Disturbances of Hearing and Balance; Vertigo 199

vated by the facial n., e. g., in the tongue. If the tongue is weak on one side, it deviates, when protruded, to the side of the lesion (Fig. 11.18).

Hemifacial Spasm

This condition is characterized by synchronous, irregular, rapid, brief contractions of all of the muscles of facial expression supplied by the facial n. on one side of the face, particularly including the platysma. On close observation, hemifacial spasm is readily distinguishable from a facial tic (Fig. 11.19). It rarely arises in the aftermath of a peripheral facial nerve palsy. The usual cause is irritation of the facial nerve root by a looping blood vessel just distal to its point of exit from the pons; this explains why neurosurgical intervention (“microvascular decompression”) is usually successful. It is very rare for hemifacial spasm to be caused by a brainstem glioma. The condition can be treated symptomatically with anticonvulsants such as carbamazepine, or with injections of botulinus toxin.

Fig. 11.19 Right hemifacial spasm in a 47-year-old patient. All of the muscles innervated by the facial nerve, including the platysma, contract repeatedly, synchronously, and involuntarily.

Disturbances of Hearing and Balance; Vertigo

Lesions of the vestibulocochlear n. can impair hearing, balance, or both. A lesion of its cochlear portion produces sensorineural hearing loss (impairment of sound perception), which must always be differentiated from conductive hearing loss (impairment of sound conduction, usually due to blockage of the external auditory canal by cerumen, or to a disease process in the middle ear). A lesion of the vestibular portion causes disequilibrium and vertigo. Vestibular vertigo usually occurs in a particular direction and is accompanied by autonomic symptoms and nystagmus. Common vestibular disorders causing vertigo include vestibular neuritis and benign paroxysmal positioning vertigo. A vestibular lesion, however, is only one possible cause of vertigo; many other disorders must be included in the differential diagnosis.

The eighth cranial nerve (vestibulocochlear n.) conducts auditory and vestibular information to the central nervous system.

Auditory impulses arise in the organ of Corti in the cochlea and travel by way of the cochlear n. to the cochlear nuclei of the brainstem and then onward in the auditory pathway to the auditory cortex in the temporal lobe.

Vestibular impulses arise in the ampullae and in the macula statica of the saccule and utricle, the organ of equilibrium; they then travel by way of the vestibular n. to the vestibular nuclei, from which they are conducted to multiple areas of the brain, including the cerebellum.

These anatomical relations are depicted in Fig. 3.11 and discussed on p. 24.

Neurological Disturbances of Hearing

The differentiation of sensorineural from conductive hearing loss helps determine whether the underlying cause is located in the middle ear or external auditory canal (more common sites, conductive hearing loss) or in the sensory cells of the inner ear or the neural apparatus of hearing (less common sites, sensorineural hearing loss). The method of examination and typical findings are summarized above on p. 22. The diagnosis and treatment of conductive hearing loss and of disorders of the cochlea are the responsibility of the otologist.

Neurological disturbances of hearing. Hearing loss due to a lesion of the inner ear or the vestibulocochlear n. may be unilateral or bilateral and its development may be more or less rapid:

Unilateral hearing loss, if acute, is usually due to an infectious process, e. g., mumps or other viral infection. If it is slowly progressive, the physician should suspect a mass lesion compressing the eighth cranial n., such as an acoustic neuroma or a meningioma in the cerebellopontine angle (Fig. 11.20). Larger masses in the cerebellopontine angle can affect not only the eighth cranial nerve, but also the facial and trigeminal nn.

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200 11 Diseases of the Cranial Nerves

Fig. 11.20 Meningioma of the left cerebellopontine angle seen by MRI. The hazelnut-sized, spherical tumor is based on the pyramid of the petrous bone.

Table 11.8 Diseases causing prominent hearing loss

Bilateral hearing loss, if acute, is also most commonly due to a viral or other infection; bacterial meningitis is a rare cause. Progressive bilateral hearing loss, whether it is slow or rapid, should prompt suspicion of, e. g., chronic basilar meningitis (e. g., in tuberculosis), carcinomatous meningitis, an infectious disease (syphilis, toxoplasmosis), or an intoxication. Very slowly progressive, bilateral hearing loss may be due to a metabolic disorder, e. g., Refsum disease or one of the collagenoses.

A number of diseases that can produce hearing loss as their most prominent manifestation are listed in Table 11.8.

Tinnitus. Noises in one or both ears are a common complaint. They are usually subjective, i. e., audible only by the patient. They are termed objective when the examiner, too, can hear them with the stethoscope.

The most common variety of subjective tinnitus involves a noise heard continually in both ears. The patient usually finds it most disturbing in quiet surroundings, particularly in bed at night. The cause is un-

Category	Disease	Remarks
Hereditary congenital	isolated hereditary deafness	Most of these malformations are genetically trans-
malformations of the	Mondini syndrome	mitted in an autosomal recessive pattern, while a
inner ear	Alport syndrome	few are dominant or X-chromosomal. The inheri-
	Klein−Waardenburg syndrome	tance pattern of mitochondrial encephalomy-
	Usher syndrome	opathies is nearly always strictly maternal, as these
	Laurence−Moon−Biedl syndrome	diseases are transmitted in mitochondrial DNA
	mitochondrial encephalomyopathies
Nonhereditary congenital	thalidomide dysplasia	In thalidomide dysplasia and measles embryopathy,
malformations of the	measles embryopathy	the ear anomalies are often accompanied by other
inner ear	hyperbilirubinemia (kernicterus)	anomalies elsewhere in the body. Kernicterus often
	perinatal asphyxia	causes athetosis; cretinism causes feebleminded-
	cretinism	ness
	congenital syphilis
	toxoplasmosis

Infections	viral: herpes, mumps, measles, mononucleosis,
	HIV, and other neurotropic viruses
	bacterial meningitis
	otitis media and malignant otitis
	chronic otitis media, cholesteatoma
	syphilis, borreliosis

Hearing loss is a common late sequela of bacterial meningitis; otitis media causes conductive (not sensorineural) hearing loss; otoscopic examination is mandatory

Polyneuropathies com-	Refsum disease	Retinitis pigmentosa in Refsum disease
bined with hearing loss	hereditary neuropathy (Charcot−Marie−Tooth)
Tumors	acoustic neuroma	Acoustic neuroma occurs sporadically or as a
	glomus tympanicum tumor	component of neurofibromatosis, type I or II. The
	paraneoplastic	presenting symptom of a glomus tympanicum
		tumor is often pulsatile tinnitus
Cerebrovascular	infarct in the territory of the labyrinthine a.
disorders	migraine
Autoimmune disorders	collagen diseases	Various types of autoantibody can be demon-
	Susac syndrome	strated in these conditions
	Cogan syndrome
Trauma	transverse fracture of petrous bone	The clinical history leads to the diagnosis
	labyrinthine contusion
	acoustic trauma
	chronic exposure to noise
	barotrauma
Toxic/iatrogenic	aminoglycosides, cytostatic agents	Usually bilateral, often with a bilateral vestibular
		deficit
		Continued

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		Disturbances of Hearing and Balance; Vertigo		201
Table 11.8 Diseases causing prominent hearing loss (Continued)
Category	Disease	Remarks
Specific ear diseases	Ménière disease	In these conditions, vestibular symptoms are often
	Lermoyez syndrome	present in combination (or in alternation) with
	otosclerosis	hearing loss
	acute hearing loss
	perilymph fistula
Miscellaneous	superficial hemosiderosis of the CNS	Progressive hearing loss and ataxia

known and the problem can resolve spontaneously. Various therapeutic measures have been proposed, including perfusion-enhancing medications and oxygen, but are of questionable benefit.

Pulsatile tinnitus is rare in comparison to continual tinnitus. It is caused by a pulsating blood vessel near the petrous bone and must be taken very seriously. The examiner, too, can often hear the pulse-synchronous bruit through a stethoscope (sometimes even without one). Some possible causes are listed in Table 11.9.

Table 11.9 Diseases that can present with pulsatile tinnitus

Carotid dissection

Fibromuscular dysplasia

High-lying carotid stenosis due to atheromatous plaque

Arteriovenous malformation

Retromastoid dural fistula

Carotid−cavernous fistula

Glomus tumor (glomus jugulare or glomus tympanicum)

Tumor in or near petrous bone

Infection in or near petrous bone

Intracranial hypertension

Pseudotumor cerebri

Disequilibrium and Vertigo

The vestibular organ (semicircular canals, saccule, and utricle) plays a central role in the regulation of balance. Disturbances of the vestibular apparatus (composed of the vestibular organ, the vestibulocochlear n., and the vestibular nuclei of the brainstem) cause dysequilibrium, the main symptom of which is vertigo. It must be emphasized, however, that vestibular disturbances are just one cause of vertigo (see below) and not even the most common one.

Regulation of equilibrium. Equilibrium (balance), i. e., the optimal static and dynamic mechanical stability of the human being in space, is maintained by the following neural processes:

impulses from the vestibular apparatus concerning the position, movement, and acceleration of the individual in space;

impulses from the visual system concerning the body’s relation to visual space;

impulses from the exteroceptive pathways concerning the body’s contact with underlying surfaces (floor, mattress, etc.);

impulses from the proprioceptive pathways concerning the positions of the joints and the spatial relations of the parts of the body to each other;

impulses concerning movements in the process of being executed, from the pyramidal, extrapyramidal, and cerebellar systems;

conscious (cognitive) and unconscious (emotional) influences;

finally, the integration of all of these signals in the brainstem.

The various components of the regulation of balance are depicted schematically in Fig. 11.21.

visual system, ocular motility

pyramidal and			brainstem
extrapyramidal			vestibular			cerebellum
motor system			nuclei
	labyrinth			spinal cord, peripheral
				nervous system

Fig. 11.21 The maintenance of balance by integration of information from multiple channels

Disturbances of the regulation of equilibrium. Vertigo arises if individual informational and/or control components of the regulatory system are lost (see below), if the information coming through different sensory channels seems to be incompatible (so-called multisensory mismatch, e. g., in seasickness), or the sensory input is highly unusual (e. g., uncommon visual input from a great height). So many different structures play a role in the maintenance of equilibrium and their interactions are so complex, that the causes of vertigo are, understandably, highly varied. Different types of vertigo result from lesions at different sites.

Types of vertigo. Directional vertigo (vestibular vertigo) is characteristic of lesions of the peripheral portion of the vestibular apparatus, i. e., the vestibular organ and/or the vestibulocochlear n. The patient perceives the

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202	11 Diseases of the Cranial Nerves
		Table 11.10 Differentiation of peripheral vestibular, central vestibular, and nonvestibular vertigo
				Type of vertigo
		Signs and symptoms	peripheral vestibular	central vestibular	nonvestibular
			(labyrinth, nerve)
		Nausea, vomiting, diaphoresis	severe	moderate	mild
		Vertigo—intensity	marked	moderate	mild
		Vertigo—type	in a specific direction	directional to some degree	not in any specific direction
		Nystagmus	spontaneous nystagmus of	spontaneous nystagmus of	nonvestibular nystagmus, or
			vestibular type	vestibular type	no pathological nystagmus
		Hearing loss, tinnitus	usual	unusual	absent
		Other neurological deficits	unusual	usually present	the neurological examination
					may or may not yield positive
					findings

environment as if it were in motion (= oscillopsia), e. g., rotating or heaving up and down like the deck of a boat. Vestibular vertigo is often accompanied by autonomic manifestations, such as nausea and vomiting, and by nystagmus. Central vestibular lesions (i. e., lesions of the vestibular nuclei in the brainstem) also cause directional vertigo, which is generally less intense than that due to peripheral lesions. The autonomic manifestations, too, tend to be milder or absent.

Nonvestibular vertigo is nondirectional and often difficult for the patient to describe. The patient may report a woozy feeling, emptiness in the head, or darkness before the eyes. Oscillopsia is absent and there are usually no autonomic manifestations. Central nervous lesions can cause pathological nystagmus, as listed in Tables 11.1, 11.2. Nonvestibular vertigo is caused either by a lesion of the nonvestibular parts of the regulatory system for balance, or else by faulty information processing within the central nervous system (e. g., because of a cerebellar lesion). Pathological processes outside the central nervous system, such as orthostatic hypotension or aortic stenosis, can also cause nonvestibular vertigo.

The characteristic features of peripheral and central vestibular vertigo and of nonvestibular vertigo are summarized in Table 11.10.

Special aspects of history taking and diagnostic evaluation. The clinician should be able to tell whether the patient is suffering from vestibular or nonvestibular vertigo based on a meticulously elicited clinical history alone. It is also important to determine whether the vertigo is episodic or continuous and to ask about any precipitating factors (e. g., changes of position or particular situations that make the vertigo worse). If the vertigo worsens in the dark or when the patient’s eyes are closed, the cause is likely to be a disturbance of proprioception (polyneuropathy, posterior column disease) or a bilateral vestibulopathy. The examiner should also always ask about accompanying symptoms (in particular, autonomic symptoms, tinnitus, hearing loss, and prior illnesses and infections). The history combined with the physical findings (nystagmus, results of balance tests, any other neurological abnormalities) usually allows localization of the functional disturbance. Further testing

(e. g., caloric testing of the vestibular organ, ENT consultation, neuroimaging of the head) mainly serves to determine the etiology.

We will now describe the main neurological causes of vertigo, particularly vestibular disturbances, in greater detail.

Vestibular Vertigo

Acute loss of vestibular function is also called vestibular neuritis, acute vestibular neuropathy, or an acute vestibular crisis. It can be produced by a variety of pathogenetic mechanisms, the most common of which is a viral infection. The patient suddenly experiences acute rotatory vertigo with nausea, vomiting, and falling to the side of the diseased vestibular organ. Every movement of the head makes the vertigo worse; therefore the patient, noting this, lies perfectly still. Examination reveals horizontally beating, spontaneous nystagmus in the direction opposite the side of the lesion, with a rotatory component. The nystagmus is more intense when the patient lies on the affected side; it can be diminished by visual fixation. The affected vestibular organ is less responsive than normal to caloric stimulation. Vertigo usually resolves fully within a few days, rarely within a few hours. Often a so-called “trigger labyrinth” remains as a residual phenomenon, i. e., vertigo on acceleration or rapid movements of the head. The condition may relapse.

Positional and positioning vertigo. These types of vertigo arise only with certain positions or positioning movements of the head and manifest themselves as brief attacks of vertigo that diminish in intensity if they are provoked in rapid succession. These conditions have a number of different causes.

Benign paroxysmal positioning vertigo is the most common type of positioning vertigo. It is provoked by changes in the position of the head, usually involving lying down rapidly, bending forward, turning in bed, or rapidly sitting up. It manifests itself as very brief (15−30 seconds) and very severe attacks of rotatory vertigo and nausea.

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Disturbances of Hearing and Balance; Vertigo 203

	Fig. 11.22 Hallpike positional testing for the demonstration of	60°
	benign paroxysmal positioning vertigo. See text.

a

30°

60° 60°

b

c

d

With respect to the pathogenesis of this condition, it is thought that small pieces of the otolith membranes of the saccule and utricle can break off and float freely in the endolymph—usually in the posterior semicircular canal, less commonly in the horizontal one. When the head is moved, these free particles move together with the endolymph and slide over the hair cells of the cupula, even after the movement is completed. The abnormally prolonged activation of the hair cells induces acute rotatory vertigo. The condition is also termed cupulolithiasis or canalolithiasis.

The Hallpike positioning maneuver can be used as a diagnostic test (Fig. 11.22). The patient is rapidly taken from an upright sitting position into the supine position with the head held down 30° below the level of the examining table and turned 60° to the right or left. Within a few seconds, the examiner should be able to observe rotatory nystagmus, which then disappears after 5−30 seconds. This is easiest to see if the patient is wearing Frenzel goggles. If the head is turned to the right, the nystagmus is counterclockwise; if to the left, clockwise.

Certain positioning maneuvers, e.g., those of Epley and Semont, have been shown to be useful as treatment for this condition. These maneuvers work by flushing the floating otoliths out of the affected semicircular canal.

Central positional vertigo is a rarer type of positionally dependent vertigo appearing with certain tilted positions of the head. The nystagmus usually beats to the uppermost ear and does not habituate on repeated provocation. The vertigo is generally not very severe.

Ménière disease is a common cause of acute vestibular vertigo. It is caused by endolymphatic hydrops and manifests itself clinically in episodes of acute rotatory vertigo, a tendency to fall to the affected side, and horizontal, directional, spontaneous nystagmus, accompanied by

nausea, vomiting, and tinnitus. Slowly progressive hearing loss is worse after each attack.

Bilateral vestibular deficits. While unilateral dysfunction of the vestibular apparatus can either recover or be compensated for by the intact opposite side within a matter of weeks, bilateral dysfunction deprives the regulatory system for balance of all incoming vestibular information. Consequently, the patient’s gait becomes very unsteady in the dark (i. e., when visual input, too, is inoperative), or when the patient must walk on an uneven or soft surface (i. e., when the incoming proprioceptive information is difficult to interpret). Subjectively, the patient suffers from oscillopsia (apparent movement of the external world), particularly when walking, because the vestibulo-ocular reflex (p. 186) is inoperative and visual fixation is, therefore, unstable.

Nonvestibular Vertigo

Dysfunction of the nonvestibular components of the regulatory system for balance can also cause vertigo.

Visually induced vertigo occurs, e. g., when an individual looks down from a great height, or when the incoming proprioceptive information is inconsistent with the visual information (polysensory mismatch). The vertigo of seasickness is a type of visually induced vertigo.

Impaired proprioception, e. g., in polyneuropathy or posterior column disease, can also cause vertigo.

Cervical vertigo is thought to be due to faulty proprioceptive information arising in diseased cervical intervertebral joints or the adjacent soft tissues, which is then transmitted to the integrating apparatus for balance in the brainstem. This type of vertigo worsens in the dark. Its existence is debated.

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