Table 1.

Histopathological studies in COVID-19

Reported in	No of patients	Procedure	Main findings	Remarks
Wuhan, China [28]	2	Lung (lobectomy specimen)	Oedema, proteinaceous exudate, focal reactive hyperplasia of pneumocytes with patchy inflammatory cellular infiltration, and multinucleated giant cells. Hyaline membranes were not prominent.	Both patients had lung carcinoma and were asymptomatic for COVID-19.
Beijing, China [29]	1	Autopsy	Bilateral diffuse alveolar damage with cellular fibro-myxoid exudates	“Early ARDS”
Hamburg, Germany [30]	12	Autopsy	Deep vein thrombosis in 7 out of 12 patients; Pulmonary thromboembolism caused death in 4 patients.	Coronary heart disease and bronchial asthma or chronic obstructive pulmonary disease were common comorbid conditions.
Graz, Austria [11]	11	Autopsy	Diffuse alveolar damage (DAD), oedema, hyaline membranes, and proliferation of pneumocytes and fibroblasts. Thrombosis of small and mid-sized pulmonary arteries was found in all 11 patients.	Ten of the 11 patients received prophylactic anticoagulant therapy; venous thromboembolism was not clinically suspected antemortem
Oklahoma, US [31]	2	Autopsy	Diffuse alveolar damage and chronic inflammation and mucosal oedema; acute bronchopneumonia	One had hypertension, post-splenectomy state; other obese with myotonic dystrophy
New York, US [32]	5 1	Skin biopsies Autopsy	Generalized thrombotic microvascular injury, haemorrhagic pneumonitis with complement C5a fraction deposition	Complement-associated microvascular injury
Wuhan, China [33]	4	Core needle biopsies taken postmortem	Injury to the alveolar epithelial cells, hyaline membrane formation, and hyperplasia of type II pneumocytes, all components of diffuse alveolar damage. Superimposed bacterial pneumonia	Immunocompromised status (chronic lymphocytic leukaemia and renal transplantation) or other conditions (cirrhosis, hypertension, and diabetes)
Wuhan, China [34]	26	Kidney biopsy	Diffuse proximal tubule injury with the loss of brush border, non-isometric vacuolar degeneration, and frank necrosis; erythrocyte aggregates obstructing the lumen of capillaries	Frank thrombosis not reported
São Paulo, Brazil [35]	10	Ultrasound-Guided Minimally Invasive Autopsy	Massive epithelial injury and microthrombi in pulmonary vessels. Microthrombi were less frequent in glomeruli, spleen, heart, dermis, testis, and liver sinusoids	Systemic thrombosis is common in COVID-19.
New York, US [36]	5	Postpartum placenta histology	Focal avascular villi and thrombi in larger foetal vessels with complement deposition.	All 5 had healthy, term deliveries
Switzerland [37]	21	Autopsy	Pulmonary thromboembolisms (n = 4), alveolar haemorrhage (n = 3), vasculitis (n = 1), generalised thrombotic microangiopathy	Patients were mostly elderly males, with arterial hypertension, obesity, and severe cardiovascular comorbidities.
Massachusetts, US [38]	7	Autopsy	Thromboses with microangiopathy. Alveolar capillary microthrombi were more prevalent in patients with COVID-19 than in those with influenza A (H1N1).	Established that angiopathy leading microthrombi are an integral part of COVID-19

COVID-19 Coronavirus-2019 disease; ARDS acute respiratory distress syndrome