Determining the impact of body mass index on ultrasound accuracy for diagnosing appendicitis: Is it less useful in obese children?

Background: Ultrasonography (US) is the preferred imaging for suspected pediatric appendicitis. We hypothesize that children with elevated Body-Mass-Index-for-age percentile (BMIP) may be more likely to have an inaccurate or equivocal (IE) US.

Methods: After IRB approval, a four-year review was performed on pediatric patients evaluated for appendicitis by US. The CDC BMIP Calculator was used. IE subgroups were analyzed together for comparison against the accurate group.

Results: 1059 patients were included: median age 11.3 years (IQR: 8.2, 14.6), 506 (47.8%) males. Median BMIP was 65.9 (IQR: 33.9, 89.6). US accurately diagnosed 857 (80.9%), incorrectly diagnosed 76 (7.2%), 126 (11.9%) were equivocal. Overall sensitivity was 0.85, specificity 0.96, PPV 0.93 and NPV 0.91. Obese children (BMIP ≥95%), had higher odds of IE US (OR: 1.86, 95% CI: 1.28, 2.70; p = 0.001). When analyzed by sex, risk increased in obese males (OR: 2.55, 95% CI:1.53, 4.24; p = 0.0003) but normalized in obese females (OR: 1.30, 95% CI:0.74, 2.28; p = 0.35).

Conclusions: An elevated BMIP may increase difficulty in visualizing the appendix, resulting in inaccurate or equivocal findings. This risk is seen specifically in obese males. If US findings do not correlate with clinical assessment in obese children with abdominal pain, further evaluation may be warranted.