CHANGE IN FACIAL-NERVE INNERVATION FOLLOWING HYPOGLOSSAL-FACIAL ANASTOMOSIS - AN ANIMAL STUDY

Hypogrossal-facial nerve anastomosis was carried out in 20 adult guine a pigs. Horseradish peroxidase (HRP) was applied to the buccal branch of the facial nerve at intervals of 2, 4 and 6 months after the anasto mosis operation. HRP labeled neurons and the number of regenerated axo ns in the buccal branch were counted to determine postoperative nerve regeneration. The number of surviving neurons in the facial and hypogl ossal nuclei was also counted to determine postoperative change of the se nuclei. Following anastomosis, 97% of the hypoglossal neurons remai ned surviving, while the facial neurons underwent pronounced degenerat ion of 65% survival ratio at 2 months and 37% at 6 months after the an astomosis operation. In 80% of the animals, a new nerve bundle regener ated from the proximal stump of the facial nerve to the anastomotic tr unk. A linear increase of HRP-labeled neurons in the facial and hypogl ossal nuclei paralleled the increase of the axons in the buccal branch . The HRP-labeled neurons in the facial nucleus were demonstrated to h ave direct connection with the newly formed bundle and the facial mime tic muscles were dually innervated by both the hypoglossal and facial nerves. Although the present study design might not fully represent th e clinical situation, possible advantages of hypoglossal-facial nerve anastomosis ale discussed from the view of nerve regeneration.