Objective To compare the similarities and differences of early CT manifestations of three types of viral pneumonia induced by SARS-CoV-2 (COVID-19), SARS-CoV (SARS) and MERS-CoV (MERS) using a systemic review.
Methods Electronic database were searched to identify all original articles and case reports presenting chest CT features for adult patients with COVID-19, SARS and MERS pneumonia respectively. Quality of literature and completeness of presented data were evaluated by consensus reached by three radiologists. Vote-counting method was employed to include cases of each group. Data of patients’ manifestations in early chest CT including lesion patterns, distribution of lesions and specific imaging signs for the three groups were extracted and recorded. Data were compared and analyzed using SPSS 22.0.
Results A total of 24 studies were included, composing of 10 studies of COVID-19, 5 studies of MERS and 9 studies of SARS. The included CT exams were 147, 40, and 122 respectively. For the early CT features of the 3 pneumonias, the basic lesion pattern with respect to “mixed ground glass opacity (GGO) and consolidation, GGO mainly, or consolidation mainly” was similar among the 3 groups (χ²=7.966, P>0.05). There were no significant differences on the lesion distribution (χ²=13.053, P>0.05) and predominate involvement of the subpleural area of bilateral lower lobes (χ ²=4.809, P>0.05) among the 3 groups. The lesions appeared more focal in COVID-19 pneumonia at early phase (χ ²=23.509, P<0.05). The proportions of crazy-paving pattern (χ ²=23.037, P<0.001), organizing pneumonia pattern (P<0.05) and pleural effusions (P<0.001) in COVID-19 pneumonia were significantly lower than the other two. Although rarely shown in the early CT findings of all three viral pneumonias, the fibrotic changes were more frequent in SARS than COVID-19 and MERS (χ ²=6.275, P<0.05). For other imaging signs, only the MERS pneumonia demonstrated tree-in-buds, cavitation, and its incidence rate of interlobular or intralobular septal thickening presented significantly increased as compared to the other two pneumonia (χ ²=22.412, P<0.05). No pneumothorax, pneumomediastinum and lymphadenopathy was present for each group.
Conclusions Imaging findings on early stage of these three coronavirus pneumonias showed similar basic lesion patterns, including GGO and consolidation, bilateral distribution, and predominant involvement of the subpleural area and the lower lobes. Early signs of COVID-19 pneumonia showed less severity of inflammation. Early fibrotic changes appeared in SARS only. MERS had more severe inflammatory changes including cavitation and pleural effusion. The differences may indicate the specific pathophysiological processes for each coronavirus pneumonia.

Key words: computer tomography, pneumonia, viral, COVID-19, severe acute respiratory syndrome coronavirus, Middle East respiratory syndrome coronavirus, severe acute respiratory syndrome coronavirus 2