Radiological Findings in COVID-19 Pneumonia
1–3Department of Radiodiagnosis, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth, Puducherry, India
4Department of Radiodiagnosis, Valduce Hospital, Como, Italy
Corresponding Author: Padhmini Balasubramaniam, Department of Radiodiagnosis, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth, Puducherry, India, Phone: +91 9487139946, e-mail: firstname.lastname@example.org
How to cite this article Balasubramaniam P, Varma LS, Das N, Lomoro P. Radiological Findings in COVID-19 Pneumonia. J Basic Clin Appl Health Sci 2020;3(2):59–64.
Source of support: Nil
Conflict of interest: None
As the global pandemic of COVID-19 progresses, apart from clinical findings, imaging also plays an equally important role in the diagnosis and management. In imaging, much of the literature is focused on chest computed tomography (CT). However, due to infection control issues and lack of availability of CT scan in many centers, bedside chest X-ray (CXR) and lung ultrasound is also being used rampantly. In cases of high clinical suspicion of COVID-19, CXR can obviate the need for CT thorax. Additionally, in areas around the world with limited access to reliable reverse transcriptase polymerase chain reaction COVID-19 testing, radiological imaging becomes crucial for diagnosis and follow-up. This article describes the most common manifestations and patterns of lung abnormalities on CXR, CT thorax, and lung ultrasound in a suspected case of COVID-19 pneumonia. Early evidence suggests that initial CXR will show abnormality in most patients. The corresponding CT scan can pick up findings that may be overlooked in CXR. The progression of the disease is assessed by follow-up CT scans/X-rays. Progression and regression of disease process can be monitored by a combination of imaging modalities that facilitate clinicians to tailor management protocols.
Keywords: Consolidation, COVID-19, Ground-glass opacities, Pneumonia..
COVID-19 is caused by a virus known as 2019 novel coronavirus/SARS-CoV2 (Severe acute respiratory syndrome coronavirus 2). The disease varies in severity from asymptomatic/mild flu-like illness to severe pneumonia that can be sometimes fatal. This highly infectious virus can cause pneumonia with increased morbidity in patients with previous medical comorbidities and chronic illness. Fever, dry cough, and dyspnea are the most common clinical features of this disease.1 The real-time reverse transcriptase polymerase chain (RT-PCR) reaction test is considered to be the gold standard test for detecting COVID-19 infection, but it does not have 100% sensitivity nor specificity.2
ROLE OF IMAGING IN COVID-19
Fleischner society has given the following guidelines for imaging in COVID-19.3
- Imaging is not indicated in patients with suspected COVID-19 and mild clinical features unless they are at risk for disease progression.
- Imaging is indicated in a patient with COVID-19 and worsening respiratory status.
- In a resource-constrained environment, imaging is indicated for medical triage of patients with suspected COVID-19 who present with moderate–severe clinical features and a high pretest probability of the disease.
X-ray, ultrasound, and computed tomography (CT) chest are the common imaging modalities used in the diagnosis and follow-up of COVID-19 pneumonia. The salient features are described below.
Chest X-ray can be insensitive in the early course of the disease and can be primarily used in follow-up of cases and to look for progression of disease and its complications such as acute respiratory distress syndrome.4 Chest X-ray has lower sensitivity and specificity when compared to RT-PCR/CT chest5
One of the most unique and somewhat specific features of COVID-19 pneumonia is the high frequency of peripheral lung involvement, often mirroring other inflammatory processes such as organizing pneumonia. Such peripheral lung opacities also tend to be multifocal, either patchy or confluent, and can be readily identified on CXR.5
To conclude the CXR findings:6
- Normal CXR is noted in many cases even if CT has ground-glass opacities.
- Ground-glass opacities with or without consolidations involving predominant lower zones (Fig. 1)
- Bilateral lung involvement is seen in majority of the cases (Fig. 2).
- High frequency of peripheral lung involvement (Fig. 3).
- No pleural effusion/abscess/lung nodules.
- Lower zone OR lower and upper zone involvement is noted in most cases.
Terms such as irregular, patchy, hazy, reticular, and widespread ground-glass opacities should be used while describing features seen on chest X-ray. Furthermore, it is noted that chest X-ray abnormalities are also seen in patients whose initial RT-PCR was negative. Although further studies are required, in a suspected case of COVID-19, a positive CXR may eliminate the need for a CT.
As the pandemic progresses, the medical community will frequently rely on portable CXR due to its widespread availability and reduced infection control issues that currently limit CT utilization.7
Ultrasound of the Lung
Lung ultrasound can predict early interstitial pneumonia. The following findings can be found in lung ultrasound in COVID pneumonia.8
- Thickening of the pleural line with pleural line irregularity (Fig. 4)
- B lines in a variety of patterns including focal, multifocal, and confluent
- Consolidations in a variety of patterns, including multifocal small, non-trans lobar, and trans lobar with occasional mobile air bronchograms
- Appearance of A lines during recovery phase
- Mixed pattern with A- and B lines can also be seen (Fig. 5)
- Pleural effusions are uncommon, and
- Subpleural consolidation with thickened pleural line.
Computed Tomography of the Chest
Computed tomography of the chest can be normal in the initial first two days of the infection.9 In the initial phases of the disease, the predominant CT findings are bilateral peripheral, subpleural basal dominant ground-glass opacities. Later on, about 9–13 days after the onset of infection, the disease can progress to crazy paving pattern/consolidation. About 1 month after the onset of the disease, clearing of the opacities can be seen. Findings of CT of tree in bud pattern, pleural effusion, and mediastinal lymphadenopathy should arise the suspicion of superadded bacterial infection.9 Compared to non-COVID-19 pneumonia, COVID-19 pneumonia has a more peripheral distribution of ground-glass opacity (GGO) or consolidation or both, fine reticular opacity, vascular thickening, and reverse halo sign but less likely to have a central and peripheral distribution, air bronchogram, pleural thickening, and pleural effusion.10,11
Ground-glass opacities and consolidation were predominant in the early stages of the disease, whereas in advanced-phase disease showed increased frequency of GGO plus a reticular pattern, vacuolar sign, fibrotic streaks, air bronchogram, bronchus distortion, a subpleural line, a subpleural transparent line, and pleural effusion, but GGO was significantly decreased.12 The CT findings of COVID pneumonia shows that both lung parenchyma and interstitium were affected.
Computed tomography can also play a role in detecting COVID infections in strong clinically suspicious cases but with negative RT-PCR.
HRCT thorax findings which favors diagnosis of COVID-19:11,13–16 (Figs 6 and 7)
- Bilateral and peripheral distribution.
- Lesion size greater than 10 cm.
- Involvement of 5 lobes.
- Presence of hilar and mediastinal lymph node enlargement.
- No pleural effusion.
- Bilateral and diffuse involvement.
- Mixed pattern of attenuation.
Common CT signs of the COVID-19:17
- Lobular distribution
- Subpleural distribution.
- Diffuse distribution.
- Parallel pleura sign: lesions show subpleural distribution with maximum diameter of the lesion being parallel to the pleura.
- Paving stone sign: lesion mainly involves the interlobular septum.
- Air bronchogram and bronchiectasis: air bronchogram can be seen without bronchial obstruction, but it is nonspecific. Bronchiectasis can be seen in late repair stages in periphery due to traction.
- Vascular sign: thickening of vessels and telangiectasia can be seen due to inflammation.
- Halo sign and reversed halo sign.
CT Findings seen after exacerbation of covid-19 when compared with previous images18 (Fig. 8):
- Increase in GGO with consolidation
- Bilateral distribution
- Multifocal lesions
- Increase in patchy shadowing
- Air bronchogram sign
- Increase in number of involved lobes.
Majority of the COVID-19 suspected cases present with fever, cough, shortness of breath, and sore throat and RT-PCR is a major diagnostic tool to confirm these cases. Due to increasing number of false-negative cases, a combination of RT-PCR, clinical features, and imaging modalities such as chest radiograph, ultrasound chest, and CT thorax could help clinicians diagnose cases and treat accordingly. Furthermore, in cases of high clinical suspicion of COVID-19, a positive CXR may obviate the need for CT.2 Additionally, CXR utilization for early disease detection may play a vital role in areas with limited access to reliable RT-PCR COVID testing. If there is high clinical suspicion of COVID-19 with negative RT-PCR and inconclusive chest radiograph, clinicians prefer ordering for a CT chest. However, chest CT has limited sensitivity and negative-predictive value early after symptom onset.19 Bedside ultrasonography of the chest for early diagnosis is becoming increasingly popular in the emergency departments of most hospitals. Lung ultrasound allows clinicians and radiologists to identify early signs of interstitial pneumonia.6,8
Hence, the combination of the above-described imaging modalities along with clinical features in suspected cases have a high sensitivity and specificity in detection of pneumonia in COVID-19 cases.
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