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Home , Abducens nucleus, Cerebellopontine angle, Chorda tympani, Cranial nerves, Facial motor nucleus, Facial muscles

A Review of Facial

Terence M. Myckatyn, M.D.1 and Susan E. Mackinnon, M.D.1

ABSTRACT

An intimate knowledge of anatomy is critical to avoid its inadvertent during , parotidectomy, maxillofacial fracture reduction, and almost any surgery of the head and . Injury to the frontal and marginal mandibular branches of the facial nerve in particular can lead to obvious clinical deficits, and areas where these are particularly susceptible to injury have been designated danger zones by previous authors. Assessment of facial nerve function is not limited to its extratemporal anatomy, however, as many clinical deficits originate within its intratemporal and intracranial components. Similarly, the facial nerve cannot be considered an exclusively given its contributions to , auricular sensation, sympathetic input to the middle meningeal , and parasympathetic innervation to the lacrimal, submandibular, and sublingual . The constellation of deficits resulting from facial is correlated with its complex anatomy to help establish the level of injury, predict recovery, and guide surgical management.

KEYWORDS: Extratemporal, intratemporal, facial nerve, , marginal

The anatomy of the facial nerve is among the components of the facial nerve reminds the surgeon that most complex of the . In his initial descrip- the facial nerve is composed not exclusively of voluntary tion of the cranial nerves, described the facial motor fibers but also of parasympathetics to the lacrimal, nerve as part of a distinct facial- submandibular, and sublingual glands; sensory innerva- complex.1,2 Although the anatomy of the other cranial tion to part of the external ; and contributions to taste nerves was accurately described shortly after Galen’s at the anterior two thirds of the . initial descriptions, it was not until the early 1800s that distinguished the motor and sensory components of the facial nerve.3,4 INTRACRANIAL ANATOMY OF Facial nerve anatomy is categorized in terms of its THE FACIAL NERVE relationship to the cranium or temporal (intracra- Voluntary control of the branchial branch of the facial nial, intratemporal, and extratemporal) or its four dis- nerve is initiated intracranially by supranuclear inputs tinct components (branchial motor, visceral motor, arising from the projecting to the facial general sensory, and special sensory). The plastic surgeon . These cortical inputs are arranged with benefits from a basic knowledge of the intracranial and representation most rostral and , midface, and intratemporal components of the facial nerve to help sequentially caudal to this.5 The pyramidal system is localize facial nerve pathology and distinguish extratem- composed of corticobulbar tracts that project voluntary, poral from facial nerve lesions at other anatomic loca- ipsilateral cortical inputs via the genu of the internal tions. Similarly, a knowledge of the four distinct capsule to the seventh cranial nerve nuclei of the pontine

Facial Paralysis; Editor in Chief, Saleh M. Shenaq, M.D.; Guest Editor, Susan E. Mackinnon, M.D. Seminars in Plastic Surgery, Volume 18, Number 1, 2004. Address for correspondence and reprint requests: Susan E. Mackinnon, M.D., Suite 17424, East Pavilion, 1 Barnes-Jewish Hospital Plaza, St. Louis, MO 63110. 1Division of Plastic Surgery, Washington University School of , St. Louis, MO. Copyright # 2004 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001 USA. Tel: +1(212) 584-4662. 1535-2188,p;2004,18,01, 005,012,ftx,en;sps00103x. 5 6 SEMINARS IN PLASTIC SURGERY/VOLUME 18, NUMBER 1 2004

. Cell bodies of the upper facial motor nerves general sensory function of the facial nerve reside in giving rise to the frontal branch receive bilateral cortical the general sensory trigeminal nucleus of the rostral inputs, and to the remainder of the facial medulla and receive afferent inputs from projections of nucleus receive contralateral cortical innervation. Spon- the geniculate within the . The taneous facial movements are centrally transmitted via within the also the , which involves diffuse axonal receives special sensory inputs from the geniculate gang- connections between multiple regions including the lion. These impulses, however, were initially generated , , , and motor cor- by taste receptors in the anterior two thirds of the tex. The extrapyramidal system regulates resting facial tongue. Ascending sensory inputs from the trigeminal tone and stabilizes the voluntary motor response; hy- and gustatory nuclei are influenced by the thalamic pothalamic inputs modulate the emotional response. nuclei prior to their reception within the sensory cortex. The facial nuclei contain the cell bodies of facial Patients with supranuclear lesions involving the nerve lower motor neurons. These cell bodies receive or present clinically with supranuclear inputs via formation with loss of volitional control of the lower facial musculature traveling through both the pyramidal and extrapyramidal but persistent facial tone and spontaneous facial move- systems. The confluence of these postsynaptic lower ments. Voluntary control of the forehead musculature is motor neurons round the and form retained because the upper halves of the facial nuclei, the at the floor of the which are populated by frontal nerve branch cell bodies, (Fig. 1). The branchial motor branch of the facial receive bilateral cortical innervation and so not all input nerve exits the at the , is lost after a unilateral supranuclear lesion. Voluntary where it is joined by the less robust nervus intermedius. , nose, and movements, however, are lost. It These nerves resemble the nerve roots of the should also be noted that facial muscle dysfunction in that they are devoid of but covered in pia caused by central injury is frequently accompanied by mater and bathed in cerebrospinal fluid. The branchial motor dysfunction of the tongue and given the motor nerve–nervus intermedius complex travels about proximity of these cortical control centers within the 15.8 mm from the cerebellopontine angle before it motor cortex and internal capsule. Reflex arcs involving begins its course within the temporal bone.6 the facial nuclei, such as the corneal blink (trigeminal- The parasympathetic component of the facial facial), are preserved following supranuclear lesions. nerve is composed of visceral motor fibers whose origi- nating cell bodies are scattered within the pontine tegmentum and collectively known as the superior sal- INTRATEMPORAL FACIAL NERVE ivatory nucleus. These nuclei are influenced by involun- The intratemporal anatomy of the facial nerve has been tary hypothalamic inputs. Cell bodies mediating the extensively studied to minimize morbidity in base

Figure 1 The facial nerve motor nuclei are located in the pontine tegmentum. (1) The . These motor nuclei contain the cell bodies of all the voluntary motor components of the facial nerve except for the nerve to stapedius. (2) The facial nerves round the abducens nuclei (cranial nerve VI) at the floor of the fourth ventricle to form the facial colliculi. (3) The cell bodies of facial motor neurons that contract the upper half of the (frontal branch) receive bilateral descending cortical inputs. (4) Cell bodies of facial motor neurons innervating the bottom half of the face receive descending cortical inputs from the contralateral side alone. A REVIEW OF FACIAL NERVE ANATOMY/MYCKATYN, MACKINNON 7 surgery while maximizing exposure. In addition, its intraneural topography has been investigated in cadavers and models.7–9 Whereas the topography in cer- tain animal models, such as the cat, is shown to be consistent,7 the topography of the intratemporal facial nerve in the human is highly variable and spatial rela- tionships to other intratemporal structures such as the carotid artery and sigmoid sinus are also variable.10–13 The branching pattern of the intratemporal facial nerve, however, is reasonably consistent. The branchial motor and nervus intermedius com- ponents of the facial nerve are loosely associated as they enter the of the temporal bone. Both the facial and acoustic nerves enter the temporal bone simultaneously with the facial nerve located superior to the acoustic nerve. The facial nerve, along with the acoustic and vestibular nerves, travel 8 to 10 mm within the internal auditory canal before only the facial nerve enters the fallopian canal. The fallopian canal consists of labyrinthine, tympanic, and mastoid segments. The la- byrinthine segment is the narrowest segment and extends 3 to 5 mm from the edge of the internal auditory canal. The resides within the distal part of the labyrinthine segment of the facial nerve and gives rise to the first branch of the facial nerve—the —which carries visceral motor parasympa- thetic fibers to the lacrimal (Fig. 2). The external petrosal nerve is a second, threadlike branch that is Figure 2 The voluntary motor component of the facial nerve occasionally present and provides sympathetic innervation exits the cerebellopontine angle with the nervus intermedius to the . The lesser petrosal nerve before entering the porous acusticus. The facial nerve traverses is the third branch extending from the geniculate gang- the labyrinthine segment before entering the geniculate ganglion. The greater petrosal, external petrosal, and lesser petrosal lion. This branch typically carries parasympathetic fibers nerves are given off at this level. The temporal or horizontal associated with the glossopharyngeal nerve (ninth cranial segment forms the second component of the intratemporal facial nerve) to the . Salivary flow from the parotid nerve and is located just distal to a sharp genu formed at the gland may not, however, be interrupted by lesions to the distal geniculate ganglion. A second genu separates the temporal and mastoid segments of the intratemporal facial nerve. The glossopharyngeal nerve. In fact, parasympathetic fibers general sensory branch of the facial nerve is given off at this level traveling along the nervus intermedius of the facial nerve and frequently travels with the general sensory branch of the can bypass the glossopharyngeal branch to the parotid and (Arnold’s nerve) and gives sensation to the external provide an alternative source of parasympathetic innerva- ear. The nerve to stapedius is a motor nerve that helps deaden loud sounds. The is the last branch of the tion to maintain salivary flow. intratemporal facial nerve and is the terminal branch of the nervus Compression of the facial nerve within the labyr- intermedius. inthine segment is particularly common given the canal’s narrow dimensions. The facial nerve occupies up to 83% of the labyrinthine canal cross-sectional area compared with only 64% of the more distal mastoid area.14 The wider cross-sectional area than the other segments, and junction of the labyrinthine and tympanic components the facial nerve gives off three branches within this of the fallopian canal is formed by an acute angle, and region. The nerve to the stapedius is the first branch shearing of the facial nerve commonly occurs as the nerve and innervates the muscle of the . traverses this genu.8 The tympanic or horizontal seg- Because the cell bodies of this motor nerve are not ment extends 8 to 11 mm through the temporal bone. located in the facial nuclei, patients with congenital The midtympanic canal represents a second region of facial palsies such as Mo¨bius syndrome retain innerva- fallopian canal narrowing and is a less common point of tion to the stapes when the other facial mimetics are nerve compression compared with the narrow labyr- paralyzed.8 The sensory branch of the facial nerve is inthine segment.15 typically the second branch. Ramsay Hunt first noted The tympanic segment connects with the mastoid this general in 1907 when patients pre- segment at a second genu. The mastoid segment has a senting with facial paralysis related to herpes zoster also 8 SEMINARS IN PLASTIC SURGERY/VOLUME 18, NUMBER 1 2004

demonstrated a vesicular eruption limited to parts of the posteriorly to the main facial nerve trunk. Advocates of external ear.16 Ten cadaveric temporal bone dissections this technique note that damage to a small branch of the revealed a small branch off the vertical component of the facial nerve during the initial exploration is far less intratemporal facial nerve that arced laterally and infer- devastating than an inadvertent injury to the entire iorly to supply the posterior and inferior external audi- motor trunk. However, these peripheral branches are tory canal. Tumor encroachment upon this sensory more difficult to identify because of their smaller size and nerve, which is thought to comprise 10 to 15% of the a lack of consistent landmarks. neurons within the intratemporal facial nerve,17 results The arborization of the extratemporal facial nerve in hypesthesia of the external and is known as typically begins within the substance of the parotid gland Hitselberger’s sign, after the physician who described and ultimately gives rise to the cervical, marginal man- it.18 The general sensory branch of the facial nerve dibular, buccal, zygomatic, and frontal (or temporal) travels with Arnold’s nerve, a sensory branch of the nerve branches. Davis et al dissected 350 cadaveric facial vagus nerve that exits the jugular and then halves and were the first to categorize the branching joins the course of the facial nerve just distal to the nerve pattern of the facial nerve into six distinct patterns.20 to the stapedius branch.8 The facial nerve trunk typically gave rise to superior and The chorda tympani is the terminal extension of inferior divisions. The marginal mandibular and cervical the nervus intermedius. It branches off the facial nerve branches of the facial nerve were exclusively derived from in the distal third of the mastoid segment and runs the inferior division, whereas the buccal branch always between the of the before exiting the received some contribution from the inferior division through the temporal bone at the pet- and either no or a variable contribution from the superior rotympanic fissure. It joins the lingual branch of the division (Fig. 3). The frontal branch consistently repre- to provide parasympathetic innervation sented a terminal branch of the superior division of the to the submandibular and sublingual glands. Special facial nerve trunk. Baker and Conley reviewed the sensory afferents from the anterior two thirds of the extratemporal facial nerve anatomy in 2000 parotidect- tongue also travel with the chorda tympani, and on omy cases.21 Their findings suggested that the facial occasion the sensory branch of the facial nerve travels nerve branching pattern was more variable than that with the chorda tympani instead of Arnold’s nerve.17 noted in Davis’ cadaveric studies, including the presence of a facial nerve trunk trifurcation with a direct buccal branch in a few instances. The zygomatic branch was EXTRATEMPORAL FACIAL NERVE The extratemporal component of the facial nerve starts when the facial nerve exits the . In the adult, it is protected laterally by the mastoid tip, tympanic ring, and mandibular ramus, whereas in chil- dren younger than 2 years it is relatively superficial. Postauricular incisions in this younger population must be carefully planned because the trunk of the facial nerve is a subcutaneous structure at this level. After exiting the stylomastoid foramen, the facial nerve gives off motor branches to the posterior belly of digastric, stylohyoid, and the superior auricular, posterior auricular, and occi- pitalis muscles. The facial nerve then travels along a course anterior to the posterior belly of the digastric and lateral to the and styloid process before dividing into its main motor branches at the posterior edge of the parotid gland. The facial nerve trunk is usually identified ap- proximately 1 cm deep and just inferior and medial to the Figure 3 The extratemporal facial nerve is characterized by tragal pointer. The parotid and superficial musculoapo- several branching patterns. The marginal mandibular, buccal, zygomatic, and frontal branches are all consistent branches, but neurotic system (SMAS) can then be carefully divided to their exact anatomic locations are somewhat variable. (1) The expose the facial nerve for facial nerve reconstruction. frontal nerve is located within a triangle bordered laterally by a Alternatively, branches of the facial nerve can be identi- line drawn from 0.5 cm below the to 2 cm above the lateral fied distally as they exit the anterior border of the parotid brow, inferiorly by the , and medially by the margin of the lateral orbital rim. (2) Posterior to the , the gland. Here, the buccal branches of the facial nerve marginal mandibular nerve is located above the inferior border of become quite superficial, lying immediately beneath the 80% of the time but almost all of the time when the SMAS.19 Facial nerve branches are then traced anterior to the facial artery.26 A REVIEW OF FACIAL NERVE ANATOMY/MYCKATYN, MACKINNON 9 found to be the most robust, and the mandibular ramus description of the facial danger zones during rhytidect- branch was found to be the smallest. omy, for example, alerts the surgeon to the location of the Specific attention has been paid to the marginal frontal, marginal mandibular, zygomatic, and buccal mandibular and frontal branches of the facial nerve, branches of the facial nerve.27 In this description, the which are more susceptible to injury following paroti- frontal branch of the facial nerve is located within the dectomy, rhytidectomy, or fixation of the mandible at superficial myoaponeurotic system below a line drawn the subcondylar region, ramus, and angle.21 Pitanguy from 0.5 cm below the tragus to 2.0 cm above the lateral and Ramos noted the frontal branch to have a consistent brow. The marginal mandibular branch is at risk for course from 0.5 cm below the tragus to 1.5 cm above the injury deep to the superficial myoaponeurotic system in lateral brow.22 Stuzin and colleagues then showed that a zone centered 2 cm posterior to the oral commissure at despite a variety of branching patterns, the frontal the midmandibular level (Fig. 3). According to Seckel, the branch of the facial nerve was consistently situated zygomatic and buccal branches of the facial nerve are within the temporoparietal . Therefore, the frontal most susceptible to injury deep to the superficial myoapo- branch could be safely avoided if a subcutaneous plane neurotic system in a zone bordered laterally by the parotid superficial to the temporoparietal fascia or a deep plane gland and medially by the . on the surface of the deep temporoparietal fascia or between the superficial and deep layers of the deep was maintained.23 Gosain et al24 further FACIAL MUSCULATURE characterized the anatomy of the frontal branch of the The extratemporal branches of the facial nerve innervate facial nerve. They demonstrated that the frontal branch the facial mimetic muscles that consist of the orbicularis consisted of two to four rami with divergent paths oris and 23 other paired muscles. The mimetic muscles crossing the zygomatic arch. In their cadaver study, can be further divided into four layers, based on depth, as rami crossing the caudal edge of the zygomatic arch demonstrated in cadaveric dissections.28 The most spanned a distance of 2.9 cm but of up to 3.6 cm at the superficial three muscle layers (layer 1, zygomaticus rostral end. Moreover, they demonstrated that both the minor; layer 2, ; layer 3, orbicularis oris) are frontal nerve and superficial temporal artery resided in innervated on their deep surfaces, and the muscles of the deep aspects of the temporoparietal fascia and that the deepest layer, consisting of the , buccinator, the posteriormost rami of the frontal branch were and , are innervated on their lateral or located both anterior and posterior to the superficial superficial surfaces.29 Freilinger et al have also used temporal artery. Sabini et al25 showed that during en- histochemical mapping of cytoskeletal adenosine tripho- doscopic brow lift procedures, the superficial temporal sphatase to establish fiber diameters and the relative artery and frontal branch of the facial nerve were located amounts of slow-twitch type I and fast-twitch type II within 2 mm of each other in 11 of 12 cadaver halves fibers in postmortem mimetic muscles.30 Group 1 mus- evaluated. Finally, numerous interconnections exist be- cles, including the procerus, are categorized as phasic, tween the frontal nerve rami, although no interconnec- contract rapidly with stimulation, and contain predomi- tions have been identified between rami from the frontal nantly fast-twitch type II fibers and only 20% type I nerve and other facial nerve branches.24 fibers. Group 2 muscles, including the zygomaticus In addition to the frontal branch, interconnec- major, contain 20 to 40% type I fibers, and group 3 tions have been identified between other facial nerve muscles such as the buccinator are composed of more branches. Baker and Conley noted the presence of than 40% type I fibers and primarily contribute to facial connections between major facial nerve divisions in 70 tone. A distinct pattern of innervation may also char- to 90% of the patients they studied.21 The marginal acterize the facial musculature. Rather than receiving a mandibular nerve, however, was particularly susceptible single, centric input, the facial muscle fibers receive to long-standing morbidity after injury because it formed multiple inputs at motor end plates distributed in an connections with other nerves only 10 to 15% of the eccentric pattern about the muscle fiber.31 time. Dingman and Grabb noted that in 100 cadavers, On occasion, some mimetic function remains the marginal mandibular branch of the facial nerve, following a severe injury to the extratemporal facial nerve. posterior to the facial artery, was located above the This function is in part explained by the numerous inferior border of the mandible in 81% of cases and interconnections that exist between the facial nerve and below in 19%.26 The marginal mandibular nerve, which the trigeminal, glossopharyngeal, vagus, spinal accessory, innervates the depressor anguli oris musculature, was hypoglossal, and nearby parasympathetic and sympa- located above the inferior border of the mandible in thetic nerves.32 Spontaneous recovery following facial 100% of cases when exposed anterior to the facial artery. nerve injury without repair may occur because of facial Paying particular attention when operating in nerve regeneration along one of these alternative paths. specific regions of the face minimizes damage to the The trigeminal nerve has most often been implicated as extratemporal branches of the facial nerve. Seckel’s an alternative pathway for regenerating facial nerve 10 SEMINARS IN PLASTIC SURGERY/VOLUME 18, NUMBER 1 2004

fibers.33,34 Alternatively, it is possible that the trigeminal 10. Harris WD. Topography of the facial nerve. Arch Otolar- and facial nuclei, which are collocated in the embryonic yngol 1968;88:264–267 medulla, retain a few cell bodies from one another’s 11. Kukwa A, Czarnecka E, Oudghiri J. Topography of the facial cranial nerves, thus producing further overlap of cranial nerve in the stylomastoid fossa. Folia Morphol (Warsz) 35,36 1984;43(4):311–314 nerve function centrally. Facial nerve injury also 12. Sunderland S. The structure of the facial nerve. Anat Rec results in synaptic stripping within the facial nucleus. 1953;116:147–165 This was demonstrated in a 77-year-old man who died of 13. Wysocki J. Correlations between topography of the main an unrelated problem 3 months after suffering mastoidi- structures of the temporal bone and the location of the tis with subsequent ipsilateral facial paralysis.37,38 Con- sigmoid sinus [in Polish]. Otolaryngol Pol 1998;52:287–290 nections between cell bodies within the facial nucleus and 14. Fisch U, Esslen E. Total intratemporal exposure of the facial the surrounding central had been lost. nerve. Pathologic findings in Bell’s palsy. Arch Otolaryngol 1972;95:335–341 15. Nakashima S, Sando I, Takahashi H, Fujita S. Computer- CONCLUSIONS aided 3-D reconstruction and measurement of the and facial nerve. I. Cross-sectional area and diameter: Facial nerve anatomy can be divided into its intracranial, preliminary report. Laryngoscope 1993;103:1150–1156 intratemporal, and extratemporal components. To dis- 16. Hunt JR. On herpetic inflammation of the geniculate tinguish between various clinical diagnoses, a basic ganglion. A new syndrome and its complications. J New understanding of the intracranial and intratemporal Ment Dis 1907;34:73–96 anatomy is required. A sound knowledge of the anatomy 17. Rouviere H, Delmas A. Nerfs de la tet et du cou. In: eds. of the extratemporal facial nerve is also critical to enable Anatomie Humaine: Descriptive Topographique et Func- safe dissection through the planes of the face during tionnelle. Paris: Masson; 1985:276 18. Hitselberger WE, House WF. Acoustic diagnosis: rhytidectomy, parotidectomy, facial trauma, and many External auditory canal hypesthesia as an early sign. Arch other craniofacial procedures. It is also important to Otolaryngol 1966;83:218–221 remember that the facial nerve is not just a pure 19. Wilhelmi BJ, Mowlavi A, Neumeister MW. The safe face lift voluntary motor nerve but comprises parasympathetic, with bony anatomic landmarks to elevate the SMAS. Plast general sensory, and special sensory components as well. Reconstr Surg 2003;111:1723–1726 Notably, the facial nerve has numerous interconnections 20. Davis RA, Anson BJ, Puddinger JM, Kurth RE. Surgical with other cranial, parasympathetic, and sympathetic anatomy of the facial nerve and parotid gland based upon study of 350 cervical facial halves. Surg Gynecol Obstet nerves along its course, which helps to explain many of 1956;102:385–412 the referred syndromes encountered in head and 21. Baker DC, Conley J. Avoiding facial nerve in neck pathology and also why residual function exists rhytidectomy. Anatomical variations and pitfalls. Plast following an apparently denervating facial nerve injury. Reconstr Surg 1979;64:781–795 22. Pitanguy I, Ramos AS. The frontal branch of the facial nerve: the importance of its variations in face lifting. Plast Reconstr REFERENCES Surg 1966;38:352–356 23. Stuzin JM, Wagstrom L, Kawamoto HK, Wolfe SA. 1. O’Rahilly R. On counting cranial nerves. Acta Anat (Basel) Anatomy of the frontal branch of the facial nerve: the signi- 1988;133(1):3–4 ficance of the temporal fat pad. Plast Reconstr Surg 1989;83: 2. Steinberg DA. Scientific and the history of the 265–271 clinical examination of selected motor cranial nerves. Semin 24. Gosain AK, Sewall SR, Yousif NJ. The temporal branch Neurol 2002;22:349–356 of the facial nerve: how reliably can we predict its path? 3. Bell C. On the nerves, giving an account of some experiments Plast Reconstr Surg 1997;99:1224–1233; discussion 1234– on their structure and functions, which leads to a new 1236 arrangement of the system. Trans R Soc Lond 1821;3:398 25. Sabini P, Wayne I, Quatela VC. Anatomical guides to 4. Bell C. The Nervous System of the . 2nd ed. precisely localize the frontal branch of the facial nerve. Arch London: Longman’s; 1830 Facial Plast Surg 2003;5:150–152 5. Crosby EC, Dejonge BR. Experimental and clinical studies of 26. Dingman RO, Grabb WC. Surgical anatomy of the the central connections and central relations of the facial mandibular ramus of the facial nerve based on the dissection nerve. Ann Otol Rhinol Laryngol 1963;72:735–755 of 100 facial halves. Plast Reconstr Surg 1962;29:266–272 6. Lang J. Anatomy of the brainstem and the lower cranial 27. Seckel BR. Facial Danger Zones: Avoiding Nerve Injury in nerves, vessels, and surrounding structures. Am J Otol 1985; Facial Plastic Surgery. Saint Louis: Quality Medical Publish- Suppl:1–19 ers; 1993 7. May M. Anatomy of the facial nerve (spatial orientation of 28. Freilinger G, Gruber H, Happak W, Pechmann U. Surgical fibers in the temporal bone). Laryngoscope 1973;83:1311– anatomy of the mimic muscle system and the facial nerve: 1329 importance for reconstructive and aesthetic surgery. Plast 8. May M. Anatomy for the clinician. In: May M, Schaitkin BM Reconstr Surg 1987;80:686–690 eds. The Facial Nerve. 2nd ed. New York: Thieme; 2000:19–56 29. Happak W, Burggasser G, Liu J, Gruber H, Freilinger G. 9. Podvinec M, Pfaltz CR. Studies on the anatomy of the facial Anatomy and histology of the mimic muscles and the supplying nerve. Acta Otolaryngol (Stockh) 1976;81:173–177 facial nerve. Eur Arch Otorhinolaryngol 1994:S85–S86 A REVIEW OF FACIAL NERVE ANATOMY/MYCKATYN, MACKINNON 11

30. Freilinger G, Happak W, Burggasser G, Gruber H. 34. Conley JJ. Accessory neuromuscular pathways to the face. Histochemical mapping and fiber size analysis of mimic Trans Am Acad Ophthalmol Otolaryngol 1964;68:1064–1067 muscles. Plast Reconstr Surg 1990;86:422–428 35. Banfai P. Applied anatomy of the facial nerve. I. Nuclei, 31. Happak W, Liu J, Burggasser G, Flowers A, Gruber H, supranuclear connections and peripheral nerve [in German]. Freilinger G. Human : dimensions, motor HNO 1976;24:253–264 endplate distribution, and presence of muscle fibers with 36. Banfai P. Applied anatomy of the facial nerve. II. Anasto- multiple motor endplates. Anat Rec 1997;249:276–284 moses [in German]. HNO 1976;24:289–294 32. Bischoff EPE. Microscopic analysis of the anastomosis 37. Graeber MB, Bise K, Mehraein P. Synaptic stripping in the between the cranial nerves. In: Sacks EJ, Valtin EW, eds. human facial nucleus. Acta Neuropathol (Berl) 1993;86:179– Hanover, NH: University Press of New England; 1977 181 33. Norris CW, Proud GO. Spontaneous return of facial motion 38. Graeber MB, Lopez-Redondo F, Ikoma E, et al. The following seventh cranial nerve resection. Laryngoscope 1981; / response in the neonatal facial 91:211–215 nucleus following . Res 1998;813:241–253