Disorders of cranial nerves - detailed technical article.
- The olfactory nerve
- Third, fourth, and sixth cranial nerves
- Pupillary abnormalities
- Trigeminal nerve
- Trigeminal neuralgia
- Facial nerve
- Glossopharyngeal nerve
- Vagus nerve
- Spinal accessory nerve
- The hypoglossal nerve
- Further reading
The 12 cranial nerves are peripheral nerves except for the optic nerve which is a central nervous system tract. Disorders of particular note include the following: Olfactory (I) nerve—anosmia is most commonly encountered as a sequel to head injury.
Third, fourth, and sixth cranial nerves—complete lesions lead to the following deficits (1) third nerve—a dilated and unreactive pupil, complete ptosis, and loss of upward, downward and medial movement of the eye; (2) fourth nerve—extorsion of the eye when the patient looks outwards, with diplopia when gaze is directed downwards and medially; (3) sixth nerve—convergent strabismus, with inability to abduct the affected eye and diplopia maximal on lateral gaze to the affected side. The third, fourth, and sixth nerves may be affected singly or in combination: in older patients the commonest cause is vascular disease of the nerves themselves or their nuclei in the brainstem. Other causes of lesions include (1) false localizing signs—third or sixth nerve palsies related to displacement of the brainstem produced by supratentorial space-occupying lesions; (2) intracavernous aneurysm of the internal carotid artery—third, fourth, and sixth nerve lesions. Lesions of these nerves can be mimicked by myasthenia gravis.
Pupillary abnormalities—these include (1) constriction (miosis)—due to paralysis of the sympathetic innervation (Horner’s syndrome); (2) dilatation—due to lesions of the third nerve. Trigeminal nerve—pathology causes numbness and tingling of the side of the face and scalp back to the vertex, loss of the corneal reflex and deviation of the jaw to the affected side. May be affected by intramedullary lesions, during the intracranial part of its course, and extracranially. Trigeminal neuralgia is usually due to compression of the nerve by aberrant vessels in the posterior fossa. It is characterized by paroxysms of intense pain strictly confined to the nerve’s distribution and often responsive to carbamazepine.
Facial nerve—in upper (but not lower) motor neuron lesions there is relative preservation of power in the upper facial muscles. In Bell’s palsy, onset is rapid and frequently heralded or accompanied by aching pain in or around the ear: treatment with prednisolone improves the prognosis. Hemifacial spasm is characterized by irregular clonic or simultaneous twitching movements of the facial muscles, usually of insidious onset; injections of botulinum toxin may be helpful. Glossopharyngeal nerve—rarely affected in isolation, when it is very difficult to detect any neurological deficit; usually affected in combination with the vagus nerve.
Vagus nerve—important symptoms of damage relate to pharyngeal and laryngeal innervation producing a bulbar palsy with dysphonia, dysathria and dysphagia. Causes include brainstem stroke, motor neuron disease, malignant infiltration anywhere along the course of the nerve and cranial polyneuropathy. Spinal accessory nerve—may be affected by lesions, often neoplastic, in the region of the jugular foramen, but more commonly by injuries to the neck or by operations for the removal of cervical glands.
Hypoglossal nerve—may be affected by tumours in the region of the anterior condyloid foramen, or by tumours or penetrating injuries in the neck. The commonest cause of bilateral lesions is the progressive bulbar palsy variant of motor neuron disease.
Multiple cranial neuropathies (cranial polyneuropathy) may be due to inflammatory conditions (such as Guillain–Barré syndrome, Miller Fisher syndrome, vasculitis, Wegener’s granulomatosis, sarcoidosis); infections (such as tuberculosis, Lyme borreliosis); diabetes mellitus; meningeal carcinomatosis or lymphomatosis; or may be mimicked by myasthenia gravis, motor neuron disease, or myopathies. Cranial MRI and cerebrospinal fluid analysis are the key investigations.
Bulbar palsy is the syndrome of abnormality of cranial nerves arising from the medulla oblongata (nerves IX, X, XI, and XII). Tongue wasting and fasciculations, absent gag reflex, and flaccid dysarthria with nasal regurgitation distinguish this lower motor neuron syndrome from pseudobulbar palsy which is an upper motor neuron lesion of the medulla. A unilateral lesion of nerves V, VII, and VIII suggests pathology in the cerebellopontine angle such as vestibular schwannoma.
The olfactory nerve
Loss of the sense of smell (anosmia) is most commonly encountered as a sequel to head injury and is probably related to severance of the central processes of the olfactory neurons as they pass through the cribriform plate to the olfactory bulb. It is usually permanent. Distortion of olfaction (parosmia) may occur and may be persistent. The sense of smell is occasionally congenitally absent or may be acutely and permanently lost after a coryzal infection. Bilateral anosmia is frequently accompanied by impairment of taste related to reduced detection of the volatile substances that impart flavours to foods. Unilateral anosmia may occur in olfactory groove meningiomas or other subfrontal tumours. This is usually not detected by the patient.
The central connections of the olfactory pathways are complex and include projections to the temporal lobes, hypothalamus, septal region, and amygdaloid nuclei. Olfactory hallucinations occur as a manifestation of temporal lobe epilepsy. Identification of odours may be impaired after bilateral medial temporal lesions and may be defective in multiple sclerosis, possibly as the result of demyelination in the olfactory tracts. Reduced sense of smell occurs in idiopathic Parkinson’s disease but not other forms. Complaints of hypersensitivity of the sense of smell commonly have a psychoneurotic basis and persistent olfactory hallucinations may be reported by psychotic patients. Persistent parosmia is sometimes produced by lesions of the temporal lobe.
Third, fourth, and sixth cranial nerves
The third, or oculomotor, nerve supplies all the external ocular muscles with the exception of the superior oblique and lateral rectus. It also carries the parasympathetic innervation of the preganglionic pupilloconstrictor fibres of the iris. A complete third nerve lesion produces a dilated and unreactive pupil, complete ptosis, and loss of upward, downward, and medial movement of the eye. The eye becomes deviated laterally and slightly downwards. Diplopia is only experienced when the lid is lifted.
The fourth or trochlear nerve supplies the superior oblique muscle. Following a lesion of this nerve, there is extorsion of the eye when the patient looks outwards. When the patient looks downwards and medially, diplopia is experienced. This is particularly disturbing because looking downwards is important for walking and especially descending stairs. The patient may compensate for this by tilting the head to the opposite side.
The sixth or abducent nerve supplies the lateral rectus. A lesion of this nerve causes convergent strabismus, inability to abduct the affected eye, and diplopia which is maximal on lateral gaze to the affected side.
The third, fourth, and sixth nerves may be affected singly or in combination, and the paralysis may be complete or partial. In some instances, the lesion is within the brainstem, where it may affect either the nuclei or the intramedullary portions of the nerve fibres. In older patients, the commonest cause is vascular disease.
Extramedullary lesions of the third, fourth, and sixth nerves are more frequent and may occur at any point along their course, either intracranially or within the orbit. A third nerve palsy may develop in the region of the tentorial hiatus as a false localizing sign related to displacement of the brainstem produced by supratentorial space-occupying lesions. Unilateral or bilateral sixth nerve palsies may also arise as a consequence of raised intracranial pressure, probably caused by traction, again secondary to brainstem displacement. These nerves can be involved singly or together in conditions such as chronic basal meningitis or carcinoma of the skull base. Gradenigo’s syndrome comprises a sixth nerve palsy and pain of trigeminal distribution. It is produced by a lesion at the apex of the petrous temporal bone. As this syndrome was most commonly infective in origin and related to chronic middle ear disease, it is now much less frequent.
The third, fourth, and sixth nerves traverse the cavernous sinus, as do the first and second divisions of the trigeminal nerve. In this situation, they are most commonly damaged by an intracavernous aneurysm of the internal carotid artery. The third nerve is affected more often than the fourth or sixth. The consequent internal and external ophthalmoplegia is frequently accompanied by pain, and sometimes sensory loss and paraesthesiae in the corresponding frontal region related to compression of the first division of the trigeminal nerve. Sometimes pain occurs in the cheek from damage to the maxillary division. In the superior orbital fissure syndrome, caused for example by a tumour invading the fissure, a total ophthalmoplegia may result, associated with pain and sensory loss in the distribution of the first division of the trigeminal nerve. The eye is often proptosed because of obstruction of the ophthalmic vein. The Tolosa–Hunt syndrome consists of a painful external ophthalmoplegia related to a granulomatous angiitis. Within the orbit, the third, fourth, and sixth nerves may be affected by conditions such as tumours and granulomas. They may be damaged as a result of trauma at any point along their course and may be affected singly or in combination or as part of a cranial neuropathy, of which diabetes, the Fisher syndrome, Lyme borreliosis, vasculitis, and sarcoidosis are the most important examples. Internal and external ophthalmoplegias are common and this list of nerve lesions causing the syndrome is by no means exhaustive. External ophthalmoplegia may also be caused by myasthenia or myopathy.
Constriction of the pupil (miosis) occurs as a result of paralysis of the sympathetic innervation of the pupillodilator fibres of the iris and may be accompanied by the other features of Horner’s syndrome, mild ptosis and vasodilatation and anhidrosis of the face on the same side. The ocular manifestations may be encountered alone if the damage is restricted to the intracranial portion of the sympathetic plexus around the carotid artery. Raeder’s syndrome consists of these components of Horner’s syndrome together with involvement of the first division of the trigeminal nerve. It may be caused by tumours of the skull base. Miosis may also be produced by the local action of cholinergic drugs and by morphine and related compounds.
Pupillary dilatation may be caused by lesions of the third nerve. The isolated third nerve palsies of presumed vascular origin that may occur in diabetes mellitus characteristically spare the pupil. In contradistinction, compressive lesions of the nerve, for instance by an aneurysm or transtentorial brain herniation, involve the pupil prominently and early. Anticholinergic drugs, such as atropine and related substances, and cocaine also cause pupillary dilatation.
The Argyll–Robertson pupil is small, fails to react to light, but constricts on ocular convergence, and, if bilateral, the pupils are frequently unequal in size (anisocoria). The pupil may be irregular in outline and does not dilate fully in response to mydriatics. Argyll–Robertson pupils are almost always related to neurosyphilis but somewhat similar pupils are occasionally encountered in diabetic neuropathy, in some hereditary neuropathies and following the use of atropine-like eyedrops.
In the Holmes–Adie syndrome, the pupil is tonic and reacts abnormally slowly both to light and on convergence, but particularly so for the response to illumination. A very bright light may be required to demonstrate any pupillary constriction. If the patient remains in a dark room for some minutes, the pupil slowly dilates. The condition may be unilateral or bilateral and is commoner in women than men. Tonic pupils may be associated with absence or depression of the tendon reflexes and occasionally with anhidrosis in the limbs.
The fifth cranial nerve is predominantly sensory in function, but also innervates the muscles of mastication. It emerges from the pons and runs forwards to the Gasserian ganglion which is situated in Meckel’s cave near the apex of the petrous temporal bone. The three sensory divisions of the nerve run anteriorly from the ganglion. The first or frontal division passes through the cavernous sinus and the superior orbital fissure. Its branches supply sensation to the anterior part of the scalp, the forehead, and the eye, including the conjunctiva and cornea. The second or maxillary division leaves the skull through the foramen rotundum, traverses the infraorbital canal, and supplies the cheek. The mandibular division emerges from the skull through the foramen ovale to reach the infratemporal fossa with the motor root with which it unites to form a single trunk. It is distributed to the lower lip, chin, and the lower part of the cheek, and its auriculotemporal branch supplies the tragus of the ear and temple. It also supplies the inner aspect of the cheek and the anterior two-thirds of the tongue, and its lingual branch carries taste fibres from the anterior two-thirds of the tongue which leave it in the chorda tympani to join the facial nerve. It is important that the skin over the angle of the jaw is supplied from the second cervical nerve root, and the absence of this ‘trigeminal notch’ may be useful in distinguishing hysterical or feigned loss of sensation on the face which usually follows the angle of the jaw.
The motor root innervates temporalis, masseter, pterygoids, mylohyoid, the anterior belly of the digastric, and also tensor tympani and tensor palati muscles. With unilateral paralysis of the masticatory muscles, the jaw is pushed towards the affected side on opening by the unopposed external pterygoid on the unaffected side.
The trigeminal nerve may be affected by intramedullary lesions. It may be damaged during the intracranial part of its course. Its branches may be compromised extracranially. A vestibular Schwannoma or other space-occupying lesion in the cerebellopontine angle may compress the nerve in the posterior fossa or the nucleus of its descending root in the brainstem. Loss of corneal sensation is usually the earliest feature. Reference has already been made to involvement of the nerve in association with damage to the sixth nerve at the apex of the petrous temporal bone (Gradenigo’s syndrome), as has involvement of the first and second divisions in the cavernous sinus, or the first division in the superior orbital fissure.
This condition is characterized by paroxysms of intense pain strictly confined to the distribution of the trigeminal nerve. It is generally encountered in individuals over the age of 50 years. It is most commonly caused by the impingement of vascular loops on the sensory root of the trigeminal nerve in the posterior fossa. It may be due to multiple sclerosis, especially in younger patients. Rarely, compression of the nerve is responsible, for example by tumours in the cerebellopontine angle.
The salient feature of the disorder is pain, which is usually unilateral and is felt either within the territory of one division of the nerve only, or may involve two adjacent divisions or affect the whole territory of the nerve. Less commonly it is bilateral.
The pain occurs in brief searing paroxysms, each attack lasting only a matter of seconds. The pain is often described as piercing or knife-like. Its intense quality may cause the patient to screw up their face in agony, hence the use of the term ‘tic doloureux’ to describe the condition. The paroxysms may be spontaneous or provoked by movements of the face and jaw, by touching the skin, or by draughts of cold air on the face. Eating and speaking may become extremely difficult. ‘Trigger spots’ on the skin of the face may be present, the touching of which provokes the paroxysms. The attacks may be followed by less severe pain of a dull, boring character and by tenderness of the skin in the affected area. Fortunately the attacks usually cease at night.
The quality of the pain is characteristic, and when trigeminal neuralgia is present the diagnosis is not usually missed, especially if a paroxysm is witnessed. The usual mistake is to regard as trigeminal neuralgia pain that is due to some other cause, and since there are many conditions that give rise to facial pain, the opportunities for error are numerous. Pain that is of a continuous character is not trigeminal neuralgia and some other cause must be sought. Absence of provocation by eating, talking, or the touching of trigger spots also makes the diagnosis unlikely.
Once the diagnosis is accepted, it is essential to exclude compressive lesions affecting the nerve.
In the early stages, remissions lasting for months or years are usual, but in older patients remissions, if they occur, are likely to be brief. In all cases the remissions tend to become shorter as time goes on, and without treatment the condition persists for the rest of the patient’s life.
The distribution of the pain is usually in the first or second divisions of the nerve or both. The third division is rarely affected primarily, but pain may spread into it from the second division.
The introduction of carbamazepine revolutionized treatment of this distressing condition. In a high proportion of cases, the paroxysms can be abolished or reduced. It is best to start with a low dose of 100 mg of a slow-release preparation twice a day and build up the dose every 2 days until control is achieved. Doses larger than 500 mg twice daily often cause ataxia and drowsiness, and some patients experience these at low doses. Allergic skin rashes occur and patients should be warned and advised to stop the drug if they do because of the danger of exfoliative dermatitis. Hyponatraemia is another common complication. Bone marrow depression may develop but is very rare.
If carbamazepine is not successful, or if the patient fails to tolerate it, oxcarbazepine, lamotrigine, or gabapentin can be tried, although they lack a solid evidence base from randomized controlled trials. If medical treatment is inadequate surgical exploration of the main sensory root or thermocoagulation of the ganglion may have to be considered. These should be undertaken only if the disorder is established so that a prolonged natural remission is unlikely to occur. Exploration of the sensory root in the posterior fossa and separation of the root from vascular loops is often curative. Despite the risks of craniotomy, this procedure is worth considering in younger patients with intolerable pain. In older patients prolonged, but not usually permanent, relief can be obtained by thermocoagulation of the trigeminal ganglion. The persistent analgesia and sometimes painful dysaesthesiae, called ‘anaesthesia dolorosa’, following thermocoagulation may sometimes be as or more troublesome than the original condition. When the first division is made anaesthetic, damage to the cornea leading to scarring has to be avoided. It may be possible to limit the anaesthesia to the affected area, sparing, for instance, the eye if the first division is not involved by the pain. If the cornea is anaesthetized, it must be protected by attaching a guard to the wing of the frame of eyeglasses.
Ophthalmic herpes zoster
In elderly individuals, the fifth nerve is prone to involvement in herpes zoster, the first division being most vulnerable, giving rise to the distressing condition of ophthalmic herpes. The clinical features and treatment of herpes zoster are considered elsewhere (see: Herpes zoster). An unfortunate sequel may be visual impairment from residual corneal scarring. Particularly in older subjects, postherpetic neuralgia may also be a sequel. This gives rise to persistent and unremitting spontaneous pain associated with cutaneous hyperaesthesia in the affected area. Treatment may be difficult. Antidepressants are the most effective drugs and there is more evidence for amitryptiline than other agents. Antiepileptic drugs, especially carbamazepine, are often used and there is evidence from randomized trials to support the use of gabapentin. There is limited evidence to support the use of topical lignocaine (lidocaine).
Isolated trigeminal neuropathy
Rarely, a slowly progressive isolated unilateral or bilateral affection of the trigeminal nerve may occur as a manifestation of Sjögren’s syndrome either without other features or with undifferentiated connective tissue disease or progressive systemic sclerosis. Amyloidosis is another rare cause. Most cases are idiopathic.
The seventh cranial nerve is largely motor. The nerve traverses the facial canal in the petrous temporal bone in close relationship to the middle ear and emerges at the stylomastoid foramen. Its branches pass forward through the parotid gland to be distributed to the muscles of the face and the platysma. Within the petrous bone, a branch is given to the stapedius muscle. The chorda tympani, carrying the taste fibres from the anterior two-thirds of the tongue, joins the nerve within the facial canal and a small branch supplies cutaneous sensation to the external auditory meatus. The nerve also carries preganglionic parasympathetic fibres destined for the lachrymal gland.
The distinction between upper and lower motor neuron lesions of the facial muscles is usually easy. In general, with upper motor neuron lesions there is relative preservation of power in the upper facial muscles, because these have a representation in both cerebral hemispheres. There is no loss of tone with upper motor neuron lesions, so that the sagging of the face that is an unsightly feature of lower motor neuron palsy does not occur.
In common with the trigeminal nerve, the facial nerve may be affected by tumours in the cerebellopontine angle. In the past, it was often involved in middle ear infections. It may be involved in meningeal carcinomatosis, fractures, and tumours of the skull base, in a variety of cranial neuropathies, and cephalic herpes zoster, but the most common lesion by far is Bell’s palsy. More peripherally, the nerve may be compromised in tumours of the parotid gland.
This term describes idiopathic facial palsy and is usually unilateral facial paralysis of relatively rapid onset due to a lesion of the nerve within the facial canal. Taste may also be affected. It has an annual incidence of 20 to 32 per 100 000 and may develop at any age, most commonly between 20 and 50 years, and affects both sexes equally. There is some, but inconclusive, evidence that it is a manifestation of herpes simplex infection. In the acute stage, the nerve is swollen and compression within the facial canal may contribute to the damage to the nerve fibres.
The onset is rapid and is frequently heralded or accompanied by aching pain below the ear or in the mastoid region. This clears within a few days and is not present in every case. The paralysis usually reaches its maximum severity after 1 or sometimes 2 days. Complete paralysis may occur. This may cause a mild dysarthria and some difficulty in eating because of food collecting between the gums and the inner sides of the cheek and the escape of fluid when drinking. The face sags, and on smiling is drawn across to the unaffected side. Paralysis of orbicularis oculi renders voluntary eye closure impossible and, particularly in the older subject, ectropion develops. This can result in conjunctival injury from foreign bodies or conjunctivitis. If the paralysis is partial, the lower face is usually affected to a greater extent than the upper.
In the more severe cases, loss of taste over the anterior two-thirds of the tongue is often present, and paralysis of the stapedius muscle may result in a lack of tolerance for high-pitched or loud sounds, called hyperacousis.
Bell’s palsy has to be distinguished from selective lesions of the facial nerve within the brainstem, in which instance taste will not be affected. Lesions in the brainstem almost always cause fifth or sixth nerves palsies and long tract symptoms or signs as well. With respect to peripheral lesions, middle ear disease requires exclusion. Facial paralysis may also be caused by herpes zoster as described below. A lesion of the facial nerve may be part of a more generalized disorder of which diabetes, Lyme borreliosis, and sarcoidosis are the most important. Bell’s palsy is rarely bilateral and bilateral facial paralysis would raise the possibility of another disorder, such as sarcoidosis, Guillain–Barré syndrome, or Lyme borreliosis.
In approximately 85% of patients with Bell’s palsy, especially those with mild weakness, the paralysis is the result of a local conduction block within the facial canal without axonal degeneration. The conduction block is presumably the consequence of segmental demyelination. Provided that such cases do not progress to more severe weakness, remyelination is rapid and all recover fully within a few weeks. In cases where there is total paralysis, axonal degeneration is likely to have occurred so that recovery has to take place by axonal regeneration, which is slow. Evidence of reinnervation does not appear in under 3 months and the ultimate recovery is often incomplete or may fail to occur altogether. After reinnervation the regenerated axons may form inappropriate connections, causing synkinesis and crocodile tears. In synkinesis, blinking results in a simultaneous twitch of the angle of the mouth. Crocodile tears are caused by aberrant parasympathetic reinnervation so that food elicits weeping instead of salivation.
Axons remain excitable distal to the lesion for 3 or 4 days after interruption. It is therefore not possible to be certain from electrodiagnostic tests whether axonal degeneration has taken place until later. After that stage, electrical stimulation of the facial nerve at the stylomastoid foramen will still elicit a muscle contraction if the paralysis is due to conduction block, whereas none will be obtained if axonal degeneration has taken place.
Because most patients with Bell’s palsy recover completely, it was difficult to discover from observational studies whether different treatments helped. However, in a large high-quality trial the percentage of patients with complete recovery after 9 months was significantly increased from 81.6% without to 94.4% with prednisolone, 25 mg twice daily for 10 days. Another trial obtained similar results with prednisolone 60 mg daily for 5 days and then a reducing dose for the next 5 days. In the same trials oral aciclovir made no difference. There is no evidence of efficacy from antiviral agents alone although it is still possible that they might have a small effect when used in conjunction with corticosteroids. In patients with severe palsy causing ectropion, stitching the lateral parts of the eyelids, lateral tarsorrhaphy, may be performed to protect the eye. Electrical stimulation of the paralysed facial muscles has not been shown to have a significant effect on the ultimate prognosis.
In those cases in which regeneration is inadequate, cosmetic operations may be considered to counteract the facial deformity. The angle of the mouth may be elevated by a fascial sling attached to the temporalis fascia, but the result is never highly satisfactory. Restoration of facial tone may be achieved by anastomosis of the hypoglossal to the facial nerve, but at the expense of denervation of the tongue on that side. Any operation should not be contemplated before an adequate length of time has been allowed for regeneration. This should be of the order of one year.
Facial paralysis related to ‘geniculate’ herpes zoster (Ramsay–Hunt syndrome)
Facial paralysis of rapid onset accompanied by severe pain in and around the external auditory meatus and in the throat may accompany ‘cephalic zoster’. Vesicles may be detectable in the ear and ulceration in the fauces, or anywhere on the head. Occasionally there is concomitant vertigo, tinnitus, and some deafness due to involvement of the eighth nerve (‘otic herpes zoster’). Prognosis for recovery of the facial paralysis is stated to be less good than in Bell’s palsy. It is not known whether antiviral agents or corticosteroids are helpful.
This consists of a unilateral disturbance affecting the facial muscles, producing irregular clonic or simultaneous twitching movements of the facial muscles, usually of insidious onset. It most commonly occurs in middle-aged women. There may be a mild degree of facial weakness, but not severe paralysis. Usually no underlying cause is demonstrable. The condition selectively affects the facial nerve, within the brainstem or in the posterior fossa. Hemifacial spasm is painless. If it is associated with pain, there may be a lesion in the cerebellopontine angle compressing both the trigeminal and facial nerves.
It begins with intermittent twitching of the facial muscles such as around the eye or at the angle of the mouth. These movements gradually become more frequent and extend to involve the rest of the facial muscles, often gradually advancing over the course of some years. If they become severe, the face is contorted by irregular clonic spasms which may keep the eye closed for prolonged periods. The facial distortion is often a considerable embarrassment to the patient, who finds that the spasms tend to be aggravated by emotional stress.
In severe cases, injections of botulinum toxin may be helpful, but these have to be repeated. If exaggeration by emotional factors is evident, the administration of diazepam or a similar preparation may produce a marginal improvement. Neurosurgical intervention to relieve compression of the facial nerve by aberrant vessels in the posterior fossa may be helpful in selected cases.
The condition must be distinguished from benign fasciculation of the face, which usually occurs around the eyes, related to fatigue or emotional tension, and from facial myokymia that is occasionally encountered as a manifestation of multiple sclerosis. The latter consists of a persisting irregular rippling movement of the facial muscles that usually subsides after a week or two. These conditions can be distinguished by electromyography.
The ninth cranial nerve leaves the skull through the jugular foramen, closely related to the tenth nerve. It supplies the stylopharyngeus muscle and the constrictor muscles of the pharynx. Parasympathetic fibres are supplied to the parotid gland. Sensory fibres are carried from the posterior third of the tongue, the ear, the fauces, and the nasopharynx, and chemoreceptor and baroreceptor afferents from the carotid sinus.
The glossopharyngeal nerve is rarely affected in isolation. If it is affected alone, it is very difficult to detect the deficits expected from its anatomical distribution. Lesions usually occur in conjunction with involvement of the vagus and give rise to some dysphagia, impaired pharyngeal sensation, and loss of taste over the posterior third of the tongue. It may be affected in the jugular foramen syndrome, along with the tenth and eleventh nerves, of which glomus tumours or metastatic carcinomas are the commonest causes. The nerve may also be involved in diphtheritic neuropathy, Fisher syndrome and in cranial polyneuropathy.
Glossopharyngeal neuralgia is rare and resembles trigeminal neuralgia but with symptoms in the distribution of the glossopharyngeal nerve. As with trigeminal neuralgia, it is most often encountered in elderly subjects, and the pain may initially be confined to individual branches. Thus it may be felt deep in the ear, related to the tympanic branch, or in the throat, related to the pharyngeal branches. It usually responds to treatment with carbamazepine. If that and other antiepileptic drugs fail, surgical treatment, usually section of the nerve, may be required.
The tenth cranial nerve is structurally complex. Within the skull it is joined by the cranial division of the eleventh nerve. It leaves the skull through the jugular foramen. Cutaneous sensory fibres are carried from the external ear and visceral afferent fibres are carried from the pharynx, larynx, trachea, oesophagus, and the thoracic and abdominal viscera. Motor fibres supply the striated musculature of the palate and pharynx and, through the internal, external and recurrent laryngeal nerves, the muscles of the larynx. Parasympathetic fibres innervate the parotid gland (through the glossopharyngeal nerve), the heart, and the abdominal viscera.
The important symptoms of damage to the vagal nerve are those relating to pharyngeal and laryngeal innervation. The cells of origin in the nucleus ambiguus of the medulla may be damaged in the lateral medullary syndrome, motor neuron disease, and acute bulbar poliomyelitis, leading to dysphagia and dysphonia. Involvement along with the glossopharyngeal nerve in the jugular foramen syndrome has already been mentioned. The recurrent laryngeal nerve may be damaged during operations on the thyroid gland or by tumours within the neck, or within the thorax, usually due to carcinoma of the bronchus. The nerve on the left is vulnerable to damage by an aneurysm of the aortic arch. Isolated and unexplained lesions of the recurrent laryngeal nerve are not uncommon.
Nuclear or high vagal lesions, as well as involving the larynx, cause palatal and pharyngeal paralysis. If unilateral, there are few symptoms from palatopharyngeal paralysis. The uvula is pulled up to the opposite side on phonation and pharyngeal sensation is impaired on the affected side. With bilateral paralysis, the palate is paretic leading to nasality of the voice and nasal regurgitation of liquids on attempts at swallowing. Bilateral palatopharyngeal paralysis may be encountered in motor neuron disease, bulbar poliomyelitis, diphtheritic neuropathy, and cranial polyneuropathy.
Unilateral intrinsic laryngeal paralysis from lesions of the recurrent nerve may be asymptomatic or give rise to hoarseness of the voice. If the superior laryngeal nerve is also involved leading to paralysis of the cricothyroid muscle, the affected cord lies in a paramedian or cadaveric position. The effects of bilateral lesions of the recurrent laryngeal nerves depend upon the degree of approximation of the vocal cords. Lesions of insidious onset give rise to dysphonia and also to stridor on exertion. In partial lesions, close approximation of the cords may result from selective paralysis of the abductor muscles, giving rise to limitation of the airway and sometimes necessitating tracheostomy. With bilateral lesions involving both the recurrent and superior laryngeal nerves, both cords are paralysed and in the cadaveric position. Phonation is impossible.
Spinal accessory nerve
The spinal accessory portion of the eleventh cranial nerve arises from the upper cervical cord and the lower medulla. The nerve passes through the foramen magnum and joins the cranial portion of the nerve before emerging from the skull through the jugular foramen. The spinal accessory nerve then separates and supplies the sternomastoid and trapezius muscles, the latter also receiving an innervation from the cervical plexus.
The nerve may be affected by lesions, often neoplastic, in the region of the jugular foramen, but more commonly it is damaged by injuries to the neck or by operations for the removal of cervical glands, particularly as it crosses the posterior triangle of the neck. Isolated and unexplained lesions of the nerve are occasionally encountered.
Unilateral paralysis of the sternomastoid usually passes unnoticed by the patient. The muscle does not stand out when the head is turned to the opposite side. Paralysis of the trapezius, on the other hand, causes difficulty in lifting the arm above the horizontal, in shrugging the shoulder, and in approximating the scapula to the midline and therefore also in carrying the extended arm backwards. The shoulder droops when the arm is hanging at the side and there is moderate winging of the scapula which is accentuated when the patient attempts to elevate the arm laterally.
The hypoglossal nerve
The twelfth cranial nerve supplies all the muscles of the tongue, both intrinsic and extrinsic. It leaves the skull through the anterior condyloid foramen. A unilateral lesion of the hypoglossal nerve causes weakness and atrophy of the tongue on the affected side. When protruded, the tongue deviates to the affected side. Articulation is unaffected. The nerve may be affected by tumours in the region of the anterior condyloid foramen, or by tumours or penetrating injuries in the neck. If damage is the result of a unilateral lower brainstem lesion, it is usually combined with a contralateral hemiplegia. Bilateral lesions give rise to generalized wasting of the tongue. Wasting of the tongue is usually accompanied by fasciculation which is best detected with the tongue at rest. Protrusion becomes impossible and articulation is disturbed. The commonest cause is the progressive bulbar palsy variant of motor neuron disease.
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