Body mass index as a predictor of sonographic visualization of the pediatric appendix

Background: Appendicitis is a common condition that is often confirmed with imaging. Ultrasound (US) is recommended as the first radiologic test in the work-up of appendicitis in children. Increased body mass index (BMI) has been implicated as a limiting factor to the sensitivity of US. This has drastic public health ramifications, as pediatric obesity has been increasing at alarming rates. Objective: The purpose of this study is to compare age-adjusted BMI z-scores to the frequency of sonographic visualization of the appendix. Materials and methods: A retrospective review of 500 consecutive reports of US exams ordered for appendicitis in patients with a documented BMI was performed. Patients were stratified by BMI z-score based on, and the visualization frequency of the appendix was compared to the BMI z-score group. A logistic regression analysis generated the odds of visualization of the appendix by BMI z-score group. Primary home language, ethnicity, sex and insurance status were included in the logistic regression model to assess these characteristics as potential effect modifiers. Results: Of the 500 patients, 52.4% were male, 56.4% were Hispanic and 62.0% had government insurance. BMI z-score distribution groups were as follows: 4.2% were <−2, 8.0% were −2 to −1, 49.8% were −1 to 1, 26.4% were 1 to 2 and 11.6% were >2. The visualization frequency was 61.1% for boys and 46.2% for girls (P<0.05). Visualization frequency by BMI z-score group was as follows: 85.7% for <2, 72.5% for −2 to −1, 57.4% for −1 to 1, 47.7% for 1 to 2 and 29.3% for >2. Children with a BMI z-score greater than 2 were less likely to have a US with visualization of the appendix compared to children with a BMI z-score between −1 and 1 (adjusted odds ratio [aOR]: 0.21, 95% CI: 0.11–0.40, P<0.0001). Boys were more likely than girls to have a US with visualization of the appendix (aOR: 1.90, 95% CI: 1.29–2.80, P=0.001). There was no effect from insurance status, ethnicity or primary home language. Conclusion: Findings show that as the BMI z-score increased, sonographic visualization of the appendix decreased even after adjusting for demographic differences. These findings have implications for pediatric radiology practice in light of the worsening obesity epidemic.