According to the guideline revised by National Health Commission of China (Trial version 6), the confirmed diagnosis of COVID–19 should be based on the positive 2019-nCoV detection. However, the positive imaging manifestation is one of the indispensable clinical diagnostic criteria. Moreover, the sensitivity of 2019-nCoV nucleic acid detection is poor despite its high specificity16. Therefore, it is of great significance to accurately recognize the imaging features of COVID–19 for its rapid screening and early diagnosis. Chest HRCT with thin-section is currently considered to be one of the most effective tools to early screening and accurate assessment for COVID–19 owing to its high sensitivity and convenience.
The present study demonstrated that: (Ⅰ) Most COVID–19 patients had bilateral lung involvement (24/30, 80%) and more than two lobes involvement (24/30, 80%). (Ⅱ) Multiple ground glass opacities were pulmonary characteristic manifestations of COVID–19. All COVID–19 patients with abnormal CT findings demonstrated either pure ground glass opacities (27/30, 90%) or ground glass opacities with consolidation (23/30, 76.7%). Numerous irregular intralobular lines were visible within the ground glass opacities in most patients (26/30, 86.7%). (Ⅲ) ground glass opacities usually appeared as round (25/30, 83.3%) or flaky (11/30, 36.7%) morphology. (Ⅳ) Pulmonary lesions of COVID–19 mainly located in the peripheral region of lung, especially the subpleural regions. In addition, some accompanying signs were occasionally found including mediastinal lymphadenopathy (3.3%) and pleural effusion (6.7%). Two patients in present study, whose family members were confirmed as COVID–19, had typical COVID–19 CT findings but negative findings in the first two etiological testings. They were finally confirmed as COVID–19 by the third etiological testing. For these patients with typical COVID–19 CT findings, it is essential to take early isolation and medical observation if they are living in or traveling from areas of the COVID–19 outbreak, even if they have the negative 2019-nCoV test.
2019-nCoV is highly homologous to the previous SARS-CoV2,17. The pathological features of COVID–19 are greatly similar to those seen in SARS and Middle Eastern respiratory syndrome (MERS) coronavirus infection18,19. Type Ⅱ alveolar epithelium is the target cell of the coronavirus. Similar to SARS CoV, 2019-nCoV adheres firstly to alveolar epithelium in peripheral lobules and then damages alveolar walls causing interstitial and intra-alveolar edema, interstitial inflammatory infiltration, dominated by lymphocytes13,20. These pathological changes simultaneously involve multiple adjacent lobules. HRCT images appear as single or multiple ground glass opacities locating peripheral lung fields accordingly. With the progress of disease, multiple patchy ground glass opacities increase and fuse to round or flaky lesions without the distribution of the pulmonary segments. Lung involvements with a peripheral predominance of ground glass opacities are also the primary CT findings of SARS21 and MERS22. On CT images, pleural effusions could be found in few patients with SARS or MERS, but lymphadenopathy could not be seen in any patient23,24. The absence of pleural effusions in most patients was also characteristic of COVID–19 in our study. According to previous research, early onset of pleural effusion with a higher pulmonary CT scores was a sign of poor prognosis25. Focal ground glass opacities and consolidations located in peripheral subpleural fields rapidly progressed to almost the whole lung and were responsible for ensuing acute respiratory distress syndrome (ARDS)25. ARDS commonly occurred in SARS and MERS26. Therefore, COVID–19 patient with pleural effusion and a short incubation period should be given adequate attention and aggressive treatment to prevent rapid progression even to ARDS.
2019-nCoVs distribute over respiratory mucosa, infect other cells, cause a cytokine storm in the body, produce a chain of immune responses, and generate changes in immune cells and peripheral white blood cells. Noticeably, 2019-nCoV mainly attacks lymphocyte, particularly T lymphocyte, thus, a decrease in lymphocyte count is a common laboratory test finding of COVID–19 infection. Degree of lymphocytopenia might be a critical predictive factor associated with disease severity and mortality7. The present study demonstrated the negative correlation between the number of lobes involved or the CT lung severity score and lymphocyte count. The CT lung severity score and the number of lobes involved may be the surrogate biomarkers in predicting disease severity of COVID–19.
There were several limitations in our study. First, the sample size of the present study was relatively small. Only 3 cases had followed-up CT scans. The progressions and outcomes of COVID–19 have not been accurately assessed. Second, our cases were all adults. The CT findings of COVID–19 in children have not been evaluated. Third, because not all of cases were from Wuhan, our results may be incomprehensive.