Appendiceal ultrasound: the importance of determinacy

Abstract

"The first job of the radiologist is to minimize doubt."-William E. Shiels, 1954Shiels, -2015 We appreciate the thoughtful comments of Drs. Trout and Larson [1] concerning our article in this issue of Pediatric Radiology and the opportunity to further this discussion with a few additional thoughts. There are striking similarities between our two studies with respect to design and results but there are substantial differences in the conclusions drawn [2,3].Patients referred for US evaluation for acute appendicitis have already been stratified into an indeterminate risk group based on their clinical data. Those thought to have a very high probability of acute appendicitis may be sent directly to surgery and those thought to have a very low probability of appendicitis often are not imaged at all. It is for those patients whose probability of acute appendicitis is indeterminate that clinicians seek our help with US imaging. When clinicians order an imaging test to assist in establishing or excluding the diagnosis of acute appendicitis, they should know the likelihood that the test will provide a determinate result and how accurate that result will be. We presented our appendiceal US data in two ways so as to clearly provide this information to our clinicians. The intention-to-diagnose analysis categorizes indeterminate results as missed cases based on the final outcome. Contrary to Trout and Larson's statement, this analysis is specifically endorsed by Fedko et al. [4] because it allows for "transparent reporting of all results and determination of diagnostic yield" and likelihood ratios and informs physicians what proportion of appendiceal US examinations will not yield determinate results. The intention-to-diagnose method does underestimate measures of the diagnostic performance of US such as accuracy and sensitivity for the determinate results. To account for this, we performed a second analysis using the standard binary approach that excludes indeterminate studies because this analysis relates to clinicians the accuracy of appendiceal US when a determinate result is given.In our opinion, indeterminate results do not yield useful information. Trout and Larson think they do. They assert that indeterminate results reflect a range of probabilities that a given patient has appendicitis and that this information is meaningful to clinicians. While we did find a narrow range of prevalences of appendicitis in our three indeterminate groups, we disagree that this information is clinically useful. Our findings do not support their assertion on two grounds.