Facial Nerve

Shortly after the facial nerve exits the skull through the stylomastoid foramen, it enters the parotid gland. At this point, the nerve usually divides into two main trunks (temporofacial and cervicofacial), the branches of which variably anastomose to form a parotid plexus. The division of the facial nerve is located between 1.5 and 2,8 cm below the lowest concavity of the bony external auditory canal.

Terminal branches of the facial nerve emerge from the parotid gland and radiate anteriorly (see Fig. 12-1). The terminal branches are commonly classified as temporal, zygomatic, buccal, marginal mandibular, and cervical. The location of the temporal branches is of particular concern during TMJ surgery, as these are the branches most likely to be damaged. As the temporal nerve branches (frequently two) cross the lateral surface of the zygomatic arch, they course along the undersurface of the temporoparietal fascia (see Fig. 6-5). The temporal branch crosses the zygomatic arch at varying locations from one individual to the next, and range anywhere from 8 to 35 mm (20 mm average) anterior to the external auditory canal (Fig. 12-2) (1). Therefore, protection of the temporal branches of the facial nerve can be achieved by routinely incising through the superficial layer of temporalis fascia and periosteum of the zygomatic arch not more than 0,8 cm in front of the anterior border of the external auditory canal.

Figure 12 2 Major branches of the facial nerve. The distance from the anterior concavity of the external auditory canal to the crossing of the zygomatic arch by the temporal branch varies from 8 to 35 mm.

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