Management of laryngotracheal stenosis in infants and children: the role of re-do surgery in cases of severe subglottic stenosis

Degrees of Inflammation in the Treatment of Subglottic Stenosis in a Rabbit Model: Histopathological Assessment of a Novel Bioabsorbable Ultra-high Ductility Magnesium Alloy Stent

OBJECTIVE

Utilizing a novel histopathological scoring system and subglottic stenosis (SGS) rabbit model, we aimed to compare degrees of inflammation and severity of narrowing in the subglottis between two minimally invasive therapeutic modalities: endoscopic balloon dilation (EBD) alone versus EBD with placement of a bioabsorbable ultra-high ductility magnesium (UHD-Mg) alloy stent.

METHODS

SGS was induced endoscopically via microsuspension laryngoscopy in 23 New Zealand white rabbits. The control group (n = 11) underwent EBD alone, the study arm (n = 12) underwent EBD with implantation of bioabsorbable UHD-Mg alloy stents. Rabbits were euthanized at 2-, 3-, and 6-weeks after SGS induction, coinciding with wound healing stages. Using Optical Coherence Tomography (OCT), cross-sectional areas of airways were compared to calculate the mean percentage of intraluminal area at sequential time points. A novel histopathological scoring system was used to analyze frozen sections of laryngotracheal complexes. The degree of inflammation was quantified by scoring changes in inflammatory cell infiltration, epithelial ulceration/metaplasia, subepithelial edema/fibrosis, and capillary number/dilation. Univariate analysis was utilized to analyze these markers.

RESULTS

We found rabbits implanted with the bioabsorbable UHD-Mg alloy stent had statistically significantly higher scores in categories of hyperplastic change (stents vs controls: 1.48 vs 0.46 p < 0.001), squamous metaplasia (22 vs 5 p < 0.001), and neutrophils/fibrin in lumen (31 vs 8, p < 0.001). Rabbits who received EBD alone had higher scores of subepithelial edema and fibrosis (2.70 vs 3.49, p < 0.0256). The stented rabbits demonstrated significantly increased mean percent stenosis by intraluminal mean area compared to controls at 2 weeks (88.56 vs 58.98, p = 0.032), however at all other time points there was no significant difference between intraluminal subglottic stenosis by mean percent stenosis area.

DISCUSSION

Rabbits with SGS treated with UHD-Mg alloy stents demonstrated histopathologic findings suggestive of lower levels of tracheal fibrosis. This could indicate a reduced tendency towards the development of stenosis when compared to EBD alone. There was not a difference in luminal size between stent and non-stented rabbits at the six-week end point. Histologically, however, overall the use of bioabsorbable UHD-Mg alloy stenting elicited a greater tissue response at the level of the superficial mucosa rather than fibrosis of the lamina propria seen in the stented rabbits. This suggests more favorable healing and less of a tendency towards fibrosis and stenosis even though there may not be a benefit from a luminal size standpoint during this early healing period. Compared to known complications of currently available non-bioabsorbable metal or silicone-based stents, this proof-of-concept investigation highlights the potential use of a novel biodegradable UHD-Mg stent as a therapeutic modality for pediatric SGS.

Revision surgery for laryngotracheal stenosis in children: A single center's 44 years experience

OBJECTIVES

Outcome measures of revision open airway surgery in pediatric laryngotracheal stenosis (LTS) are reported.

METHODS

Data on 46 pediatric LTS patients undergoing revision open airway surgery were collected retrospectively. The measured outcomes were decannulation rate, time to decannulation, postoperative complications, additional surgery to achieve decannulation, and functional results.

RESULTS

The most common revision surgery was partial cricotracheal resection (PCTR) in 21/46, followed by extended PCTR (ePCTR) in 20/46, and laryngotracheal reconstruction (LTR) in 5/46 patients. A 90.7% overall decannulation rate (ODR) and a 74.4% operation-specific decannulation rate (OSDR) were achieved. Delayed decannulation was identified in children aged 5 years or less (p = 0.038) and in patients with previous primary open airway surgery (p = 0.039). Complications were observed in 52.2% of patients. To achieve optimal airway patency, additional open or endoscopic airway surgeries were necessary in 30.4% and 47.7% of patients, respectively. Age 5 years or less (p = 0.034), multiple comorbidities (p = 0.044), revision ePCTR (p = 0.023), and laryngeal stenting (p = 0.018) were risk factors requiring additional open surgery to achieve age-appropriate airway. Failed primary open airway surgery (p = 0.034) and comorbidities (p = 0.044) were risk factors for a higher rate of additional endoscopic surgeries. Postoperatively 63.0% of patients achieved normal breathing, 82.2% were dysphonic and 91.1% were orally fed.

CONCLUSIONS

In this report, the patient's age under 5 years, previous primary open airway surgery, medical comorbidities, and laryngeal stenting had a significant negative impact on revision open airway surgery outcomes.

LEVEL OF EVIDENCE

Level 4 Laryngoscope, 133:3200-3207, 2023.

Laryngeal inhalational injuries: A systematic review

Laryngeal inhalation injury carries a significant increase in mortality rate and often indicates immediate airway evaluation. This may be difficult in the setting of clinical deterioration necessitating immediate intubation, which itself can synergistically cause mucosal damage. Prior studies do not encompass predictive factors or long-term outcomes for the laryngotracheal complex. This systemic review of PubMed, Embase, and Cochrane identified studies investigating inhalational injuries of the upper airway. Demographic data as well as presentation, physical findings, and delayed sequelae were documented. Laryngotracheal burn patients were divided into two cohorts based on timing of laryngeal injury diagnosis (before- versus after-airway intervention). 1051 papers met initial search criteria and 43 studies were ultimately included. Airway stenosis was more common in patients that were intubated immediately (50.0%, n = 18 versus 5.2%, n = 13; p = 0.57). Posterior glottic involvement was only identified in patients intubated prior to airway evaluation (71.4%, n = 15). All studies reported a closed space setting for those patients in whom airway intervention preceded laryngeal evaluation. Laryngeal inhalational injuries are a distinct subset that can have a variety of minor to severe laryngotracheal delayed sequelae, particularly for thermal injuries occurring within enclosed spaces. Given these findings, early otolaryngology referral may mitigate or treat these effects.

In-vivo efficacy of biodegradable ultrahigh ductility Mg-Li-Zn alloy tracheal stents for pediatric airway obstruction

Pediatric laryngotracheal stenosis is a complex congenital or acquired airway injury that may manifest into a potentially life-threatening airway emergency condition. Depending on the severity of obstruction, treatment often requires a combination of endoscopic techniques, open surgical repair, intraluminal stenting, or tracheostomy. A balloon expandable biodegradable airway stent maintaining patency while safely degrading over time may address the complications and morbidity issues of existing treatments providing a less invasive and more effective management technique. Previous studies have focused on implementation of degradable polymeric scaffolds associated with potentially life-threatening pitfalls. The feasibility of an ultra-high ductility magnesium-alloy based biodegradable airway stents was demonstrated for the first time. The stents were highly corrosion resistant under in vitro flow environments, while safely degrading in vivo without affecting growth of the rabbit airway. The metallic matrix and degradation products were well tolerated by the airway tissue without exhibiting any noticeable local or systemic toxicity.

Subglottic Stenosis: Development of a Clinically Relevant Endoscopic Animal Model

OBJECTIVE

Develop a clinically relevant and reproducible endoscopic animal model for subglottic stenosis amenable to testing of minimally invasive therapeutic modalities.

STUDY DESIGN

Cohort study.

SETTING

Division of Laboratory Animals Research, University of Pittsburgh.

SUBJECTS AND METHODS

Subglottic stenosis was induced endoscopically via microsuspension laryngoscopy in 26 New Zealand white rabbits. A trimmed polypropylene brush connected to a novel electronic stenosis induction apparatus was used to create circumferential trauma to the subglottis. By using open source image analysis software, the cross-sectional areas of the stenotic and native airways were compared to calculate the percentage of stenosis and the Myer-Cotton classification grade.

RESULTS

Of the 26 rabbits, 24 (92%) exhibited stenosis after the first attempt. The mean percentage of airway stenosis was 57% (range, 34%-85%; SD, 15%). Five rabbits (19.2%) died on the day of stenosis induction from procedural complications. Of the 21 rabbits, 2 demonstrated no stenosis 7 days after initial injury and so underwent reinduction of airway injury, upon which they developed stenosis. Overall, 14 of the 21 rabbits (67%) exhibited moderate to severe stenosis (grade 2 or 3).

CONCLUSION

The stenosis induction apparatus reliably induced stenosis with a low mortality rate as compared with that of other methods in the literature. The device could be improved to generate a predetermined potentially reproducible grade of stenosis as desired by the operator. This method sets the stage for a clinically relevant and reproducible subglottic stenosis disease model that is amenable to testing of minimally invasive treatment modalities.

Relationship between degree of obstruction and airflow limitation in subglottic stenosis

OBJECTIVES

Subglottic stenosis (SGS) is one of the most common airway disorders in pediatric patients. Currently, treatment decisions rely primarily on the Cotton-Myer scale, which classifies SGS severity based on percentage reduction in airspace cross-sectional area (CSA). However, the precise relationship between upper airway resistance and subglottic CSA is unknown. We hypothesize that airway resistance can be described by the Bernoulli Obstruction Theory, which predicts that airway resistance is inversely proportional to airspace CSA ( R∝A-1) in cases of severe constriction.

METHODS

Computed tomography (CT) scans of six healthy subjects and five SGS patients were used to create three-dimensional models of the respiratory tract from nostrils to carina. Cylindrical segments of varying lengths and varying diameters were digitally inserted in the subglottis of the healthy subjects to create simulated SGS models. Computational fluid dynamics simulations were run, and airway resistance was computed in the simulated SGS models and actual SGS models.

RESULTS

Constriction diameter had a greater impact in airway resistance than constriction length. In agreement with the Bernoulli Obstruction Theory, airway resistance in the simulated SGS models was well represented by the power law R=aAb, where a is a constant and the exponent b ranged from -0.85 to -1.07. The percentage reduction in airflow (QOBSTRUCTIONQHEALTHY) at a constant pressure drop was found to be directly proportional to the percentage reduction in CSA (AOBSTRUCTIONAHEALTHY) in the limit of severe constrictions, namely QOBSTRUCTIONQHEALTHY=kAOBSTRUCTIONAHEALTHY, where k=2.25 ± 0.15. Airway resistances in the simulated SGS models were similar to resistances in models based on CT scans of actual SGS patients, suggesting that our simulated SGS models were representative of airway resistance in actual SGS patients.

CONCLUSION

Our computer simulations suggest that the degree of airflow limitation in SGS patients may be estimated based on anatomic measurements alone. Future studies are recommended to test these predictions in larger cohorts.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:1551-1557, 2018.

Ground zero: not asthma at all

Upper airway obstruction is commonly misdiagnosed as asthma. We report on four children with recurrent respiratory symptoms who had been erroneously diagnosed as having asthma and who received anti-asthma medication for several years. The evaluation of spirometry tracing was neglected in all cases. Subglottic stenosis, tracheomalacia secondary to tracheo-esophageal fistula, double aortic arch, and vocal cord dysfunction were suspected by direct inspection of the flow-volume curves and eventually diagnosed. The value of clinical history and careful evaluation of spirometry tracing in children with persistent respiratory symptoms is critically discussed.

Demonstration of the role of an implantable bioscaffold in airway reconstruction: a pilot study utilizing an animal model

INTRODUCTION

Laryngotracheal reconstruction is a common procedure to repair subglottic stenosis. Despite a success rate upwards of 85%, this procedure has significant morbidity associated with it, specifically with the site of the graft harvest and recurrence of stenosis. We propose that a recently described cellular bioscaffold xenograft may be useful in reducing these complications.

METHODS AND MATERIALS

10 Sprague Dawley rats were divided into 2 groups of 5. One group underwent incision through the cricoid and the first two tracheal rings followed by primary closure (G1); the second group underwent incision through the cricoid and the first two tracheal rings followed by placement of the xenograft (G2); additionally, a specimen was harvested from an animal which did not undergo any surgical procedure to compare to the two surgical groups. Specimen harvest occurred on post-operative days 1, 7, 14, 21, and 28.

RESULTS

6 of 10 animals provided usable data. All animals receiving the xenograft survived until the time of specimen harvest. Only 1 animal undergoing primary closure survived beyond post-operative day one. On histology review, the xenograft animals showed a progressive decrease in fibrosis relative to the animals that underwent primary closure. On POD 28, restoration of the respiratory epithelium and intact basement membrane was noted in the xenograft group.

CONCLUSION

We believe that this pilot study shows the potential of utilizing bio-implantable biomaterials, specifically a cellular bioscaffold which encourages the ingrowth of native tissue instead of fibrosis. Histologic analysis shows that use of the xenograft can initiate the proliferation of native tissues decreasing the amount of fibrosis present post-operatively, although significant further analysis is needed before definitively concluding that this approach is superior to utilization of a graft.