COVID-19 progressive stage imaging findings in a patient with initially negative RT-PCR

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.

Background

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[1]. In February 2020, the World Health Organization named the disease “COVID-19” and by March it was declared a global pandemic[2].

Clinical Perspective

COVID-19 varies from asymptomatic or paucisymptomatic to severe forms of pneumonia[2]. The most frequent symptoms are fever, dry cough and dyspnea[2]. 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[4].

Imaging Perspective

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)[3]. 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 [6]. 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[7]. 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)[8]. Pleural effusions and hilar/mediastinal lymphadenopathies are rare[8].

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[9].

Outcome

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

• Radiologists must be familiar with the COVID-19 imaging findings according to its different stages.
• Standardized reporting with the use of probability categories are helpful to guide physicians.