Invasive Necrotizing Tracheobronchial Aspergillosis in Children: A Case Series and Literature Review

Introduction

Invasive aspergillosis is a leading cause of infectious morbidity and mortality in immunocompromised children, with incidences ranging from 5% to 25% in high-risk cohorts, such as those receiving intensive chemotherapy for acute leukemia or undergoing allogeneic hematopoietic stem cell transplantation [1,2]. Although invasive pulmonary aspergillosis (IPA) represents the classical presentation, Aspergillus may also establish infection along the tracheobronchial tree, producing a spectrum of disease collectively termed tracheobronchial aspergillosis. Invasive tracheobronchial aspergillosis (ITBA) is relatively rare, and invasive necrotizing tracheobronchial aspergillosis (INTA) represents the rarest and most aggressive variant. Mortality rates in immunocompromised children with invasive aspergillosis range from 20% to 50% and may be higher in those with tracheobronchial involvement [3]. Here, we describe 3 cases of IPA with INTA in children.

Case Reports

CASE 1:

An 8-year-old girl with leukemia was readmitted to our hospital because of recurrent fever, a cough persisting for more than 1 month, and 1 day of hemoptysis. She had been diagnosed with acute monocytic leukemia and was undergoing standard chemotherapy at our hospital; her most recent discharge had occurred 20 days earlier. Laboratory investigations revealed the following: white blood cell count, 13.18×109/L; neutrophils, 68%; absolute neutrophil count, 8.96×109/L; lymphocytes, 12%; absolute lymphocyte count, 1.64×109/L; hemoglobin, 105 g/L; platelet count, 224×109/L; and C-reactive protein, 24.55 mg/L. On physical examination, her temperature was 98.8°F (admission occurred between episodes of fever), respiratory rate was 28 breaths/min, pulse was 108 beats/min, and blood pressure was 115/76 mmHg. Chest examination revealed wet rhonchi in the right lung; findings from other systemic examinations were unremarkable. The serum β-D-glucan level was 206.12 pg/mL. Chest computed tomography (CT) demonstrated scattered lesions in the upper and lower lobes of the right lung, as well as the lingular segment of the left upper lobe; progression was evident compared with previous imaging investigations (Figure 1).

Four bronchoscopic procedures were performed for diagnostic confirmation, airway debridement, and pseudomembrane removal. The diagnosis of necrotizing tracheobronchitis was confirmed by bronchoscopy (Figure 2). Concurrently, next-generation sequencing (NGS) of bronchoalveolar lavage fluid (BALF) detected Aspergillus flavus. NGS analysis of peripheral blood identified Aspergillus with a sequence number of 3 and relative abundance of 100%. Intravenous caspofungin and voriconazole were administered for approximately 20 days, after which the patient was discharged with partial remission. Oral posaconazole therapy was subsequently initiated. After discharge, recurrent cough with hemoptysis was reported. Chest CT indicated pneumonia in the upper and middle lobes of the right lung. Narrowing of the right main bronchial lumen and obstruction of the proximal lumina of the right upper and middle lobe bronchi were observed (Figure 3). Chest CT at the 2-week follow-up demonstrated absorption of the pneumonia; however, bronchial stenosis persisted. Three additional bronchoscopic examinations (separate from the initial 4 examinations) showed improvement in mucosal necrosis compared with previous findings. Nevertheless, destruction of the cartilage rings and hyperplasia of scar tissue were noted, resulting in tracheobronchial stenosis (Figure 4). The patient was rehospitalized and treated with nebulized amphotericin B (AmB) for 10 days. The treatment was effective, although airway narrowing was not reversed. During this period, no obvious fever, cough, or hemoptysis was observed; thus, the patient was discharged after completion of nebulized AmB treatment. Given the effectiveness of antifungal therapy, she was readmitted for continued monitoring and continuation of her chemotherapy regimen (venetoclax plus azacitidine) for leukemia.

CASE 2:

An 8-year-old girl with fever for 4 days and cough for 2 days was admitted to our hospital. After admission, recurrent fever occurred, and hemophagocytic syndrome and coronavirus disease 2019 (COVID-19)–related multisystem inflammatory syndrome were diagnosed. High-dose methylprednisolone (10 mg/kg/day) was administered for 3 days. On physical examination, the patient’s temperature was 100.0°F, respiratory rate was 28 breaths/min, pulse was 142 beats/min, and blood pressure was 96/58 mmHg. Laboratory findings were as follows: white blood cell count, 0.51×109/L; neutrophils, 20.2%; absolute neutrophil count, 0.10×109/L; lymphocytes, 77.2%; absolute lymphocyte count, 0.40×109/L; hemoglobin, 74 g/L; platelet count, 9×109/L; and C-reactive protein, 3.60 mg/L. Sputum culture results were positive for A. fumigatus. The serum β-D-glucan level was 77.21 pg/mL, and the β-D-glucan level in BALF was 600 pg/mL. Chest CT demonstrated atelectasis of the right upper lobe and left lower lobe. Initial bronchoscopy indicated necrotizing tracheobronchitis (Figure 5). NGS of BALF detected A. fumigatus. Antifungal therapy included oral and intravenous voriconazole for nearly 3 months and nebulized AmB for nearly 1 month. Repeated bronchoscopic lavage was performed more than 20 times for airway clearance, necrotic tissue removal, and reduction of fungal burden. The patient was hospitalized for more than 3 months; after discharge, no recurrence was observed during the 6-month follow-up period.

CASE 3:

A 4-year-old boy was admitted for mesenchymal stem cell infusion. His primary diagnosis was acute lymphoblastic leukemia, and bone marrow transplantation had been performed 6 months before admission. Occasional cough and fever were noted after admission; however, hypoxemia developed 5 days later and was treated with nasal cannula oxygen. On examination, the patient’s temperature was 97.9°F (admission occurred between episodes of fever), respiratory rate was 26 breaths/min, pulse was 132 beats/min, and blood pressure was 107/57 mmHg. Laboratory findings were as follows: white blood cell count, 2.33×109/L; neutrophils, 75.1%; absolute neutrophil count, 1.75×109/L; lymphocytes, 19.8%; hemoglobin, 71 g/L; platelet count, 75×109/L; and C-reactive protein, 0.76 mg/L. The serum β-D-glucan level was 318.11 pg/mL. Chest CT demonstrated bilateral hazy patchy opacities, with predominance in the left lower lobe. Bronchoscopy suggested necrotizing tracheobronchitis (Figure 6). NGS detected A. fumigatus. Antifungal therapy included oral posaconazole for approximately 2 weeks, intravenous voriconazole, and nebulized AmB for around 1 month. The patient was successfully discharged after completion of nebulized AmB treatment.

Discussion

Aspergillus spores – common in the environment – are usually nonpathogenic in individuals with normal immune function. Immunosuppression greatly increases the risk of airway colonization and subsequent progression to the full spectrum of Aspergillus-related pulmonary diseases. A. fumigatus is the most frequent pathogen overall [2]; however, A. flavus has been identified as the predominant pathogen in children [4]. In the present case series, NGS identified 1 case of A. flavus infection and 2 cases of A. fumigatus infection.

Tracheobronchial aspergillosis resembles pulmonary aspergillosis in that it may present in saprophytic, allergic (allergic bronchopulmonary aspergillosis), or invasive forms. In 1991, Kramer et al classified Aspergillus tracheobronchitis into invasive airway infection (pseudomembranous and ulcerative Aspergillus tracheobronchitis) and noninvasive airway colonization (simple Aspergillus tracheobronchitis and obstructive Aspergillus disease) [5]. ITBA has been described as an isolated or dominant local manifestation in only a small proportion of patients, representing approximately 6.9% of intrathoracic aspergillosis cases [6]. High-risk children reportedly display an Aspergillus infection incidence of 10% or greater; such children include those with acute leukemia, recipients of allogeneic hematopoietic cell transplantation (particularly in the presence of graft-versus-host disease), as well as those with chronic granulomatous disease, severe and prolonged neutropenia, or high-dose corticosteroid exposure [3,7]. INTA is even rarer. A PubMed search – encompassing all articles from database inception to November 2024 (the approximate search date) – using the keywords “invasive tracheobronchial aspergillosis” and “children” yielded few relevant reports. Generally, IPA represents the most common form of Aspergillus invasion, and ITBA often coexists with IPA. Among pediatric patients with Aspergillus infection, central nervous system dissemination has been reported in up to 15% of cases [8]. ITBA is most frequently observed in immunosuppressed patients, including those with hematologic malignancies, recipients of lung or hematopoietic stem cell transplantation, and patients receiving high-dose corticosteroids. ITBA has also been reported in individuals without known immunosuppression and individuals recently infected with influenza virus [9,10]. A summary of ITBA cases reported over the past 5 years is provided in Table 1 [11–15]; all reported cases involved adults, and no pediatric cases were noted.

INTA and IPA differ in 3 key respects: (1) anatomical focus – INTA confines necrotizing inflammation to the tracheal and mainstem bronchial walls, with sparing of the distal bronchioles and alveoli, whereas IPA primarily involves the pulmonary vasculature, producing peripheral nodular or wedge-shaped parenchymal lesions secondary to vascular invasion; (2) endoscopic appearance – serial bronchoscopy in INTA reveals circumferential ulceration, pseudomembrane formation, and progressive cartilage destruction (Figures 2, 4), whereas the endobronchial mucosa in IPA is typically intact, and diagnosis relies on imaging and bronchoalveolar lavage rather than direct visualization; and (3) CT patterns – INTA is characterized by circumferential airway wall thickening with resultant luminal narrowing, usually without accompanying parenchymal nodules, whereas IPA manifests classic features such as the halo sign, air-crescent sign, or cavitating nodules or masses, which are seldom associated with central airway wall involvement. These distinctions underscore the differing pathophysiology of INTA and IPA; they provide practical diagnostic clues for differentiation.

The pathogenesis of this disease primarily involves systemic impairment of immune function and local destruction of airway structures, including reduced mucociliary clearance, impairment of the cough reflex, tracheal mucosal injury, and ischemia. Aspergillus induces local tissue necrosis via release of proteolytic toxins and acidic metabolites, suppresses the function of neutrophils and macrophages in vivo, inhibits cytokine release by T cells, interferes with spore killing and phagocytosis, and ultimately leads to airway tissue necrosis [16]. Tracheobronchial aspergillosis lacks specific clinical signs; however, common symptoms include fever, cough, progressive dyspnea, and hemoptysis. In the present series, all patients had fever and cough, 2 experienced progressive dyspnea, and 1 presented with hemoptysis.

The diagnosis of Aspergillus infection remains challenging due to the absence of specific clinical manifestations. The conventional gold standard is microbial culture; however, only 1 of the 3 cases in this series yielded a positive culture result. Additionally, β-D-glucan testing and galactomannan assays are used as screening tools for early diagnosis of invasive mycoses in children. The β-D-glucan assay was performed using the Fungitell® kinetic chromogenic method; values of 80 pg/mL or greater are considered positive for invasive fungal infection, with a specificity of 97% when the threshold is set at 120 pg/mL. Accordingly, β-D-glucan levels were elevated in all 3 patients, indicating fungal infection. Although galactomannan testing is recommended for IPA, its sensitivity in tracheobronchial disease is limited. Moreover, galactomannan is specific to Aspergillus and may fail to detect other fungal pathogens. When NGS identified the causative organism, galactomannan testing was considered redundant and thus omitted. In contrast, β-D-glucan testing offers broader pathogen coverage, earlier positivity, and more consistent performance across diverse patient populations, making it a suitable first-line diagnostic tool. In the present cases, β-D-glucan levels were consistently elevated and readily available, thereby guiding initial antifungal therapy. Chest CT offers substantial value in the diagnosis of invasive pulmonary fungal infection. INTA may appear on CT as circumferential bronchial wall thickening, bronchial obstruction or interruption, intrabronchial masses, obstructive pneumonia or atelectasis, and, in some cases, bronchus-centered nodular changes resulting from airway wall thickening [17]. CT may also demonstrate signs of airway wall destruction [18]. Furthermore, histopathologic examination has been suggested as a valuable adjunct for diagnostic confirmation of Aspergillus infection.

Another important examination in the diagnosis of Aspergillus infection is bronchoscopy combined with bronchoalveolar lavage [19]. Bronchoalveolar lavage is recommended for patients with suspected INTA. Because the radiographic findings and clinical symptoms of IPA are nonspecific, bronchoalveolar lavage increases the likelihood of establishing a diagnosis. Thus, bronchoscopy represents an important diagnostic modality for INTA. Bronchoscopic findings closely resemble those of endobronchial tuberculosis and include hyperemia and edema of the involved bronchial mucosa, proliferative granulation tissue, mucosal surfaces covered with necrotic material, purulent secretions within the lumen, luminal stenosis or obstruction, mucosal ulceration, and neoplastic-appearing changes [20]. Additionally, Aspergillus species in BALF may be rapidly detected by NGS [21]. Clinical experience with NGS for the diagnosis of pulmonary fungal infections remains limited. This technique has several inherent limitations, including difficulty in distinguishing colonization from infection or contamination, interference from human nucleotide sequences, challenges related to read mapping, and variability associated with cell-free DNA extraction. NGS results alone cannot establish a definitive diagnosis of fungal infection and should be considered an adjunct for rapid and early pathogen identification. However, when integrated with β-D-glucan testing, chest CT findings, bronchoscopic evidence of tracheobronchial mucosal injury, and response to antifungal therapy, a comprehensive diagnostic assessment may be achieved. In the present cases, early detection of pathogens in BALF by NGS, combined with clinical and radiologic evaluation, enabled timely initiation of appropriate therapy and resulted in favorable outcomes.

With respect to treatment, children with aspergillosis generally receive the same recommended therapies as adults; however, dosing regimens differ [1]. Management in adult patients includes systemic antifungal therapy with mycoactive triazoles or lipid formulations of AmB. Considerable challenges remain in pediatric treatment, and voriconazole is often preferred by pediatric clinicians due to its superior central nervous system penetration. Nevertheless, the availability of pediatric pharmacokinetic data and evidence from adult comparative trials support posaconazole as a reasonable initial option for non–central nervous system invasive aspergillosis. Current evidence does not support routine use of combination antifungal therapy as standard treatment [22]. The Infectious Diseases Society of America recommends that aerosolized AmB preparations may be considered in patients with prolonged neutropenia, including those undergoing induction or reinduction therapy for acute leukemia, allogeneic hematopoietic stem cell transplant recipients with graft-versus-host disease, and lung transplant recipients [21]. Recent experience in adults further expands therapeutic considerations. Tramper et al [23] described 2 patients with Aspergillus tracheobronchitis complicating postseptic immunoparalysis who were successfully treated with adjunctive interferon-γ therapy, suggesting that immune reconstitution strategies contribute to the management of refractory INTA. Although cytokine immunotherapy was not administered in the present pediatric cases, this proof of concept highlights the potential value of host-directed interventions and warrants evaluation in future pediatric studies.

In the present case 1, intravenous caspofungin and voriconazole were administered during hospitalization, followed by oral posaconazole after discharge. Nebulized AmB therapy was effective. The role of inhaled AmB in prevention of Aspergillus infection has been demonstrated [24]. However, treatment experience remains limited, and no head-to-head trials have compared inhaled AmB with systemic mycoactive antifungal agents [25]. Nevertheless, inhaled AmB offers several advantages. First, it avoids the substantial nephrotoxicity associated with intravenous AmB. Second, because infected anastomotic or necrotic airway sites are often devascularized, parenteral therapy may fail to achieve therapeutic concentrations, whereas inhalation allows direct delivery to the affected airway. A limitation of inhaled AmB is its lack of protection against extrapulmonary fungal infection. Accordingly, inhaled AmB may be of particular value in children who respond poorly to azole therapy, potentially due to azole resistance. In the present cases 2 and 3, combined intravenous azole therapy and inhaled AmB were also administered, with subsequent symptom relief. Given the increasing prevalence of azole resistance, inhaled AmB may become a preferred option for pulmonary aspergillosis; however, further evidence is required to support this approach. The present experience represents an initial step in this direction. The success of inhaled AmB in our series is consistent with emerging adult data [26], but this therapy remains off-label in pediatric patients. A formal dose-finding study powered for pharmacokinetic endpoints is urgently needed. Additionally, a prospective, multicenter registry capturing baseline immune status, antifungal minimum inhibitory concentrations, number of bronchoscopic debridements, and long-term airway outcomes – similar to the methodology proposed by Aljutaily and Al-Shamrani [27] – would facilitate the transition from expert opinion to evidence-based guidance for pediatric INTA.

Repeated bronchoscopy also plays an important role in the management of INTA and may be used for removal of pseudomembranes and mucus plugs. However, this procedure may be complicated by bleeding, particularly when necrotizing pseudomembranes extend into pulmonary vessels, and should therefore be performed by experienced clinicians. In the present cases, biopsy forceps and cryotherapy were also utilized (Figure 7).

The patient in case 1 developed clinically significant airway stenosis, which may result in shortness of breath, dyspnea, and respiratory failure and can be life-threatening in severe cases. The causes of airway stenosis are multifactorial. Endotoxins and lysoproteases produced by Aspergillus induce tissue necrosis and dissolution, leading to ulcer formation on the tracheal and bronchial mucosal surfaces. Invasive growth of Aspergillus into the airway wall results in destruction of bronchial cartilage rings throughout the airway layers. Pronounced inflammation of the affected mucosa was observed, characterized by telangiectasia, congestion, and localized inflammatory granulation tissue hyperplasia [28]. Airway stenosis secondary to tracheobronchial aspergillosis may warrant balloon dilation, laser therapy, or stent placement; some patients may ultimately require surgical repair [1]. In the present case, no obvious dyspnea or activity limitation was observed; therefore, interventional treatment was not performed.

Recent guidelines strongly recommend antifungal prophylaxis, including echinocandins or mycoactive azoles, for children receiving therapy for acute myeloid leukemia, which is expected to cause severe and prolonged neutropenia; for children undergoing allogeneic hematopoietic cell transplantation during the pretransplant phase; and for children receiving immunosuppressive therapy for graft-versus-host disease [29]. In the present series, patients received oral fluconazole prophylaxis; however, invasive fungal infection still developed.

Conclusions

INTA is a rare disease, particularly in children. The predominant pathogens identified were A. fumigatus and A. flavus.

This report has described 3 pediatric patients – 2 with acute leukemia and 1 with allogeneic hematopoietic stem cell transplantation – who developed INTA. Early diagnosis was established through a combination of high-resolution CT, serum β-D-glucan testing, and, most decisively, NGS of BALF. Repeated flexible bronchoscopy with cryoextraction relieved critical airway obstruction; systemic therapy with intravenous AmB, voriconazole, or caspofungin, supplemented by nebulized AmB, achieved mycological remission without major toxicity. At the 6-month follow-up, all 3 patients remained free of fungal relapse, and their underlying malignancies were in remission.

Our experience, considered within the context of the limited contemporary literature, underscores 4 key messages. First, INTA should be considered early in any immunocompromised child who develops unexplained fever, cough, or atelectasis. Second, bronchoscopy serves not only a diagnostic role; serial debridement and cryoextraction constitute essential therapeutic interventions that may obviate the need for balloon dilation, stent placement, or thoracic surgery. Third, systemic triazoles remain first-line agents. Fourth, nebulized AmB achieves high airway concentrations with minimal systemic exposure and should be incorporated into treatment algorithms, although prospective pediatric pharmacokinetic studies remain necessary.

Finally, fluconazole prophylaxis failed in all 3 patients, suggesting that current guidelines should be revised to recommend antimold prophylaxis during periods of prolonged neutropenia or graft-versus-host disease. The combination of early bronchoscopy, molecular diagnostics, guideline-based systemic antifungal therapy, and selective nebulized treatment represents a best-practice approach for this rare but potentially devastating condition.