A 57-year-old male patient with history of recent travel presented to the emergency department with dry cough, fever and increasing shortness of breath for 2 weeks. Laboratory analysis revealed elevated c-reactive protein (7.71mg/dL), LDH (892U/L), CK (1215U/L) and slighty elevated d-dimers (0.32 ug/ml). RT-PCR testing was initially negative for COVID-19.
On admission, the chest radiography revealed mild bilateral patchy areas of ill-defined lung opacities with peripheral and lower zone distribution (Fig.1). Due to progressive respiratory deterioration, a pulmonary embolism (PE) was suspected by the physicians. Accordingly, a chest contrast-enhanced computed tomography (CT) was requested which was negative for a PE but revealed bilateral multifocal and predominantly peripheral ground-glass opacities with superimposed interlobular septal thickening and visible intralobular lines (“crazy-paving” pattern) together with some discrete consolidative opacities with evidence of air bronchogram in the affected lung areas (Fig. 2). In the lower left lobe, a central ground-glass opacity surrounded by a denser consolidation of crescentic shape was also noticed which was interpreted as an emerging atoll sign (Fig.3). About 25-50% of lung parenchyma was affected bilaterally with slight posteroinferior predominance. Increased size lymph nodes, pleural or pericardial effusion were not found.
The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV- 2), is a novel zoonotic pathogen that first appeared among several pneumonia cases in Wuhan (China) during December 2019 and rapidly spread worldwide. In February 2020, the World Health Organization named the disease “COVID-19” and by March it was declared a global pandemic.
COVID-19 varies from asymptomatic or paucisymptomatic to severe forms of pneumonia. The most frequent symptoms are fever, dry cough and dyspnea. Although laboratory-based performance of RT-PCR test demonstrates high sensitivity and specificity, in clinical practice its sensitivity can be reduced with incorrect specimen collection or low viral load[3,4]. Initially, false-negative RT-PCR tests can occur in patients with CT findings of COVID-19 who later test positive.
Chest CT has a high positive rate and clinical symptoms are closely related to imaging findings allowing severity and progression assessment[4,5]. CT is more sensitive for early disease than chest x-ray, better for differential diagnosis, and can evaluate pulmonary thromboembolism (if contrast-enhanced CT is performed). Early-stage COVID-19 manifest as patchy ground-glass opacities (GGOs) with vascular dilation mainly in subpleural or peribronchovascular regions of one or both lungs, with posterior lower lobes predominance[4,5]. Progressive stage is revealed by increasing GGOs and involvement of multiple lobes, development of crazy pattern, and some GGOs converting into consolidations with air bronchograms[4,5]. Patients with nodular opacities on initial CT show an increase in number, size, or fusion of these . Advanced/peak stage presents with diffuse distribution, mostly consolidations, and increasing reticular opacities[4,5]. Indeed, the imaging findings correlate with the histologic pattern of an acute fibrinous and organizing pneumonia. In some cases, the atoll sign may occur during the progressive stage (consolidation developing around GGO) or during the absorption phase of the disease (lesion absorption leaving a decreased intensity in the center). Pleural effusions and hilar/mediastinal lymphadenopathies are rare.
Four categories have been proposed with standardized reporting of CT imaging features (typical, undeterminate, atypical for COVID-19 and negative for pneumonia) which can provide guidance and confidence to radiologists reducing variability of reporting as well as increased clarity to physicians for management decision.
In our case, the chest CT findings were structurally reported and categorized as “typical appearance of COVID-19 pneumonia”. This prompted a second RT-PCR testing for COVID-19 which confirmed the infection.
Take-Home Message / Teaching Points
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 Copin M-C, Parmentier E, Duburcq T, Poissy J, Mathieu D (2020). Time to consider histologic pattern of lung injury to treat critically ill patients with COVID-19 infection. Intensive Care Medicine. 2020.
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 Simpson S, Kay FU, Abbara S, et al (2020). Radiological Society of North America Expert Consensus Statement on Reporting Chest CT Findings Related to COVID-19. Endorsed by the Society of Thoracic Radiology, the American College of Radiology, and RSNA. Journal of Thoracic Imaging. 2020:1.