COVID-19 pandemic has affected millions of people worldwide. Thorough comprehension of CT imaging features of COVID-19 is mandatory for effective patient management. Hence, we meticulously assessed the CT studies of 772 participants with RT-PCR proved COVID-19.
About one-quarter of them, with statistically significant younger age, showed normal initial CT study. This is consistent with the previous studies done by Ojha et al., Yang et al., Asefi and Safaie Xu et al., and Zhang et al. [6, 10,11,12,13]. They stated that up to half of patients with positive RT-PCR may show a normal CT especially in the early phase or in asymptomatic infections. Therefore, CT cannot completely exclude COVID-19 infection.
In conformity with nearly all published studies [6, 7, 11, 13,14,15,16,17,18,19,20,21,22,23,24,25], the most prevailing CT imaging finding of COVID-19 in our population was GGO with or without consolidation/crazy paving followed by peri-lobular fibrosis combined with vascular thickening and bronchiectasis in a bilateral predominantly peripheral distribution with lower lobe predilection. On the other hand, lobar pneumonia and lung cavitation as well as diffuse, unilateral, or unifocal distributions were uncommon with the middle lobe and lingula being the least affected.
Similar to Carotti et al. , the most common associated imaging finding in COVID-19 was minimal lower lobar posterior pleural thickening.
In accordance with Salehi et al. and Kim et al. [14, 26], pleural effusion, pericardial effusion, and mediastinal lymphadenopathy were infrequently described associated findings.
It is worth noting that pleural and/or pericardial effusion were particularly reported in cases with advanced lung affection in the form of extensive multi-lobar consolidation and/or crazy paving. This agrees with Ojha et al.’s  declaration that pleural and pericardial effusion occur in advanced cases.
More than two-thirds of the mediastinal lymph nodes reported in our study were calcified, likely being a sequel of healed previous granulomatous infection. This may be attributed to the fact that tuberculosis is endemic in Egypt.
In few of our cases, a lung cyst was recognized among the other CT findings. A limited number of articles mentioned the presence of cyst(s) in cases of COVID-19; however, the etiology and relation to COVID-19 pneumonia are unclear [19, 22].
On searching the literature, none of the previous studies described thymic abnormalities in association with COVID-19. Nevertheless, thymic hyperplasia was identified in a considerable number of our cases with statistically significant young age and female predilection; most of them had no lung abnormalities on CT. The thymus is a lymphoid organ that plays a cardinal role in development of the immune system during childhood. It gradually involutes throughout maturation yet maintains the ability to re-grow (9). Hence, we suggest that thymic hyperplasia is an immune response to the viral infection; yet, further studies are warranted to validate this hypothesis.
Employing the previously illustrated RSNA Expert Consensus Statement, typical category was the most frequently encountered, while indeterminate and atypical categories were unusual. Correspondingly, CT can confidently diagnose COVID-19 in about 69% of cases. Taking into consideration the current pandemic and resources constraints (e.g., RT-PCR availability), the implementation of CT as a screening tool can be disputed.
Regarding follow up, progression was defined as an increase in the number, size, extent, or density of previously noted lesion(s) and/or development of new lesions, while regression would represent decrease in those finding(s). In this study, nearly half of the evaluated studies showed regression, one-third remained unchanged, and few cases showed progression.
On reviewing previously published studies, the percentage of cases with progressive CT findings ranged from 32 to 94.75%. This wide range may be explained by the variability in study duration, number of cases, and time interval between initial and follow up CT studies [13, 14, 16, 17, 19, 20, 27].
Twenty of our cases had persistent normal CT on follow up. In Xu et al.’s study , 75% of cases had normal initial and follow up scans. Also, 13% of patients evaluated by Zhang et al.  and 1.8% of those assessed by Guan et al.  remained negative on follow up. Consequently, we suggest that patients may not develop CT manifestations of pneumonia along the course of COVID-19 infection.
One of the major strengths of this study is its timing; as it was conducted early along the course of this not yet fully understood pandemic. Thereby, the whole radiological spectrum of COVID-19 was captured making this one of the most sensitive radiological studies of COVID-19 cases in Egypt.
However, our study had some limitations including the unavailability of laboratory data and limited number of follow up studies. Furthermore, this is a hospital not a population-based study; therefore, sensitivity and specificity could not be calculated; yet, we could deduct the percentage of different CT imaging categories. It is thus recommended to perform future studies to confirm the generalizability of this study and similar ones.