The effect of abdominal pain duration on the accuracy of diagnostic imaging for pediatric appendicitis

Study objective: Advanced imaging with computed tomography (CT) or ultrasonography is frequently used to evaluate for appendicitis. The duration of the abdominal pain may be related to the stage of disease and therefore the interpretability of radiologic studies. Here, we investigate the influence of the duration of pain on the diagnostic accuracy of advanced imaging in children being evaluated for acute appendicitis. Methods: A secondary analysis of a prospective multicenter observational cohort of children aged 3 to 18 years with suspected appendicitis who underwent CT or ultrasonography was studied. Outcome was based on histopathology or telephone follow-up. Treating physicians recorded the duration of pain. Imaging was coded as positive, negative, or equivocal according to an attending radiologist's interpretation. Results: A total of 1,810 children were analyzed (49% boys, mean age 10.9 years [SD 3.8 years]); 1,216 (68%) were assessed by CT and 832 (46%) by ultrasonography (238 [13%] had both). The sensitivity of ultrasonography increased linearly with increasing pain duration (test for trend: odds ratio=1.39; 95% confidence interval 1.14 to 1.71). There was no association between the sensitivity of CT or specificity of either modality with pain duration. The proportion of equivocal CT readings significantly decreased with increasing pain duration (test for trend: odds ratio=0.76; 95% confidence interval 0.65 to 0.90). Conclusion: The sensitivity of ultrasonography for appendicitis improves with a longer duration of abdominal pain, whereas CT demonstrated high sensitivity regardless of pain duration. Additionally, CT results (but not ultrasonographic results) were less likely to be equivocal with longer duration of abdominal pain.