Acute and chronic changes in the subglottis induced by graded carbon dioxide laser injury in the rabbit airway

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.

Comparative evaluation of mechanical injury methods for establishing stable tracheal stenosis animal models

The study aimed to assess the stability of various mechanical injury techniques in creating tracheal stenosis animal models using endoscopic assistance and investigate the viability of tracheal stoma in this process. Twenty-six healthy adult New Zealand white rabbits were randomly assigned to an experimental and control group. The experimental group underwent tracheal incision followed by steel brush scraping with endoscopic assistance, while the control group received nylon brush scraping. Within the control group, two subgroups were formed: Group A underwent scraping without tracheal stoma, and Group B underwent scraping followed by tracheal stoma. Additionally, a sham operation was performed on a separate group without subsequent scratching, resulting in no stenosis formation. Endoscopic observations were conducted at 7, 14, and 21 days post-scraping, followed by histological examinations of euthanized rabbits on the 21st day. Notably, all rabbits in the non-stoma group survived without complications, whereas Group B rabbits faced mortality post-operation. Histological assessments revealed inflammatory cell infiltration, fibroblast proliferation, and collagen fiber deposition in narrowed tracheal specimens. Steel brush scraping with endoscopic assistance proved more effective in inducing stable tracheal stenosis compared to nylon brush scraping. However, the survival challenges of rabbits with tracheal fistula require further investigation.

Inhalation of Carboxymethyl Chitosan Alleviates Posttraumatic Tracheal Fibrosis

OBJECTIVES

The present study was performed to determine whether the inhalation of carboxymethyl (CM)-chitosan can alleviate tracheal fibrosis in a rabbit model.

METHODS

We designed a rabbit model of tracheal stenosis involving electrocoagulation with a spherical electrode. Twenty New Zealand white rabbits were randomly divided into experimental and control groups (10 animals each). Tracheal damage was successfully established by electrocoagulation in all animals. The experimental group was given CM-chitosan (inhalation for 28 days), while the control group inhaled saline. The effects of CM-chitosan inhalation on tracheal fibrosis were analyzed. Laryngoscopy was performed to evaluate and grade tracheal granulation, while tracheal fibrosis was evaluated by histological examination. The effects of CM-chitosan inhalation on the tracheal mucosa were examined by scanning electron microscopy (SEM), and hydroxyproline content in tracheal scar tissue was determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Laryngoscopy showed that the tracheal cross-sectional area was smaller in the experimental than control group. The amounts of loose connective tissue and damaged cartilage, as well as the severity of collagen and fibrosis, decreased following inhalation of CM-chitosan. According to the ELISA, the experimental group had low levels of hydroxyproline in the tracheal scar tissue.

CONCLUSION

The findings presented here showed that inhalation of CM-chitosan mitigated posttraumatic tracheal fibrosis in a rabbit model, thus suggesting a potential new treatment for tracheal stenosis.

Efficacy of Cricotracheal Stenosis Resection (CTSR) Among Children with Congenital vs. Acquired Sub-glottic Stenosis

Sub-glottic Stenosis (SGS) treatment in children is challenging because there is no standard algorithm to follow; however, the use of endoscopic techniques in SGS treatment has emerged over the last decades and has advanced. The aim of this study was to assess the efficacy of Cricotracheal Stenosis Resection (CTSR) among children with congenital vs. acquired SGS. In this retrospective study, we reviewed the charts of 22 patients who underwent endoscopic intervention as the primary modality of treatment for SGS at King Abdulaziz Medical City from January 1, 2011 to October 31, 2019. Successful treatment was defined as: resolution of symptoms, restoration of a normal patent airway with no stenosis, and decannulation. Out of 22 patients, 14 cases were acquired and 8 were congenital SGS. Most of the patients had grade 3 stenosis before surgery 15 (68%), followed by grade 1 stenosis among 4 (18.2%) and grade 2 stenosis was present in 3 (13.6%) patients. Postoperatively, 17 (77.3%) patients improved to grade zero, whereas grade 3 stenosis was not reported in any patient. The Mc-Nemar's test showed significant improvement between pre- and post-operative stenosis grade with test value = 22, and P value = 0.003. This technique was successful among 18 (82%) patients with P value ≤ 0.01. Irrespective of the differences in the age of patients, length, and character of stenosis among congenital and acquired groups, the endoscopic CTSR technique proved to be successful in both groups. We achieved a success rate of 86% in the acquired series, and 75% in the congenital series, which is a very promising result.

Laryngotracheal stenosis: Mechanistic review

Background

The purpose of this review article is to summarize the existing literature surrounding wound healing mechanisms in laryngotracheal stenosis.

Methods

A review of general wound healing pathophysiology, followed by a focused review of iatrogenic laryngotracheal stenosis (iLTS) and idiopathic subglottic stenosis (iSGS) as conditions of aberrant wound healing.

Results

iLTS is the scarring of the laryngotracheal complex, coming secondary to injury from prolonged intubation. iSGS is a chronic fibroinflammatory scarring and narrowing of the subglottic airway in the absence of any obvious preceding injury or trauma. They are both thought to result from a prolonged and dysregulated wound healing response that promotes the deposition of pathologic scar in the airway.

Conclusions

Understanding the mechanisms that underlie wound healing will help identify and intervene on the process early in its development and discover future therapies that target individual wound healing mechanisms limiting the incidence of this recalcitrant disease process.

Establishing an Endoscopic Chronic Subglottic Stenosis Rabbit Model

OBJECTIVES/HYPOTHESIS

To develop a reproducible and consistent chronic subglottic stenosis (SGS) in an endoscopic animal model.

STUDY DESIGN

Prospective study.

METHODS

We conducted a prospective study using New Zealand white rabbits. Chronic SGS was induced endoscopically by Bugbee electrocautery to 50% to 75% of the subglottic area's circumference, followed by 4-hour endotracheal intubation. The rabbit airways were endoscopically assessed and sized with uncuffed endotracheal tubes (ETTs) before the injury, during follow-up, and at the endpoints. There were four endpoints: 2, 4, 6, and 8 weeks post SGS induction. Animals were humanely euthanized for histopathological examination of the subglottic injury site and microscopic measurement of the cricoid lumen.

RESULTS

Twenty-two rabbits reached the endpoints, and 18 rabbits developed chronic SGS. ETT size significantly decreased by 0.5 from preinjury to the endpoint in all groups, P < .001. Control median cricoid lumen measurements were 20.48 mm² , the median cricoid lumen measurement for the 2 weeks endpoint was 14.3 mm² , 4 weeks 11.69 mm² , 6 weeks 16.03 mm² , and 8 weeks endpoint median was 16.33 mm² . Histopathological examination showed chronic scar tissue and new cartilage formation at the cricoid level, mainly at the posterior subglottic injury site starting from 4 weeks postinjury. Collagen staining revealed substantial amounts of organized collagen and different collagen orientation starting 4 weeks postinjury lasting until 8 weeks postinjury.

CONCLUSION

We developed an animal model to study chronic SGS. This model will be utilized to compare different endoscopic treatment interventions in acute SGS versus chronic SGS and further define the molecular basis of SGS.

LEVEL OF EVIDENCE

NA Laryngoscope, 2021.

Endoscopic Repair of Type 1 Laryngeal Clefts and Deep Interarytenoid Notches: Cold Steel Versus Laser

OBJECTIVES/HYPOTHESIS

Endoscopic repair is the preferred surgical treatment for type 1 laryngeal clefts (T1LCs) and deep interarytenoid notches (DINs). No studies exist showing differences in repair rates using laser and cold steel. Our objective is to assess overall success and revision rate for endoscopic cleft repair and determine whether there is any difference in surgical outcomes between cold steel and laser techniques.

STUDY DESIGN

Retrospective chart review, cohort study.

METHODS

Retrospective review at a quaternary care pediatric hospital. Included all patients who underwent endoscopic repair for T1LCs and DINs between January 2010 and December 2019. Demographics, comorbidities, surgical data, outcomes, and revision status were collected and analyzed. We excluded patients who did not have a follow-up at our institution.

RESULTS

A total of 194 patients were identified, 14 were excluded for lack of follow-up data so 180 were analyzed. Of these, 127 had cold steel repair and 53 had laser repair. There is no significant difference in demographics or comorbidities. In the cold steel group, 4 of 127 (3.1%) had breakdown and in the laser group, 10 of 53 (18.9%) had breakdown. Patients who failed after a cold steel repair tended to break down later (median 12.7 months) when compared to laser repairs (median 2.1 months). Nine of the 10 patients with breakdown after laser repair were noted on initial postoperative evaluation.

CONCLUSIONS

Endoscopic cleft repair is a well-described and effective method for repair of T1LCs and DINs. Both cold steel and laser have high success rates; however, higher failure rates were noted in the laser repair group. Failure after laser repair may occur earlier than failure after cold steel repair. But this did not reach significance.

LEVEL OF EVIDENCE

III Laryngoscope, 2021.

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.

Effects of Fractional CO2 Laser Treatment on Subglottic Scar in a Rabbit Model

OBJECTIVE

The objective of this study was to investigate the effects of fractional CO₂ laser on subglottic scar.

STUDY DESIGN

Randomized controlled animal study.

SETTING

Academic medical center.

METHODS

Subglottic scar was induced in 12 New Zealand white rabbits via an endoscopic brush technique. This was followed by an open airway surgery that included vertical division of the cricoid and proximal trachea. Eight rabbits underwent fractional CO₂ laser treatment of the scar via a Lumenis Ultrapulse Deep FX handpiece. Four rabbits underwent the open surgical approach without laser treatment. Bronchoscopy was performed at weeks 1, 2, 4, and 8. The animals were euthanized and laryngotracheal complexes harvested 12 weeks postsurgery. Immunohistochemistry was performed to determine the collagen composition of treated and untreated scars.

RESULTS

All 12 subjects survived to the study endpoint with no significant respiratory complications, despite 10 of 12 developing some degree of lateral tracheal narrowing. The median ratio of type I collagen to type III collagen in the laser group (1.57) was significantly more favorable than that of the untreated group (2.84; P = .03).

CONCLUSION

Treatment with fractional CO₂ laser appears to have similar effects on subglottic scars as with cutaneous scars, improving the ratio of type I to type III collagen. Additionally, we developed an open airway approach in the rabbit model to deliver fractional CO₂ laser treatment to the subglottis without introducing respiratory complications or compromising survival.

Rabbit model of consistently survivable subglottic stenosis using a modified brush technique

INTRODUCTION

Several animal models of subglottic stenosis (SGS) have been described in the literature, however many result in severe stenosis that requires early intervention and carry a high mortality rate. This limits the application of the model and may require the use of additional animals to achieve desired results due to procedural complications. A novel endoscopic method of inducing SGS in a rabbit model was developed as part of a larger investigation on the treatment of this condition. The objective of this study was to develop an animal model for survivable subglottic stenosis.

METHODS

12 New Zealand white rabbits underwent 2 trials of prolonged intubation that were not successful in inducing SGS. A partially sheathed nylon brush injury technique was then designed and implemented. Airway assessment consisted of rigid bronchoscopy 6 weeks and 8 months after injury.

RESULTS

12 rabbits undergoing subglottic brush injury had focal posteriorly based subglottic stenosis on bronchoscopy at 6 weeks and 8 months post-injury. One rabbit was euthanized after the brush induced subglottic injury but prior to 6 week bronchoscopy due to an unrelated orthopedic injury. This animal was therefore excluded from analysis and replaced. No rabbits required early airway intervention or sacrifice. All survived a period of 8 months.

CONCLUSION

Inducing subglottic injury with a partially-sheathed nylon brush safely and reliably creates a controlled SGS with zero procedure-related mortality over 8 months. This model could be the basis for a longer-term evaluation of subglottic scar evolution and intervention.

Laser-Assisted Endoscopic Cricotracheal Stenosis Resection (CTSR) in Paediatric Congenital Cartilaginous Subglottic Stenosis

Subglottic stenosis (SGS) in children can be a congenital condition or acquired through injury such as from prolonged intubation. Surgeons face challenges in choosing the best SGS treatment for a particular patient because of variability in the success rate of each technique. Conventional open surgical resection and reconstruction have been proven effective but, in recent years, endoscopic surgery has become more prevalent as it eliminates the incision and reduces the surgery time and subsequent hospital stay. The purpose of this retrospective case study was to report on an endoscopic technique using a CO₂ laser for cricotracheal stenosis resection (CTSR) for high-grade congenital SGS. From forty-five paediatric patients who underwent endoscopic intervention as a primary modality of treatment for high-grade SGS in a tertiary referral centre, a total of eight patients who met the inclusion criteria have been included in our study. This small patient series is the first to use a CO₂ laser alone as a single excision tool to eliminate complex congenital SGS and restore airway patency. The procedure's goal was to return the airway to an early stage of postintubation injury prior to scar formation; therefore, surgical sessions at intervals of 2-3 weeks were performed to ensure natural epithelization, to remove any granulation tissue, and manage fibrosis. Successful treatment was defined as a resolution of symptoms, restoration of a normal patent airway with no stenosis, and decannulation. The success rate was 75%. Two outcomes need to be highlighted. First, the CO₂ laser should be reconsidered as an excision tool for congenital SGS because of its low risk of exacerbating preexisting stenosis. It allows the surgeon to restore and augment the airway without the need for open surgery or dilatation. Second, the shorter interval between procedures is crucial for controlling the healing process and making sure that it is proceeding properly.

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.

Development of a survival animal model for subglottic stenosis

OBJECTIVE

To develop a reproducible survival animal model for subglottic stenosis.

STUDY DESIGN

Prospective study.

METHODS

We evaluated five methods of inducing airway injury in 30 New Zealand white rabbits to produce a subglottic stenosis model. Experimental groups comprised: group 1 (n = 5), which underwent 4-hour intubation; group 2 (n = 5), which underwent induced subglottic injury with a nylon brush; group 3 (n = 10), which underwent subglottic injury with a nylon brush, followed by 4-hour intubation; group 4 (n = 5), which underwent subglottic injury with Bugbee cautery in 50% of the subglottic circumference, followed by 4-hour intubation; and group 5 (n = 5), which underwent subglottic injury with Bugbee cautery in 75% of the subglottic circumference, followed by 4-hour intubation. Five animals were used as controls. Endoscopy of the airway and sacrifice of animals were planned at an interval of 14 days postinjury. Histologic measurements were analyzed.

RESULTS

No animals in groups 1 or 2 developed stenosis. In group 3, 50% of animals developed symptomatic grade 3 subglottic and tracheal stenosis, necessitating early endoscopy and sacrifice in three animals. Four animals in group 4 developed grade 1 subglottic stenosis, and four in group 5 developed grade 2 subglottic stenosis. Histologic measurements of lumen areas within each of these two groups were similar; all animals survived the follow-up period.

CONCLUSION

We successfully developed a reproducible survival model for induced subglottic stenosis using a combination of cautery-induced subglottic injury followed by 4-hour intubation. This model lays the foundation for future studies that evaluate endoscopic interventions for the management of subglottic stenosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:989-994, 2019.

The Effect of Human Adipose Tissue-Derived Mesenchymal Stem Cells in Rat's Subglottic Stenosis Model

OBJECTIVE

Subglottic stenosis remains a clinical challenge. The aim of this study was to evaluate the effect of human adipose tissue-derived mesenchymal stem cells (hAMSCs) in rat model of subglottic stenosis.

SUBJECTS AND METHODS

Ninety-six 13-week-old male rats were enrolled in this study. They were divided into 3 groups as normal control (NC) group, a subglottic injury and media injection (SM) group, and a subglottic injury and media-stem cell injection (SMSC) group. The hAMSCs were immediately injected into subglottis after injury. Histologic characteristics of subglottis; the mRNA expressions of interleukin-1β, cyclooxygenase-2, tumor growth factor-β and basic fibroblast growth factor; and hAMSCs' survival were evaluated.

RESULTS

The hAMSCs survived in the subglottis of the rat until 10 days after implantation. The NC and SMSC groups had a significantly wider subglottic lumen and thinner lamina propria than the SM group at 56 days after injury. Collagen intensity of subglottis was significantly higher in the SM group than in the NC and SMSC groups at 28 days after injury. Gene expression didn't show significant difference between the SM group and the SMSC group.

CONCLUSIONS

The hAMSCs injection was found to be helpful for preventing subglottic stenosis in a rat model.

Helical computed tomography scanning of the larynx and upper trachea in rabbits

Background

Computed tomography (CT) is used to evaluate the human tracheobronchial tree because of its unsurpassed ability to visualize the airway and surrounding structures. To establish an ideal animal model for studying subglottic stenosis, we assessed the size and morphology of the normal rabbit’s laryngotracheal airway by helical CT. We measured luminal dimensions at the levels of the arytenoid and cricoid cartilages and the first, third, and eighth tracheal rings. At all levels, the axial slices were used to calculate the maximum anteroposterior (AP) dimension, transverse dimension, and cross-sectional areas. We measured the tracheal length from the cricoid to the third and eighth tracheal rings on sagittal reformation. We assessed the hyoid, thyroid, cricoid, arytenoid, and tracheal rings for the presence of calcific or soft tissue densities. We also addressed the presence or absence of pre-epiglottic and paraglottic fat.

Results

The mean AP tracheal dimension ± standard deviation (SD) was 8.6 ± 0.5 mm at the arytenoid level, 8.2 ± 0.7 mm at the cricoid level, and 7.7 ± 0.2 mm at the first tracheal ring level. The transverse tracheal dimension ±SD was 5.3 ± 0.1 mm at the arytenoid level, 5.5 ± 0.5 mm at the cricoid level, and 6.1 ± 0.6 mm at the first tracheal ring level. The mean tracheal area ±SD was 35.7 ± 2.2 mm² at the arytenoid level, 35.8 ± 5.1 mm² at the cricoid level, and 39.2 ± 4.3 mm² at the first tracheal ring level. The tracheal length ±SD was 10.7 ± 2.3 mm from the cricoid to the third tracheal ring and 19.1 ± 1.14 mm to the eighth tracheal ring. There was complete calcification of the hyoid in all rabbits. Only two rabbits showed complete thyroid, arytenoid, or tracheal ring calcification. The remaining airway components were otherwise either uncalcified or partially calcified. The uvula, epiglottis, aryepiglottic fold, vallecula, piriform sinus, true/false vocal cords, and pre-epiglottic/paraglottic fat were not seen in any rabbit.

Conclusions

Helical CT investigation provides good, highly definitive anatomic details of the larynx and trachea in rabbits. Such results may be used in further evaluation of the normal airway and in cases of subglottic stenosis.

Microscopic examination of iatrogenic subglottic tracheal stenosis: observations that may elucidate its histopathologic origin

OBJECTIVES

The histopathologic origin of iatrogenic subglottic tracheal stenosis (ISTS) remains unclear. The purpose of this study was to use detailed operative microscopy to systematically examine the operative en bloc specimens of patients with ISTS and to observe the histologic and morphological changes in the hopes that these observations will provide insight into the histopathologic origin of these devastating injuries.

METHODS

The operative specimens of 18 patients who underwent open tracheal or laryngotracheal resection for ISTS were examined. Precise morphological characteristics were investigated for each tissue layer, including the adventitia, the outer surface of the perichondrium, the cartilage, the inner surface of the perichondrium, the submucosa, and the mucosa. Each tissue layer was evaluated independently and in relationship to the other layers. The cartilaginous airway was further evaluated relative to the pars membranacea.

RESULTS

The most common morphological finding in the epithelium was squamous metaplasia with occasional intense inflammation visible in the underlying mucosa, including cicatrization. The underlying cartilage demonstrated ossific metaplasia with sequestration in many cases. By far the most pronounced changes were found in the outer perichondrium and overlying adventitia and included diffuse paucicellular or hyperplastic fibrosis with intense hyperplastic scar formation or hyaline cicatrization. In the pars membranacea, severe scar formation and hyperplastic fibrosis were predominant. Ossific metaplasia was particularly severe in the lateral or outer parts of the tracheal ring, particularly in the vicinity of the adventitia and outer perichondrium. These changes were much more pronounced than the relatively minor changes observed in the submucosa and mucosa.

CONCLUSIONS

The most severe pathologic observations occurred in the lateral tissue layers, ie, the outer perichondrium and adventia. Given that an injury occurs from the tracheal lumen, these tissue layers have the greatest distance from the site of injury. As only minor changes occurred in the inner tissue layers, we hypothesize that these tissues have a greater regenerative capacity than the outer layers. This study supports the theory that the depth of the airway injury is more critical to the development of ISTS than is the extent or length of the injury.

A new rat model for investigation of subglottic stenosis

CONCLUSION

This study attempted to develop a new rat model of subglottic stenosis (SGS), resulting from subglottic mucosal injury administered by electrocauterization. Despite failure of the posterior SGS model, the anterior SGS model was considered feasible.

OBJECTIVE

To investigate the feasibility of using rats as an animal model for SGS.

METHODS

Thirty-seven female Sprague-Dawley rats were assigned to the control group or to the anterior or posterior subglottic injury group. Electrical cauterization was performed on the anterior or posterior 180° of the subglottic mucosa. Animals were euthanized at 4 weeks after injury. Histologic features of the subglottis were evaluated as regards changes in the subglottic lumen, lamina propria, cartilage, and epithelium after hematoxylin and eosin and Masson trichrome staining.

RESULTS

Survival in the anterior injury group was 80% (13/15) until 4 weeks, and results of histologic evaluation showed an increase in thickness of lamina propria with fibrosis and cartilage damage, resulting in luminal narrowing. A high rate of mortality was observed in the posterior injury group.

Cyclooxygenase-2 inhibition for the prevention of subglottic stenosis

OBJECTIVE

To evaluate the role of targeted cyclooxygenase-2 inhibition in reducing scarring associated with a subglottic airway mucosal injury.

DESIGN

Thirty-four New Zealand white rabbits underwent anterior cricothyroidotomy. Subglottic stenosis (SGS) was created by carbon dioxide laser injury.

INTERVENTION

Treatment consisted of intraperitoneal injection of celecoxib or vehicle for 4 days. Endoscopies were performed to assess injury and healing. Subglottic mucosal secretions were collected with Gelfoam swabs (Pfizer Inc) before and after injury and at subsequent time points. Animals were humanely killed at 3 or 8 weeks after injury and airways were excised, followed by gross examination and histologic analysis to assess the severity of SGS. Secretions were analyzed for interleukin-1β, prostaglandin E2 (PGE2), and matrix metalloproteinase-8 by enzyme-linked immunosorbent assays.

RESULTS

Endoscopy showed mild to moderate stenosis in the celecoxib group, but mild to severe stenosis in the vehicle group. Histologic assessment confirmed and quantified reduction in stenosis and scarring as well as advanced reepithelialization. In the healing tissue, mucosal thickening (stenosis) was reduced significantly (P = .02) in celecoxib-treated animals compared with those treated with vehicle, at 3 and 8 weeks (decrease in thickness by 32% and 49%, respectively). Collagen density (fibrosis) was also reduced 25% at both 3 and 8 weeks but the difference was not statistically significant (P = .20). Reduced level of PGE2 in the subglottic mucosal secretions was correlated with mucosal thickness at 8 weeks (P = .02).

CONCLUSION

Short-duration, anti-inflammatory therapy resulted in reduced stenosis and fibrosis with correlation of PGE2 levels in subglottic mucosal secretions.

A model of canine tracheal stenosis induced by radiofrequency cauterization

OBJECTIVE

The current methods of management of tracheal stenosis have disadvantages and are controversial, therefore ideal experimental animal models for the further studies are required. The aim of this study was to establish a new model of canine tracheal stenosis by radiofrequency cauterization.

METHODS

The tracheal cartilage ring was injured by radiofrequency at the level of the sixth tracheal ring in 12 mongrel dogs. A fibrolaryngoscope was used to guide the procedure. The animals were observed after operation and examined after euthanasia. Endoscopic and histological examinations were undertaken to evaluate the progress of stenosis. The degree of stenosis was calculated using the formula: degree of stenosis=(initial lumen area-final lumen area)/initial lumen area × 100%.

RESULTS

Tracheal stenosis had developed in all dogs by the 21st day post operation. Costal retraction was observed in all dogs after the 18th day post operation. At the end of the study, gross and endoscopic examinations showed that stenosis had been induced to a satisfactory degree and without any complications. The median of the degree of stenosis was 92%, with a range of 84-94%. Histological examination showed that cartilage was damaged and that granulation tissue and collagen fibres had formed.

CONCLUSIONS

The model of canine tracheal stenosis induced by radiofrequency cauterization is a relatively simple, reliable, and reproducible animal model. This model may be useful in the development of new methods of treatment for tracheal stenosis.

Subglottic stenosis examined as a fibrotic response to airway injury characterized by altered mucosal fibroblast activity

OBJECTIVE

To investigate the association between mucosal fibroblast activity and subglottic stenosis (SGS) development.

DESIGN

Prospective study of an animal model of SGS.

SETTING

Academic research laboratory.

SUBJECTS

New Zealand white rabbits were assigned to either the cricothyroidotomy and carbon dioxide laser injury group or the cricothyroidotomy and silver nitrate injury group. Airways were excised for histologic analysis and the establishment of primary fibroblast cultures. Lesions from surgical excision of established SGS and subglottic tissue were used to analyze SGS recurrence.

INTERVENTIONS

The subglottis was approached via cricothyroidotomy and was subjected to either carbon dioxide laser or silver nitrate injury before closure. The SGS lesions were excised at 8 to 10 weeks and were used to establish explants for fibroblast culture. The animals underwent recovery for an additional 14 days to follow recurrence of SGS. After 14 days, all the animals were killed humanely, and subglottic tissue was harvested for histologic evaluation. Rates of migration and contraction of SGS and normal airway fibroblasts were assayed using established in vitro methods under basal conditions and with prostaglandin E(2) treatment.

MAIN OUTCOME MEASURES

For in vivo studies, injury, healing, and scarring of the mucosa and cartilage were the primary measures. For cultured fibroblast experiments, cellular responses of fibroblasts from normal and stenosed mucosa were compared and contrasted.

RESULTS

Mucosal injury resulted in acute fibroplasia and chronic SGS, surgical excision of mature SGS at 8 weeks resulted in rapid recurrence of stenosis, and SGS-derived fibroblasts were relatively refractory to the effects of prostaglandin E(2) on migration and contraction.

CONCLUSIONS

Subglottic stenosis represents a fibrotic airway repair process that involves fibroblasts that produce recurrent, excessive scar formation. We suggest that SGS development and recurrence may be partially dictated by altered fibroblast responsiveness to antifibroplastic signals during mucosal repair.

Prostaglandin E2 is activated by airway injury and regulates fibroblast cytoskeletal dynamics

OBJECTIVES/HYPOTHESIS

To characterize the activation of cyclooxygenase (COX)-2/prostaglandin (PG) E2 signaling during airway mucosal repair and its subsequent role during the wound healing process.

STUDY DESIGN

Prospective animal study.

METHODS

The subglottis was approached via cricothyroidotomy. Sham airways were closed, and wounded airways were subjected to laser injury and closed. Subglottic tissue was harvested at 12 hours, 24 hours, 48 hours, and 72 hours postinjury. Secretions were collected preoperatively and at time of sacrifice. Inflammatory gene expression was analyzed using quantitative reverse transcriptase polymerase chain reaction. Subglottic/tracheal explants were exposed to exogenous IL-1beta in the presence or absence of COX inhibitors. Explant-produced PGE2 levels were assayed using enzyme linked immunoassays. Human airway fibroblast migration and collagen contraction were assayed in the presence or absence of prostaglandin E2.

RESULTS

Laser injury triggers a rapid, dose-dependent increase in mucosal IL-1beta and COX-2 gene expression, with an anatomical distribution proportional to the distance from the site of injury. Gene upregulation correlates with dose-dependent increases in PGE2 mucosal secretion levels. Ex vivo analysis indicates IL-1beta is responsible for the activation of the COX-2 / PGE2 pathway. Prostaglandin E2 differentially inhibits airway fibroblast migration and contraction in a specific, dose-dependent manner.

CONCLUSIONS

PGE2 is activated during mucosal inflammation and acts to decrease fibroplastic activity in the mucosal wound bed. During subglottic stenosis (SGS) development, the levels of PGE2 generated in response to injury may be insufficient to blunt the intrinsically fibroplastic phenotype of SGS fibroblasts, resulting in excessive scarring.