Histological Changes in the Lung Tissue in Association with COVID-19: Review Article

ABSTRACT Background: It has been shown that SARS-CoV-2 is a multi-systemic virus and can affect number of body systems including the respiratory tract, the gastro-intestinal tract, the liver, the kidney and the nervous system. Despite the high mortality rate, there is little literature on postmortem findings of this unique virus, perhaps due to its highly contagious nature, inadequate information on prevention, and a lack of robust infrastructure for appropriate management of infected cases at various centers throughout the world. Aim of the study: The aim of the current study was to review and list the main histological changes seen in patients died because of COVID-19. Methods: A systemic search was carried out including Google Scholar, PubMed, and MEDLINE and the Google search Engine in order to scan all available published articles dealing with histological changes affection the lung in patients with documented COVID-19. The following key words were used to accomplish the search mission: COVID-19, SARS-CoV-2, Lung Histology, Pulmonary Histology, Histopathology. The search was limited to articles written in English language. Any article published between the end of 2019 and the time of initiating the current work was reviewed. The information in the current review is totally based on reviewed articles that are mentioned in the section of references. Results: The main sources of lung tissues were Whole lung biopsy, Postmortem study, Core needle biopsy and Ultrasound based samples from autopsy. The exudative changes include injury to pneumocytes, congestion of capillaries, giant cell formations, dilation of alveolar ducts, thickening of capillaries, edema of interstitium and formation of hyaline membrane. The proliferative changes include hyperplasia of Type-2 pneumocytes with some reactive atypia with proliferation of myofibroblastic cells leading to granulation tissue formation, thickening of alveolar wall accumulation of alveolar macrophages, interstitial thickening which harbors collections of proliferating fibroblasts together with foci of hemorrhage and lymphocytic infiltration. Conclusion: The main histopathological changes in lung of patients with COVID-19 can be grouped into three main phases, exudative, proliferative and fibrotic phases in addition to changes involving vascular tissues, bronchi and bronchioles and the main changes are the diffuse alveolar damage seen in exudative and proliferative phases