European Journal of Cardiovascular Medicine

SARS-CoV-2, declared a global pandemic by the World Health Organization, causes diverse multiorgan pathology, most prominently in the lungs, presenting as diffuse alveolar damage, microthrombi, bronchopneumonia, necrotizing bronchiolitis, and viral pneumonia. While several clinical reports on COVID-19 deaths exist, post-mortem pathological findings from this region of India remain limited. Understanding histopathological changes is crucial for improving patient management and treatment strategies in both mild and severe cases.

A clear knowledge of the spectrum and frequency of pulmonary histologic changes in COVID-19 is vital for understanding disease pathophysiology and its broader public health impact. Although many international studies have documented such findings, no reports from a pathologist’s perspective are available from South India. This study, therefore, aims to highlight specific histological alterations in COVID-19 lungs and to validate them using immunohistochemistry with SARS-CoV-2 spike antibody.

OBJECTIVES

1. To describe the histopathological features in the lung tissues of patients who have died due to pulmonary pathology during the pandemic period and to check its association with COVID-19 infection with the help of COVID 19 -IHC marker.
2. To find out the specific histopathology findings in the lung tissue due to SARS- COVID 19 infection and expression of COVID 19 -IHC marker in the tissue.

The current Descriptive cross-sectional study was conducted in the Department of Pathology, Government Medical College, Manjeri from 1st March 2020 – 1st April 2021. Study Subjects All autopsy lung specimens with pulmonary pathology as cause of death, including diffuse alveolar damage, microthrombi, bronchopneumonia, necrotizing bronchiolitis, and viral pneumonia. Inclusion Criteria Lung specimens showing the above features. Exclusion Criteria Specimens with histology other than the above. Operational Definitions • Diffuse Alveolar Damage (DAD) oAcute/exudative phase: intra-alveolar edema, interstitial widening, hyaline membranes, thrombi. oOrganizing/proliferative phase: fibroblastic proliferation with myxoid stroma, type II pneumocyte hyperplasia, squamous metaplasia, residual fibrin, interstitial fibrosis. • Pulmonary vascular damage: endothelitis, thrombosis, angiogenesis. • Bronchopneumonia: neutrophils in bronchi/bronchioles and alveoli; lipid pneumonia with lipid-laden macrophages. • Lobar pneumonia: congestion → red hepatization → gray hepatization → resolution. • Necrotizing bronchiolitis: acute inflammation of lower airways. • Viral changes: multinucleated pneumocytes with enlarged nuclei, amphophilic cytoplasm, nucleoli, intranuclear inclusions. Methods We studied 70 autopsy lung specimens showing DAD, vascular damage, bronchopneumonia, necrotizing bronchiolitis, or viral pneumonia. Clinical and post-mortem details were retrieved from Department of Pathology records, Government Medical College, Manjeri. Two H&E slides and corresponding blocks from each lung were reviewed. Histopathology and Immunohistochemistry Lesions were graded as absent (0), focal (≤50%), or diffuse (>50%). Microthrombi were defined in arteries <1.0 mm; larger vessels >1.0 mm were classified as medium-sized. Immunohistochemistry was performed on all cases using anti–SARS-CoV/SARS-CoV-2 spike antibody (GeneTex, 1:100–1:500) after citrate buffer antigen retrieval. Positivity was validated against RT-PCR–confirmed cases. Two pathologists independently evaluated slides. Analysis Data were compiled in Excel and analyzed with IBM SPSS 28.0. Variables were expressed as mean and percentage.

Demographics

Subjects ranged from 7 days to 89 years (mean 45 years), most between 40–50 years. Males were predominant (44; 62.9%) compared to females (26; 37.1%), ratio 1.69.

COVID Status

18 cases were RT-PCR positive, while 52 had unknown status.

Histopathology

Lesions included DAD, vascular changes, bronchopneumonia, lobar pneumonia, necrotizing bronchiolitis, and viral cytopathic features.

• Epithelial injury (DAD): Seen in 28/70.
• Acute/exudative phase: 23 cases with intra-alveolar edema, interstitial widening, hyaline membranes, thrombi.
• Organizing phase: 5 cases with type II pneumocyte hyperplasia; fibrin rests in 3.
• Vascular injury: Found in 17/70. Endothelitis and microthrombi in 15; congestion in 2. Angiogenesis was absent.
• Interstitial/viral changes: Four cases showed multinucleated pneumocytes, intranuclear inclusions, and cytopathic alterations.
• Mixed patterns: Most frequent, seen in 21/70, combining DAD, interstitial pneumonia, vascular injury, and/or bronchopneumonia.
• Bronchopneumonia: 9 cases (2 red hepatization, 1 resolution).
• Lobar pneumonia: 2 cases.
• Pulmonary arterial infarct: 1 case.

The histopathology and immunohistochemistry findings are given in figure 1-6 and table 1, 2 & 3.

Immunohistochemistry findings

IHC in 70 cases showed 25 positive for SARS-CoV/SARS-CoV-2 spike antibody, with staining in alveolar macrophages, interstitial macrophages, and type II pneumocytes. Nuclear, cytoplasmic, or combined staining was considered positive. Among 18 RT-PCR–positive cases, 4 were negative for spike antibody.

Comorbidities

Among 70 cases, 23 had comorbidities, most commonly atherosclerosis (17 cases, including 5 with prior myocardial infarction). Other conditions included diabetes (3), obesity (3), and one case each of chronic kidney disease, alcoholic liver disease, and sickle cell anemia.

We analyzed 70 autopsy cases of COVID-19–related lung pathology, revealing diverse findings such as diffuse alveolar damage (DAD) in acute/exudative and organizing/proliferative phases, microthrombi, bronchopneumonia, necrotizing bronchiolitis, viral pneumonia, and pulmonary edema. The patients ranged from a 7-day-old neonate to 89 years, with a mean age of 45 years; most were between 40–50 years. Males predominated (44 vs. 26; ratio 1.69), consistent with literature that older males with comorbidities are more affected.[1]

Of 70 cases, 18 were RT-PCR positive, 52 had unknown status. 4 PCR-positive cases were negative for SARS-CoV-2 spike protein by immunohistochemistry (IHC). Of 25 IHC-positive cases, 11 lacked PCR data. Borczuk et al.[2] demonstrated that viral antigen detection is higher in the first two weeks of illness and declines later, explaining the IHC negativity in some of our PCR-positive cases.

Histological findings paralleled previous SARS (2002–03) and COVID-19 autopsy reports.[3-7] Bradley et al.[8] also emphasized DAD as the key lesion and noted IHC-negative cases despite PCR positivity, concordant with our data. Thus, our study supports the central role of DAD and hyaline membrane formation as the hallmark of severe COVID-19.

Epithelial injury predominated (40%), while mixed patterns with vascular lesions occurred in 30%, higher than prior reports. Microthrombi (21.4%) and large vessel thrombi (10%) confirmed the prothrombotic tendency of SARS-CoV-2. Despite vascular lesions, endothelial cell immunopositivity was absent. Instead, staining was confined to type II pneumocytes and macrophages, suggesting selective viral tropism or immune-mediated damage, or limitations of spike protein marker.

Limitations include lack of RT-PCR status in two-thirds of cases, selection bias due to inclusion of lungs with pathology only, single-institution origin, and restricted clinical information. Using only one IHC marker may underestimate viral detection; inclusion of nucleocapsid or endothelial markers (e.g., CD34, vWF) would yield greater clarity.

Future studies with larger cohorts, confirmed molecular data, and expanded IHC/molecular panels could enhance understanding of viral load, tissue tropism, and host responses. Comparative analyses with non-COVID respiratory deaths may help distinguish disease-specific changes and inform targeted interventions.

Our study confirms diffuse alveolar damage as the dominant pathological feature of COVID-19 lungs, with acute and organizing phases both represented. Other findings included vascular injury, bronchopneumonia, necrotizing bronchiolitis, and edema. IHC demonstrated SARS-CoV-2 spike protein in pneumocytes and macrophages, supporting direct viral injury. These results reinforce the interplay of epithelial and vascular pathology in COVID-19 and highlight the value of combined histology, IHC, and molecular testing in future research. Ethical Considerations Approval was obtained from the Institutional Research Committee and Ethics Committee, Government Medical College, Manjeri. Data were collected from histopathology records with departmental permission. Financial assistance was provided by SBMR.

[1]           Guan WJ, Ni ZY, Hu Y, et al. Clinical characteristics of coronavirus disease 2019 in China. N Engl J Med 2020;382:1708-20.

[2]           Borczuk AC, Steven P. COVID-19 pulmonary pathology: a multi-institutional autopsy cohort from Italy and New York City. Modern Pathology 2020;33:2156-68.

[3]           Barton LM, Duval EJ, Stroberg E, et al. COVID-19 autopsies, Oklahoma, USA. Am J Clin Pathol 2020;153:725-33.

[4]           Xu Z, Shi L, Wang Y, et al. Pathological findings of COVID-19 associated with acute respiratory distress syndrome. Lancet Respir Med 2020;8:420-22.

[5]           Tian S, Hu W, Niu L, et al. Pulmonary pathology of early-phase 2019 novel coronavirus pneumonia in two patients with lung cancer. J Thorac Oncol 2020;15:700-4.

[6]           Gu J, Gong E, Zhang B, et al. Multiple organ infection and the pathogenesis of SARS. J Exp Med 2005;202:415-24.

[7]           Nicholls JM, Poon LLM, Lee KC, et al. Lung pathology of fatal severe acute respiratory syndrome. Lancet 2003;361:1773-8.

[8]           Bradley BT, Maioli H, Johnston R, et al. Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State: a case series. Lancet 2020;396:320-32.