Purpose or Case Report: We sought to determine factors associated with sonographic non-visualization of the appendix in patients being evaluated for appendicitis.
Methods & Materials: We retrospectively identified all appendix ultrasound (US) studies performed on patients younger than 19 between 2012 and mid 2019. The studies were performed by dedicated pediatric sonographers and/or radiologists. Standardized radiology report impressions were classified by pattern matching into four categories: found (e.g. reported as appendicitis or appendix identified, normal, or partially seen), not found (e.g. reported as not seen, limited, or nondiagnostic), status post appendectomy, or unclassifiable. The latter two categories were excluded. Demographic factors, time of day of exam performance, weight (and when available, body mass index {BMI}) were recorded for the encounter +/- 90 days. Univariate and multivariate association and logistic regression analyses were performed.
Results: We identified 11,320 patients (6,437 female) with an appendix-focused US and recorded weight. Overall, 6,743 appendices were found; 4,577 were not found; 25 were post appendectomy, searching for abscess; and 430 were unclassified. We found 6,718 of 11,067 appendices (61%) in patients weighing less than 95 kg and 25 of 253 (10%) in patients weighing more. In 2,235 patients with BMI available, we found 1,138 of 2,111 (54%) appendices in BMI less than 30 and 14 of 124 (11%) in BMI greater than 30. Increasing patient age and weight and female gender were all significantly associated with appendix nonvisualization (p<0.0001), but the effect sizes were small (AUC between 0.52 and 0.58). On univariate analysis weight was significantly associated with not finding the appendix (odds ratio {OR} 1.03 {95% CI 1.02-1.02}). In multivariate analysis, weight more than 95 kg (OR 9.6 {95% CI 6.45-14.94}), age (OR 1.07 {95% CI 1.06-1.08}), and female gender (OR 1.52 {95% CI 1.41-1.65}) were significantly associated with nonvisualization of the appendix. The percentage visualization of the appendix was 69%, 67%, and 59% for day, evening, and overnight shifts, respectively (p<0.0001).
Conclusions: Older, heavier, and female patients are more likely to have an appendix ultrasound that fails to demonstrate the appendix or show positive secondary signs. The working shift also affects the rate of appendix visualization. Consideration should be given to alternate modalities when there is clinical concern for appendicitis in patients weighing over 95 kg, especially overnight.