Tracheobronchoplasty for airway collapse: does the label matter?

In this issue of The Annals of Thoracic Surgery, Cho and colleagues (1) report the short-term outcomes and post-operative complications of tracheobronchoplasty (TBP) for excessive central airway collapse (ECAC), a condition increasingly recognized as an important cause for respiratory symptoms, including cough and exertional dyspnea, and a controversial and challenging pathology.

This novel study is the largest direct comparison between the two conditions encompassed by the umbrella term ECAC, namely excessive dynamic airway collapse (EDAC) and tracheobronchomalacia (TBM). The former describes an abnormal invagination of the posterior tracheal membrane during expiration, whereas TBM is more strictly defined as a pathological weakness or ‘malacia’ of the cartilaginous portion of the tracheobronchial tree (2).

Obtaining a robust diagnosis of ECAC can be challenging. This condition is most commonly assessed with forced expiratory or coughing maneuvers, performed during dynamic expiratory imaging, most frequently computed tomography, or bronchoscopy (which remains the considered gold standard) (3). The two approaches often offer important complementary information, including characterization of airway morphology, differentiation of cartilaginous malacia and posterior membranous collapse, and assessment of the anatomical extent of disease, all of which may inform subsequent clinical decision making and therapeutic initiation. Nevertheless, the diagnostic criteria for ECAC remain somewhat arbitrary and based largely on subjective expert opinion and typically defined by the presence of expiratory collapse (i.e., a reduction in large airway caliber) of greater than 50% to 70%. However, this remains contentious, and this degree of collapse can be encountered in asymptomatic and healthy individuals (3).

This diagnostic ambiguity also appears to be a problem in the report from Cho et al. (1). The panel of four airway experts failed to reach a consensus on diagnosis in approximately one in ten patients selected for TBP and found ten patients (10%) who were deemed to have a ‘normal airway’ on selected static CT images, despite having a previous diagnosis of severe ECAC. Thus, diagnosing ECAC consistently can be difficult, yet even with a secure diagnosis, subsequent sub-categorization is complicated by the considerable clinical and radiological overlap between EDAC and TBM. Collectively, these issues highlight the limitations of assessing large airway movement with voluntary and highly effort-dependent maneuvers in a supine position. These movements certainly do not reflect real-life activity and there is a need to develop a more precise investigational strategy that defines appropriate cut-offs and evaluates large airway movement in a more real-world scenario, with commensurate measures of dyspnea. In this context, a novel approach utilizing bronchoscopic visualization of the large airway found no evidence of ECAC in healthy individuals during exercise, despite approximately two-thirds demonstrating this problem with an imaging-based diagnostic protocol (4).

Even when a diagnosis of ECAC is robust, a question remains whether the predominant problem is TBM or EDAC. Traditionally, this has been considered an important distinction, because it was thought to influence treatment strategy, and specifically, eligibility for TBP. The latter involves placement of a surgical mesh to reinforce or plicate the posterior large airway wall thereby limiting collapse in EDAC, or by restoring the D-shaped tracheal structure and subsequently splinting the collapsible anterior cartilaginous wall in TBM. Despite shared indications, uncertainty remains as to whether the surgical risk and post-operative outcome differs between patients with EDAC and TBM.

The findings published in the Journal progress understanding in this area. In the one hundred patients who were reviewed between 2018 and 2023, 73 underwent TBP, of whom approximately half had EDAC (n=47), and a quarter had TBM (n=26). Overall, the treatment outcome and complication rates were comparable between the two conditions. Specifically, the rate of major complications (21% in the EDAC group vs. 35% in the TBM group) and hospital length of stay was similar when comparing two distinct pathologies, and TBP modalities (robotic vs. open thoracotomy). Both groups also demonstrated decreased symptom burden and achieved the minimally clinically important difference (MCID) in questionnaire scores. The complication rate and short-term outcome data is in keeping with studies of both robotic-assisted TBP and open thoracotomy approaches, although higher mortality rates have been previously reported (5,6). This highlights the complexity and high procedural risk of these cases and underscores the importance of careful patient selection when considering invasive intervention, such as TBP and temporary central airway stenting. Although temporary central airway stents may provide short-term symptomatic benefit, their long-term use is limited by well recognized, and relatively high rates of complications, including stent migration, granulation tissue formation, mucus plugging, and stent-related airway injury (7). Indeed, the majority of work in this area uses stenting as a short-term trial and temporary strategy to determine TBP suitability.

A high comorbidity burden is common in patients with ECAC (8,9). The majority of the group presented with coexisting diseases including obesity, chronic obstructive pulmonary disease and asthma. These overlapping conditions worsen the clinical presentation of ECAC but also confound symptom attribution, i.e., determining if symptoms, such as dyspnea, arise from ECAC directly. Such complexity further emphasizes the importance of comprehensive assessment and optimization before considering surgical intervention. A proposed pathway for which is outlined in Figure 1.

Figure 1 Apeny proposed management pathway for excessive central airway collapse. *, exercise bronchoscopy is still undergoing research validation. 6MWT, 6-minute walk test; COPD, chronic obstructive pulmonary disease; CPAP, continuous positive airway pressure; CPET, cardiopulmonary exercise testing; CT, computed tomography; ECAC, excessive central airway collapse; GORD, gastro-oesophageal reflux disease; mMRC, modified Medical Research Council; PEP, positive expiratory pressure; SGRQ, St. George’s Respiratory Questionnaire.

The precise relationship between measures of functional capacity, pulmonary physiology and TBP is not yet clear. The majority of the work in this area found improvements in walk test distance following TBP (6,10,11), and the study by Cho et al. (1) supports this finding in part. Whilst improvements in quality of life were found in both groups, only the EDAC group achieved the MCID in six-minute walk test distance (median change of 36 metres compared to 6 metres in the TBM group). The authors do not allude to the reasons for the sub-group discrepancy, however, the differences in follow-up duration and relatively small sample size may partly explain the variation in walk test distance. As such, this observation may be viewed as a signal to potential improvement in an area with confounded results.

The impact of TBP on resting measures of pulmonary function is inconsistent across studies. While some report little or no change in spirometric indices following TBP surgery (1,10), others have demonstrated improvements of approximately 13% in spirometry percent predicted values (5). The current study found no improvement in forced expiratory volume in one second in either EDAC or TBM groups. Taken together, these findings suggest that the mechanism of symptom relief post TBP does not appear solely attributed to any change in expiratory flow-volume mechanics, determined by simple pulmonary function tests. Regardless, further research should continue to better understand the relationship between potentially more complex, objective physiological measurements and patients undergoing TBP.

The authors of the Cho et al. (1) study highlight some selection bias within their population, specifically, with the preferential selection of robotic-assisted TBP for EDAC patients compared to the TBM group (30% vs. 4%, respectively). Their report also represents retrospective data from a high-volume, expert center, and as such, may not be generalizable when applied to other centers, with less experience. Caution should be taken when applying these findings and the diagnostic work-up in this setting.

Despite similar outcomes between EDAC and TBM groups, an additional limitation is the relatively modest sample size, which due to the specialized nature of the TBP procedure and challenging recruitment suitability, may limit the ability to detect between-group differences. Thus, it remains a consideration when interpreting findings.

Although the overall benefit of TBP for EDAC and TBM groups is comparable, the classification between pathologies remains an important, challenging area in this field. The precise diagnostic criteria and method of assessment remains inconsistent and continues to have relevance in other settings such as research and assessment of disease mechanisms.

Regardless, Cho et al. (1) should be commended for a meticulous evaluation that adds to our understanding and should promote larger multi-centre randomized control studies, to help better define this important condition and truly evaluate the impact of TBP and the patients who are most likely to benefit from this intervention.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Current Challenges in Thoracic Surgery. The article has undergone external peer review.

Peer Review File: Available at https://ccts.amegroups.com/article/view/10.21037/ccts-2025-1-57/prf

Funding: G.C. has received funding from the European Respiratory Society Clinical Training Fellowship 2024 for this work. Z.J.W.’s salary is funded by the RELACS charity, as part of Royal Brompton and Harefield Hospitals Charity.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://ccts.amegroups.com/article/view/10.21037/ccts-2025-1-57/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.

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