Use of the peritracheal fold in the dog tracheal transplantation model

Objective: To investigate the technical aspects of the canine model of huma n tracheal transplantation for potential application to reconstruction of e xtremely long tracheal defects (>10 cm). Design: In phase 1, long tracheal segments were skeletonized and pedicled w ith the thyroid glands, cranial thyroid arteries and veins, and internal ju gular vein branches. The segments were elevated completely, attached to the vascular pedicle only, and replaced with primary tracheal anastomoses. In phase 2, long segments were elevated along with a diffuse soft tissue "blan ket" that envelops the trachea and thyroid glands. Because this study was d esigned to primarily address, in situ, tracheal perfusion territories of a cranially located vascular pedicle, microvascular anastomoses were not cond ucted. Subjects: Two small-bodied beagles (10-15 kg) and 5 large-bodied mixed-bree d dogs (20-30 kg) were humanely killed 2 to 41 days after surgery, and anat omic and histological analyses were conducted. Results: Unlike that of humans, the thyroid gland complex of dogs is not in timately associated with the trachea but is conjoined with a peritracheal s oft tissue "fold." Within this fold, blood is transmitted to the trachea vi a a diffuse, segmental vascular plexus. In phase 1, pronounced tracheal nec rosis occurred within 2 to 5 days. In phase 2, extremely long tracheal segm ents (10-12 cm), based only on a cranially located pedicle, were still viab le at 2 to 6 weeks. Conclusions: Preservation of the "peritracheal fold" in the dog model of tr acheal transplantation is critical to the onset and maintenance of vascular perfusion in a long tracheal segment. Furthermore, the use of large-bodied dogs is necessary to provide for a usable venous efflux component.