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 Table of Contents  
REVIEW ARTICLE
Year : 2021  |  Volume : 1  |  Issue : 1  |  Page : 5-9

Imaging features of COVID-19 pneumonia


1 Department of Internal Medicine, DM Wayanad Institute of Medical Sciences, Wayanad, Kerala, India
2 Department of Pulmonology, DM Wayanad Institute of Medical Sciences, Wayanad, Kerala, India

Date of Submission20-Nov-2020
Date of Acceptance02-Dec-2020
Date of Web Publication28-Jan-2021

Correspondence Address:
Dr. Charitha Puvvada
DM Wayanad Institute of Medical Sciences, Meppadi, Wayanad - 673 577, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jalh.jalh_9_20

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  Abstract 


Coronavirus disease 2019 after its origin in Wuhan, China, had spread globally and was declared as a pandemic by the WHO on March 11, 2020.? The WHO identifies it as a controllable pandemic with the key role existing in precautionary measures to curb the recent global crisis. The current diagnostic methodologies include the rapid antigen test, serology tests to detect antibodies, and the real-time polymerase chain reaction.? Anecdotal experiences have shown that imaging characteristics are crucial in the diagnosis and management of the disease as radiological evidence of disease appears before the clinical manifestations and evolves overtime as the disease progresses, which is useful in predicting the stage, severity, and prognosis of the disease. Owing to few specific features and early changes, computed tomography scan is more sensitive than a chest roentgenogram in highlighting these changes.

Keywords: Angiopathy, coronavirus disease, crazy paving, vascular tree in bud


How to cite this article:
Puvvada C, Chetambath R. Imaging features of COVID-19 pneumonia. J Adv Lung Health 2021;1:5-9

How to cite this URL:
Puvvada C, Chetambath R. Imaging features of COVID-19 pneumonia. J Adv Lung Health [serial online] 2021 [cited 2021 Feb 24];1:5-9. Available from: http://www.jalh.com/text.asp?2021/1/1/5/308273




  Introduction Top


Coronavirus disease 2019 (COVID 19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).[1],[2] As of November 2020, about 47 million confirmed cases were identified with more than six million cases in India.[3] The number of deaths from COVID-19 exceeds 1.2 million globally, owning a fatality rate of 2%–3%.[3] The basic reproduction number of SARS-CoV-2 has been estimated to be around 2.2–3.28 in a nonlockdown population, meaning that, each infected individual on an average causes 2–3 new infections.[4]

COVID-19 typically presents with systemic and/or respiratory manifestations.[5],[6] A significant majority of individuals infected with SARS-CoV-2 are asymptomatic throughout the course of their illness.[5] The full spectrum of clinical presentation of COVID-19 is broad with non-specific signs and symptoms.[6]

The definitive diagnostic test for COVID-19 is real-time polymerase chain reaction (RT-PCR) test,[7] which is believed to be highly specific but with sensitivity reported as low as 60%–70% and as high as 95%–97%.[7],[8]

Multiple radiological organizations and learned societies state that computed tomography (CT) should not be relied upon as screening/diagnostic tool for COVID-19.[9],[10],[11] The threshold for imaging of patients with potential/confirmed COVID-19 shows global variation due to local resources, individual country's guidelines, and sociocultural approach to imaging.[9]


  Indications for Imaging Top


According to Fleischner Society Consensus statement from April 7, 2020:[12]

  • Imaging is not indicated in suspected COVID-9 patients and patients with 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 suspected COVID-19 who present with moderate-to-severe clinical features and a high pretest probability of disease.


The British Society of Thoracic Imaging (BSTI) suggests that all seriously ill patients oxygen saturation <94% (unless known COPD in which it is <90%) must initially have a chest radiograph and that those who do not meet those criteria should have a chest radiograph if clinically required.[13] If the patient is breathless, with oxygen saturation of <94%, and the chest radiograph is normal or uncertain for COVID-19, BSTI guidelines advise chest CT.[13]

Performing CT routinely for large cohorts carries additional risks such as depletion of finite resources, especially PPE due to excessive usage; increased risk of viral transmission (to staff, patients and caregivers) as COVID-19 positive and negative patients come into close proximity in the radiology department and additional ionizing radiation hazards.[9],[12]


  Radiographic Features Top


The primary findings of COVID-19 on chest X-ray and CT are those of atypical pneumonia[13],[14] or organizing pneumonia.[14] Imaging has limited sensitivity for COVID-19, as up to 18% demonstrate normal chest radiographs or CT when mild or early in the disease course which decreases to 3% in severe disease.[15] Bilateral and/or multilobar involvement is common.[9],[15]


  Chest Radiograph Top


Chest radiography is the first-line imaging modality used for patients with suspected COVID-19.[16] For ease of decontamination, the use of portable radiography units is preferred.[10]

Chest radiographs may be normal in early/mild disease. Findings are extensive in about 10–12 days of symptom onset.[16] In the COVID-19 cases requiring hospitalization, 69% have an abnormal chest radiograph at the initial time of admission, and about 80% have radiographic abnormalities sometime during hospitalization.[9],[16]

The most frequent findings are consolidation or ground-glass opacities.[16],[17] The distribution is most often bilateral and peripheral with lower zone predominance.[16] Pleural effusion is rarely reported in around 3% of patients.[16],[17]


  Computed Tomography of Chest Top


Primary CT findings of COVID-19 in adults reported are as follows:[17],[18]

  1. Ground-glass opacities: Ground-glass opacity refers to an area of increased attenuation in the lung with preserved bronchial and vascular markings. Ground-glass pattern is the most common finding in COVID-19 infections. They are usually multifocal, bilateral, peripheral, and basal in distribution.[19] However, in the early phase of the disease, the GGO may present as a unifocal lesion, most commonly located in the inferior lobe of the right lung[20]
  2. Crazy-paving appearance: Crazy-paving appearance refers to the appearance of ground-glass opacity with superimposed interlobular septal thickening and intralobular septal thickening[20]
  3. Airspace opacification: Airspace opacification refers to increased attenuation of the lung parenchyma causing obscuration of pulmonary vessels, without significant loss of volume, in the segments affected[17],[20]
  4. Organizing pneumonia: This includes patchy consolidation, ground-glassing, small ill-defined peribronchial or peribronchiolar nodules, large nodules, and bronchial wall thickening[17],[20]
  5. Perilobular pattern with ill-defined linear opacities which are thicker than the thickened interlobular septa and have an arcade or polygonal appearance referred to as the arcade-like sign
  6. Central ground-glass opacity corresponding to alveolar septal inflammation and cellular debris in the alveolar spaces surrounded by peripheral airspace consolidation corresponding to granulomatous tissue within the distal airspace referred to as reversed halo sign or “Atoll sign.”[20]


Other findings reported in COVID-19 patients CT include:

  1. Vascular tree-in-bud appearance: It refers to the presence of dilated peripheral vessels. Vascular tree-in-bud appearance is a unique CT finding which may be attributed to hypercoagulability and lack of fibrinolysis leading to pulmonary thrombosis that enhances the peripheral pulmonary vessels on CT imaging. Vascular tree-in-bud appearance signifies to be a marker of poor prognosis in COVID-19 patients[21]
  2. Angiopathy: Vascular dilatation in the areas of ground glassing leading to angiopathy[20]
  3. Band sign: Sub-pleural bands leading to architectural distortion may be seen in some cases. Both thick and thin bands are seen with an curvilinear pattern having pleural attachment on both ends[17],[20]
  4. Traction bronchiectasis: Distortion of the airways secondary to mechanical traction on the bronchi or bronchioles from fibrosis or distorted surrounding lung parenchyma[17]
  5. Pleural effusion, pericardial effusion, lymphadenopathy, cavitation, CT halo sign, and pneumothorax are some of the uncommon but possible findings seen with disease progression.[22]


A retrospective study of 112 patients reported that, 54% of asymptomatic patients had pneumonic changes on CT.[19]


  Resolution (resorption stage) Top


Resolution of most of the radiological lesions begins by the second week except for a few patients who develop complications such as cytokine storm syndrome or pulmonary thromboembolism. Lesions regress with mild ground glassing and reticular lesions. Resolution once started is so rapid that it is sometimes referred “melted sugar sign,” “collar candy sign,” or “tinted sign.” Sometimes, the ground-glass shadows progress transiently before resolution. This is called creeping ground-glass sign. It is noted that during resolution band like reticular lesions appear which is mistaken for fibrosis. However, it is not well established whether these patient will develop fibrosis in due course. Most of the studies predict that these reticular lesions are transient fibrosis or edematous airway walls which may disappear by 8–12 weeks' time. At the same time, caution should be raised against progress of fibrosis in a patient already having fibrosis due to underlying lung disease such as interstitial fibrosis.


  Computed Tomography Changes Over Time Top


Four temporal CT stages have been identified:[23],[24]

  1. Early/initial stage (0–4 days): Normal CT or GGO only, partial crazy paving; More than 50% of the patients have normal CT scans within two days of symptom onset
  2. Progressive stage (5–8 days): Extension of GGO and crazy-paving appearance
  3. Peak stage (9–13 days): consolidation
  4. Resorption stage (>14 days): Gradual resolution.



  Covid rads Top


In April 2020, Radiological Society of North America has released a consensus statement endorsed by the Society of thoracic radiology and the American College of Radiology that classifies the CT appearance of COVID-19 into four categories for standardized reporting language:[25]

  • Typical appearance


    • Peripheral, bilateral, GGO with or without consolidation, crazy-paving pattern
    • Multifocal GGO of rounded morphology with or without consolidation and crazy paving pattern
    • Reverse halo sign or other findings of organizing pneumonia.


  • Indeterminate appearance


    • Absence of typical CT findings and the presence of multifocal, diffuse, perihilar, or unilateral GGO with or without consolidation lacking a specific distribution and are nonrounded or nonperipheral distribution.


  • Atypical appearance


    • Absence of typical or indeterminate features and the presence of isolated lobar or segmental consolidation without GGO; discrete small nodules (e.g. centrilobular and tree-in-bud), lung cavitation, and smoother interlobular septal thickening with pleural effusion.


  • Negative for pneumonia


    • No CT features to suggest pneumonia, in particular, absent GGO and consolidation.



  CO-RADS Top


CO-RADS refers to the COVID-19 Reporting and Data System proposed by the COVID-19 standardized reporting working group of the Dutch association of Radiology to ensure CT reporting is uniform and replicable.[26],[27]

The level of suspicion increases from very low (CO-RADS Category-1) to very high (CO-RADS Category-5). Two additional categories includes CO-RADS Category 0 wherein the CT is un-interpretable and CO-RADS Category 6 in case of RT-PCR proven SARS-CoV-2 infection at the time of examination.


  Computed Tomography Involvement Score Top


The severity of lung involvement in CT corresponds to the severity of the disease.[28]

This can be calculated by scoring the percentages of each lobe that is involved:

  1. <5% involvement
  2. 5%–25% involvement
  3. 26%–49% involvement
  4. 50%–75% involvement
  5. >75% involvement.


The total CT score is the sum of individual scores and can vary from 0 (no involvement) to 25 (maximum involvement), when all the five lobes show more than 75% involvement.


  Differentials Based on Computed Tomography Findings Top


The CT findings of COVID-19 overlap with other diseases like H1N1 influenza, other viral pneumonias like adenovirus, cytomegalovirus, organizing pneumonia and acute interstitial pneumonia.


  Ultrasound Top


Initial workup based on COVID-19 patients from China suggests that Ultrasound may be useful in the evaluation of critically ill COVID-19 patients.[29] The following patterns have been observed with bilateral and posterobasal predominance:

  • Multiple B-lines: ranging from focal to diffuse, representing thickened subpleural interlobular septa[30]
  • Irregular, thickened pleural line with scattered discontinuities[22]
  • Subpleural consolidations can be associated with a discrete, localized pleural effusion; pneumonic consolidation typically associated with preservation of flow or hyperemia[30]
  • Alveolar consolidation: tissue-like appearance with dynamic and static air bronchograms. Usually seen in severe, progressive disease[30]
  • Restitution of aeration during recovery: reappearance of bilateral A-lines.[30]



  Positron-Emission Tomography-Computed Tomography Top


Fluorodeoxyglucose uptake is increased in ground-glass opacities in those with presumed/confirmed COVID-19.[31],[32] It has been hypothesized that those with higher standard uptake values in lung lesions take longer to heal.[32]


  Conclusion Top


Chest radiography is the first-line modality of imaging for patients with suspected COVID-19. Radiological changes may be witnessed in asymptomatic individuals also. The use of CT scan as primary diagnostic tool has to be discouraged. CT has more sensitivity and less specificity in COVID-19. The typical features of COVID-19 in CT imaging include ground-glass opacities of rounded morphology which are mostly of peripheral and bilateral distribution; crazy paving pattern, band sign, vascular tree-in-bud appearance, angiopathy, reverse halo sign, and other signs of organizing pneumonia. CT severity corresponds to severity of the disease and helps in assessing the prognosis. Vascular tree-in-bud appearance is indicative of vascular thrombosis and signifies poor prognosis in COVID-19. Imaging characteristics of COVID-19 are crucial in the management of the disease. CT scan has to be performed diligently in case of absolute indications to prevent unwarranted radiological exposure, increased risk of viral transmission, and depletion of finite resources.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  In this article
Abstract
Introduction
Indications for ...
Radiographic Fea...
Chest Radiograph
Computed Tomogra...
Resolution (reso...
Computed Tomogra...
Covid rads
CO-RADS
Computed Tomogra...
Differentials Ba...
Ultrasound
Positron-Emissio...
Conclusion
References

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