Peripheral Nerve Regeneration: The Effects of Postoperative Irradiation

Abstract

The purpose of this study was to evaluate the effects of postoperative external cobalt-60 beam irradiation on nerve regeneration. Sixty-five 250-gm male Sprague-Dawley rats were studied. Peripheral nerve regeneration was measured by walking track analysis and histomorphology of the proximal, graft, and distal nerve segments. These 65 animals underwent a 1.5-cm interpositional nerve graft into the right posterior tibial nerve. The left leg served as a control. Each animal was then randomly allocated into one of four groups. Group 1 served as control. Groups 2 through 4 were subjected to external cobalt-60 gamma-ray irradiation through a 2.5-cm circular portal for a total fractionated dose of 30, 50, and 70 Gy beginning on postoperative day 3. Radiation was administered in 2-Gy fractions, 5 fractions per week, with a top-up dose of 16 Gy given at the end of the fractionated irradiation. Walking track analysis was performed at 30, 60, 90, and 120 days after nerve grafting. At the conclusion of 120 days, sections of the proximal, grafted, and distal nerve were harvested, stained, and examined histomorphologically. Hematoxylin and eosin stains also were obtained. Evaluation of the print-length index demonstrated no statistical difference between the unirradiated controls and the irradiated groups. The total number of axons per square millimeter and nerve fiber density per square millimeter were significantly decreased in the distal segment of all the irradiated groups when compared with controls. Despite the reduction in myelinated regenerating fibers, no reduction in function was observed, as measured by walking track analysis. We would therefore recommend immediate reconstruction of peripheral nerve defects in the face of postoperative irradiation.

Postoperative Irradiation: Are There Long‐Term Effects on Nerve Regeneration?

“…The nerve fiber density was not significantly different between the irradiated groups and controls at either the grafted segment or the distal segment (Fig. 3, p = 0.05) The animals in Group 1 (control) and Group 2 (66 Gy) were compared to their corresponding groups in the previous study, 1 and there was no statistically significant difference, validating a consistent protocol.…”

“…2 " 14 Previous work in our laboratory has evaluated nerve regeneration through nerve grafts after postoperative irradiation in the rat posterior tibial nerve model. 1 Irradiation dosing was purposefully designed to simulate the clinical situation. Evaluation included histomorphology and functional assessment by walking-track analysis.…”

Reconstruction of Lateral Skull Base Defects after Tumor Ablation

“…22,25,26 Previous studies have illustrated that postoperative radiation does not negatively affect nerve regeneration. [27][28][29] Gullane and Havas 29 showed that postoperative radiation after extensive resection of parotid cancers with sacrifice of the facial nerve in four of six patients and reconstruction with nerve grafting resulted in excellent function. Therefore patients who may undergo postoperative radiation should not be denied facial nerve repair.…”

Preliminary Report of the Effect of High-Dose Adjuvant Intensity Modulated Radiation Therapy on the Sural Nerve Graft for Cavernosal Nerve Sacrifice After Radical Prostatectomy

“…29 Results from peripheral motor nerves irradiated 3 days after grafting to doses of 66 Gy and 106 Gy showed decreased distal axonal growth compared with controls with no functional difference. 30 Clinical correlation in limited cohorts with facial nerve grafts appears to support this conclusion.…”