3.3. Chest imaging
Radiological examinations are of great importance in the early detection and management of COVID-19. According to current experience, lung imaging manifests can be found earlier than clinical symptoms, so imaging examination is vital in preclinical screening(Sohrabi et al., 2020). Therefore, suspected cases should undertake chest examination as soon as possible.
In early stage, multiple small patchy shadows and interstitial changes were detected in the extra pulmonary zone. And then, it developed into multiple ground-glass infiltration (D. Wang et al., 2020). In severe and critically cases, lung lesions usually involved most commonly 4-5 lobes in the bilateral lower and upper lobes. The first report of COVID-19 patients described that bilateral lung involvement was detected in 80% of patients, and consolidative pattern changes were always observer in most patients in intensive care unit (ICU), but ground-glass pattern always showed in patients not in the ICU(Bernheim et al., 2020). Shi et al. analyzed the CT changes and found that most patients even the asymptomatic patients showed dynamic changes from focal unilateral to diffuse bilateral ground-glass opacities and then progressed to consolidations within 1-3 weeks(X.-W. Xu et al., 2020). In general, combining assessment of imaging features with clinical and laboratory findings can facilitate diagnosis of COVID-19 pneumonia and evaluate severity of the disease.
4.Thepathological changes in COVID-19 patients
A recent study reported the biopsy results from two patients who underwent surgery for malignancy and then were found to have been infected with SARS-CoV-2, which provided first opportunities to study the pathology of COVID-19. It revealed that the lungs of patients exhibited edema, proteinaceous exudate, focal reactive hyperplasia of pneumocytes with patchy inflammatory cellular infiltration, and multinucleated giant cells, but hyaline membranes were not prominent(Tian et al., 2020). This study may describe early phase changes of the lung pathology of COVID-19 pneumonia. After that some academics performed autopsy from 12 dead patients and the results were released by the national health commission. The histopathological changes for different organs are summarized below:
Lung The lungs showed evident multi-pulmonary consolidation, acute interstitial inflammatory infiltrates and congestion in the alveolar septae. The lumina of alveoli and bronchioles were variably filled with proteinrich oedema fluid, erythrocytes, cellular debris and lymphocytes. The exudation cells were mainly mononuclear, macrophages and multinucleated giant cells. Type II alveolar epithelial cells proliferated obviously with Inclusion bodies inside. The blood vessel of the alveolar septum had congestion and edema, in which the infiltration of mononuclears lymphocytics, and intravascular hyaline thrombosis can be seen. Focal hemorrhage and necrosis of the lung tissue caused hemorrhagic infarction. Diffuse interstitial pulmonary fibrosis would be presented with the disease progress. Bronchial epithelial cells were denaturation, necrosis and defluvium. Mucus plugs were visible in the bronchial lumen. Due to over-inflation of the alveoli, a small number of the alveolar septum was broken, or the cysts were formed. SARS-CoV-2 particles could be observed in the cytoplasm of bronchial mucosal epitheliums and type II alveolar epithelial cells under an electron microscope. Immunohistochemical staining showed that some alveolar epitheliums and macrophages were positive for SARS-CoV-2 antigens. RT-PCR was positive for SARS-CoV-2 nucleic acids.
Immune systemThe volume of spleen decreased significantly and the number of lymphocytes was significantly reduced. There were focal patchy hemorrhages, necrosis and proliferation and phagocytosis of macrophages in the splenic tissue, with atrophy of white pulp lymphoid aggregates. The number of lymphocytes decreased obviously, and necrosis was visible in lymph nodes. Immunohistochemical staining showed that CD4 + T and CD8 + T cells were reduced in the spleen and lymph nodes. The number of three cell lines in the bone marrow was reduced.
Cardiovascular system There was notable degeneration and necrosis in the myocardial cells, and a few monocytes, lymphocytes and neutrophils infiltrated in the interstitium. Endothelial shedding, endovascular inflammation and thrombosis were visible in the blood vessel.
Liver and gallbladder The volume of the liver increased and its color was dark red. there are degeneration of hepatocytes, congestion of hepatic sinus, focal necrosis with neutrophil infiltration and microthrombosis, which feature the repeated interchange of these kinds of pathological course. The gallbladder was filled with bile.
Kidney There was proteinaceous exudate in the glomerular cavity and degeneration and necrosis in renal tubular epitheliums. Hyperemia, microthrombus and focal fibrosis can be observed in the renal interstitium.
other organs Within the cerebrum, there was evidence of ongestion, edema, mild neuronophagia and some cases showed neurons degeneration. There were focal necrosis in the adrenal glands. Mucosal epitheliums of the esophagus, stomach and intestine had varying degrees of the degeneration, necrosis and shedding.
5. Diagnosis ofCOVID-19
As the number of cases increased rapidly, the first task for the clinical diagnostic workflow is to identify the suspected cases and isolating them immediately, which is critical to cutting off the source of infection. The National Health Commission of China released the Diagnosis and Treatment Scheme for Novel Corona Virus Pneumonia (Trial) Edition. Patients comply any item of the epidemiological history and any two items of the clinical manifestations, or comply 3 items of the clinical manifestations mentioned above can be considered as the suspected cases(Table.2) . Based upon the evidence from clinical research, the detection of SARS-CoV-2 nucleic acids in nasopharyngeal swabs, sputum, lower respiratory tract secretions and SARS-CoV-2-specific antibodies (IgM and IgG) may be the final etiology diagnosis for the confirmed case (Table.2 ). In addition, COVID-19 can be divided into four classes: mild, moderate, severe, and critical according to the severity of symptoms (Table 3 ). There are some clinical signs and symptoms closely related to the severity of the confirmed cases (Table 4 ).