Tracheal replacement: a critical review

Use of autologous bronchial cartilage to repair an intraoperative bronchial airway defect after pneumonectomy for lung mesothelioma

Tracheobronchial defects may occur intraoperatively because of surgical trauma after resection of thoracic tumors. The repair of large, circumferential tracheobronchial defects with tissue loss may pose a major challenge. In an effort to solve this problem, different techniques have been used with little success. Attempts with foreign materials, nonviable tissues, autogenous noncartilaginous tissues, tissue engineering, and allotransplantation have all been associated with disappointing or suboptimal results. In each category, biologic problems are noted. Hence, the reconstruction and substitution of large, circumferential tracheobronchial defects has so far remained an unsolved surgical dilemma. We report a unique case in which an airway defect in the bronchus, made inadvertently intraoperatively, was repaired using autologous bronchial cartilage obtained from the resected specimen. In the literature, autologous bronchial cartilage has never been used before in reconstructing a large tracheobronchial defect.

Patient-specific models of human trachea to predict mechanical consequences of endoprosthesis implantation

Nowadays, interventions associated with the implantation of tracheal prostheses in patients with airway pathologies are very common. This surgery may promote problems such as migration of the prosthesis, development of granulation tissue at the edges of the stent with overgrowth of the tracheal lumen or accumulation of secretions inside the prosthesis. Among the movements that the trachea carries out, swallowing seems to have harmful consequences for the tracheal tissues surrounding the prosthesis. In this work, a finite-element-based tool is presented to construct patient-specific tracheal models, introducing the endotracheal prosthesis and analysing the mechanical consequences of this surgery during swallowing. A complete description of a patient-specific tracheal model is given, and a fully experimental characterization of the tracheal tissues is presented. To construct patient-specific grids, a mesh adaptation algorithm has been developed and the implantation of a tracheal prosthesis is simulated. The ascending deglutition movement of the trachea is recorded using real data from each specific patient from fluoroscopic images before and after implantation. The overall behaviour of the trachea is modified when a prosthesis is introduced. The presented tool has been particularized for two different patients (patient A and patient B), allowing prediction of the consequences of this kind of surgery. In particular, patient A had a decrease of almost 30 per cent in his ability to swallow, and an increase in stresses that were three times higher after prosthesis implantation. In contrast, patient B, who had a shorter trachea and who seemed to undergo more damaging effects, did not have a significant reduction in his ability to swallow and did not present an increase in stress in the tissues. In both cases, there are clinical studies that validate our results: namely, patient A underwent a further intervention whereas the outcome of patient B's surgery was completely successful. Notwithstanding the fact that there are a lot of uncertainties relating to the implantation of endotracheal prostheses, the present work gives a new insight into these procedures, predicting their mechanical consequences. This tool could be used in the future as pre-operative planning software to help thoracic surgeons in deciding the optimal prosthesis as well as its size and positioning.

Interventional bronchoscopy from bench to bedside: new techniques for central and peripheral airway obstruction

This article discusses how basic scientific concepts, based on a greater understanding of airway physiology, support the development and dissemination of multidimensional classification systems for tracheal stenosis, expiratory central airway collapse, and innovative interventional bronchoscopic procedures for patients with asthma and chronic obstructive pulmonary disease.

Moving towards in situ tracheal regeneration: the bionic tissue engineered transplantation approach

In June 2008, the world's first whole tissue-engineered organ - the windpipe - was successfully transplanted into a 31-year-old lady, and about 18 months following surgery she is leading a near normal life without immunosuppression. This outcome has been achieved by employing three groundbreaking technologies of regenerative medicine: (i) a donor trachea first decellularized using a detergent (without denaturing the collagenous matrix), (ii) the two main autologous tracheal cells, namely mesenchymal stem cell derived cartilage-like cells and epithelial respiratory cells and (iii) a specifically designed bioreactor that reseed, before implantation, the in vitro pre-expanded and pre-differentiated autologous cells on the desired surfaces of the decellularized matrix. Given the long-term safety, efficacy and efforts using such a conventional approach and the potential advantages of regenerative implants to make them available for anyone, we have investigated a novel alternative concept how to fully avoid in vitro cell replication, expansion and differentiation, use the human native site as micro-niche, potentiate the human body's site-specific response by adding boosting, permissive and recruitment impulses in full respect of sociological and regulatory prerequisites. This tissue-engineered approach and ongoing research in airway transplantation is reviewed and presented here.

Surgical technique and results of tracheal and carinal replacement with aortic allografts for salivary gland-type carcinoma

OBJECTIVE

We describe the surgical technique and peroperative management of tracheal and carinal replacement with aortic allografts for large salivary gland-type carcinoma and report the results with a mean 34 months' follow-up.

METHODS

We performed tracheal and carinal replacements with aortic allografts in 6 patients with extensive mucoepidermoid (n = 1) or adenoid cystic (n = 5) carcinomas. Tracheal tumor resection was followed by carinal restitution (n = 3) and interposition of the graft, splinted by a silicone stent. The allograft consisted of an aortic segment, either fresh (in the first 2 patients) or cryopreserved (in the last 4). All grafts were wrapped with bulky and well-vascularized flaps (pectoral muscle flap all patients, with an additional "thymopericardial fat flap" in the last 2) to promote revascularization and to prevent erosion of adjacent large vessels or fistulas. No immunosuppressive therapy was administered.

RESULTS

Complete resection (R0) was achieved in 5 (83%) of 6 patients. Three of the first 4 patients experienced major morbidity, mainly fistulas between the esophagus and graft. The last 2 patients had an uneventful outcome. All grafts transformed into well-vascularized conduits focally lined with respiratory epithelium. So far, the last 4 patients are disease-free and 3 of them have returned to full-time employment. Stent removal has not been attempted in any patient.

CONCLUSION

Tracheal replacement with aortic allografts enables resection of extensive tumors with a curative intent. Efficient protective wrap around the graft is mandatory. Further follow-up is required to determine whether cartilage rings are generated within the graft, as in animal models.

Tissue-engineered tracheal transplantation

Regenerative medicine offers new tools with which to tackle disorders for which there is currently no good therapeutic option. The trachea is an ideal organ in which to explore the clinical potential of tissue engineering because severe large airway disease is poorly managed by conventional treatments, and the success of a graft is determined only by its ability to conduct air lifelong: that is, whether it can become a sustainable biological conduit. We define the component parts of tissue engineering and review the experimental methods used to produce airway implants to date, including a recent successful, first-in-man experience.

Tracheal replacement with a silicone-stented, fresh aortic allograft in sheep

BACKGROUND

Tracheal tissue regeneration after allogeneic aortic transplants in sheep has been reported. We sought to confirm these findings and elucidate the mechanism of this transformation.

METHODS

Ten male sheep underwent cervical tracheal replacement with fresh, descending thoracic aortic allografts, 8 cm long, from female sheep, without postoperative immunosuppressive therapy. A 10-cm silicone stent was placed to prevent airway collapse. Graft evaluations with flexible bronchoscopy and computed tomography were conducted between 2 weeks and 1 year after surgery.

RESULTS

There were no procedural deaths, but 6 animals died or required euthanasia between 12 days and 3 months postoperatively owing to severe tracheitis, cervical lymphadenitis, pneumonia, graft necrosis, stent migration, or airway obstruction after stent removal. The 4 remaining sheep were euthanized as planned at 6 to 12 months after surgery. Harvested tracheas revealed no evidence of graft incorporation into the surrounding tissue, and there was no histologic evidence of any neocartilage within or around the graft at any point. Bronchoscopy revealed marked graft necrosis in the 4 animals surviving to planned euthanasia. In all sheep, computed tomography imaging revealed that the graft was replaced by connective tissue without any signs of cartilage regeneration. Image analysis also indicated profound shortening of the grafted area up to 87.5% at 1 year after implantation, secondary to axial shift of the native trachea.

CONCLUSIONS

Fresh aortic allografts appear to be unsuitable for primary tracheal replacement. However, the observed graft shortening may allow for two-staged, end-to-end reconstruction of large tracheal defects with temporary grafting techniques.

Tissue-engineered trachea for airway reconstruction

OBJECTIVES/HYPOTHESIS

Scaffold-free cartilage has been used to engineer biocompatible and mechanically stable neotracheas in vivo. The purpose of this animal study was to determine if neotracheal constructs, implanted paratracheally, could successfully be used for segmental tracheal reconstruction.

STUDY DESIGN

Animal study.

METHODS

Culture-expanded auricular rabbit chondrocytes were used to engineer scaffold-free cartilage sheets. Cartilage and a strap muscle flap were wrapped around a tube and implanted paratracheally. At 12 to 14 weeks postimplantation neotracheas were used to reconstruct 20 mm tracheal defects. Surgical technique was modified several times in an attempt to decrease the amount of neotracheal obstruction and fibrosis. In one of the six rabbits, neotrachea with its intact strap muscle flap was dropped into the defect followed by an end-to-end anastomosis; in two animals the muscle flap was partially, and in one rabbit completely removed. In two animals the muscle flap was partially removed, the tube reinserted, and the construct reimplanted for 5 weeks to allow formation of a fibrous lining over the exposed cartilage followed by tracheal reconstruction.

RESULTS

All implants developed into vascularized and mechanically sound neotracheas. Following reconstruction, none of the animals showed immediate signs of respiratory distress; however, one died after 24 hours due to extensive endotracheal muscle flap edema, whereas rabbits who had undergone partial or complete muscle flap removal survived up to 39 days before developing cicatricial stenosis.

CONCLUSIONS

Tissue-engineered neotracheas proved to have excellent biocompatibility and stability to function under physiologic conditions, but lacked adequate endotracheal lining resulting in neotracheal stenosis.

Tracheal replacement with cryopreserved allogenic aorta

BACKGROUND

Radical resection of primary tracheal tumors may be challenging when more than one-half of the tracheal length is concerned. The present study evaluated the use of cryopreserved aortic allografts (CAAs) to replace long tracheal segments.

METHODS

Sixteen adult minipigs underwent tracheal replacement with a CAA. A silicone stent was used to splint the CAA for the first 12 months. Animals were followed-up using bronchoscopic evaluation and killed at predetermined times, for a period up to 18 months long.

RESULTS

Intense inflammation and progressive disappearance of typical histologic structures of the aorta were seen within the first 3 months. All animals studied for more than 3 months showed progressive transformation of the graft into a chimerical conduit sharing aortic and tracheal histologic patterns (eg, islands of disorganized elastic fibers/mature respiratory ciliated epithelium, respiratory glands, islets of cartilage). Stent removal was attempted after 12 months in 10 animals, and critical tracheal stenosis was found in six animals and moderate asymptomatic stenosis in four. Clinical course in these latter animals was uneventful until they were killed at 15 to 18 months. In situ hybridization showed that collagen2a1 mRNA was expressed in the cartilage islets at 1 year. Polymerase chain reaction analysis of the SRY gene demonstrated that the newly formed cartilage cells derived from the host.

CONCLUSIONS

CAA may be considered as a valuable tracheal substitute for patients with extensive tracheal tumors. Prolonged stenting will be probably mandatory for the clinical application of the procedure in humans.

Tracheal replacement with an aortic homograft

We report a case of acquired tracheoesophageal fistula, which was confounded by a long segment of necrotic trachea, requiring a desperate attempt at tracheal reconstruction using an aortic homograft. This is followed by a brief review of the literature in support of this useful technique of salvaging long-segment tracheal resection.

A double-chamber rotating bioreactor for the development of tissue-engineered hollow organs: from concept to clinical trial

Cell and tissue engineering are now being translated into clinical organ replacement, offering alternatives to fight morbidity, organ shortages and ethico-social problems associated with allotransplantation. Central to the recent first successful use of stem cells to create an organ replacement in man was our development of a bioreactor environment. Critical design features were the abilities to drive the growth of two different cell types, to support 3D maturation, to maintain biomechanical and biological properties and to provide appropriate hydrodynamic stimuli and adequate mass transport. An analytical model was developed and applied to predict oxygen profiles in the bioreactor-cultured organ construct and in the culture media, comparing representative culture configurations and operating conditions. Autologous respiratory epithelial cells and mesenchymal stem cells (BMSCs, then differentiated into chondrocytes) were isolated, characterized and expanded. Both cell types were seeded and cultured onto a decellularized human donor tracheal matrix within the bioreactor. One year post-operatively, graft and patient are healthy, and biopsies confirm angiogenesis, viable epithelial cells and chondrocytes. Our rotating double-chamber bioreactor permits the efficient repopulation of a decellularized human matrix, a concept that can be applied clinically, as demonstrated by the successful tracheal transplantation.

Structural and morphologic evaluation of a novel detergent-enzymatic tissue-engineered tracheal tubular matrix

OBJECTIVE

We sought to bioengineer a nonimmunogenic tracheal tubular matrix of 6 cm in length and test its structural, functional, and immunologic properties in vitro and in vivo.

METHODS

Twelve-centimeter tracheal segments were harvested from Yorkshire boars. Half of each segment was subjected to a detergent-enzymatic method (containing sodium deoxycholate/DNase lavations) of decellularization for as many cycles as needed, and the other half was stored in phosphate-buffered saline at 4 degrees C as a control. Bioengineered and control tracheas were then implanted in major histocompatibility complex-unmatched pigs (allograft) or mice (xenograft) heterotopically for 30 days. Structural and functional analysis and immunostaining were performed after each detergent-enzymatic method cycle and transplantation.

RESULTS

Compared with control tracheas, bioengineered matrices displayed no major histocompatibility complex class I and II antigens after 17 detergent-enzymatic method cycles, without significant (P > .05) differences in their strain ability (rupture force, 56.1 +/- 3.3 vs 55.5 +/- 2.4 N; tissue deformation at 203% +/- 13% vs 200% +/- 8% or 12.2 +/- 0.8 vs 12 +/- 0.5 cm; and applied maximum force, 173.4 +/- 3.2 vs 171.5 +/- 4.6 N). Thirty days after implantation, significantly (P < .01) smaller inflammatory reactions (392 vs 15 macrophages/mm(2) and 874 vs 167 T lymphocytes/mm(2)) and P-selectin expressions (1/6 vs 6/6) were observed in both the xenograft and allograft models with bioengineered matrices compared with those seen with control tracheas. There was no development of anti-pig leukocyte antigen antibodies or increase in both IgM and IgG content in mice implanted with bioengineered tracheas.

CONCLUSIONS

Bioengineered tracheal matrices displayed similar structural and mechanical characteristics to native tracheas and excite no immune response to 30 days when implanted as allografts or xenografts. This method holds great promise for the future of tissue-engineered airway replacement.

Tracheal replacement with cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts

BACKGROUND

Seven years of experimental research provided a valuable tracheal substitute, the aortic allograft, which can promote the regeneration of epithelium and cartilage. In human application, both fresh and preserved aortic allografts could be used. The optimal method of aortic allograft preservation remains to be evaluated. This study assessed the use of cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts as tracheal substitutes.

METHODS

Twenty-two sheep underwent tracheal replacement using cryopreserved (n = 10), decellularized (n = 7) or glutaraldehyde-treated (n = 5) allografts, supported by a temporary stent to prevent airway collapse. Aortic segments were retrieved at regular intervals up to 12 months after implantation to analyze the regenerative process.

RESULTS

All animals survived the operation. Major complications such as infection, stent migration, or obstruction were predominantly encountered in the decellularized group. The lack of major inflammatory response within the aortic graft observed in the glutaraldehyde group was associated with the absence of tracheal regeneration. Histologic examinations showed a progressive transformation of the aorta into a tracheal tissue comprising respiratory epithelium and cartilage only in the cryopreserved group.

CONCLUSIONS

This study demonstrated that regeneration of a functional tissue could be obtained after tracheal replacement with a cryopreserved aortic allograft. The regenerative process followed the same pattern as previously described for fresh allografts. Cryopreserved aortic allografts present major advantages: availability in tissue banks, permanent storage, and no need for immunosuppression. This offers a new field of perspectives for clinical application in patients with extensive tracheal cancer.

Bone morphogenetic protein-2 stimulation of cartilage regeneration in canine tracheal graft

BACKGROUND

Graft stenosis is among the most serious post-surgical complications that can occur after tracheal transplantation. Typically, stenosis is caused by resorption of tracheal cartilage. Bone morphogenetic protein-2 (BMP-2) is efficient at stimulating bone or cartilage regeneration. In this study, BMP-2 is tested for its effects on stimulation of cartilage regeneration in tracheal transplantation.

METHODS

For tracheal autotransplantation, 24 mongrel dogs were divided equally into four groups and BMP-2 was injected between the cartilage rings at doses of 1, 3, 5 or 7 mg. For tracheal allotransplantation, 12 mongrel dogs were divided equally into two groups. One group received 5 mg of BMP-2 per graft, and the other received collagen only as a control. The grafts were harvested after 4 weeks and subjected to pathologic analysis. The diameter of the graft lumen and areas of new cartilage regeneration were measured.

RESULTS

Regenerated cartilage areas were found in both the injected area and around the perichondrium. The areas of regenerated cartilage, as well as the diameter of the tracheal lumen, increased significantly with increasing concentrations of BMP-2. Five milligrams per milliliter was the most effective dose of BMP-2 in this study.

CONCLUSIONS

BMP-2 can significantly stimulate cartilage regeneration in tracheal grafts and also can be used to prevent stenosis after tracheal transplantation.

In vitro precultivation alleviates post-implantation inflammation and enhances development of tissue-engineered tubular cartilage

Tissue-engineered tubular cartilage is a promising graft for tracheal reconstruction. But polylactic acid/polyglycolic acid (PLA/PGA) fibers, the frequently used scaffolds for cartilage engineering, often elicit an obvious inflammation response following implantation into immunocompetent animals. We propose that the inflammation could be alleviated by in vitro precultivation. In this study, after in vitro culture for either 2 days (direct implantation group (DI)) or for 2 weeks (precultivation implantation group (PI)), autologous tubular chondrocyte-PLA/PGA constructs were subcutaneously implanted into rabbits. In the PI group, after 2 weeks of precultivation, most of the fibers were found to be completely embedded in an extracellular matrix (ECM) produced by the chondrocytes. Importantly, no obvious inflammatory reaction was observed after in vivo implantation and homogeneous cartilage-like tissue was formed with biomechanical properties close to native tracheal cartilage at 4 weeks post-implantation. In the DI group, however, an obvious inflammatory reaction was observed within and around the cell-scaffold constructs at 1 week implantation and only sporadic cartilage islands separated by fibrous tissue were observed at 4 weeks. These results demonstrated that the post-implantation inflammatory reaction could be alleviated by in vitro precultivation, which contributes to the formation of satisfactory tubular cartilage for tracheal reconstruction.

Clinical transplantation of a tissue-engineered airway

BACKGROUND

The loss of a normal airway is devastating. Attempts to replace large airways have met with serious problems. Prerequisites for a tissue-engineered replacement are a suitable matrix, cells, ideal mechanical properties, and the absence of antigenicity. We aimed to bioengineer tubular tracheal matrices, using a tissue-engineering protocol, and to assess the application of this technology in a patient with end-stage airway disease.

METHODS

We removed cells and MHC antigens from a human donor trachea, which was then readily colonised by epithelial cells and mesenchymal stem-cell-derived chondrocytes that had been cultured from cells taken from the recipient (a 30-year old woman with end-stage bronchomalacia). This graft was then used to replace the recipient's left main bronchus.

FINDINGS

The graft immediately provided the recipient with a functional airway, improved her quality of life, and had a normal appearance and mechanical properties at 4 months. The patient had no anti-donor antibodies and was not on immunosuppressive drugs.

INTERPRETATION

The results show that we can produce a cellular, tissue-engineered airway with mechanical properties that allow normal functioning, and which is free from the risks of rejection. The findings suggest that autologous cells combined with appropriate biomaterials might provide successful treatment for patients with serious clinical disorders.

Human nasal turbinates as a viable source of respiratory epithelial cells using co-culture system versus dispase-dissociation technique

OBJECTIVE

To compare a co-culture system with a conventional dispase-dissociation method for obtaining functional human respiratory epithelial cells from the nasal turbinates for tissue engineering application.

METHODS

Human respiratory epithelial cells were serially passaged using a co-culture system and a conventional dispase-dissociation technique. The growth kinetics and gene expression levels of the cultured respiratory epithelial cells were compared. Four genes were investigated, namely cytokeratin-18, a marker for ciliated and secretory epithelial cells; cytokeratin-14, a marker for basal epithelial cells; MKI67, a proliferation marker; and MUC5B, a marker for mucin secretion. Immunocytochemical analysis was performed using monoclonal antibodies against the high molecular-weight cytokeratin 34 beta E12, cytokeratin 18, and MUC5A to investigate the protein expression from cultured respiratory epithelial cells.

RESULTS

Respiratory epithelial cells cultured using both methods maintained polygonal morphology throughout the passages. At passage 1, co-cultured respiratory epithelial showed a 2.6-times higher growth rate compared to conventional dispase dissociation technique, and 7.8 times higher at passage 2. Better basal gene expression was observed by co-cultured respiratory epithelial cells compared to dispase dissociated cells. Immunocytochemical analyses were positive for the respiratory epithelial cells cultured using both techniques.

CONCLUSION

Co-culture system produced superior quality of cultured human respiratory epithelial cells from the nasal turbinates as compared to dispase dissociation technique.

Fabrication of a neotrachea using engineered cartilage

OBJECTIVES

Surgical management of long-segment tracheal stenosis is an ongoing problem. Many types of tracheal prostheses have been tried but with limited success because of immune rejection, graft ischemia, or restenosis. Tissue engineered cartilage may offer a solution to this problem, although scaffolds, which are currently often used for support, can lead to biocompatibility problems. This study investigated the feasibility of scaffold-free cartilage to tissue engineer a vascularized neotrachea in rabbits.

STUDY DESIGN

Animal study.

METHODS

Autologous neotracheal constructs were implanted in the abdomen of six New Zealand white rabbits. Auricular chondrocytes were used to engineer scaffold-free cartilage sheets. A muscle flap raised from the external abdominal oblique muscle and the engineered cartilage were wrapped around a silicone stent to fabricate a vascularized neotrachea in vivo. In two of the six rabbits, a full thickness skin graft was used to create an epithelial lining. The constructs were harvested after either 6 or 10 weeks.

RESULTS

All neotracheal constructs were healthy with well-vascularized and integrated layers. The implanted engineered cartilage underwent a remodeling process, forming a solid tracheal framework. Constructs harvested after 10 weeks proved to have significantly better mechanical properties than after 6 weeks and were comparable with the rabbit's native trachea.

CONCLUSION

Scaffold-free engineered cartilage can successfully fabricate a well-vascularized, autologous neotrachea with excellent mechanical properties. The results suggest that this approach can be used to reconstruct tracheal defects in rabbits.

Tracheal replacements: Part 2

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we covered the historical highlights of grafts, flaps, tube construction, and tissue transplants and addressed the progress made in tracheal stenting as a means of temporary tracheal support. In Part 2 we analyze solid and porous tracheal prostheses in experimental and clinical trials and provide a summary of efforts aimed at generating a bioengineered trachea. In both parts, we provide an algorithm on the spectrum of options available for tracheal replacement.

Reconstruction of functional tissues with cell sheet engineering

The field of tissue engineering has yielded several successes in early clinical trials of regenerative medicine using living cells seeded into biodegradable scaffolds. In contrast to methods that combine biomaterials with living cells, we have developed an approach that uses culture surfaces grafted with the temperature-responsive polymer poly(N-isoproplyacrylamide) that allows for controlled attachment and detachment of living cells via simple temperature changes. Using cultured cell sheets harvested from temperature-responsive surfaces, we have established cell sheet engineering to create functional tissue sheets to treat a wide range of diseases from corneal dysfunction to esophageal cancer, tracheal resection, and cardiac failure. Additionally, by exploiting the unique ability of cell sheets to generate three-dimensional tissues composed of only cultured cells and their deposited extracellular matrix, we have also developed methods to create thick vascularized tissues as well as, organ-like systems for the heart and liver. Cell sheet engineering therefore provides a novel alternative for regenerative medicine approaches that require the re-creation of functional tissue structures.

Postintubation multisegmental tracheal stenosis: treatment and results

BACKGROUND

A number of postintubation tracheal stenoses involve different and separate segments. Treatment of these types of strictures is complicated with obscure results, infrequently reported in literature.

METHODS

A total of 648 patients underwent treatment for tracheal or subglottic stenosis from September 1993 through October 2005; of those, 26 cases had two separate stenotic segments. Four types of therapeutic approaches were considered for these 26 patients: one-stage resection of the stenotic sites; two-stage resection of the stenotic sites; resection of one stricture and treatment of the second one by nonresectional methods such as dilatation, laser, stenting, T-tube, or tracheostomy; or treatment of both lesions by nonresectional methods. The therapeutic approach for each patient was determined by the surgeon and was based on the nature and location of stenoses, length of stenoses and the distance between the two stenotic sites.

RESULTS

There were 20 male patients (76.9%) and 6 female patients (23.1%), with a mean age of 23.9 years (range, 4 to 64). Fourteen patients had tracheal stenosis and 12 had both tracheal and subglottic involvement. Five patients underwent type 1 therapeutic approach whereas 4, 9, and 8 patients underwent types 2, 3, and 4, respectively. Mean length of resection was 58.9 mm in those who underwent complete resection of the stenotic sites (range, 30 to 90 mm). There were 2 complications, 1 stomal fistula and 1 wound infection. Follow-up was accomplished in all patients with a mean period of 21.5 months (range, 1 to 108). Sixteen patients achieved satisfactory results (good voice and airway), 7 are still under treatment (requiring stent, tracheostomy, or repeated dilatation), and 3 died (2 type 3 and 1 type 4). Two deaths were due to T-tube obstruction, and 1 was due to acute obstruction of the stenotic part.

CONCLUSIONS

Resection of both strictures and reconstruction of airway are feasible in some patients with multisegmental tracheal stenosis with good results. When resection of both strictures is not feasible, a combination of resectional and nonresectional managements could be helpful for the vast majority of patients.

Tissue engineering in head and neck reconstructive surgery: what type of tissue do we need?

Craniofacial tissue loss due to congenital defects, disease or injury is a major clinical problem. The head and neck region is composed of several tissues. The most prevalent method of reconstruction is autologous grafting. Often, there is insufficient host tissue for adequate repair of the defect side, and extensive donor site morbidity may result from the secondary surgical procedure. The field of tissue engineering has the potential to create functional replacements for damaged or pathologic tissues.

Tracheobronchial stenting and central airway replacement

PURPOSE OF REVIEW

The present paper reviews the recent literature on the management of malignant large airway obstruction using tracheobronchial stenting and airway replacement by aortic allografts.

RECENT FINDINGS

Airway stenting is a valuable adjunct to therapeutic bronchoscopy to relieve malignant airway obstruction. Over 80% of patients with obstructing lesions who were treated by airway stenting presented immediate symptom improvement in recent series. Stenting may also function as a bridge until further curative treatment can be used. Different stent models are available; their advantages and disadvantages depend on materials and constructions; clinical experience is larger with silicon-based models than with metallic stents. An alternative strategy for the management of nonresectable primary tracheal tumors aiming to replace the central airway with an allogenic aortic allograft has been proposed. Experimental studies showed that an aortic allograft produced a respiratory conduit that shared fundamental elements of the trachea and newly formed cartilage rings were observed.

SUMMARY

Airway stenting provides efficient palliation of symptoms in patients with malignant central airway obstruction. Evidence-based studies are needed to identify patients who may have the greatest benefit from stenting. Tracheal replacement with allogenic aortic allografts is a novel technique which brings hope to the management of extensive tracheal lesions.

[Segmental tracheal resection for the treatment of tracheal stenoses]

BACKGROUND

Segmental tracheal resection is considered to be the standard treatment of tracheal stenoses.

MATERIALS/METHODS

During the time period 1985-2002, segmental tracheal resection with a primary end-to-end anastomosis was performed in 117 patients with a cervical or upper thoracal stenosis of the trachea. The age distribution of the patients was between 7 and 77 years. Of the patients with a benign tracheal stenosis, sufficient data for a retrospective analysis were available in 101 patients. The length of the resected tracheal segments varied between 2 and 6 cm which required mobilisation of the trachea and the larynx and, if necessary, incision of the pulmonary ligament.

RESULTS

In 5 patients a permanent damage of the recurrent laryngeal nerve was seen, of which 4 had undergone revision surgery and 10 months after surgery 93% presented with a large and stable tracheal lumen without any relevant restenosis. Due to a restenosis of 70-80% causing dyspnea at rest, 3% of the 101 patients had to undergo revision surgery. In 4% a mild and asymptomatic restenosis of 30-40% was seen which did not require any further treatment.

CONCLUSION

These results demonstrate that segmental tracheal resection can safely and effectively remove stenotic tracheal segments of up to 6 cm and is therefore the treatment of choice.

SIS with tissue-cultured allogenic cartilages patch tracheoplasty in a rabbit model for tracheal defect

CONCLUSIONS

In the rabbit model, small intestinal submucosa (SIS) compounded with tissue-cultured allogenic cartilages appeared to be an efficacious method for the patch repair of partial circumferential tracheal defects instead of autologous grafts. SIS appears to be a safe and promising means of facilitating neovascularization and tissue regeneration. The long-term use of SIS and tissue-cultured allogenic cartilages warrants further investigation.

BACKGROUND

Tracheal defect reparation remains a challenging surgical problem that can require reconstruction using autologous grafts or artificial stents. This study was performed to evaluate the efficacy of SIS, a biocompatible, acellular matrix, compounded with different tissue-cultured allogenic cartilages, in the repair of a critical-size tracheal defect.

MATERIALS AND METHODS

A full-thickness defect (4 x 8 mm) was created in tracheal rings four to six in adult rabbits. A piece of 8-ply SIS sandwiched in thyroid cartilage, auricular cartilage, or without cartilage, respectively (designated experiment 1, 2, or 3, respectively), was sutured to the edges of the defect with interrupted 4-0 polypropylene sutures. In control animals, the defect was closed with lamina praetrachealis. All animals were followed until signs of dyspnea became apparent or for 4 or 12 weeks. After follow-up and euthanasia, the trachea was harvested and prepared for histologic evaluation using conventional techniques.

RESULTS

All animals tolerated the procedure well but two animals in group 1 (n=5), three in group 2 (n=5), and one in group 3 (n=5) had stridor after operation and expired within <1 month with different degrees of obstruction. The other animals in these groups and the control animals (n =3) all survived >1 month. Histologically, neovascularization of the patch was noted with moderate inflammation. The surface of the SIS patch was covered with a lining of ciliated epithelial cells. The tissue-cultured allogenic cartilages degraded to some extent.

Tracheal replacement by allogenic aorta in the pig

BACKGROUND

To assess whether fresh aortic allografts (AAs) can be used for tracheal replacement.

METHODS

Twenty-one male minipigs underwent tracheal replacement using AAs harvested from female pigs. The length of replaced segments exceeded 50% of the trachea. A stent was implanted into the lumen of the AA to prevent collapse. The animals were killed at 3-month intervals, and AAs were assessed for ingrowth of respiratory epithelium and cartilage formation and tested for type II collagen formation and the presence of the SRY gene.

RESULTS

A high stent migration rate was observed. Only 10 pigs and 4 pigs made it to follow-up periods exceeding 3 months and 9 months, respectively. Neither rejection nor ischemia were observed. At 3 months, a metaplastic epithelium lined the graft. At 10 months, a posterior membrane could be seen with immature cartilage and disorganized elastic fibers. SRY gene assay showed that the cells engrafted in the AAs, particularly at the level of the newly formed cartilage, were of male origin and thus originated from the recipient.

CONCLUSION

This study confirms that a fresh AA, replacing more than half of the trachea of the pig, transforms into a conduit containing the major tracheal components. These components are relatively immature and do not as of yet replicate the form and function of the native trachea. Questions remain concerning the exact mechanisms of this process. Further research on the role of tracheal replacement is recommended.

Development of tracheal prostheses made of porous titanium: a study on sheep

Authors report the development of a biomaterial to be used for tracheal and laryngeal reconstruction. This experimentation follows the replacement of trachea in rats with porous titanium implants. The aim of the study is to test this type of prosthesis on sheep, whose trachea is of comparable size to that of humans. Six ewes were implanted with porous titanium implants after resection of 5 cm of trachea. The planned period for the implantation was from 3 to 6 months before the sacrifice of the animals for histological analysis. After a simple immediate postoperative course, the implantations developed complications of tracheal patency, responsible for four deaths (tracheal obstruction by mucous plug n = 2, inferior necrosis of trachea n = 1, pneumopathy n = 1). The two remaining sheep presented no complications. The mechanical performance of the prostheses was good. The histological results showed an inflammatory stenosis of the tracheo-prosthetic junctions, which was not the direct result of death. The protheses were integrated by the surrounding tissue, but endoprosthetic colonisation by pseudostratified ciliated columnar epithelium was low or nil. The absence of endoprosthetic lining was responsible for the complications. The biocompatibility of the biomaterial is not in question, but the surgical procedure will have to be modified by an endoprosthetic mucous graft before implantation so as to accelerate healing process.

ADENOID CYSTIC CARCINOMA OF THE TRACHEA: A LONG-TERM PROBLEM

Adenoid cystic carcinoma of the trachea, although rare, is the second most common primary tumour of the trachea. It is a slow-growing tumour found in younger patients than the more common squamous cell carcinoma and is relatively resistant to treatment, but metastasizes late in the course of disease and even in unresectable cases can be palliated successfully for many years. We present a retrospective 20-year series of this condition from a single institute encompassing 13 patients of whom 6 were resected and 7 treated by palliative methods. A review of hospital records was carried out over the period 1984-2003. Details collected included symptoms before diagnosis, length of time from onset of the first symptom to diagnosis, resection details, survival statistics and accessory procedures tried before and after consideration of resection. The overall 5-year survival was 38.5%, but the mean survival in resected patients was 66 months as against 36 months for unresectable patients. Although most patients presented with dyspnoea, this was initially often attributed to other factors. The mean time of diagnosis from the onset of symptoms was 16 months. Although complete resection remains the management of choice if feasible, modern techniques of maintaining the airway in unresectable patients can give useful palliation for years.

Fetal cartilage engineering from amniotic mesenchymal progenitor cells

We determined whether cartilage could be engineered from mesenchymal progenitor cells (MPCs) normally found in amniotic fluid. Mesenchymal amniocytes were isolated from ovine amniotic fluid samples (n = 5) and had their identity confirmed by immunocytochemistry. Cells were expanded and then cultured as micromass pellets (n = 5) in a chondrogenic medium containing transforming growth factor-beta2 (TGF-beta2) and insulin growth factor-1 (IGF-1) for 6-12 weeks. Pellets derived from fetal dermal fibroblasts (n = 4) were cultured under identical conditions. Additionally, expanded mesenchymal amniocytes were seeded onto biodegradable polyglycolic acid scaffolds (n = 5) and maintained in the same chondrogenic medium within a rotating bioreactor for 10-15 weeks. Engineered specimens were analyzed quantitatively and compared with native fetal hyaline cartilage samples (n = 5). Statistical analysis was by the unpaired Student's t-test (p < 0.05). The isolated cells stained positively for vimentin and cytokeratins-8 and -18, but negatively for CD31. Micromass pellets derived from mesenchymal amniocytes exhibited chondrogenic differentiation by both standard and matrix-specific staining. In contrast, these findings could not be replicated in dermal fibroblast-based pellets. The engineered constructs derived from mesenchymal amniocytes similarly displayed histological evidence of chondrogenic differentiation and maintained their original size and three-dimensional architecture. Quantitative assays of the engineered constructs revealed lower concentrations of collagen type II, but similar amounts of glycosaminoglycans, elastin, and DNA, when compared to native fetal hyaline cartilage. We conclude that mesenchymal amniocytes can be used for the engineering of cartilaginous tissue in vitro. Cartilage engineering from the amniotic fluid may become a practical approach for the surgical treatment of select congenital anomalies.

Cell delivery in regenerative medicine: the cell sheet engineering approach

Recently, cell-based therapies have developed as a foundation for regenerative medicine. General approaches for cell delivery have thus far involved the use of direct injection of single cell suspensions into the target tissues. Additionally, tissue engineering with the general paradigm of seeding cells into biodegradable scaffolds has also evolved as a method for the reconstruction of various tissues and organs. With success in clinical trials, regenerative therapies using these approaches have therefore garnered significant interest and attention. As a novel alternative, we have developed cell sheet engineering using temperature-responsive culture dishes, which allows for the non-invasive harvest of cultured cells as intact sheets along with their deposited extracellular matrix. Using this approach, cell sheets can be directly transplanted to host tissues without the use of scaffolding or carrier materials, or used to create in vitro tissue constructs via the layering of individual cell sheets. In addition to simple transplantation, cell sheet engineered constructs have also been applied for alternative therapies such as endoscopic transplantation, combinatorial tissue reconstruction, and polysurgery to overcome limitations of regenerative therapies and cell delivery using conventional approaches.

Tracheal regeneration following tracheal replacement with an allogenic aorta

BACKGROUND

Tracheal replacement remains an unsolved surgical problem. Attempts to use tracheal substitutes have failed to achieve reliable results. In this study, tracheal regeneration was obtained after tracheal replacement with an allogenic aorta.

METHODS

Twenty female sheep underwent a 8-cm tracheal replacement with a fresh aortic allograft. In the six last animals, aortic grafts came from male sheep. A stent prevented airway collapse. No immunosuppressive therapy was used. Aortic segments were retrieved at regular intervals up to 16 months. A polymerase chain reaction for the SRY gene was performed in specimens with aortic grafts from male sheep.

RESULTS

All animals but one survived the operation without complications. Clearly identified between the suture lines, the aortic segments were completely transformed into a tracheal structure. Histology showed initially an inflammatory reaction with proliferation of a squamous epithelium followed by mucociliary epithelium and newly formed cartilage rings. SRY gene was not found in newly formed cartilage rings showing that the regeneration originated from recipient cells.

CONCLUSIONS

This study presents a new type of tissue regeneration and brings hopes to the treatment of extensive tracheal lesions.

Experimental study of replacing circumferential tracheal defects with new prosthesis

PURPOSE

To investigate the feasibility of using a new tracheal prosthesis made of biomaterials to replace extensive circumferential tracheal defects.

DESCRIPTION

Three types of tracheal prostheses were developed and studied. Type I prosthesis was used in 8 mongrel dogs (group A), type II in 4 dogs (group B), and type III in 4 dogs (group C).

EVALUATION

In group A, one died from prosthetic dehiscence, another from anastomotic leakage, and the others had uneventful postoperative courses. The implanted prosthesis was completely incorporated with the recipient trachea, where different lengths of reepithelialization occurred on the luminal surface of the reconstructed trachea. Macroscopic examination showed scattered and different sizes of neo-ossification surrounding the implanted prosthesis. The prosthesis was radioopaque when exposed to routine x rays. In contrast, a relatively high number of complications occurred postoperatively in groups B and C.

CONCLUSIONS

Type I tracheal prosthesis, with further improvements, may be the optimal tracheal graft to replace circumferential tracheal defects, and appears very promising for clinical application.

Repair of non-circumferential cervical trachea defects by three different latissimus dorsi flaps. A comparative studyin an experimental setting

BACKGROUND

Large intrathoracic airway defects may be closed using a pedicled latissimus dorsi (LD) flap, with rewarding results. This study addresses the question of whether this holds true for extrathoracic non-circumferential tracheal defects.

METHODS

A cervical segment of the trachea of 4 x 1 cm was resected in 9 white male pigs. The defect was stented with a silicone stent for 3 months and closed either by an LD flap alone (group a, n = 3), an LD flap with an attached rib segment covered by pleura (group b, n = 3), or an LD flap reinforced by a perforated polylactide (MacroPore) plate (group c, n = 3). The trachea was assessed by rigid endoscopy at 3 and 4 months and histologically at 4 months postoperatively.

RESULTS

The degree of stenosis at the level of the reconstruction at 4 months was 25, 50 and 75% in group a, 15, 50 and 60% in group b, and 20, 95 and 95% in group c, respectively. The percentage of the defect covered by columnar epithelium was 100% in all animals of group a, 60, 100 and 100% in group b, and 10, 0 and 0% in group c. Resorption of the rib was seen in all animals of group b and obstructive inflammatory polyps were found in 2 animals of group c.

CONCLUSION

Pedicled LD flaps provided less satisfactory results for closure of large non-circumferential extrathoracic airway defects than observed after intrathoracic reconstruction. A pedicled rib segment added to the LD flap did not improve the results obtained from LD flap repair alone, and an embedded MacroPore prosthesis may result in severe airway stenosis due to plate migration and intense inflammatory reaction protruding into the tracheal lumen.