Histopathology of COVID-19: An illustration of the findings from fatal cases

COVID-19 represents the greatest global public health crisis since the influenza pandemic of 1918 (1). Since its first report in December, 2019, the SARS-CoV-2 coronavirus responsible for coronavirus disease 2019 (COVID-19) has efficiently transmitted from person to person, and two years after the declaration of the pandemic by the World Health Organization (WHO), it has caused approximately 481,756,671 infections and 6,127,981 deaths worldwide (2).

and hypertrophy in the myocardium were observed (14).Additionally, pulmonary lesions, such as the desquamation of pneumocytes and the presence of hyaline membranes and edema, have been observed, signs of acute respiratory distress syndrome.Tracheobronchitis with mononuclear cell inflammation, epithelial denudation and submucosal congestion, alveolar infiltrate with alveolar macrophage hyperplasia and mononuclear inflammatory interstitial infiltrate have also been observed (15,16).These alterations are not exclusive to SARS-CoV-2.There are predominant histopathological patterns, such as diffuse alveolar damage, that are shared with other respiratory viruses, such as SARS and influenza; however, vascular alterations, such as thrombosis and microthrombosis, seem to be more frequent in cases of COVID-19 and SARS, which suggests that coronaviruses in general could be associated with an increase in pulmonary microthrombi (17).
Other organs that have presented histological alterations associated with SARS-CoV-2 infection are the liver, kidney and heart.For example, in the liver, cirrhosis, moderate microvesicular steatosis and mild portal and lobular activity have been observed; these alterations can be associated with viral infection or drug-induced damage.In the kidney, chronic kidney disease and acute duct lesions have been described, and in the heart, myocardial fibrosis and mild mononuclear inflammatory infiltrate have been observed (3).
In Colombia, due to biosecurity issues in the framework of the health emergency due to COVID-19, the routine execution of necropsies, viscerotomies and postmortem tissue sampling by invasive methods was restricted; therefore, there is little material from tissues of infected patients as sources of useful information to understand the pathogenesis of the disease and thus few studies on the histopathology of viral infection by SARS-CoV-2.However, among some fatal cases in the Red Nacional de Laboratorios that were initially associated with mortality due to non-COVID acute respiratory infection that underwent routine necropsy, SARS-CoV-2 infection was confirmed by differential laboratory diagnosis, postmortem or some time before death.The tissue samples obtained in these cases are in the archives of the Laboratorio de Patología of the Instituto Nacional de Salud.

Figure 1 .
Figure 1.Normal histology of the lung.a) Alveolar region; note the completely free alveoli for oxygen supply through the capillaries located in the interalveolar septa, b) bronchiole in longitudinal section and c) trachea -upper respiratory tract.H&E stain.

Figure 6 .Figure 7 .Figure 8 .Figure 9 .Figure 10 .
Figure 6.Histopathological alterations in splenic tissue associated with COVID-19.a) Normal histology of the spleen in which a lymphatic node -white pulp -and an extensive area of red pulp is observed, b) reduction in the white pulp, c) hemorrhage in the red pulp, d) parenchymal necrosis.H&E stain.