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

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.

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.

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.

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.