PURPOSE:Recent studies suggest regeneration of tracheal tissue following tracheal replacement with allogeneic aorta in sheep and pig. The aim of this study was to test this exciting hypothesis in an ovine system using freshly procured allograft.
METHODS:Ten male sheep underwent cervical tracheal replacement (8cm) using fresh descending thoracic aortic allograft procured from a female donor. A silicon stent (10cm) was placed to prevent airway collapse. Metallic markers were placed at either end of the native trachea. No postoperative immunosuppressive therapy was given. Regular bronchoscopy and CT scans were planned beginning at two weeks and extending to 1 year after engraftment.
RESULTS:There were no procedural deaths. Six of ten sheep died or required euthanasia at times ranging from 12 days to 3 months postoperatively due to severe tracheitis, cervical lymphadenitis, pneumonia, graft necrosis, stent migration or airway obstruction after stent removal. The four remaining sheep are surviving 6 months up to 12 months after surgery. Harvested tracheas revealed no aortic graft incorporation into surrounding tissue. There was no histologic evidence of any neo-cartilage within or around the aortic grafted area. Bronchoscopic findings revealed significant graft necrosis in surviving animals. CT imaging in sacrificed and surviving sheep revealed that the grafted area was replaced by connective tissue without any signs of regenerative cartilage. Metallic markers indicated profound shortening of the grafted area secondary to axial contraction of the native trachea. The maximum axial contraction was 87.5% at one year after the implantation.
CONCLUSION:In contrast to earlier reports, we do not find fresh aortic allograft to be a feasible tracheal replacement material. Our data suggests that what was thought to be tracheal regeneration is in fact native tracheal axial shortening.
CLINICAL IMPLICATIONS:The native tracheal axial shortening phenomenon may serve as a bridge to allow for two- staged end- to- end reconstruction of large tracheal defect using a temporary biologic grafting technique.
DISCLOSURE:Hisashi Tsukada, No Financial Disclosure Information; No Product/Research Disclosure Information