The first cases of COVID-19 pneumonia occurred in Wuhan, Hubei Province, China, in December 2019. Since then, there have been many cases of COVID-19 pneumonia with human-to-human transmission by close contacts in other cities and provinces in China and in other countries around the world . The clinical symptoms of the disease are very similar to 2003 SARS-CoV with patients frequently developing acute respiratory distress syndrome and which may lead to death. We have thus been interested to analyze the CT features and the evolution of COVID-19 pneumonia to provide a reference for early diagnosis, timely isolation, and treatment.
Our preliminary investigation has revealed some common findings on lung CT images obtained from patients with COVID-19 pneumonia. Firstly, the number of opacities is often more than one. The types of opacities including ground-glass without consolidation and ground-glass with consolidation are very often seen. Moreover, small vessels often identified to be thickened within the opacities. Secondly, multiple lung lobes and especially the lower lobe are often involved. Thirdly, the opacities may be distributed peripherally and centrally or peripherally but never occur just centrally. Other findings including a crazy-paving pattern, interlobular septal thickening, and air bronchograms may sometimes be seen. Nevertheless, the appearance of the CT features also depends on the stage of COVID-19 pneumonia.
In the early stage of the disease, CT images predominantly show unilateral or bilateral ground-glass opacities accompanied with enlarged small vessels. Sometimes, ground-glass with focal consolidation can be seen. In terms of distribution, the lower lobe and peripheral (i.e., subpleural area) are most commonly affected. The early involvement of the peripheral and subpleural regions may be related to the pathological mechanism of viral pneumonia, such as the early involvement of bronchioles and parenchyma around the bronchioles, and then the involvement of whole pulmonary lobule and diffuse alveolar damage .
As the disease progresses, CT images show enlargement of opacities and an increased number of new ground-glass opacities affecting more and larger regions of multiple lung lobes. Furthermore, some of the original ground-glass opacities begin to consolidate. Thus, ground-glass opacities and consolidation are commonly seen. At this stage, if the patients could not receive effective treatment promptly or if the immunity is low, COVID-19 pneumonia may be life-threatening. CT images may show diffuse opacities to be present in both lungs and in severe cases so-called white lung manifestation. However, there are fewer patients in the stage. In the study, only two cases showed “white lungs.” If the patient accepts effective treatment or if immunity is enhanced, pneumonia will be gradually absorbed and the opacity will be diminished . The disease will improve, possibly leaving the lung fibrous stripes and thickened pleural. In the present study, 40 patients were cured and discharged and before discharge, the RT-PCR test result for each patient was negative and the appearance of opacities in both lungs was improved and their size obviously diminished.
Nevertheless, we found that COVID-19 pneumonia has many similar CT features to those reported with SARS [15, 16] and MERS [17, 18]; thus, it is difficult to distinguish COVID-19 pneumonia from them. Our findings were in accordance with the present studies [12, 19]. It is not surprising since the responsible viruses of SARS and MERS are also coronaviruses and viruses in the same viral family have similar pathogenesis.
However, there are interesting new findings. Firstly, the features on CT images of some patients may not be consistent with the results of RT-PCR tests. For example, two patients with a Wuhan exposure history who showed expected features on CT images had a negative result on the initial but not on a follow-up RT-PCR test. Therefore, when the result of the RT-PCR test is negative for a patient with CT features typical of viral pneumonia and history of potential exposure, the patient should be isolated, closely observed, and undergo further RT-PCR testing.
Besides, we occasionally found that the CT findings of some patients may not be consistent with their clinical symptoms. For example, three patients with mild clinical symptoms only showed pharyngeal discomfort but because one of their family members had been diagnosed with COVID-19 pneumonia, they underwent CT scans. Their CT images revealed multiples opacities to be present in the lungs, and subsequently, they also tested positive for SARS-CoV-2 on a RT-PCR test. In addition, some patients showed obvious improvements of symptoms after receiving treatment but the follow-up CT suggested there would have been a significant progression. Therefore, for some suspicious patients with mild clinical symptoms, CT examination is recommended for the detection of lesions, early diagnosis, and assessment of the disease progression. Moreover, follow-up CT scans should be performed for evaluating the efficacy of treatment during hospitalization.
Incidentally, we additionally found that COVID-19 pneumonia showed obvious characteristics of crowd aggregation, especially family aggregation in that sixteen patients who were members of just five families were all infected with SARS-CoV-2.
There are limitations to our study that should be noted. Firstly, the sample size is relatively small and the reported CT features of COVID-19 pneumonia should be considered preliminary rather than definitive. Secondly, follow-up CT scans were only obtained for 40 of the 55 patients and thus the full range of disease appearance may not be represented. Thirdly, the relatively small sample size may account for why no children are included in this study. Whether children may be less likely to become infected or, if infected, display milder symptoms is obviously an important question to be addressed in future studies.
In conclusion, the predominant finding on CT images obtained for patients with COVID-19 pneumonia is multiple ground-glass opacities with or without consolidation and, with both lungs, multiple lobes and especially the lower lobe affected. Although CT findings alone may not be sufficient for definitive diagnosis of COVID-19 pneumonia, in combination with epidemiological history, laboratory test results, and clinical symptoms, the diagnosis of COVID-19 pneumonia could potentially be made in newly referred cases.