Giant thymolipoma in a patient with severe COVID-19 pneumonia: case report

Introduction

Thymolipomas are rare benign slow-growing tumors of the anterior mediastinum, representing 2–9% of thymic tumors (1-3). Thymolipomas are characterized by slow growth with symptoms developing when their size is large enough to generate a significant local mass effect in the mediastinum. They can manifest with shortness of breath, chest pain, decreased exercise tolerance, and cough (1-3). When incidentally found in the initial diagnostic approach of respiratory failure, it is challenging to define the actual contribution of thymolipoma to the pathophysiology of acute respiratory failure. In patients with coronavirus disease 2019 (COVID-19), it is paramount to identify the primary etiology of respiratory failure to decide on the timing of surgery while balancing the risk of early surgical intervention after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (4). We present this article in accordance with the CARE reporting checklist (available at https://shc.amegroups.com/article/view/10.21037/shc-23-44/rc).

Case presentation

A previously healthy 24-year-old man presented to the emergency department with three days of sore throat, productive cough, fevers, chills, malaise, myalgias and fatigue. Physical examination revealed fever, tachycardia, oxygen saturation of 90% on room air, and reduced breath sounds in the right lung base. A nasopharyngeal swab polymerase chain reaction test for SARS-CoV-2 returned positive. A chest radiograph suggested right hemidiaphragm elevation, pleural effusion, and patchy airspace opacities in the left lung base (Figure 1A). A computed tomography (CT) of the chest identified a 25 cm primarily adipose mediastinal mass with intervening denser soft tissue areas, causing compressive atelectasis of the right lung and leftward displacement of the heart and mediastinum (Figure 1B). There were also bilateral lung infiltrates compatible with COVID-19 pneumonia (Figure S1). A broad differential diagnosis was considered with especial concern for a malignant etiology such as mediastinal liposarcoma. Serum tumor markers, including alpha-fetoprotein, beta human chorionic gonadotropin (HCG), and carcinoembryonic antigen (CEA), were normal. Magnetic resonance imaging (MRI) of the chest showed T2-weighted and diffusion-weighted hyperintense internal architectures in the mass and no evidence of invasion into nearby structures (Figure 1C). A positron emission tomography (PET) scan showed no hypermetabolic areas within the mass or elsewhere (Figure 1D). A percutaneous CT-guided core needle biopsy ruled out elements suggestive of sarcoma and favored a benign diagnosis of thymolipoma based on the presence of benign thymic and adipose tissue, and mature lymphocytes.

Figure 1 Giant thymolipoma diagnosed concomitantly with COVID-19. Chest radiograph at presentation (A). CT scan (B), T2-weighted MRI (C), and PET scan (D) showing adipose nature, large size, mass effect and absence of hypermetabolic areas. Intraoperative photograph (E). Follow up chest film (F). COVID-19, coronavirus disease 2019; CT, computed tomography; MRI, magnetic resonance imaging; PET, positron emission tomography.

Meanwhile, while this work up was being completed, the patient progressed to acute hypoxemic respiratory failure consistent with severe COVID-19 pneumonia. During the first 48 hours after admission, he developed desaturation episodes <90% which required treatment with supplemental oxygen with a progressive requirement of up to 5 L/min via a regular nasal cannula. However, by 72 hours after admission hypoxemia had progressed more profoundly requiring treatment with a high-flow nasal cannula at 70% FiO₂ with a flow of 60 L/min. In addition, he was subjected to periods of prone positioning to assist with oxygenation/ventilation. Because of the severity of COVID-19 pneumonia he received treatment with remdesivir (100 mg intravenous daily for 5 days), baricitinib (4 mg orally daily for 14 days), and dexamethasone (6 mg intravenously daily for 10 days). After ruling out malignancy and local invasion, it was decided to allow for resolution of severe COVID-19 pneumonia before surgical resection. He was discharged from the hospital with supplemental oxygen at 4 L/min via nasal cannula and gradually wean off of it. A follow up chest CT scan revealed tumor stability and interval improvement in bilateral pulmonary infiltrates. Clinically, the patient had complete resolution of the respiratory distress with no further need for supplemental oxygen at rest or with activity. His oxygen saturation was consistently >95% on room air. Preoperative pulmonary function tests showed a forced expiratory volume in the first second (FEV₁) of 1.88 L (47% predicted), forced vital capacity (FVC) of 2.31 L (49% predicted), and diffusing capacity of the lungs for carbon monoxide (DLCO) of 18.3 mL/min/mmHg (64% predicted). This was consistent with a moderate to severe restrictive pattern that was attributed to the presence of the mediastinal mass. Nutritionally, there were no preoperative concerns. His body mass index (BMI) was 31.96 kg/m² and serum albumin level was 3.7 g/dL. Therefore, surgical treatment proceeded 8 weeks after COVID-19 diagnosis. Intraoperative monitoring included infradiaphragmatic central venous access given compression of the superior vena cava, which was anticipated to worsen with intraoperative manipulation. An arterial line was used due to the anticipated hemodynamic changes from manipulating the mass around the heart. A double lumen endotracheal tube was used to isolate the right lung. The mass was completely resected through a median sternotomy (Figure 1E). Pathology examination revealed a mass with a homogenous cut surface measuring 35 cm × 22 cm × 10.5 cm and weighing 3,355 g. Histologically, it was comprised of benign thymic and mature adipose tissue consistent with a diagnosis of thymolipoma. The patient’s postoperative course was uncomplicated and he was discharged home on postoperative day 3. Outpatient follow-up three weeks later showed resolution of respiratory symptoms and complete re-expansion of the right lung (Figure 1F). The case timeline can be seen in Figure 2. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Publication of this case report and accompanying images was waived from patient consent according to the Mayo Clinic institutional review board.

Figure 2 Case timeline. SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; COVID-19, coronavirus disease 2019.

Discussion

The differential diagnosis of mediastinal masses is vast. When faced with a large adipose prevascular mediastinal mass, thymolipoma should be considered (1-3,5). However, the diagnostic work up must rule out malignancies such as mediastinal liposarcoma (1,2,4). A thymolipoma is suspected when imaging studies show a large anterior mediastinal mass composed of adipose tissue with areas of soft tissue density representing thymic tissue, without local invasion but rather mass effect on adjacent structures such as compression of the lungs, heart, great vessels, and hemidiaphragm (1,5). A remarkable radiologic finding is the absence of vascular invasion (1,5). The final surgical pathologic features are microscopically mixed fragments of mature adipose tissue and benign thymic tissue with mature lymphocytes (CD20 and CD3⁺) (5).

This case posed a challenge when trying to determine the individual contributions of COVID-19 and the large mediastinal mass to the patient’s clinical presentation. The diagnostic work up suggested a benign, slow-growing etiology, which suggested that COVID-19 pneumonia was the primary driver of the respiratory failure. An analysis of 5,479 patients showed that major elective surgery within 8 weeks after SARS-CoV-2 infection is associated with a high risk of complications such as pneumonia, respiratory failure, pulmonary embolism, and sepsis (4). Therefore, determining the appropriate timing for intervention is crucial. Allowing 8 weeks of recovery before proceeding with an operation can reduce the risk of major postoperative complications. This is particularly true for patients with benign pathologies or not severely symptomatic who can wait. Moreover, this should be strongly considered in cases that involve surgery in the chest using single lung ventilation. Our successful outcome following severe COVID-19 pneumonia argues in favor of this approach.

Given the very large sizes that thymolipomas can reach before diagnosis, the typical approaches to resection using minimally invasive techniques are limited (3). An initial approach to thymolipoma with a median sternotomy is versatile, as it allows extension into a hemi-clamshell configuration, if needed (2,3). A median sternotomy also provides direct exposure along the heart and great vessels with excellent access if extracorporeal support becomes necessary in the event of airway compression or hemodynamic instability (3).

Conclusions

Thymolipomas are slow growing benign tumors of the anterior mediastinum that can reach giant sizes before diagnosis. In patients presenting with mediastinal masses and concomitant serious acute cardiopulmonary conditions, a comprehensive work up is important to determine the contribution of the mediastinal mass to the clinical picture and the behavior of the mass. This information can help determine the best timing of surgical intervention.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://shc.amegroups.com/article/view/10.21037/shc-23-44/rc

Peer Review File: Available at https://shc.amegroups.com/article/view/10.21037/shc-23-44/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://shc.amegroups.com/article/view/10.21037/shc-23-44/coif). L.F.T. serves as an unpaid editorial board member of Shanghai Chest from October 2023 to September 2025. L.F.T. has served as a consultant for Atricure Inc., Intuitive Surgical, and AstraZeneca. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Publication of this case report and accompanying images was waived from patient consent according to the Mayo Clinic institutional review board.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Gaerte SC, Meyer CA, Winer-Muram HT, et al. Fat-containing lesions of the chest. Radiographics 2002;22:S61-78. [Crossref] [PubMed]
2. Damadoglu E, Salturk C, Takir HB, et al. Mediastinal thymolipoma: an analysis of 10 cases. Respirology 2007;12:924-7. [Crossref] [PubMed]
3. Hamouri S, Syaj S, Al-Kraimeen L, et al. Thymolipoma and its Association with Myasthenia Gravis: a Multi-center Experience. Med Arch 2021;75:375-81. [Crossref] [PubMed]
4. Deng JZ, Chan JS, Potter AL, et al. The Risk of Postoperative Complications After Major Elective Surgery in Active or Resolved COVID-19 in the United States. Ann Surg 2022;275:242-6. [Crossref] [PubMed]
5. Moran CA, Rosado-de-Christenson M, Suster S. Thymolipoma: clinicopathologic review of 33 cases. Mod Pathol 1995;8:741-4. [PubMed]