2023 was recorded in an activity log, from which 3478 eligible reports were identified as ED-based referrals assessing for possible AA. There was "appendicitis possibility" in 581/3478 (17%) reports and "no evidence of appendicitis" in 2897/3478 (83%). These were retrospectively compared with the medical record findings of 557/3478 proven cases of AA (16%). Report availability and reliability metrics have been assessed. : Overall, 2583/3478 reports (74%) were finalized within 2 h of MRI study completion, 3254/3478 (94%) within 4 h. The 3478 reports combined had 98% sensitivity, 98% specificity, 98% accuracy, 94% positive predictive value, and 99% negative predictive value for AA (φ = 0.95). The largest 5-year subgroup, females 15-19 years old, 66/440 with proven AA, had 98% report accuracy. Pregnant women, 21/171 with proven AA, had 99% report accuracy. : 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.