Pulmonary pathology of COVID-19: a review of autopsy studies

COVID-19 lung injury is a common manifestation of severe illness. Lung tissue examination has been largely derived from autopsy - a combination of case reports, small and moderately sized series with international scope. Common and uncommon histopathology provides insight into the progression of severe, fatal disease.

COVID-19 lung histology is most commonly diffuse alveolar damage as part of acute respiratory distress syndrome. Lung injury can be temporally heterogeneous, with patterns of healing alongside new injury. Viral studies, including immunohistochemistry, RNA in-situ hybridization, and tissue-based Polymerase chain reaction (PCR) assist in discerning complications of therapy (e.g. ventilator-associated pneumonia) from primary viral-induced injury. Response to viral infection produces systemic effects, and one major manifestation is thrombosis of micro-circulation and larger vessels. Less common patterns include neutrophil-rich inflammation, raising speculation that neutrophil extra-cellular traps may play a role in both viral control and exaggerated immune response.

The heterogeneity of fatal cases- persistence of viral infection in lung, clearance of virus but severe lung injury, thrombosis, and exaggerated immune response - suggest that antiviral, antithrombotic, anti-inflammatory, and supportive therapy play a role in treatment, but that the patient-specific cause and timing of the lung injury is important in choosing intervention.