Vestibular nerve

1. D R . N I S H T H A J A I N
S E N I O R R E S I D E N T
D E P A R T M E N T O F N E U R O L O G Y
G M C , K O T A .
Vestibulocochlear Nerve

2.  The eighth cranial nerve consists of two separate functional
components: the auditory (cochlear) nerve concerned with
hearing and the vestibular nerve concerned with
equilibrium.
 The auditory nerve receives information from the
tonotopically organized cochlea, the organ of hearing.
 The vestibular nerve derives its input from the saccular and
utricular macules (which sense linear acceleration) and the
cristae of the semicircular canals (which sense angular
acceleration of the head).

3. COCHLEAR NERVE

4. Anatomy
 The labyrinth is a complex of interconnecting cavities,
tunnels, ducts, and canals that lies in the petrous portion of
the temporal bone.
 The bony labyrinth is filled with perilymph, a thin watery
fluid similar to cerebrospinal fluid (CSF).
 The membranous labyrinth is an arrangement of sacs and
ducts that lies within the bony labyrinth, generally follows its
outline, and is filled with endolymph (Scarpa's fluid).

5.  The membranous labyrinth has two major components: the
vestibular apparatus and the cochlear duct.
 The ossicles span the middle ear cavity and transmit the
oscillations of the tympanic membrane to the footplate of
the stapes, which sits in the oval window (fenestra
vestibuli).
 The oval window opens into the vestibule of the inner ear,
which connects on one side to the cochlea and on the other
to the semicircular canals.
 The base of the cochlea faces the internal acoustic meatus
and contains myriad fenestrations that admit the filaments
of the cochlear nerve.

8.  The scala media, or cochlear duct, is part of the
membranous labyrinth.
 It lies in the center of the spirals of the cochlea, completing
the partition between the scala tympani and scala vestibuli.
 The spiral ganglion of the cochlear nerve lies in the spiral
canal of the modiolus (Rosenthal's canal).
 The organ of Corti rests on the basilar membrane and
contains inner and outer hair cells.
 The inner hair cells are the receptors, or end-organs, of the
cochlear nerve.

9.  Sound waves induce vibrations in the cochlea, which cause
movement of the basilar and tectorial membranes.
 This movement flexes the stereocilia, which activates the
hair cell, causing impulses in the spiral ganglion.
 Because of the varying width of the basilar membrane,
sound of a certain frequency induces oscillations maximal
at a certain point along the cochlear duct, which focally
activates hair cells and encodes the frequency.

10.  The spiral ganglion consists of type I and type II bipolar
neurons that lie in the modiolus.
 Inner hair cells synapse on type I neurons, which make up
95% of the ganglion.
 Axons of the spiral ganglion cells form the cochlear nerve,
which contains some 30,000 fibers.
 Axons from type I cells are myelinated and form the bulk of
the nerve.
 The type II cells connect with the outer hair cells and
modulate the activity of the inner hair cells.

12.  The acoustic nerve traverses the internal auditory canal,
where it lies lateral and inferior to the facial nerve.
 It crosses the cerebellopontine angle, passes around the
inferior cerebellar peduncle, and enters the upper medulla
at its junction with the pons near the lateral recess of the
fourth ventricle.
 Each entering fiber bifurcates to synapse in both the dorsal
(posterior) and ventral (anterior) cochlear nuclei.

14.  In the cochlear nuclei, low frequency tones are processed
ventrally, high frequencies dorsally.
 Second order neurons in the cochlear nuclei give rise to the
dorsal, ventral, and intermediate acoustic stria.
 Fibers in the dorsal and intermediate acoustic stria run to
the contralateral inferior colliculus, most directly, some after
a relay in the nucleus of the lateral lemniscus.
 This crossed, monaural auditory pathway primarily carries
information about sound frequency.

15.  Fibers of the ventral acoustic stria are both crossed and
uncrossed and may synapse in the nuclei of the trapezoid
body, superior olive, or lateral lemniscus.
 The binaural pathway, especially the superior olivary
complex component, can determine the time difference
between the two ears and aid in the localization of sound.

16.  Fibers from the lateral lemnisci ascend to synapse in
the central nucleus of the inferior colliculus.
 Axons from the inferior colliculus pass through the
brachium of the inferior colliculus to the medial
geniculate body (MGB), a special sensory nucleus of
the thalamus that is the final relay station in the
auditory pathway.
 From the MGB, auditory fibers pass through the
posterior limb of the internal capsule as the
geniculotemporal tract, or auditory radiations, which
runs through the sublenticular portion of the internal
capsule.

17.  The fibers terminate in the cortex of the transverse
temporal convolutions (Heschl's gyrus) and the adjacent
planum temporale portion of the superior temporal gyrus
which make up the primary and secondary auditory cortex
(Brodman's areas 41 and 42).
 The primary auditory cortex is tonotopically organized with
high frequencies medial and low frequencies lateral.
 The auditory association cortex (Wernicke's area in the
dominant hemisphere) lies just posterior to the primary
auditory cortex.

19. Blood supply
 The blood supply to the cochlea and auditory brainstem
nuclei arises from the internal auditory (labyrinthine) artery,
usually a branch of the anterior inferior cerebellar artery.
 The superior olivary complex and lateral lemniscus are
supplied by circumferential branches of the basilar artery
 the inferior colliculus is vascularized by branches of the
superior cerebellar and quadrigeminal arteries
 whereas the medial geniculate bodies receive their blood
supply from the thalamogeniculate arteries.
 Branches of the middle cerebral artery supply the primary
auditory and associated cortices.

20. Clinical Examination
 Before testing hearing, otoscopic examination should be
done to ensure the tympanic membrane is intact, and to
exclude the presence of wax, pus, blood, foreign bodies,
and exudate.
 The mastoid region should be examined for swelling and
tenderness.

21. Audiometry
 An audiometer is an instrument by which sounds of varying
intensity and frequency are presented to a patient.
 There are many different audiologic techniques; those used
most commonly for neurologic purposes are pure tone and
speech audiometry.
 The pure tone audiogram displays the severity of any
hearing loss in relation to established reference values, and
the pattern may suggest the etiology.

22.  As with tuning fork testing, a decrease in AC with normal
BC, an air-bone gap, indicates conductive hearing loss,
and a decrease in both AC and BC indicates sensorineural
loss.
 The pure tone audiogram is usually normal with lesions
involving the central auditory pathways.

23.  Speech audiometry uses spoken words and sentences
instead of pure tones.
 The speech reception threshold (SRT) is considered the
intensity level at which the patient can correctly understand
50% of the material presented.
 Speech discrimination, or intelligibility, is the proportion of
the material the patient can understand when presented at
a level that should be easily heard.

24.  The loss of discrimination is proportional to the severity of
the hearing loss in patients with cochlear lesions.
 Poor speech discrimination, out of proportion to pure tone
hearing loss, is characteristic of a retrocochlear lesion,
such as cerebellopontine angle tumor.
 In CN VIII lesions, discrimination may even paradoxically
decline as intensity is raised.

25.  Impedance audiometry uses an electroacoustic device,
which measures the impedance, or compliance, of the
conductive hearing mechanism, like measuring the
tightness of a drumhead.
 A very stiff drumhead has high impedance, or low
compliance, and reflects sound back to the source.
 Low impedance allows for greater transmission of sound
through the system and less reflection.

26.  A tympanogram measures the impedance of the tympanic
membrane.
 An abnormal tympanogram is seen in such conditions as
otitis media, tympanic membrane perforation, ossicular
dislocation, otosclerosis, cerumen impaction, and
eustachian tube dysfunction.

27.  The stapedius reflex, or acoustic reflex, measures the
change in compliance in response to loud sounds to
assess the function of the stapedial muscle.
 The reflex arc is via CN VIII, brainstem interneurons, and
CN VII.
 In the absence of severe hearing loss, an abnormal
stapedius reflex may suggest a lesion of CN VII or VIII or
the brainstem.

28.  The auditory evoked potential (AEP), also known as the
auditory evoked response, or brainstem auditory evoked
potential/response (BAEP/BAER), is a minuscule potential
produced by auditory stimuli and recorded using
electroencephalogram (EEG) electrodes.
 The waves that occur in the first 10 milliseconds after an
auditory stimulus are short latency far field potentials due to
electrical activity at various points along the auditory
pathway.
 BAERs are used primarily for evaluating suspected CN VIII
and brainstem lesions.

29.  There are five to seven waves in the AEP.
 Wave I is the auditory nerve action potential.
 Wave II reflect activity in the cochlear nuclei, although it
may be generated by the intracranial segment of the
auditory nerve.
 Wave III is thought to come from the superior olive.
 Waves IV and V the inferior colliculus.
 The wave VI may come from the medial geniculate body.
 Wave VII from the auditory radiations.

31.  A delay between waves I and III suggests a lesion between
the eighth nerve near the cochlea and the lower pons.
 An interpeak latency delay between waves III and V
suggests a lesion between the lower pons and midbrain.
 The primary clinical applications of BAERs have been in
the evaluation of patients with cerebellopontine angle
tumors and demyelinating disease, and in coma and brain
death.
 also useful in newborn and infant hearing assessment.

33.  Auditory reflex responses are occasionally useful in
evaluating hearing in children, patients with altered mental
status, and in hysteria or malingering.
 The auditory-palpebral reflex (auro- or acousticopalpebral,
cochleopalpebral, or cochleoorbicularis reflex) is a blink or
reflex eye closure in response to a loud, sudden noise.

34.  The cochleopupillary reflex is pupillary dilation, or
contraction followed by dilation, in response to a loud
noise.
 The auditory-oculogyric reflex is eye deviation toward a
sound.
 The general acoustic muscle reflex is a general jerking of
the body in response to a loud, sudden noise.

35.  In bedside qualitative assessment of hearing loss, a tuning
fork (256 or preferably 512 Hz) is used to distinguish
between two types of hearing loss.
 Three major tuning fork tests are used for the evaluation of
hearing loss:
 Weber's test
 Rinne's test
 Schwabach's test.

36. The Weber's Test
 The purpose of the Weber's test is to help differentiate a
conductive from a sensorineural hearing loss in a unilateral
hearing loss.
 This test is conducted by placing a vibrating tuning fork
over the midline of the skull or forehead, over the nasal
bone, or over the anterior upper incisors.
 Normally, the vibrations are perceived equally in both ears
(no lateralization) because bone conduction is equal
bilaterally.

37.  In conductive hearing loss, the vibrations are louder in the
deaf ear (lateralized to the diseased ear).
 In sensorineural hearing loss, the sound is louder in the
normal ear (lateralized to the normal ear).

38. The Rinne's Test
 The Rinne's test compares the patient's air and bone
conduction.
 The stem of the vibrating tuning fork is applied against the
mastoid process.
 When the patient no longer hears the vibration, the fork is
placed next to the ear (approximately 1 cm from the
external auditory meatus).
 In normal individuals, because air conduction is better than
bone conduction, the vibrations are perceived in the ear
after they are no longer perceived at the mastoid.

39.  The Rinne's test is said to be normal, or positive, when the
tuning fork is heard approximately twice as long by air
conduction as by bone conduction.
 In cases of conduction deafness, bone conduction is better
than air conduction, and therefore the tuning fork cannot be
heard when it is placed next to the ear.
 With sensorineural hearing loss, both air and bone
conduction are diminished to a similar extent, and air
conduction remains greater than bone conduction.

40. The Schwabach's Test
 As in the Rinne's test, the tuning fork is held against the
mastoid process until the patient is unable to perceive any
sound.
 The examiner then places the tuning fork over his or her
own mastoid bone and compares the bone conduction to
that of the patient.
 If the examiner hears the tuning fork after the patient no
longer hears it, a sensorineural hearing loss is suspected.

41. Localization of Lesions Causing Sensorineural
Deafness
 Unilateral dominant posterior temporal lesions or bilateral
temporal lesions affecting Heschl's gyri may cause pure
word deafness.
 Left hemispheric lesions predominantly impair speech
discrimination, whereas right hemispheric lesions
predominantly impair complex-pitch discrimination.

42.  Irritative lesions of the temporal cortex may result in
subjective auditory hallucinations. Auditory hallucinations
may be simple (e.g., tinnitus) or complex (e.g., voices,
music).
 These auditory sensations are most often referred to the
contralateral ear
 occur more frequently with irritative lesions of Brodmann's
areas 42 and 22 than with lesions of Brodmann's area 41.

43.  Bilateral hearing loss may occur with severe bilateral
brainstem lesions (e.g., hemorrhage or infarction).
 Pineal and midbrain tumors may also cause sudden and
complete bilateral deafness (central stem deafness of
Brunner) presumably because the auditory pathways in this
region are closely packed together.

44.  Peripheral cochlear nerve lesions account for partial or
complete deafness, often associated with ipsilateral
tinnitus.
 Deafness is most prominent for high-frequency tones and
may be secondary to
 trauma (e.g., basal skull fracture)
 infections (e.g., syphilis, bacterial infections)
 drugs (e.g., streptomycin, neomycin)
 aneurysms of the anterior inferior cerebellar artery
 tumors of the cerebellopontine angle (e.g., vestibular
schwannomas, epidermoids, meningiomas, arachnoid
cysts).

45. VESTIBULAR NERVE

46. Anatomy
 The peripheral vestibular system is composed of three
semicircular canals, the utricle and saccule, and the
vestibular component of the eighth cranial nerve.
 Each semicircular canal has a sensory epithelium called
the crista; the sensory epithelium of the utricle and saccule
is called the macule.
 The semicircular canals sense angular movements, and
the utricle and saccule sense linear movements.

47.  Two of the semicircular canals (anterior and posterior) are
oriented in the vertical plane nearly orthogonal to each
other; the third canal is oriented in the horizontal plane
(horizontal canal).
 The crista of each canal is primarily activated by movement
occurring in the plane of that canal.
 When the hair cells of these organs are stimulated, the
signal is transferred to the vestibular nuclei via the
vestibular portion of cranial nerve VIII.

48.  Because of its orientation, the macula of the utricle
responds maximally to head movement in the sagittal
plane, whereas the macula of the saccule responds
maximally to head movement in the coronal plane.
 The horizontal canal best detects rotational head
movement in the side-to-side (“no-no”) direction (with the
chin tucked to bring the canal fully horizontal).
 The posterior canal best detects movement in the
anteroposterior plane (“yes-yes”), and the anterior canal is
oriented to detect lateral tilting movement.

49.  The nerve divide into ascending and descending branches
that end primarily in the four vestibular nuclei: lateral,
medial, superior, and inferior.
 Some fibers form the vestibulocerebellar tract and pass
directly to the cerebellum, without synapsing in the
vestibular nuclei, in the juxtarestiform body.
 The medial (Schwalbe's) vestibular nucleus is the largest
subdivision of the vestibular nuclear complex, extending
from the medulla into the pons.

50.  Vestibular afferents to the superior and medial subnuclei
arise predominantly from the semicircular canals.
 Afferents to the lateral and inferior subnuclei arise
predominantly from the otolith organs.
 The vestibular nuclei make connections with four primary
areas: cerebellum, spinal cord, oculomotor system, and
cortex.

51.  Fibers from the lateral vestibular nucleus go down the
ipsilateral spinal cord as the lateral vestibulospinal tract,
which is important in the regulation of muscle tone and
posture by increasing extensor muscle tone.
 Impulses from the medial vestibular nuclei descend to the
cervical and upper thoracic spinal cord through the crossed
medial vestibulospinal tract.

52.  Ascending vestibular connections extend rostrally to the
ventrolateral and ventral posterior thalamic nuclei, and from
the thalamus to the somatosensory cortex to provide
conscious perception of head position and movement.

54.  The blood supply to the membranous labyrinth is from the
internal auditory or labyrinthine artery.
 After giving off a branch to the eighth nerve in the
cerebellopontine angle, the internal auditory artery
transverses the internal auditory meatus and, at the
labyrinth, branches into
 (a) the anterior vestibular artery to the anterior and lateral
semicircular canals and the utricular macula,
 (b) the posterior vestibular artery to the posterior
semicircular canal, the saccular macula, and part of the
cochlea, and
 (c) the cochlear artery.

55. Clinical Examination

56. Vestibulospinal Reflexes
 Past pointing is a deviation of the extremities caused by
either cerebellar or vestibular disease.
 With acute vestibular imbalance, the normal labyrinth will
push the limb toward the abnormal side, and the patient will
miss the target.
 The past pointing will always be to the same side of the
target and will occur with either limb.

57.  With a cerebellar hemispheric lesion, the ipsilateral limbs
have ataxia and incoordination; past pointing occurs only
with the involved arm and may be to the side of the lesion
or erratically to either side of the target.
 In vestibulopathy, after a period of compensation the past
pointing disappears and may even begin to occur in the
opposite direction.

58.  In rombergs test, in unilateral vestibulopathy if balance is
lost with eyes closed the patient will tend to fall toward the
side of the lesion, as the normal vestibular system pushes
him over.
 If the patient has spontaneous nystagmus due to a
vestibular lesion, the fall will be in the direction of the slow
phase.
 The Fukuda stepping test is analogous.
 The patient, eyes closed, marches in place for one minute.
 A normal individual will continue to face in the same
direction, but a patient with acute vestibulopathy will slowly
pivot toward the lesion.

59.  In the star walking test, the patient, eyes closed, takes
several steps forward then several steps backward, over
and over.
 A normal individual will begin and end oriented
approximately along the same line.
 A patient with acute vestibulopathy will drift toward the
involved side walking forward, and continue to drift during
the backward phase.
 The resulting path traces out a multipointed star pattern.

60. Vestibulo-Ocular Reflexes
 The vestibulo-ocular reflex (VOR) serves to move the eyes
at an equal velocity but in the direction opposite the head
movement.
 This keeps the eyes still in space and maintains visual
fixation while the head is in motion.
 There are several ways to examine the VOR including
 Doll's eye test
 Head thrust test
 Dynamic visual acuity
 Calorics.

61. Oculocephalic Reflex (Doll's Eye Test)
 The oculocephalic response is primarily useful in the
evaluation of comatose patients.
 Turning the head in one direction causes the eyes to turn in
the opposite direction.
 This response indicates that the pathways connecting the
vestibular nuclei in the medulla to the extraocular nuclei in
the pons and midbrain are functioning and that the
brainstem is intact.

62. Head Thrust
 The head thrust test is done in an awake patient.
 Abrupt, rapid movements are made in each direction while
the patient attempts to maintain fixation straight ahead, as
on the examiner's nose.
 Normally the VOR will maintain fixation and the eyes will
hold on target.

63.  When the VOR is impaired, the compensatory eye
movement velocity is less than the head movement
velocity; the eyes lag behind the head movement and a
corrective “catch-up” saccade must be made to resume
fixation in the eccentric position.

65. Dynamic Visual Acuity
 The ability of the VOR to maintain ocular fixation means
that a patient can read even while shaking the head to and
fro.
 The dynamic visual acuity test is performed by obtaining a
baseline acuity, and then determining the acuity during
rapid head shaking.
 Degradation by more than three lines on the Snellen chart
suggests impaired vestibular function.

66. Caloric Tests
 Cold calorics in a comatose patient with an intact brainstem
causes tonic deviation of the eyes toward the side of
irrigation as the normally active labyrinth pushes the eyes
toward the hypoactive, irrigated labyrinth.
 In an awake patient, cold calorics cause nystagmus with
the fast component away from the irrigated side because
the cerebral cortex produces a compensatory saccade that
jerks in the direction opposite the tonic deviation.

67.  Nystagmus is seen only when the cortex is functioning
normally.
 Warm water irrigation has opposite effects.
 Bilateral simultaneous cold calorics induce tonic downgaze,
warm calorics upgaze.

68. Localization of Lesions Causing Vertigo
 Localizing lesions causing vertigo may be
approached by considering three general categories:
 peripheral causes (vestibular labyrinthine disease)
 central causes (dysfunction of the vestibular
connections)

70.  Peripheral vestibular syndromes are usually of short
duration and characterized by severe, often paroxysmal
vertigo accompanied by auditory dysfunction (tinnitus and
hearing loss).
 Nystagmus is often present and is characteristically
unidirectional (fast phase away from•
the side of the lesion),
horizontal rotatory (never vertical or exclusively rotatory),
and inhibited by visual fixation.

71.  The subjective environmental twirl, past-pointing, deviation
of the outstretched hands, and fall associated with the
Romberg's maneuver are toward the slow phase of the
nystagmus (toward the side of the lesion).
 The peripheral vestibular syndrome is therefore complete
(has all of the clinical elements of vestibular dysfunction,
e.g., vertigo, nystagmus, deviation of the outstretched
hands, Romberg's sign, and so on) and congruent (all the
slow deviations•
are toward the same side, i.e., ipsilateral to
the responsible lesion).

72. Benign Paroxysmal Positioning Vertigo
 very common mechanical disorder of the inner ear in which
brief attacks of acute and severe vertigo with concomitant
nystagmus and autonomic symptoms is precipitated by
certain head movements (often while patients turn in bed).
 Commonly, BPPV involves the posterior semicircular canal.

73.  BPPV may follow head trauma, viral labyrinthitis, meniere's
disease, migraines, or inner ear surgery, but most cases
(50%-70%) are primary or idiopathic and best explained by
the canalithiasis or cupulolithiasis theory.
 Most cases of posterior canal BPPV are due to
canalithiasis.
 Other patients (10%-30%) display the lateral or horizontal
semicircular canal BPPV variant (HC-BPPV) in which there
is a strong linear horizontal nystagmus beating toward the
lowermost ear induced by rapid turning of the head from
side to side around the longitudinal axis.

74.  The nystagmus exhibits short latency without fatigability,
and often reverses its direction on the pathologic side.
 The vertigo can be induced by turning the head to either
side in the supine position, and is always more prominent
on the pathologic side.
 The horizontal variant of BPPV tends to resolve more
quickly than the posterior canal BPPV.

75.  The provocative positioning maneuver (Dix-Hallpike
maneuvers) (patient is briskly moved from the seated
position to a position where the head is hanging 45
degrees below the horizontal and rotated 45 degrees to
one side)allows for a differentiation between a peripheral or
a central origin for positional vertigo.

76.  In normal individuals, these maneuvers do not induce
nystagmus.
 With peripheral lesions, vertigo, nausea, vomiting, and
nystagmus appear several seconds (1 to 15 seconds) after
the head position is changed (latency of response due to
the period of time for the otoconial mass to be displaced).
 The nystagmus is usually torsional, with the upper pole of
the eye beating toward the ground.
 Fatigue with repeated positioning is seen.

77.  The nystagmus fatigues and abates within 10 seconds of
appearance (fatigability due to dispersion of particles in the
endolymph), and when the patient is rapidly brought back
to a sitting position, the nystagmus beats maximally in the
opposite direction (rebound).
 With repetition of the maneuver, the nystagmus becomes
progressively less severe (habituation).

78.  A central lesion should be suspected and further
investigations initiated when
 (a) the positioning testing maneuver is positive with the
head turned to either side
 (b) the nystagmus changes direction immediately after the
shift in position and remains for as long as the head is
down
 (c) the nystagmus is unaccompanied by nausea or
vomiting, and if present, vertigo is mild and lasts <60
seconds and
 (d) the nystagmus does not display features of adaptability
or fatigability.

80. Peripheral Vestibulopathy
 This term refers to conditions characterized by acute or
recurrent attacks of episodic vertigo caused by
extramedullary disorders of the vestibular system.
 These conditions encompass such entities as acute
vestibular neuronitis, acute labyrinthitis, epidemic vertigo,
and viral labyrinthitis.

81.  Acute vestibular neuronitis, also known as acute vestibular
neuritis, neurolabyrinthitis, or unilateral vestibulopathy of
unknown cause, is characterized by sudden attacks of
severe and prolonged vertigo, nausea, vomiting, and
abnormal vestibular function on caloric testing in otherwise
healthy patients.
 It is unrelated to positional changes of the head and may
be recurrent.
 Some patients exhibit residual dizziness and imbalance
lasting for months.
 Cochlear symptoms are absent.

82.  Vestibular neuronitis has been attributed to viral upper
respiratory infections.
 Vestibular neuronitis affects only a part of the vestibular
nerve trunk, usually the superior division (horizontal
saccular canal paresis), which travels separately and has
its own ganglion, whereas the inferior part (the posterior
semicircular canal) is spared.
 Patients may also have a combined superior and inferior
vestibular neuronitis.

83.  Acute labyrinthitis resembles vestibular neuronitis except
that there is associated tinnitus and sensorineural hearing
loss.
 This syndrome may follow systemic, acute, or chronic
middle ear infections (i.e., viral or bacterial labyrinthitis) or
occur in association with ototoxic drugs such as
aminoglycosides and diuretics (i.e., toxic labyrinthitis).
 Viral labyrinthitis have been reported in association with
measles, mumps, and rubella.

84.  Episodic vertigo followed by gait imbalance and oscillopsia
may be familial (autosomal dominant).
 Patients with this familial vestibulopathy have profound
bilateral vestibular loss despite normal hearing, sometimes
in combination with a spinocerebellar ataxia.

85.  These episodes occurred regularly at 2-minute intervals,
each attack lasting for 15 seconds.
 This repetitive paroxysmal nystagmus and vertigo was
thought to be due to pathologic brief bursts of hyperactivity
of the vestibular nuclei.

86. Meniere's Disease
 progressive disorder characterized by episodic acute and
severe attacks of vertigo, fluctuating sensorineural hearing
loss, and tinnitus.
 Typically, the hearing loss in the early stages of Meniere's
disease affects only low frequencies, fluctuates, and
increases during the acute attack.
 Hearing returns to normal after each attack in the
beginning of the disease, but as the disease progresses,
residual hearing loss after each attack accumulates and the
hearing loss spreads to higher frequencies.
 There is also often a sensation of uncomfortable pressure
or fullness in and around the affected ear.

87.  more often unilateral, although it may be bilateral in
approximately 20%-45% of cases.
 When bilateral, the disease is usually asynchronous.
 Pathologically, there is an increased volume of
endolymphatic fluid leading to distention of the semicircular
canals: endolymphatic hydrops.

88.  Patients with meniere's disease complain initially of
distressing, fluctuating, and episodic vertigo of variable
duration and intensity.
 Nonpulsatile, low-pitched, continuous tinnitus, usually
described as roaring and sensorineural hearing loss
may precede the onset of vertigo by months or years.
 Individual attacks last several minutes to several
hours.
 Between attacks, patients are initially symptom free.

89.  Two main variants are recognized:
 cochlear Meniere's, in which vertigo and imbalance are
absent, and
 vestibular Meniere's, in which vertigo is prominent, but
hearing loss, tinnitus, and fullness, or ear pressure are
absent in the early stages.

91. Referrences
 DeJong’s The Neurologic examination, sixth edition.
 Localization in clinical neurology, sixth edition.
 Bradley’s Neurology in Clinical Practice, sixth edition.