Chest imaging is often obtained to evaluate for pneumonia and progressive lung injury due to Covid-19. Given the concerns over healthcare worker exposure and environmental contamination, radiographic imaging should be minimized and obtained only when clinically indicated (1).

 
Routine chest radiograph: In a study involving over 1000 hospitalized patients with Covid-19, chest Xray abnormalities on admission were observed in about half of patients with nonsevere disease and three-quarters of those with severe disease (2). Many infiltrates are bilateral, patchy and peripheral in distribution (2,3).

 
Chest CT (without IV contrast):  CT abnormalities on admission have been observed in 84% of patients with nonsevere and 94% of patients with severe disease (2). Ground glass opacities (GGOs) and consolidation have been reported in the majority of patients. Infiltrates are often bilateral, peripheral, and posterior in distribution ( 2-5).

Compared to other causes of pneumonia, the most discriminating features of Covid-19 pneumonia on CT include peripheral distribution of infiltrates (80% vs 57%) and GGOs (91% vs 68%) (5).

CT findings are time dependent. Early during the course of infection, peripheral focal or bilateral multifocal GGOs are frequently observed, later giving rise to “crazy paving” and consolidation with occasional “reverse halo sign” as the disease progresses (see Bonus Pearl below), peaking around 9-13 days (6,7) . Pleural effusion and lymphadenopathy are uncommon (5,7).

 
Point of care ultrasound (POCUS): This relative newcomer offers a potentially useful and rapid means of evaluating for pneumonia or lung injury in Covid-19 and may be more sensitive than chest Xray. Its findings are not specific for Covid-19 lung pathology, however. In a preliminary report involving 12 patients with Covid-19 pneumonia (without ARDS) who underwent POCUS, a diffuse B-line pattern with spared areas was seen in all patients (8,9). Strict adherence to proper isolation precautions and decontamination of the ultrasound probe are essential.

Bonus Pearl: “Crazy paving” pattern on CT refers to GGOs with superimposed interlobular septal thickening and intralobular septal thickening, while “reversed halo sign” is a central GGO surrounded by denser consolidation of crescentic shape ring at least 2 mm in thickness (reference 7 has nice photos).

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References
1. ACR recommendations for the use of chest radiography and computed tomography (CT) for suspected COVID-19 infection. March 19, 2020. https://www.acr.org/Advocacy-and-Economics/ACR-Position-Statements/Recommendations-for-Chest-Radiography-and-CT-for-Suspected-COVID19-Infection
2. Guan WJ, Zheng-yi N, Hu Y, et al. Clinical characteristics of Coronavirus disease 2019 in China. N Engl J Med 2020; February 28. https://www.nejm.org/doi/full/10.1056/NEJMoa2002032
3. Ai T, Yang Z, Hou H, et al. Correlation of chest CT and RT-PCR testing in Coronavirus disease 2019 (COVID-19) in China: A report of 1014 cases. Radiology 2020. https://pubs.rsna.org/doi/10.1148/radiol.2020200642
4. Yoon SH, Lee KH, Kim JY, et al. Chest radiographic and CT findings of the 2019 Novel Coronavirus disease (COVID-19): Analysis of nine patients treated in Korea. Korean J Radiol 2020;21 :494-500. https://www.kjronline.org/Synapse/Data/PDFData/0068KJR/kjr-21-494.pdf
5. Bai HX, Hsieh B, Xiong Z, et al. Performance of radiologists in differentiating COVID-19 from viral pneumonia on chest CT. https://pubs.rsna.org/doi/10.1148/radiol.2020200823
6. Kanne JP, Little BP, Chung JH, et al. Essentials for radiologists on COVID-19: An update—Radiology scientific expert panel. Radiology 2020; February 27. https://pubs.rsna.org/doi/10.1148/radiol.2020200527

7. Bernheim A, Mei X, Huang M, et al. Chest CT findings in Coronavirus Disease-19 (COVID-19):Relations to duration of infection. Radiology 2020 Feb 20:200463.  https://pubs.rsna.org/doi/pdf/10.1148/radiol.2020200463
8. Poggiali E, Dacrema A, Bastoni D, et al. Can lung US help critical care clinicians in the early diagnosis of novel Coronavirus (COVID-19) pneumonia? Radiology 2020; https://www.ncbi.nlm.nih.gov/pubmed/32167853

9. Peng QY, Wang XT, Zhang LN, et al. Findings of lung ultrasonography of novel Coronavirus pneumonia during the 2019-2020 epidemic. Intensive Care Med 2020. https://doi.org/10.1007/s00134-020-05996.

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