Pneumothorax size measurements on digital chest radiographs: Intra- and inter- rater reliability

•This study shows that Rhea’s method for calculating pneumothorax size in three measurement points from digital chest X-rays has high intrarater and interrater reliability (reliability coefficients of 0.98 and 0.95 respectively).•The results are valid across gender, side of pneumothorax and whether the patient is diagnosed with primary or secondary pneumothorax.•Current guidelines are divergent on approach to pneumothorax size, with a low grade of evidence grade on this matter. Reliable methods to describe pneumotorax size is crucial, to clearifyif size matters, then guide the clinician’s choice of treatment for the individual patient.

PurposeDetailed and reliable methods may be important for discussions on the importance of pneumothorax size in clinical decision-making. Rhea’s method is widely used to estimate pneumothorax size in percent based on chest X-rays (CXRs) from three measure points. Choi’s addendum is used for anterioposterior projections.The aim of this study was to examine the intrarater and interrater reliability of the Rhea and Choi method using digital CXR in the ward based PACS monitors.Materials and methodsThree physicians examined a retrospective series of 80 digital CXRs showing pneumothorax, using Rhea and Choi’s method, then repeated in a random order two weeks later. We used the analysis of variance technique by Eliasziw et al. to assess the intrarater and interrater reliability in altogether 480 estimations of pneumothorax size.ResultsEstimated pneumothorax sizes ranged between 5% and 100%. The intrarater reliability coefficient was 0.98 (95% one-sided lower-limit confidence interval C 0.96), and the interrater reliability coefficient was 0.95 (95% one-sided lower-limit confidence interval 0.93).ConclusionThis study has shown that the Rhea and Choi method for calculating pneumothorax size has high intrarater and interrater reliability. These results are valid across gender, side of pneumothorax and whether the patient is diagnosed with primary or secondary pneumothorax.