key: cord-0873124-mz8hb8f9
authors: Diaz, Ashley; Bujnowski, Daniel; McMullen, Phillip; Lysandrou, Maria; Ananthanarayanan, Vijayalakshmi; Husain, Aliya N.; Freeman, Richard; Vigneswaran, Wickii T.; Ferguson, Mark K.; Donington, Jessica; Madariaga, Maria Lucia; Abdelsattar, Zaid M.
title: Pulmonary parenchymal changes in COVID-19 survivors
date: 2021-07-31
journal: Ann Thorac Surg
DOI: 10.1016/j.athoracsur.2021.06.076
sha: 0bcdc4ef3e705bca8fb0881b730e6b5c636ca9ae
doc_id: 873124
cord_uid: mz8hb8f9

Background As the COVID-19 pandemic moves into the survivorship phase, questions regarding long-term lung damage remain unanswered. Previous histopathological studies are limited to autopsy reports. We studied lung specimens from COVID-19 survivors who underwent elective lung resections to determine whether post-acute histopathological changes are present. Methods In this multicenter observational study, we included adult COVID-19 survivors (n=11) who had recovered but subsequently underwent unrelated elective lung resection for indeterminate lung nodules or lung cancer. We compared these to an age- and procedure-matched control group who never contracted COVID-19 (n=5), and an end-stage COVID-19 group (n=3). A blinded pulmonary pathologist examined the lung parenchyma focusing on four compartments: airways, alveoli, interstitium, and vasculature. Results Eleven COVID-19 survivors with asymptomatic (n=4), moderate (n=4), and severe (n=3) COVID-19 infections underwent elective lung resection at a median 68.5 days (range 24-142) after COVID-19 diagnosis. The most common operation was lobectomy (75%). On histopathological examination, no differences were identified between the lung parenchyma of COVID-19 survivors and controls across all compartments examined. Conversely, patients in the end-stage COVID-19 group showed fibrotic diffuse alveolar damage with intra-alveolar macrophages, organizing pneumonia, and focal interstitial emphysema. Conclusions In this first study to examine the lung parenchyma of COVID-19 survivors, we did not find distinct post-acute histopathological changes to suggest permanent pulmonary damage. These results are reassuring for COVID-19 survivors who recover and become asymptomatic.

One year into the COVID-19 pandemic, over 116 million people worldwide have been infected with SARS-CoV-2 and over 2.5 million lives have been lost. 1 Post-mortem autopsies or pathologic studies from patients with end-stage lung disease from COVID-19 report severe fibrosis, diffuse alveolar damage (DAD), perivascular T-cell infiltration, severe endothelial injury, intracellular viral particles, and cell membrane disruption in lung tissue. [2] [3] [4] It is unknown whether there are long-lasting histopathological changes in the lung parenchyma of COVID-19

survivors. 9, 10 A growing number of people have survived COVID-19, but some have experienced a prolonged and strenuous recovery. In population-based studies, an estimated 35% of survivors had not returned to their usual state of health 14-21 days post infection, while some patients remained symptomatic several months after infection, [5] [6] [7] [8] even showing persistent radiographic findings such as ground glass opacities. 9 Although a lung biopsy is unlikely to be performed on an otherwise healthy survivor, there is a unique opportunity to examine the lung parenchyma of COVID-19 survivors who subsequently underwent elective thoracic operation or lung resection for different indications, such as solitary lung nodules or lung cancer. Examining the lung parenchyma of this patient population can provide important insights into this disease and its longterm pulmonary impact.

In this context, we study the histopathological changes in a unique subset of patients, who recovered from COVID-19, became asymptomatic, and underwent lung resection for other unrelated indications. We sought to identify the spectrum of disease in COVID-19 survivors, which would help inform expectations in a growing surviving population currently exceeding millions.

J o u r n a l P r e -p r o o f

This is a multicenter, observational, retrospective, cohort study conducted at Loyola University Medical Center and the University of Chicago Medicine. The study was approved by the Loyola University Chicago and the University of Chicago Institutional Review Boards (LU214441 and IRB210055). Eleven adult patients (over age 18) who had previously contracted COVID-19 confirmed by a positive RT-PCR and were asymptomatic at the time of their subsequent elective lung resections between July 2020 and February 2021 (COVID-19 survivors) were included. For comparison, we also included three patients who had prolonged symptoms and did not fully recover from COVID-19 (COVID-19 end-stage lung disease). The negative control group included five age-and elective thoracic procedure-matched patients who underwent lung resection between 2019 and 2020 and did not have a history of COVID-19. Patient clinical, histological and radiological data was collected from electronic medical records. 12 

Details of the COVID-19 course including date of positive RT-PCR test, symptoms, hospital and intensive care unit (ICU) admissions were included. COVID-19 survivors were classified by their symptoms during infection into three groups: asymptomatic, moderate, or severe based on prior literature. [13] [14] [15] [16] [17] Asymptomatic patients did not experience symptoms of COVID-19. 13 Moderate COVID-19 cases were defined by symptoms such as fever, chills, aches, cough, headache, nausea, sore throat, fatigue, and congestion not requiring ICU admission. [13] [14] [15] [16] Severe disease was determined by admission to the ICU. 16, 17 Pathological Review 

Results are descriptively reported with percentages or medians with standard deviations or ranges as appropriate.

Among COVID-19 survivors, median age was 65 years (range 36-72), median body mass index was 27.9 kg/m 2 (range 23.8-34.7) and seven (64%) were female. Four (36%) COVID-19 J o u r n a l P r e -p r o o f survivors had moderate COVID-19 and three (27%) had a severe course requiring ICU admission.

The remainder (36%) were asymptomatic. Common pre-existing conditions included hypertension (36%), obesity (27%), and heart disease (18%) ( Table 1) . While no COVID-19 survivors were current smokers, the majority were former smokers (82%). At time of surgery, all patients had resolution of COVID-19 radiographic sequalae ( Figure 1 ) and all were asymptomatic from a COVID-19 perspective.

Three patients with COVID-19 end-stage lung disease were included: a 56-year-old previously healthy male (Patient 17); a 53-year-old male (Patient 18) with type II diabetes, hyperlipidemia, and hypertension; and a 77-year-old female (Patient 19) with chronic kidney disease and chronic lymphocytic leukemia ( Table 2) .

Specimens from five age-and procedure-matched patients without a prior COVID-19 diagnosis served as control tissues and were obtained from lung cancer resection specimens in a similar fashion to the COVID-19 survivors. The controls all had a history of smoking.

No patient received any COVID-19 vaccine at the time of this study.

Eleven COVID-19 survivors underwent a total of 12 operations (resulting in 12 specimens available for analysis). The median time from infection to elective thoracic surgery was 68.5 days (range 24-125; Figure 2 ). The most common procedure was lobectomy (75%), followed by wedge resection (25%) ( Table 2 ). The indications for surgery included management of indeterminate pulmonary nodules (58%), resection of biopsy-proven lung cancer (33%), and spontaneous pneumothorax (8%). There were no postoperative complications in the COVID-19 survivors. 

All five control patients underwent elective thoracic operations for lung cancer with the most common procedure being lobectomy (60%) and wedge resection (40%).

In COVID-19 survivors and controls there was evidence of small airway disease, including basement membrane fibrosis, which was present in 67% of COVID-19 survivors and 60% of control patients (Table 3 , Figure 3A -B). Airway inflammation was minimal in COVID-19 survivors and controls ( Figure 3A-B) . Examination of the airways in the patient who died of acute COVID-19 was somewhat limited by post-mortem changes, but overall there was scant-to-mild lymphocytic inflammation and minimal changes to the basement membrane or smooth muscle ( Figure 3C ). In Patient 17, there was evidence of basement membrane fibrosis and moderate mixed inflammation in the submucosa with intraepithelial extension suggestive of potential superimposed infectious processes ( Figure 3D ).

Alveoli COVID-19 survivors and controls had high rates of emphysema (92% COVID-19 survivors and 100% controls; Figure 4A -B). Smoker's macrophages, metaplastic changes, and occasional poorly formed granulomas were seen in the alveolar spaces in a subset of both groups as well (Table 3 ). In Patient 19, alveolar COVID-19 disease was characterized by findings of DAD ( Figure   4C ). In Patient 18, scattered intra-alveolar macrophages and rare foci of organizing pneumonia were seen within the alveoli (Table 3) .

Interstitium Areas of mild fibrosis were seen in both COVID-19 survivors and controls, with 50% COVID-19 survivors having focal fibrosis and 60% control patients having some areas of fibrosis ( Figure 4A-B) . The pattern of fibrosis seen in both COVID-19 survivors and control patients was largely attributable to smoking-related changes. The interstitium of Patient 19 was inflamed with predominantly lymphocytic inflammation and edema ( Figure 4C ). This was in contrast to Patient 17 in whom the interstitium was diffusely fibrotic ( Figure 4D ) with a brisk inflammatory infiltrate composed primarily of lymphocytes and was not the same pattern of fibrosis seen in COVID-19 survivors and controls.

Histologic evidence of mild pulmonary hypertension was present in 42% of COVID-19

survivors and 60% of controls, but the vasculature was otherwise unremarkable (Figure 5A-B) .

There was no significant vasculitis in any of the assessed COVID-19 survivors nor the end-stage patients. While scattered microthrombi and gross pulmonary emboli have been reported in the acute COVID-19 setting, 17 the vessels in Patient 19 were patent with no significant inflammation or occlusive thrombi ( Figure 5C ). Areas of recanalized thrombi were, however, rarely seen in Patient 17 ( Figure 5D ).

An experienced pulmonary pathologist blinded to the clinical histories for each case was unable to distinguish between COVID-19 survivors and controls in any of the assessed compartments. In addition, there were no significant differences appreciated between the COVID-

In this first observational study of patients who survived COVID-19, recovered and became asymptomatic, and then underwent an elective lung resection for other indications, we examined the potential for any post-acute histopathological lung changes in COVID-19 survivors.

We found that in recovered COVID-19 survivors there were no discernible histopathological changes suggesting permanent parenchymal damage.

It is reassuring that none of the COVID-19 survivors included in this study had any lasting damage that was directly attributable to COVID-19. These findings fill an important gap in our understanding of the COVID-19 pandemic, 18 especially as we move into its survivorship phase.

Clinicians and patients alike now have observational evidence that once the patient recovers from their disease, it is unlikely to have permanent lung parenchymal sequelae at least up to four months from their infection, which was the maximal duration of this study.

A strength of this study is the rigorous use of a blinded pathology methodology in analyzing the difference between COVID-19 survivors' lung tissue and non-COVID-19 infected controls, while also providing a COVID-19 end-stage lung disease comparison group. With this approach, we were able to obtain unbiased, dependable results that showed no discernable differences between the lungs of COVID-19 patients and controls. In addition, the systematic examination across the four histologic compartments provided a complete picture of the airways, alveoli, interstitium, and vasculature, all of which can be affected as shown in the COVID-19 end-stage lung disease comparison group.

On the other hand, the COVID-19 end-stage lung disease patients likely represent those who have progressed to fibrosis as a result of organization of the original acute lung injury; a phenomenon which has been reported both prior to the COVID-19 pandemic, 19, 20 and in severe cases of acute COVID-19. 21 The reasons why some patients progress to COVID-19 end-stage lung disease while others recover with pathology undiscernible from controls is unclear. In the present study, we included the spectrum of COVID-19 disease courses from asymptomatic to J o u r n a l P r e -p r o o f severe disease requiring ICU admission. It is noteworthy that even in those with severe disease, their recovery was complete without notable lasting parenchymal damage.

COVID-19 can severely injure vascular endothelium and can progress to acute respiratory distress syndrome and viral pneumonia regardless of age or preexisting conditions. 22 This was the case for the end-stage patients included in this study. These patients had changes consistent with fibrotic DAD 23-26 as well as diffuse lymphocytic inflammation, pulmonary interstitial emphysema, and recanalized thrombi. The cumulative changes in these three cases were entirely attributable to the subsequent organization of diffuse acute lung injury (i.e. DAD and organizing pneumonia) and need for prolonged mechanical ventilation.

This investigation further reveals important information regarding the safety of lung resection in COVID-19 survivors. No postoperative complications occurred in the patients in this series. We found that the lung parenchyma did not exhibit clinically relevant changes that would hamper or prolong postoperative recovery after lung resection. This is valuable information to surgeons and patients when discussing potential surgical risks in this growing subset of patients.

In addition, previous studies have suggested that elective operations be postponed by 6 weeks to maximize safety. 28 This study has several limitations. This is an observational study subject to inherent confounding and selection bias. It is possible that the surgeons selected patients to undergo lung resection who would have a low probability of long-standing parenchymal changes. Second, the majority of patients had smoking-related parenchymal changes that may obscure any possible COVID-19 related changes. However, the absence of any discernible differences and the inability of a blinded pathologist to differentiate between COVID-19 survivors and controls makes subtle changes less likely. 4, 27 In addition, we did not have data on pulmonary function tests before and after COVID-19 infection which can meaningfully add to the overall functional assessment of these patients beyond the histopathological assessment. Finally, the study is limited by its sample size, though we included patients along the spectrum of COVID-19 disease course.

J o u r n a l P r e -p r o o f One patient underwent two elective thoracic surgeries and therefore those two specimens (n=12 total specimens) were included.

Negative control thoracic surgery patients (n=5) 

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