Review of the Chest CT Differential Diagnosis of Ground-Glass Opacities in the COVID Era

Coronavirus disease 2019 (COVID-19), a recently emerged lower respiratory tract illness, has quickly become a pandemic. The purpose of this review is to discuss and differentiate typical imaging findings of COVID-19 from those of other diseases, which can appear similar in the first instance. The typical CT findings of COVID-19 are bilateral and peripheral predominant ground-glass opacities. As per the Fleischner Society consensus statement, CT is appropriate in certain scenarios, including for patients who are at risk for and/or develop clinical worsening. The probability that CT findings represent COVID-19, however, depends largely on the pretest probability of infection, which is in turn defined by community prevalence of infection. When the community prevalence of COVID-19 is low, a large gap exists between positive predictive values of chest CT versus those of reverse transcriptase polymerase chain reaction. This implies that with use of chest CT there are a large number of false-positive results. Imaging differentiation is important for management and isolation purposes and for appropriate disposition of patients with false-positive CT findings. Herein the authors discuss differential pathology with close imaging resemblance to typical CT imaging features of COVID-19 and highlight CT features that may help differentiate COVID-19 from other conditions.