COVID-19 disease progression on lung CT

7th Jan 2021

To explore the time course of imaging changes in patients with COVID-19, let’s summarize a study published in The Lancet during the COVID-19 pandemic.1

Patient sample and methods

The patients were divided into four groups based on the time between symptom onset and their first computer tomography (CT) scan. There was a subclinical group, who were healthcare workers without symptoms, and three clinical groups with CT scans acquired in the 1st, 2nd, and 3rd weeks after symptom onset. The CT scan findings were compared between groups. 

Healthy woman. Man with cough, fever. Man with fever. Woman with fever and blue face. Illustration.

Figure 1. In a study published in The Lancet, Shi and colleagues found that patients diagnosed with COVID-19 were divided into four groups based on the time between symptom onset and their first computer tomography (CT) scan—a subclinical group without symptoms, and three clinical groups with CT scans at one, two or three weeks after symptom onset.1

Time course of changes in CT findings in patients with COVID-19

Number of involved lung segments

When comparing the CT scans among these four groups, the number of involved lung segments increased rapidly from the subclinical phase until the 2nd week, then started to decline in the 3rd week after symptom onset. 

Graph of the number of involved lung segments in 3 patient groups with COVID-19—subclinical, 1 week after symptom onset, 2 weeks after symptom onset, 3 weeks after symptom onset.

Figure 2.  In patients diagnosed with COVID-19, CT scans show the number of involved lung segments increases rapidly from the subclinical phase to the 2nd week after symptom onset, then starts to decline in the 3rd week. 

This finding is consistent across several other studies where patients showed a continuously worsening clinical course and CT changes which peaked in the 2nd week after symptom onset and then started to improve.

Predominant CT findings

With regard to the pattern of imaging changes over time, ground-glass opacities were found to predominate in the early stages, with consolidation peaking synchronously with the worst clinical and imaging situation in the 2nd week after symptom onset. 

Then a mix of ground-glass opacities and consolidations or pure ground-glass opacity patterns predominated in the 3rd week, indicating dissipation of the previous consolidations into ground-glass opacities in the 3rd week.

Reticular opacities were mainly seen in the 3rd week after symptom onset, which is consistent with the description of reticular changes in the late stages of disease course that mostly represent residual fibrotic changes.

Graph showing predominant chest CT findings compared to the time since COVID-19 symptom onset.

Figure 3. Predominant chest CT findings over time since COVID-19 symptom onset. 

 

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Common patterns of CT changes over time in COVID-19

So, there are four patterns of evolution of CT changes in COVID-19 patients:

  1. Initial progression to a peak level, followed by radiographic improvement
  2. Continuous deterioration of imaging changes
  3. Continuous improvement
  4. Static

The most common pattern of CT changes over time observed in this study and in some other studies was the initial progression of CT findings to a peak level, followed by radiographic improvement. A less common pattern of continuous deterioration of imaging changes was mostly observed in patients who entered the ICU or died. Continuous improvement is another less common pattern. And few cases have shown a relatively static picture throughout the study period. 

Graphs depicting patterns of CT changes over time in patients with COVID-19. Peak deterioration then improvement. Continuous deterioration. Continuous improvement. Static. Illustration.

Figure 4. Common patterns of CT changes over time in patients with COVID-19, a) progression to a peak then radiological improvement, b) continuous deterioration, c) continuous improvement, d) static. 

Case study—progress to peak level, followed by improvement

Now let’s look at a typical example of the most commonly described evolution pattern in COVID-19 pneumonia. In this case study, a 42-year-old woman with COVID-19 had serial CT scans and the radiological findings were tracked.

Figure 5. Case study—42-year-old female with COVID-19.

On day 3 after symptom onset, there were multifocal consolidations involving bilateral, subpleural lung parenchyma. 

COVID-19 CT image of chest in cross section with bilateral consolidations.

Figure 6. Multifocal consolidations in bilateral, subpleural lung parenchyma are seen on chest CT imaging in a 42-year-old female three days after COVID-19 symptom onset (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

On day 7 the lesions had increased in extent and the density became heterogeneous, with internal bronchovascular enlargement. 

. COVID-19 CT image of chest in cross section with large heterogeneous bilateral lung lesions and internal bronchovascular enlargement.

Figure 7. Seven days after symptom onset, the chest CT of a 42-year-old-female with COVID-19 shows large bilateral lung lesions with heterogeneous density and internal bronchovascular enlargement (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

On day 11, the previously observed lesions have dissipated into ground-glass opacities and some irregular linear opacities.

COVID-19 chest CT showing ground-glass and linear opacities. CT image.

Figure 8. Chest CT of a 42-year-old woman 11 days after the onset of COVID-19 symptoms shows ground-glass opacities and some linear opacities bilaterally (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

On day 18, further clearing of the lesions was observed. 

COVID chest CT showing clear lungs. CT image.

Figure 9. Chest CT of a 42-year-old woman shows clearing of COVID-19 lung lesions at 18 days after symptom onset (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

The patient was discharged from the hospital two days after this final scan.

 

Case study—continuous deterioration

As an example of a pattern of continuous deterioration, let’s look at the serial chest CT findings of this 77-year-old man with COVID-19. 

77-year-old male. Illustration.

Figure 10. Case study—77-year-old male with COVID-19. 

On day 5 after symptom onset, there were few patchy ground-glass opacities affecting the bilateral subpleural lung parenchyma. 

COVID-19 CT chest showing patchy ground-glass opacities affecting the bilateral subpleural lung parenchyma. CT image.

Figure 11. Five days after symptom onset, the chest CT of a 77-year-old man with COVID-19 showed few patchy ground-glass opacities affecting the bilateral subpleural lung parenchyma (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

On day 15, there was more extensive subpleural crescent-shaped ground-glass opacities in both lungs, as well as posterior reticular opacities and subpleural crescent-shaped consolidations. 

Chest CT showing bilateral extensive ground-glass opacities, reticular opacities and consolidations in COVID-19. CT image.

Figure 12. 15 days after symptom onset, the chest CT of a 77-year-old man with COVID-19 showed extensive subpleural crescent-shaped ground-glass opacities in both lungs, as well as posterior reticular opacities and subpleural crescent-shaped consolidations (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

On day 20, there was enlargement and denser pulmonary consolidations as well as some more ground-glass opacities and bilateral pleural effusions.

Chest CT with large consolidations, ground-glass opacities and bilateral pleural effusions in COVID-19.

Figure 13. 20 days after symptom onset, the chest CT of a 77-year-old man with COVID-19 showed expansion of previous subpleural consolidations, more ground-glass opacities, and bilateral pleural effusion (Image courtesy of Shi, H, Han, X, Jiang, N, et al., 2020).

This patient died 10 days after the final scan.

Pleural effusion is a rare finding in COVID-19 patients. It may indicate a co-existing bacterial pneumonia, but some experts suggest that it’s associated with severe cases of COVID-19 and a worse prognosis, as seen in this patient.

So, you can see how the evolution of COVID-19 is reflected through serial imaging, and how this may help predict the clinical outcomes in these patients. 

 

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References

  1. Shi, H, Han, X, Jiang, N, et al. 2020. Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: A descriptive study. Lancet Infect Dis20: 425–434. PMID: 32105637