In general, most of the publications were case reports and case series with two case-control study and 1 cohort study. Majority of the articles were published in the year 2020. As for the country of origin, 8 articles originated from the USA, followed by two from Italy, two from Germany and one each from Switzerland, China, Romania, Turkey, Brazil, Zambia, Ghana and France. The lowest number of cases being examined and reported was one whilst the highest was 348 cases. The age of the reported cases varied with the majority of the deceased being elderly. Almost all studies described the majority of the cases have known pre-existing comorbidities with cardiovascular disease and hypertension being the frequently stated risk factors.
Respiratory system
Almost all studies reported on the autopsy pulmonary findings in COVID-19 death except for one article reported by Santoriello et al. (2020) that focused on kidney pathology in COVID-19 deaths. Heavy, firm and edematous lungs have been mostly described in (Roden et al. 2021; Konopka et al. 2020; Falasca et al. 2020; Barton et al. 2020; Keresztesi et al. 2020; Attoh et al. 2020) There was patchy to diffuse consolidation in the lungs as mentioned by (Fig. 2).(Roden et al. 2021; Keresztesi et al. 2020; Menter et al. 2020; Arslan et al. 2021)
There were also changes in colour and pattern of the lungs in COVID-19 patients. Edler et al. (2020) described a mosaic-like pattern of pale and dark purple lung sections with prominent capillary drawings. Other than that, Barton et al. (2020) reported a mottled red appearance of the lungs from one of the cases they examined. There was pleural effusion noted in the studies of (Roden et al. 2021; Falasca et al. 2020)
Almost all studies except the study by Santoriello et al. (2020) reported on the histological features of lungs in COVID-19 cases. The most reported finding in all those studies is the features of diffuse alveolar damage (DAD) in the lung histology. Proliferative to exudative diffuse alveolar damage characterized with hyaline membrane deposition, alveolar necrosis, type II pneumocytes hyperplasia and the presence of lymphocytes, macrophages, multinucleated giant cells were considered as distinctive features of COVID-19 infection. Bloom et al. (2020) described the findings as multifocal to diffuse alveolar necrosis and bronchiolar respiratory epithelial necrosis. On the other hand, Edler et al. (2020) reported a diffuse alveolar damage with an accumulation of activated type II pneumocytes, fibroblasts, protein-rich exudate and hyaline membranes. A prominent capillary congestion with hyaline membrane formation, reactive pneumocytes changes and the presence of syncytial cells were the most prominent findings in the study of Menter et al. (2020) (Fig. 3).
There were several studies that described microscopic thrombi formation in the lung histology. Eight out of ten patients in the study of Duarte-Neto et al. (2020) have fibrinous thrombi in alveolar vessels. In addition to that, a study in Northern Italy revealed 33 out of 38 cases have platelet-fibrin thrombi deposited in small alveolar vessels.(Carsana et al. 2020) Elsoukkary et al. (2021) reported 84% of the cases to have microscopic and/or macroscopic thrombi at autopsy and most commonly seen was in the respiratory system. This study also reported the coagulation profile of all patients was prolonged, with the mean prothrombin time of 24 s and mean activated partial thromboplastin time of 51.6 s.
Cardiovascular system
Pathology of the cardiovascular system was mostly chronic diseases related changes. Duarte-Neto et al. (2020) described the extrapulmonary findings in COVID-19 patients can be categorized into findings related to comorbidities, attributed to shock and unascertained aetiologies. From the study, nine cases were reported with the presence of myocardial hypertrophy and myocardial fibrosis. Myocardial hypertrophy was one of the common findings of the cardiovascular system described in these studies by (Attoh et al. 2020; Menter et al. 2020; Elsoukkary et al. 2021; McMullen et al. 2021) In the study of Menter et al. (2020), 70% of the cases have severe generalized atherosclerosis of the aorta.
Apart from that, there were several studies reported features of cardiac inflammation in the COVID-19 patients. There were two cases of myositis and two cases of mild lymphomononuclear myocarditis in the study of Duarte-Neto et al. (2020). In the study of Falasca et al. (2020), active myocarditis was observed microscopically, characterized by lymphocytic infiltrates and associated with focal myocyte necrosis. There was one case reported by Edler et al. (2020) with a feature of myocarditis such as small lymphocytic infiltrates in the right ventricle of the heart.
Renal system
The most common finding of the renal system was mainly described as acute tubular injury. Menter et al. (2020) reported features such as widened tubular lumina, flattened tubular epithelium and interstitial oedema which were related to the findings of acute tubular injury. In the study of Santoriello et al. (2020) which more specified towards the kidney pathology in COVID-19 cases, acute tubular injury was the most common finding, especially in patients with acute kidney injury. Acute tubular injury in this study was graded into absent, mild and moderate-to-severe based on the histological changes and its distribution. From their study, they revealed that despite 11 cases that cannot be determined due to autolysis, 39% of the remaining cases were absent or minimal, 39% were mild and 23% were moderate-to-severe.
Other than that, there were also findings related to chronic diseases described in these findings. Chronic changes such as arteriosclerosis, intimal fibrosis of the arteries and vascular scarring were found in the majority of the cases (Fig. 4a, b).(Menter et al. 2020) These findings were also similar to the study of Santoriello et al. (2020) which reported findings such as arteriosclerosis, interstitial fibrosis and tubular atrophy. Such findings also could be found in the study of Duarte-Neto et al. (2020) and Elsoukkary et al. (2021).
Hepatobiliary and other systems
Congested liver was among the common finding described in these studies of, Falasca et al. (2020), Attoh et al. (2020) and Edler et al. (2020). Other than that, steatosis or fatty changes of liver was also one of the frequently found pathology in these studies by Falasca et al. (2020), Menter et al. (2020) and Elsoukkary et al. (2021). Sign of shock associated necrosis of the liver was described by Menter et al. (2020).
Apart from those liver pathology, haematopoietic system such as spleen and lymph nodes pathology was one of the extrapulmonary organs that often described in these articles (Fig. 4c, d). Elsoukkary et al. (2021) reported in their study that except for one case with splenic marginal zone lymphoma, the lymph nodes were in preserved architecture, morphologically intact germinal centre, paracortical areas and patent sinuses. The subcapsular and intraparenchymal sinuses contained CD20 positive large, transformed cells with prominent nucleoli and amphophilic cytoplasm. These transformed cells were also seen in vascular sinuses and paracortical regions.