Specific branches of hypoglossal nerve to genioglossus muscle as a potential target of selective neurostimulation in obstructive sleep apnea: anatomical and morphometric study

Abstract

Purpose: To determine the ideal implantation site for selective tongue neurostimulation in obstructive sleep apnea, anatomy of the distal branching of the hypoglossal nerve (HGN) was revisited. Methods: The HGN distal course and intramuscular distribution to the tongue muscles were studied in 17 embalmed and 5 fresh heads (age 60–98, BMI 20–35). Medial branches supplying selectively the genioglossus (GG) muscle were identified. Then, the distinct bundles entering the oblique (GGo) and horizontal (GGh) parts of the GG were located. Morphometric data were compared to similar measurements made on MRI sections from 12 patients (age 43–71, BMI 18–47). Results: The key facts relevant to optimize stimulation and electrode design are the following: the mean width of both GG muscles in embalmed and fresh cadavers was 20.7 ± 2.9 and 21.4 ± 5 mm, respectively; it is significantly (p < 0.05) superior to the MRI value of 18.26 ± 2.0 mm. Selective nervous branches for GGh and GGo were located at 52 ± 8% of hyoid bone-mandibular symphysis distance and at 5.8 ± 1.1 mm from the inferior border of the GG muscle. The surface of stimulation is a 4.4 ± 1.1 × 6.9 ± 3.8 mm ellipse. Conclusions: According to our observations, the optimal selective or supra-selective stimulation of the tongue protractor muscles can be performed on the lateral surface of the GG at roughly equal distance between the mandibular symphysis and the hyoid bone, at a depth of about 0.6 cm above the GG lower border.