Table 3.

Histopathology and pathogenesis of COVID-19.

Organ	Histopathology	Features of vascular involvement	References
Lung	Diffuse alveolar damage with lymphocytic/ monocytic infiltrate together with intra-alveolar fibrinous exudate, hyaline membrane formation at acute stage. Type II pneumocyte hyperplasia with interstitial fibrosis at late stage Increase in pulmonary megakaryocytes	Perivascular cuffing by lymphocytes with fibrin/ hyaline thrombi seen within pulmonary vessels and capillaries Congested vessels	[143, 151, 153]
Heart	Small or multifocal lymphocytic infiltrate with dysmorphic cardiomyocyte and rare necrosis (milder pathology when compared with the lung) Eosinophilic myocarditis (rare)	Epicardial capillaries with prominent lymphomonocytic endotheliitis Macrovascular or microvascular thrombi Intraluminal megakaryocytes	[144, 151]
Brain	Activation of astrocytes and microglia with infiltration of cytotoxic T cell mainly in brainstem and meninges Occasional expression of viral antigen at cortical neurons	Intravascular thrombi with perivascular microhaemorrhages and intramural inflammatory infiltrates Multiple microscopic ischaemic infarct with or without antigen expression at endothelium	[174-179]
Kidney	Acute tubular injury Interstitial fibrosis Podocyte vacuolation Loss of brush border in proximal tubule Focal segmental glomerulosclerosis Granulomatous interstitial nephritis	Hemosiderin granules and pigmented casts, together with abundant erythrocyte with obstruction of peritubular capillary lumen with activation of endothelium	[143, 145, 167]
Liver	Histiocytic hyperplasia Focal macrovascular and microvascular steatosis Patchy hepatic necrosis in centrilobular and periportal areas	Platelet fibrin thrombi in sinusoid, central vein or portal vein Megakaryocytes in sinusoid Sinusoidal congestion Ischaemic necrosis	[143, 145, 167]
Spleen	White pulp depletion	Splenic infarction	[143]
Skin	Parakeratosis, acanthosis, dyskeratotic keratinocytes, necrotic keratinocytes, acantholytic clefts, lymphocyte satellitosis and pseudoherpetic of the epidermis	Dermal infiltrate with perivascular and intramural lymphocyte in muscular wall of small vessels Occasional intravascular hyaline/ fibrin thrombi Vascular deposition of C4d by immunohistochemical staining	[145, 162]
Placenta		Villous infarction, atherosis and fibrinoid necrosis of maternal vessels	[146]
Testis	Interstitial edema with leukocyte infiltration Sertoli cells showed swelling, vacuolation and cytoplasmic rarefaction, detachment from tubular basement membranes, and loss and sloughing into lumens of the intratubular cell mass		[147]