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Tracheal Replacement with Aortic Allograft
P. de Delva, J. C. Wain, D. J. Mathisen. Massachusetts General Hospital, Boston, MA,
Background:
Impressive advancements in the management of tracheal pathology have been achieved in the last 50 years. Despite numerous experimental attempts to replace long tracheal defects, no clinically applicable protocol has been developed to manage defects greater than 50% of the length of the adult trachea. Recent reports describe the use of aorta for tracheal replacement. Allogeneic and autologous aortic grafts have been used in large animal models to bridge long tracheal defects. Three to nine months after transplantation, the authors report replacement of the aortic graft by what appears to be a functional neotrachea consisting of new cartilage in the form of tracheal rings and a mucociliary epithelium. The objective of this project is to assess the feasibility of utilizing aortic segments for tracheal replacement.
Methods:
Male sheep underwent resection of eight to 10 centimeters of cervical trachea. The tracheal defect was reconstructed with allogeneic thoracic aortic graft. The aortic segment was radially stabilized by a silicone endotracheal stent. No immunosuppression was administered. Animals were sacrificed between 45 and 365 days. Tracheal transplants underwent gross and histological analysis.
Results:
Nine sheep underwent tracheal replacement with aortic graft. Three died unexpectedly from anesthetic or infectious complications. Six animals survived to an elective necropsy. The mean time from transplantation to graft excision was 202 days (45-365). Gross analysis revealed dense scar formation at the site of aortic interposition. Longitudinal contraction of the scar reduced the tracheal defects by 56% ±10. Histological analysis of the aortic grafts revealed preservation of the external elastic lamina but replacement of the media with dense fibrous tissue. Two specimens had evidence of immature islands of chondrogenesis within the fibrous tissue. No organized cartilage formation or new tracheal rings were seen. The intima was replaced in a time dependent fashion by continuous squamous metaplasia (n=4) or mucociliary epithelium (n=2). There was no evidence of acute or chronic rejection. Long-term morbidity was limited to cough and sputum production. Three animals required intermittent bronchoscopy for management of secretions.
Conclusions:Reconstruction of the trachea with allogeneic aorta may be a feasible strategy for the management of long segment defects in the trachea. Scar contraction led to a significant decrease in the length of the tracheal defects. Over time, epithelium can migrate from the native trachea along the graft lumen and span the length of the aortic segment. Foci of immature, disorganized cartilage can be identified in the wall of the graft without the development of neotracheal rings. Although a neotrachea with cartilaginous rings was not observed, scar formation with migration of respiratory epithelium and contraction of the defect may provide an acceptable biologic replacement for long tracheal defects.
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