Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State: a case series

Abstract

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of an ongoing pandemic, with increasing deaths worldwide. To date, documentation of the histopathological features in fatal cases of the disease caused by SARS-CoV-2 (COVID-19) has been scarce due to sparse autopsy performance and incomplete organ sampling. We aimed to provide a clinicopathological report of severe COVID-19 cases by documenting histopathological changes and evidence of SARS-CoV-2 tissue tropism.

Methods: In this case series, patients with a positive antemortem or post-mortem SARS-CoV-2 result were considered eligible for enrolment. Post-mortem examinations were done on 14 people who died with COVID-19 at the King County Medical Examiner's Office (Seattle, WA, USA) and Snohomish County Medical Examiner's Office (Everett, WA, USA) in negative-pressure isolation suites during February and March, 2020. Clinical and laboratory data were reviewed. Tissue examination was done by light microscopy, immunohistochemistry, electron microscopy, and quantitative RT-PCR.

Findings: The median age of our cohort was 73·5 years (range 42-84; IQR 67·5-77·25). All patients had clinically significant comorbidities, the most common being hypertension, chronic kidney disease, obstructive sleep apnoea, and metabolic disease including diabetes and obesity. The major pulmonary finding was diffuse alveolar damage in the acute or organising phases, with five patients showing focal pulmonary microthrombi. Coronavirus-like particles were detected in the respiratory system, kidney, and gastrointestinal tract. Lymphocytic myocarditis was observed in one patient with viral RNA detected in the tissue.

Interpretation: The primary pathology observed in our cohort was diffuse alveolar damage, with virus located in the pneumocytes and tracheal epithelium. Microthrombi, where observed, were scarce and endotheliitis was not identified. Although other non-pulmonary organs showed susceptibility to infection, their contribution to the pathogenesis of SARS-CoV-2 infection requires further examination.

Funding: None.

Figure 1

Lung with subsegmental pulmonary embolism (indicated by arrowheads) in patient 12

Figure 2

Lung pathology of fatal COVID-19 infections (A) Hyaline membranes in patient 4. Haematoxylin and eosin; magnification ×100. (B) Diffuse alveolar damage, organising phase, in patient 2. Arrowheads indicate fibroblast proliferations. Haematoxylin and eosin; magnification ×100. (C) Multinucleated giant cells and pleomorphic, reactive pneumocytes in patient 5. Haematoxylin and eosin; magnification ×400. (D) Pleomorphic multinucleated giant cells stained positive for pneumocyte marker TTF-1 and negative for macrophage marker CD68 by immunohistochemistry in patient 5. Magnification ×600. (E) Perivascular lymphocytic inflammation in patient 10. Haematoxylin and eosin; magnification ×200. (F) Reactive airway cells and bronchial epithelium (indicated by arrowheads) positive for SARS-CoV-2 spike protein in patient 10. Haematoxylin and eosin; magnification ×400. (G) Pneumocytes and alveolar macrophages positive for SARS-CoV-2 spike protein by immunohistochemistry in patient 10. Magnification ×200. SARS-CoV-2=severe acute respiratory syndrome coronavirus 2.

Figure 3

Organ findings in fatal COVID-19 infections (A) Trachea with submucosal lymphocytic inflammation in patient 8. Haematoxylin and eosin; magnification ×100. (B) Lymphocytes (left panel) and submucosal glands (right panel) in the trachea stained positive for SARS-CoV-2 spike protein by immunohistochemistry in patient 8. Magnification ×200. (C) Heart with lymphocytic myocarditis and associated myocyte damage in patient 8. Haematoxylin and eosin; magnification ×40. (D) Heart with lymphocytic myocarditis and necrotic myocyte (indicated by arrowhead) in patient 8. Haematoxylin and eosin; magnification ×400. (E) Spleen with decreased white pulp in patient 9. Haematoxylin and eosin; magnification ×40. Inset image shows CD45 immunohistochemistry. (F) Renal tubular epithelium positive for SARS-CoV-2 spike protein by immunohistochemistry in patient 8. Magnification ×400. SARS-CoV-2=severe acute respiratory syndrome coronavirus 2.

Figure 4

Coagulopathy of fatal COVID-19 infections (A) Small vessel thrombus in patient 12. Haematoxylin and eosin; magnification ×40. (B) Pulmonary microthrombus in patient 3. Haematoxylin and eosin; magnification ×200. (C) Pulmonary microthrombus in patient 8. Haematoxylin and eosin; magnification ×200. (D) Pulmonary microthrombus in patient 14. Haematoxylin and eosin; magnification ×400. (E) Renal vein organising thrombus in patient 13. Haematoxylin and eosin; magnification ×40.

Figure 5

Ultrastructural features in fatal COVID-19 infections Ultrastructural finding of viral particles in tracheal epithelial cells (A and B) in patient 13, lung pneumocytes (C and D) in patient 13, enterocytes (E and F) in patient 13, and kidney endothelial cells (G) in patient 8 and proximal tubular epithelial cells (H) in patient 13. Viral particles (indicated by green arrows) were observed either outside cells (A and F) in close proximity to the cell membrane or inside the cells (B, C, D, E, G, and H) in aggregates confined within vesicles (indicated by green arrowheads). Some of the particles were associated with double membranes (indicated by white arrowheads) resembling double membrane vesicles. Asterisks in (A) and (F) mark the cells adjacent to the viral particles in the extracellular space.