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.