Effects of irradiation on nerve graft vasculature

Increasing doses of therapeutic irradiation are known to impair nerve regeneration after grafting. One possible factor is the effect of irradiation on the endoneurial vasculature. This study investigates the effects of postoperative irradiation on the size, number, and cross-sectional area of endoneurial vessels in the rat posterior tibial nerve graft model. Sixty-five Sprague-Dawley rats underwent 1.5-cm interposition grafts to the tibial nerve. Postoperatively, they were assigned to one of five groups. The animals in Group 1 were unirradiated controls. Groups 2 to 5 received postoperative irradiation in the amounts of 46, 66, 86, and 106 Gy, respectively. One hundred and twenty days after grafting, sections of the proximal, grafted, and distal nerve were harvested and analyzed with digital morphometry. Statistical analysis of the average vessel area, number of vessels, and total vascular area was performed. The grafted segments of Groups 4 and 5 and the distal segments of all irradiated groups showed a statistically significant decrease in the number of vessels, compared to controls. The average size of the vessel was smaller in the proximal segment of the irradiated groups, compared to controls. There was no difference in size in either the grafted or distal segments of the irradiated groups, compared to controls. The observed changes in the endoneurial vasculature resulted from both the action of regeneration and the effects of irradiation. The irradiation effects appear to be dose-dependent.