Late-onset fungal infection of the bronchial stump post-lung resection: a report of two rare cases of Aspergillus flavus and mixed Candida/Cryptococcus coinfection diagnosed via metagenomic next-generation sequencing

Introduction

Bronchial stump complications remain a significant concern after pulmonary resection, with postoperative inflammation most commonly attributed to bacterial infection, foreign-body reaction, or ischemic changes. Recent reports have highlighted the complex microbiology of post-lobectomy infections, including polymicrobial and occasional mixed bacterial-fungal infections, alongside evolving patterns of postoperative empyema in the contemporary era of antibiotic resistance and advanced thoracic surgery (1). These trends underscore the complexity of airway colonization in surgically altered bronchi and highlight the diagnostic challenges clinicians face when symptoms persist despite standard antibacterial therapy.

Although fungal involvement of the bronchial stump is uncommon, Aspergillus species—particularly Aspergillus fumigatus—have been reported as emerging pathogens in this setting (2). However, the true incidence of fungal stump infections remains unclear, and coinfection with less common organisms such as Cryptococcus has not been systematically described. Importantly, while established guidelines provide structured recommendations for managing invasive pulmonary aspergillosis, no consensus exists for the diagnosis or treatment of bronchial stump aspergillosis (BSA) or stump cryptococcosis. This guideline gap leaves clinicians without standardized criteria for early recognition, risk stratification, or therapeutic decision-making in stump-specific fungal infections.

Given the rarity of these presentations and the absence of dedicated management frameworks, detailed case descriptions are essential for improving clinical awareness, refining diagnostic pathways, and informing future guideline development. Our case series contributes to this unmet need by characterizing the clinical, radiological, and microbiological features of stump-localized fungal infections, including the first reported instance of cryptococcal involvement at a bronchial stump. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-321/rc).

Case presentation

Case 1

The patient, a 53-year-old man, had no history of smoking. In 2020, the patient underwent left upper lobectomy for stage IA3 (pT1cN0M0) lung adenocarcinoma. Three months postoperatively, chest computed tomography (CT) demonstrated a 22-mm nodule adjacent to the aortic arch. Serial follow-up positron emission tomography-computed tomography (PET-CT) examinations from 2021 to 2023 showed no significant interval change.

In January 2024, the patient presented with hoarseness of unclear etiology, accompanied by exertional chest tightness. Laryngoscopy revealed left vocal cord fixation. PET-CT demonstrated a metabolically active soft-tissue nodule adjacent to the surgical suture line, which showed increased size and metabolic activity compared with the previous examination.

On April 3, 2024, the patient was admitted to Shanghai Chest Hospital for bronchoscopy and endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). Bronchoscopy revealed postoperative changes in the left upper lobe, with exposed sutures at the bronchial stump covered by white necrotic material. Endobronchial mucosal biopsies were performed, and EBUS detected lymph nodes in stations 4R and 7. No definite mass lesion was observed at the left upper lobectomy site, and TBNA was performed on the lymph nodes. Histopathological examination of the mucosal biopsy demonstrated numerous fungal hyphae, consistent with fungal infection.

The patient was admitted to the Institute of Antibiotics, Huashan Hospital, Fudan University, on April 22, 2024. Physical examination revealed no abnormal findings. Routine laboratory tests, including the serum galactomannan (GM) assay and serum cryptococcal antigen (CrAg) test, were negative. A repeat chest CT scan (Figure 1) was performed on April 23, and the tracheobronchial biopsy specimen obtained from Shanghai Chest Hospital was submitted for further evaluation. Repeat histopathological analysis revealed abundant fungal spores and hyphae (Figure 2). The pathological specimen was subjected to pathogen-targeted metagenomic next-generation sequencing (mNGS), which detected 18,622 sequence reads of Aspergillus flavus.

Figure 1 Chest CT enhanced scan prior to posaconazole treatment on April 23, 2024. (A,B) Lung window; (C,D) mediastinal window. The arrows indicate the nodule. CT, computed tomography.

Figure 2 Histopathological manifestations of the mucosal biopsy tissue obtained from the bronchial stump. (A) Hematoxylin and eosin staining (×200); (B) unstained section (×200). The arrows indicate fungal hyphae.

Meanwhile, the patient’s hoarseness progressively worsened. Given that the patient declined additional surgical intervention to remove the staples and opted for conservative antifungal therapy, empirical antifungal therapy with oral posaconazole tablets was initiated at a dose of 300 mg once daily (300 mg every 12 hours on the first day). On April 25, repeat bronchoscopic evaluation was performed. Under laryngoscopy, the left vocal cord remained fixed, and white secretions were adherent to the postoperative stump of the left upper lobe bronchus. Bronchoalveolar lavage and biopsy were performed (Figure 3). Fluorescence microscopy of the bronchoalveolar lavage fluid (BALF) demonstrated hyaline, septate hyphae with acute-angle branching (Figure 4). A total of 6,300 sequence reads of Aspergillus flavus were detected by mNGS in BALF. The BALF GM assay was negative, while fungal culture yielded Aspergillus flavus (2+). Histopathological examination of the biopsy showed no definitive evidence of malignancy.

Figure 3 Bronchoscopic manifestation of the bronchial stump: (A) Aspergillus ball at the bronchial stump; (B) after the Aspergillus at the bronchial stump was removed, the sutured nail chamber (titanium alloy) was revealed.

Figure 4 Fluorescent staining of bronchoalveolar lavage fluid demonstrates the presence of fungal hyphae. (A) Light microscope (×400); (B) fluorescence microscope (×40).

Further review of the medical history revealed that the patient had undergone linear stapling with a titanium alloy device during lung cancer surgery in 2020. Based on the clinical, microbiological, pathological, and imaging findings, BSA was diagnosed. On the fifth day of antifungal therapy, the patient’s hoarseness began to improve, and after 1 month, his voice had largely returned to normal.

During follow-up, serial chest CT scans showed findings comparable to previous imaging (Figure 5). Serum posaconazole concentrations were monitored regularly. On June 14, 2024, a mild elevation in plasma drug concentration was observed (5.036 µg/mL; reference range, 1–3.75 µg/mL). Accordingly, the posaconazole dose was reduced to 200 mg once daily.

Figure 5 Chest CT plain scan conducted on August 26, 2024, following a 4-month course of posaconazole treatment. (A,B) Lung window; (C,D) mediastinal window. The arrows indicate the nodule. CT, computed tomography.

After 7 months of posaconazole therapy, follow-up bronchoscopy demonstrated complete resolution of white secretions and necrotic material at the residual bronchial stump of the left upper lobe. Biopsy pathology, BALF mNGS, and fungal cultures were all negative for fungal organisms. Posaconazole was discontinued, and no recurrence was observed during subsequent follow-up.

Case 2

The patient, a 77-year-old woman who was a retired schoolteacher, had no smoking history. In 2019, she underwent right lower lobectomy for stage IA3 (pT1cN0M0) lung adenocarcinoma. On March 25, 2025, following an upper respiratory tract infection, the patient presented with cough, accompanied by viscous expectoration, chest tightness, and mild right-sided chest pain, along with intermittent fatigue. On March 31, 2025, the chest CT demonstrated bilateral pneumonia with focal consolidation/atelectasis and a small volume of bilateral pleural effusion (Figure 6).

Figure 6 Chest CT plain scan prior to treatment on March 31, 2025. (A,B) Lung window; (C,D) mediastinal window. CT, computed tomography.

On April 1, 2025, she was admitted to the hospital. Routine blood tests revealed a white blood cell count of 10.2×10⁹/L, an absolute neutrophil count of 3.12×10⁹/L, and a C-reactive protein (CRP) level of 106.8 mg/L. Empirical anti-infective therapy with moxifloxacin was initiated, and follow-up CT demonstrated progression of bilateral pulmonary exudative lesions. Bronchoscopic examination was subsequently performed. At the postoperative bronchial stump of the right lower lobe, post-surgical changes were observed, including exposed sutures with adherent white material (Figure 7), along with copious pale-yellow, clear secretions that persisted despite repeated suctioning.

Figure 7 Bronchoscopic presentation of the bronchial stump. (A) Alterations in the bronchial stump; (B) white adherent substances and exposed sutures at the stump.

Bronchoscopy with brush biopsy was performed at the right lower lobe bronchial orifice. The secretions and BALF were submitted for pathogen mNGS, which detected 2,789 sequence reads of Candida albicans DNA, 620 sequence reads of Cryptococcus neoformans DNA, and one sequence read of Candida albicans RNA. Cytological examination of BALF and brush biopsy specimens revealed no malignant cells. The serum 1,3-β-D-glucan assay, serum GM test, and BALF GM test were all negative. Peripheral T-lymphocyte counts were markedly reduced with total T cell count at 578 cells/µL and CD4⁺ at 319 cells/µL. The type of sutures or stapling devices used during the 2019 lung cancer surgery could not be determined. The patient reported exposure to live pigeons at a market. A fungal infection of the bronchial stump was diagnosed. Antibacterial therapy with meropenem was administered, combined with antifungal therapy using caspofungin and fluconazole.

Subsequently, the patient’s body temperature normalized, and inflammatory markers decreased. A chest CT re-examination on April 18, 2025, revealed marked absorption of bilateral pulmonary lesions. The patient was prescribed oral moxifloxacin 0.4 g once daily and fluconazole 400 mg once daily and was discharged from the hospital. On May 22, 2025, the patient returned for outpatient follow-up, primarily for repeat chest CT, which demonstrated near-complete resolution of inflammatory changes (Figure 8). The patient declined repeat bronchoscopy, and no recurrence of symptoms has been reported since discharge.

Figure 8 Chest CT plain scan post-treatment on May 22, 2025. (A,B) Lung window; (C,D) mediastinal window. CT, computed tomography.

Ethical statement

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 and its subsequent amendments. Written informed consent was obtained from the patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Endobronchial aspergilloma (EBA) is a fungal mass resulting from the excessive proliferation of Aspergillus within the bronchial cavity. It is frequently observed in patients with structural lung diseases (e.g., bronchiectasis, post-tuberculosis cavities) or in immunocompromised individuals. Currently, there is no consensus regarding whether EBA represents an invasive or noninvasive form of aspergillosis.

BSA refers to infection of the bronchial granulation tissue surrounding the suture line at the bronchial stump by Aspergillus following lung resection. It commonly occurs in patients without overt immunosuppression. Some scholars classify BSA as a rare subtype of EBA (3). Guidelines or consensus providing a clear and unified definition and classification of BSA are still lacking.

As of November 8, 2025, a total of 24 cases of BSA have been reported (3-14), including 11 males and 13 females, aged 20–70 years, with a median age of 49 years. BSA can occur from 1 month to 20 years after lung resection, with a median interval of 31 months. Reported pathogens include Aspergillus fumigatus (9/24), Aspergillus niger (3/24), Aspergillus oryzae (3/24), Aspergillus flavus (1/24), Aspergillus chevalieri (1/24), Aspergillus versicolor (1/24), and Aspergillus tamarii (1/24). In several cases, the pathogen was reported only at the genus level.

CT imaging of BSA may reveal bronchial stump thickening or nodular lesions, and PET-CT may demonstrate increased metabolic activity. BSA is easily misdiagnosed as postoperative bronchopleural fistula or tumor recurrence (4-6,8-10). There have also been reports of Aspergillus-associated septic pleural effusion following lung resection and paratracheal cavity aspergillosis (15). Diagnosis relies on histopathological examination or bronchoscopic biopsy demonstrating fungal hyphae.

Some researchers postulate that suture materials used during lung resection play a key role in the development of BSA, as local inflammation around sutures occurs frequently, and these areas are more susceptible to secondary Aspergillus infection, particularly compared with nylon sutures (3-7). Two reported cases were secondary to titanium staples (8).

In Case 1, BSA was secondary to titanium staple sutures and was diagnosed through BALF mNGS, BALF culture, and histopathological examination, underscoring the critical importance of pathogen identification and pathological confirmation. Whether the retention of the titanium staples will lead to a recurrence of fungal infection, as there is currently no clinical data. Long-term surveillance remains necessary due to the uncertain risk of recurrence.

The GM assay is highly valuable in the diagnosis of aspergillosis (16). However, in Case 1, the GM tests of the patient’s serum (obtained before posaconazole administration) and BALF (obtained after posaconazole administration) were both negative. False-negative serum GM results may be attributed to the fact that BSA is often localized colonization or superficial invasion, resulting in low fungal burden and insufficient GM antigen release into the bloodstream. Meanwhile, false-negative BALF GM results may occur due to interference from prior antifungal therapy with posaconazole.

Treatment modalities for BSA include systemic antifungal therapy, bronchoscopic interventions (such as removal of exposed sutures or laser ablation), and surgical management. As there is a lack of guidelines or expert consensus in this area at present, most case reports refer to the guidelines or expert consensus on pulmonary fungal infections. Commonly used antifungal agents include voriconazole, amphotericin B, and itraconazole (17,18). Karcioglu reported a case of BSA in 2020 caused by mixed infection with Aspergillus flavus complex and other Aspergillus species. The patient initially received oral voriconazole for 4 months, which resulted in bullous skin rash, leading to drug discontinuation and subsequent treatment with oral posaconazole (300 mg once daily for 6 months), achieving cure (12). In Case 1, posaconazole was selected in accordance with the Chinese Thoracic Society guidelines for invasive pulmonary fungal diseases (19). Blood drug concentrations, as well as liver and renal function, were closely monitored throughout treatment to ensure therapeutic efficacy and minimize adverse effects.

Pulmonary cryptococcosis is a deep-seated fungal infection caused by Cryptococcus neoformans or Cryptococcus gattii. It is more prevalent in individuals with impaired immune function (e.g., patients with HIV infection or those receiving long-term immunosuppressive therapy), but can also occur in immunocompetent hosts (20-22). To date, no cases of isolated Cryptococcus infection or mixed Cryptococcus and other fungal infections involving the bronchial stump have been reported.

In Case 2, the patient exhibited markedly reduced T-lymphocyte counts, suggesting possible impairment of cellular immunity in the absence of other known immunosuppressive factors. The patient had a history of pigeon exposure, and it is plausible that local microenvironmental changes, ischemia at the bronchial stump and suture site, and the presence of foreign bodies facilitated coinfection with Candida albicans and Cryptococcus neoformans. Cryptococcal infection is typically treated with amphotericin B combined with flucytosine or fluconazole, whereas Candida albicans infection is primarily treated with echinocandins (e.g., caspofungin) or fluconazole.

The clinical manifestations of cryptococcal infection are nonspecific, making differential diagnosis challenging. CrAg testing is considered the “gold standard” for the diagnosis of cryptococcosis (23), with a reported sensitivity of approximately 70–90% in pulmonary cryptococcosis (24). A positive CrAg test indicates that cryptococcal capsular polysaccharide has entered the bloodstream.

In Case 2, the CrAg test was negative. Possible explanations include: (I) the mixed Cryptococcus and Candida albicans lesions were confined to the bronchioles, without involvement of the lung parenchyma or central nervous system, resulting in insufficient antigen release; (II) overgrowth of Candida albicans may have competitively inhibited Cryptococcus proliferation; and (III) typical CT findings of pulmonary cryptococcosis—such as solitary or multiple nodules, consolidation, cavitation, marked pleural effusion, or mediastinal lymphadenopathy—were absent, suggesting that the bilateral pulmonary exudates were more likely attributable to concurrent bacterial infection.

Given the patient’s rapid clinical deterioration, we adopted a “hard-hitting” regimen: caspofungin targeting Candida albicans and fluconazole targeting Cryptococcus neoformans, meropenem for potential bacterial pathogens. The negative CrAg result underscores that even in patients at high risk for cryptococcal infection, diagnosis should be confirmed using histopathology, culture, and mNGS, rather than relying solely on serological testing. In recent years, mNGS has emerged as an important diagnostic tool in infectious diseases due to its rapidity and high diagnostic accuracy (25,26).

Conclusions

Despite its rarity, fungal infection of the bronchial stump should be considered in the differential diagnosis of severe postoperative complications following lung resection, particularly when antibiotic therapy is ineffective. This paper presents two rare cases, providing reference information for similar clinical scenarios. Clinicians should perform a comprehensive evaluation based on endoscopic findings and histopathology, and to avoid excessive reliance on any single diagnostic indicator.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-321/rc

Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-321/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-321/coif). The 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 and its subsequent amendments. Written informed consent was obtained from the patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

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/.

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