PURPOSE OF REVIEW: 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 .
RECENT FINDINGS: 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 .
SUMMARY: 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.