Beware of possible COVID-19 related chest CT abnormalities on hybrid imaging studies

Attenuation or localization CT scans on SPECT/CT or PET/CT studies incorporating the chest should be screened in lung window regardless of their clinical indication. In case abnormalities are identified an experienced radiologist should be consulted in order to ensure appropriate patient referral. Learn how!

COVID-19 and chest CT abnormalities

The bottom line Attenuation or localization CT scans on SPECT/CT or PET/CT studies incorporating the chest should be screened in lung window regardless of their clinical indication. In case abnormalities are identified an experienced radiologist should be consulted in order to ensure appropriate patient referral.

 

The current COVID-19 crisis is hampered by issues relating to case finding and diagnosis. Up to approximately 50% of patients with COVID-19 infection may have normal CT scans 0–2 days after onset of flu-like symptoms from COVID-19 and the RT-PCR sensitivity may be as low as 60-70%.(1) Conversely, a recently published cohort study in patients who tested positive for SARS-CoV-2 using RT-PCR on the cruise ship “Diamond Princess” showed abnormal chest CT findings in 54% of asymptomatic patients.(2) Another recent study found that in patients receiving chest CT and RT-PCR assay within 3 days, the sensitivity of CT for COVID-19 infection was 98% and significantly higher compared to RT-PCR sensitivity of 71% (P<0.001).(3)

While the clinical significance of pulmonary changes on CT in non-symptomatic COVID-19 patients is still undetermined, it raises the possibility that patients may contract COVID-19 and possibly infect others whilst unaware of the infection.

Coincidentally, nuclear medicine physicians may be confronted with abnormal pulmonary findings on hybrid imaging modalities such as SPECT/CT and PET/CT in asymptomatic patients receiving an imaging study for other clinical indications. In addition, these data suggest that all attenuation correction and localization CT scans that include the thorax should be screened in lung window for changes that may suggest infection with SARS-CoV-2. In case such abnormalities are identified, an experienced radiologist should be consulted in order to properly direct patients to appropriate management.

Common CT findings in COVID-19 patients

An excellent pictorial overview of COVID-19 related CT changes can be found here. While the epidemiology of CT findings in COVID-19 patients is still evolving, the following CT patterns in the initial phase of infection have been reported with abnormalities during the early course of COVID-19 infection usually being peripheral focal or multifocal ground-glass opacities (1-4):

• Single or multiple half-round or rectangular-shaped ground-glass opacities (GGO) in subpleural areas with or without intra- or interlobular septal thickening.
• Single or multiple rounded GGO in both peribronchial and subpleural areas.
• Bilateral diffuse or multiple patchy GGO with or without intra- or interlobular septal thickening consolidation in both peribronchial and subpleural areas, with a lower lobe predilection.
• As the disease progresses, crazy paving and consolidation become the dominant CT findings, peaking around 9–13 days followed by slow clearing at approximately 1 month and beyond.

Typically, there are no associated pleural effusions or adenopathies. Patients with more severe chest CT changes have a higher likelihood of having symptoms.(2) Examples of typical chest CT findings compatible with COVID-19 pneumonia:

Bilateral subpleural ground glass opacities (GGO). For more CT pictures: https://pubs.rsna.org/doi/full/10.1148/radiol.2020200432

Ground‐glass opacities with a rounded morphology (arrows) in the right middle and lower lobes. For more CT pictures: https://pubs.rsna.org/doi/10.1148/radiol.2020200463

Routine CT screening recommendations

Despite the above, the Society of Thoracic Radiology (STR) at this time, does not recommend routine CT screening for the diagnosis of patients under investigation for COVID-19. Chest CT can be restricted to patients who test positive for COVID-19 and who are suspected of having complicating features such as abscess or empyema.

More chest CT resources

• Pictorial overview of general thoracic radiology terminology
• Fleischner Society: Glossary of Terms for Thoracic Imaging
• Belgian Society of Radiology summary of published CT images of COVID-19 cases

Conclusions

Even though routine chest CT screening for the diagnosis of COVID-19 in suspected patients is not recommended, nuclear medicine physicians should know and recognize the CT patterns that can be associated with SARS-CoV-2 infection as patients may be asymptomatic while incidentally receiving hybrid imaging studies for other clinical indications.

Attenuation or localization CT scans on SPECT/CT or PET/CT studies incorporating the chest should be screened in lung window regardless of their clinical indication. In case abnormalities are identified an experienced radiologist should be consulted in order to ensure appropriate patient referral.

References

1. Kanne JP, Little BP, Chung JH, Elicker BM, Ketai LH. Essentials for Radiologists on COVID-19: An Update—Radiology Scientific Expert Panel. Radiology.0:200527. [Link]
2. Inui S, Fujikawa A, Jitsu M, et al. Chest CT Findings in Cases from the Cruise Ship “Diamond Princess” with Coronavirus Disease 2019 (COVID-19). Radiology: Cardiothoracic Imaging. 2020;2:e200110. [Link]
3. Fang Y, Zhang H, Xie J, et al. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. Radiology.0:200432. [Link]
4. Bernheim A, Mei X, Huang M, et al. Chest CT Findings in Coronavirus Disease-19 (COVID-19): Relationship to Duration of Infection. Radiology.0:200463. [Link]