The document summarizes the findings of a pathology presentation on COVID-19 pulmonary pathology. It describes the histopathological examination of lung tissue from 38 COVID-19 patient deaths in Italy which found evidence of diffuse alveolar damage, hyaline membrane formation, thrombi in small arteries, and type II pneumocyte hyperplasia. It also discusses the similarities to findings from SARS, MERS, and influenza, including epithelial infection, microvascular damage, and organizing pneumonia that can progress to pulmonary fibrosis.

1. JOURNAL PRESENTATION
PULMONARY PATHOLOGY OF COVID-19
Sansar Babu Tiwari, MBBS, PGY I
Department of Pathology
TUTH
3rd May 2020
1

2. Pulmonary post-mortem findings in
a large series of COVID-19 cases
from Northern Italy
• Aurelio Sonzogni, MD et. al.
• Pathology Unit, L. Sacco Hospital, Milan, Italy
• Department of Pathology- Papa Giovanni XXIII
Hospital - Bergamo, Italy

3. INTRODUCTION:
• Italy has been the first country in Europe to be
reached by the epidemic and Lombardy was
devastated in just one month.
• L. Sacco Hospital, Milan and Papa Giovanni XXIII,
Bergamo have been the first hospitals in this
region to manage the epidemic crisis.
• The clinical spectrum of SARS-CoV-2 disease
(COVID-19) is reported to include mild
asymptomatic infection, mild upper respiratory
disease with fever and cough, and severe
pneumonia that can lead to ARDS in 15% of the
hospitalized cases.

4. INTRODUCTION:
• They described the first available large series of
lung histopathological findings in patients died
from COVID-19 in Northern Italy, with the aim to
report the main microscopic pulmonary lesions in
SARS-CoV-2 infection and severe respiratory failure.

5. METHODS:
• Histological analysis of post-mortem lung tissues
from 38 cases who died for COVID-19 between
February and March in two referral centres for the
management of the COVID-19 outbreak in
Northern Italy, Luigi Sacco Hospital, Milan, and
Papa Giovanni XXIII, Bergamo (patient permission
given by the Ethics Committees of the two hospitals
to use personal and sensitive data for scientific
research related to the disease was collected).

6. METHODS:
• The autopsies were performed in Airborne Infection
Isolation Autopsy Rooms and the personnel used the
correct Personal Protection Equipment (PPE), according
to “Engineering control and PPE recommendations for
autopsies”.
• A medium of 7 tissue blocks were taken from each lung
(range 5-9), selecting the most representative areas at
macroscopic examination. Tissues were fixed in 10%
buffered formalin for >48 hours. Three-μm paraffin
sections were stained by hematoxylin-eosin.
Immunohistochemistry reactions were performed on
selected cases (CD45, CD68, CD61, TTF1, p40, Ki67,
Masson Trichome) to better characterize inflammatory
infiltrate, epithelial cells and fibrosis.

7. METHODS:
• Histological evaluation was performed blindly by
two pathologists from each hospital, with expertise
in the field. Histological features of the cellular and
interstitial damage were described and graded by
using a semi-quantitative scale.
• Additional samples from selected cases were fixed
in glutaraldehyde for electron microscopy and
examined by EM-109 ZEISS and CCD-Megaview G2
(I-TEM imaging platform software).

8. RESULTS:
• Patients were 33 males and 5 females, average age
of 69 years (range 32-86); the time that the
patients spent in the Subintensive/Intensive Care
Unit ranged from 1 to 23 days (6.87 days).
• Regarding past comorbidities, data were available
in 31/38 patients: 9 diabetes, 18 hypertension, 4
past malignancies, 11 cardiovascular disorders, 3
mild chronic obstructive pulmonary disorders.

9. RESULTS:
• At the time of hospitalization, all the patients had
throat swab sample positive for SARS-CoV-2
infection and had clinical and radiological features
of interstitial pneumonia. D-dimer was available in
26/38 patients, with high value in all of them (>10 x
the upper reference limit).
• Patients died after a median time of 16.27 days
(range 5-31) from the onset of symptoms.

10. RESULTS:
• Macroscopic examination of the lungs revealed heavy,
congested and oedematous organs, with spotty
involvement.
• At histological examination, the features of Diffuse
Alveolar Disease (DAD) were found, corresponding to
those observable in the exudative and
early/intermediate proliferative phases of the disease.
• Both phases often overlapped in the different areas of
the lungs, with pluri-focal pattern of distribution. The
fibrotic phase was rarely observed, possibly due to the
short duration of the disease. Moreover, five patients
also had bacterial (4) and fungal (1) abscesses.

11. RESULTS:
Hyaline membrane Microthrombus
Megakaryocyte
entrapment
Type II pneumocyte
hyperplasia

12. RESULTS:
• Capillary congestion, interstitial edema, dilated
alveolar ducts, hyaline membranes composed of
serum proteins and condensed fibrin, loss of
pneumocytes were the histological patterns of the
exudative phase mostly observed in all the cases.
• Platelet-fibrin thrombi in small arterial vessels
(<1mm in diameter) were found in 33 cases.
• Moreover, type II pneumocyte hyperplasia showing
reactive atypia, myofibroblast proliferation, alveolar
granulation tissue and obliterating fibrosis were
present in half of the patients but were focal.

13. RESULTS:
Luminal organizing
fibrosis
Interstitial myofibroblastic
reaction

14. RESULTS:
• Microcystic honeycombing and mural fibrosis were
occasionally present.
• Inflammatory component was represented by a few
CD45 positive lymphocytes located in the
interstitial space; a large number of CD68 positive
macrophages were mainly localized in the alveolar
lumens.
• Immunohistochemistry with anti CD61 antibody
identified increased number of megakaryocytes in
lung capillaries

15. RESULTS:
CD68 macrophages CD45 Interstitial
lymphocytes

16. RESULTS:
• Ultrastructural examination
revealed viral particles,
with morphology typical of
the family of Coronaviridae
and localized along
plasmalemmal membranes
and within cytoplasmic
vacuoles of pneumocytes.
• Virions had an average
diameter of 82nm and viral
projection about 13nm in
length.

17. DISCUSSIONS:
• The peculiar histopathological findings were
atypical pneumocytes (reactive atypia) and diffuse
thrombosis of the peripheral small vessels.
• In their study, fibrin thrombi of small arterial
vessels (diameter < 1mm) were observed in 33 /38
patients, half of them with >25% of tissue
involvement and associated with high levels of D-
dimer in blood.
• These findings might explain the severe hypoxemia
which characterizes the clinical feature of ARDS in
SARS-CoV-2 patients.

18. DISCUSSIONS:
• Their data strongly support the hypothesis
proposed by recent clinical studies, that COVID-19
is complicated or anyway strictly related to
coagulopathy and thrombosis.
• Moreover detection of D-dimer values >1 μg/ml
have been associated with fatal outcome of COVID-
19.
• For these reasons, the use of anticoagulants has
been recently suggested as potentially beneficial in
patients with severe COVID-19, albeit its efficacy
and safety have not been demonstrated.

19. DISCUSSIONS:
• Finally, the search for viral particles was carried out
in a subset of patients and highlighted the
presence of rare virions in the cytoplasm of
pneumocytes. Despite the low number of cases,
these findings may suggest that the virus remains
in lung tissue for many days, even if in small
quantities, possibly being the trigger of the
mechanism that leads to and feeds lung damage.

20. Histopathology and genetic
susceptibility in COVID-19
pneumonia.
• von der Thüsen, MD, PhD
• Menno van der Eerden, MD PhD
• Dept. of Pathology and Dept. of Pulmonology,
Erasmus MC, Rotterdam, The Netherlands

21. INFLUENZA VIRUS:
• The respiratory tract histology of influenza
reflects its cellular tropism, as influenza virus
replicates in respiratory epithelial cells
throughout the respiratory tree, with non-fatal
infections predominantly involving the upper
respiratory tract and trachea, but fatal cases of
influenza usually result from pneumonia.
• Changes in the smaller airways include necrosis
and complete loss of the epithelial layer (both
ciliated and goblet cells), often resulting in the
formation of hyaline membranes at these sites.
Neutrophilic inflammation may be present in
the lumen, and extend into surrounding alveoli.

22. INFLUENZA VIRUS:
• In addition, a more chronic lymphoplasma-
histiocytic infiltrate is often seen in influenza-
infected airways. The parenchyma shows
evidence of acute injury with interstitial
congestion, edema, and inflammation
(predominantly neutrophilic with some
eosinophils), as well as desquamated alveolar
epithelial cells, intra-alveolar edema, intra-
alveolar hemorrhage, fibrin, hyaline membrane
formation, and sometimes necrosis of the
alveolar septa (necrotizing alveolitis), the latter
possibly resulting from frequently observed
vascular changes with capillary congestion and
thrombosis.

23. COVID-19:
• They have recently also observed similar
changes in COVID-19 autopsy cases, with
evidence of extensive microvascular damage
and thrombotic occlusion as the foremost
pattern of injury, resulting in intra-alveolar
fibrinous exudates akin to acute fibrinous
and organizing pneumonia (AFOP).

24. COVID-19 :
• This spectrum of abnormalities is highly
reminiscent of changes seen in the context of
the chronic lung allograft rejection (CLAD) of the
restrictive phenotype (restrictive allograft
syndrome (RAS)), which is presumed to occur
secondary to antibody-mediated endothelial
damage and complement activation of humoral
rejection episodes.
• Such vascular changes are likely to play a central
role in the pathogenesis of COVID-19, and may
in part be attributable to dysregulation of the
endothelial ACE2 receptor with ensuing
bradykinin-dependent local lung edema, as well
as a highly pro-thrombotic state, which can
manifest itself in the lung as well as in extra-
pulmonary tissues.

25. COVID-19 :
• Direct infection of endothelial cells may play a central
role in this process. More chronic changes included
intra-alveolar organization with fibroblastic
proliferation and diffuse fibrotic thickening of
alveolar walls, consisting of proliferating interstitial
fibroblasts.
• In RAS, we have found this to eventually result in
chronic fibrotic patterns of intra-alveolar
fibroelastosis and non-specific interstitial pneumonia
(NSIP).
• Time will tell if a similar progression to fibrosis will
take place in a subset of survivors of severe COVID-
19, and whether this is indeed secondary to vascular
damage, primarily related to the initial epithelial
infection, or a combination of these response
patterns.

26. OTHERS CORONA VIRUS:
• Apart from the prominent microvascular
changes, the pathological features of COVID-
19 thereby appear to resemble those seen in
SARS and Middle Eastern respiratory
syndrome (MERS) coronavirus infection.
• Early SARS-CoV infections were found to be
typified by acute diffuse alveolar damage,
and late stages by a combination of diffuse
alveolar damage and acute fibrinous and
organizing pneumonia.

27. OTHERS CORONA VIRUS:
• MERS-CoV infections also showed exudative
diffuse alveolar damage with hyaline
membranes, pulmonary edema, type II
pneumocyte hyperplasia, (lymphocytic)
interstitial pneumonia, and multinucleated
syncytial cells.

28. FUTURE GUIDANCE:
• Poor oxygenation requiring ventilation and oxygen
administration in influenza as well as coronavirus infection is
likely to be in part directly related to decreased diffusion
capacity due to parenchymal destruction as well as
increased diffusion distances due to
1) intra-alveolar aggregates of edema, fibrin, hyaline
membranes, cells and organization
2) widening of alveolar septa due to edema and
inflammation,
3) vascular changes with capillary congestion and
thrombosis and
4) eventually, intrabronchiolar, intra-alveolar and interstitial
fibrosis.

29. FUTURE GUIDANCE:
• While regeneration and reversal of the first 3 phenomena is
theoretically possible, and as in influenza may be related to
the regenerative capacity of the host, it may occur at lower
rates in SARS-CoV-2 infection as compared to other viral
pneumonias.
• Intra-alveolar and interstitial fibrosis, however, are most
likely irreversible, and may have contributed to the
remarkably high number of patients who cannot be weaned
off ventilation in the current COVID-19 outbreak.

30. FUTURE GUIDANCE:
• Also, in survivors we may eventually see a significant number
of cases with irreversible fibrotic lung damage and limited
pulmonary function, which has previously been termed COLD
(‘Corona Obstructive Lung Disease’).
• To which extent this term truly reflects the underlying
physiology remains to be seen, as the interstitial fibrotic
changes which have thus far been observed are likely to also
lead to a restrictive lung defect as well as permanently
decreased diffusion capacity, and are thus more akin to other
types of (idiopathic) interstitial lung fibrosis, such as forms of
the abovementioned intra-alveolar fibroelastosis and fibrotic
NSIP, and could therefore perhaps be more accurately termed
Corona-Associated Lung Disease (‘CALD’). This will require
multi-center studies which correlate histopathological findings
with clinical and radiological data.

31. WHY COVID-19 AFFECTS MALE:
• Interestingly, as an X-linked phenotype, the effectiveness of
interaction-booster and interaction-inhibitor variants of
ACE2 can be more definite in males than females, and could
contribute towards a higher mortality rate in males,
accounting for up to ∼70% of death caused by SARS-CoV2,
SARS-CoV or MERS-CoV.
• ACE inhibitors or ARB increases the ACE2 receptor thereby
increasing the viral entry.
• However it would to premature to say that ACE2 inhibitors
should be stopped.

33. • In the lung tissue of patients who died of respiratory failure
due to COVID19 pneumonia, there can be evidence of
epithelial infection with
• cytopathic effects of pneumocytes (A, box); denudation of
bronchiolar epithelium (B), evidence of diffuse alveolar
damage (DAD) with hyaline membrane formation with
organization (C).
• Observed vascular changes include extensive bilateral and
diffuse (micro)vascular damage and its sequelae, with
arterial thrombosis with organization (D), microvascular
fibrinoid change with hyaline thrombi (E, fibrin-Lendrum
(MSB) stain, arrows) and edema (**), and extensive intra-
alveolar fibrinous aggregates (F) with an acute fibrinous and
organizing pneumonia (AFOP) pattern (F, *).
COVID-19 :

34. • Fibrotic changes vary in appearance and include
organizing pneumonia with progression to fibrosis
(G), intra-alveolar fibro-elastosis (Elastic-van
Gieson, H) and fibrotic non-specific interstitial
pneumonia (F-NSIP; I).
• There is often relatively sparse interstitial chronic
inflammation with an acute interstitial pneumonia
pattern (AIP; J), foci of lymphocytic vasculitis (K)
and acute inflammation, especially in relation to
areas of necrosis and possible secondary infection
(L).
COVID-19 :

35. Thank You!!