Materials and Methods
Following institutional review board approval, autopsy cases from patients with either premortem or postmortem RT-PCR–confirmed SARS-CoV-2 were reviewed.
The autopsies of confirmed or suspected COVID-19 cases were performed using the Virchow technique and recommendations provided by the US Centers for Disease Control and Prevention.
The lungs were serially sectioned, and samples were taken from grossly or radiographically identified abnormal regions. If neither was evident, at minimum one section from each lobe of the lung was taken.
Microscopic Evaluation: Overview
Analyses were performed based on the microscopic pulmonary patterns identified. First, all microscopic patterns were categorized as either "major" or "minor." Second, "novel" pathologic findings were defined as a deviation from the current literature, which describes ALI as the main underlying pulmonary pathologic pattern in COVID-19 and unexpected clinically. Third, "discordant" was characterized as incongruity of microscopic patterns with the radiologic findings.
Microscopic Evaluation: Major vs Minor Patterns
All H&E-stained lung slides were reviewed. A comprehensive list of features, including quantification where appropriate, was generated (Supplemental Table 1; all supplemental materials can be found at American Journal of Clinical Pathology online). All slides were evaluated for each of the features, and from these, a case diagnosis was formulated.
Following review of all cases, microscopic patterns were categorized as either "major" or "minor" findings depending upon whether they were present in 50% or more or less than 50% of all cases, respectively. In addition, to qualify as "major," the morphologic features had to be present in more than one slide and encompass 5% or more of the area of all slides with the exception of intravascular fibrin or platelet-rich aggregates (IFPAs), which had to be present in at least one slide. IFPAs were designated as such to reflect their unknown etiology—thrombi vs emboli. The IFPAs were further characterized by their location (including in the pulmonary artery, pulmonary vein, or other small vessels), quantity (including focal [rare vessels] or diffuse [three or more vessels in a single slide]), and size (including large or small). Large IFPAs corresponded to either proximal elastic arteries accompanying airways or veins within interlobular septa.
When performed and available, ancillary tests (histochemical or immunohistochemical stains) were reviewed.
Clinical and Laboratory Data
For each case, the electronic medical record was reviewed for demographics, initial presentation, comorbidities, hospital course, laboratory values, and therapies.
All available chest imaging, including chest radiographs and computed tomography (CT) scans, was reviewed. When multiple chest radiographs were performed, the first and last available were graded on a scale of 0 to 3: grade 0, lung with no alveolar opacities; grade 1 (minimal), less than one-third of the lung with alveolar opacities; grade 2 (moderate): one-third to two-thirds of the lung with alveolar opacities; and grade 3 (marked), more than two-thirds of the 2/3 lung with alveolar opacities. Change of the grade between the first and last chest radiographs was recorded.
Novel and Discordant Findings
Each component—clinical, laboratory data, imaging and pathology—was first reviewed independently by the corresponding subspecialists (pulmonologists who managed patients with COVID-19, a thoracic radiologist, a thoracic pathologist, and pathologists who performed the prosections). Following the microscopic review, the major pulmonary pathology patterns were assessed for novel and discordant findings.
Additional data were obtained, as needed, to adjudicate discordant findings. This included further comprehensive evaluation of clinical, laboratory, and radiologic data as well as the cause of death, which was determined based on macroscopic and microscopic pulmonary and extrapulmonary pathology. Assessment of cardiac findings, performed by a cardiac pathologist (C.C.M.), included but was not limited to evaluation for early or late ischemic changes and myocarditis. In the absence of pathologic evidence, cause of death was established based on adjudication of the clinical and pathologic findings. The cause of death was categorized into major categories: cardiac failure, respiratory failure, cardiorespiratory failure, neurologic (eg, intracranial hemorrhage), sepsis, thromboembolic event, or multiorgan failure. The level of certainty was stratified into definite (identifiable macroscopic and microscopic pathology) and probable (no identifiable macroscopic or microscopic pathology).
H&E slides from prepandemic, non–COVID-19 postmortem examinations with ALI (n = 7) and non-ALI (n = 7) were reviewed.
To correlate the "major" pathologic, clinical, and laboratory data, Pearson or ϕ correlation coefficients were calculated for all pairwise combinations of clinical, laboratory, radiologic, and major pathologic findings. To account for missing values, all correlations were computed on complete pairwise observations. The statistical significance of differences in the distributions of clinical, laboratory, radiologic, or major pathologic findings between patients with ALI and without ALI was assessed using a two-tailed Wilcoxon rank-sum test for continuous or ordinal variables and a Fisher exact test for binary variables. For all analysis, Holm-adjusted P < .05 was considered significant. All statistical analyses were performed in R version 3.6.3 (R Foundation for Statistical Computing).
Am J Clin Pathol. 2020;154(6):748-760. © 2020 American Society for Clinical Pathology