Observer agreement and clinical significance of chest CT reporting in patients suspected of COVID-19

Abstract

Objectives: To assess interobserver agreement and clinical significance of chest CT reporting in patients suspected of COVID-19.

Methods: From 16 to 24 March 2020, 241 consecutive patients addressed to hospital for COVID-19 suspicion had both chest CT and SARS-CoV-2 RT-PCR. Eight observers (2 thoracic and 2 general senior radiologists, 2 junior radiologists, and 2 emergency physicians) retrospectively categorized each CT into one out of 4 categories (evocative, compatible for COVID-19 pneumonia, not evocative, and normal). Observer agreement for categorization between all readers and pairs of readers with similar experience was evaluated with the Kappa coefficient. The results of a consensus categorization were correlated to RT-PCR.

Results: Observer agreement across the 4 categories was good between all readers (κ value 0.61 95% CI 0.60-0.63) and moderate to good between pairs of readers (0.54-0.75). It was very good (κ 0.81 95% CI 0.79-0.83), fair (κ 0.32 95% CI 0.29-0.34), moderate (κ 0.56 95% CI 0.54-0.58), and moderate (0.58 95% CI 0.56-0.61) for the categories evocative, compatible, not evocative, and normal, respectively. RT-PCR was positive in 97%, 50%, 31%, and 11% of cases in the respective categories. Observer agreement was lower (p < 0.001) and RT-PCR positive cases less frequently categorized evocative in the presence of an underlying pulmonary disease (p < 0.001).

Conclusion: Interobserver agreement for chest CT reporting using categorization of findings is good in patients suspected of COVID-19. Among patients considered for hospitalization in an epidemic context, CT categorized evocative is highly predictive of COVID-19, whereas the predictive value of CT decreases between the categories compatible and not evocative.

Key points: • In patients suspected of COVID-19, interobserver agreement for chest CT reporting into categories is good, and very good to categorize CT "evocative." • Chest CT can participate in estimating the likelihood of COVID-19 in patients presenting to hospital during the outbreak, CT categorized "evocative" being highly predictive of the disease whereas almost a third of patients with CT "not evocative" had a positive RT-PCR in our study. • Observer agreement is lower and CTs of positive RT-PCR cases less frequently "evocative" in presence of an underlying pulmonary disease.

Keywords: Coronavirus infections; Pneumonia; Tomography, X-ray computed.

Fig. 1

Flow chart of the study. SARS-CoV-2 RT PCR and chest CT were performed at presentation, except in 7 cases for which RT-PCR had been performed 1 to 3 days earlier. Among 158 COVID-19 confirmed cases, RT-PCR was positive at admission in 151 cases and in subsequent days during hospitalization in 7 cases.*Clinical and chest CT follow-up. **Absence of follow-up available because the patient had been transferred to another hospital or turned back home

Fig. 2

Chest CT scan categorized “evocative of COVID-19 pneumonia” in two different patients with positive nasopharyngeal SARS-CoV-2 RT-PCR at admission and secondarly (panels a and b and panels c and e, respectively). Multifocal bilateral ground-glass opacities with subpleural and posterior predominance, associated with band-like (panel b) or more extensive consolidations (panel d)

Fig. 3

Chest CT scan categorized “compatible with COVID-19 pneumonia,” in association with fibrosing interstitial lung disease (ILD) showing a non-specific interstitial pneumonia pattern (panel c, axial plane through the lung bases). Pure ground-glass opacities, both centrally and peripherally distributed, have appeared in the left upper lobe (panels a, b), as compared to the previous CT performed 4 months earlier (panel d). Such new opacities could be attributable to COVID-19, another infection, or acutisation of ILD. Nasopharyngeal SARS-CoV-2 RT-PCR positive

Fig. 4

Chest CT scan categorized “compatible with with COVID-19 pneumonia,” in association with pulmonary edema, manifesting as ground-glass opacities with a predominant central distribution, septal lines, and bilateral pleural effusion (panels a, b, axial plane; panel c, coronal plane) in a patient with history of chronic renal insufficiency on dialysis. Subpleural consolidation (panel a) in the posterior zone of the right upper lobe is consistent with associated COVID-19 pneumonia. Nasopharyngeal SARS-CoV-2 RT-PCR positive

Fig. 5

Chest CT scan categorized “not evocative of COVID-19 peumonia,” showing small consolidations in the left lower lobe associated with bronchial thickening and endobronchial filling, in favor of bronchopneumonia. Nasopharyngeal SARS-CoV-2 RT-PCR negative

Fig. 6

Chest CT scan categorized “not evocative of COVID-19 pneumonia” showing combination of areas of ground-glass opacity and consolidation systematized in the middle lobe (arrows), evoquing a lobar pneumonia. Despite positivity of the SARS-CoV-2-RT-PCR, bacterial co-infection was suspected and the patient received antibiotics with favorable evolution