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 COVID-19 typical imaging findings from 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 patients who are at risk for and/or develop clinical worsening. The probability, that CT findings represent COVID-19, however, depends largely on the pre-test 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 vs. RT-PCR. This implies that with usage 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 CT false positive patients. We will discuss differential pathology with close imaging resemblance to typical CT imaging features of COVID-19, and, highlight CT features that may help in differentiation from other conditions.