Broad Differential Diagnosis of Chest CT Ground-Glass Opacities

By Will Boggs MD

July 17, 2020

NEW YORK (Reuters Health) - While the presence of ground-glass opacities is common in chest CTs of patients with COVID-19, numerous other conditions can present with similar findings, researchers report.

"The typical chest CT imaging features of COVID-19 pneumonia have low specificity," Dr. Achala Donuru of Thomas Jefferson University Hospitals, in Philadelphia, told Reuters Health by email. "It is important to note that when the prevalence of COVID-19 is high, even atypical imaging features are more likely to be COVID-19."

Typical chest CT findings in COVID-19 pneumonia include bilateral, peripheral and basal-predominant ground-glass opacities (GGOs) and/or consolidation, followed later by a mixed pattern of crazy paving, architectural distortion and perilobular abnormalities superimposed on GGOs that slowly resolve.

Upper lobe or peribronchovascular distribution of GGOs, cavitation, lymphadenopathy, and pleural thickening are found atypically, Dr. Donuru and colleagues note in Radiology.

They discuss and differentiate COVID-19 typical image findings from other diseases in their review. Bacterial pneumonia can present with focal segmental or lobar pulmonary opacities without lower lung predominance, but other common findings (cavitation, lung abscess, lymphadenopathy, and so on) can usually differentiate it from COVID-19.

Other viral pneumonias can be more challenging to distinguish from COVID-19. For example, GGOs can be seen in up to 75% of adenovirus cases, more than 75% of cytomegalovirus and herpes simplex virus cases, and up to 25% of measles and human meta-pneumovirus cases.

GGOs can be widespread in pneumocystis pneumonia, but, unlike in COVID-19, they tend to predominate in the upper lobes.

Similarly, various interstitial lung diseases can present with GGOs, but the predominant location differs by diagnosis, and other clinical factors are useful for differentiating them from COVID-19.

GGOs can also be common in hypersensitivity pneumonitis, lung injury from use of electronic cigarettes or vaping products, pulmonary edema, diffuse alveolar hemorrhage, pulmonary alveolar proteinosis, and eosinophilic pneumonia. But clinical features and GGO patterns are generally useful for differentiating these conditions from COVID-19.

"Although CT is not diagnostic, as per the Fleischner Society consensus statement, CT is more sensitive for early lung changes with COVID-19 infection," Dr. Donuru said. "CT is valuable in identifying underlying cardiopulmonary abnormalities in patients with moderate to severe disease. CT can help clinicians triage resources towards patients at risk of disease progression and may identify a cause in case of clinical worsening. CT may also identify an alternate diagnosis."

"Ultimately," she concluded, "clinical judgment should dictate the use of imaging through consideration of patient risk factors and local resources."

Dr. Marcello Migliore of the University of Catania, in Italy, who recently reviewed the management of GGOs in the lung-cancer screening era, told Reuters Health by email, "CT is not useful to diagnose COVID-19, but it is certainly useful to follow up patients with preexisting lung pathology who go rapidly worse."

"GGO are also a presenting picture of early lung cancer and therefore it should be taken into account," said Dr. Migliore, who was not involved in the new review. "I think that a short discussion about 'missed' diagnosis of early lung cancer should have been done."

SOURCE: Radiology, online July 7, 2020.