The effects of mitomycin-C and stenting on airway wound healing after laryngotracheal reconstruction in a pig model

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.

The effectiveness of Mitomycin C in Otolaryngology procedures: A systematic review

OBJECTIVE

Many studies have evaluated the effectiveness of topical intraoperative mitomycin (MCC) usage in a wide range of Otolaryngologic procedures with variable conclusions on effectiveness. This systematic review aims to provide a qualitative estimation of mitomycin C's treatment effectiveness in maintaining or preventing stenosis after surgical interventions.

DESIGN AND MAIN OUTCOME MEASURES

Following the PRISMA guideline, a comprehensive systematic search of MEDLINE, EMBASE, and CINAHL databases was performed including hand-searching and cross-reference checking. The search was limited to humans, sample size greater than two, and study designs including a comparative arm.

RESULTS

571 unique abstracts and 109 full articles were reviewed. 77 studies were included in the final analysis. The available evidence ranged from case series to randomized control studies. Meta-analysis was deemed inappropriate due to heterogeneity of study design. 38 studies assessed the effective of MCC in dacryocystorhinostomy, which is reported in a separate meta-analysis. All other studies were categorized into otolaryngologic site and pathology including: choanal atresia (n=5), endoscopic sinus surgery (n=12), airway procedures (n=9), esophageal procedures (n=8), and other (n=2).

CONCLUSIONS

The published literature on the effectiveness of MMC was mixed, but suggested topical MMC improved surgical outcomes in many Otolaryngologic procedures compared to controls. This was the first review to assemble literature on MMC usage for different surgical procedures. Comprehensive interpretation of the data was limited due to heterogeneity in primary outcome, procedure type, and study quality. High quality prospective and randomized controlled studies are required to further confirm the positive effect of MMC use on surgical outcomes.

Mechanical properties of de-epithelialized tracheal allografts

Background

Many studies have shown that mucosa-treated tracheas can be used for allotransplantation without the use of immunosuppressants. However, no literature has reported whether the transplanted trachea has normal biomechanics. In this study, fresh dog trachea was used as a control to determine the mechanical properties of allograft trachea after mucous membrane removal.

Methods

Cervical tracheas (~10 cm in length, consisting of the cartilage rings down to the tracheal carina) and the surrounding connective tissues were removed from 20 mixed-breed dogs and then divided into 4 groups with 5 samples in each group. The groups were defined as follows: group A, fresh canine tracheas without any treatment; group B, canine tracheas after sodium dodecyl sulphate (SDS) de-epithelialization; group C, canine tracheas implanted into the dorsal fascia of beagle dogs for 1 month after SDS de-epithelialization; group D, canine tracheas implanted into the dorsal fascia of beagle dogs for 6 months after SDS de-epithelialization. All heterotopically implanted beagle dogs were free of any immunosuppressive treatment. Uniaxial tensile (n=20) and compressive (n=20) experiments were performed on the 4 groups of trachea using a universal testing machine; the tensile load was recorded at 150% of the original tracheal length (50% displacement), and the compressive load was recorded at 50% of the initial anteroposterior diameter (50% displacement). The average difference in tensile and compressive loads between groups was compared by analysis of variance.

Results

No significant difference was found in the mean compressive strength among groups (group A =2.38±0.87 N, group B =3.33±1.03 N, group C =5.39±2.44 N, group D =3.04±2.12 N; P=0.07 for all groups). The mean tensile strength of group C was 9.68±0.86 N, resulting in a significant difference in tensile strength compared to group A (22.51±3.91 N) and B (24.24±7.46 N) (P<0.001). No significant difference in tensile strength was observed among groups A, B, and D.

Conclusions

The de-epithelialized trachea showed no significant change in mechanical properties after 6 months of implantation.

Biomechanical changes of freezer-storaged and decellularized pig tracheal scaffoldings

BACKGROUND

As an excellent xenotransplant, the pig trachea can be decellularized and cryopreserved to reduce its immunogenicity. However, few reports are found on the changes of its mechanical properties after cryopreservation and decellularization.

OBJECTIVE

To evaluate the structure and biomechanical properties in pig tracheal scaffolds resulting from decellularized and cryopreserved.

MATERIAL AND METHODS

Twenty-five pig tracheal segments were separated into five groups: untreated (group A), only decellularized (group B), only cryopreserved (group C), decellularized after cryopreserved (group D) and cryopreserved after decellularized (group E). Tracheal segments were subjected to uniaxial tension or compression using a universal testing machine to determine structural biomechanical changes.

RESULTS

It showed that there was no statistically significant difference in the tensile strength of the trachea in each group. The compressive strength of group B, C and D were same as the group A (P > 0.05), while the group E was lower than that of the group A (P < 0.05).Conclusions and significance: The histological examination of the decellularization after cryopreservation shows that the removal of epithelial cells and submucosal cells is more thorough, and the biomechanical structure of the trachea is better preserved. This proved to be a new method to prepare xenotransplantation of trachea graft.

Validation of Animal Models for Simulation Training in Pediatric Laryngotracheal Reconstruction

OBJECTIVES

To assess and compare the face (FV) and content validity (CV) of three ex vivo animal models for simulation training in pediatric laryngotracheal reconstruction (LTR).

METHODS

Feasibility of performing LTR was assessed on the head and neck of three different animals (lamb/suckling-pig/rabbit) and laryngeal dimensions and qualitative observations were recorded. A 19-item five-point Likert scale questionnaire was completed for each model to assess FV and CV. Data was prospectively collected and analyzed using descriptive and nonparametric statistics.

RESULTS

All three models were suitable for LTR simulation with laryngeal dimensions corresponding to 0-2 years (rabbit), 5-10 (pig) and >10 years (lamb model). Five trainees and five expert pediatric otolaryngologists performed LTR on each model. The overall median FV score was 5 for the lamb model (IQR 4-5), 3 for the rabbit (IQR 2-3), and 4 for the pig (IQR 4-4). The overall median CV score was 5 for the lamb (IQR 5-5), 2 for the rabbit (IQR 2-3), and 4 for the pig model (IQR 4-4). Comparison of the models demonstrated the lamb to be favored as the most realistic and practical model for simulation training in pediatric LTR, with both the lamb and the porcine model attaining validation thresholds.

CONCLUSION

Our study is the first comparative validation assessment of animal models for use in pediatric LTR simulation and it supports the use of ex vivo lamb and porcine models for use in LTR surgical skills training. The lamb model was the favored simulation model while the rabbit was considered inferior for simulation training in pediatric LTR.

LEVEL OF EVIDENCE

3b.

Characterization of the biomechanical properties of canine trachea using a customized 3D-printed apparatus

OBJECTIVES

The canine trachea is considered to be an excellent preclinical model for tracheal research due to its similar mechanical and dimensional characteristics to the human trachea. However, normative biomechanical properties have yet to be defined and it is one of the main reasons tracheal reconstruction has not succeeded in animal models at large scale. Variation and inaccurate measurement due to a lack of proper apparatus for mechanical tests further prevent determination of normative mechanical data of the trachea. The goal of this study was to overcome these shortcomings by designing the measuring apparatus using 3D-printing technology. Using this apparatus, we determined the normative biomechanical properties of the canine trachea.

METHODS

Whole tracheas were obtained from thirteen mongrel dogs. Biomechanical measurements were performed to determine the radial compressive strength and tensile strength of the intact trachea, and the elastic modulus of the tracheal cartilage.

RESULTS

Structural parameter data indicated the canine trachea to have inner-diameters similar to those of the human trachea and other widely used animal models. The compressive strength was 4.24N while the tensile strength was 29.96N. The elastic modulus of the cartilage portion of the trachea was 1.58N without showing a significant difference in value based on the location of the trachea.

CONCLUSIONS

This study delineates a comprehensive and foundational characterization of the biomechanical properties of both the intact and cartilage portion of the canine trachea. The parameters were in agreement with those of the human trachea, confirming the canine trachea to be an excellent preclinical model for tracheal research.

A systematic review of simulated laryngotracheal reconstruction animal models

OBJECTIVES

Review of the literature to identify practical, high-fidelity, commercially available animal models for simulation training and surgical skills maintenance in laryngotracheal reconstruction (LTR).

METHODS

A systematic review of PubMed and Embase databases was conducted independently by two authors, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "laryngotracheal reconstruction," "laryngotracheoplasty," "pig and larynx," "sheep and larynx," and "rabbit and larynx." Articles were then assessed, identifying model cost and availability, model validation, feasibility as a training tool, and verisimilitude to pediatric LTR.

RESULTS

In total, 79 articles were considered suitable for inclusion in the study, incorporating both in vitro and in vivo models. Models utilized included rabbit (n = 69), pig (n = 7), sheep (n = 1), and goat (n = 2). The rabbit model was similar in size to the neonate, but differences in laryngeal anatomy and cartilage texture made graft insertion difficult. The anatomy of the pig, sheep, and goat larynges more closely resembled the pediatric patient, allowing improved grafting, but corresponded more in size to that of an older child. Commercial availability of the pig and sheep was considered greatest, and was reflected in cost. None of the animal models identified in the literature have been validated as a simulation tool.

CONCLUSIONS

The rabbit, sheep and pig models seemed to demonstrate the greatest potential for use as advanced pediatric airway surgery simulation models, with the rabbit model being most utilized in the literature. However, as yet there have been no models formally validated as a simulation training tool. Laryngoscope, 129:235-243, 2019.

Role of Topical Medication in Prevention of Post-extubation Subglottic Stenosis

Iatrogenic laryngotracheal injury is the most serious complication of endotracheal intubation since this method of establishing airway was first described by Eugene Bouchut in 1858. Even today, subglottic stenosis is the most dreaded complication of intubation. This animal study is focused on the host tissue response to intubation induced injury resulting in subglottic stenosis and methods to prevent this complication. To assess the role of topically applied Mitomycin-C and Triamcinolone Acetonide in wound healing process following post-extubation subglottic injury. Prospective Randomized block, single-blinded, experimental study. Forty New-Zealand white rabbits where block randomized and allocated into 4 groups based on the type of topical medication that was applied post-extubation. Further these groups where subdivided into 3 subgroups based on the time of sacrifice (4, 6 and 12 weeks) to study the histopathological changes that occurred in a temporal sequence at the subglottis. It was observed that the rabbits in the control group and those that received Mitomycin-C only had more respiratory distress compared to those treated with Triamcinolone Acetonide. Statistically significant histopathological changes were observed in all the 4 groups. Mitomycin-C applied topically did not alter the wound healing process following post-extubation injury in the subglottis. Triamcinolone Acetonide significantly altered wound healing in the subglottis and prevented occurrence of respiratory distress.

Benefits and risks of mitomycin use in the traumatized tracheal mucosa

Objective

To investigate the efficacy and early complications of mitomycin C (MMC) in tracheal wound models.

Study Design and Setting

Rabbits (N = 60) were randomized to undergo mucosal injuries to the upper and lower trachea including anterior 120° full thickness (group A, n = 20), anterior 120° partial thickness (group B, 20), and circumferential partial thickness (group C, 20). In each rabbit, the wounds were separately treated with MMC 1.0 mg/mL or saline, and the animals were sacrificed after three weeks.

Results

Twenty-seven of the 60 animals experienced early death because of tracheal rupture or airway obstruction caused by unresolved scabs on the preinjured tracheal mucosa; the incidence of early death was higher in groups A and C than in group B. In each group, the degree of tracheal stenosis was comparable in wounds treated with MMC and saline.

Conclusion

These findings suggest that topical MMC has no benefit when used to prevent tracheal stenosis. Acute airway obstruction may occur in MMC-treated rabbits with tracheal wounds.

Drug Eluting Stents for Malignant Airway Obstruction: A Critical Review of the Literature

Lung cancer being the most prevalent malignancy in men and the 3(rd) most frequent in women is still associated with dismal prognosis due to advanced disease at the time of diagnosis. Novel targeted therapies are already on the market and several others are under investigation. However non-specific cytotoxic agents still remain the cornerstone of treatment for many patients. Central airways stenosis or obstruction may often complicate and decrease quality of life and survival of these patients. Interventional pulmonology modalities (mainly debulking and stent placement) can alleviate symptoms related to airways stenosis and improve the quality of life of patients. Mitomycin C and sirolimus have been observed to assist a successful stent placement by reducing granuloma tissue formation. Additionally, these drugs enhance the normal tissue ability against cancer cell infiltration. In this mini review we will concentrate on mitomycin C and sirolimus and their use in stent placement.

Defining the biomechanical properties of the rabbit trachea

OBJECTIVES/HYPOTHESIS

Surgical advancements rely heavily on validated animal models. The New Zealand White (NZW) rabbit is a widely used model for airway research, including regenerative medicine applications. Currently, the biomechanical properties of the normal rabbit trachea are not known. Our objective was to define these properties to assist in the standardization and understanding of future airway research using this model.

STUDY DESIGN

Laboratory-based study.

METHODS

Fresh tracheas from four adult NZW rabbits were dissected into 20 segments. To examine the biomechanical properties, segments were subjected to uniaxial tension (n = 9) and compression (n = 11) testing. Yield and maximum load (tension) and force at 50% displacement (compression) were recorded, and differences between segments were examined using analysis of covariance.

RESULTS

Normative data for native rabbit trachea show mean maximum load = 6.44 newtons (N), yield load = 5.93 N, and compressive strength = 2.10 N. In addition to establishing the baseline measurements, statistically significant differences in tensile measures based on location along the trachea and diameter were identified. Proximal segments had significantly higher maximum load (P = .0029) and yield load (P = .0062) than distal segments. Association between diameter and both maximum load (P = .0139) and yield load (P = .0082) was observed.

CONCLUSIONS

The adult NZW rabbit trachea is intrinsically less able to withstand tensile and compressive forces, compared to other airway models such as sheep or cadaveric human. Establishment of normative values will enable future research into changes in tracheal biomechanical properties during regenerative medicine manipulation and processing.

Dose-dependent effect of mitomycin C on human vocal fold fibroblasts

BACKGROUND

The purpose of this study was to evaluate in vitro cytotoxicity and antifibrotic effects of mitomycin C on normal and scarred human vocal fold fibroblasts.

METHODS

Fibroblasts were subjected to mitomycin C treatment at 0.2, 0.5, or 1 mg/mL, or serum control. Cytotoxicity, immunocytochemistry, and Western blot for collagen I/III were performed at days 0, 1, 3, and 5.

RESULTS

Significant decreases in live cells were measured for mitomycin C-treated cells on days 3 and 5 for all doses. Extracellular staining of collagen I/III was observed in mitomycin C-treated cells across all doses and times. Extracellular staining suggests apoptosis with necrosis, compromising the integrity of cell membranes and release of cytosolic proteins into the extracellular environment. Western blot indicates inhibition of collagen at all doses except 0.2 mg/mL at day 1.

CONCLUSION

A total of 0.2 mg/mL mitomycin C may provide initial and transient stimulation of collagen for necessary repair to damaged tissue without the long-term risk of fibrosis.

Synthesis of a novel CS-g-MMCs conjugate and the inhabitation on the proliferation of Tenon's capsule fibroblasts in vitro

A novel anti-proliferative macromolecular conjugate, CS-g-MMCs, was synthesized in order to decrease the cytotoxicity of Mitomycin C (MMC) which was a traditional anti-proliferative agent of fibroblast in trabeculectomy. The structure of CS-g-MMCs was characterized by (1)H NMR, FT-IR spectroscopy and GPC analysis. The grafting degree (dg) of MMC onto chitosan (CS) was determined to be in the range of 2.8-11.3%, which could be controlled by variation of the molar ratios of MMC to oxidized chitosan (CS-CHO). In the drug release profiles of CS-g-MMCs in vitro, an initial burst followed by slow leakage was observed, and addition of acid or lysozyme obviously accelerated the MMC release. The MTS assay indicated that CS-CHO of 8 mg/ml has no cytotoxicity against human Tenon's capsule fibroblasts (HTCFs). The inhibition of HTCFs proliferation by CS-g-MMCs increased along with increasing the dg of conjugate. The CS-g-MMCs also caused the apoptosis of HTCFs and interfered in the active DNA synthesis in HTCFs. Furthermore, the expression of a-SMA at gene and protein levels were obviously lower when HTCFs were treated with CS-g-MMCs, as compared to MMC or blend of MMC/CS-CHO (p<0.05). Our results primarily demonstrated that the CS-g-MMCs conjugates have low cytotoxicity and have the effect to inhibit fibroblast proliferation.

Study of Wound Healing in Rats Treated with Topical and Injected Mitomycin C

Objectives:

Mitomycin C, a widely used chemotherapeutic drug, has been proposed as a potential adjuvant for the control of scar tissue in surgical wounds because of its capacity to inhibit fibroblast proliferation. The current study used a combination of topical and injected mitomycin C to slow the healing process of surgical wounds in rats.

Methods:

An experimental model of surgical wounding at the dorsum of rats was used. A total of 43 animals were subdivided into 3 groups: Control, topical mitomycin C, and a combination of topical treatment and intradermal injections of the drug at 30 and 60 days after the initial topical treatment. After 3 months, the animals were painlessly sacrificed and the surgical scars were removed for microscopic analysis.

Results:

The group that received only topical mitomycin C presented milder inflammatory signs and consequently had a less intense healing process than the control group. The group treated with a combination of both topical and injected mitomycin C presented results comparable to those of the control group.

Conclusions:

The toxic characteristics of mitomycin C were most likely responsible for the greater tissue damage that occurred when it was used in the injected form, causing increased scar tissue formation. Mitomycin C slows the healing process of surgical wounds when used topically, but causes enhanced scar tissue formation when injected.

Mitomycin C and airway surgery: How well does it work?

Objective

Systematically review and critically evaluate all available published data on the use of topical mitomycin C (MMC) as an adjunctive in airway surgery.

Data Sources

Published studies indexed in MEDLINE, EMBASE, or Cochrane databases. Inclusion criteria were English language, sample size greater than five, and publication of data applicable to the analysis of topical MMC and airway surgery outcomes.

Review Methods

Evidence tables were compiled to include sample size, study design, and evidence level. Summary statistics, random-effects modeling, and subgroup analysis were performed.

Results

Twenty manuscripts (eight human, 12 animal) met the inclusion criteria. Seven of eight (87.5%) of the human studies and eight of 12 (66%) animal studies concluded topical MMC was beneficial to airway surgical outcomes. Eleven of twelve animal studies included randomization and a control group, compared with only two of eight human studies. Random-effects modeling of human studies (k=7) indicated that 81.4 percent (95% CI, 72.0%-90.9%; P < 0.001) of patients had improved outcomes attributable to MMC. Random-effects modeling of animal data included modeling of change in airway diameter (Hedge's G = −0.03; 95% CI, −0.66-0.60; P = 0.924) and the change in histologic measures (Hedge's G = 1.26; 95% CI, 0.596-1.92; P < 0.001) in MMC-treated animals vs controls.

Conclusion

The majority of the published literature individually suggests the use of topical MMC improves airway surgery outcomes. However, heterogeneity within the clinical studies, the lack of controlled data, and the lack of significance in the pooled animal data (other than histologic outcomes) suggest that the utility of MMC is still undetermined.

Halofuginone prevents subglottic stenosis in a canine model

OBJECTIVES

Halofuginone is a low-molecular weight quinazolinone alkaloid coccidiostat that inhibits collagen type I synthesis, extracellular matrix deposition, and angiogenesis. This study was conducted to assess its potential in preventing subglottic stenosis (SGS).

METHODS

We induced SGS in 10 dogs randomly divided into 2 groups. Each group received treatment between 3 days before and 21 days after the induction of SGS. One group received oral halofuginone 40 microg/kg, and the other was given placebo. The area of the subglottic lumen was measured at baseline and 3 months later. In addition, human tracheal fibroblasts were cultured. The inhibitory effect of halofuginone was compared to the effect of mitomycin.

RESULTS

All dogs survived throughout the study with no side effects. Three months after the operation, no halofuginone-treated dog had SGS, in contrast to a 66% to 80% stenosis rate (mean, 72%) in controls (p < .008). Thick fibrotic tissue was found in the placebo-treated larynges, whereas an almost normal architecture was observed in halofuginone-treated larynges. Halofuginone inhibited the growth of human tracheal fibroblasts by 75%, in comparison with 60% inhibition by mitomycin (no statistically significant difference).

CONCLUSIONS

This preliminary study shows that halofuginone is effective in preventing SGS caused by an acute injury. Halofuginone has a potential therapeutic role in preventing SGS in humans.

High-Level Expression of Matrix-Associated Transforming Growth Factor-β 1 in Benign Airway Stenosis

STUDY OBJECTIVES

Acquired tracheal and subglottic stenosis frequently leads to severe airway narrowing, which requires repeated interventions, such as dilatation, laser resection, stent implantation, or surgery. To get a more detailed insight into the pathogenesis of this condition, we investigated the expression of profibrotic cytokines and the proliferation of the airway wall in benign human airway stenoses.

METHODS

Specimens from patients with subglottic and tracheal stenosis and stent-related stenoses were obtained (n = 20) for reverse transcription (RT) polymerase chain reaction (PCR) analysis and immunohistochemistry testing.

RESULTS

Transforming growth factor (TGF)-beta1 messenger RNA expression was significantly increased in biopsy specimens from stent-related stenoses compared to nonstenotic control sections. In contrast, TGF-beta3 and interleukin-1beta showed no such differences in messenger RNA expression. Immunohistochemistry revealed a strong matrix-associated, subepithelial expression of TGF-beta1 in tracheal stenosis. Proliferating Ki-67-positive cells were mainly localized in the basal epithelial layer. Only 2 of 16 patients with tracheal stenoses and 3 of 4 patients with stent-related stenoses showed a weak expression of Ki-67-positive cells in the subepithelium. Furthermore, TGF-beta1 dose-dependently enhanced the proliferation of human lung fibroblasts in vitro, even in the presence of mitomycin-C.

CONCLUSION

While a weak subepithelial proliferation occurs in stent-related stenoses, the dominant factor in late stages of untreated tracheal stenoses seems to be the high-level expression of TGF-beta1 and the deposition of extracellular matrix.

Can Mitomycin C Really Prevent Airway Stenosis?

BACKGROUND/OBJECTIVES

Mitomycin C (MMC) is used in the prevention of upper airway stenosis. However, the efficacy of MMC is still debatable, and the potential complications of MMC use have been scarcely reported. We evaluated the efficacy and early complications of MMC in a wound model of the subglottis.

STUDY DESIGN

A randomized animal study.

METHODS

Sixty rabbits underwent a full-thickness injury to the posterior subglottis by diode laser. The animals were randomly assigned to three groups according to the different topical treatments of MMC 0.4 or 10 mg/mL or saline alone for 5 minutes. Animals were killed at 4 weeks, and gross and histologic findings were compared among different groups and 10 age-matched, non-wound, normal controls.

RESULTS

Thirty-two of the 60 (53%) animals died mainly of acute airway obstruction by necrotic debris, sloughs on, or cartilage collapse of the unhealed posterior subglottis during early weeks after wounding, higher in the MMC-treated animals (67%) than in the wound controls (25%) (P = .007). This resulted from the significant delay of wound healing in the MMC-treated groups compared with the wound controls (P = .012). The degree of subglottic stenosis was comparable among different groups (P > .8), although collagen deposition was significantly lower in the MMC-treated groups compared with the untreated controls (P = .036).

CONCLUSIONS

There was a significant risk of acute airway obstruction from delayed wound healing in rabbits that received subglottic laser wounding and MMC treatment. This risk should be considered in the use of MMC in clinical practice.

Successful treatment of laryngeal stenosis in laryngo-onycho-cutaneous syndrome with topical mitomycin C

Laryngo-onycho-cutaneous syndrome is a very rare entity found in Punjabi families. It affects the skin, nails, and larynx. Laryngeal involvement may cause lethal airway obstruction, and has in the past proved very difficult to treat. Mitomycin C is an antibiotic that acts as an alkylating agent, inhibiting DNA synthesis. It reduces fibroblast proliferation, and has previously been used to treat choanal atresia and laryngeal stenosis. We report an 18-year-old man with complete transglottic laryngeal stenosis secondary to laryngo-onycho-cutaneous syndrome. An airway was established by dissection with a bougie and sickle knife, and was initially maintained by the upper limb of a Montgomery T-tube. Laryngeal granulation tissue present on removal of the T-tube was treated with topical mitomycin C (2 mg/mL) applied for 4 minutes on two occasions with an interval of 1 month. A year later, the airway remained patent, with no granulation tissue.

Use of mitomycin C for treatment of keloid: a preliminary report

OBJECTIVES

Mitomycin C (MC) is an anti-neoplastic agent with an anti-proliferative effect on fibroblasts. We set out to evaluate the effect of MC application following keloid excision.

STUDY DESIGN AND SETTING

Patients with keloid in a tertiary referral center were enrolled in a prospective study. The scar was excised and prior to skin closure, a pledget with 1 cc of MC 0.4 mg/mL was applied for 5 minutes. Patient satisfaction and keloid thickness were assessed.

RESULTS

All patients were satisfied with the results, although complete disappearance of the keloid was evident only in two. Keloid thickness was measured and ranged from 5 to 26 mm. Following surgery and treatment at 2 months thickness ranged from 0 to 8 mm.

CONCLUSIONS

MC application following scar resection appears to be effective in treatment of keloid.

SIGNIFICANCE

As no specific effective treatment for keloid is currently available, utilization of this readily available therapeutic agent may improve treatment outcome.

Feasibility and safety of airway bypass stent placement and influence of topical mitomycin C on stent patency

OBJECTIVE

Airway bypass via transbronchial fenestration has been shown to improve forced expiratory volume and flow in explanted human emphysematous lungs. The aim of this study was to evaluate the feasibility and safety of in vivo airway bypass stent placement by using a canine model and to assess the influence of topical mitomycin C on the prolongation of stent patency.

METHODS

With dogs under general anesthesia, suitable segmental and subsegmental bronchial wall sites were selected by direct visualization with a flexible bronchoscope. Peribronchial blood vessel injury was avoided by using a Doppler probe. Transbronchial fenestration was formed with a 22-gauge transbronchial needle, and the passage was then dilated with a 2.5-mm angioplasty balloon. A balloon expandable stainless-steel stent (3 mm long x 3 mm wide) with a sleeve of silicone rubber covering was placed within the fenestration. Animals were bronchoscoped weekly to assess stent patency. Seventy stents were placed in 12 dogs. Thirty-five served as controls, and the other 35 received transbronchoscopic topical application of mitomycin C once weekly to evaluate the effect on the maintenance of stent patency. Mitomycin C stents were divided into 4 groups according to the number of treatments: group A, 1 treatment only; group B, 4 weeks; group C, 7 weeks; and group D, 9 weeks. Each once-weekly mitomycin C application consisted of 0.2 mL at a concentration of 1 mg/mL, delivered through a small polyethylene catheter.

RESULTS

Four instances of minor and brief bleeding occurred during stent placement and resolved without incident. One pneumothorax occurred and was treated by chest tube placement, without any adverse sequelae. There was no mortality associated with stent placement. No delayed hemorrhage or pneumothorax occurred. All control stents were occluded at the 1-week follow-up. The median durations of stent patency for group A (n = 8), group B (n = 9), group C (n = 10), and group D (n = 8) were 3, 8, 13, and greater than 20 weeks, respectively.

CONCLUSIONS

Airway bypass stent placement can be performed safely. In an animal model, most stents became occluded within 1 week, but topical mitomycin application resulted in significant prolongation of patency.

Influence of a dexamethasone-eluting covered stent on tissue reaction: an experimental study in a canine bronchial model

This study was designed to evaluate the feasibility and efficacy of a dexamethasone (DXM)-eluting, covered, self-expanding metallic stent to reduce tissue reaction following stent placement in a canine bronchial model. We placed a DXM-eluting, polyurethane-covered, self-expanding metallic stent (drug stent, DS) and a polyurethane-covered, self-expanding metallic stent (control stent, CS) alternately in each left main bronchus and left lower lobe bronchus in 12 dogs. The stents were 20 mm in diameter and length when fully expanded. The dose of DXM was approximately 36.7 mg in each DS, but was absent in the CS. The dogs were euthanased 1 week (n=4), 2 weeks (n=4) or 4 weeks (n=4) after stent placement. Histologic findings, such as epithelial erosion/ulcer or granulation tissue thickness, were obtained from the mid-portion of the bronchus, where the stent had been placed, and evaluated between DS and CS. There were no procedure-related complications or malpositioning of any of the bronchial stents. Stent migration was detected in one dog just before euthanasia 1 week following stent placement. Stent patency was maintained until euthanasia in all dogs. Epithelial erosion/ulcer (%) was significantly less in the DS (mean+/-standard deviation, 46.88+/-23.75) than in the CS (73.75+/-14.08) (P=0.026) for all time-points. There was a decrease in epithelial erosion/ulcer as the follow-up period increased in both DS and CS. The granulation tissue thickness (mm) was less in DS (2.63+/-2.05) than in CS (3.49+/-2.95), although the difference was not significant (P=0.751) for all time-points. There was a tendency toward an increase in granulation tissue thickness and chronic lymphocytic infiltration as the follow-up period increased in both DS and CS. In conclusion, DXM-eluting, covered, self-expanding metallic stent seems to be effective in reducing tissue reaction secondary to stent placement in a canine bronchial model.

Mitomycine C : prévention et traitement des synéchies glottiques antérieures

OBJECTIVES

Topical applications of mitomycin C to the anterior glottis may prevent anterior glottic synechia (prevention group) or restenosis (treatment group).

METHODS

In the prevention group, six patients with glottic carcinoma involving the anterior commissure were treated by transoral laser surgery. Repeated procedures were performed in one patient. For the six patients in the treatment group, the anterior glottic synechia was secondary to frontolateral laryngectomy (three patients), transoral laser therapy for laryngeal papillomatosis (two patients) or bilateral glottic carcinoma (one patient). Mitomycin C (0.4 mg/ml) was used as a topical application on the anterior commissure for a duration of 4 minutes. Outcome was assessed clinically at three months using a visual scale: no synechia (success), micro-synechia (partial failure), and synechia (failure).

RESULTS

In the prevention group, there were six successes and one partial failure. In the treatment group, there were two successes, three partial failures, and one failure. No side effects were noted.

CONCLUSION

Topical application of mitomycin C was effective to prevent anterior glottic synechia after transoral laser surgery for glottic carcinoma involving the anterior commissure. It is an alternative to endolaryngeal keel in patients with sequellar synechia. These preliminary results should be further evaluated in a larger series.

Mitomycin Does Not Prevent Laryngotracheal Repeat Stenosis After Endoscopic Dilation Surgery: An Animal Study

OBJECTIVES/HYPOTHESIS

Conflicting data exist in the literature regarding the role of mitomycin in the prevention and treatment of laryngotracheal stenosis. The purpose of the study was to assess the value of mitomycin in preventing repeat stenosis after endoscopic dilation surgery of well-established stenoses.

STUDY DESIGN

Prospective controlled animal study.

METHODS

Laryngotracheal stenosis was induced in 16 dogs. After a period of 3 months the dogs underwent endoscopic dilation and were randomly divided into two groups. The control group received immediate topical application of normal saline. Dogs in the mitomycin group received immediate topical application of 0.5 mg mitomycin. The animals were then observed for 3 more months before euthanasia. The laryngeal lumens were measured endoscopically at baseline, before dilation, and before euthanasia. A comparison was made between the two study groups by means of the Wilcoxon rank-sum test for change in the percentage of stenosis attained by the endoscopic dilation.

RESULTS

Nine dogs were included in the control group, and seven in the mitomycin group. Group comparison for initial occlusion before endoscopic dilation using Wilcoxon rank-sum test showed no difference between the two groups (z = 0.16 [P =.87]). Three months after endoscopic dilation, no difference was observed between the two groups regarding the change in the percentage of occlusion (z = -0.21 [P =.83]).

CONCLUSION

Mitomycin exerts a benefit equal to that of normal saline when applied to a well-established laryngotracheal stenosis in dogs and does not prevent repeat stenosis after endoscopic dilation surgery.

Animal models for tracheal research

Tracheal research covers two main areas of interest: tracheal reconstruction and tracheal fixation. Tracheal reconstructions are aimed at rearranging or replacing parts of the tracheal tissue using implantation and transplantation techniques. The indications for tracheal reconstruction are numerous: obstructing tracheal tumors, trauma, post-intubation tissue reactions, etc. Although in the past years much progress has been made, none of the new developed techniques have resulted in clinical application at large scale. Tissue engineering is believed to be the technique to provide a solution for reconstruction of tracheal defects. Although developing functional tracheal tissue from different cultured cell types is still a challenge. Tracheal fixation research is relatively new in the field and concentrates on solving fixation-related problems for laryngectomized patients. In prosthetic voice rehabilitation tracheo-esophageal silicon rubber speech valves and tracheostoma valves are used. This is often accompanied by many complications. The animal models used for tracheal research vary widely and in most publications proper scientific arguments for animal selection are never mentioned. It showed that the choice on animal models is a multi-factorial process in which non-scientific arguments tend to play a key role. The aim of this study is to provide biomaterials scientists with information about tracheal research and the animal models used.

The successful management of congenital laryngeal web with endoscopic lysis and topical mitomycin-C

Laryngeal web is a rare congenital anomaly. The primary goals of management for congenital laryngeal web are to provide a patent airway and to achieve a good voice quality. However, vocal cords have a tendency for fibrosis and granulation tissue formation after surgical interventions. Traditionally, the treatment of choice for laryngeal web is laryngofissure and placement of a stent or keel. This report presents the successful management of a congenital laryngeal web in a 10-month-old boy with endoscopic lysis and topical mitomycin-C application.

Clinical and Histological Healing of Surgical Wounds Treated With Mitomycin C

OBJECTIVES/HYPOTHESIS

The proven ability of mitomycin C to inhibit fibroblasts in vitro has stimulated its use in research animals and in humans to control healing. The objective of the study was to follow the healing process of surgical wounds in the dorsum of rats treated topically with mitomycin C.

STUDY DESIGN

Prospective experimental study.

METHODS

Two distinct surgical wounds were made to the dorsum of 10 adult rats. One of the wounds received topical mitomycin C diluted at 0.5 mg/mL during a 5-minute period, and the other wound was used as a control. The healing process was followed clinically and histologically after the rats were killed at different post-treatment periods. The degree of fibrosis was evaluated histologically by two different pathologists.

RESULTS

Surgical wounds treated with mitomycin C presented delayed healing when compared with the untreated wounds, with remission of scabs 7 days after the control wounds. Histological analysis at 1 month after treatment revealed a significant reduction in fibrosis of the wounds treated with mitomycin C when compared with the untreated wounds. After the third month the degree of fibrosis was comparable in both wounds.

CONCLUSION

Topical mitomycin C delays the healing of surgical wounds in rats up to the fourth week following treatment, but the degree of fibrosis is comparable in both treated and untreated wounds after 12 weeks. In otolaryngology this characteristic of the drug may be useful in the treatment of external ear canal stenosis, choanal atresias, nasal cicatricial stenosis, laryngeal stenosis, and keloids.

Tratamento cirúrgico da otite média com efusão: tubo de ventilação versus aplicação tópica de mitomicina C

O uso do tubo de ventilação (TV) da orelha média, tratamento cirúrgico eleito da otite média com efusão (OME), não é isento de complicações, promovendo ainda limitação social pela necessidade de abandono dos banhos de imersão. A mitomicina C (MMC) é um antineoblástico, cuja aplicação tópica retarda a fibrose e previne a estenose cicatricial. Em cobaias, retardou o fechamento de timpanotomias, permitindo maior tempo de aeração da orelha média, à semelhança dos tubos de ventilação. FORMA DE ESTUDO: Clínico prospectivo. OBJETIVO: Comparar a eficácia entre timpanotomia, aspirado da efusão e inserção de tubo de ventilação (grupo TV) versus timpanotomia, aspirado da efusão e aplicação tópica de mitomicina C (grupo MMC). Comparar o tempo de manutenção da timpanotomia e a incidência de complicações nos dois grupos. RESULTADOS: O grupo MMC apresentou eficácia significativamente menor (52% versus 80%) que o grupo TV (p= 0,34). A presença de timpanometria tipo "B" e a ausência de comprometimento do óstio faríngeo tubário pelo tecido adenóide no pré-operatório representaram fatores de mau prognóstico. A aplicação tópica de MMC nas bordas da timpanotomia proporcionou um tempo de abertura da membrana timpânica por duas a três semanas. No grupo TV, a otorréia foi observada em 13,3% dos pacientes. No grupo MMC, apesar da menor eficácia, nenhum paciente apresentou complicações nem sofreu prolongada proibição dos banhos de imersão. CONCLUSÃO: Apesar de concluirmos que o TV apresenta maior eficácia, novos estudos utilizando maior concentração, maior tempo de aplicação ou o uso seriado de MMC no tratamento da otite média com efusão devem ser realizados.

O comportamento clínico e histológico da pele do rato submetida ao uso tópico e injetável de Mitomicina C

OBJETIVO: A Mitomicina C é um quimioterápico que apresenta a capacidade de inibir fibroblastos in vitro. Esta característica a levou a ser usada experimentalmente em animais de laboratório e no ser humano, principalmente em oftalmologia, para inibir o processo cicatricial. Este trabalho visa acompanhar o processo de cicatrização de feridas cirúrgicas feitas em dorsos de ratos e tratadas topicamente com Mitomicina C, comparando-as com feridas no mesmo local, não tratadas. Propõe-se também a avaliar a resposta da pele quando injetada com concentrações diferentes do medicamento. FORMA DE ESTUDO: Experimental. MATERIAL E MÉTODO: Foram feitas, em 10 ratos, duas feridas cirúrgicas em seus dorsos. Uma delas foi tratada topicamente com Mitomicina C na diluição de 0,5 mg/ml por 5 minutos e outra não. O processo de cicatrização destas feridas foi acompanhado clinicamente. Posteriormente, os ratos foram sacrificados em períodos diferentes, e suas feridas estudadas histologicamente quanto ao grau de fibrose por dois anatomopatologistas. Posteriormente, três ratos foram submetidos a injeções intradérmicas com concentrações diferentes de Mitomicina C, e o comprometimento local foi avaliado clínica e histologicamente, sendo que apenas na concentração de 0,01mg/ml não se observou necrose tecidual. RESULTADOS: As feridas tratadas com Mitomicina C tiveram seu processo cicatricial retardado, com o desaparecimento das crostas locais 7 dias após o das feridas não tratadas. Ao exame histológico, observado separadamente por dois anatomopatologistas, observou-se no primeiro mês uma nítida diminuição do grau de fibrose nas feridas tratadas com Mitomicina C em relação às não tratadas. Este grau de fibrose se iguala, nas duas feridas, no terceiro mês. Quanto às diluições injetadas, notou-se clínica e histologicamente uma necrose tecidual proporcional ao grau de concentração (0,5; 0,1; e 0,05 mg/ml), que não foi observada na concentração de 0,01mg/ml. CONCLUSÃO: A Mitomicina C usada topicamente em feridas cirúrgicas em ratos retarda seu processo de cicatrização até a 4ª semana. Na 12ª semana este processo se equaliza. Quando usada intradermicamente, causa necrose tecidual apenas em concentrações elevadas. Estas características da Mitomicina C podem ser usadas, em otorrinolaringologia, como coadjuvante no tratamento de estenoses do meato acústico externo, imperfurações coanais, sinéquias nasais, estenoses laríngeas e quelóides.

Effect of exposure to mitomycin C on cultured tympanic membrane fibroblasts

OBJECTIVE

Recently, attempts have been made to prolong the patency of myringotomy site with topical use of mitomycin C (MMC). It has been shown that MMC inhibits mitosis and proliferation of ocular fibroblasts, however, there are no studies of MMC's effect on tympanic membrane fibroblasts. To investigate the effects of MMC on cultured human tympanic membrane fibroblasts and understand the cellular basis of MMC for maintain myringotomy patency, cultured fibroblasts were exposed to various concentrations of MMC for periods of 5-10 min.

METHODS

Effect of MMC on cultured fibroblasts was assessed by microscopic observation and cell viability test.

RESULTS

Dose-, time- dependent relationship of MMC on cultured fibroblasts was revealed. There was a significant difference between the inhibition effects of MMC at concentrations of 0.4 mg/ml and control following 5 and 10 min exposure intervals. Phase-contrast microscopy showed consistency with the antiproliferative effect of MMC at higher concentration.

CONCLUSIONS

Therefore, it would appear that intraoperative use of MMC could be effective in delaying the healing of the myringotomy site and extending the period of time for myringotomy patency.

Mitomycin C for control of recurrent bronchial stenosis: a case report

A 27-year-old patient with cystic fibrosis underwent a bilateral lung transplantation despite the presence of multiresistant Burkholderia cepacia. Postoperatively, the patient presented with bilateral bronchial necrosis. During the 14th week, his FEV(1) dropped to 2.5 L from a baseline level of 3.4 L. A subtotal occlusion of the right mainstem bronchus below the suture was noted. Using argon electrocoagulation, the right upper lobe bronchus, the intermediate bronchus, and the right middle lobe bronchus were reopened. During the period between weeks 20 and 42 post-transplantation, a recurrent stenosis required eight endoscopic interventions combining dilatation and stenting. During the 42nd week, dilatation followed by mitomycin C application stabilized the right lung function. This case report is the first to describe the effectiveness of the local application of mitomycin C to stop recurring extensive bronchial stenosis following bronchial necrosis secondary to lung transplantation.