Objective: The purpose of this study was to characterize the normal pediatric appendix and the variables that affect its diameter.
Materials and methods: Imaging and medical records, including CT studies, from 420 unique patients with normal appendixes were reviewed by two pediatric radiologists. Appendiceal diameter was measured on the axial images, and appendiceal content and the presence of enlarged lymph nodes were recorded.
Results: The mean appendiceal diameter was 5.6 ± 1.4 and 5.7 ± 1.5 mm for reviewer 1 and reviewer 2, respectively, with 34% and 39% of appendixes measuring larger than 6 mm. Appendiceal diameter was normally distributed across the population and was significantly associated with patient age (p < 0.0001). Diameter increased by 0.4 mm/y until 6-7 years of age, after which, it remained stable. The quantity of pericecal fat (p = 0.03 and p < 0.0001) and type of appendiceal content (p = 0.0002 and p < 0.0001), respectively, were multivariate predictors of diameter. Lymphoid stimulation was a multivariate predictor of diameter for only one reviewer (p = 0.0008). Patient sex and the month or season of imaging were not predictors of diameter.
Conclusion: Uniform diameter cutoffs for appendiceal diameter should not be applied across the pediatric population because the appendix grows during childhood. Additionally, this study calls into question a 6-mm diameter cutoff for appendicitis. Normal pediatric appendixes measure up to 8.7 mm, with up to 39% measuring more than 6 mm in diameter. Nonpathologic factors, including pericecal fat, appendiceal content, and presence of lymphoid stimulation, influence appendiceal diameter in healthy children.