Intra- and inter-reader variability of pulmonary nodule classification according to the Fleischner guidelines: clinical consequences

PURPOSE Recently published recommendations by the Fleischner Society differentiate between non-solid and partsolid nodules. For the latter follow up or invasive diagnostic procedures are recommended depending on the size of the solid core. For solid nodules, different recommendations apply. We evaluated inter- and intra-reader variability of nodule classification and the impact on patient management. METHOD AND MATERIALS 20 part-solid, 10 non-solid and 10 solid nodular lesions were randomly selected from the NELSON screening trial. Data had been acquired using a low dose (16x0.75mm, 120-140 kVp, 30 mAs) protocol. Complete CTs were shown with axial and coronal projections with 1mm section thickness. Readers could interactively scroll through the scans, use magnification, windowing and manual calibre measurements as warranted. Four readers of varying experience were asked to classify the lesions as solid (1), part-solid with a core > 5mm and < 5mm, respectively (2 and 3), or as non-solid (4). All readings were done twice in six sessions, in which all permutations of nodules and section thicknesses were presented in different random orders. Inter- and intra-reader agreement were calculated using CohenAC/a,!a,,C/s kappa statistics. To evaluate possible consequences on patient management, the number of differences between assigned scores of 1 or 2 (invasive diagnosis) and scores of 3 or 4 (follow up) were calculated. All results stated are averaged over all reading sessions. RESULTS Inter-reader agreement was low with mean kappa of 0.33 (range 0.02-0.58). Intra-reader agreement was moderate with mean kappa 0.54 (range 0.31-0.72). Patient management would have differed in 27% caused by interreader disagreement, and would have changed in 8% caused by intrareader variability. 28% of all nodules were uniformly classified over all reading sessions. Of these, 18% were classified as solid and 73% as non-solid. CONCLUSION Inter- and intra-reader agreement are low and moderate for the classification of pulmonary nodules according to Fleischner criteria if pure visual analysis is used. This may affect patient management. CLINICAL RELEVANCE/APPLICATION Variability in nodule classification may have consequences on patient management; use of digital analysis tools appears to be necessary to improve classification.