The Fifth, or Trigeminal, Nerve
The fifth nerve (Fig. 47-1) is a mixed sensory and motor nerve. It conducts sensory impulses from the greater part of the face and head; from the mucous membranes of the nose, mouth, and paranasal sinuses; and from the cornea and conjunctiva. It also provides the sensory innervation of the dura in the anterior and middle cranial fossae. The cell bodies of the sensory part of the nerve lie in the gasserian, or semilunar, ganglion. This, the largest sensory ganglion in humans, lies in the inferomedial part of the middle cranial fossa in a recess called Meckel's cave. The central axons of the ganglion cells form the sensory root of the nerve. These fibers, on entering the lateral mid pons, divide into short ascending and long descending branches. The former are concerned mainly with tactile and light pressure sensation and synapse with second-order neurons in the principal sensory nucleus. Proprioceptive afferents from facial muscles and the masseter also ascend to terminate in the mesencephalic nucleus. The fibers that mediate pain and temperature sensation do not end in these nuclei but form long descending branches of the spinal trigeminal tract. This pathway, which contains both facilitatory and inhibitory fibers, together with its adjacent nucleus, extends from the junction of the pons and medulla to the uppermost segments (C2 or C3) of the spinal cord (as evidenced by the relief of facial pain after medullary trigeminal tractotomy).
Scheme of the trigeminal nuclei and some of the trigeminal reflex arcs. I, ophthalmic division; II, maxillary division; III, mandibular division. (Originally from Ramon y Cajal S: La Textura del Sistema Nervista del Hombre y los Vertebrados, Madrid, Moya, as adapted from Carpenter MB, Sutin J: Human Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1982, by permission.)
The spinal trigeminal nucleus in the upper cervical cord is a continuation of the spinal tract of Lissauer and substantia gelatinosa; the main trigeminal sensory nucleus in the pons and medulla is a continuation of the nucleus of the medial lemniscus. From all parts of the principal sensory and spinal trigeminal nuclei, second-order fibers cross to the opposite side and ascend to the thalamus. They come to lie in the most medial part of the spinothalamic tract and lateral part of the medial lemniscus. These systems of fibers are called the trigeminothalamic tract. In addition, the secondary trigeminal neurons project to the facial and hypoglossal nuclei bilaterally, the salivatory nuclei, the cuneate nuclei of the upper cervical segments, and other cranial nerve nuclei. The principal sensory and spinal trigeminal nuclei receive fibers from the reticular formation, the thalamus, the nucleus tractus solitarius, and the somatosensory cortex.
The peripheral branches of the gasserian ganglion form the three sensory divisions of the nerve. The first (ophthalmic) division passes through the cavernous sinus and superior orbital fissure; the second (maxillary) division also passes through the cavernous sinus and leaves the middle fossa through the foramen rotundum; and the third (mandibular), does not traverse the cavernous sinus and instead exits Meckel's cave inferiorly through the foramen ovale.
The motor portion of the fifth nerve, which supplies the masseter and pterygoid muscles, has its origin in the trigeminal motor nucleus in the mid pons; the exiting fibers pass underneath (but not through) the gasserian ganglion and become incorporated into the mandibular nerve. The masseter and pterygoid muscles are used in chewing and are implicated in a number of brainstem reflexes, the best known of which is the jaw jerk. Tapping the chin with the jaw muscles relaxed stimulates proprioceptive afferents that terminate in the mesencephalic nucleus of the midbrain, which sends collaterals to the motor nucleus of the fifth nerve and causes the masseters to contract. This reflex is enhanced in spastic bulbar (pseudobulbar) palsy. Another pontine reflex that uses afferent trigeminal sensory nerves is the blink reflex. Tapping of the brow or bridge of the nose evokes bilateral blink through activation of the orbicularis oculi muscles (facial nerve efferents). Touching the eyelids and cornea (corneal reflex) does the same.
Because of their wide anatomic distribution, complete interruption of both the motor and sensory fibers of the trigeminal nerve is rarely observed. In contrast, partial dysfunction of the trigeminal nerve, particularly of the sensory part, is common, the main symptoms being facial numbness and pain. The various cranial nerve and brainstem syndromes in which the fifth nerve is involved are listed in Tables 47-1, 31-5, and 34-3, the last in relation to stroke syndromes of the brainstem that affect the nerve in its fascicular course or in its nucleus.
Table 47-1 Extramedullary Cranial Nerve Syndromes ||Download (.pdf)
Table 47-1 Extramedullary Cranial Nerve Syndromes
CRANIAL NERVES INVOLVED
III, IV, ophthalmic, V, VI
Invasive tumors of sphenoid bone, aneurysms
Lateral wall of cavernous sinus
III, IV, ophthalmic (occasionally maxillary), V, VI
Aneurysms or thrombosis of cavernous sinus; invasive tumors from sinuses and sella turcica; sometimes recurrent, benign granulomatous reactions, responsive to steroids
Retrosphenoidal space fossa
II, III, IV, V, VI
Large tumors of middle cranial
Apex of petrous bone
Petrositis, tumors of petrous bone
Internal auditory meatus
Tumors of petrous bone (dermoids, etc.), vestibular schwannoma
V, VII, VIII, and sometimes IX
Vestibular schwannomas, meningiomas
IX, X, XI
Tumors (glomus jugulare), venous sinus thrombosis, and aneurysms
Posterior laterocondylar space
IX, X, XI, XII
Tumors of parotid gland, carotid body; secondary and lymph node tumors, tuberculous adenitis, carotid artery dissection
Posterior retroparotid space
IX, X, XI, XII, and Horner syndrome
Same as above, and granulomatous lesions (sarcoid, fungi)
Posterior retroparotid space
X and XII, with or without XI
Parotid and other tumors of, or injuries to, the high neck
Diseases Affecting the Fifth Nerve
A variety of diseases may affect the peripheral branches of the trigeminal nerves, the gasserian ganglion, and the roots (sensory and motor). Hughes has summarized them and the main ones are described below. The role of the nerve in migraine is discussed in Chap. 10.
(See also "Trigeminal Neuralgia" in Chap. 10) The most frequent and at the same time the most elusive disease of the fifth nerve from the standpoint of its pathologic basis is trigeminal neuralgia (tic douloureux). This condition has been known since ancient times, having been described by Arateus in the first century A.D., by John Locke in 1677, by Nicolaus Andre in 1756, and by John Fothergill in 1776 (according to Katusic et al). The overall incidence rate for both sexes combined is 4.3 per 100,000 persons per year, but it is higher for women than for men (in a ratio of 3:2) and is much higher in the elderly. The mean age of onset is 52 to 58 years for the idiopathic form and 30 to 35 years for the symptomatic forms, the latter being caused by trauma or vascular, neoplastic, and demyelinative diseases. In the last decade it has become apparent, mainly from the work of Jannetta, that a proportion of cases is a result of compression and secondary demyelination of trigeminal nerve rootlets by small branches of the basilar artery (see Love and Coakham).
The paroxysmal nature of the facial pain, its unilaterality, the tendency to involve the second and third divisions of the trigeminal nerve, an intensity that makes the patient grimace or wince (tic), the presence of a trigger point on the face, the lack of demonstrable sensory or motor deficit, and its response in more than half of the cases to antiepileptic drugs are characteristic. The diagnosis of "idiopathic" trigeminal neuralgia and its differentiation from other forms of intermittent facial pain described below—as well as from cluster headache, dental neuralgia, temporomandibular joint pain, and atypical facial pain—is usually not difficult, especially if there is a trigger point and no demonstrable evidence of sensory or motor impairment. Furthermore, the vascular compressive form is difficult to diagnose without high-resolution neuroimaging or exposure at operation and most such cases are therefore characterized as idiopathic until revealed as vascular in causation.
In rare instances, trigeminal neuralgia is preceded or accompanied by hemifacial spasm, a combination that Cushing called tic convulsif. This may be indicative of a tumor (cholesteatoma), an aneurysmal dilatation of the basilar artery or one of its branches, or an arteriovenous malformation that compresses both the trigeminal and facial nerves. Trigeminal neuralgia and glossopharyngeal neuralgia (pain in the tonsillar region) may also be combined in these conditions.
Trigeminal Neuropathies and Neuritis
Of the conditions that damage the branches of the trigeminal nerve, facial and cranial injuries, and fractures are probably the most common, but they do not usually come to the attention of neurologists. The most superficial branches of the nerve—the supratrochlear, supraorbital, and infraorbital—are the ones usually involved by trauma. The sensory loss is present from the time of the injury, and partial regeneration may be attended by constant pain.
Of the various inflammatory and infectious diseases that affect the trigeminal nerves or ganglia, herpes zoster ranks first. Persistent pain after herpetic infection of the fifth nerve is a serious problem, not responding well to any type of treatment. This subject is discussed in Chap. 10 with other forms of facial pain. Middle ear infections and osteomyelitis of the apex of the petrous bone may spread to the ganglion and root, also implicating the sixth cranial nerve (Gradenigo syndrome). HIV infection has not been clearly implicated in infection of the fifth nerve (as it has in the seventh nerve), but reactivation of latent herpes zoster is seen with AIDS.
The trigeminal root may be compressed or invaded by intracranial meningiomas, vestibular schwannomas, trigeminal schwannomas, cholesteatomas, and chordomas and by tortuous branches of the basilar artery. Sinus tumors and metastatic disease may also infiltrate the nerve, causing pain and a gradually progressive sensory loss. Demyelination at the trigeminal root entry point into the pons is another well-characterized cause in cases of multiple sclerosis (Fig. 47-2).
Left-sided facial sensory loss due to demyelination of the trigeminal root entry zone in a patient with multiple sclerosis. Abnormal enhancement of the nerve root is seen on T1 postgadolinium MRI.
The ophthalmic division of the fifth nerve may be involved in the wall of the cavernous sinus in combination with the third, fourth, and sixth nerves by a variety of processes, including thrombosis of the cavernous sinus. Tumors of the sphenoid bone (myeloma, metastatic carcinoma, squamous cell carcinoma, and lymphoepithelioma of the nasopharynx) may involve branches of the trigeminal nerve at their foramina of entry or exit. An unusual perineural infiltration of superficial branches of the nerve by squamous cell skin cancers of the face is discussed further on under "Multiple Cranial-Nerve Palsies." The mandibular division of the nerve may be compressed by the roots of an impacted third molar (wisdom) tooth. Well known to clinicians is a sign of numbness of the chin and lower lip from infiltration of the mental nerve as the first indication of metastatic carcinoma of the breast, prostate, or multiple myeloma. Massey and colleagues have described the details of 19 such cases of the "numb-chin" sign.
Neurologists also encounter instances of slowly evolving unilateral or bilateral trigeminal neuropathy in which sensory impairment is confined to the territory of the trigeminal nerve, sometimes associated with pain, paresthesias, or disturbances of taste. This type of loss of facial sensation can also occur as part of a widespread sensory neuropathy or ganglionopathy that occurs as a paraneoplastic effect of cancer (see Chap. 31) or with Sjögren disease.
As common is an association between isolated trigeminal neuropathy and immune-mediated connective tissue diseases. Of 22 such cases described by Lecky and colleagues, 9 had either scleroderma or mixed connective tissue disease, and a similar number had either organ- or nonorgan-specific serum autoantibodies. Several specific antibody tests are used to establish the diagnosis of scleroderma. The symptoms may involve the other side of the face years later. Hughes has also described cases of trigeminal neuropathy with scleroderma, lupus erythematosus, and Sjögren disease. We have seen several patients with Sjögren disease in whom the trigeminal neuropathy and the associated antibodies or inflammation of the minor salivary glands were evident well before the characteristic sicca syndrome or other systemic manifestations of the disease. The condition may remain troublesome for years. Pathologic data are limited but point to an inflammatory lesion of the trigeminal ganglion or sensory root. Stilbamidine and trichloroethylene are known to cause sensory loss, tingling, burning, and itching exclusively in the trigeminal sensory territory.
Spillane and Wells, many decades ago, discussed an isolated trigeminal neuropathy (it had been called Spillane's trigeminal neuritis). Four of their 16 patients had an associated paranasal sinusitis, but subsequent reports have failed to substantiate a causal relationship between sinusitis and cranial neuritis. One wonders how many of these individuals had connective tissue disease. A less common form of idiopathic trigeminal sensory neuropathy with which we have limited experience has an acute onset and a tendency to resolve completely or partially, in much the same manner as Bell's palsy, with which it is sometimes associated (Blau et al). A recurrent variety of acute trigeminal symptoms of uncertain origin has been reported in the dental literature. We have had experience with two patients whose facial numbness was a component of an upper cervical disc syndrome that included numbness on the same side of the body; presumably the cervical spinal trigeminal nucleus or tract was compressed. Facial numbness, of course, also occurs with diverse conditions such as syringomyelia that affect the spinal nucleus of the trigeminal nerve but there are additional signs of brainstem or upper cervical cord disease.
An idiopathic pure unilateral trigeminal motor neuropathy is known but is a clinical rarity. Chia described five patients in whom an aching pain in the cheek and unilateral weakness of mastication were the main features. Electromyography (EMG) showed denervation changes in the ipsilateral masseter and temporalis muscles. The outcome was favorable.
In most cases of trigeminal neuropathy, except those caused by tumor, herpes zoster, and demyelination, the results of gadolinium-enhanced MRI are normal, as is the cerebrospinal fluid (CSF). The function of the nerve may be studied by the recording of blink reflexes. A few laboratories have developed an evoked potential test specifically of the trigeminal nerve.
The Seventh, or Facial, Nerve
The seventh nerve is mainly a motor nerve, supplying all the muscles concerned with facial expression on one side.
The sensory component is small (the nervus intermedius of Wrisberg); it conveys taste sensation from the anterior two-thirds of the tongue and, variably, cutaneous sensation from the anterior wall of the external auditory canal. The taste fibers at first traverse the lingual nerve (a branch of the trigeminal mandibular) and then join the chorda tympani, which conveys taste sensation via the facial nerve to the nucleus of the tractus solitarius. Secretomotor fibers originate in the superior salivatory nucleus and innervate the lacrimal gland through the greater superficial petrosal nerve and the sublingual and submaxillary glands through the chorda tympani (Fig. 47-3).
Scheme of the seventh cranial (facial) nerve. The motor fibers are represented by the heavy blue line. Parasympathetic fibers are represented by regular dashes; special visceral afferent (taste) fibers are represented by long dashes and dots. A, B, and C denote lesions of the facial nerve at the stylomastoid foramen, distal to the geniculate ganglion, and proximal to the geniculate ganglion. Disturbances resulting from lesions at each of these sites are described in the text. (From Carpenter MB, Sutin J: Human Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1982, by permission.)
Several other anatomic facts are worth noting. The motor nucleus of the seventh nerve lies ventral and lateral to the abducens nucleus, and the intrapontine fibers of the facial nerve partly encircle and pass dorsolaterally to the abducens nucleus before emerging from the lower pons, just lateral to the corticospinal tract. The impression made by these looping fibers of the seventh nerve is visible in the floor of the upper fourth ventricle as a protuberance, the facial colliculus. In this region of the pons, infiltrative lesions affect the sixth and seventh nerves simultaneously.
The facial nerve enters the internal auditory meatus with the vestibulocochlear nerve bundle and then bends sharply forward and downward around the anterior boundary of the vestibule of the inner ear. At this angle (genu) lies the sensory ganglion (named geniculate because of its proximity to the genu). The nerve continues in its own bony channel, the facial canal, within which, just distal to the geniculate ganglion, it provides a branch to the pterygopalatine ganglion, i.e., the greater superficial petrosal nerve, which exits the skull through the vidian canal and innervates the lacrimal, nasal, and palatine glands. Somewhat more distally, it gives off a small motor branch to the stapedius muscle and is then joined by the chorda tympani, which projects to the submandibular ganglion and in turn, the submandibular and sublingual glands. The motor root of the facial nerve exits the skull at the stylomastoid foramen and then passes through the parotid gland and subdivides into five branches that supply the facial muscles, the stylomastoid muscle, the platysma, and the posterior belly of the digastric muscle.
A complete interruption of the facial nerve at the stylomastoid foramen paralyzes all muscles of facial expression on the same side. The corner of the mouth droops, the creases and skin folds are effaced, the forehead is unfurrowed, the palpebral fissure is widened and the eyelids will not close completely. Upon attempted closure of the lids, both eyes roll upward (Bell phenomenon), but the one on the paralyzed side remains visible because of lack of eyelid closure. The lower lid sags also, and the punctum falls away from the conjunctiva, permitting tears to spill over the cheek. (In contrast, the paralyzed frontalis muscle in patients of Asian origin sometimes lowers the eyelid and makes the palpebral fissure appear narrowed.) Food and secretions collect between the teeth and cheek, and saliva may dribble from the corner of the mouth. The patient complains of heaviness or numbness and sometimes an aching pain in the face, but sensory loss can usually not be demonstrated. Taste, however, is intact because the chorda tympani has separated from the main trunk of the facial nerve proximal to the stylomastoid foramen.
If the lesion is in the facial canal above the junction with the chorda tympani but below the geniculate ganglion, all the preceding symptoms are present but in addition, taste is lost over the anterior two-thirds of the tongue on the same side. The nerve to the stapedius muscle is also usually involved with a lesion at this site and there is hyperacusis (sensitivity to sudden loud sounds). If the geniculate ganglion or the motor root proximal to it is damaged, lacrimation and salivation may be reduced. Lesions at this point may also affect the adjacent eighth nerve, causing deafness, tinnitus, or dizziness.
The most common disease of the facial nerve is Bell's palsy (incidence rate of 23 per 100,000 people annually according to Hauser et al). The disorder affects men and women more or less equally and occurs at all ages and all times of the year. There is controversy regarding an increased incidence in women during the third trimester of pregnancy, particularly in the 2 weeks preceding delivery and in the first 2 weeks postpartum; up to a threefold increase has been cited by some authors, but others have failed to find this disproportion. Bell's palsy is probably more common in diabetic patients and possibly in those with hypertension than in the healthy population.
Regarding the causation of Bell's palsy, a viral agent has long been suspected, as was discussed by Baringer, any such a mechanism has been established with a reasonable certainty for the majority of cases. Burgess and colleagues identified the DNA of herpes simplex virus (HSV) in the geniculate ganglion of an elderly man who died 6 weeks after the onset of Bell's palsy. Murakami and coworkers (1996), using the polymerase chain reaction, found HSV type I in the endoneurial fluid surrounding the seventh nerve in 11 of 14 cases of Bell's palsy; the fluid was obtained during surgical decompression of the nerve in severe cases. The same investigators produced facial paralysis by inoculating HSV into the ears and tongues of mice; virus antigens were then found in the facial nerve and geniculate ganglion. Varicella zoster virus (VZV) was not found in any of their patients but was isolated from patients with the Ramsay Hunt syndrome, which overtly follows shingles (see further on). Patients with fracture or other infections of the temporal bone yielded neither HSV nor VZV gene sequences. In the light of these findings, the term idiopathic facial paralysis, until now the accepted synonym for Bell's palsy, is not entirely appropriate. As one might expect, the opportunity to examine the facial nerve in the course of Bell's palsy occurs very rarely. Only a handful of such cases are on record, all showing varying degrees of degeneration of nerve fibers. One case was said to show inflammatory changes, but these may have been misinterpreted (see Karnes).
The onset of Bell's palsy is acute; about one-half of cases attain maximum paralysis in 48 h and practically all within 3 or 4 days. Pain behind the ear may precede the paralysis by a day or two and in a few patients is intense and persistent. Although a report by the patient of fullness or numbness in the face is common, in a small number there is hypesthesia in one or more branches of the trigeminal nerve. The explanation of this finding is not clear. Impairment of taste is present in most patients but it rarely persists beyond the second week of paralysis. This indicates that the lesion has extended proximal to the point at which the chorda tympani joins the facial nerve. Hyperacusis or distortion of sound is then experienced in the ipsilateral ear and, as mentioned, indicates paralysis of the stapedius muscle.
The facial nerve in Bell's palsy often displays abnormal signal on gadolinium-enhanced MRI although this may be difficult to appreciate in axial sections if the change is in the vertical part of the facial canal. There is a mild increase of lymphocytes and mononuclear cells in the CSF in a few instances. Cases with more pronounced contrast enhancement of the facial nerve apparently have a worse prognosis (Kress). The enhancement presumably reflects inflammation and swelling along the course of the facial nerve.
Fully 70 percent of patients recover completely within a month or two and 85 percent achieve near-normal facial function, as reviewed by Gilden. Recovery of taste precedes recovery of motor function; if taste returns in the first week, it is a good prognostic sign. But early recovery of some motor function in the first 5 to 7 days is the most favorable sign. EMG may be of value in distinguishing temporary conduction defects from a pathologic interruption of nerve fibers; if there is evidence of denervation after 10 days, one may expect a long delay in the onset of recovery, measured in terms of months. Recovery then proceeds by axonal regeneration, a process that may take 2 years or longer and is often incomplete.
Bell's palsy recurs in approximately 8 percent of cases in several series (van Amstel and Devriese; Pitts et al), presumably as a result of reactivation of the latent herpes virus. The palsy reemerges during an infection or pregnancy, or for no apparent reason. The interval between episodes is unpredictable but has been 10 years, on average. Recurrent forms of facial paralysis also occur with Lyme disease and sarcoidosis, and in a familial variety as mentioned below.
Protection of the eye during sleep is generally employed in the management of Bells' palsy. There is no evidence that surgical decompression of the facial nerve is effective, and it may be harmful. The administration of prednisone (40 to 60 mg/d, or an equivalent corticosteroid) during the first week to 10 days after onset has been beneficial in several trials. These medications are thought to decrease the possibility of permanent paralysis from swelling of the nerve in the tight facial canal.
The finding of viral genome surrounding the seventh nerve suggested that antiviral agents might be useful in the management of Bell's palsy but most evidence from large randomized trials, particularly the one conducted by Sullivan and colleagues, fails to support the use of these drugs alone or in combination with steroids The numerous earlier studies suggesting benefit from the combined antiviral and steroid treatments must be viewed in the context of these larger prospective trials. In appropriate circumstances, testing should be undertaken for infectious causes that would require alternative therapy (e.g., Lyme, HIV, and perhaps mycoplasma) but this is not routinely required. The treatment of facial palsy caused by VZV (Ramsay Hunt syndrome) with antiviral drugs is discussed later.
Other Causes of Facial Palsy
Lyme disease commonly involves the facial nerve, as indicated in Chap. 32. The mechanism is uncertain but there is, so far, no evidence of direct spirochetal infection of the nerve. The diagnosis is likely when there has been a tick bite with well-documented erythema migrans or arthritis. Several of our Lyme-infected patients have had almost simultaneous facial palsy and mild distal sensory polyneuropathy. HIV infection is another well-known infectious cause of facial palsy. The facial palsy of both Lyme and HIV infections is associated with a pleocytosis in the spinal fluid, for which reason serologic and CSF examination may be useful if there is suspicion of either process. Rarely, chicken pox in children may be followed in 1 to 2 weeks by facial paralysis. Tuberculous infection of the mastoid and middle ear or of the petrous bone is a cause of facial paralysis in parts of the world where this infection is particularly common. Facial palsy may occur during or soon after infectious mononucleosis and was observed occasionally in poliomyelitis. The facial nerve is also frequently involved in leprosy. Bilateral involvement of the facial nerve is commented on below. The nerve is often involved in sarcoidosis, where the lesion is probably in the meninges as discussed in the following section.
The Ramsay Hunt syndrome, caused by herpes zoster of the geniculate ganglion, consists of a facial palsy associated with a vesicular eruption in the external auditory canal, other parts of the cranial integument, and mucous membrane of the oropharynx. This infection may be initially indistinguishable from Bell's palsy as the vesicles may not become apparent for days, or they never appear. Often the eighth cranial nerve is affected as well, causing nausea, vertigo, and deafness. Murakami and colleagues (1998) showed that the virus can be detected even before the emergence of typical vesicles by collecting exudate from the skin of the pinna on a Schirmer strip (otherwise used to quantitate tearing) and applying polymerase chain reaction (PCR) techniques. In this way, in a matter of a few hours, they documented VZV infection in 71 percent of patients with Ramsay Hunt syndrome without vesicles. Currently, treatment with acyclovir, valacyclovir, or famciclovir is recommended, and there is no clear role for corticosteroids. The randomized trial by Whitley et al and review by Sweeney and Gilden are recommended to the interested reader.
Tumors of the parotid gland or ones that invade the temporal bone (carotid body, cholesteatoma, and dermoid) or granulomatosis including the earlier mentioned sarcoidosis, or pachymeningitis at the base of the brain may produce a facial palsy; the onset is insidious and the course progressive. Fracture of the temporal bone (usually with damage to the middle or internal ear), otitis media, and middle ear surgery are uncommon causes. The orientation of the petrous fracture determines the prognosis (see discussion in Chap. 35). Acoustic neuromas, neurofibromas, glomus jugulare tumors, and aneurysmal dilatations of the vertebral or basilar artery may involve the facial nerve. Pontine lesions, most often vascular or neoplastic, cause facial palsy, usually in conjunction with other neurologic signs. Weakness of only a portion of the facial musculature, associated with numbness in the same region, may be the result of perineural tumor invasion by squamous cell or other skin cancers (see further on under "Multiple Cranial-Nerve Palsies"). An autosomal dominant syndrome of facial palsy, multiple truncal café-au-lait spots and mild developmental delay was described by Johnson and colleagues.
Bell's palsy may be bilateral, but only rarely is the involvement on the two sides simultaneous. The truly contemporaneous appearance of bilateral facial paralysis (facial diplegia) is most often a manifestation of the Guillain-Barré syndrome (GBS) and may also occur in Lyme disease and rarely, with HIV infection. There are numerous other causes of bilateral facial palsy, all of them infrequent. Keane (1994) listed the idiopathic (now presumably mainly viral) variety, GBS, and meningeal infiltration by tumor as the most common causes, but also found two cases of syphilis among 43 patients. The bilateral syndrome has been reported in approximately 7 of every 1,000 patients with sarcoidosis, although our impression is that it is more frequent. When acute in onset and associated with parotid gland swelling from sarcoidosis, it has been referred to as uveoparotid fever, or Heerfordt syndrome. In typical cases of sarcoidosis, the paralysis on each side tends to be temporally separated by weeks or more. Mononucleosis may affect both sides of the face almost simultaneously; this is probably a form of GBS. Bifacial palsy is also a feature of the developmental disorder, Möbius syndrome (see Chap. 38).
Less common is the Melkersson-Rosenthal syndrome, consisting of the triad of recurrent facial paralysis, facial (particularly labial) edema, and less constantly, plication of the tongue. The syndrome begins in childhood or adolescence and may be familial. Biopsy of the lip or skin may reveal a granulomatous inflammation. The cause is not known and, despite the cardinal feature of angioneurotic edema, complement levels are normal. A series of biopsied cases has been reported by Elias and colleagues.
Kennedy syndrome, causes bifacial weakness in addition to bulbar palsy as the disease progresses; preceding facial fasciculations are characteristic. Facioscapulohumeral muscular dystrophy, as the name implies, incorporates facial weakness but would not be mistaken for Bell's palsy (see Chap. 48). The same is true for the rare form of amyloidosis associated with crystal lattice deposits in the cornea that typically involves both facial nerves.
Causes of recurrent Bell's palsy have been listed earlier and are summarized by Pitts and colleagues.
Facial Hemiatrophy (Parry-Romberg Syndrome)
This obscure disorder occurs mainly in females and is characterized by a disappearance of fat in the dermal and subcutaneous tissues on one or both sides of the face, giving the appearance of facial paresis. It usually begins in adolescence or early adulthood and is slowly progressive. In its advanced form, the affected side of the face is gaunt and the skin thin, wrinkled, and rather dark; the hair may turn white and fall out, and the sebaceous glands become atrophic; the muscles and bones are not involved as a rule. The condition is a form of lipodystrophy, but the localization within a myotome suggests the operation of some neural factor (possibly a growth factor) of unknown nature. A variegated coloration of the iris and a congenital oculosympathetic paralysis are found in some cases. Rarely, certain central nervous system abnormalities referable to the ipsilateral hemisphere (mainly focal seizures, migraine, trigeminal neuralgia, and ventricular dilatation), are conjoined (Hosten). The significance of these associations is unclear. Wilson and Hoxie have pointed out the frequent coexistence of facial asymmetry in adults with congenital or early onset superior oblique palsy and compensatory head tilt or torticollis.
Aberrant Effects of Recovery from Facial Nerve Palsy
If a peripheral facial paralysis has existed for some time and return of motor function has begun but is incomplete, a contracture with diffuse myokymic activity may appear. The palpebral fissure becomes narrowed, and the nasolabial fold deepens. Spasms of facial muscles may develop and persist indefinitely, being initiated by any facial movement. With the passage of time, the corner of the mouth and even the tip of the nose may become pulled to the affected side. This is a special acquired form of hemifacial spasm, the more common variety of which is described below.
Anomalous or aberrant regeneration of the seventh nerve fibers, following Bell's palsy or other injury, may result in other curious disorders that represent limited types of synkineses. The most common is the "jaw-winking" phenomenon (also called Wartenberg or inverse Marcus-Gunn sign), in which jaw movements, especially lateral movements (engaging the pterygoid muscle), cause an involuntary closure of the eyelid ipsilateral to the movement. If regenerating fibers originally connected with the orbicularis oculi become connected with the orbicularis oris, closure of the lids may cause a retraction of the corner of the mouth; or if visceromotor fibers originally innervating the salivary glands later come to innervate the lacrimal gland, anomalous tearing (crocodile tears) occurs whenever the patient salivates. A similar mechanism explains gustatory sweating of the cheek and upper lip.
The facial muscles on one side may be involved in painless irregular clonic contractions of varying degree (hemifacial spasm). This condition usually develops in the fifth and sixth decades, affects women more than men, and often proves to be caused by a compressive lesion of the facial nerve, usually by a tortuous branch of the basilar artery that lies on the ventral surface of the pons and forms a loop under the proximal seventh nerve. Less often the cause of compression is a fusiform basilar artery aneurysm or a vestibular schwannoma or meningioma. Multiple sclerosis is another rare cause.
The spasm usually begins in the orbicularis oculi muscle and gradually spreads to other muscles on that side of the face, including the platysma. Paroxysms may be induced or aggravated by voluntary and reflexive movements of the face.
The pathophysiology of the spasm is believed to be focal demyelination at the site of nerve root compression by the vessel. The demyelinated axon is presumed to activate adjacent nerve fibers by ephaptic transmission ("artificial" synapse of Granit et al). Another possible source of the spasm is spontaneous ectopic excitation arising in injured fibers. Nielsen and Jannetta have shown that ephaptic transmission disappears after the nerve is decompressed.
Jannetta has attributed virtually all cases to a compression of the root of the facial nerve by an aberrant looped blood vessel. Microsurgical decompression of the root with the interposition of a pledget between the vessel and the facial nerve relieved the facial spasm in most of his operative patients. These results were corroborated by Barker and associates in a series of 705 patients followed postoperatively for an average period of 8 years; 84 percent achieved an excellent result. An even higher rate of benefit was obtained in a prospective series by Illingworth and colleagues (cure of 81 of 83 patients).
Surgical decompression of the aforementioned vascular loop, which involves exploration of the posterior fossa, however, carries some risk. The facial muscles may be weakened, sometimes permanently. Another complication has been deafness as a result of injury of the adjacent eighth nerve. Also, there is a risk of recurrence of the spasms, usually within 2 years of the operation (Piatt and Wilkins). Tight dural closure is required to prevent CSF leakage from the posterior fossa.
We suggest that patients with idiopathic hemifacial spasm should first be treated medically. Alexander and Moses noted that carbamazepine in doses of 600 to 1,200 mg/d controls the spasm in two-thirds of the patients. Baclofen or gabapentin can be tried if carbamazepine fails. Some patients cannot tolerate these drugs, have only brief remissions, or fail to respond; they may be treated with botulinum toxin injected into the orbicularis oculi and other facial muscles. The hemifacial spasms are relieved in this way for 4 to 5 months and injections can be repeated without danger. Some patients have been injected repeatedly for more than 5 years without apparent adverse effects. Failing these conservative measures, surgery may be appropriate.
Other Disorders of the Facial Nerve
Facial myokymia is a fine rippling activity of all the muscles of one side of the face mentioned earlier and in Chap. 48. It develops most often in the course of multiple sclerosis or a brainstem glioma, and can be seen in some disorders of the neuromuscular junction (e.g., neuromyotonia). It has also occurred after other diseases of the facial nerve, e.g., in GBS, in which case it is usually bilateral. We have seen it more often in the recovery stage than in the early phase of GBS. The fibrillary nature of the involuntary movements and their arrhythmicity tend to distinguish them from the coarser intermittent facial spasms and contracture, tics, tardive dyskinesia, and clonus. The EMG pattern is one of spontaneous asynchronous discharge of adjacent motor units, appearing singly or in doublets or triplets at a rate varying from 30 to 70 cycles per second. Demyelination of the intrapontine part of the facial nerve and possibly supranuclear disinhibition of the facial nucleus, have been the postulated mechanisms. But the observation of facial myokymia in GBS informs us that the abnormal movement may have its origin in a lesion at any point along the nerve.
A clonic or tonic contraction of one side of the face may be the sole manifestation of a cerebral cortical seizure. Involuntary recurrent spasm of both eyelids (blepharospasm, as discussed in Chaps. 6 and 14) may occur with almost any form of dystonia, but is most frequent in elderly persons as an isolated phenomenon, and there may be varying degrees of spasm of the other facial muscles (see Chap. 6). Although relaxant and tranquilizing drugs are of little help in this disorder, injections of botulinum toxin into the orbicularis oculi muscles give temporary or lasting relief. A few of our patients have been helped (paradoxically) by L-dopa; baclofen, clonazepam, and tetrabenazine in increasing doses may be helpful as well. In the past, failing these measures, the periorbital muscles were destroyed by injections of doxorubicin or surgical myectomy. With the advent of botulinum treatment, there is no longer a need to resort to these extreme and irreversible measures. In some cases, blepharospasm subsides spontaneously. Rhythmic unilateral myoclonus, akin to palatal myoclonus (actually a tremor as noted in Chap. 6), may be restricted to facial, lingual, or laryngeal muscles.
Hypersensitivity of the facial nerve occurs in hypocalcemic tetany; spasm of the facial muscles is elicited by tapping in front of the ear (Chvostek sign) but this phenomenon is seen in many normal individuals.
The Ninth, or Glossopharyngeal, Nerve
This nerve arises from the lateral surface of the medulla by a series of small roots that lie just rostral to those of the vagus nerve. The glossopharyngeal, vagus, and spinal accessory nerves leave the skull together through the jugular foramen and are then distributed peripherally. The ninth nerve is mainly sensory, with cell bodies in the inferior, or petrosal, ganglion (the central processes of which end in the nucleus solitarius) and the small superior ganglion (the central fibers of which enter the spinal trigeminal tract and nucleus). Within the nerve are afferent fibers from baroreceptors in the wall of the carotid sinus and from chemoreceptors in the carotid body. The baroreceptors are involved in the regulation of blood pressure, and chemoreceptors are responsible for the ventilatory responses to hypoxia. The somatic efferent fibers of the ninth nerve are derived from the nucleus ambiguus, and the visceral efferent (secretory) fibers, from the inferior salivatory nucleus. These fibers contribute in a limited way to the motor innervation of the striated musculature of the pharynx (mainly of the stylopharyngeus, which elevates the pharynx), the parotid gland, and the glands in the pharyngeal mucosa. A discussion of its role in swallowing is found in Chap. 26.
It is commonly stated that this nerve mediates sensory impulses from the faucial tonsils, posterior wall of the pharynx, and part of the soft palate as well as taste sensation from the posterior third of the tongue. However, an isolated lesion of the ninth cranial nerve is a rarity and therefore the effects are not fully known. In one personally observed case of bilateral surgical interruption of the ninth nerves, verified at autopsy, there had been no demonstrable loss of taste or other sensory or motor impairment. This suggests that the tenth nerve may be responsible for these functions, at least in some individuals. The role of the ninth nerve in the reflex control of blood pressure and ventilation has been alluded to earlier but referable clinical manifestations from damage of this cranial nerve are infrequent except perhaps for syncope as noted below.
One may occasionally observe glossopharyngeal palsy in conjunction with vagus and accessory nerve involvement because of a tumor in the posterior fossa or an aneurysm or intracranial dissection of the vertebral artery, or thrombosis of the sigmoid sinus or internal jugular vein. The nerves may be compressed as they pass through the jugular foramen. Hoarseness as a result of vocal cord paralysis, some difficulty in swallowing, deviation of the soft palate to the sound side, anesthesia of the posterior wall of the pharynx, and weakness of the upper trapezius and sternomastoid muscles make up the clinical picture (see Table 47-1, jugular foramen syndrome). On leaving the skull, the ninth, tenth, and eleventh nerves lie adjacent to the cervical internal carotid artery, where they can be damaged (presumably made ischemic) by a dissection of that vessel.
(See additional discussion of this subject in Chap. 10)
This disorder, first described by Weisenburg in 1910, resembles trigeminal neuralgia in many respects except that the unilateral stabbing pain is localized to one side of the root of the tongue and throat. It is far less common than trigeminal neuralgia. Sometimes the pain overlaps the vagal territory beneath the angle of the jaw and external auditory meatus. It may be triggered by coughing, sneezing, swallowing, and pressure on the tragus of the ear. Temporary blocking of the pain by anesthetizing the tonsillar fauces and posterior pharynx with 10 percent lidocaine spray is diagnostic. Rarely, herpes zoster may involve the glossopharyngeal nerve. Fainting as a manifestation of vagoglossopharyngeal neuralgia is described in Chap. 10.
The same antiepileptic and other drugs that are helpful in the treatment of tic douloureux may be used to treat glossopharyngeal neuralgia, but their efficacy is difficult to judge. Regarding vascular compression of the nerve as a cause of glossopharyngeal neuralgia, Resnick and colleagues have reported the results of microvascular decompression of the ninth nerve in 40 patients; in 32 of these, relief of symptoms was complete and was sustained during an average followup of 4 years; 3 patients remained with permanent weakness of structures ostensibly innervated by the ninth nerve. A similar high rate of success has been achieved by others. If syncope is associated with the pain, it can be expected to cease with abolition of the attacks of pain. Syncope can also occur when the ninth nerve is involved by tumors of the parapharyngeal space; most of these are squamous cell carcinomas and both the ninth and tenth nerves are implicated. Section of rootlets of the ninth nerve has reportedly reduced or abolished the episodes of fainting in these cases.
The Tenth, or Vagus, Nerve
This nerve has an extensive sensory and motor distribution and important autonomic functions. It has two ganglia: the jugular, which contains the cell bodies of the somatic sensory nerves (innervating the skin in the concha of the ear), and the nodose, which contains the cell bodies of the afferent fibers from the pharynx, larynx, trachea, esophagus, and thoracic and abdominal viscera. The central processes of these two ganglia terminate in relation to the nucleus of the spinal trigeminal tract and the tractus solitarius, respectively. The motor fibers of the vagus are derived from two nuclei in the medulla—the nucleus ambiguus and the dorsal motor nucleus. The former supplies somatic motor fibers to the striated muscles of the larynx, pharynx, and palate; the latter supplies visceral motor fibers to the heart and other thoracic and abdominal organs. The distribution of vagal fibers is illustrated in Fig. 47-4, and their participation in swallowing is described in Chap. 26, which the reader is encouraged to consult.
Anatomic features of the vagus nerve. Note the relationship to the spinal-accessory and glossopharyngeal nerves at the jugular foramen and the long course of the left recurrent laryngeal nerve, which is longer than the right and hooks around the aortic arch (not shown).
Complete interruption of the intracranial portion of one vagus nerve results in a characteristic pattern of paralysis. The soft palate droops on the ipsilateral side and does not rise in phonation. The uvula deviates to the normal side on phonation, but this is an inconstant sign in disease. There is loss of the gag reflex on the affected side and of the curtain movement of the lateral wall of the pharynx, whereby the faucial pillars move medially as the palate rises in saying "ah." The voice is hoarse, often nasal, and the vocal cord on the affected side lies immobile in a "cadaveric" position, i.e., midway between abduction and adduction. With partial lesions, movements of abduction are affected more than those of adduction (Semon's law). There may be a loss of sensation at the external auditory meatus and back of the pinna. Usually no change in visceral function can be demonstrated with a unilateral lesion except by special autonomic testing. If the pharyngeal branches of both vagi are affected, as in diphtheria, the voice has a nasal quality, and regurgitation of liquids through the nose occurs during the act of swallowing.
Diseases Affecting the Vagus
Complete bilateral paralysis is said to be incompatible with life, and this is probably true if the nuclei are entirely destroyed in the medulla by poliomyelitis or some other disease. However, in the cervical region, both vagi were blocked with procaine in the treatment of intractable asthma in past days without mishap. Of interest in this regard, Johnson and Stern reported a case of bilateral vocal cord paralysis in association with familial hypertrophic polyneuropathy, and Plott relates three brothers with congenital laryngeal abductor paralysis caused by bilateral dysgenesis of the nucleus ambiguus. Bannister and Oppenheimer have called attention to defects of phonation and laryngeal stridor as early features of autonomic failure in multiple system atrophy (see Chap. 39). We have seen several such patients in whom stridor was a prominent feature of the illness, in one patient for almost a year before other features of the degenerative disease became evident.
The vagus nerve may be implicated at the meningeal level by tumors neoplastic meningitis, and infectious processes and within the medulla by vascular lesions (e.g., the lateral medullary syndrome of Wallenberg, as described in Chap. 34), by motor neuron disease, and occasionally by sarcoid. Herpes zoster may attack this nerve, either alone or together with the ninth nerve as part of a jugular foramen syndrome. The vagus is often affected along with the glossopharyngeal nerve in spontaneous dissection of the carotid artery at the base of the skull. The nerves may be damaged in the course of thyroid surgery and may be involved in cases of advanced alcoholic or diabetic neuropathy. A fact of some importance is that the left recurrent laryngeal nerve, because of its long course under the aortic arch, is damaged as a result of thoracic disease. There is no dysphagia with lesions at this point in the nerve because the branches to the pharynx (but not to the larynx) have already been given off. For this reason, an aneurysm of the aortic arch, an enlarged left atrium, mediastinal lymph nodes from bronchial carcinoma, and a mediastinal or superior sulcus lung tumor are more frequent causes of an isolated (left) vocal cord palsy than are intracranial diseases. Finally, the vagus is compressed by lesions of the jugular foramen as part of a multiple cranial nerve syndrome as summarized in Table 47-1; metastatic tumors such as from the prostate or breast and jugular vein thrombosis are typical causes.
It is estimated that in one-quarter to one-third of all cases of paralysis of the recurrent laryngeal nerve no cause can be established, i.e., they are idiopathic. The highest incidence is in the third decade, and males are more susceptible than females. Of the 21 cases reported by Blau and Kapadia, 5 recovered completely and 5 partially within a few months; no other disease appeared in the 8-year period that followed. Berry and Blair described palsies of the superior and recurrent laryngeal nerves, occurring as part of isolated vagal neuropathies. A few were bilateral and, again, the majority of the cases were idiopathic and had much the same prognosis as isolated palsies of the recurrent laryngeal nerve.
Laryngeal neuralgia is a rare entity in which paroxysms of pain are localized over the upper portion of the thyroid cartilage or hyoid bone on one or both sides. The pain may be evoked by coughing, yawning, talking, or sneezing. In the case reported by Brownstone and coworkers, the symptoms were relieved by carbamazepine.
Neurologic Diagnosis of Vocal Cord Paralysis
When confronted with a case of vocal cord palsy, the physician is advised to determine the site of the lesion. If intramedullary, there are usually ipsilateral cerebellar signs, loss of pain and temperature sensation over the ipsilateral face and contralateral arm and leg, and an ipsilateral Bernard-Horner syndrome (see Table 34-3). If the lesion is extramedullary but intracranial, the glossopharyngeal and spinal accessory nerves are frequently involved as well (jugular foramen syndrome; see Table 47-1). If extracranial in the posterior lateral condylar or retroparotid space, there may be a combination of ninth, tenth, eleventh, and twelfth cranial-nerve palsies and a Horner syndrome. Combinations of these lower cranial-nerve palsies, which have a variety of eponymic designations (see Table 47-1) are caused by various tumors, both primary and metastatic, or by chronic inflammations or granulomas involving lymph nodes at the base of the skull. If there is no palatal weakness and no pharyngeal or palatal sensory loss, the lesion is below the origin of the pharyngeal branches, which leaves the vagus nerve high in the cervical region. The usual site of disease is then the mediastinum.
The Eleventh, or Spinal Accessory, Nerve
This is a purely motor nerve, of spinal rather than cranial origin. Its fibers arise from the anterior horn cells of the upper four or five cervical segments and enter the skull through the foramen magnum. Intracranially, the accessory nerve travels for a short distance with the part of the tenth nerve that is derived from the caudalmost cells of the nucleus ambiguus; together, the two roots are referred to as the vagal-accessory nerve or the cranial root of the accessory nerve. The two roots together leave the skull through the jugular foramen. The vagus fibers then rejoin the main trunk of the vagus. The motor fibers derived from the upper cervical segments of the spinal cord form an "external ramus" and innervate the ipsilateral sternocleidomastoid and trapezius muscles. Only the somatic motor fibers constitute the accessory nerve in the strict sense. In patients with torticollis, however, division of the upper cervical motor roots or the spinal accessory nerve has often failed to ablate completely the contraction of the sternocleidomastoid muscle. This suggests a wider innervation of the muscle, perhaps by fibers of apparent vagal origin that join the accessory nerve for passage through the jugular foramen.
A complete lesion of the accessory nerve results in weakness of the sternocleidomastoid muscle and upper part of the trapezius (the lower part of the trapezius is innervated by the third and fourth cervical roots through the cervical plexus). Weakness can be demonstrated by asking the patient to shrug his shoulders; the affected side will be found to be weaker, and there will often be evident atrophy of the upper part of the trapezius. With the arms at the sides, the shoulder on the affected side droops and the scapula is slightly winged; the latter defect is accentuated with lateral movement of the arm (with serratus anterior weakness, winging of the scapula is more prominent and occurs on forward elevation of the arm). When the patient turns his head forcibly against the examiner's hand, preferably starting with the head deviated to the opposite side, the sternocleidomastoid of the opposite side does not contract firmly beneath the fingers. This muscle can be further tested by having the patient press his head forward against resistance or lift his head from the pillow.
Motor neuron disease, poliomyelitis, syringomyelia, and spinal cord tumors may involve the cells of origin of the spinal accessory nerve. In its intracranial portion, the nerve is usually affected along with the ninth and tenth cranial nerves by herpes zoster or by lesions of the jugular foramen (glomus tumors, neurofibromas, metastatic carcinoma, internal jugular vein thrombosis). Tumors at the foramen magnum may also damage the nerve. In the posterior triangle of the neck, the eleventh nerve can be damaged during surgical operations and by external compression or injury. Compressive-invasive lesions of this nerve may be visualized by CT or MRI of the posterior cervical space.
A benign disorder of the eleventh nerve, akin to Bell's palsy, has been described by Spillane and by Eisen and Bertrand. It begins with pain in the low lateral neck that subsides in a few days and is followed by weakness and atrophy in the distribution of the nerve. Also, a recurrent form of spontaneous accessory neuropathy has been described (Chalk and Isaacs). About one-quarter to one-third of eleventh nerve lesions are estimated to be of this idiopathic type; most, but not all, of the patients recover.
Bilateral sternocleidomastoid and trapezius palsy, which occurs with primary disease of muscles—e.g., polymyositis and muscular dystrophy—may be difficult to distinguish from a bilateral damage to the accessory nerves or the motor nuclei (progressive bulbar palsy). The supranuclear innervation of the spinal accessory nuclei is apparently mainly ipsilateral as evidenced by contraversive turning of the head during a seizure, the result of contraction of the ipsilateral sternocleidomastoid muscle. Whether this is attributable to a direct ipsilateral tract, or to double crossing of the supranuclear tracts, is not known.
The Twelfth, or Hypoglossal, Nerve
This is also a pure motor nerve, which supplies the somatic musculature of the tongue. It arises as a series of rootlets that issue from the ventral medulla between the pyramid and inferior olivary complex. The nerve leaves the skull through the hypoglossal foramen and innervates the genioglossus muscle, which acts to protrude the tongue; the styloglossus, which retracts and elevates its root; and the hypoglossus, which causes the upper surface to become convex. Complete interruption of the nerve results in paralysis of one side of the tongue. The tongue curves slightly to the healthy side as it lies in the mouth, but on protrusion it deviates to the affected side, owing to the unopposed contraction of the healthy genioglossus muscle. By pushing against the tongue in the cheek, one can judge the degree of weakness. The tongue also cannot be moved with natural facility, causing difficulty with handling food in the mouth as well as mild but characteristic lingual dysarthria. The denervated side becomes wrinkled and atrophied, and fasciculations can be seen.
Isolated lesions of the hypoglossal nerve roots are rare. Occasionally an intramedullary lesion, usually a stroke, damages the emerging fibers of the hypoglossal nerve, corticospinal tract, and medial lemniscus (see Table 34-3). The result is paralysis and atrophy of one side of the tongue, together with spastic paralysis and loss of vibration and position sense in the opposite arm and leg. Poliomyelitis and motor neuron disease may destroy the hypoglossal nuclei. The latter is the most common cause of a bilaterally atrophic and fasciculating tongue. Lesions of the basal meninges and of the occipital bones (tumor invasion, platybasia, invagination of the occipital condyles, Paget disease) may involve the nerve in its extramedullary course, and it is sometimes damaged in operations on the neck including carotid endarterectomy. Goodman and coworkers showed a dissecting aneurysm of the carotid artery to have compressed the hypoglossal nerve, with resultant weakness and atrophy of the tongue. Rare instances of temporal arteritis and Takayasu arteritis affecting the carotid artery and adjacent twelfth nerve have been described. Lance and Anthony have described the simultaneous occurrence of nuchal-occipital pain and ipsilateral numbness of the tongue, provoked by the sudden, sharp turning of the head and termed it the neck–tongue syndrome. The phenomenon has been attributed to compression in the atlantoaxial space of the second cervical root, which carries some of the sensory fibers from the tongue, via the hypoglossal nerve, to the C2 segment of the spinal cord.
It is worth mentioning here that the tongue is often red and smooth in vitamin-deficiency states. Glossodynia (burning mouth syndrome discussed in Chap. 10), a condition most frequently seen in the elderly and in young women, may or may not be accompanied by redness and dryness, but not by lingual weakness. A habit of tongue-thrusting and teeth-clenching is often associated. The ascription of these motor abnormalities to a psychogenic mechanism does not agree with the authors' experience (see Quinn).