Imaging diagnosis
Case 213
【Progress】
PCR test was positive at the day, leading to diagnosis of viral pneumonia of COVID-19. Six days later, he received chest CT (Figs 3, 4) again when PCR test was negative. Further, sixteen days later also when PCR test was negative, he received chest CT for follow-up (Figs 5, 6).
【Discussion】
Chest CT findings for COVID-19 are relatively specific, ground glass opacity appearing in the marginal area of the lung (1-4). Pathological examination of biopsy specimen or infected lung by COVID-19 is reported to show alveolitis including swollen alveolar wall, proliferation of abundant macrophages, hyperplasia of type II pneumocytes (2-4). These findings are, in a sense, interstitial pneumonia. Although ground glass opacity is visualized on CT with 5 mm slices, ground glass opacity is clarified to be composed of fine network on CT with 1 mm slices (Figs 1, 2). As days progress, ground glass opacity becomes more dense turning into wide network wall such as melon skin appearance or consolidation (Figs 3, 4). Pathologically, it indicates dense infiltration of lymphocyte and/or dense hyaline membranes (2, 3). As days progress further, it comes to disappear the opacity and/or to appear fibrous components in slight and/or moderate cases with CVID-19 (Figs 5, 6). However, in severe cases, it occurs intensive acute alveolar damages with interstitial edema, capillary congestion, intravascular microthrombi and pulmonary thromboembolism, indicating acute respiratory distress syndrome. Cytokines produced from macrophages and monocytes induce to create intravascular microthrombi (1-3). In short, tissue factor stimulates coagulopathic system. Interleukin 1(IL1), Interleukin 6 (IL6) and tumor necrosis factor (TNF) stimulate endothelial system, inducing adhesion of platelets. Cytokine storm following severe corona virus infection leads to create microthrombi.
There are four defense lines of immune response against microorganism infection in our body. The first defense line always works ordinarily in a usual life. Cilia, secreted mucin, surfactant in a respiratory tract, Ig A, Ig M, alveolar macrophages, type II pneumocytes, and killer T cells belong to the first defense line. The second defense line works when the first line defense is not sufficient for much volume of microorganisms or new toxic microorganism. Monocytes, leukocytes, lymphocytes or other immune cells come to migrate from bone marrow to the infected organ via the message (cytokine) from the first line defense cells which says the necessity of support for the first defense line. Third line defense line begins to work from the information (cytokine) based on materials phagocyted by macrophages and/or killer T cells. T cells and B cells play a main role for the third defense line. Namely, T cells get the information of the materials of the microorganisms from the first and the second line defenses and give the information to B cells. B cells produce antibody against microorganisms. It takes several days to create antibody. The fourth defense line works when the second defense line and the third defense line do not work sufficiently. In this situation, macrophages produce much more inflammatory cytokine such as IL1, IL6 and TNF not only to attack microorganisms but also the infected alveolar cells and immune cells. It induces acute respiratory distress syndrome.
Influenza virus attacks the first line defense line and usually damages the first defense line more extensively, inducing much inflammatory cytokine release and causing high fever in the early stage. Further, it damages to oral, nasal and bronchial membranes causing severe redness and pain. It is reported both infection of influenza virus and bacterial infection occur in 50-60% (5). Influenza virus infection damages to first line defense, making bacteria easy to invade and break through the first line defense line. However, based on our experiences, no case with both infection of corona virus and bacteria was encountered. It is considered the potency for corona virus to damage to the first line defense line is not so strong as that of influenza virus.
It is controversial and feared now when simultaneous infection of influenza and corona occur. When corona virus infects to the respiratory tract in the situation of both infections of influenza and bacteria, corona virus will be embarrassed to realize less volume of healthy epithelial cells to invade for their surviving. Further, the circumstances with inflammatory cytokine around the epithelial cells are not appropriate for corona virus habitat.
In this situation, it is considered that corona virus infection hardly occurs following influenza virus infection.
Meanwhile, it is possible that corona virus infection first occurs followed by influenza virus infection. In this situation, influenza virus surely embarrasses to realize the less volume of virgin healthy epithelial cells for their surviving and the circumstances of high fever by cytokine release. Virus and bacteria are hard to survive for high body temperature.
【Summary】
We presented a sixty nine-year-old male with corona virus. Chest CT revealed characteristic findings of ground glass opacity in the marginal area of the lung. Follow up chest CT revealed that ground glass opacity turned to thick fine network and later, disappearance or fibrous changes. It is borne in mind that ground glass opacity comes out from alveolitis with type II alveolar cells hyperplasia and macrophages proliferation, thick networks reflect hyaline membrane thickness and lymphocytes proliferation. Further, influenza virus infection is associated with bacterial infection in 50-60%, while corona virus infection is least with bacterial infection. It is thought that corona virus infection is hard to happen to associate with influenza virus infection probably because of the least number of healthy epithelial cells for their habitat to survive and the intensive circumstances of cytokine activation caused by influenza virus.
【References】
1.Mohanty SK, et al. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and coronavirus disease 19 (COVID-19) - anatomic pathology perspective on current knowledge. Diagn Pathol. 2020 Aug 14;15(1):103
2.Tian S, et al. Pulmonary Pathology of Early-Phase 2019 Novel Coronavirus (COVID-19) Pneumonia in Two Patients With Lung Cancer. Journal of Thoracic Oncology, 2020;15: 675-678.
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4.Zhu N. et al. A novel coronavirus from patients with pneumonia in China, 2019. N Engl J Med. 2020; 382: 727-733
5.Josef C, et al. Bacterial and viral infections associated with influenza. Influenza Other Respir Viruses. 2013 ;7 :105-13.
2020.12.2