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 variants 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 +/- 0.88 mm from the external auditory meatus, 5.31 +/- 1.50 mm from the mastoid tip, 15.65 +/- 0.85 mm from the lateral end of C1, 17.19 +/- 1.64 mm from the border of the mandible condyle, and 4.86 +/- 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 +/- 1.21 mm and 18.93 +/- 1.41 mm, respectively. The average distance from the bifurcation of the facial nerve to the hypoglossal nerve turn is 31.56 +/- 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.