INNERVATION OF THE FACE AND SCALP

The numerous muscles of facial expression are supplied by the facial nerve, while the two muscles of mastication that relate to the face are innervated by the mandibular division of the trigeminal nerve. The sensory innervation is primarily from the three divisions of the mandibular nerve, with smaller contributions from the cervical spinal nerves. The detailed innervation of the auricle is considered on page 651.
UPDATE Date Added: 17 December 2004
Abstract: New one-stage nerve pedicle grafting technique using the great auricular nerve for reconstruction of facial nerve defects.
Click on the following link to view the abstract: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15237353 New one-stage nerve pedicle grafting technique using the great auricular nerve for reconstruction of facial nerve defects.
Koshima I, Nanba Y, Tsutsui T, Takahashi Y, Itoh S. New one-stage nerve pedicle grafting technique using the great auricular nerve for reconstruction of facial nerve defects. J Reconst Microsurg. 2004; Jul;20(5): 357-61.
TRIGEMINAL NERVE
Three large areas of the face can be mapped out to indicate the peripheral nerve fields associated with the three divisions of the trigeminal nerve. The fields are not horizontal but curve upwards (Fig. 29.9A), apparently because the facial skin moves upwards with growth of the brain and skull. Embryologically, each division of the trigeminal nerve is associated with a developing facial process which gives rise to a specific area of the face in the adult. Thus the ophthalmic nerve is associated with the frontonasal process, the maxillary nerve with the maxillary process and the mandibular nerve with the mandibular process.
 
The sensory nerves of the left side of the scalp, face and neck, and the branches of the facial nerve, which are distributed to the muscles of 'facial expression'. The pinna has been reflected forwards. B, Cutaneous innervation of the face and neck, showing dermatomes
    Figure 29.9 A, The sensory nerves of the left side of the scalp, face and neck, and the branches of the facial nerve, which are distributed to the muscles of 'facial expression'. The pinna has been reflected forwards. B, Cutaneous innervation of the face and neck, showing dermatomes.
Ophthalmic nerve (Fig. 29.9B)
The cutaneous branches of the ophthalmic nerve supply the conjunctiva, skin over the forehead, upper eyelid and much of the external surface of the nose.
Supratrochlear nerve
The supratrochlear nerve is the smaller terminal branch of the frontal nerve. It runs anteromedially in the roof of the orbit, passes above the trochlea, and supplies a descending filament to the infratrochlear branch of the nasociliary nerve. The nerve emerges between the trochlea and the supraorbital foramen at the frontal notch, curves up on the forehead close to the bone with the supratrochlear artery and supplies the conjunctiva and the skin of the upper eyelid. It then ascends beneath the corrugator and the frontal belly of occipitofrontalis before dividing into branches which pierce these muscles to supply the skin of the lower forehead near the midline.
Supraorbital nerve
The supraorbital nerve is the larger terminal branch of the frontal nerve. It traverses the supraorbital notch or foramen and supplies palpebral filaments to the upper eyelid and conjunctiva. It ascends on the forehead with the supraorbital artery, and divides into medial and lateral branches, which supply the skin of the scalp nearly as far back as the lambdoid suture. These branches are at first deep to the frontal belly of the occipitofrontalis. The medial branch perforates the muscle to reach the skin, while the lateral pierces the epicranial aponeurosis.
Lacrimal nerve
The lacrimal nerve is the smallest of the main ophthalmic branches and pierces the orbital septum to end in the lateral region of the upper eyelid, which it supplies. It joins filaments of the facial nerve. Occasionally it is absent, in which case it is replaced by the zygomaticotemporal nerve: the relationship is reciprocal, and when the zygomaticotemporal nerve is absent it is replaced by a branch of the lacrimal nerve.
Infratrochlear nerve
The infratrochlear nerve branches from the nasociliary nerve. It leaves the orbit below the trochlea and supplies the skin of the eyelids, the conjunctiva, lacrimal sac, lacrimal caruncle and the side of the nose above the medial canthus.
External nasal nerve (Fig. 29.9A,B)
The external nasal nerve is the terminal branch of the anterior ethmoidal nerve. It descends through the lateral wall of the nose, and supplies the skin of the nose below the nasal bones, excluding the alar portion around the external nares.
Maxillary nerve
The maxillary nerve passes through the orbit to supply the skin of the lower eyelid, the prominence of the cheek, the alar part of the nose, part of the temple, and the upper lip. It has three cutaneous branches, namely the zygomaticotemporal, zygomaticofacial and infraorbital nerves.
Zygomaticotemporal nerve
The zygomaticotemporal nerve is a terminal branch of the zygomatic nerve. It traverses a canal in the zygomatic bone to emerge into the anterior part of the temporal fossa, ascends between the bone and temporalis and finally pierces the temporal fascia c.2 cm above the zygomatic arch to supply the skin of the temple. It communicates with the facial and auriculotemporal nerves. As it pierces the deep layer of the temporal fascia it sends a slender twig between the two layers of the fascia towards the lateral angle of the eye. This lacrimal ramus conveys parasympathetic postganglionic fibres from the pterygopalatine ganglion to the lacrimal gland.
UPDATE Date Added: 22 May 2006
Abstract: Surgical anatomy of the zygomaticotemporal nerve in the orbit and temporal area
Click on the following link to view the abstract: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15167230&query_hl=24&itool=pubmed_docsum Zygomaticotemporal nerve passage in the orbit and temporal area. Hwang K, Suh MS, Lee SI, Chung IH: J Craniofac Surg 15:209-214, 2004.
UPDATE Date Added: 25 October 2005
Publication Services, Inc.
Abstract: Zygomaticotemporal nerve passage in the orbit and temporal area
Click on the following link to view the abstract: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve=pubmed=Abstract_uids=15167230_hl=9 Zygomaticotemporal nerve passage in the orbit and temporal area. Hwang K, Suh MS, Lee SI et al: J Craniofac Surg 15(2):209-214, 2004.
Zygomaticofacial nerve
The zygomaticofacial nerve is a terminal branch of the zygomatic nerve. It traverses the inferolateral angle of the orbit, and emerges on the face through a foramen in the zygomatic bone. It next perforates orbicularis oculi to supply the skin on the prominence of the cheek. It forms a plexus with zygomatic branches of the facial nerve and palpebral branches of the maxillary nerve. Occasionally the nerve is absent.
Infraorbital nerve
The infraorbital nerve emerges onto the face at the infraorbital foramen, where it lies between levator labii superioris and levator anguli oris. It divides into three further groups of branches. The palpebral branches ascend deep to orbicularis oculi, and pierce the muscle to supply the skin in the lower eyelid and join with the facial and zygomaticofacial nerves near the lateral canthus. Nasal branches supply the skin of the side of the nose and of the movable part of the nasal septum, and join the external nasal branch of the anterior ethmoidal nerve. Superior labial branches, large and numerous, descend behind levator labii superioris, to supply the skin of the anterior part of the cheek and upper lip. They are joined by branches from the facial nerve to form the infraorbital plexus.
Mandibular nerve
The mandibular nerve supplies skin over the mandible, the lower lip, the fleshy part of the cheek, part of the auricle of the ear and part of the temple via the buccal, mental and auriculotemporal nerves.
Buccal nerve
The buccal nerve emerges onto the face from behind the ramus of the mandible and passes laterally in front of the masseter to unite with the buccal branches of the facial nerve. It supplies the skin over the anterior part of buccinator.
Mental nerve
The mental nerve is the terminal branch of the inferior alveolar nerve. It enters the face through the mental foramen, where it is directed backwards. It supplies the skin of the lower lip.
Auriculotemporal nerve
The auriculotemporal nerve emerges onto the face behind the temporomandibular joint within the superior surface of the parotid gland. It ascends posterior to the superficial temporal vessels, over the posterior root of the zygoma, and divides into superficial temporal branches. The cutaneous branches of the auriculotemporal nerve supply the tragus and part of the adjoining auricle of the ear and the posterior part of the temple. It communicates with the facial nerve, usually by two rami that pass anterolaterally behind the neck of the mandible. The communications with the temporofacial division of the facial nerve anchor the facial nerve close to the lateral surface of the condylar process of the mandible, limiting its mobility during surgery. Communications with the temporal and zygomatic branches loop around the transverse facial and superficial temporal vessels.


FACIAL NERVE


The facial nerve emerges from the base of the skull at the stylomastoid foramen. At this point the facial nerve lies c.9 mm from the posterior belly of the digastric muscle and 11 mm from the bony external acoustic meatus. It gains access to the face by passing through the substance of the parotid gland. Although mainly motor, there are some cutaneous fibres from the facial nerve which accompany the auricular branch of the vagus and which probably innervate the skin on both auricular aspects, in the conchal depression and over its eminence.
Close to the stylomastoid foramen the facial nerve gives off the posterior auricular nerve, which supplies the occipital belly of occipitofrontalis, and some of the auricular muscles, and the nerves to the posterior belly of digastric and stylohyoid. The nerve then enters the parotid gland high up on the posteromedial surface and passes forwards and downwards behind the mandibular ramus. Within the substance of the gland the facial nerve branches into the temporofacial and cervicofacial trunks, just behind (within c.5 mm) the retromandibular vein. In c.90% of cases, the two trunks lie superficial to the vein, in intimate contact with it. Occasionally the trunks pass beneath the retromandibular vein (temporofacial trunk c.9%; cervicofacial trunk c.2%). The trunks branch further to form a parotid plexus (pes anserinus), which exhibits variations in branching pattern. Five main terminal branches arise from the plexus and diverge within the gland. They leave the parotid gland by its anteromedial surface, medial to its anterior margin and supply the muscles of facial expression.


The temporal branches are generally multiple and pass across the zygomatic arch to the temple to supply intrinsic muscles on the lateral surface of the auricle, and the anterior and superior auricular muscles. They join with the zygomaticotemporal branch of the maxillary nerve and the auriculotemporal branch of the mandibular nerve. The more anterior branches supply the frontal belly of occipitofrontalis, orbicularis oculi and corrugator and join the supraorbital and lacrimal branches of the ophthalmic nerve.
Zygomatic branches are generally multiple and cross the zygomatic bone to the lateral canthus of the eye, to supply the orbicularis oculi and join filaments of the lacrimal nerve and zygomaticofacial branch of the maxillary nerve. The branches may also help supply muscles associated with the buccal branch of the facial nerve.
The buccal branch has a variable origin and passes horizontally to a distribution below the orbit and around the mouth. It is usually single, but two branches occur in 15% of cases. The buccal branch has a close relationship to the parotid duct, and usually lies below it. Superficial branches run deep to subcutaneous fat and the superficial musculo-aponeurotic system (SMAS) (p. 499). Some branches pass deep to procerus and join the infratrochlear and external nasal nerves. Upper deep branches pass under zygomaticus major and levator labii superioris, supply them and form an infraorbital plexus with the superior labial branches of the infraorbital nerve. They also supply levator anguli oris, zygomaticus minor, levator labii superioris alaequae nasi and the small nasal muscles. These branches are sometimes described as lower zygomatic branches. Lower deep branches supply the buccinator and orbicularis oris, and join filaments of the buccal branch of the mandibular nerve.
The marginal mandibular branches, of which there are usually two, run forwards towards the angle of the mandible under platysma, at first superficial to the upper part of the digastric triangle, then turning up and forwards across the body of the mandible to pass under depressor anguli oris. The branches supply risorius and the muscles of the lower lip and chin, and join the mental nerve. The marginal mandibular branch has an important surgical relationship with the lower border of the mandible, and may pass below the lower border with a reported incidence varying between 20% and 50%, the furthest distance being 1.2 cm.
The cervical branch issues from the lower part of the parotid gland and runs anteroinferiorly under platysma to the front of the neck, to supply platysma and communicate with the transverse cutaneous cervical nerve. In 20% of cases, there are two branches.
The peripheral branches of the facial nerve described above are joined by anastomotic arcades between adjacent branches to form the parotid plexus of nerves which shows considerable variation. In surgical terms these anastomoses are important, and presumably explain why accidental or essential division of a small branch often fails to result in the expected facial nerve weakness. Six distinctive anastomotic patterns were originally classified by Davis et al (1956) and these are illustrated in Fig. 29.10. These observations have been confirmed by others, although some variation in the frequency has been reported.
Surgery of the facial nerve
When operating on the face, a detailed understanding of the anatomy of the facial nerve is essential if iatrogenic trauma is to be avoided. Three surgical manoeuvres are used to identify the facial nerve trunk as it exits the stylomastoid foramen. The blood-free plane immediately in front of the cartilaginous external acoustic meatus can be opened up by blunt dissection, and this leads the surgeon to the skull bases just superficial to the styloid process and the stylomastoid foramen. This plane can then be gently opened up in an inferior direction by further blunt dissection until the trunk of the facial nerve is encountered. Second, the trunk of the facial nerve can be identified by exposing the anterior border of sternocleidomastoid just below its insertion into the mastoid process, and retracting the muscle posteriorly to expose the posterior belly of digastric, which is then traced upwards and backwards to the mastoid process. This point lies immediately below the stylomastoid foramen and the facial nerve trunk. A third option is to identify a terminal branch of the facial nerve peripherally - commonly the marginal mandibular branch - and to trace it back centripetally until the facial nerve trunk is identified.
Complications of facial nerve dissection
UPDATE Date Added: 01 December 2004
Update: Preoperative determination of the location of parotid gland tumors by analysis of the position of the facial nerve
Knowledge of the course of the facial nerve, which separates the deep and superficial lobes of the parotid gland, is helpful in determining the location of parotid neoplasms and the resultant need for either superficial lobectomy or total parotidectomy, respectively. To date, there is no radiologic technique to visualize the facial nerve,1 but there are several predictive tools for determination of the course of the facial nerve.2-5 In this study, 2 new hypothetical lines for the determination of the facial nerve location were compared with the hypothetical facial nerve line (FN-line; connecting the lateral surface of the posterior belly of the digastric muscle to the lateral surface of the cortical bone of the ascending ramus), which has been shown to successfully diagnose the location of parotid gland tumors.5
The two new lines, connecting the most dorsal (Line 1) and the most lateral (Line 2) points visible on the ipsilateral half of the vertebra to the dorsal side of the retromandibular vein, and the FN-line, were drawn on transverse sections of 5 cadaver heads. The shortest and longest distances to the facial nerve from these lines were determined, scored, and compared (chi-squared test for significance). Line 1 had the shortest distance to the facial nerve (average shortest distance=0.8 mm), and was closest to the facial nerve in 44 cases compared with 16 cases for the FN-line (p<0.001). Line 1 also had the shortest "longest distance" in 58 cases compared with 11 cases for the FN-line (p<0.001).
These results indicate that Line 1 is superior to the FN-line for locating the facial nerve in the parotid gland. Line 1 runs nearly parallel to the course of the facial nerve in the parotid gland and would be well suited for in vivo studies because it was created on the basis of the location of the retromandibular vein, and therefore has a constant relationship to the facial nerve. Moreover a parotid gland tumor would displace the facial nerve, retromandibular vein, and Line 1 in similar manners. In contrast, a similar displacement would not occur with the digastric muscle (used to create the FN-line), which is a fixed structure outside the parotid gland. Although a predictive technique that uses a hypothetical line has obvious limitations, the new Line 1 described here shows promise for predicting the course of the facial nerve and assessing the location of parotid tumors.
1. Eracleous E, Kallis S, Tziakouri C, et al. Sonography, CT, CT sialography, MRI and MRI sialography in investigation of the facial nerve and the differentiation between deep and superficial parotid lesions. Neuroradiology. 1997; 39: 506. Medline Similar articles
2. Conn G, Wiesenfeld D, Ferguson MM. The anatomy of the facial nerve in relation to CT sialography of the parotid gland. Br J Radiol. 1983; 56: 901. Medline Similar articles
3. Rice DH, Mancuso AA, Hanfee MN. Computerized tomography with simultaneous sialography in evaluating parotid tumors. Arch Otolaryngol. 1980; 106: 472. Medline Similar articles
4. Kurabayashi T, Ida M, Ohbayashi N, et al. criteria for differentiating superficial from deep lobe tumours of the parotid gland by computed tomography. Dentomaxillofac Radiol. 1993; 22: 81. Medline Similar articles
5. Ariyoshi Y, Shimahara M. Determining whether a parotid tumour is in the superficial or deep lobe using magnetic resonance imaging. J Oral Maxillofac Surg. 1998; 56: 23. Medline Similar articles
6. de Ru JA, Bleys RLA, van Benthem PPG, Hordijk GJ. Preoperative determination of the location of parotid gland tumors by analysis of the position of the facial nerve. J Oral Maxillofac Surg. 2001; 59: 525-528, 529-530. Medline Similar articles
 
Pattern of branching of the facial nerve
    Figure 29.10 Pattern of branching of the facial nerve. (Modified with permission from Berkovitz BKB, Moxham BJ 2002 Head and Neck Anatomy. London: Martin Dunitz, and from Davis RA, Anson BJ, Budinger JM, Kurth IE 1956 Surgical anatomy of the facial nerve and parotid gland based upon a study of 350 cervicofacial halves. Surg Gynecol Obstet 102: 385-412, with permission from the American College of Surgeons.)
The facial nerve is routinely dissected as part of a superficial parotidectomy operation - typically in the treatment of parotid tumours - in which that part of the gland lying superficial to the plane of the facial nerve is removed. Although all branches of the facial nerve are preserved, there is often some postoperative facial weakness caused by bruising and ischaemia of the nerve which results in a temporary and reversible demyelination of the nerve fibres. Although this can affect all the branches of the facial nerve, the weakness is often confined to the territory innervated by the marginal mandibular branch and is manifested by a weakness of the lower lip on the affected side. This is because anastomotic arcades between the marginal mandibular branch and other branches of the facial nerve are relatively rare, whereas they are plentiful between the various branches of the temporofacial division and the buccal branch of the cervicofacial division of the facial nerve.
Facial nerve lesions
Facial nerve paralysis may be due to an upper motor neurone lesion (when frontalis is partially spared due to the bilateral innervation of the muscle of the upper part of the face), or a lower motor neurone lesion (when all branches may be involved). Bell's palsy and acoustic neuromas can produce a complete lower motor neurone facial paralysis as a result of compression of the facial nerve trunk as it passes through the middle ear. More commonly, cheek lacerations or malignant parotid tumours result in weakness in part of the face depending upon which branch of the nerve is involved. Unfortunately the presence of facial paralysis is not a reliable diagnostic sign of a malignant tumour. It is not uncommon for a facial nerve infiltrated by a malignant tumour to continue to function normally. However when paralysis does accompany a parotid mass it is certainly malignant.
UPDATE Date Added: 17 April 2006
Abstract: Temporalis muscle transposition versus free functional muscle transplantation in facial palsy
Click on the following link to view the abstract: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15468391&query_hl=12&itool=pubmed_docsum Dynamic reconstruction of eye closure by muscle transposition or functional muscle transplantation in facial palsy. Frey M, Giovanoli P, Tzou CH et al: Plast Reconstr Surg 114:865-875, 2004.


CERVICAL SPINAL NERVES (Fig. 29.9A,B)

Cervical spinal nerves have cutaneous branches which supply areas of skin in the face and scalp. The named branches are the great auricular, lesser occipital and greater occipital nerves.
Great auricular nerve
The great auricular nerve forms part of the cervical plexus (p. 555) and is derived from the anterior primary rami of the second and third cervical spinal nerves. It passes up from the neck, lying on sternocleidomastoid, towards the angle of the jaw, and supplies much of the lower part of the auricle of the ear, and skin overlying the parotid gland.
Lesser occipital nerve
The lesser occipital nerve is a branch of the cervical plexus (p. 555). It ascends along the posterior border of sternocleidomastoid to supply the scalp above and behind the ear and a small area on the cranial surface of the auricle.
Greater occipital nerve
The greater occipital nerve represents the posterior primary ramus of the second cervical spinal nerve. It pierces trapezius close to its attachment to the superior nuchal line and ascends to supply the skin of the back of the scalp up to the vertex of the skull. Greater occipital neuralgia is a syndrome of pain and paraesthesiae felt in the distribution of the greater occipital nerve and is usually due to an entrapment neuropathy of the nerve as it pierces the attachment of the neck extensors to the occiput.