Microsurgical Anatomy of the Terminal Hypoglossal Nerve Relevant for Neurostimulation in Obstructive Sleep Apnea.

BACKGROUND Neurostimulation of the hypoglossal nerve has shown promising results in the treatment of obstructive sleep apnea. This anatomic study describes the detailed topography of the hypoglossal nerve's motor points as a premise for super-selective neurostimulation in order to optimize results and minimize the risk of complications related to main nerve trunk manipulation. METHODS Thirty cadaveric hypoglossal nerves were dissected and characterized by number of branches, arborization pattern, and terminal branch motor point location. For each motor point, the distance to cervical midline (x axis), distance to posterior aspect of the symphysis (y axis), and depth from the plane formed by the inferior border of symphysis and anterior border of hyoid (z axis) were recorded. RESULTS The average number of distal branches for each hypoglossal nerve was found to be 9.95 ± 2.28. The average number of branches per muscle was found to be 3.3 ± 1.5 for the hyoglossus muscle, 1.8 ± 0.9 for the geniohyoid muscle, and 5.0 ± 1.6 for the genioglossus muscle. It was found that branches to the genioglossus and geniohyoid muscles were located closer to midline (relative lengths of 0.19 ± 0.07 and 0.19 ± 0.05, respectively) while hyoglossus branches were located more laterally (0.38 ± 0.10 relative length). On the y-axis, the branches to the genioglossus were the most anterior and therefore closest to the posterior symphysis of the mandible (relative length of 0.48 ± 0.11), followed by the geniohyoid (0.66 ± 0.09), and the hyoglossus (0.76 ± 0.16). The branches to the geniohyoid were the most superficial (relative length of 0.26 ± 0.06), followed by the genioglossus (0.36 ± 0.09), and finally, the hyoglossus branches (0.47 ± 0.11), which were located deeply. CONCLUSION A topographical map of the hypoglossal nerve terminal motor points was successfully created and could provide a framework for the optimization of the neurostimulation techniques.