COVID-19: CXR & CT scan

The typical finding is patchy ground glass opacities, which tend to be predominantly peripheral and basal (Shi et al 2/24). The number of involved lung segments increases with more severe disease. Over time, patchy ground glass opacities may coalesce into more dense consolidation.
Infiltrates may be subtle on chest X-ray (example above from Silverstein et al).
- Image of example chest X-ray here.
- Image of example CT scans here.
Findings which aren't commonly seen, and might argue for an alternative or superimposed diagnosis:
- Pleural effusion is uncommon (seen in only ~5%).
- COVID-19 doesn't appear to cause masses, cavitation, or lymphadenopathy.

Limitations in the data
- Data from different studies conflict to a certain extent. This probably reflects varying levels of exposure intensity and illness severity (cohorts with higher exposure intensity and disease severity will be more likely to have radiologic changes).
Sensitivity of CT scanning?
- Sensitivity among patients with positive RT-PCR is high. Exact numbers vary, likely reflecting variability in how scans are interpreted (there currently doesn't seem to be any precise definition of what constitutes a “positive” CT scan).
  - Sensitivity of 86% (840/975) in Guan et al.
  - Sensitivity of 97% (580/601) in Ai et al.
- Among patients with constitutional symptoms only (but not respiratory symptoms), CT scan may be less sensitive (e.g., perhaps ~50%)(Kanne 2/27).
CT scan abnormalities might emerge before symptoms?
- Shi et al. performed CT scanning in 15 healthcare workers who were exposed to COVID-19 before they became symptomatic.
- Ground glass opacification on CT scan was seen in 14/15 patients! 9/15 patients had peripheral lung involvement (some bilateral, some unilateral).
- Emergence of CT abnormality before symptoms could be consistent with the existence of an asymptomatic carrier state (discussed above).

Chest X-ray
- Sensitivity of chest X-ray is lower than CT scan for subtle opacities.
- In Guan et al., the sensitivity of chest x-ray was 59%, compared to 86% for CT scan.
- In Arentz et al. from Washington State, clear chest X-ray was only recorded in 1/21 patients. However a variety of different findings were reported (including bilateral reticular nodular opacities, ground-glass opacities, focal consolidation, and pulmonary edema).

Anesthesiology and Intensive Care