Purpose or Case Report: Non-contrast magnetic resonance imaging (MRI) and ultrasound studies in pediatric patients with suspected appendicitis are often non-diagnostic. The primary objective of this investigation was to determine if combining these non-diagnostic imaging results with white blood cell (WBC) cutoffs improves their negative predictive values. The secondary objective was to determine the test characteristics of the fast, non-contrast MRI protocol used for suspected appendicitis.
Methods & Materials: A retrospective chart review was conducted including patients ≤ 18 years old with suspected appendicitis who had MRI performed with or without a preceding ultrasound study in a pediatric emergency department. Imaging results were sorted into 2 diagnostic and 5 non-diagnostic categories. Negative predictive values were calculated for the non-diagnostic MRI and ultrasound categories with and without combining them with WBC cutoffs of < 10.0 and < 7.5 × 10⁹/L. Sensitivity, specificity, predictive values, and likelihood ratios were calculated for the MRI protocol.
Results: Of the 612 patients with MRI studies included, 402 had ultrasound studies performed. MRI with incomplete visualization of a normal appendix without secondary signs of appendicitis had a negative predictive value of 97.9% that changed to 98.1% and 98.2% when combined with WBC cutoffs of < 10.0 and < 7.5, respectively. Ultrasound studies with incomplete visualization of a normal appendix without secondary signs had a negative predictive value of 85.3% that improved to 94.8% and 96.5% when combined with WBC cutoffs of < 10.0 and < 7.5, respectively. The MRI protocol, with equivocal results excluded (7.7% of studies), had a sensitivity of 94.9%, specificity of 99.6%, positive predictive value of 98.2%, negative predictive value of 98.7%, positive likelihood ratio of 212.5, and negative likelihood ratio of 0.05.
Conclusions: In pediatric patients with suspected appendicitis, MRI studies with incomplete visualization of a normal appendix without secondary signs have a high negative predictive value that does not significantly change with the use of these WBC cutoffs. In contrast, combining WBC cutoffs with ultrasound studies with the same interpretation identifies low-risk groups. The fast, non-contrast MRI protocol is limited by a high number of equivocal results, but demonstrated excellent test characteristics for the 92.3% of studies that were evaluable.

This research study has been published in The American Journal of Emergency Medicine. Citation: Kennedy TM, Thompson AD, Choudhary AK, Caplan RJ, Schenker KE, DePiero AD. Utility of applying white blood cell cutoffs to non-diagnostic MRI and ultrasound studies for suspected pediatric appendicitis. Am J Emerg Med, 2019 Sep;37(9):1723-1728.