COVID-19 pneumonia and its lookalikes: How radiologists perform in differentiating atypical pneumonias

Abstract

Purpose: To examine the performance of radiologists in differentiating COVID-19 from non-COVID-19 atypical pneumonia and to perform an analysis of CT patterns in a study cohort including viral, fungal and atypical bacterial pathogens.

Methods: Patients with positive RT-PCR tests for COVID-19 pneumonia (n = 90) and non-COVID-19 atypical pneumonia (n = 294) were retrospectively included. Five radiologists, blinded to the pathogen test results, assessed the CT scans and classified them as COVID-19 or non-COVID-19 pneumonia. For both groups specific CT features were recorded and a multivariate logistic regression model was used to calculate their ability to predict COVID-19 pneumonia.

Results: The radiologists differentiated between COVID-19 and non-COVID-19 pneumonia with an overall accuracy, sensitivity, and specificity of 88% ± 4 (SD), 79% ± 6 (SD), and 90% ± 6 (SD), respectively. The percentage of correct ratings was lower in the early and late stage of COVID-19 pneumonia compared to the progressive and peak stage (68 and 71% vs 85 and 89%). The variables associated with the most increased risk of COVID-19 pneumonia were band like subpleural opacities (OR 5.55, p < 0.001), vascular enlargement (OR 2.63, p = 0.071), and subpleural curvilinear lines (OR 2.52, p = 0.021). Bronchial wall thickening and centrilobular nodules were associated with decreased risk of COVID-19 pneumonia with OR of 0.30 (p = 0.013) and 0.10 (p < 0.001), respectively.

Conclusions: Radiologists can differentiate between COVID-19 and non-COVID-19 atypical pneumonias at chest CT with high overall accuracy, although a lower performance was observed in the early and late stage of COVID 19 pneumonia. Specific CT features might help to make the correct diagnosis.

Keywords: Atypical; Bacteria; COVID-19; CT; Fungal; Viral.

Fig. 1

Flowchart of patient enrolment.

Fig. 2

Pie charts demonstrating the size of the COVID-19 and non-COVID-19 group, as well as the distribution of the different pathogens in the non-COVID-19 group.

Fig. 3

CT scans of non-COVID-19 atypical pneumonia misinterpreted as COVID-19 pneumonia (a) Only CT scan misdiagnosed by all five radiologists: 52-year-old man with influenza A pneumonia, 7 days after symptom onset, showing subpleural curvilinear lines (arrows). (b, c) Examples misdiagnosed by four of five radiologists: (b) 66-year-old woman with CMV-pneumonia, 3 days after symptom onset, with ground glass opacities and peripheral crazy paving (arrow), (c) 57-year-old man with influenza A H1N1 pneumonia, 20 days after symptom onset, demonstrating extensive, mostly subpleural ground glass opacities. (d) Example misdiagnosed from three of five radiologists: 50-year-old-man with RSV B pneumonia, 2 days after symptom onset, with solitary rounded ground glass opacity in left upper lobe (arrow). Note the complete atelectasis of the left lower lobe.

Fig. 4

CT scans of COVID-19 pneumonia mistaken for non-COVID-19 pneumonia (a) Only case misdiagnosed by all five radiologists: 64-year-old woman with COVID-19 pneumonia, 14 days after symptom onset, showing nodules of ground glass opacity (arrows). (b-d) Examples misdiagnosed by four of five radiologists: (b) 79-year-old man, 2 days after symptom onset, demonstrating diffuse ground glass opacities, (c) 67-year-old woman, 20 days after symptom onset, demonstrating consolidation in the right lower lobe (arrow). (d) Example misdiagnosed by three of five radiologists: 70-year-old man, 4 days after symptom onset, demonstrating a solitary rounded ground glass opacity in the left upper lobe (arrow).

Fig. 5

CT-scans of COVID-19 patients, demonstrating signs suggestive of COVID-19 pneumonia (a) 39-year-old man, 6 days after symptom onset, showing rounded (arrow) and band-like (arrowhead) ground glass opacities in the periphery of the lung. (b) 70-year-old woman, 8 days after symptom onset, showing subpleural curvilinear lines in both lungs. (c) 54-year-old woman, 2 days after symptom onset, demonstrating enlargement of segmental and subsegmental vessels inside areas of ground glass opacity in both lower lobes. (d) 59-year-old man, 22 days after symptom onset, demonstrating extended perilobular opacities in both lungs (arrows).