Facial nerve injury is a risk in virtually all ear procedures and its injury is the most dreaded complication in routine otologic surgery. Historically, it was sometimes said that “God put the facial nerve in the mastoid to keep the general surgeons out.” As the facial nerve winds through the temporal bone in its course from the internal auditory canal to the stylomastoid foramen, it lies in close relationship with the cochlea, semicircular canals, ossicles, oval window, and jugular bulb. Detailed knowledge of the normal anatomy of the facial nerve and how it is characteristically involved with ear disease is central to safe otologic surgery. It is also key to the effectiveness of ear procedures, as an inexperienced surgeon who is excessively cautious out of fear of the nerve is likely to be less thorough in addressing the disease process. Avoiding iatrogenic facial nerve injury is assisted by neurophysiological monitoring, but it is no substitute for a detailed knowledge of its anatomical relationships. Learning the techniques needed to locate the facial nerve when it is embedded in disease which has obscured its customary landmarks is a crucial skill. See also section 7.6 The Facial Nerve in Mastoidectomy in Chapter 7 and section 8.7 The Facial Nerve in Cholesteatoma Chapter 8.
Repair of intratemporal facial nerve injury usually involves either direct repair or grafting. Iatrogenic injuries usually involve the tympanic or second genu segments, while tumor may occur anywhere along the length but are most common at the geniculate ganglion. Direct repair is not usually possible in a severed facial nerve within the temporal bone because clean knife injuries are rare. Most injuries leave a gap which can be bridged either by rerouting or interposition grafting. Because of the convoluted course of the intratemporal facial nerve, a defect can be overcome by rerouting across the base of a genu. Interposition grafting is usually with the greater auricular nerve, as it is a good size match, is readily accessible, and leaves only a minor deficit of an anesthetic ear lobe. Long defects, or those that require branching such as for lesions extending beyond the pes anserinus, may require sural nerve grafting.
When repair of the facial nerve is not possible due the lack of a proximal stump to graft, most commonly following resection of a cerebellopontine angle tumor, various strategies exist for reanimating the paralyzed face. The traditional hypoglossal–facial anastomosis gives excellent tone at rest, but much synkinesis during movement. Newer techniques using a portion of the hypoglossal nerve for tone and the masseteric branch of the trigeminal nerve for restoration of smile appear to have superior results. When the facial muscles have atrophied due to long-standing paralysis, or the distal branches have been resected (e.g., parotid malignancy), cross-facial anastomosis with gracilis muscle microvascular transfer offers improvement, but it is a multistage procedure. Static or dynamic (temporalis muscle) slings are alternatives, especially in older patients for whom the microvascular muscle transfer procedure works less well.
Further Reading
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Bayrak SB, Kriet JD, Humphrey CD. Masseteric to buccal branch nerve transfer. Curr Opin Otolaryngol Head Neck Surg 2017;25(4):280–285 PubMed
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Hu J, Fleck TR, Xu J, Hsu JV, Xu HX. Contemporary changes with the use of facial nerve monitoring in chronic ear surgery. Otolaryngol Head Neck Surg 2014;151(3):473–477 PubMed
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Kochhar A, Albathi M, Sharon JD, Ishii LE, Byrne P, Boahene KD. Transposition of the intratemporal facial to hypoglossal nerve for reanimation of the paralyzed face: the VII to XII transposition technique. JAMA Facial Plast Surg 2016;18(5):370–378 PubMed
Linder T, Mulazimoglu S, El Hadi T, et al. Iatrogenic facial nerve injuries during chronic otitis media surgery: a multicentre retrospective study. Clin Otolaryngol 2017;42(3):521–527 PubMed
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Rozen SM. Facial reanimation: basic surgical tools and creation of an effective toolbox for treating patients with facial paralysis: Part B. Nerve transfer combined with cross-facial nerve grafting in the acute facial palsy patient. Plast Reconstr Surg 2017;139(3):725–727 PubMed
Ryu NG, Kim J. How to avoid facial nerve injury in mastoidectomy? J Audiol Otol 2016;20(2):68–72 PubMed
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Socolovsky M, Martins RS, di Masi G, Bonilla G, Siqueira M. Treatment of complete facial palsy in adults: comparative study between direct hemihypoglossal-facial neurorrhaphy, hemihipoglossal-facial neurorrhaphy with grafts, and masseter to facial nerve transfer. Acta Neurochir (Wien) 2016;158(5):945–957, discussion 957 PubMed
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9.2 Anatomy of the Facial Nerve
Fig. 9.1 Overview of facial nerve anatomy from the brainstem exit to the terminal branches on the face.
Fig. 9.2 Note the three-dimensional complexity of the bends and turns en route from the brainstem exit to the stylomastoid foramen.
Fig. 9.3 Muscles of facial expression.
Fig. 9.4 Lateral overview of the facial nerve in the mastoid. Note how the facial nerve crosses lateral to the jugular bulb en route to the stylomastoid foramen.
Fig. 9.5 The anatomical relationships of the intratemporal facial nerve. Lab, labyrinthine segment; GG, geniculate ganglion; Horiz, horizontal (tympanic) segment; Vert, vertical (mastoid) segment; RW, round window; PSCC, posterior semicircular canal; LSCC, lateral semicircular canal.
Fig. 9.6 The proximal course of the facial nerve in the temporal bone. Lateral dissection exposing the transparent floor of the middle ear and the internal auditory canal illustrating the proximal course of the nerve between the geniculate ganglion and the internal auditory canal. Note that the semicircular canals have been removed.
Fig. 9.7 The relationships of the facial nerve as seen from above via the middle fossa approach. Note the intimate relationship of the labyrinthine and upper tympanic sections to the cochlea. The external auditory canal (EAC), middle ear (ME), cochlea (Co), and superior semicircular canal (SSCC) normally lie beneath bone but are made visible as an aid to orientation. GG, geniculate ganglion; GSPN, greater superficial petrosal nerve; 7, facial nerve; SVN, superior vestibular nerve; SPS, superior petrosal sinus; MMA, middle meningeal artery.
Fig. 9.8 In its tympanic course superior to the stapes, the facial nerve may be fully bony covered (A), dehiscent on its under surface (B)—which is common, fully dehiscent (C), or both dehiscent and protuberant. In rare cases, a protuberant facial nerve will impinge on the stapes and cause conductive hearing loss.
Fig. 9.9 Branches of the facial nerve which provide sensation to the conchal bowl may be seen on the ear canal. The digastric ridge is a useful landmark in identification of the facial nerve at the stylomastoid foramen. The digastric ridge is the bony protuberance crossing the mastoid, just above the mastoid tip, made by the posterior belly of the digastric muscle.
Fig. 9.10 The fascial lining of the superficial surface of the digastric muscle merges with the periosteum lining the stylomastoid foramen. This is a useful method in identifying the distal mastoid segment of the nerve.
Fig. 9.11 Connecting the mastoid with the parotid segments of the nerve by cutting the tenacious periosteum of the foramen with a no. 12 blade.
Fig. 9.12 The nervus intermedius (NI) conveys the parasympathic and sensory components of the facial nerve (7). It exits the pons between the main facial trunk (motor) and the audiovestibular nerve (8). (Used with permission from El Ashram YA, Jackler RK, Pitts LH, Yingling CD. Intraoperative electrophysiologic identification of the nervus intermedius. Otol Neurotol 2005;26:274–279.)
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