Tiam Mana Saffari

89 REVASCULARIZATION PATTERNS OF NERVE ALLOGRAFTS 5 INTRODUCTION The outcome of tissue transplantation critically depends on the revascularization process and consequently regeneration of nerve is similarly dependent on this process 1-5 . Neovascularization precedes neural regeneration and stimulates injured axons and non-neuronal cells to produce a supportive microenvironment 6 . The nerve vascularization consists of both an extrinsic and intrinsic blood supply 7 . The intrinsic system is formed by an extensive microvascular network that maintains blood supply within a nerve (epineural, perineural and endoneural vessels) 7,8 . The extrinsic system consists of vessels that accompany a nerve outside of its epineurium. While it is known that both the intrinsic and extrinsic blood supply systems are interrupted during injury 7 , little is known about the revascularization patterns after such an injury. In 1945, Tarlov and colleagues demonstrated by roentgenographic studies of transplanted sciatic nerves that an important source of blood supply for grafts is from the surrounding tissue 9 . Furthermore, they suggested that the vascular pattern between normal nerves and vascularized nerve autografts is similar and revascularization occurs along the preexistent vascular channels by ingrowth of blood vessels from the host stumps (proximal and distal) as well as from the surrounding tissues 9 . In order to improve clinical outcomes of free autologous nerve grafting, multiple nerve grafts (cable grafts) were applied to increase surface area as it was postulated that this would improve graft revascularization and avoid central necrosis which was observed in larger diameter nerve grafts 9,10 . To improve outcomes of nerve autografts in severely scarred tissue beds, the application of either vascularized nerve grafts or vascularized f laps around nerve grafts has been suggested 11-14 . These theories can not be extrapolated to the revascularization of nerve allografts, as in processed nerve allografts, preexistent vascular channels have been removed during the process. Little has been published regarding other strategies to revascularize processed nerve allografts or the patterns that revascularization follows, partly due to the lack of an appropriate model. Thus, there are remaining questions regarding the mechanism and pattern of peripheral nerve allograft revascularization. The purpose of this study was to explore the effect of surgical angiogenesis on processed nerve allografts and to compare the revascularization patterns in nerve autografts, allografts and allografts placed in a vascularized bed to provide insight into neovascularization of nerve grafts.