Facial--hypoglossal nerve end-to-side neurorrhaphy: anatomical study in rats

Assessment of axonal sprouting and motor performance after hypoglossal-facial end-to-side nerve repair: experimental study in rats

Hypoglossal-facial nerve anastomosis (HFA) aims to reanimate denervated mimic muscles with hypoglossal axons when the transected facial nerve is not accessible. The aim of this study was to evaluate the recovery of HFA using a "Y" tube in two variants: (1) the proximal stump of the hypoglossal nerve was entubulated to the "Y" tube (classic "Y" tube HFA) and (2) the "Y" tube was sutured to an epineurial window of a slightly damaged hypoglossal nerve (end-to-side "Y" tube HFA). A total of 48 adult female rats were divided into four groups: intact controls (group 1), sham operated (group 2), classic "Y" tube HFA (group 3) and end-to-side "Y" tube HFA (group 4). The abdominal aorta with both common iliac arteries of isogeneic male rats served as the Y-tube conduit. Animals from group 4 recovered better than those from group 3: the degree of collateral axonal branching (3 ± 1%) was significantly lower than that determined in group 3 (13 ± 1%). The mean deviation of the tongue from the midline was significantly smaller in group 4 (6 ± 4°) than that measured in animals from group 3 (41 ± 6°). In the determination of vibrissal motor function in group 3 and group 4, a decrease in amplitude was found to be - 66% and - 92%, respectively. No differences in the reinnervation pattern of the target muscles were detected. As a result, these surgical models were not determined to be able to improve vibrissal movements. It was concluded that performance of end-to-side "Y" tube HFA diminishes collateral axonal branching at the lesion site, which in turn, promotes better recovery of tongue- and vibrissal-motor performance.

Comparison of 4 Different Methods for Direct Hypoglossal-Facial Nerve Anastomosis in Rats

BACKGROUND

Classic hypoglossal-facial nerve anastomosis inevitably causes hemitongue atrophy and dysfunction. Thus, many variants have been developed to reduce tongue-related morbidities. A comparative study concerning these techniques was conducted in rats to systematically evaluate long-term functional and histologic outcomes of the recipient and donor systems.

METHODS

Rats (8 per group) were treated by end-to-end neurorrhaphy (EEN), EEN using the hemisectioned and longitudinally split donor nerve (EEN-Hemi), end-to-side neurorrhaphy through a perineurial window (ESN-PW), or 30% to 40% partial neurotomy (ESN-PN). Four additional rats were left intact. At 8 months postoperatively, behavioral, electrophysiologic, and morphologic studies were carried out to compare the groups.

RESULTS

All techniques resulted in partial functional recovery, but complete restoration was not obtained. There were no significant differences between the experimental groups in axon diameter or myelin thickness. The facial nerve fiber count after ESN-PN, but not after EEN-Hemi or ESN-PW, was comparable with that after EEN, which agreed with the behavioral and electrophysiologic results. The hypoglossal nerve fiber count after ESN-PN was slightly less than that after ESN-PW, but markedly more than that after EEN-Hemi, corresponding to the electrophysiologic examination. Quantitative measures of muscle fiber cross-sectional area and connective tissue area density of the tongue demonstrated severe muscle atrophy on the operated side after EEN and EEN-Hemi when compared with ESN-PW and ESN-PN.

CONCLUSIONS

ESN with 30% to 40% partial donor neurotomy offers the best balance between motor reinnervation and donor deficits. The method of nerve split for provision of hemihypoglossal nerve stump may not effectively preserve the tongue function.

Muscle reinnervation in one or two stages?: experimental study in rats with end-to-side nerve graft

PURPOSE: To compare muscle reinnervation in one and two surgical stages using end-to-side neurorrhaphy (ESN) without donor nerve injury. METHODS: The experiment was performed on four groups of 20 rats. Group 1 (G1), one stage, received the graft which was sutured to the tibial nerve, with ESN, and its free stump was sutured end-to-end to the distal stump of the sectioned peroneal nerve (PN), all in the same operation. In Group 2 (G2), two stages, the nerve graft was sutured to the tibial nerve, with ESN. Two months later the PN was sectioned and its distal stump connected to the distal stump of the graft as in G1. Normal control group (Gn) received the graft only sutured to the tibial nerve, with ESN. Denervated control group (Gd), as well received the graft and had the PN sectioned and its two stumps buried in adjacent musculature, with the aim of denervating the cranial tibial muscle (CTM), the target of this study. The parameters used to evaluate CTM reinnervation were muscle mass, muscle fiber's minimum diameter and area. RESULTS: The mean CTM mass, the average of the muscular fibers areas and the average of the muscular fiber minimum diameters was higher (all p<0.0001) in G2 than in G1. Comparing the four groups, these parameters had their maximum expression in Gn and the minimum in Gd, as expected. CONCLUSION: The two stages showed better muscle reinnervation than one stage.