1355. Using the Post-Descendens Hypoglossal Nerve in Hypoglossal-Facial Anastomosis: An Anatomic and Histological Analysis

Authors: Leandro Borba Moreira; Ali Tayebi Meybodi, MD; Evgenii Belykh, MD; Xiaochun Zhao, MD; Jennifer Eschbacher, MD; Michael Lawton, MD; Mark Preul, MD (Phoenix, AZ)

Introduction: Hypoglossal-facial anastomosis (HFA) is a facial reanimation technique following facial nerve disconnection in the cerebellopontine angle. Mobilizing the intratemporal segment of facial nerve and performing side-to-end anastomosis with the hypoglossal nerve (CNXII) have been proposed to reduce the incidence of hemilingual atrophy and severe facial synkinesis compared to using full-thickness CNXII. The exact anastomosis location to the hypoglossal nerve relative to the origin of descendens hypoglossi is undetermined. The present study sought to: 1)assess feasibility of mobilizing the intratemporal facial nerve to reach the post-descendens CNXII; 2)assess microscopic structure of post-descendens CNXII and its compatibility with the facial nerve stump to define the optimal type of CNXII sectioning for a successful HFA. Methods: Facial and CNXII were exposed in 10 cadaveric head sides. Facial nerve was exposed from tympanic segment to extratemporal bifurcation. Feasibility of a tensionless side-to-end HFA using post-descendens CNXII was assessed. In 4 specimens: axonal count and cross-sectional areas of the facial nerve stump and CNXII at point of anastomosis were assessed. Results: The HFA was feasible in all specimens with an average of 5.5 mm of extra length on facial nerve. Axonal counts and cross-sectional areas of CNXII and facial nerves matched. Average axons counts: CNXII(11,303) and facial nerve(9,689). Average cross-sectional areas: CNXII (1.6x10 6 m m 2 ) and facial nerve (1.5 x10 6 m m 2 ). Considering average 60% reduction in cross-sectional area of paralyzed facial nerve, a beveled 45˚ hemi-transection of the post-descendens CNXII would provide adequate donor axonal count to accommodate the facial nerve. Conclusion: Using the post-descendens CNXII is anatomically feasible for HFA. This novel technique can provide adequate axonal count for facial reanimation while avoiding the complications of hemilingual atrophy due to complete transection of the facial nerve. Sparing the descendens hypoglossi could also avoid glottic complications of severing C1 nerve fibers coursing in the pre-descendens CNXII.