Secondary imaging for suspected appendicitis after equivocal ultrasound: time to disposition of MRI compared to CT

James F. Martin, David J. Mathison, Paul C. Mullan, Hansel J. Otero

The purpose of this study was to compare MRI to CT as a secondary imaging modality for children age 5 years and older with suspected appendicitis after an equivocal abdominal ultrasound in terms of (1) the time to ED disposition decision, (2) surgery consultation rate, and (3) imaging test accuracy. We retrospectively studied children with suspected appendicitis and equivocal ultrasound results who underwent MR or CT as secondary imaging in a pediatric emergency department over two-consecutive 9-month periods. No oral or intravenous contrast was utilized for MRI. No sedation was utilized for any modality. Time of disposition is the time to admission or discharge order. Twenty-five patients underwent CT and 30 underwent MRI, with no significant difference in the median time from ultrasound to disposition between the CT (5.9 h, IQR 4.5, 8.4) and the MRI (5.9 h, IQR 4.6, 6.9) groups (p = 0.65). Fifteen patients had appendicitis. Of the 40 negative or equivocal studies, surgery was consulted for 79% in the CT and 48% in the MRI group (odds ratio 4.12, 95% CI 1.02-16.67). Diagnostic accuracy was as follows: MRI: sensitivity of 90%, specificity of 97.1%, positive predictive value of 90%, and negative predictive value of 97.1%. Abdominal CT: sensitivity of 88%, specificity of 98.6%, positive predictive value of 95.7%, and negative predictive value of 95.8%. MRI is a feasible alternative to CT for secondary imaging in acute appendicitis for showing comparable ED throughput metrics and diagnostic accuracy, with added benefits of reduced radiation and avoidance of intravenous contrast.