Facial reanimation by means of the hypoglossal nerve: Anatomic comparison of different techniques

OBJECTIVE: The goal of this study was to determine the various anatomical and surgical relationships between the facial and hypoglossal nerves to define the required length of each for a nerve transfer, either by means of a classical hypoglossal-facial nerve anastomosis or combined with any of its variant's developed to reduce tongue morbidities. METHODS: Five adult cadaver heads were bilaterally dissected in the parotid and submaxillary regions. Two clinical cases are described for illustration. RESULTS: The prebifurcation extracranial facial nerve is found 4.82 +/not superset of 0.88 mm from the external auditory meatus, 5.31 +/not superset of 1.50 mm from the mastoid tip, 15.65 +/not superset of 0.85 mm from the lateral end of C1, 17.19 +/not superset of 1.64 mm from the border of the mandible condyle, and 4.86 +/not superset of 1.29 mm from the digastric muscle. The average lengths of the mastoid segment of the facial nerve and the prebifurcation extracranial facial nerve are 16.35 +/not superset of 1.21 mm and 18.93 +/not superset of 1.41 mm, respectively. The average distance from the bifurcation of the facial nerve to the hypoglossal nerve turn is 31.56 +/not superset of 2.53 mm. For a direct hypoglossal-facial nerve anastomosis, a length of approximately 19 mm of the hypoglossal nerve is required. For the interposition nerve graft technique, a 35 mm-long graft is required. For the technique using a longitudinally dissected hypoglossal nerve, an average length of 31.56 mm is required. Exposure of the facial nerve within the mastoid process drilling technique requires 16.35 mm of drilling. CONCLUSION: This study attempts to establish the exact graft, dissection within the hypoglossal nerve, and mastoid drilling requirements for hypoglossal to facial nerve transfer.