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.