Purpose or Case Report: Ultrasound is often the initial imaging modality in evaluation for pediatric appendicitis, but there is concern that the increasing prevalence of pediatric obesity may affect both the sensitivity of ultrasound and the interpretation of an equivocal result. We hypothesized that higher BMI percentile would correlate with lower ultrasound sensitivity, higher equivocal rate, and higher rate of CT acquisition.

Methods & Materials: A retrospective review of consecutive ultrasounds for suspected appendicitis over three months at a dedicated pediatric healthcare institution was performed. Patients without weight and height recorded within two weeks of their exam were excluded. Patients were designated as underweight, healthy weight, overweight or obese according to CDC guidelines. Studies were reported as positive, negative (normal appendix), or equivocal (with low, moderate, or high suspicion) using a predefined rubric. Equivocal low suspicion was reserved for non-visualization of the appendix or normal appearance of a partially visualized appendix without secondary signs of appendicitis. Data regarding ultrasound result, CT acquisition, appendectomy, and pathology was obtained from the medical record.

Results: 499 ultrasounds on patients ranging in age from 12 months to 18 years were reviewed. Sensitivity of ultrasound for appendicitis in underweight, healthy weight, overweight, and obese patients was 94%, 72%, 80%, and 48%, respectively. Equivocal ultrasound rates for these groups were 18%, 48%, 48%, and 75%. Percentages of equivocal low suspicion results for which an ultimate diagnosis of appendicitis was made were 0%, 8%, 14%, and 13%. Of the patients with equivocal low suspicion results that had a final diagnosis of appendicitis, 65% (13) were greater than the 90th percentile for BMI, and 95% (19) were greater than the 50^th percentile for BMI. There was no apparent correlation between BMI percentile and CT acquisition for equivocal results.

Conclusions: Decreased ultrasound sensitivity and higher equivocal ultrasound rate for appendicitis is observed in obese pediatric patients. Furthermore, an equivocal low suspicion result may be insufficient to exclude appendicitis in this population, as there are higher rates of subsequently diagnosed appendicitis. For underweight patients, the high negative predictive value of an equivocal low suspicion result may provide reassurance to the clinician. Without high suspicion of an alternate emergent diagnosis, CT utilization in these cases may be unwarranted.