[Metaplasia of aortic tissue into tracheal tissue. Surgical perspectives]

Tracheal replacement with aortic grafts: Bench to clinical practice

Tracheal reconstruction following extensive resection for malignant or benign lesions remains a major challenge in thoracic surgery. Numerous studies have attempted to identify the optimal tracheal replacement with different biological or prosthetic materials, such as various homologous and autologous tissues, with no encouraging outcomes. Recently, a few clinical studies reported attaining favorable outcomes using in vitro or stem cell-based airway engineering and also with tracheal allograft implantation following heterotopic revascularization. However, none of the relevant studies offered a standardized technology for airway replacement. In 1997, a novel approach to airway reconstruction was proposed, which involved using aortic grafts as the biological matrix. Studies on animal models reported achieving in-vivo cartilage and epithelial regeneration using this approach. These encouraging results inspired the subsequent application of cryopreserved aortic allografts in humans for the first time. Cryopreserved aortic allografts offered further advantages, such as easy availability in tissue banks and no requirement for immunosuppressive treatments. Currently, stented aortic matrix-based airway replacement has emerged as a standard approach, and its effectiveness was also verified in the recently reported TRITON-01 study. In this context, the present review aims to summarize the current status of the application of aortic grafts in tracheal replacement, including the latest advancements in experimental and clinical practice.

Airway replacement using stented aortic matrices: Long-term follow-up and results of the TRITON-01 study in 35 adult patients

Over the past 25 years, we have demonstrated the feasibility of airway bioengineering using stented aortic matrices experimentally then in a first-in-human trial (n = 13). The present TRITON-01 study analyzed all the patients who had airway replacement at our center to confirm that this innovative approach can be now used as usual care. For each patient, the following data were prospectively collected: postoperative mortality and morbidity, late airway complications, stent removal and status at last follow-up on November 2, 2021. From October 2009 to October 2021, 35 patients had airway replacement for malignant (n = 29) or benign (n = 6) lesions. The 30-day postoperative mortality and morbidity rates were 2.9% (n = 1/35) and 22.9% (n = 8/35) respectively. At a median follow-up of 29.5 months (range 1-133 months), 27 patients were alive. There have been no deaths directly related to the implanted bioprosthesis. Eighteen patients (52.9%) had stent-related granulomas requiring a bronchoscopic treatment. Ten among 35 patients (28.6%) achieved a stent free survival. The actuarial 2- and 5-year survival rates (Kaplan-Meier estimates) were respectively 88% and 75%. The TRITON-01 study confirmed that airway replacement using stented aortic matrices can be proposed as usual care at our center. Clinicaltrials.gov Identifier: NCT04263129.

Feasibility of Bioengineered Tracheal and Bronchial Reconstruction Using Stented Aortic Matrices

IMPORTANCE

Airway transplantation could be an option for patients with proximal lung tumor or with end-stage tracheobronchial disease. New methods for airway transplantation remain highly controversial.

OBJECTIVE

To establish the feasibility of airway bioengineering using a technique based on the implantation of stented aortic matrices.

DESIGN, SETTING, AND PARTICIPANTS

Uncontrolled single-center cohort study including 20 patients with end-stage tracheal lesions or with proximal lung tumors requiring a pneumonectomy. The study was conducted in Paris, France, from October 2009 through February 2017; final follow-up for all patients occurred on November 2, 2017.

EXPOSURES

Radical resection of the lesions was performed using standard surgical techniques. After resection, airway reconstruction was performed using a human cryopreserved (-80°C) aortic allograft, which was not matched by the ABO and leukocyte antigen systems. To prevent airway collapse, a custom-made stent was inserted into the allograft. In patients with proximal lung tumors, the lung-sparing intervention of bronchial transplantation was used.

MAIN OUTCOMES AND MEASURES

The primary outcome was 90-day mortality. The secondary outcome was 90-day morbidity.

RESULTS

Twenty patients were included in the study (mean age, 54.9 years; age range, 24-79 years; 13 men [65%]). Thirteen patients underwent tracheal (n = 5), bronchial (n = 7), or carinal (n = 1) transplantation. Airway transplantation was not performed in 7 patients for the following reasons: medical contraindication (n = 1), unavoidable pneumonectomy (n = 1), exploratory thoracotomy only (n = 2), and a lobectomy or bilobectomy was possible (n = 3). Among the 20 patients initially included, the overall 90-day mortality rate was 5% (1 patient underwent a carinal transplantation and died). No mortality at 90 days was observed among patients who underwent tracheal or bronchial reconstruction. Among the 13 patients who underwent airway transplantation, major 90-day morbidity events occurred in 4 (30.8%) and included laryngeal edema, acute lung edema, acute respiratory distress syndrome, and atrial fibrillation. There was no adverse event directly related to the surgical technique. Stent removal was performed at a postoperative mean of 18.2 months. At a median follow-up of 3 years 11 months, 10 of the 13 patients (76.9%) were alive. Of these 10 patients, 8 (80%) breathed normally through newly formed airways after stent removal. Regeneration of epithelium and de novo generation of cartilage were observed within aortic matrices from recipient cells.

CONCLUSIONS AND RELEVANCE

In this uncontrolled study, airway bioengineering using stented aortic matrices demonstrated feasibility for complex tracheal and bronchial reconstruction. Further research is needed to assess efficacy and safety.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01331863.

Current Solutions for Long-Segment Tracheal Reconstruction

This article is a continuation of previous reviews about the appropriate method for long-segment tracheal reconstruction. We attempted to cover the most recent, successful and promising results of the different solutions for reconstruction that are rather innovative and suitable for imminent clinical application. Latest efforts to minimize the limitations associated with each method have been covered as well. In summary, autologous and allogenic tissue reconstruction of the trachea have been successful methods for reconstruction experimentally and clinically. Autologous tissues were best utilized clinically to enhance revascularization, whether as a definitive airway or as an adjunct to allografts or tissue-engineered trachea (TET). Allogenic tissue transplantation is, currently, the most suitable for clinical application, especially after elimination of the need for immunosuppressive therapy with unlimited supply of tissues. Similar results have been reported in many studies that used TET. However, clinical application of this method was limited to use as a salvage treatment in a few studies with promising results. These results still need to be solidified by further clinical and long-term follow-up reports. Combining different methods of reconstruction was often required to establish a physiological rather than an anatomical trachea and have shown superior outcomes.

Tracheal bioengineering: the next steps. Proceeds of an International Society of Cell Therapy Pulmonary Cellular Therapy Signature Series Workshop, Paris, France, April 22, 2014

There has been significant and exciting recent progress in the development of bioengineering approaches for generating tracheal tissue that can be used for congenital and acquired tracheal diseases. This includes a growing clinical experience in both pediatric and adult patients with life-threatening tracheal diseases. However, not all of these attempts have been successful, and there is ongoing discussion and debate about the optimal approaches to be used. These include considerations of optimal materials, particularly use of synthetic versus biologic scaffolds, appropriate cellularization of the scaffolds, optimal surgical approaches and optimal measure of both clinical and biologic outcomes. To address these issues, the International Society of Cell Therapy convened a first-ever meeting of the leading clinicians and tracheal biologists, along with experts in regulatory and ethical affairs, to discuss and debate the issues. A series of recommendations are presented for how to best move the field ahead.

Aortic squamous metaplasia in a patient with aortoesophageal fistula secondary to thoracic aortic aneurysm: an autopsy case

Aortoesophageal fistula (AEF) is highly lethal. A 74-year-old man presented with hematemesis and consciousness loss. He had a long-term history of hypertension and gout. Computed tomography revealed an aneurysm of the distal descending thoracic aorta, which was treated by insertion of an aortic stent graft. After 24 days of stenting, endoscopic examination revealed an AEF. After 6 months of stenting, he died owing to mediastinitis. On autopsy, macroscopically, we found a 4 × 2.5-cm, oval, well-circumscribed AEF. We identified squamous epithelium in the area surrounding the AEF that covered the thoracic aorta inner cavity. Immunohistochemical analysis revealed that the squamous epithelium in the thoracic aorta was positive for p63 and 34βE12. In conclusion, we encountered a long-term AEF case with aortic squamous metaplasia. To the best of our knowledge, human aortic metaplasia has never been reported. In the present case, aortic squamous metaplasia retained continuity with the esophageal squamous epithelium; therefore, the migration of the squamous epithelium through the AEF may have been induced by aortic erosion.

Airway transplantation: a challenge for regenerative medicine

After more than 50 years of research, airway transplantation remains a major challenge in the fields of thoracic surgery and regenerative medicine. Five principal types of tracheobronchial substitutes, including synthetic prostheses, bioprostheses, allografts, autografts and bioengineered conduits have been evaluated experimentally in numerous studies. However, none of these works have provided a standardized technique for the replacement of the airways. More recently, few clinical attempts have offered encouraging results with ex vivo or stem cell-based engineered airways and tracheal allografts implanted after heterotopic revascularization. In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction. In vivo regeneration of epithelium and cartilage were demonstrated in animal models. This led to the first human applications using cryopreserved aortic allografts that present key advantages because they are available in tissue banks and do not require immunosuppressive therapy. Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

Experimental Replacement of Pig Trachea with Novel Bioprosthesis from Harp Seal

Tracheal replacement has been a challenging problem for thoracic surgeons for over half of a century. We evaluated the in-vivo performance of a new tracheal bioprosthesis derived from Harp seal (Phoca groelandica) trachea that was fixed and preserved in 0.625% buffered glutaraldehyde solution for 3 months. Ten young male pigs weighing 27–32 kg (mean, 28.7 kg) underwent replacement of a tracheal segment with this new bioprosthesis. The length of replaced trachea was 1.8–2.4 cm (mean, 2.17 cm), representing 2–3 cartilage rings. All pigs survived the operation uneventfully. No immunosuppression drugs were used. The pigs eventually developed dyspnea and were euthanized on postoperative day 17–39 (mean, 30.8 days). Macroscopic and histological analysis showed an intact bioprosthesis but near-total occlusion of the native trachea by a ring of inflammatory infiltration at the site of distal anastomosis. More experiments involving a different concentration of the preservation agent, different management, and perhaps the use of bioengineering techniques are needed to improve the performance of this novel bioprosthesis.

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 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.

The fate of homograft tracheal transplants in sheep

OBJECTIVE

An established method of tracheal substitution is not yet available, but homograft tracheal transplantation might provide a realistic tracheal replacement. With the objective of sequentially examining the healing of tracheal homografts, we have established a suitable large-animal model.

METHODS

Five sheep received orthotopic tracheal transplantation of a 4-cm cervical tracheal homograft. The trachea was supported for 6 weeks with a self-expanding polyester stent. The plan was to euthanize the animals after 2, 4, 8, 12 and 16 weeks, or whenever complications occurred.

RESULTS

The implantation itself was performed without complications. After 2 weeks the homograft was firmly encapsulated by connective tissue, without signs of necrosis or abscess. The original mucous membrane no longer existed; the cartilage rings were exposed. In all animals that were euthanized at the later dates, the homografts were completely absorbed and replaced by inflammatory scar tissue. This, in turn, was covered with a shiny cellular surface layer.

CONCLUSIONS

The results from this animal experiment reveal-contrary to data published to date-that tracheal homografts are not incorporated but absorbed. They are replaced by scar/granulation tissue that cannot secure the stability of the trachea. Therefore, further experiments with respect to the biocompatability of homografts appear to be necessary.

Tracheal replacements: part 1

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we cover the historical highlights of grafts, flaps, tube construction, and tissue transplants and address the progress made in tracheal stenting as a means of temporary tracheal support. This is followed in Part 2 by an analysis of solid and porous tracheal prostheses in experimental and clinical trials. We conclude Part 2 with a summary of recent efforts toward generating a bioengineered trachea. Finally, we provide an algorithm on the spectrum of options available for tracheal replacement.

[Tracheal replacement using the abdominal aorta. Comments on a case report]

Tracheal replacement is an uncommon option because of the very limited number of indications and the large number of possibilities for resection anastomosis. There may nevertheless be situations were extensive resection leaves only one solution, tracheal replacement. To date, no prosthesis has provided long-term satisfaction. For tracheal replacement, the prosthesis must provide a large caliber airway which does not collapse during expiration and which enables the development of a ciliary lining, in addition to tolerance without rejection. Recent experimental work, then several clinical cases, would suggest that the abdominal aorta can be successfully transformed into a neotrachea. A temporary endoprosthesis is however necessary to prevent collapse until new tracheal rings develop. Experimental and early clinical work has provided promising results but with problems concerning the endoprosthesis. In our patient, we used the abdominal aorta as a tracheal substitute but replaced the endoprosthesis with an exoprosthesis leaving the aortic lumen free. The result was also encouraging, but the absence of integration of the aortic tissue did not confirm the observations reported by others. Other hypotheses concerning the regeneration of the neotrachea should be put forward.

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.

The management of congenital tracheal stenosis

This paper reviews current concepts and results in the management of congenital tracheal stenosis (CTS). Diagnostic options are considered and the requirements for successful management defined. Chief amongst these is a multi-disciplinary approach with individualised patient management. Severe long-segment CTS represents the biggest challenge to clinicians and the worst problems for affected families. Near-death episodes are frequent in affected infants and some cannot be ventilated and require ECMO. Associated cardiovascular anomalies are frequent. Patients require immediate resuscitation and transfer to a specialist unit. After careful assessment, accurate diagnosis and discussion, primary resection and end-to-end repair with a slide technique should always be the first option, with concomitant repair of associated cardiac anomalies. If this is impossible because of the severity of the lesion, some form of patch tracheoplasty will be indicated. Cardiopulmonary bypass is often required. Patches include pericardium, autograft trachea, carotid artery, cartilage, and allograft trachea. Mortality ranges from 0 to 30% in the literature, which largely comprises single-centre long-term experience. Recurrence is common and can be managed by stenting and tracheal homograft implantation. Long-term quality of life of survivors is little reported but seems good. Physiological data are lacking. To improve results, we suggest a treatment algorithm to rationalise care.

Long-term evaluation of the replacement of the trachea with an autologous aortic graft

BACKGROUND

Tracheal reconstruction after extensive resection remains a challenge in thoracic surgery. The goal of this experimental study was to analyze the long-term evolution of tracheal replacement using an autologous aortic graft.

METHODS

In 21 sheep, a 5-cm segment of the cervical trachea was replaced by a segment of the descending thoracic aorta that was reconstructed to a prosthetic graft. Because of the airway collapse reported in a previous series, a permanent (n = 13) or temporary (n = 8) stent was systematically placed in the lumen of the graft. Clinical, bronchoscopic, and histologic examinations were performed up to 3 years after implantation.

RESULTS

All animals survived the operation with no paraplegia. In the group with a permanent stent, three complications occurred: one stent displacement, one laryngeal edema, and one infection. Stent removal was tolerated after 6 months in the group with a temporary stent. Histologic examination showed a progressive transformation of the arterial segment into first extensive inflammatory tissue with a squamous epithelium, and after 6 to 36 months well-differentiated tracheal tissue including a continuous mucociliary epithelium and regular rings of newly formed cartilage.

CONCLUSIONS

An autologous aortic graft used as a substitute for extensive tracheal replacement in sheep remained functional for periods up to 3 years. The progressive transformation of the graft into a structure resembling tracheal tissue seems to be a key factor in long-term patency. The mechanism of this regenerative process and the possibility of using arterial homografts, which would make clinical application easier, remain to be evaluated.

The anatomical basis for disease localisation in seronegative spondyloarthropathy at entheses and related sites

The 2 major categories of idiopathic inflammatory arthritis are rheumatoid arthritis and the seronegative spondyloarthropathies. Whilst the synovium is the primary site of joint disease in the former, the primary site in the latter is less well defined. However, it has recently been proposed that enthesitis-associated changes in the spondyloarthropathies are primary and that all other joint manifestations are secondary. Nevertheless, some of the sites of disease localisation have not been adequately explained in terms of enthesitis. This article summarises current knowledge of the structure, function, blood supply, innervation, molecular composition and histopathology of the classic enthesis (i.e. the bony attachment of a tendon or ligament) and introduces the concept of 'functional' and articular 'fibrocartilaginous' entheses. The former are regions where tendons or ligaments wrap-around bony pulleys, but are not attached to them, and the latter are synovial joints that are lined by fibrocartilage rather than hyaline cartilage. We describe how these 3 types of entheses relate to other, and how all are prone to pathological changes in spondyloarthropathy. We propose that the inflammatory responses characteristic of spondyloarthropathies are triggered at these seemingly diverse sites, in genetically susceptible individuals, by a combination of anatomical factors which lead to higher levels of tissue microtrauma, and the deposition of microbes.