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 Table of Contents  
EDITORIAL
Year : 2022  |  Volume : 3  |  Issue : 3  |  Page : 59-66

Chest computed tomography findings in COVID-19: A pictorial review


1 Department of Interventional Radiology, Shanti Mukand Hospital, New Delhi, India
2 College of Nursing, Institute of Liver and Biliary Sciences, New Delhi, India

Date of Submission15-May-2021
Date of Decision10-Jun-2021
Date of Acceptance20-Jun-2021
Date of Web Publication03-Nov-2022

Correspondence Address:
Tarika Sharma
College of Nursing, Institute of Liver and Biliary Sciences, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jascp.jascp_11_21

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How to cite this article:
Singh J, Sharma T. Chest computed tomography findings in COVID-19: A pictorial review. J Appl Sci Clin Pract 2022;3:59-66

How to cite this URL:
Singh J, Sharma T. Chest computed tomography findings in COVID-19: A pictorial review. J Appl Sci Clin Pract [serial online] 2022 [cited 2022 Dec 6];3:59-66. Available from: http://www.jascp.org/text.asp?2022/3/3/59/360441




  Introduction Top


In December 2019, an outbreak of a highly contagious lung infection was reported in the region of Wuhan, China. It was rapidly spread to other countries and on March 12, 2020, World Health Organization (WHO) declared coronavirus disease (COVID-19) as a pandemic disease.[1],[2] The etiological agent was a coronavirus (SARS-CoV-2) isolated from airway epithelial cells of infected patients, which belongs to Sarbecovirus subgenus, Orthocoronavirinae subfamily, and is seventh member of the coronavirus family.[1] The infection was described as COVID-19. The second wave of COVID-19 pandemic has strike hard particularly in India due to new and more virulent viral strains resulting in more number of infected young adults. This has put a large strain on healthcare infrastructure resulting in a longer waiting list and more waiting time for reverse-transcriptase polymerase chain reaction (RT PCR) results with increasing false-negative reports. Hence, there is an increased demand for computed tomography (CT) chest imaging for screening and initial evaluation. There were concerns for irradiation exposure hazards due to rational use of imaging modality, however ultra-low-dose chest CT almost nullify the risk associated with radiation exposure particularly in young individual and children.[3] CT chest has important roles in the initial evaluation, disease burden, management planning, diagnosis, and follow-up of patients with COVID-19. This article aimed to discuss the pictorial review of CT chest findings in COVID-19 pneumonia.


  Indications for Computed Tomography Chest in COVID-19 Top


Most of the health organizations do not support diagnostic imaging in patients having mild disease especially when RT-PCR and immunokits are easily available. Centre for Disease Control does not recommend the use of chest radiographs or CT for diagnosis of COVID-19.[4] The American College of Radiology and the Royal College of Radiologists recommended that CT should be used for specific indications in hospitalized, symptomatic patients and acknowledged that limited resources may play a role in determining the need for CT in diagnosis.[5],[6] Guidelines from Spain recommended that imaging can be considered in emergency patients when RT-PCR results are suspected of being false negative or assays are either limited.[7],[8] Although recommendations from China and Italy suggested the use of chest CT with RT-PCR assay in diagnosis of COVID-19, the WHO advised against the use of imaging as first-line diagnosis.[9]

The multinational consensus statement from Fleischner Society on the role of chest imaging in COVID-19 statement supports the use of imaging in worsening respiratory status in COVID-19 patients as well as suspected COVID-19 patients having moderate to severe presentation with a high pretest probability.[10]

When RT-PCR assays have limited availability, diagnostic imaging (CT/X-ray chest) can be used in patients with moderate to severe symptoms suggestive of COVID-19 pneumonia. However, for assessing the severity of COVID-19 pneumonia, the routine use of CT chest is not recommended.[6],[7]


  Computed Tomography Chest Findings in COVID-19 Top


Different studies reported wide variety of CT findings in COVID-19. These findings differ according to the stage and severity of the disease as well as associated comorbidities. Lungs are commonly affected by COVID-19. Lower zones/lobes of lungs are commonly involved and the right middle lobe is the least affected.[11] Various CT chest findings in COVID-19 have been described subsequently.

Ground glass opacity/GGO

Ground-glass opacity (GGO) is defined as lung opacification without obscure the bronchovascular margins. GGO is common and earliest manifestation, however, it is a nonspecific sign of COVID-19 pneumonia [Table 1] The distribution of GGOs is patchy, irregular, peripheral, subpleural, and bilateral. Ground glass opacity has been depicted pictorially in [Figure 1], [Figure 2] [Figure 3].[11],[12],[13],[14]
Table 1: Ground glass opacity sign on computed tomography chest in COVID-19 lung infection depicted by various studies

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Figure 1: Evolution of ground-glass opacities in COVID-19 patients on computed tomography chest imaging depends on the stage of the disease (a) subtle ground glass infiltration (arrow). (b) Dense ground glass opacification (curved arrow). (c) Consolidation formation along with spider web pattern (open arrow). (d and e) Graphic depiction of Ground-glass opacity (d) and consolidation (e)

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Figure 2: Different patterns of Ground-glass opacities and consolidations in COVID-19 patients on computed tomography chest imaging depends on the stage of the disease (a) bilateral multifocal ground glass infiltration (arrow). (b) Diffuse confluencing Ground glass associated with crazy paving pattern (curved arrow). (c) Multifocal consolidatory patches in bilateral lung fields (open arrow) associated with early changes of fibrosis

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Figure 3: Atypical finding on computed tomography chest images in COVID-19 pneumoniae (a) focal consolidation (arrow) and unilateral Ground-glass opacities (b) nodule (curved arrow). (c) Pleural effusion (open arrowhead) with bibasal consolidation and ground-glass opacities. (d) Cavitating consolidation mostly due to secondary bacterial infection (open arrow)

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Subpleural transparent line

It is a thin translucent line/space between the area of opacification and the visceral pleura and was reported in 53.2% of cases of COVID-19.[15] Another study reported that the incidence of this sign decreases with the progression of disease and seen as; 45.3%, 47.7%, and 6.5% in the early stage, advanced stage, and absorption stage respectively. Subpleural transplant line sign has been depicted pictorially in [Figure 4].[16]
Figure 4: Subpleural transparent line sign. (a) Graphic depiction of subpleural transparent line. Computed tomography chest of two COVID-19 patients (a-d) shows extensive, symmetric ground-glass opacities predominately in the peripheral location with subpleural sparing (arrows in Figure a and b and curved arrows in c and d)

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Bat wing/butterfly/angel wing sign

It is an air-space infiltration may be patchy, diffuse, and confluencing in bilateral perihilar GGOs sparing the periphery of the lungs.[15],[17] In COVID-19 pneumonia, consolidations and GGOs progressively get confluent in the central part sparing the peripheral part and depicted as “Batwing sign” appearance. A similar sign on CT imaging can be seen in patients with alveolar proteinosis, pulmonary hemorrhage, sarcoidosis, and bronchoalveolar carcinoma. Bat wing sign has been shown pictorially in [Figure 5].
Figure 5: Bat wing sign (a) graphic representation of batwing sign. Computed tomography chest axial and coronal sections shows symmetric infiltrating opacities in perihilar region (b and c) with interspersed areas of thickened interlobular septa with subpleural sparing (open arrow), and scattered ground-glass opacities in the periphery of both lungs

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Halo sign

The halo sign is defined as a solid pulmonary consolidatory nodule surrounded by GGO.[18] It has classically been described in angioinvasive fungal infections.[19] This sign is not helpful in differentiating COVID-19 pneumonia from other viral pneumonia.[20] Other noninfectious causes are metastatic cancers, amyloidosis, sarcoidosis, and granulomatosis with polyangitis. HAlo sign has been depicted pictorially in [Figure 6].[21],[22]
Figure 6: Halo sign. (a) Graphic depiction showing Halo sign. The computed tomography image (cone down view) shows the “halo sign” in three different reverse-transcriptase polymerase chain reaction positive patients: in the left upper lobe (a and b) and left lower pole (b), a round irregular consolidation (open arrowhead, open arrow) with peripheral ground glass (arrows)

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Atoll sign/reverse halo sign

Reverse halo sign is a manifestation of organizing pneumonia which manifest as central GGO/normal parenchyma surrounded by rim of consolidation. It has been classically described in cryptogenic organizing pneumonia but is not specific for the disease.[23] The central GGO of the reverse halo sign corresponds to alveolar septal inflammation and cellular debris, whereas the peripheral consolidation represents organizing pneumonia. Atoll sign has been shown pictorially in [Figure 7].[24],[25],[26]
Figure 7: Atoll/reverse halo sign (a). Graphic depiction showing reverse halo sign. It is represented by a central ground glass (arrow in b and arrow head in c) area surrounded by a peripheral consolidation. This axial computed tomography finding (b and c)—similar to the sea atoll (arrowhead and arrow)

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Consolidation

Consolidation is increase in the parenchymal opacity that obscures the vascular margins and the airway walls. In COVID-19 pneumonia, consolidations usually appear as patchy or segmental, irregular or nodular, in subpleural and peripheral distribution with the incidence of 2%–64% depending on the duration of the illness.[27],[28],[29]

It is a sign of severe or advanced disease and is associated with high mortality in patients. Consolidation has been shown in [Figure 2] and [Figure 8].[9],[30],[31]
Figure 8: Computed tomography chest image of COVID-19 pneumonia patient showing (a) air bronchogram (arrow) due to prominent bronchiole in the consolidatory patch. (b) Tram track appearance (due to dilated bronchus on min MIP image (curved arrow)

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Reverse batwing sign

COVID-19 causes organizing pneumonia in the lung with peripheral consolidations and central sparing.[32] This pattern is first described in chronic eosinophilic pneumonia (CEP) by Gaensler and Carrington.[33] The reverse batwing sign help in narrow imaging differentials such as CEP, pulmonary vasculitis, adenocarcinoma of the lung, and organizing pneumonia. Reverse batwing sign can be seen pictorially in [Figure 9].[34]
Figure 9: Reverse bat wing sign. (a) Graphic depiction of reverse batwing sign. Axial computed tomography chest (b and d) and coronal (c) images of two different patients who were reverse-transcriptase polymerase chain reaction positive (b-d) shows bilateral peripheral consolidations (arrow) with sparing (open arrow) of central region represents reverse batwing appearance

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Pulmonary target sign

The sign has been described as a central high attenuation focus surrounded by one or more dense complete or incomplete ring-like consolidation, forming one or more circles on chest CT in patients with COVID-19 pneumonia.[35] The pathophysiology of this sign is that it is a manifestation of organizing pneumonia (OP).[36],[37] The pulmonary target sign usually coexists with other typical OP features including the reverse halo or halo sign. Pulmonary target sign has been depicted pictorially in [Figure 10].[38]
Figure 10: Target sign and halo sign (a). Graphic depiction showing target sign (b) high-resolution computed tomography image of the right lung in a 37-year-old woman with COVID-19 pneumonia shows an irregular ring-like opacity containing in its center a small nodular ground-glass opacity surrounding a very small vessel (curved arrow). (c) The combination of central nodular opacity and the peripheral ring of increased opacity resemble a shooting target. Also noted are small patchy ground-glass opacities in a different COVID-19, reverse-transcriptase polymerase chain reaction positive patient

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Crazy paving sign

The pattern resembles paths made from broken pieces of concrete stone. Crazy paving of the lung is represents thickened interlobular septae on the background of scattered or diffuse GGOs.[39] It is a nonspecific finding and classically described in pulmonary alveolar proteinosis.[40] It can also be seen in pulmonary edema, lymphangitic carcinomatosis, lipoid pneumonia, pulmonary hemorrhage, and pneumocystis jiroveci pneumonia.[41],[42]

Crazy paving appearance is a sign of progressive disease and may indicate that the disease is progressed into its peak stage [Table 2]. It is the first CT sign to resolve in the absorptive stage while the consolidation and GGO may persist for a longer time. Crazy paving sign has been presented in [Figure 11].[43]
Table 2: Crazy paving sign on computed tomography chest in COVID-19 lung infection depicted by various studies

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Figure 11: Crazy paving. (a) Graphic depiction of a crazy-paving pattern. Computed tomography images axial sections of three different patients with COVID-19 pneumonia show ground glass attenuation of the lungs with superimposed reticulations. This appearance looks like the “roman crazy paving” (arrow in b, curved arrow in c and arrowhead in d)

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Vascular signs

Vascular signs are a common finding in COVID-19 and are broadly classified here as vascular enlargement and feeding vessel sign and are described subsequently [Table 3]. Vascular enlargement is the dilatation of the pulmonary vessels around or within the GGO/consolidation. Vascular signs can be seen in [Figure 12].
Table 3: Vascular enlargement on computed tomography chest in COVID-19 lung infection depicted by various studies

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Figure 12: Vessel feeding and dilated vessel sign (a). Graphic depiction showing vessel feeding sign. A 42-year-old female (a) and two 35 year male patients (c and d) with fever and cough were diagnosed with COVID infection, computed tomography lung axial section (b-d) coned down view shows a irregular consolidatory (c) patches (open arrowhead) with a feeding vessel and dilated vessel in patch (white curved arrow [d] and arrow [b]) to it producing the radiologic sign, feeding vessel and dilated vessel sign

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Feeding vessel sign

The sign represents a distinct pulmonary vessel leading into a lung nodule or mass. It was first described in septic emboli with a prevalence of 67%–100%.[49],[50],[51] The sign has also seen in pulmonary infarctions, metastasis, and pulmonary arteriovenous malformations.[52] We have noted feeder vessel in COVID-19 consolidatory patches. Therefore considering the current scenario, COVID-19 should be considered in the differential diagnosis. [Figure 10] represents the feeding vessel sign.

Air bubble sign/vacuolar sign

Air bubble/cavity sign refers to a small air-containing space <5 mm within resolving consolidation.[13],[17],[53] It represents of progressive disease and can be differentiated from the dilated bronchus/bronchioles as they does not have wall. Air bubble sign can be seen in [Figure 13].
Figure 13: Air lucencies sign (a) Graphic depiction showing air bubble sign. A 31-year-old male patient (b) and two female patients (c and d) with COVID-19, computed tomography chest axial image (a) shows right lower lobe predominantly subpleural ground-glass opacity with air lucency (arrow), (b) shows right lower lobe subpleural consolidation with tiny lucency “vacuolar sign” (open arrow), similar finding noted in figure (c) (open arrow)

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  Fibrosis Top


This sign carries good prognosis and represents a regression of disease severity. The incidence of fibrosis is around 17% in COVID-19.[21] In some studies, it is considered as a warning sign of development of interstitial fibrosis.[54]


  Reticulations Top


Reticulation is thickening of inter/intralobular septa and appears as several linear opacities. Its reported incidence is 48.5%–59%.[55],[56] Reticular pattern represents the third common pattern after GGO and consolidation.[13]

Spider web sign

Spider web sign is a common sign of COVID-19 pneumonia which represents subpleural, triangular residual opacity of resolving GGO with web-like thickening of the interlobular septa and thickened retraction adjacent pleura.[12],[13] Spider web sign was reported from 39 to 45% of patients in various studies. Spider web sign has been shown in [Figure 14].[12],[13]
Figure 14: Spider web sign (a) Graphic depiction of spider web sign. The computed tomography image shows the “spiderweb sign” in two different reverse-transcriptase polymerase chain reaction positive patients for COVID-19, in the Right lower lobe (b) and right lower pole (c) represent subpleural triangular area of Ground-glass opacity, with web-like thickening (arrow) of the interlobular septa and retraction of the adjacent pleura

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Parenchymal band sign/subpleural curvilinear line

Parenchymal band or subpleural curvilinear line manifest as thin irregular linear band of opacity which is mostly 1–3 m thick and lying parallel to the pleural surface mostly in the lower posterior segments of the lung.[43] It may represent edema or fibrosis.[1],[6].This sign was reported in 10%–15% of patients.[15],[57] This finding usually seen in advanced stage of disease than early disease.[15] Parenchymal band sign has been depicted pictorially in [Figure 15].
Figure 15: Parenchymal band sign. (a) Graphic depiction of Subpleural band/curvilinear subpleural lines. A 60-year-old female patient with COVID-19 (b) and a 50 year reverse-transcriptase polymerase chain reaction positive patient (c and d). Computed tomography chest axial image shows bilateral subpleural ground-glass opacities architectural distortion, and perilobular thickening. An irregular subpleural band is seen on the left (black arrow in Figure b and c) and right (open arrowhead in Figure d)

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Bronchial changes

Bronchovascular thickening and bronchiectasis (dilatation of normal bronchus more than adjacent artery) are two common signs in later stage of the disease. Bronchial wall thickening is common in pediatric patients.[58]

Zhao et al.[46] have reported bronchiectasis in 52.5% of their patients, and representative of the severity of the disease and marker of high viral load and virulence of the disease. Bronchial changes in COVID 19 have been shown in [Figure 8]b.


  Other Atypical Imaging Features Top


Nodules

Nodules are round opacities less in < 3 cm in size with 3%–13% incidence in patients with COVID-19 pneumonia is 3%–13% and represent progressive course of disease. [Figure 3] represents the nodules.[59],[60]

Pleural/pericardial effusion

Pleural/pericardial effusion is rare in patients with COVID-19 and indicates severe disease.[24]

Pleural thickening is relatively less common findings and reported incidence of pleural thickening is about 27%–32%.[6],[10] The presence of pleural effusion reflects high viral load and virulence. Pleural/Pericardial effusion can be seen in [Figure 3].[23],[27]

Mediastinal lymphadenopathy

Enlargement of lymph nodes more than 10 mm (in short axis diameter) is known as lymphadenopathy. Mediastinal lymphadenopathy is not a typical feature and has an incidence of 1%–6%.[13],[18],[19] It was considered as a sign of severity particularly in critically ill patients.[61]

Accuracy of computed tomography chest in diagnosis of COVID-19 pneumonia

Previous literature has reported sensitivity of chest CT in the diagnosis of COVID-19 is 60%–98%, and specificity is 25%–56%.[62],[63],[64],[65] Lymphopenia, C-reactive protein, and serum ferritin show significant correlation with CT severity. Ai et al.[62] and Fang et al.[66] Concluded that in epidemic areas CT chest might be used as a primary tool for the detection of COVID-19.


  Conclusion Top


CT Chest has an utmost role in the diagnosis, management planning, and prognostication of COVID-19 disease. Although chest CT does not have high specificity in the diagnosis of COVID-19 pneumonia context with pandemic situation, the CT chest can be used as a screening tool in symptomatic patients which help rapid triage and isolation. Future studies that define the prognostic role of CT chest and therefore defining the standard management plans are needed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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