Imaging of COVID-19 pneumonia: a critical care perspective

Author: Dr Greg Brogan – Peer Reviewer: A/Prof Chris Nickson

OVERVIEW

COVID-19 lung imaging is generally indicated in any COVID-19 patient with worsening respiratory status

  • commonly manifests as ground glass opacities (CT chest), distributed bilaterally in bases and peripheries 
  • evolves rapidly and lung involvement is associated with severity; findings progress over 1-3 weeks, typically peaking at 10-14 days
  • findings may be present in asymptomatic individuals or pre-symptomatic individuals and may be absent early in the course of disease

In general, the lung imaging findings of COVID-19 patients are consistent with other viral pneumonias – there is no proven specific finding for COVID-19, though there may be suggestive patterns.


CHEST RADIOGRAPHY

Abnormalities are seen on chest x-ray (CXR) and are more common in severe COVID-19 disease 

Features Include (Guan, WJ et. al. 2020 Wong, HYF, et al. 2020)

  • Bilateral shadowing (72.9%) – mostly ground glass opacity (68.5%)
  • Unilateral disease (25%)
  • Local patchy shadowing
  • Interstitial abnormalities (less common finding, <5% in some studies)
  • Pleural effusions are uncommon
Chest x-ray from Canada’s first case of COVID-19
Figure 1: Chest x-ray from Canada’s first case  of COVID-19 (Silverstein, et al. 2020) : it shows bilateral peribronchovascular, ill defined opacities in all zones of the lung. 

COMPUTED TOMOGRAPHY (CT)

Abnormalities are seen on CT in a majority of COVID-19 cases (86% (Guan, WJ et. al. 2020))

Common CT features (Guan, WJ et. al. 2020 Ye, Z et al 2020 Zhao, W et al. 2020)

  • Ground Glass Opacities (GGOs)(Ye, Z et al 2020)
    • Hazy areas with increased density and no obscuring of bronchial or vascular markings (see figure 2)
    • Most common manifestation – in approximately 88% of cases (Salehi S et al. 2020)
    • Most often bilateral (87.5%), peripherally distributed (76%) and multilobar (78.8%) (Salehi S et al. 2020)
  • Reticular Pattern (Ye, Z et al 2020)
    • Multiple small linear opacities (see figure 2)
    • Common, perhaps second most common pattern to GGOs
  • Consolidation (Ye, Z et al 2020)
    • Air spaces replaced with fluid which obscures margins of vessels and airways (see figure 3)
    • Sign of progression of disease
    • Multifocal, patchy or segmental
    • Often subpleural or along bronchovascular bundles
  • Crazy Paving Pattern (Ye, Z et al 2020)
    • Resembles irregular paving stones from thickened interlobular septa/intralobular lines superimposed onto GGO (see figure 3)
    • Seen in 5-36%

Uncommon CT manifestations include (Salehi S et al. 2020, Rodriguez JCL. et al 2020)

  • Pleural effusion
  • Pericardial effusion 
  • Lymphadenopathy
  • Cavitation
  • CT Halo sign
  • Pneumothorax

Super-infection may be suggested by pleural effusion, extensive tiny lung nodules, tree-in-bud and lymphadenopathy (Rodriguez JCL. et al 2020)

When followed over time, a pattern to stages of disease emerges (Li, M et al 2020)

  • Early Phase – Moderate clinical manifestations with lesions limited to single or multiple areas
  • Progressive phase – Lesions progress in extent and density with the accumulation of cellular exudate in alveoli 
  • Severe Phase – Pulmonary lesions reach a peak at around 14 days with dense bilateral infiltration and a large amount of cellular exudate
  • Dissipative Phase – after 14 days, gradual absorption of lesions occurs (may occur earlier if disease course shorter) 

Role of CT in diagnosis: 

  • A single study of 1014 patients in Wuhan suggested high sensitivity (97%), but low specificity (25%) to detect disease the during outbreak (Ai, T et al. 2020)
  • A small study of CT-radiologists were able differentiate COVID from non-COVID viral pneumonias (Bai, HX 2020), however they had a wide range of sensitivity (67-93%) and specificity (7-100%)
  • Advantage of faster availability than PCR tests, though non-specific and risks of transport remain 
  • Changes can even be seen in asymptomatic patients (Shi, H et al. 2020)
  • However, findings are time dependent (Rodriguez JCL. et al 2020) – Approximately half may have normal study 2 days after symptoms onset. 
Shows isolated ground glass opacity in right lower lobe
Figure 2: a. isolated ground glass opacity in right lower lobe; b. subpleural consolidation (Ye, Z et al 2020)
Shows a reticular pattern in the left lower lobe
Figure 3: a. reticular pattern in the left lower lobe; b. Right middle lobe demonstrates the crazy paving pattern from reticular pattern superimposed on ground glass opacities. (Ye, Z et al 2020)

Lung Ultrasonography (US)

The role of lung ultrasonography is still being defined, but no specific COVID-19 findings have been confirmed (Soldati G et al. 2020, Vetrugno, L et al 2020)

  • Only sparse case series and case reports currently available

Uses

  • May help reduce the amount of CT scans and X-rays required (Vetrugno et al 2020
  • May provide a useful alternative in a climate where transport capabilities, staffing and imaging availabilities are stressed (Smith et al 2020)

Cases exhibit presence of viral pneumonia with features including (Buonsenso, D et al. 2020):

  • Irregular pleural line
  • B-lines (may be irregular and even confluent)
  • Patchy pattern with bilateral sparing
  • Areas of white lung
  • Subpleural consolidations

Risks

  • It is important to consider infection control and prevention of transmission via contact with ultrasound machine
Images from confirmed COVID-19 patient.
 Figure 5: Images from confirmed COVID-19 patient. White boxes: demonstrate pleural line irregularities; White arrows: Thick irregular B lines; White arrowheads: Subpleural consolidations; Red arrow: areas of white lung (Buonsenso, D et al. 2020)

References

LITFL

Journal articles

FOAM and web resources

SARS-CoV-2

novel coronavirus of COVID-19

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