The non-diagnostic ultrasound in appendicitis: is a non-visualized appendix the same as a negative study?

PurposeThe purpose of this retrospective study was to investigate outcomes in children who underwent a non-diagnostic ultrasound (US) evaluating for appendicitis and to identify predictors of a negative diagnosis.MethodsAn IRB-approved retrospective chart review was performed on patients age 0–18, who underwent an abdominal US evaluating for acute appendicitis from 2004 through 2013. Clinical data and specified outcomes were recorded, and exams were categorized into non-diagnostic studies and further separated into studies where the appendix was non-visualized.ResultsOf the 1383 studies included for analysis, 876 were non-diagnostic for acute appendicitis (63.34%) with 777 specifically because the appendix was non-visualized. Seven hundred forty of the 876 non-diagnostic studies and 671 of the 777 non-visualized studies were ultimately considered true negatives, corresponding to a negative predictive value (NPV) of 84.47 and 86.36%, respectively. In patients with WBC < 7.5 × 109/L, the NPV of non-diagnostic and non-visualized studies increased to 97.12 and 98.86%, respectively. Patients with WBC < 11.0 × 109/L have similarly high NPVs of 95.59 and 96.99% (non-diagnostic and non-visualized).ConclusionBased on the high NPV of a non-diagnostic US in children without leukocytosis, these patients may safely avoid further diagnostic imaging for the workup of suspected appendicitis.