Classification of CT Pulmonary Opacities as Perifissural Nodules: Reader Variability

Abstract

Purpose To study interreader variability for classifying pulmonary opacities at CT as perifissural nodules (PFNs) and determine how reliably radiologists differentiate PFNs from malignancies. Materials and Methods CT studies were obtained retrospectively from the National Lung Screening Trial (2002-2009). Nodules were eligible for the study if they were noncalcified, solid, within the size range of 5 to 10 mm, and scanned with a section thickness of 2 mm or less. Six radiologists classified 359 nodules in a cancer-enriched data set as PFN, non-PFN, or not applicable. Nodules classified as not applicable by at least three radiologists were excluded, leaving 316 nodules for post-hoc statistical analysis. Results The study group contained 22.2% cancers (70 of 316). The median proportion of nodules classified as PFNs was 45.6% (144 of 316). All six radiologists uniformly classified 17.7% (56 of 316) of the nodules as PFNs. The Fleiss κ was 0.50. Compared with non-PFNs, nodules classified as PFNs were smaller and more often located in the lower lobes and attached to a fissure (P < .001). Thirteen (18.6%) of 70 cancers were misclassified 21 times as PFNs. Individual readers' misclassification rates ranged from 0% (0 of 125) to 4.9% (eight of 163). Of 13 misclassified malignancies, 11 were in the upper lobes and two were attached to a fissure. Conclusion There was moderate interreader agreement when classifying nodules as perifissural nodules. Less than 2.5% of perifissural nodule classifications were misclassified lung cancers (21 of 865) in this cancer-enriched study. Allowing nodules classified as perifissural nodules to be omitted from additional follow-up in a screening setting could substantially reduce the number of unnecessary scans; excluding perifissural nodules in the upper lobes would greatly decrease the misclassification rate.

Association between the number and size of intrapulmonary lymph nodes and chronic obstructive pulmonary disease severity

“…All radiologists were familiar with the morphology of PFNs as described in the literature ( Ahn et al, 2010 ; De Hoop et al, 2012 ; Mets et al, 2018 ; Schreuder et al, 2018 ). Non-calcified solid nodules with sharp margins and an oval or polygonal shape were eligible as PFNs.…”

“…In an attempt to accurately identify benign intrapulmonary lymph nodes from malignant pulmonary nodules on CT, some of these typical lymph node features were used to define the perifissural nodule (PFN), a purely radiologic classification ( Ahn et al, 2010 ; De Hoop et al, 2012 ; Mets et al, 2018 ; Schreuder et al, 2018 ). On the premise that more pulmonary inflammation leads to more identifiable intrapulmonary lymph nodes, we hypothesized that more and larger PFNs would be detected as the COPD severity increases.…”

CT Diagnosis and Management of Focal Lung Disease

“…They characteristically have a lentiform, triangular, or polygonal shape with 1-3 interlobular septal extensions and are located on or within 10 mm of the visceral . In a recent study, there was moderate inter-reader agreement when classifying nodules as perifissural nodules [4]. Under the revised 2017 Fleischner Society guidelines for management of incidentally detected pulmonary nodules on CT, a PFN with a morphology consistent with an intrapulmonary lymph node does not require follow-up CT, even if the average dimension exceeds 6 mm [5].…”

Consistency of radiologists in identifying pulmonary nodules based on low-dose computed tomography

“…There were a few studies dealing with the inter-reader variability of pulmonary nodules on CT screening (10)(11)(12). Inter-observe variability performance for the detection of pulmonary nodules has been found to be relatively high with both standard-dose and LDCT (13).…”