[Experimental study of hypoglossal facial anastomosis and accessory-facial anastomosis in guinea pigs].

Hypoglossal facial nerve anastomosis (XII-VII anastomosis) or accessory-facial anastomosis (XI-VII anastomosis) have been chosen for facial rehabilitation when the facial nerve is widely sacrificed and end-to-end anastomosis or nerve grafting is unavailable. However, no detailed study has been conducted to determine which donor nerve is better for the anastomosis procedure in view of regeneration of the facial nerve. To compare and evaluate nerve regeneration after XII-VII anastomosis and XI-VII anastomosis, animal models of these anastomoses were made in guinea pigs by using a Y-shaped silicon tube. The proximal cut-ends of the hypoglossal nerve and accessory nerve were suspended in the paired inlet limbs of a Y-shaped silicone tube with a 9-0 nylon suture, and the distal cut-end of the facial nerve was suspended in the single outlet limb in a similar manner. After 4 and 8 weeks, histological studies were carried out. An electrophysiological study of conduction velocity and amplitude of evoked electromyography were measured at 8 weeks postoperation. The nerve fibers regenerated from the hypoglossal nerve were significantly more numerous than those from the accessory nerve at both 4 and 8 weeks after anastomosis. The amplitude of evoked electromyography elicited from the hypoglossal nerve was greater than that from the accessory nerve, even though there is no significant difference in conduction velocities between the two anastomoses. The nerve regeneration by the cross-over procedure was influenced by many factors such as the number of nerve fibers in the donor nerve and the affinity between donor and recipient nerves. The number of nerve fibers in the hypoglossal nerve was significantly greater than that in the accessory nerve. However, there was no significant difference in the ratios of regenerated nerve fibers to the preoperative nerve fibers. Accordingly, we concluded that the affinity of the hypoglossal or accessory nerve to the facial nerve is a minor factor if it exists, and the difference in the fiber count in these nerves is a major factor in the outcome of nerve regeneration.