Surgical anatomy for direct hypoglossal-facial nerve side-to-end "anastomosis"

Object. In this study the authors investigated the histomorphometric background and microsurgical anatomy associated with surgically created direct hypoglossal-facial nerve side-to-end communication or nerve "anastomosis." Methods. Histomorphometric analyses of the facial and hypoglossal nerves were performed using 24 cadaveric specimens and three surgically obtained specimens of severed facial nerve. Both the hypoglossal nerve at the level of the atlas and the facial nerve just distal to the external genu were monofascicular. The number of myelinated axons in the facial nerve (7228 +/- 950) was 73.2% of those in the normal hypoglossal nerve (9778 +/- 1516). Myelinated fibers in injured facial nerves were remarkably decreased in number. The cross-sectioned area of the normal facial nerve (0.948 mm(2)) accounted for 61.5% of the area of the hypoglossal nerve (1.541 mm(2)), whereas that of the injured facial nerve (0.66 mm(2)) was less than 50% of the area of the hypoglossal nerve. Surgical dissection and morphometric measurements were performed using 18 sides of 11 adult cadaver heads. The length of the facial nerve from the pes anserinus to the external genu ranged from 22 to 42 mm (mean 30.5 +/- 4.4 mm). The distance from the pes anserinus to the nearest point on the hypoglossal nerve ranged from 14 to 22 mm (mean 17.3 +/- 2.5 mm). The former was always longer than the latter; the excess ranged from 6 to 20 mm (mean 13.1 +/- 3.4 mm). Surgical anatomy and procedures used to accomplish the nerve connection are described. Conclusions. The size of a half-cut end of the hypoglossal nerve matches a cut end of the injured facial nerve very well. By using the technique described, a length of facial nerve sufficient to achieve a tensionless communication can consistently be obtained.