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Facial Nerve Injury

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Hany Emam, Courtney Jatana, and Gregory M. Ness

Introduction

Minimizing risk to the integrity of the facial nerve is a critical measure of surgical success in temporomandibular joint (TMJ) surgeries. The surgeon must have a keen understanding of the regional anatomy combined with a planned dissection to protect the facial nerve in their approach to the joint [1]. Facial nerve injury may have devastating effects on the patient esthetically and functionally due to impairment of the frontalis and/or orbicularis oculi muscles. According to Liu et al., the most current review of the literature reveals that the incidence of facial nerve injury in conjunction with open TMJ surgery ranges from 12.5 to 32% [2]. The chapter will provide a review on the anatomy of the facial nerve, procedures leading to potential injury, recognition of injury, and multiple methods of management.

Pathophysiology

The course of the facial nerve and its branches (Fig. 5.1) must be known to avoid violating the boundaries of safe surgery and creating a potentially paralyzing injury. The temporal and zygomatic branches of the facial nerve are most at risk of injury in TMJ surgery. These two branches of the facial nerve are situated deep to the superficial temporal fascia and superficial to the superficial layer of the deep temporal fascia and periosteum, overlying the root of the zygoma. (Fig. 5.2). In their landmark 1979 article, Al-Kayat and Bramley measured the location of the facial nerve’s main trunk and found that it runs no nearer than 1.5 cm below the inferior margin of the bony external auditory meatus. The temporal branch of the nerve crosses the zygomatic

H. Emam, BDS, MS • C. Jatana, DDS, MS, FACS • G.M. Ness, DDS, FACS (*) Division of Oral and Maxillofacial Surgery & Dental Anesthesiology, The Ohio State University College of Dentistry, Columbus, OH, USA e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

© Springer International Publishing AG 2017

G.F. Bouloux (ed.), Complications of Temporomandibular Joint Surgery, DOI 10.1007/978-3-319-51241-9_5

Fig. 5.1 Facial nerve branches (Adapted from Ness [3]; with permission - Courtesy of Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist, Yale University School of Medicine, Center for Advanced Instructional Media, New Haven,

CT. Published under Creative Commons Attribution 2.5 License 2006)

Frontal diagram showing the tissue planes superficial and slightly anterior to the TMJ

Fig. 5.2 Frontal diagram showing the tissue planes superficial and slightly anterior to the TMJ.

The central bony structure is the cut end of the zygomatic arch (Adapted from Ness [3]; with permission - From Agarwal, et al. [4])

Distance between the external auditory canal and temporal (frontal) branch of the facial nerve (Adapted from Ness [3]; with permission - Miloro, et al. [6])

Fig. 5.3 Distance between the external auditory canal and temporal (frontal) branch of the facial nerve (Adapted from Ness [3]; with permission - Miloro, et al. [6])

Area in which the temporal

Fig. 5.4 Area in which the temporal (frontal) branch of the facial nerve transitions from lying deep in the superficial temporal fascia to piercing it from below (Adapted from Ness [3]; with permission - Agarwal, et al. [4])

arch at a minimum distance of 0.8 cm and a mean of 2.0 cm anterior to the bony external auditory meatus. Similar cadaver studies by Woltmann found a minimum distance of 0.7 cm and a mean of 1.5 cm, whereas a high-resolution MRI study of live subjects by Miloro and others measured a minimum distance of 1.7 cm and a mean of 2.1 cm (Fig. 5.3). Agarwal and others have further increased our knowledge of the facial nerve’s path in three dimensions. They showed that the temporal branch lies in the loose areolar connective tissue layer between the superficial and deep temporal fascia as it crosses the zygomatic arch before entering the superficial temporal fascia from its undersurface in a consistent region 1.5. to 3.0 cm above the zygomatic arch and 0.9 to 1.4 cm posterior to the lateral orbital rim [3-7] (Fig. 5.4).

Temporofacial

division

division

T

T

Z

Z

B

M

M

T

Z

Z

Z

B

M

M

Type II (27.5%)

T

Z

Z

Z

B

B

M

M

Type III (20%)

Type I (20%)

Z

Z

Z

B

B

M

Type IV (15%)

T

Z

Z

M

M

T

Z

Z

B

M

M

Type VI (2.5%)

Type V (15%)

Fig. 5.5 Terminal branches of the facial nerve, demonstrating its variability. B buccal, M mandibular, T temporal, Z zygomatic (Adapted from Callander [8])

The TMJ surgeon should also be aware of the variability of the terminal branches: temporal, zygomatic, buccal, mandibular, and cervical. In another landmark study performed with 100 cadaver heads, there were eight variations in the distribution of the facial nerve. Of surgical significance, the author found distal branching of the temporal branch in four separate patterns [8]. This variation allows for several pathways to innervate the frontalis muscle. Hall et al. found that the most distal branching of the facial nerve occurs 63% of the time. With this common pattern, the temporal branch can be injured without losing frontalis function [9] (Fig. 5.5).

 
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