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Keywords:

  • anatomy;
  • surgery;
  • skull base;
  • iatrogenic injury;
  • communicating;
  • anastomoses

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

Descriptions of the anatomy of the neural communications among the cranial nerves and their branches is lacking in the literature. Knowledge of the possible neural interconnections found among these nerves may prove useful to surgeons who operate in these regions to avoid inadvertent traction or transection. We review the literature regarding the anatomy, function, and clinical implications of the complex neural networks formed by interconnections among the lower cranial and upper cervical nerves. A review of germane anatomic and clinical literature was performed. The review is organized in two parts. Part I concerns the anastomoses between the trigeminal, facial, and vestibulocochlear nerves or their branches with any other nerve trunk or branch in the vicinity. Part II concerns the anastomoses among the glossopharyngeal, vagus, accessory and hypoglossal nerves and their branches or among these nerves and the first four cervical spinal nerves; the contribution of the autonomic nervous system to these neural plexuses is also briefly reviewed. Part I is presented in this article. An extensive anastomotic network exists among the lower cranial nerves. Knowledge of such neural intercommunications is important in diagnosing and treating patients with pathology of the skull base. Clin. Anat. 27:118–130, 2014. © 2013 Wiley Periodicals, Inc.

“… Nerves … by free communication between neighboring branches form a plexus or network from which emerge finally the nerve trunks. … A knowledge of these networks is essential to the study of nerve wounds.”

Silas Wier Mitchell, 1872 (quoted from Brown et al., 1988).

INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

The neural anastomotic network between the lower cranial and upper cervical nerve is complex and shows considerable individual variability. Knowledge of the anatomy of these neural connections is particularly important during neck surgery including various nerve transfer procedures, skull base surgery, as well as for understanding the pathophysiology of various skull base and neck disorders (Brown, 2002). Moreover, clinical presentations and exams following nerve injury may have unanticipated findings based on such variable neural interconnections. This anatomy, therefore, deserves to be expounded upon just as other neural plexuses e.g. brachial and lumbosacral plexuses.

During fetal development, the fibers of the vagus, accessory, and hypoglossal nerves are closely associated with each other and the communications they receive from the cervical nerves further complicate their embryogenesis (Streeter, 1904; Downman, 1939; Schneider et al., 1996). Streeter (1904) noted a common ganglion crest of the hindbrain in a human embryo of ∼20 days gestation, which was located ventrolateral to the neural tube and extended from the otic vesicle rostrally to the first cervical nerve caudally (Figs. 1A–1D). This ganglion crest is interrupted proximally by a cleft; the small, rostral and larger caudal cell masses were the anlages of the glossopharyngeal nerve and the vagus-accessory nerve complex, respectively. With further development, the nerve fibers sprout from the ventral and dorsal borders of the crest to form the nerve trunks. The vagus and accessory nerves develop from a same anlage. The glossopharyngeal anlage is initially separate from the vagus-accessory anlage (Streeter, 1904). Later, when a nerve trunk ganglion (ganglion petrosum of glossopharyngeal and ganglion nodosum of vagus) develops in the fibers originating from the ventral border of the ganglion crest, the two anlages partially merge and become continuous (Fig. 1B). The hypoglossal nerve develops independently. However, with development of nearby structures, the ganglia and nerve fibers of the lower cranial nerves and first cervical nerve are brought close together, which gives them an opportunity to anastomose and exchange nerve fibers (Streeter, 1904). It is prudent to assume that some of these anastomoses occur by chance due to the proximity of nerve trunks and their branches during embryogenesis, and that they may not reflect a programmed development. Therefore, it is not surprising that these nerves will communicate randomly and may be quite variable in this respect (May and Gasser, 2000). On the other hand, some anastomoses occur in a significant percentage of cases and tend to be more consistent, probably implying a programmed development.

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Figure 1. Development of the last cranial nerves and the upper cervical nerves in human embryos at 3 weeks old (A), 4 weeks old (B and C), and 5 weeks old (D) (Reproduced with permission from Streeter, Am J Anat, 1904, 4, 83–116, ©John Wiley & Sons, Inc.). Note that the anlages of the glossopharyngeal, vagus and accessory nerves merge together through their ganglia and nerve roots. The cranial nerves are shown by Roman numerals. mn, masticatory nerve (motor root of the trigeminal nerve); mnn, mandibular nerve; mxn, maxillary nerve; ng, nodose ganglion; on, ophthalmic nerve; ot, otic vesicle; pg, petrous ganglion; sln, superior laryngeal nerve.

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To our knowledge, a comprehensive review of the literature regarding neural connections of trigeminal, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves as well as cervical spinal nerves 1-4 is not extant. Therefore, the aim of this review is to provide the surgeon and clinician with detailed information regarding the variable neural connections in the craniocervical region so that potential complications from operating in this area can be minimized (Reichman and Simon, 2004). Most of the anastomoses described in this review have been detected through gross or stereomicroscopic dissections. The current review is organized into two parts. Part I addresses the anastomoses among the trigeminal, facial, and vestibulocochlear nerves or their branches with any other nerve trunk or branch in the vicinity. Part II addresses the anastomoses among the glossopharyngeal, vagus, accessory, and hypoglossal nerves and their branches or among these nerves and the first four cervical spinal nerves; the contribution of the autonomic nervous system to the neural plexus of interest is also briefly reviewed. Part I is presented in this article.

TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

Although there are instances of anastomoses of various branches of the trigeminal nerve with each other, the majority of trigeminal nerve interconnections are with the facial nerve (May, 2000). In 1974, Baumel stated that the cutaneous branches of all three divisions of the trigeminal nerve show variable anastomoses with branches of the facial nerve. Martin and Helsper (1957) reported that as trigeminal to facial nerve connections were closely associated with motor endplates, voluntary motor impulses might find their way from the brain to facial muscles by way of such interconnections. It is quite possible that the proprioceptive innervation of the facial muscles traverses the peripheral trigeminal-facial nerve communications. Moreover, through its communications with other cranial nerves, the sensory and parasympathetic neural fibers classically belonging to the distribution of facial nerve may also travel through an alternative pathway (Sachs, 1968; Woodburne and Burkel, 1994). This explains why lacrimation and the sense of taste are sometimes preserved following transection of the nervus intermedius (nerve of Wrisberg) for treatment of facial neuralgia (Sachs, 1968).

Auriculotemporal Branch of the Trigeminal Nerve

Baumel et al. (1971) described the auriculotemporal-facial nerve communication as the strongest and most consistent of all the facial nerve communications. Kwak et al. (2004) reported connections between the facial and auriculotemporal nerves as occurring within the parotid gland in 93.3% of cases. Also, they reported that the communicating auriculotemporal nerve joined the temporofacial division of the facial nerve at the posterior border of the masseter muscle (Fig. 2). Namking et al. (1994) traced the fibers of the communicating auriculotemporal nerves in the facial nerve branches and found that they consistently innervated some of the muscles of upper facial expression, including the frontalis, orbicularis oculi and zygomaticus major muscles.

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Figure 2. Anastomosis of the auriculotemporal nerve with the temporofacial division of the facial nerve and anastomosis of the greater auricular nerve with the cervicofacial division of the facial nerve at the parotid and peri-parotid regions (Reproduced with permission from Testut, Tratado de anatomia humana, tomo tercero, sexta edicion, 1902, ©Salvat with slight modifications).

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In addition to communicating with the branches of the facial nerve, the auriculotemporal nerve occasionally anastomoses with other branches of the trigeminal nerve, notably the zygomaticotempral branch of the zygomatic branch of the maxillary nerve and the inferior alveolar nerve (a branch of the mandibular nerve). The connection of the auriculotemporal nerve (posteriorly) with zygomaticotempral nerve (anteriorly) has been noted superficially within the temporal fossa in ∼13% of specimens (Tubbs et al., 2012). A branch from the auriculotemporal nerve may occasionally join the inferior alveolar nerve within the infratemporal fossa, and this anastomosis may lead to pain being referred from the anatomical territory of one nerve to the other. In a study of 32 infratemporal fossae, this anastomosis was found on four sides (∼13%) (Gülekon et al., 2005). Other sporadic reports of this variant also exist in the literature (Shoja et al., in press; Anil et al., 2003). Notably, in such cases, the second part of the maxillary artery passes through the neural loop formed by the auriculotemporal nerve, its communicating branch and proximal portion of the mandibular nerve (Anil et al., 2003; Gülekon et al., 2005).

Buccal Branch of the Trigeminal Nerve or Long Buccal Nerve

These nerve anastomoses occur most commonly via the so-called “communicating buccal nerve” (Scähfer and Thane, 1903; Braus, 1960; Pegington, 1986; Hendy et al., 1996; Tohma et al., 2004). Tohma et al. (2004) reported observing the communicating buccal nerve at the outer layer of deep fascia of the anterior portion of the buccinator muscle in all their dissections. These authors also described several branches of the communicating buccal nerve that joined proximally with the zygomatic and buccal branches of the facial nerve (Hendy and Robinson, 1994). Bernstein and Nelson (1984), Fujita (1934), and Pons-Tortella (1947) also reported twigs of the communicating buccal nerve joining the lower buccal branch of the facial nerve. The twigs, which joined the lower buccal branch of the facial nerve, emerged from the communicating buccal nerve both anterior and posterior to the facial vein (Fujita, 1934; Pons-Tortella, 1947; Bernstein and Nelson, 1984; Tohma et al., 2004). In terms of the function of this communication, several authors (DeLacure et al., 1990; Tanaka, 1994; Cheney et al., 1997) have described the communicating buccal nerve as a possible explanation of motor pathways following facial nerve injury (Hendy et al., 1996).

Mental Branch of the Trigeminal Nerve

Hwang et al. (2004) reported interconnections between the marginal mandibular branch of the facial nerve and mental nerve in all of their cases. Shimada et al. (1994) found the same connection as well as one between the mental nerve and the buccal branch of the facial nerve (Hwang et al., 2007).

Lingual Branch of the Trigeminal Nerve

The well-known connection between the lingual nerve and the chorda tympani branch of the facial nerve forms when the embryo is 18 mm in length (Futamura, 1906; Gasser, 1969; Gasser et al., 1994). The fibers of the chorda tympani widely distribute within the lingual nerve and do not show a consistent and discernible pattern (Girod et al., 1989). Because of such irregularity in the fiber distribution, repair of a transected lingual nerve seldomly leads to regeneration of the gustatory fibers (Girod et al., 1989; McManus et al., 2011).

Infraorbital Branch of the Trigeminal Nerve

Hu et al. (2007), as well as Hwang et al. (2004), have described the infraorbital nerve and facial nerves as forming the infraorbital plexus at the level of the infraorbital foramen. In these cases, the lateral-most divisions of the lateral branches of the superior labial branch of the infraorbital nerve communicated with the zygomatic branch of the facial nerve (Hwang et al., 2005). Ferreira et al. (1997) described the infraorbital nerve as providing motor innervation to the levator labii superioris muscle along with the inferior branch of the zygomatic branch of the facial nerve.

Branches of the Zygomatic Branch of the Trigeminal Nerve

Shimada et al. (1994) described connections between the zygomaticotemporal nerve and temporal branches of the facial nerve and between the zygomaticofacial nerve and zygomatic branches of the facial nerve. The former anastomosis (one or two in number), which penetrates the superficial layer of the deep temporal fascia, has been found at ∼3.5 cm lateral to the lateral canthus in 14 out of 17 specimens and contains proprioceptive and/or motor fibers (Odobescu et al., 2012). Well known is the branch that unites the lacrimal and zygomaticotemporal nerve inside the orbit (Fig. 3), thus providing parasympathetic fibers to the lacrimal gland (Bourgery and Jacob, 1831; Jones, 1946; Clara, 1959). Traction on the zygomaticotemporal nerve during pterional craniotomies may potentially injure the postganglionic fibers carried by its communicating branch to the lacrimal nerve, resulting in a dry eye (Tubbs et al., 2012).

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Figure 3. Anastomosis between the lacrimal nerve and zygomaticotemporal branch of the zygomatic nerve (a branch of the maxillary nerve) within the orbit (Reprinted with permission from Tubbs et al., World Neurosurg, 2012, 78, 515–518, ©Elsevier).

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Cutaneous Branches of the Ophthalmic Division of the Trigeminal Nerve

Hwang et al. (2005) reported that the horizontal branch of the supraorbital nerve may join the temporal branch of the facial nerve in 44% of cases. Infrequently mentioned is a branch of the facial nerve that connects to the external nasal nerve (Duke-Elder, 1961; Loukas et al., 2011).

FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

Cruveilhier (1844) described interconnecting fibers between the facial and vestibulocochlear nerves within the internal acoustic meatus (Fig. 4). Paturet (1951) described several patterns of this neural connection within the internal acoustic meatus. He found consistent connections between the nervus intermedius (nerve of Wrisberg) and the vestibular nerve as well as between fibers of the genu of the facial nerve and the vestibular ganglion (Scarpa's ganglion) (Fisch, 1973). Additionally, he described an inconsistent pattern of communication between the facial and vestibular nerve bundles, an observation that was later confirmed (House, 1961; Fish and Esslen, 1972). Özdogmus et al. (2004) reported a connection between the superior vestibular and facial nerves, but no connection between the cochlear and facial nerves. Nageris et al. (2000) noted a communication between the facial and vestibular nerves in 14 of 17 specimens. They observed that the connection occurred between the facial and either superior or inferior vestibular nerves, showing no consistent pattern. Chouard (1975) correlated Meniere's disease to such connections.

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Figure 4. Bischoff's illustrations demonstrating variable interneural connections between the facial (a) and vestibulocochlear (b) nerves. The greater petrosal nerve is seen as (d) and fibers of the nervus intermedius is seen as (c) (see Mikroskopische Analyse der Anastomosen der Kopfnerven; Bischoff, 1865).

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Clinically, this vestibular-facial communication is significant due to reports of patients developing spontaneous nystagmus and vertigo as a side-effect of facial nerve block for the treatment of hemifacial spasm (Wakasugi, 1972). Additionally, such connections have been implicated in the vestibular disturbance seen in patients with facial paralysis (Fisch and Esslen, 1972). Sachs (1968) reported a patient with facial neuralgia in whom sectioning of the nervus intermedius did not relieve the pain. Stimulation of the eighth cranial nerve resulted in facial pain, and neuralgia subsided subsequent to its resection. He concluded that the anastomoses, which existed between the nervus intermedius and eighth cranial nerve within internal auditory canal, allowed sensory impulses from the facial nerve distribution to bypass this nerve into the eighth cranial nerve.

FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

According to Monkhouse (1990), there are several means by which connections between the facial and glossopharyngeal nerves are established: (1) through a branch from the geniculate ganglion of the facial nerve into the middle cranial fossa to join the lesser petrosal nerve (Vidic and Wozniak, 1969), (2) through a branch from the facial nerve in the facial canal to the tympanic plexus, (3) through a branch from the nerve to the posterior belly of the digastric muscle, and (4) through a branch from the chorda tympani in the infratemporal fossa. However, other types of communication between the facial nerve with the glossopharyngeal may exist, either directly connecting their trunks or indirectly connecting one of their branches. A direct communicating branch to the glossopharyngeal nerve may arise from the trunk of the facial nerve immediately after it exits the stylomastoid foramen; this branch has been noted by Salame et al. (2002) in 2 of 46 sides (4%) and was found to originate from the facial nerve before the origin of the posterior auricular nerve. This inconstant and direct connection between the two nerve trunks is sometimes referred to as the ansa of von Haller (Fig. 5), which forms a loop in front of the internal jugular vein and connects the facial nerve with the glossopharyngeal nerve slightly below its inferior ganglion (Testut, 1902; Gould, 1904). Notably, communications between the glossopharyngeal nerve with the facial (or one of its branches) or with the vagus nerve have variably been referred to as von Haller's ansa (or ansa of von Haller) in the literature. Henle (1871) referred to anastomoses between a branch of the glossopharyngeal nerve and the styloid (or stylohyoid) branch of the facial nerve as ansa Halleri Sappey (Haller-Sappey ansa) and postulated that it contains facial nerve motor fibers, which ultimately depart through the branches of the glossopharyngeal nerve (Fig. 6).

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Figure 5. Schematic drawing showing connections between cranial nerves VII, IX, and X and some of their branches. Notable here is the loop-shaped connection (black star) between the proximal portions of the facial and glossopharyngeal nerve trunks.

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Figure 6. Haller-Sappey ansa (Reproduced with permission from Henle, Handbuch der systematischen anatomie des menschen: Nervenlehre, 1871, 424–426, ©Vieweg with modification). Note the styloid branch of the facial nerve receives a communication from the glossopharyngeal nerve and then divides into the digastric and stylohyoid nerve branches to supply the posterior belly of the digastric muscle and stylohyoid muscle, respectively. Note the Y-shaped communication between the pharyngeal branches of the vagus and glossopharyngeal nerves as both branches join to form a single trunk before supplying the pharynx.

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In the middle ear, the tympanic plexus is formed on the tympanic promontory by branches of Jacobson's nerve (tympanic branch of the glossopharyngeal nerve) and caroticotympanic nerves originating from the internal carotid artery plexus (Fig. 7). This plexus, which also receives a branch from the facial nerve in the facial canal, largely supplies the mucosa of the middle ear. The chorda tympani communicates with the tympanic plexus within the tympanic cavity (Knight and Bryant, 1909). The communication between the facial nerve and the lesser petrosal nerve at the level of the geniculate ganglion has been mentioned by several authors (Cochet 1967; Vidic and Young, 1967; Nageris et al., 2000). Some authors have mentioned a neural branch connecting the sympathetic plexus around the middle meningeal artery with the geniculate ganglion (Holden, 1891); this branch is known as the external petrosal nerve and travels extradurally lateral to the greater and lesser petrosal nerves on the anterior surface of the petrous ridge before joining the geniculate ganglion (Fig. 8). The functional significance of this anastomosis is unknown.

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Figure 7. The tympanic and internal carotid artery plexuses and their communications. Tympanic plexus (1) is formed by the tympanic branch of the glossopharyngeal nerve (2), and superior (3) and inferior (4) caroticotympanic nerves from the internal carotid artery sympathetic plexus (5). Lesser petrosal nerve (6) is derived from tympanic plexus and is joined by a branch from the facial nerve, known as the communicating branch of facial nerve with tympanic plexus (7). The latter usually arises from the geniculate ganglion, and in such cases, it is also referred to as the geniculotympanic nerve. The lesser petrosal nerve mainly contains preganglionic parasympathetic fibers of the glossopharyngeal nerve and ultimately ends in the otic ganglion (7). The greater petrosal nerve (8) branches from the geniculate ganglion, contains preganglionic parasympathetic fibers of the facial nerve and is joined by a branch from the carotid sympathetic plexus—known as the deep petrosal nerve (9)—to form the vidian nerve (10), which ultimately ends in the pterygopalatine (Meckel's) ganglion (11). Carotid plexus also communicates with Gasserian ganglion and abducens nerve (not shown here) (Cunningham, 1903).

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Figure 8. Communicating branch of the geniculate ganglion of the facial nerve with the sympathetic plexus surrounding the middle meningeal artery (Reproduced with permission from Holden, Manual of the Dissection of the Human Body, 1891, ©P. Blakiston, Son & Co. with slight modifications). Note that geniculate ganglion gives rise to the greater petrosal nerve, communicates with the lesser petrosal nerve and receives sympathetic fibers from the plexus surrounding the middle meningeal artery. The nerve connecting the latter with the geniculate ganglion is known as the external petrosal nerve. The greater, lesser and external petrosal nerves are superficial petrosal nerves.

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In an interesting macroscopic and stereomicroscopic dissection of 490 head sides, Kawai et al. (1989) distinguished three types of facial nerve-glossopharyngeal nerve communication at the posterior digastric region in 18.8% of neck sides. In the majority of cases (88%), the anastomotic loop or ansa pierced the posterior belly of the digastric muscle and partly travelled within this muscle before re-emerging (Fig. 9); this neural communication is the Haller-Sappey ansa mentioned by Henle in 1871. In the remaining 12% of neck sides, the ansa either travelled medial or lateral to the posterior digastric belly. These authors also made other interesting observations: (1) only in a portion of specimens, the intramuscular ansa supplied motor branches to the posterior digastric belly. This indicated that the ansa does not essentially serve to supply motor innervation to the posterior digastric belly; (2) after travelling medial, lateral or within the posterior digastric belly, the communicating branch joined with either stylohyoid or digastric branches en route to the facial nerve and sometimes with the nerve trunk directly; (3) in all cases, the communication between the facial and glossopharyngeal nerves originated from the latter; (4) the fibers traversing the communication ultimately entered the facial nerve and were distributed through two facial nerve branches destined to the posterior auricular region; (5) in addition to the above-mentioned anastomoses at the region of the posterior belly of the digastric muscle, Kawai et al. (1989) also noted more distally located communications between the cervical branch of the facial nerve and a glossopharyngeal nerve branch coursing lateral to the posterior digastric belly. The distal anastomosis was present in a very small percentage of specimens (∼1%) with or without an associated proximal anastomosis (Kawai et al., 1989). Ultimately, these authors concluded that the facial nerve-glossopharyngeal nerve anastomosis as exemplified in Figure 9 in fact represents the auricular branch of the glossopharyngeal nerve (Kawai et al., 1989).

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Figure 9. The communication between the glossopharyngeal and facial nerves travelling through the posterior belly of the digastric muscle (Reproduced with permission from Spalteholz, Hand-Atlas of Human Anatomy, Viscera, Brain, Nerves, Sense-Organs, 1923, Vol. III, ©J.B. Lippincott Company with modifications). Note that in this case, the ansa is continuous with a digastric branch of the facial nerve. Other communications are seen in this picture: (1) connection of the glossopharyngeal nerve with the jugular nerve of the superior cervical sympathetic ganglion and the nodose ganglion of the vagus nerve and (2) connection between the auricular nerve of the vagus nerve and the facial nerve trunk.

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The greater petrosal branch of the facial nerve is joined by a small ascending branch, the sphenoidal branch, from the otic ganglion while traversing the pterygoid canal (Pick, 1901; Krmpotic et al., 1965; Last, 1984; Drummond, 1988; Kakizawa et al., 2007). Monkhouse (1990) mentioned another connection with the otic ganglion, this time directly from the chorda tympani as it emerges from the skull in the infratemporal fossa, eventually providing parasympathetic secretomotor innervation to the parotid gland. The secretomotor innervation of the parotid gland by the chorda tympani is clinically significant as secretions of the parotid gland are reduced by ∼50% following an ipsilateral chorda tympani lesion (Vollrath et al., 1982). It is not clear whether these parotid parasympathetic fibers belong to the nervus intermedius or if they are carried by the branches of the glossopharyngeal nerve, which ultimately join the facial nerve intratemporally or the chorda tympani in its intratemporal or infratemporal course. Monkhouse (1990) described yet another connection whereby the facial nerve provides a twig in the facial canal that joins the tympanic plexus. The lesser petrosal branch of the glossopharyngeal nerve receives a communicating branch composed of fibers from the nervus intermedius and the auricular branch of the vagus nerve (Arnold's nerve) from the facial nerve either at the geniculate ganglion (geniculotympanic nerve), distal to the geniculate ganglion, or from the greater petrosal nerve (Popowsky, 1895; Vidic and Young, 1967; Kakizawa et al., 2007; Tubbs et al., 2009).

Müller and Rude (2000) described an anastomosis between the facial and glossopharyngeal nerves near the skull base that was formed by an ascending branch of the stylopharyngeal or tonsilar branches of the glossopharyngeal nerve and a branch from the stylohyoid branch of the facial nerve. Notably, concomitant anastomoses were also found between the ascending branch of the glossopharyngeal nerve and the sympathetic plexus around the internal carotid artery. Therefore, it was postulated that the ascending branch serves to transmit parasympathetic and gustatory fibers of the facial nerve to and from the oropharyngeal region and also provide sympathetic innervation to this region (Müller and Rude, 2000).

FACIAL TO VAGUS NERVE ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

Gasser et al. (1994) reported a branch of the facial nerve arising from its rostral side in the embryo between the origins of the stapedius and chorda tympani nerves and coursing toward the external acoustic meatus. He described it as providing a few fibers, which communicate with a plexus located lateral to the glossopharyngeal and vagus nerves. Monkhouse (1990) reported that the communicating fibers may arise from the posterior auricular branch of the facial nerve. The communications between the auricular branch of the vagus nerve and the facial nerve and its posterior auricular branch will be discussed in detail later (please see part II).

FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

The facial nerve connects to multiple cutaneous branches of the cervical plexus. These are outlined below.

Anastomoses With the Great Auricular Nerve (C2–C3)

Schäfer and Thane (1903) have described a communicating branch between the facial nerve and the great auricular nerve (Fig. 2). This nerve consists of branches from cervical nerves C2 and C3 and supplies the skin of the parotid and mastoid regions, as well as the outer ear (Gasser, 1967; Moore and Dalley, 1999; Ginsberg and Eicher, 2000). Occasionally, more than one communicating branch from the great auricular nerve exists. These branches originate from the great auricular nerve after it turns around the posterior border of the sternocleiodmastoid muscle, and join the cervicofacial devision, cervical or mandibular branches of the facial nerve (Sappey, 1872; Testut, 1902; Brown et al., 1988). The great auricular nerve may also communicate with the posterior auricular branch of the facial nerve (Sappey, 1872).

Anastomoses With the Greater and Lesser Occipital Nerves (C2)

Schäfer and Thane (1903) and Baumel (1974) reported connecting branches between the facial nerve and greater and lesser occipital nerves. This so-called facial-lesser occipital communication has been described as involving the posterior auricular branch of the facial nerve (Baumel, 1974; Nageris et al., 2000; Loukas et al., 2011).

Anastomoses With the Transverse Cervical Nerve (C2–C3)

Domet et al. (2005) found that the transverse cervical nerve sends one to two communicating branches to the cervical branch of the facial nerve that make a consistent [faciocervical] anastomosis inferior or posterior to the submandibular gland and sometimes, within the parotid gland.

VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

The communication between the vestibular and cochlear nerves is known as von Oort's anastomosis; this anastomosis usually occurs within the internal auditory canal and rarely within the cerebellopontine angle (Ozdoğmuş et al., 2004; Tian et al., 2008; Unel et al., 2012). Labrousse et al. (2004) found this anastomosis to have an average diameter of 0.5 mm and average length of 0.5-1 mm at the bottom of the internal auditory meatus in seven out of 10 specimens (70%). Tian et al. (2008) described the vestibulocochlear anastomoses as a single connecting branch or a brush-like nerve fiber bundle in 24 out of 30 cadaveric specimens (80%). In a magnetic resonance imaging study, theses connections were noted in 31 out of 138 ears (∼22%), and in the majority of cases, it was located in the midportion of the auditory canal. Using scanning electron microscopy, Ozdoğmuş et al. (2004) revealed that the Oort's anastomosis is specifically between the inferior vestibular and cochlear nerves. Some authors have postulated an afferent role for the vestibulocochlear anastomosis, stating that it accounts for the persistence of tinnitus in some cases after cochlear neurectomy (if it conveys the afferent cochlear fibers to the brain stem cochlear nucleus through the vestibular nerve) or persistence of vertigo in some cases after vestibular neurectomy (if it conveys the afferent vestibular fibers to the brain stem vestibular nucleus through the cochlear nerve) (Ozdoğmuş et al., 2004; Unel et al., 2012). An efferent role has also been suggested. For example, the uncrossed and crossed fibers of the olivocochlear bundle originating from the ipsilateral and contralateral brainstem superior olivary complex initially travel in the vestibular nerve (Møller, 2011). These fibers then enter the cochlear nerve through Oort's anastomosis to ultimately end in the cochlear outer hair cells; this pathway is responsible for the otoacoustic emissions or sounds generated intrinsically within the cochlea (Møller, 2011).

CONCLUSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES

There is considerable number of anastomoses among trigeminal, facial and vestibulocochlear nerves or their branches and other nearby nerve trunks or branches (Table 1). Various motor-to-motor, motor-to-sensory and sensory-to-sensory nerve communications exist. The anastomoses between the sensory and motor nerves often provide a route for distribution of proprioceptive fibers. Several examples of these anastomoses and their functional significance are discussed in this review. The functional significance of some of the anastomoses are yet to be fully understood. The anatomy of the anastomoses among the cranial nerves or their branches needs to be understood as such anastomoses are subject to inadvertent sacrifce during intracranial, skull base, or upper neck surgeries.

Table 1. The Neural Anastomoses of the Trigeminal, Facial, and Vestibulocochlear Nerves or Their Branches
Cranial nerveAnastomoses
Trigeminal nerve (CN V)1. Auriculotemporal nerve (a branch of mandibular nerve) with the temporofacial division of the facial nerve.
2. Auriculotemporal nerve (a branch of mandibular nerve) with the zygomaticotemporal nerve (a branch of maxillary nerve).
3. Auriculotemporal nerve (a branch of mandibular nerve) with the inferior alveolar nerve (a branch of mandibular nerve).
4. Lacrimal nerve (a branch of the ophthalmic nerve) with zygomaticotemporal nerve (a branch of maxillary nerve).
5. Long buccal nerve (from mandibular nerve) with the zygomatic and buccal branches of the facial nerve.
6. Mental nerve (from inferior alveolar nerve) with the marginal mandibular branch of the facial nerve.
7. Lingual nerve (from mandibular nerve) with chorda tympani branch of the facial nerve.
8. Infraorbital nerve (a branch of maxillary nerve) with the zygomatic branch of the facial nerve.
9. Supraorbital nerve (from the ophthalmic nerve) with the temporal branch of the facial nerve.
10. External nasal nerve (from anterior ethmoidal nerves, a branch of the ophthalmic nerve) with a branch from the facial nerve.
11. Otic ganglion with the chorda tympani
Facial nerve (CN VII)1. Facial nerve with the superior or inferior vestibular nerve.
2. Geniculate ganglion or main trunk with the lesser petrosal nerve.
3. Geniculate ganglion with the sympathetic plexus around the middle meningeal artery.
4. Greater petrosal nerve with the lesser petrosal nerve.
5. A twig from the main trunk with the tympanic plexus.
6. Main facial nerve trunk with the main trunk of glossopharyngeal nerve.
7. Main trunk or its digastric, styloid or stylohyoid branch with a cummunicating branch form the glossopharyngeal nerve (aka ramus communicans nervi facialis cum nervo glossopharyngeo).
8. Cervical branch of the facial nerve with a branch from the glossopharyngeal nerve.
9. Stylohyoid branch with the ascending branch of the stylopharyngeal or tonsilar branches of the glossopharyngeal nerve.
10. Main facial nerve trunk with the auricular branch of the vagus nerve.
11. Greater petrosal nerve with the sphenoidal (ascending) branch of the otic ganglion.
12. Posterior auricular nerve with the auricular branch of the vagus nerve.
13. Chorda tympani with the tympanic plexus.
14. Chorda tympani with the lingual nerve
Vestibulocochlear nerve (CN VIII)1. Cochlear nerve with the inferior vestibular nerve.
2. Superior vestibular nerve with the inferior vestibular nerve.
3. Superior vestibular nerve with the facial nerve.
4. Inferior vestibular nerve with the facial nerve

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. TRIGEMINAL TO TRIGEMINAL AND TRIGEMINAL TO FACIAL NERVE ANASTOMOSES
  5. FACIAL TO VESTIBULOCOCHLEAR NERVE ANASTOMOSES
  6. FACIAL TO GLOSSOPHARYNGEAL NERVE ANASTOMOSES
  7. FACIAL TO VAGUS NERVE ANASTOMOSES
  8. FACIAL NERVE TO CERVICAL PLEXUS ANASTOMOSES
  9. VESTIBULAR TO COCHLEAR NERVE ANASTOMOSES
  10. CONCLUSION
  11. ACKNOWLEDGMENT
  12. REFERENCES
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