Download Disorders of Hearing and Vestibular Function

CHAPTER
Disorders of Hearing
and Vestibular Function
55
Susan A. Fontana and Carol M. Porth
DISORDERS OF AUDITORY FUNCTION
The External Ear
Disorders of the External Ear
The Middle Ear and Eustachian Tube
Eustachian Tube Dysfunction
Barotrauma
Otitis Media
Otosclerosis
Disorders of the Inner Ear
Neural Pathways
Tinnitus
Disorders of the Central Auditory Pathways
Hearing Loss
Conduction Hearing Loss
Sensorineural Hearing Loss
Diagnosis and Treatment
Hearing Loss in Infants and Children
Hearing Loss in the Elderly
DISORDERS OF VESTIBULAR FUNCTION
The Vestibular System and Vestibular Reflexes
Peripheral Vestibular Apparatus
Neural Pathways
Nystagmus
Postural Reflexes
Vertigo
Motion Sickness
Disorders of Peripheral Vestibular Function
Benign Paroxysmal Positional Vertigo
Acute Vestibular Neuronitis
Ménière’s Disease
Disorders of Central Vestibular Function
Diagnostic Tests of Vestibular Function
Electronystagmography
Caloric Stimulation
Rotational Tests
Romberg Test
Treatment of Vestibular Disorders
Pharmacologic Methods
Vestibular Rehabilitation Exercises
T
he ears are paired organs consisting of an external and
middle ear, which function in capturing, transmitting,
and amplifying sound, and an inner ear that contains
the receptive organs that are stimulated by sound waves
(i.e., hearing) or head position and movement (i.e., vestibular function). Otitis media, or inflammation of the middle
ear, is a common disorder of childhood. Hearing loss is one
of the most common disabilities experienced by persons
in the United States, particularly among the elderly. Vertigo, a disorder of vestibular function, is also a common
cause of disability among the elderly. This chapter is divided into two parts: the first focuses on disorders of the
ear and auditory function and the second on disorders of
the inner ear and vestibular function.
Disorders of Auditory Function
After completing this section of the chapter, you should be able to
meet the following objectives:
✦ List the structures of the external, middle, and inner ear
and cite their function
✦ Describe two common disorders of the outer ear
✦ Relate the functions of the eustachian tube to the devel-
✦
✦
✦
✦
✦
✦
✦
opment of middle ear problems, including acute otitis
media and otitis media with effusion
Describe anatomic variations as well as risk factors that
make infants and young children more prone to develop
acute otitis media
List three common symptoms of acute otitis media
Describe the disease process associated with otosclerosis
and relate it to the progressive conductive hearing loss
that occurs
Characterize tinnitus
Differentiate between conductive, sensorineural, and
mixed hearing loss and cite the more common causes
of each
Describe methods used in the diagnosis and treatment of
hearing loss
Define the term presbycusis and describe factors that
contribute to its development
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UNIT XIII
Special Sensory Function
✦ Characterize the causes of hearing loss in infants and
children and describe the need for early diagnosis and
treatment
THE EXTERNAL EAR
The external ear consists of the auricle, which collects
sound, and the external acoustic meatus or ear canal,
which conducts the sound to the tympanic membrane1,2
(Fig. 55-1). The auricle, or pinna, is composed of elastic cartilage covered with thin skin, and an occasional hair. Its rim
is somewhat thicker, and its fleshy earlobe lack surrounding
cartilage. The funnel shape of the auricle concentrates
high-frequency sound entering from the lateral-forward
direction into the ear canal. This shape also helps to prevent
front–back confusion of sound sources. The external acoustic meatus, or ear canal, is a short (2 to 3 cm in adults)
S-shaped canal. A thin layer of skin containing fine hairs,
sebaceous glands, and ceruminous glands lines the ear canal.
Ceruminous glands secrete cerumen, or earwax, which has
certain antimicrobial properties and is thought to serve a
protective function.
The anterior portion of the auricle and external part
of the ear canal are innervated by branches of the trigeminal nerve (cranial nerve [CN] V). The posterior portions of
the auricle and the wall of the ear canal are innervated by
auricular branches of the facial (CN VII), glossopharyngeal
(CN IX), and vagus (CN X) nerves. Because of the vagal innervation, the insertion of a speculum or an otoscope into
the external ear canal can stimulate coughing or vomiting
reflexes, particularly in young children.
Inner
ear
Middle
ear
Tympanic
membrane
Semicircular
canals
The tympanic membrane, which separates the external
ear from the middle ear, has three layers: an outer layer of
thin skin continuous with the lining of the external ear
canal, a middle layer of tough collagenous fibers mixed with
fibrocytes and some elastic fibers, and an inner epithelial
layer continuous with the lining of the middle ear. It is
attached in a manner that allows it to vibrate freely when
audible sound waves enter the external auditory canal.
When viewed through an otoscope, the tympanic
membrane appears as a shallow, almost circular cone pointing inward toward its apex, the umbo (Fig. 55-2). Light
usually is reflected from the pars tensa at approximately
the 4-o’clock position. Landmarks include the lightened
stripe over the handle of the malleus; the umbo at the end
of the handle; the pars tensa, which constitutes most of
the drum; and the pars flaccida, the small area above the
malleus attachment. The tympanic membrane is semitransparent, and a small, whitish cord, which traverses the
middle ear from back to front, can be seen just under its
upper edge. This is the chorda tympani, a branch of the
intermedius component of the facial nerve (CN VII).
Disorders of the External Ear
The function of the external ear is disturbed when sound
transmission is obstructed by impacted cerumen, inflammation (i.e., otitis externa), or drainage from the external
ear (otorrhea).
Impacted Cerumen. Cerumen, or earwax, is a protective
secretion produced by the ceruminous glands of the skin
that lines the ear canal. Although the ear normally is selfcleaning, the cerumen can accumulate and narrow the
Cranial
nerve
VIII
Cochlear
portion
Vestibular
portion
Incus
Cochlea
Eustachian
tube
Malleus
Auricle
External
acoustic
meatus
Stapes
Pharynx
FIGURE 55-1 External, middle, and
internal subdivisions of the ear.
CHAPTER 55 Disorders of Hearing and Vestibular Function
Pars flaccida
Short process
of malleus
Posterior fold
Anterior
fold
Pars
tensa
Handle of
malleus
1331
Treatment usually includes the use of ear drops containing an appropriate antimicrobial agent in combination
with a corticosteroid to reduce inflammation. An antifungal
agent may also be used. Protection of the ear from additional moisture and avoidance of trauma from scratching
are important. Preventing recurrences is important, particularly in persons who swim frequently. Instillation of a dilute alcohol, acetic acid, or Burow’s otic solution (available
in over-the-counter ear drops) immediately after swimming
usually is an effective prophylaxis.
Umbo
Cone of
light
Posterior
Anterior
FIGURE 55-2 Right eardrum.
canal. Impaction is a common cause of reversible hearing
loss.3 Impacted cerumen usually produces no symptoms
until the canal becomes completely occluded, at which
point the person experiences a feeling of fullness, loss of
hearing, tinnitus (i.e., ringing in the ears), or coughing because of vagal stimulation.
In most cases, cerumen can be removed by gentle irrigation using a bulb syringe and warm tap water. Warm
water is used to avoid inducing a feeling of disequilibrium
owing to the vestibular caloric response. The ear canal
should be dried thoroughly after irrigation to avoid introducing an infection. Irrigation should be avoided in an
only-hearing ear or one that is postsurgical, prone to infection, or suspect for perforation of the tympanic membrane. Alternatively, health care professionals may remove
cerumen using an otoscope and a wire loop or blunt cerumen curette.
Cerumen that has become hardened or impacted can
be softened by instillation of a few drops of a ceruminolytic agent available commercially (e.g., dilute hydrogen
peroxide solution) or by prescription. Typically, these
agents are instilled in the affected ear one or two times
daily for up to 4 days before irrigation. Ceruminolytic agents
should not be used in ears that may have a perforated tympanic membrane.
Otitis Externa. Otitis externa is an inflammation of the external ear that can vary in severity from a mild eczematoid
dermatitis to severe cellulitis. It can be caused by infectious
agents, irritation (e.g., wearing earphones), or allergic reactions. Predisposing factors include moisture in the ear
canal after swimming (i.e., swimmer’s ear) or bathing and
trauma resulting from scratching or attempts to clean the
ear. Most infections are caused by gram-negative bacteria
(e.g., Pseudomonas, Proteus) or fungi that grow in the presence of excess moisture.4 Otitis externa commonly occurs
in the summer and is manifested by itching, redness, tenderness, and narrowing of the ear canal because of swelling. Inflammation of the pinna or canal makes movement
of the ear painful. There may be watery or purulent drainage
and intermittent hearing loss.
THE MIDDLE EAR AND EUSTACHIAN TUBE
The middle ear, or tympanic cavity, is a small, mucosalined cavity within the petrous portion of the temporal
bone (Fig. 55-3). It is bounded laterally by the tympanic
membrane and medially by a bony wall with two openings, the superior oval (vestibular window) and the round
(cochlear window). The middle ear is connected anteriorly
with the nasopharynx by the eustachian tube, also called
the pharyngotympanic tube. Posteriorly, it is connected
with small air pockets in the temporal bone called mastoid
air spaces or cells.
Three tiny bones, the auditory ossicles, are suspended
from the roof of the middle ear cavity and connect the tympanic membrane with the oval window (see Fig. 55-3). They
are connected by synovial joints and are covered with the
epithelial lining of the cavity.1,2 The malleus (“hammer”)
has its handle firmly fixed to the upper portion of the tympanic membrane. The head of the malleus articulates with
the incus (“anvil”), which articulates with the stapes (“stirrup”), which is inserted and sealed into the oval window by
an annular ligament. Arrangement of the ear ossicles is such
that their lever movements transmit vibrations from the
tympanic membrane to the oval window and from there to
the fluid in the inner ear. Two tissue-covered openings in
the medial wall, the oval and the round windows, provide
Petreous portion of
the temporal bone
Incus
Malleus
Base (footplate) of
stapes occupying
oval window
Stapes
Tympanic
cavity
Eustachian
tube
External acoustic
meatus
Tympanic
membrane
FIGURE 55-3 Anterior view of the ossicles in the middle ear.
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UNIT XIII
Special Sensory Function
is opened by the action of the trigeminal (CN V)–innervated
tensor veli palatini muscles (Fig. 55-5). Opening of the
eustachian tube, which normally occurs with swallowing
and yawning reflexes, provides the mechanism for equalizing the pressure of the middle ear with that of the atmosphere. This equalization ensures that the pressures on
both sides of the tympanic membrane are the same, so
that sound transmission is not reduced and rupture does
not result from sudden changes in external pressure, as
occurs during plane travel.
The eustachian tube is lined with a mucous membrane
that is continuous with the pharynx and the mastoid air
cells. Infections from the nasopharynx can travel from the
nasopharynx along the mucous membrane of the eustachian tube to the middle ear, causing acute otitis media.
Toward the nasopharynx, the eustachian tube becomes
lined by columnar epithelium with mucus-secreting cells.
Hypertrophy of the mucus-secreting cells is thought to
contribute to the mucoid secretions that develop during
certain types of otitis media.
Abnormalities in eustachian tube function are important factors in the pathogenesis of middle ear infections.
There are two important types of eustachian tube dysfunction: abnormal patency and obstruction (see Fig. 55-5).
The abnormally patent tube does not close or does not close
completely. In infants and children with an abnormally
patent tube, air and secretions often are pumped into the
eustachian tube during crying and nose blowing.
Obstruction can be functional or mechanical. Functional obstruction results from the persistent collapse of the
eustachian tube due to a lack of tubal stiffness or poor
function of the tensor veli palatini muscle that controls
the opening of the eustachian tube. It is common in infants and young children because the amount and stiffness of the cartilage supporting the eustachian tube are
less than in older children and adults. Changes in the craniofacial base also render the tensor muscle less efficient
for opening the eustachian tube in this age group. In addition, craniofacial disorders, such as a cleft palate, alter the
DISORDERS OF THE MIDDLE EAR
➤ The middle ear is a small, air-filled compartment in the
temporal bone. It is separated from the outer ear by the
tympanic membrane; communication between the nasopharynx and the middle ear occurs through the eustachian
tube; and tiny bony ossicles that span the middle ear transmit sound to the sensory receptors in the inner ear.
➤ Otitis media (OM) refers to inflammation of the middle ear,
usually associated with an acute infection (acute OM) or an
accumulation of fluid (OME). It commonly is associated with
disorders of eustachian tube function.
➤ The function of the middle ear is to conduct sound waves
from the external to the inner ear. Impaired conduction of
sound waves and hearing loss occur when the tympanic
membrane has been perforated; air in the middle ear has
been replaced with fluid (OME); or the function of the bony
ossicles has been impaired (otosclerosis).
for the transmission of sound waves between the air-filled
middle ear and the fluid-filled inner ear. It is the piston-like
action of the stapes footplate that sets up compression
waves in the inner ear fluid.
Eustachian Tube Dysfunction
The eustachian tube, which connects the nasopharynx
with the middle ear, is located in a gap in the bone between the anterior and medial walls of the middle ear
(Fig. 55-4). The eustachian tube serves three basic functions: (1) ventilation of the middle ear, along with equalization of middle ear and ambient pressures; (2) protection of the middle ear from unwanted nasopharyngeal
sound waves and secretions; and (3) drainage of middle
ear secretions into the nasopharynx.4,5 The nasopharyngeal
entrance to the eustachian tube, which usually is closed,
Nasopharynx
Nose
Mastoid
Middle ear
Eustachian
tube
Palate
FIGURE 55-4 Nasopharynx–eustachian tube–mastoid air cell
system. (Bluestone C.D. [1981]. Recent advances in pathogenesis, diagnosis, and management of otitis media. Pediatric Clinics of North America 28[4], 36. Reproduced with
permission)
CHAPTER 55 Disorders of Hearing and Vestibular Function
Normal
patency
TVP
Functional obstruction
Floppy tube
Poor TVP
function
Mechanical obstruction
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izes air pressure in the middle ear. Intranasal (e.g., phenylephrine HCl) or systemic decongestants may be used to prevent symptoms. Acute negative middle ear pressure that
persists on the ground is treated with decongestants and
attempts at autoinflation. More severe hearing loss or discomfort may require that the person consult an otolaryngologist. Myringotomy (i.e., surgical incision in the tympanic membrane) provides immediate relief and may be
used in cases of acute otalgia and hearing loss. Placement of
ventilation tubes may be considered for persons with repeated episodes of barotrauma related to frequent air travel.
Otitis Media
Intrinsic
Inflammation
Extrinsic
Tumor or
adenoids
FIGURE 55-5 Pathophysiology of the eustachian tube. TVP, tensor
veli palatini. (Bluestone C.D. [1981]. Recent advances in the pathogenesis, diagnosis, and management of otitis media. Pediatric Clinics
of North America 28[4], 737. With permission from Elsevier Science)
attachment of the tensor muscles, producing functional
obstruction of the eustachian tube.
Mechanical obstruction results from internal obstruction
or external compression of the eustachian tube. Ethnic differences in the structure of the palate may increase the
likelihood of obstruction. The most common internal obstruction is caused by swelling and secretions resulting
from allergy and viral respiratory infections. External compression by prominent or enlarged adenoidal tissue surrounding the opening of the eustachian tube may make
drainage less effective. Tumors also may obstruct drainage.
With obstruction, air in the middle ear is absorbed, causing
a negative pressure and the transudation of serous capillary fluid into the middle ear.
Barotrauma
Barotrauma represents injury resulting from the inability to
equalize the barometric stress on the middle ear imposed by
air travel or, less commonly, by underwater diving. It occurs
most often during air travel when there is a sudden change
in atmospheric pressure. The pressure in the middle ear parallels atmospheric pressure; it decreases at high altitudes
and increases at lower altitudes. The problem occurs during
rapid airplane descent, when the negative pressure in the
middle ear tends to cause the eustachian tube to collapse. If
air cannot pass back through the eustachian tube, hearing
loss and discomfort develop.
This most often occurs in persons who travel while suffering from an upper respiratory tract infection. Autoinflation measures such as yawning, swallowing, and chewing
gum facilitate opening of the eustachian tube, which equal-
Otitis media (OM) is an infection of the middle ear that is
associated with a collection of fluid. Although OM may
occur in any age group, it is the most common diagnosis
made by health care providers who care for children.6–10 Infants and young children are at highest risk for OM, with
the peak occurrence between 6 and 20 months of age.11 The
occurrence of the disease tends to decrease as a function of
age, with a marked decline after 6 years of age. The incidence is higher in boys, non–breast-fed infants, those who
use pacifiers beyond infancy, children in large day care settings, children exposed to tobacco smoke, those with siblings or parents with a significant history of OM, those with
allergic rhinitis, and children with congenital or acquired
immune deficiencies (e.g., acquired immunodeficiency syndrome). The incidence of OM also is higher among children
with craniofacial anomalies (e.g., cleft palate, Down syndrome) and among Canadian and Alaskan Eskimos and
Native Americans. It is more common during the winter
months, reflecting the seasonal patterns of upper respiratory tract infections.
There are two reasons for the increased risk for OM in
infants and young children: the eustachian tube is shorter,
more horizontal, and wider in this age group than in older
children and adults; and infection can spread more easily
through the eustachian canal of infants who spend most of
their day lying supine. Bottle-fed infants have a higher incidence of OM than breast-fed infants, probably because
they are held in a more horizontal position during feeding,
and swallowing while in the horizontal position facilitates
the reflux of milk into the middle ear. Breast-feeding also
provides for the transfer of protective maternal antibodies
to the infant.
Otitis media may present as acute otitis media (AOM),
recurrent OM, or OM with effusion (OME) or fluid in the
middle ear.
Acute Otitis Media. Acute OM is characterized by the presence of fluid in the middle ear in combination with signs
and symptoms of an acute or systemic infection. Acute otitis media can fail to resolve despite antibiotic treatment
(persistent OM), or it may resolve and then recur (recurrent OM). It is estimated that AOM resolves spontaneously
without treatment in approximately 60% of children.11
Most cases of AOM follow an upper respiratory tract infection that has been present for several days. The mucosal
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UNIT XIII
Special Sensory Function
lining of the middle ear is continuous with the eustachian
tube and nasopharynx, and most middle ear infections
enter through the eustachian tube (see Fig. 55-4). AOM
may be of either bacterial or viral origin. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis
are the three major bacterial pathogens isolated from the
middle ear in children with AOM.7–12 There may be more
than one type of bacteria present in some children. S. pneumoniae causes the largest proportion (40% to 50%) of cases
generated by a single organism, and it is the least likely to
resolve without treatment.8,11 Emergence of a multidrugresistant strain of S. pneumoniae (DRSP) has led to increased
numbers of treatment failures.13 Children may be considered as at either high or low risk for DRSP. Children who
are at high risk for DRSP include those younger than 2 years
of age, those who attend day care, and those who have
received antibiotics in the past 3 months.8,11
The role of viruses as etiologic agents in AOM is controversial. Viruses have been identified as a single pathogen in only a few middle ear aspirates obtained from children with AOM. Viruses may promote bacterial infection
by impairing eustachian tube function and other host defenses.11 The respiratory syncytial virus is the virus most
frequently associated with AOM. Parainfluenza and influenza viruses are other common viral pathogens in AOM.
As with bacterial infections, more than one type of respiratory virus may be present in the middle ear fluid of children with AOM.14
Manifestations. Acute OM is characterized by otalgia
(earache), fever (temperature up to 104°F), and hearing
loss. Children older than 3 years of age may have rhinorrhea or running nose, vomiting, and diarrhea. In contrast, younger children often have nonspecific signs and
symptoms that manifest as ear tugging, irritability, nighttime awakening, and poor feeding. Ear pain usually increases as the effusion accumulates behind the tympanic
membrane. Perforation of the tympanic membrane may
occur acutely, allowing purulent material from the eustachian tube to drain into the external auditory canal. This
may prevent spread of the infection into the temporal
bone or intracranial cavity. Spontaneous perforation with
discharge occurs most frequently in children of high-risk
ethnic groups.
Diagnosis. Diagnosis of AOM is made by associated signs
and symptoms and otoscopic examination. In persons
with AOM, a bulging yellow or red tympanic membrane
with subsequent obliteration of the bony landmarks and
cone of light is observed. Gentle movement of the pinna
can help to differentiate OM from otitis externa. This maneuver does not produce pain in AOM but causes severe
discomfort in otitis externa. Although diagnosis of AOM
often can be made by otoscopic examination alone, pneumatic otoscopy usually is performed to document middle
ear effusion and immobility of the tympanic membrane.15
The use of the pneumatic otoscope permits the introduction of air into the ear canal for the purpose of determin-
ing tympanic membrane flexibility. The movement of the
tympanic membrane is decreased in some cases of AOM
and absent in chronic middle ear infection.
The diagnosis of AOM can be confirmed using tympanometry or acoustic reflectometry. Tympanometry is helpful
in detecting effusion in the middle ear or high negative
middle ear pressure. A tympanogram is obtained by inserting a small probe into the external auditory canal; a tone of
fixed characteristics is then presented through the probe,
and the mobility of the tympanic membrane is measured
electronically while the external canal pressure is artificially
varied. The tympanogram provides a determination of the
degree of negative pressure present in the middle ear. It detects disease when present but is less reliable when disease
is absent. Acoustic reflectometry is used to reflect sound
waves from the middle ear and provides information as to
whether an effusion is absent or present. Increased reflected sound correlates with an increased likelihood of effusion. This technique is most useful in children older
than 3 months, and its success depends on user technique.
Tympanocentesis may be done to relieve pain from an
effusion or to obtain an organism for culture and sensitivity testing. The procedure involves the insertion of a needle
through the inferior part of the tympanic membrane. Because of the cost, effort, and lack of availability, it is not routinely used in management of AOM.12 In selected cases of
refractory or recurrent middle ear disease, tympanocentesis
can serve to improve diagnostic accuracy, guide treatment,
and avoid unnecessary medical or surgical interventions. In
instances in which the tympanic membrane has perforated
with resultant drainage into the external ear, a culture c
an be made and microbiologic studies done to identify a
microorganism.
Treatment. The treatment of AOM includes the judicious
use of antibiotic therapy in high-risk children, especially
those younger than 2 years of age who are at increased risk
for intracranial complications and speech and language
impairment.8,11 The dramatic emergence of DRSP in the
United States has led to increased treatment failures for
AOM. Current recommendations suggest that if there is a
lack of improvement in symptoms by day 3 of the initial
antibiotic therapy, a switch to an antibiotic that targets resistant pathogens is recommended.16 Older children who
have no fever or a low-grade fever usually do not require
antibiotic treatment provided follow-up evaluation of
symptoms occurs within 1 to 3 days. Regardless of whether
antibiotic therapy is indicated, supportive therapy that
includes analgesics, antipyretics, and local heat often is
helpful. If the tympanic membrane is bulging and painful
because of the accumulation of purulent drainage, a
myringotomy may be done to relieve the pressure, thus reducing pain and hearing loss. In addition, this procedure
prevents the ragged opening that can follow spontaneous
rupture of the tympanic membrane.
Residual middle ear effusions are part of the continuum of AOM and persist regardless of whether antibiotics
have been used. The effusion usually clears spontaneously
within 1 to 3 months and does not require further treatment unless it persists beyond this period.
CHAPTER 55 Disorders of Hearing and Vestibular Function
Recurrent Otitis Media. Recurrent OM is defined as three
new AOM episodes within 6 months or four episodes in
1 year that occur with almost every upper respiratory tract
infection. Reinforcement of environmental controls, such
as avoidance of passive tobacco smoke, is important. Children with recurrent OM should be evaluated to rule out any
anatomic variations (e.g., enlarged adenoids) and immunologic abnormalities. Children with immunoglobulin G subclass deficiencies (see Chapter 21) and poor responses to
polysaccharide vaccines are more likely to develop recurrent OM.11
Traditionally, prophylactic antibiotics or antibiotics
given at one half the therapeutic dose may be given once
daily for up to 6 months during winter and spring. Although
children with recurrent OM respond well to such treatment,
increasing concern regarding the emergence of bacterial
resistance has emerged as a rationale for more judicious
use of prophylactic antibiotics. Another approach to prevent recurrent OM is immunization with pneumococcal
and influenza vaccines. Referral for placement of tympanostomy tubes is another alternative, particularly for children who have experienced five or more OM episodes
within a 12-month period.
Otitis Media With Effusion. Otitis media with effusion is a
condition in which the tympanic membrane is intact and
there is an accumulation of fluid in the middle ear without
signs or symptoms of infection. The type of effusion often
is described as serous, nonsuppurative, or secretory, but
these terms may not be correct in all cases. The duration
of the effusion may range from less than 3 weeks to more
than 3 months. The similarity between OME and AOM is
that hearing loss may be present in both conditions. The
major distinction is that signs and symptoms of infection
are lacking in OME, although some children may complain
of a feeling of ear fullness. Distinguishing between OME
and AOM often is difficult because of the variability and
overlap of symptoms, particularly in young children.
Diagnosis is based on otoscopic examination, which
frequently reveals opacification of the tympanic membrane, making it difficult to visualize the effusion and,
thus, characterize the type. If the tympanic membrane is
translucent, a yellow or bluish fluid may be seen, as may
an air–fluid level or bubbles, or both. Pneumatic otoscopy often reveals decreased mobility of the tympanic
membrane, with a shape that is either retracted or convex. Alternatively, fullness or bulging may be noted.
Most cases of persistent middle ear effusion resolve
spontaneously within a 3-week to 3-month period. The
management options for this duration include observation only, antibiotic therapy, or combination antibiotic
and corticosteroid therapy. Topical and systemic decongestants usually are of little value in clearing middle ear
effusion. Because there is concern over hearing loss and its
effect on learning and speech, a hearing evaluation may
be indicated and usually is done after 6 weeks.
If the effusion persists for 3 months or longer and is accompanied by hearing loss of 20 decibels (dB) or greater
in children of normal development, tympanostomy tube
placement may be indicated.11 The tubes usually are placed
1335
under general anesthesia. The ears of children with tubes
must be kept out of water. Spontaneous extrusion of tubes
usually occurs after 5.5 to 7 months.17 Complications of
tube placement include recurrent otorrhea; persistent perforation, scarring, and atrophy of the tympanic membrane;
and cholesteatoma.
Complications. Since the advent of antimicrobial therapy, the intracranial suppurative complications of OM
have been uncommon. However, extratemporal complications, including those affecting the middle ear, mastoid, and adjacent structures of the temporal bone, continue to occur.
Hearing loss, which is a common complication of
OM, usually is conductive and temporary based on the duration of the effusion. Hearing loss that is associated with
fluid collection usually resolves when the effusion clears.
Permanent hearing loss may occur as the result of damage
to the tympanic membrane or other middle ear structures.
Cases of sensorineural hearing loss are rare. Persistent and
episodic conductive hearing loss in children may impair
their cognitive, linguistic, and emotional development.8,9
Children younger than 3 years of age with recurrent OME
are at increased risk for impaired language development.8
Additional studies indicate that before 3 years of age, time
spent with middle ear effusion correlates with decreased
cognitive development as measured by standardized inventories.18 However, the degree and duration of hearing
loss required to produce such effects are unknown.
Perforation of the tympanic membrane can occur
spontaneously or result from surgical interventions. Temporary perforations are created for surgical treatment of
AOM (myringotomy) or for tube placement. Usually, the
perforations heal spontaneously. Antimicrobial treatment
for AOM with acute perforation is the same as for AOM
without perforation.13 When chronic drainage is present,
cultures usually are performed and the antimicrobial regimen adjusted accordingly. Otic drops also may be instilled
in the external ear to prevent or treat an external canal infection.13 Healing of the tympanic membrane usually follows resolution of the middle ear infection.
Adhesive OM involves an abnormal healing reaction
in an inflamed middle ear. It produces irreversible thickening of the mucous membranes and may cause impaired
movement of the ossicles and possibly conductive hearing
loss. Tympanosclerosis involves the formation of whitish
plaques and nodular deposits on the submucosal surface
of the tympanic membrane, with possible adherence of
the ossicles and conductive hearing loss.
A cholesteatoma is a saclike mass containing silverywhite debris of keratin, which is shed by the squamous
epithelial lining of the tympanic membrane.19 As the lining of the epithelium sheds and desquamates, the lesion
expands and erodes the surrounding tissues. The lesion,
which is associated with chronic middle ear infection, is
insidiously progressive, and erosion may involve the temporal bone, causing intracranial complications. Although
often thought of as a complication of otitis media, a cholesteatoma may also occur as a congenital condition. Symptoms commonly include painless drainage from the ear
1336
UNIT XIII
Special Sensory Function
and hearing loss. Treatment involves microsurgical techniques to remove the cholesteatomatous material.
The mastoid antrum and air cells constitute a portion
of the temporal bone and may become inflamed as an
extension of acute or chronic OM. The disorder causes
necrosis of the mastoid process and destruction of the
bony intercellular matrix, which are visible by radiologic
examination. Mastoid tenderness and drainage of exudate
through a perforated tympanic membrane can occur.
Chronic mastoiditis can develop as the result of chronic
middle ear infection. The usefulness of antibiotics for this
condition is limited. Mastoid or middle ear surgery, along
with other medical treatment, may be indicated. The incidence of mastoiditis has markedly decreased compared
with the preantimicrobial era. It remains uncertain
whether this decrease is due to antimicrobial treatment,
changes in the natural history of OM, changes in organism virulence, or increased host resistance.20
Intracranial complications, although rare, can develop
if the infection spreads through vascular channels, by direct
extension, or through preformed pathways such as the
round window. These complications are seen more often
with chronic suppurative OM and mastoiditis. They include meningitis, focal encephalitis, brain abscess, lateral
sinus thrombophlebitis or thrombosis, labyrinthitis, and
facial nerve paralysis. Any child who develops persistent
headache, tinnitus, stiff neck, or visual or other neurologic
symptoms should be investigated for possible intracranial
complications.
Otosclerosis
Otosclerosis refers to the formation of new spongy bone
around the stapes and oval window, which results in progressive deafness21 (see Fig. 55-3). In most cases, the condition is familial and follows an autosomal dominant pattern
with variable penetrance. Otosclerosis may begin at any
time in life but usually does not appear until after puberty,
most frequently between the ages of 20 and 30 years. The
disease process accelerates during pregnancy.
Otosclerosis begins with resorption of bone in one or
more foci. During active bone resorption, the bone structure
appears spongy and softer than normal (i.e., osteospongiosis). The resorbed bone is replaced by an overgrowth of new,
hard, sclerotic bone. The process is slowly progressive, involving more areas of the temporal bone, especially in front
of and posterior to the stapes footplate. As it invades the
footplate, the pathologic bone increasingly immobilizes the
stapes, reducing the transmission of sound. Pressure from
the otosclerotic bone on inner ear structures or the vestibulocochlear nerve (CN VIII) may contribute to the development of tinnitus, sensorineural hearing loss, and vertigo.
The symptoms of otosclerosis involve an insidious
hearing loss. Initially, the affected person is unable to hear
a whisper or someone speaking at a distance. In the earliest stages, the bone conduction by which the person’s own
voice is heard remains relatively unaffected. At this point,
the person’s own voice sounds unusually loud, and the
sound of chewing becomes intensified. Because of bone
conduction, most of these persons can hear fairly well on
the telephone, which provides an amplified signal. Many
are able to hear better in a noisy environment, probably
because the masking effect of background noise causes
other persons to speak louder.
The treatment of otosclerosis can be medical or surgical. A carefully selected, well-fitting hearing aid may allow
a person with conductive deafness to lead a normal life.
Sodium fluoride has been used with some success in the
medical treatment of osteospongiosis. Because much of
the conductive hearing loss associated with otosclerosis is
caused by stapedial fixation, surgical treatment involves
stapedectomy with stapedial reconstruction using the patient’s own stapes or a stapedial prosthesis. The argon laser
may be used in the surgical procedure.
DISORDERS OF THE INNER EAR
The inner ear contains the receptors for hearing.1,2,22 It
contains a labyrinth or system of intercommunicating
channels and the receptors for hearing and position sense.
Structurally, it consists of an outer bony labyrinth located
in the temporal bone and an inner, fluid-filled membranous labyrinth (Fig. 55-6). Two separate fluids are found
in the inner ear. The perilymph or periotic fluid separates the
bony labyrinth from the membranous labyrinth, and the
endolymph or otic fluid fills the membranous labyrinth. The
composition of the perilymph is similar to that of the CSF,
and a tubular perilymphatic duct connects the perilymph
with the CSF in the arachnoid space of the posterior fossa.
The endolymph has a potassium content that is similar to
that of intracellular fluid. A small-diameter tubular extension, the endolymphatic sac, connects this system with
the subdural space near the jugular foramen, providing an
exit for the slowly circulating endolymph.
The bony labyrinth occupies a volume with a diameter less than the size of a dime. It is divided into a series of
perilymph-filled interconnected cavities: the cochlea, the
semicircular canals, the utricle, and the saccule. The receptors for hearing are contained in the cochlea, and those
for head position sense are contained in the semicircular
canals, the utricle, and the saccule. The vestibule is the
central egg-shaped cavity of the bony labyrinth that lies
posterior to the cochlea and anterior to the semicircular
canals. The oval window that connects the inner ear with
the middle ear is located in its lateral wall.
The cochlea is enclosed in a bony tube shaped like a
snail shell that winds around a central bone column called
the modiolus. A membranous triangular cochlear duct
stretches across the cochlea, separating it into two parallel
tubes, each containing perilymph: the scala vestibuli and the
scala tympani (Fig. 55-7). One side of the cochlear duct,
the basilar membrane, stretches under tension laterally
from the modiolus to an elastic spiral ligament. A second
side, the vestibular membrane (i.e., Reissner’s membrane),
is a delicate double layer of squamous epithelial cells. The
third side consists of a well-vascularized epithelium, the
stria vascularis, which is the source of the endolymph.
The cochlear duct separates the scala vestibuli and the
scala tympani from the base of the cochlea throughout its
two and one-half spiral turns to its apex. An opening at the
CHAPTER 55 Disorders of Hearing and Vestibular Function
1337
Semicircular canals
Common
limb
Vestibular
ganglion
Anterior
Semicircular ducts
Posterior
Lateral
Vestibular
nerve
Cochlear
nerve
Vestibulocochlear nerve
(CN VIII)
Spiral ganglion
Cochlea
Ampullae of semicircular ducts
Utricle
Saccule
Basal turn
of cochlea
Spiral canal
site of spiral
organ (of Corti)
FIGURE 55-6 Schematic lateral view of the bony and membranous labyrinths showing the membranous
labyrinth in a closed system of ducts and chambers filled with endolymph and bathed in perilymph with
the bony labyrinth. Observe the parts of membranous labyrinth: the cochlear duct, the saccule and utricle within the vestibule, and the semicircular ducts within the semicircular canals. (From Moore K.L.,
Dalley A.F. [1999]. Clinically oriented anatomy [4th ed., p. 1102]. Philadelphia: Lippincott Williams & Wilkins)
Scala vestibuli (perilymph)
Oval window
Vestibular membrane
Cochlear duct
(endolymph)
Tectorial membrane
Organ of Corti
Basilar membrane
Middle ear
Round window
Scala tympani (perilymph)
Cochlear nerve Spiral ganglion
A
Inner hair cell
Outer hair cell
Tectorial
membrane
FIGURE 55-7 (A) Path taken by sound
waves reaching the inner ear. (B) Spiral organ of Corti has been removed
from the cochlear duct and greatly
enlarged to show the inner and outer
hair cells, the basilar membrane, and
cochlear nerve fibers.
Cochlear
nerve fibers
B
Basilar
membrane
1338
UNIT XIII
Special Sensory Function
apex, called the helicotrema, permits fluid waves to move
between the two scalae.
Unlike light, which can be transmitted through a vacuum such as outer space, sound is a pressure disturbance
originating from a vibrating object and propagated by the
molecules of an elastic medium. Sound waves, delivered
by the stapes footplate to the perilymph, travel throughout the fluid of the inner ear, including up the scala
vestibuli, to the apex of the cochlea. Because fluids are incompressible, each time the fluid adjacent to the oval window is forced medially by the stapes, the membrane in the
round window bulges out into the middle ear and acts as
a pressure valve.
As the pressure wave descends through the flexible
vestibular membrane, it sets the entire basilar membrane
into vibrations. The basilar membrane becomes progressively more massive from base to its distal apex and resonates to higher frequencies near the base and to lower
frequencies toward the apex as the fluid pressure wave travels up the cochlear spiral. This “tuned” aspect of the basilar
membrane results in increased amplitude of displacement
at the resonant locations, responding to a particular sound
frequency and greater firing of cochlear neurons innervating this region. This mechanism provides the major basis
for the discrimination of sound frequency.
Perched on the basilar membrane and extending along
its entire length is an elaborate arrangement of columnar
epithelium called the organ of Corti (see Fig. 55-7). Continuous rows of hair cells separated into inner and outer
rows can be found within the columnar arrangement.
The cells have hairlike cilia that protrude through openings in an overlying supporting reticular membrane into
the endolymph of the cochlear duct. A gelatinous mass,
the tectorial membrane, extends from the medial side
of the duct to enclose the cilia of the outer hair cells. The
traveling compression waves moving from base to apex
through the periotic fluid distort the organ of Corti, causing the hairs to bend against the less flexible tectorial
membrane. Each inner hair cell is innervated by several
nerve fibers and the outer hair cells, by many cochlear afferent neuron terminals.
Selective destruction of hair cells in a particular segment of the cochlea can lead to hearing loss of particular
tones. The outer rows of hair cells appear to provide the
signals on which the experience of loudness, a correlate of
the sound’s physical intensity, is based.
Neural Pathways
Afferent fibers from the organ of Corti have their cell bodies in the spiral ganglion in the central portion of the
cochlea. Nerve fibers from the spiral ganglion (i.e., vestibulocochlear or auditory nerve [CN VIII]) travel to the cochlear
nuclei in the caudal pons. Many secondary nerve fibers
from the cochlear nuclei pass to the opposite side of the
pons. These secondary fibers may project to such cell
groups as the trapezoid or the superior olivary nucleus, or
rostrally toward the inferior colliculus of the midbrain.
Ipsilateral (same side) projections and interconnections
between the nuclei of the two sides occur throughout the
central auditory system. Consequently, impulses from either ear are transmitted through the auditory pathways to
both sides of the brain stem.
From the inferior colliculus, the auditory pathway
passes to the medial geniculate nucleus of the thalamus,
where all the fibers synapse. Considerable evidence supports the capability of this level of organization to provide
crude auditory experience, including crude tone and intensity discrimination and the directionality of a sound
source. From the medial geniculate nucleus, the auditory
tract spreads through the auditory radiation to the primary
auditory cortex (area 41), located mainly in the superior
temporal gyrus and insula (see Chapter 49, Fig. 49-24). This
area and its corresponding higher-order thalamic nucleus
are required for high-acuity loudness discrimination and
precise discrimination of pitch. The auditory association
cortex (areas 42 and 22) borders the primary cortex on the
superior temporal gyrus. This area and its associated higherorder thalamic nuclei are necessary for auditory gnosis, or
the meaningfulness of sound, to occur. Experience and the
precise analysis of momentary auditory information are integrated during this process.
Tinnitus
Tinnitus (from the Latin tinniere, meaning “to ring”) is the
perception of abnormal ear or head noises, not produced by
an external stimulus.23–25 Although it often is described as
“ringing of the ears,” it may also assume a hissing, roaring,
buzzing, or humming sound. Tinnitus may be constant, intermittent, and unilateral or bilateral. It has been estimated
that 37 million people in the United States have the disorder. Nearly 10 million of these are estimated to have severe or troubling tinnitus.24 The condition affects males and
females equally, is most prevalent between 40 and 70 years
of age, and occasionally affects children.23
Although tinnitus is subjective, for clinical purposes it
is subdivided into objective and subjective tinnitus. Objective tinnitus refers to those rare cases in which the sound is
detected or potentially detectable by another observer.
Typical causes of objective tinnitus include vascular abnormalities or neuromuscular disorders. In some vascular
disorders, for example, sounds generated by turbulent
blood flow (e.g., arterial bruits or venous hums) are conducted to the auditory system. Vascular disorders typically
produce a pulsatile form of tinnitus.
Subjective tinnitus refers to noise perception when there
is no noise stimulation of the cochlea. A number of causes
and conditions have been associated with subjective tinnitus. Intermittent periods of mild, high-pitched tinnitus
lasting for several minutes are common in normal-hearing
persons. Impacted cerumen is a benign cause of tinnitus,
which resolves after the earwax is removed. Medications
such as aspirin and stimulants such as nicotine and caffeine can cause transient tinnitus. Conditions associated
with more persistent tinnitus include noise-induced hearing loss, presbycusis (sensorimotor hearing loss that occurs
with aging), hypertension, atherosclerosis, head injury,
and cochlear or labyrinthine infection or inflammation.
CHAPTER 55 Disorders of Hearing and Vestibular Function
The physiologic mechanism underlying subjective
tinnitus is largely unknown. It seems likely that there are
several mechanisms, including abnormal firing of auditory receptors, dysfunction of cochlear neurotransmitter
function or ionic balance, damage to the auditory nerve,
or alterations in central processing of the signal.
Because tinnitus is a symptom, the diagnosis relies
heavily on the person’s description of the problem, including onset, frequency, description, and location of the
tinnitus; perceived cause; and extent to which the person
is bothered by the problem.26 A history of medication or
stimulant use and dietary factors that may cause tinnitus
should be obtained. Tinnitus often accompanies hearing
disorders, and tests of auditory function usually are done.
Causes of objective tinnitus, such as serious vascular abnormalities, should be ruled out.
Treatment measures are designed to treat the symptoms rather than effect a cure.23–25 They include elimination of drugs or other substances such as caffeine, some
cheeses, red wine, and foods containing monosodium glutamate that are suspected of causing tinnitus. The use of an
externally produced sound (noise generators or tinnitusmasking devices) may be used to mask or inhibit the tinnitus. Medications, including antihistamines, anticonvulsant
drugs, calcium channel blockers, benzodiazepines, and
antidepressants, have been used for tinnitus alleviation,
but most are not effective, and many produce undesirable
side effects. For persistent tinnitus, psychological interventions may be needed to help the person deal with the stress
and distraction associated with the condition. Tinnitus retraining therapy, which includes directive counseling and
extended use of low-noise generators to facilitate auditory
adaptation to the tinnitus, has met with considerable success. Surgical intervention (i.e., cochlear nerve section, vascular decompression) is a last resort for persons in which
all other interventions have failed and in whom the disorder is disabling.
DISORDERS OF THE CENTRAL
AUDITORY PATHWAYS
The auditory pathways in the brain involve communication between the two sides of the brain at many levels. As
a result, strokes, tumors, abscesses, and other focal abnormalities seldom produce more than a mild reduction in
auditory acuity on the side opposite the lesion. For intelligibility of auditory language, lateral dominance becomes
important. On the dominant side, usually the left side,
the more medial and dorsal portion of the auditory association cortex is of crucial importance. This area is called
Wernicke’s area, and damage to it is associated with auditory receptive aphasia (and agnosia of speech). Persons
with damage to this area of the brain can speak intelligibly and read normally but are unable to understand the
meaning of major aspects of audible speech.
Irritative foci that affect the auditory radiation or the
primary auditory cortex can produce roaring or clicking
1339
sounds, which appear to come from the auditory environment of the opposite side (i.e., auditory hallucinations).
Focal seizures that originate in or near the auditory cortex
often are immediately preceded by the perception of ringing or other sounds preceded by a prodrome (i.e., aura).
Damage to the auditory association cortex, especially if bilateral, results in deficiencies of sound recognition and
memory (i.e., auditory agnosia). If the damage is in the
dominant hemisphere, speech recognition can be affected
(i.e., sensory or receptive aphasia).
HEARING LOSS
Nearly 30 million Americans have hearing loss.27,28 It affects
persons of all age groups. One of every 1000 infants born in
the United States is completely deaf, and more than 3 million children have hearing loss. Between 25% and 40% of
people older than 65 years of age have hearing loss.29
Hearing is a specialized sense that provides the ability to perceive vibration of sound waves. Functions of the
ear include receiving sound waves, distinguishing their
frequency, translating this information into nerve impulses, and transmitting these impulses to the CNS. The
compression waves that produce sound have frequency
and intensity. Frequency indicates the number of waves
per unit time (reported in cycles per second [cps] or hertz
[Hz]). The human ear is most sensitive to waves in the frequency range of 1000 to 3000 Hz. Most persons cannot
hear compression waves that have a frequency higher
than 20,000 Hz. Waves of higher frequency are called ultrasonic waves, meaning that they are above the audible
range. In the audible frequency range, the subjective experience correlated with sonic frequency is the pitch of a
HEARING LOSS
➤ Hearing is a special sensory function that incorporates the
sound-transmitting properties of the external ear canal,
the eardrum that separates the external and middle ear,
the bony ossicles of the middle ear, the sensory receptors
of the cochlea in the inner ear, the neural pathways of the
vestibulocochlear or auditory nerve, and the primary
auditory and auditory association cortices.
➤ Hearing loss represents impairment of the ability to detect
and perceive sound.
➤ It can range from mild, affecting sounds of different tones
and intensities, to moderate or profound.
➤ Hearing loss can be caused by conductive disorders, in
which auditory stimuli are not transmitted through the structures of the outer and middle ears to the sensory receptors
in the inner ear; by sensorineural disorders that affect the
inner ear, auditory nerve, or auditory pathways; or by a
combination of conductive and sensorineural disorders.
1340
UNIT XIII
Special Sensory Function
sound. Waves below 20 to 30 Hz are experienced as a rattle or drum beat rather than a tone.
Wave intensity is represented by amplitude or units of
sound pressure. By convention, the intensity (in power
units, or ergs per square centimeter) of a sound is expressed as the ratio of intensities between the sound and
a reference value. A 10-fold increase in sound pressure is
called a bel, after Alexander Graham Bell. Because this
representation is too crude to be of use, the decibel (dB),
or one tenth of a bel, is used. For purposes of hearing
evaluation, the threshold for perception of sound at a
given frequency in persons with normal hearing is set at
0 dB.30
Hearing loss is qualified as mild, moderate, severe, or
profound. “Hard of hearing” is defined as hearing loss
greater than 20 to 25 dB in adults and greater than 15 dB
in children. Profound deafness is defined as hearing loss
greater than 100 dB31 or 70 dB in children.32 There are many
causes of hearing loss or deafness. Most fit into the categories of conductive, sensorineural, or mixed deficiencies
that involve a combination of conductive and sensorineural
function deficiencies of the same ear.30 Chart 55-1 summarizes common causes of hearing loss. Hearing loss may be
genetic or nongenetic, sudden or progressive, unilateral
or bilateral, partial or complete, reversible or irreversible.
Age and suddenness of onset provide important clues as
to the cause of hearing loss.
Conductive Hearing Loss
Conductive hearing loss occurs when auditory stimuli are
not adequately transmitted through the auditory canal,
tympanic membrane, middle ear, or ossicle chain to the
inner ear. Temporary hearing loss can occur as the result of
impacted cerumen in the outer ear or fluid in the middle
ear. Foreign bodies, including pieces of cotton and insects,
may impair hearing. More permanent causes of hearing
loss are thickening or damage of the tympanic membrane
or involvement of the bony structures (ossicles and oval
window) of the middle ear due to otosclerosis or Paget’s
disease (see Chapter 58).
CHART 55-1
Common Causes of Conductive
and Sensorineural Hearing Loss
Conductive Hearing Loss
• External ear conditions
• Impacted earwax or foreign body
• Otitis externa
Middle
ear conditions
•
• Trauma
• Otitis media (acute and with effusion)
• Otosclerosis
• Tumors
Sensorineural Hearing Loss
• Trauma
• Head injury
• Noise
• Central nervous system infections (e.g., meningitis)
• Degenerative conditions
• Presbycusis
• Vascular
• Atherosclerosis
• Sudden deafness
• Ototoxic drugs (e.g., aminoglycosides, salicylates,
loop diuretics)
• Tumors
• Vestibular schwannoma (acoustic neuroma)
• Meningioma
• Metastatic tumors
• Idiopathic
• Ménière’s disease
Mixed Conductive and Sensorineural Hearing Loss
• Middle ear conditions
• Barotrauma
• Cholesteatoma
• Otosclerosis
Temporal
bone fractures
•
Sensorineural Hearing Loss
Sensorineural, or perceptive, hearing loss occurs with disorders that affect the inner ear, auditory nerve, or auditory pathways of the brain. With this type of deafness,
sound waves are conducted to the inner ear, but abnormalities of the cochlear apparatus or auditory nerve decrease or distort the transfer of information to the brain.
Tinnitus often accompanies cochlear nerve irritation. Abnormal function resulting from damage or malformation
of the central auditory pathways and circuitry is included
in this category.
Sensorineural hearing loss may have a genetic cause or
may result from intrauterine infections such as maternal
rubella, or developmental malformations of the inner ear.
Genetic hearing loss may result from mutation in a single
gene (monogenetic) or from a combination of mutations in
different genes and environmental factors (multifactorial).
It has been estimated that 50% of profound deafness in
children has a monogenetic basis.30,31 The inheritance pat-
tern for monogenetic hearing loss is autosomal recessive in
approximately 75% of cases.32 Hearing loss may begin before development of speech (prelingual) or after speech development (postlingual). Most prelingual forms are present
at birth. Genetic forms of hearing loss also can be classified
as being part of a syndrome in which other abnormalities
are present, or as nonsyndromic, in which deafness is the
only abnormality.
Sensorineural hearing loss also can result from trauma
to the inner ear, tumors that encroach on the inner ear
or sensory neurons, vascular disorders with hemorrhage,
or thrombosis of vessels that supply the inner ear. Other
causes of sensorineural deafness are infections and drugs.
Sudden sensorineural hearing loss represents an abrupt
loss of hearing that occurs instantaneously or on awakening. It most commonly is caused by viral infections, circulatory disorders, or rupture of the labyrinth membrane
that can occur during tympanotomy.33
CHAPTER 55 Disorders of Hearing and Vestibular Function
Environmentally induced deafness can occur through
direct exposure to excessively intense sound, as in the
workplace or at a concert. This is a particular problem in
older adults who were working in noisy environments before the mid-1960s, when there were no laws mandating
use of devices for protective hearing. This type of deafness
was once called boilermaker’s deafness because of the intense reverberating sound to which riveters were exposed
when putting together boiler tanks. Sustained or repeated
exposure to noise pollution at sound intensities greater
than 100 to 120 dB can cause corresponding mechanical
damage to the organ of Corti on the “tuned” basilar membrane. If damage is severe, permanent sensorineural deafness to the offending sound frequencies results. Wearing
earplugs or ear protection is important under many industrial conditions and for musicians and music listeners
exposed to high sound amplification. Noise pollution
often is characterized by high-intensity sounds of a specific frequency that cause corresponding damage to the
organ of Corti. Temporary threshold shift is a reversible
hearing loss that occurs in individuals who attend loud
concerts and hear ringing sounds after the event.
A number of infections can cause hearing loss. Deafness or some degree of hearing impairment is the most
common serious complication of bacterial meningitis in
infants and children, reportedly resulting in sensorineural
hearing loss in 5% to 35% of persons who survive the infection.30 The mechanism causing hearing impairment
seems to be a suppurative labyrinthitis or neuritis resulting in the loss of hair cells and damage to the auditory
nerve. Untreated suppurative OM also can extend into the
inner ear and cause sensorineural hearing loss through the
same mechanisms. Congenital and acquired syphilis can
cause unilateral or bilateral sensorineural hearing loss.
Hypothyroidism is a potential cause of sensorineural hearing loss in older persons.
Among the neoplasms that impair hearing are acoustic
neuromas. Acoustic neuromas are benign Schwann cell tumors affecting CN VIII. These tumors usually are unilateral
and cause hearing loss by compressing the cochlear nerve
or interfering with blood supply to the nerve and cochlea.
Other neoplasms that can affect hearing include meningiomas and metastatic brain tumors. The temporal bone is
a common site of metastases. Breast cancer may metastasize to the middle ear and invade the cochlea.
Drugs that damage inner ear structures are labeled ototoxic. Vestibular symptoms of ototoxicity include lightheadedness, giddiness, and dizziness; if toxicity is severe,
cochlear symptoms consisting of tinnitus or hearing loss
occur. Hearing loss is sensorineural and may be bilateral or
unilateral, transient or permanent. Several classes of drugs
have been identified as having ototoxic potential, including the aminoglycoside antibiotics and some other basic
antibiotics, antimalarial drugs, some chemotherapeutic
drugs, loop diuretics, and salicylates (e.g., aspirin). The
symptoms of drug-induced hearing loss may be transient,
as often is the case with salicylates and diuretics, or they
may be permanent. The risk for ototoxicity depends on
the total dose of the drug and its concentration in the
bloodstream. It is increased in persons with impaired kid-
1341
ney functioning and in those previously or currently
treated with another potentially ototoxic drug.
Diagnosis and Treatment
Although approximately 10% of Americans have some
degree of hearing loss, including one third of persons
older than 65 years of age, hearing loss often is underdiagnosed. While visual impairments are readily accepted and vigorously treated, loss of hearing often is
denied, minimized, or ignored. In a society that favors
youth, glasses and contact lens are considered normal
and even fashionable, whereas hearing aids often are regarded as a sign of “graceless aging.”31
Diagnosis of hearing loss is aided by careful history of
associated otologic factors such as otalgia, otorrhea, tinnitus,
and self-described hearing difficulties; physical examination
to detect the presence of conditions such as otorrhea, impacted cerumen, or injury to the tympanic membrane;
and hearing tests.28,29 A history of occupational and noise
exposure is important, as is the use of medications with
ototoxic potential. Testing for hearing loss includes a
number of methods, including a person’s reported ability
to hear an observer’s voice, use of a tuning fork to test air
and bone conduction, audioscopes, and auditory brain
stem evoked responses (ABRs).
Tuning forks are used to differentiate conductive and
sensorineural hearing loss. A 512-Hz or higher-frequency
tuning fork is used because frequencies below this level
elicit a tactile response. The Weber test evaluates conductive hearing loss by lateralization of sound. It is done by
placing the lightly vibrating tuning fork on the forehead or
vertex of the head. In persons with conductive losses, the
sound is louder on the side with the hearing loss, but in
persons with sensorineural loss, it radiates to the side with
the better hearing. The Rinne test compares air and bone
conduction. The test is done by alternately placing the tuning fork on the mastoid bone and in front of the ear canal.
In conductive losses, bone conduction exceeds air conduction; in sensorineural losses, the opposite occurs.
Audioscopes can be used to assess a person’s ability to
hear pure tones at 1000 to 2000 Hz (usual speech frequencies). If a person cannot hear these tones, referral for a full
audiogram should be done. The audiogram is an important method of analyzing a person’s hearing and is generally considered the gold standard for diagnosis of hearing
loss. It is done by an audiologist and requires highly specialized sound production and control equipment. Pure
tones of controlled intensity are delivered, usually to one
ear at a time, and the minimum intensity needed for hearing to be experienced is plotted as a function of frequency.
The ABR is a noninvasive method that permits functional evaluation of certain defined parts of the central auditory pathways. Electroencephalographic (EEG) electrodes
and high-gain amplifiers are required to produce a record
of the brain wave activity elicited during repeated
acoustic stimulations of either or both ears. ABR recording
involves subjecting the ear to loud clicks and using a computer to pick up nerve impulses as they are processed in the
midbrain. With this method, certain of the early waves
that come from discrete portions of the pons and midbrain
1342
UNIT XIII
Special Sensory Function
auditory pathways can be correlated with specific sensorineural abnormalities. Imaging studies such as computed
tomography scans and magnetic resonance imaging can be
done to determine the site of a lesion and the extent of
damage.27
Treatment. Untreated hearing loss can have many consequences. Social isolation and depressive disorders are common in hearing-impaired elderly. Hearing-impaired people
may avoid social situations in which background noise
makes conversation difficult to hear. Safety issues, both in
and out of the home, may become significant. Treatment
of hearing loss ranges from simple removal of impacted
cerumen in the external auditory canal to surgical procedures such as those used to reconstruct the tympanic
membrane. For other people, particularly the frail elderly,
hearing aids remain an option. Cochlear implants also are
an option for some people.
Hearing aids remain the mainstay of treatment for
many persons with conductive and sensorineural hearing
loss. With the advent of microcircuitry, hearing aids are
now being designed with computer chips that allow multiple programs to be placed in a single hearing aid. The various programs allow the user to select a specific setting for
different listening situations. The development of microcircuitry has also made it possible for hearing aids to
be miniaturized to the point that, in many cases, they
can be placed deep in the ear where they take advantage
of the normal shape of the external ear and ear canal.
Although modern hearing aids have improved greatly,
they cannot replicate the hearing person’s ability to hear
both soft and loud noises. They also fail to filter out distorted or background noise consistently. Many persons
who are fitted with hearing aids use them inconsistently,
often because of social embarrassment, increase in background noise, or the sound of their own voice being transmitted through the hearing aid.34 Other aids for the
hearing impaired include alert and signal devices, assistedlistening devices from telephone companies, and dogs
trained to respond to various sounds.
Most important, hearing impairment produces a loss
of the important communicative function of auditory language, leading to social isolation. Although many assistance devices are available to persons with hearing loss,
understanding on the part of family and friends is perhaps
the most important.31 The interpretation of speech involves both visual and auditory clues. It is important that
people speaking to persons with hearing impairment face
the person and articulate so that lip reading cues can be
used. Adequate lighting is important. Distractions such as
background noise can make communication difficult and
should be avoided when possible.
Surgically implantable cochlear prostheses for the profoundly deaf have been developed and are available for use
in adults and children 2 years of age or older.35 These prostheses are inserted into the scala tympani of the cochlea
and work by providing direct stimulation to the auditory
nerve, bypassing the stimulation that typically is provided
by transducer cells but that is absent or nonfunctional in
a deaf cochlea. For the implant to work, the auditory nerve
must be functional. Whereas early implants used a single
electrode, current implants use multielectrode placement,
enhancing speech perception. Much of the progress in implant performance has been achieved through improvements in the speech processors that convert sound into
electrical stimuli. Advances in the development of the
multichannel implant have improved performance such
that cochlear implants have been established as an effective option for adults and children with profound hearing
impairment.36,37 Most persons who are deafened after learning speech derive substantial benefit when cochlear implants are used in conjunction with lip reading; some are
able to understand selected types of speech without lip
reading; and some are able to communicate by telephone.
Hearing Loss in Infants and Children
Even mild or unilateral hearing loss can have a detrimental effect on the language development and hearingassociated learning of the young child. Although estimates
vary dependent on the group surveyed and testing methods used, from 1 to 2 per 1000 newborns have moderate
(30 to 50 dB), severe (50 to 70 db), or profound (≥70 dB)
sensorineural hearing loss.11 An additional 1 to 2 per
1000 may have milder or unilateral impairments. When
considering less severe or transient conductive hearing
loss that is commonly associated with middle ear disease
in young children, the numbers are even greater.
The cause of hearing impairment in children depends
on whether the hearing loss is conductive or sensorineural.
Most cases of conductive hearing loss is caused by middle
ear infections. Causes of sensorineural hearing impairment
include genetic, infectious, traumatic, and ototoxic factors.
Genetic causes are probably responsible for as many as 50%
of sensorineural hearing loss in children. The most common infectious cause of congenital sensorineural hearing
loss is cytomegalovirus (CMV), which infects 1 in 100 newborns in the United States each year; of these, about 1200
to 2000 have sensorineural hearing loss.11 Of particular
concern is the fact that congenital CMV can cause both
symptomatic and asymptomatic hearing loss in the newborn. Some children with congenital CMV infection, who
were asymptomatic as newborns, have suddenly lost residual hearing at 4 to 5 years of age.11 Postnatal causes of sensorineural hearing loss include β streptococcal sepsis in the
newborn and bacterial meningitis. Streptococcus pneumoniae
is the most common cause of bacterial meningitis that
results in sensorineural hearing loss after the neonatal period; this cause may become less frequent with the routine
administration of the conjugate pneumococcal vaccine.
Other causes of sensorineural hearing loss are toxins and
trauma. Early in pregnancy, the embryo is particularly sensitive to toxic substances, including ototoxic drugs such as
the aminoglycosides and loop diuretics. Trauma, particularly head trauma, may cause sensorineural hearing loss.
Because hearing impairment can have a major impact
on the development of a child, early identification through
screening programs is strongly advocated. The American
Academy of Pediatricians (AAP) and the Joint Commission
on Infant Hearing (JCIH) recently published a position
CHAPTER 55 Disorders of Hearing and Vestibular Function
paper calling for universal screening of all infants by physiologic measurements before 3 months of age, with proper
intervention no later than 6 months of age.37,38 Many states
have now enacted legislation supporting the position
paper; as result, newborn hearing screening programs have
been implemented in newborn nurseries throughout the
United States.39 The currently recommended screening
techniques are either the evoked otoacoustic emissions
(EOAE) or the ABR. Both methodologies are noninvasive,
relatively quick (<5 minutes), and easy to perform. The
EOAE measures sound waves generated in the inner ear
(cochlea) in response to clicks or tone bursts emitted and
recorded by a minute microphone placed in the external ear
canals of the infant. The ABR uses three electrodes pasted to
the infant’s scalp to measure the EEG waves generated by
clicks. Because many children become hearing impaired
after the neonatal period and are not identified by neonatal
screening programs, the AAP Joint Commission on Infant
Hearing Impairment recommends that all infants with risk
factors for delayed onset of progressive hearing loss receive
ongoing audiologic and medical monitoring for 3 years
and at appropriate intervals thereafter.
Once hearing loss has been identified, a full developmental and speech and language evaluation is needed.
Parenteral involvement and counseling are essential.
Children with sensorineural hearing loss should be evaluated for possible hearing aid use by a pediatric audiologist.40 Hearing aids may be fitted for infants as young as
2 months of age. The use of surgically implanted cochlear
implants in children with profound hearing loss has currently been approved for use in children 2 years of age
and older.35,36,41 At present, more than 25,000 children
worldwide have received cochlear implants. One limitation is that the earliest age for implantation in children
in the United States is no earlier than 2 years of age,
which is beyond the critical period of auditory input for
the acquisition of oral language. Because of the increased
risk for pneumococcal meningitis, children who undergo
implants should receive age-appropriate immunization
against pneumococcal disease.11 At present, the best educational approach to children with significant hearing loss
is open to controversy. Some members of the hearingimpaired community have objected to the use of cochlear
implants in children, maintaining that the child can develop adequate communication skills using more conventional strategies such as sign language and lip reading.
Hearing Loss in the Elderly
The term presbycusis is used to describe degenerative hearing loss that occurs with advancing age. Approximately
23% of persons between 65 and 75 years of age and 40%
of the population older than 75 years of age are affected.42
Men are affected earlier and experience a greater loss than
women.
The degenerative changes that impair hearing may
begin in the fifth decade of life and may not be clinically apparent until later.43 Onset may be associated with chronic
noise exposure or vascular disorders.43 The disorder involves
loss of neuroepithelial (hair) cells, neurons, and the stria
1343
vascularis.30 High-frequency sounds are affected more than
low-frequency sounds because high and low frequencies
distort the base of the basilar membrane, but only low frequencies affect the distal (apical) region. Through the years,
permanent mechanical damage to the organ of Corti is
more likely to occur near the base of the cochlea, where the
high sonic frequencies are discriminated.
Although hearing loss is a common problem in the
elderly, many older persons are not appropriately assessed
for hearing loss. When assessing an older person’s ability to
hear, it is important to ask both the person and the family
about awareness of hearing loss. The ability to hear highfrequency sounds usually is lost first. Loss of high-frequency
discrimination is characterized by difficulty in understanding words in noisy environments, in hearing a speaker in an
adjacent room, or in hearing a speaker whose back is
turned. Hearing loss may be estimated by having the person report hearing of softly whispered, normally spoken,
or shouted words. In the English language, vowels are lowfrequency sounds, whereas consonants are of higher frequency. A ticking watch also may be used to test for the
higher frequencies.
In summary, hearing is a specialized sense whose external
stimulus is the vibration of sound waves. Our ears receive sound
waves, distinguish their frequencies, translate this information
into nerve impulses, and transmit them to the CNS. Anatomically, the auditory system consists of the outer ear, middle ear,
and inner ear, the auditory pathways, and the auditory cortex.
The middle ear is a tiny air-filled cavity in the temporal bone. A
connection exists between the middle ear and the nasopharynx. This connection, called the eustachian tube, allows equalization of pressure between the middle ear and the atmosphere.
The inner ear contains the receptors for hearing.
Disorders of the auditory system include infections of the
external and middle ear, otosclerosis, and conduction and sensorineural deafness. Otitis externa is an inflammatory process
of the external ear. The middle ear is a tiny, air-filled cavity located in the temporal bone. The eustachian tube connects the
middle ear to the nasopharynx and allows for equalization of
pressure between the middle ear and the atmosphere. Infections can travel from the nasopharynx to the middle ear along
the eustachian tube, causing OM or inflammation of the middle ear. The eustachian tube is shorter and more horizontal in
infants and young children, and infections of the middle ear
are a common problem in these age groups.
Otitis media is an infection of the middle ear that is associated with a collection of fluid. OM may present as AOM, recurrent OM, or OME. AOM usually follows an upper respiratory
tract infection and is characterized by otalgia, fever, and hearing loss. The effusion that accompanies OM can persist for
weeks or months, interfering with hearing and impairing
speech development. Otosclerosis is a familial disorder of the
otic capsule. It causes bone resorption followed by excessive replacement with sclerotic bone. The disorder eventually causes
immobilization of the stapes and conduction deafness.
Deafness, or hearing loss, can develop as the result of a
number of auditory disorders. It can be conductive, sensorineural, or mixed. Conduction deafness occurs when transmission
1344
UNIT XIII
Special Sensory Function
of sound waves from the external to the inner ear is impaired.
Sensorineural deafness can involve cochlear structures of the
inner ear or the neural pathways that transmit auditory stimuli. Sensorineural hearing loss can result from genetic or
congenital disorders, trauma, infections, vascular disorders,
tumors, or ototoxic drugs. Hearing loss in infants and young
children impairs language and speech development. Treatment of hearing loss includes the use of hearing aids and, in
some cases of profound deafness, implantation of a cochlear
prosthesis.
Disorders of Vestibular Function
After completing this section of the chapter, you should be able to
meet the following objectives:
✦ Explain the function of the vestibular system with respect
✦
✦
✦
✦
✦
to postural reflexes and maintaining a stable visual field
despite marked changes in head position
Relate the function of the vestibular system to
nystagmus and vertigo
Differentiate the structures of peripheral and central
vestibular function
Characterize the physiologic cause of motion sickness
Compare the manifestations and pathologic processes
associated with benign positional vertigo and Ménière’s
disease
Differentiate the manifestations of peripheral and central
vestibular disorders
THE VESTIBULAR SYSTEM
AND VESTIBULAR REFLEXES
The vestibular receptive organs, which are located in the
inner ear, and their central nervous system connections
contribute to the reflex activity necessary for effective posture and movement in a physical world governed by momentum and a gravitational field. Because the vestibular
apparatus is part of the inner ear and located in the head, it
is head position and acceleration that are sensed. The
vestibular system serves two general and related functions.
It maintains and assists recovery of stable body and head position through control of postural reflexes, and it maintains
a stable visual field despite marked changes in head position.
Peripheral Vestibular Apparatus
The vestibular system consists of the peripheral vestibular
apparatus and its CNS connections. The peripheral apparatus of the vestibular system, which is contained in the bony
labyrinth of the inner ear next to and continuous with the
cochlea of the auditory system, is divided into five prominent structures: three semicircular canals, a utricle, and a
saccule (Fig. 55-8). Receptors in these structures are differentiated into the angular acceleration-deceleration receptors of the semicircular canals and the linear accelerationdeceleration and static gravitational receptors of the utricle
and saccule.
DISORDERS OF THE VESTIBULAR SYSTEM
➤ The receptors concerned with the sense of balance and position in space are located in fluid (endolymph)-filled semicircular canals of the vestibular system of the inner ear.
➤ The vestibular system has extensive interconnections with
neural pathways controlling vision, hearing, and autonomic nervous system function. Disorders of the vestibular
system are characterized by vertigo, nystagmus, tinnitus,
nausea and vomiting, and autonomic nervous system
manifestations.
➤ Disorders of vestibular function can result from repeated
stimulation of the vestibular system such as during car, air,
and boat travel (motion sickness); acute infection of the
vestibular pathways (acute vestibular neuritis); dislodgment
of otoliths that participate in the receptor function of the
vestibular system (benign positional vertigo); or distention
of the endolymphatic compartment of the inner ear
(Ménière’s disease).
The three semicircular canals, each subtending approximately two thirds of a circle, are arranged at right angles to
one another, with the horizontal duct tilted approximately
12 degrees above the normal horizontal plane of the head.
The horizontal canals in the inner ears on the two sides of
the head are in the same plane, whereas the superior (anterior) duct of one side is parallel with the inferior (posterior)
duct on the other side, and the two function as a pair. Each
canal is filled with endolymph and has a swelling at the
base called the ampulla. Each ampulla contains a hair cell
sensory surface raised into a crest, or crista, at right angles
to the duct (see Fig. 55-8). The hair bundles extend into a
flexible gelatinous mass, called the cupula, which essentially
closes off fluid flow through the semicircular ducts.
When the head begins to rotate around the axis of a
semicircular canal (i.e., undergoes angular acceleration), the
momentum of the endolymph causes an increase in pressure on one side of the cupula. This is similar to the lagging
behind of the water in a glass that is suddenly rotated, except that the endolymph cannot flow past the cupula. Instead, the endolymph applies a differential pressure to the
two sides of the cupula, bending the hair bundles. Because
all the hair bundles in each semicircular canal share a common orientation, angular acceleration in one direction depolarizes hair cells and excites afferent neurons, whereas
acceleration in the opposite direction hyperpolarizes the receptor cells and diminishes afferent nerve activity. Thus,
the semicircular canals of the vestibular system provide a
mechanism for signaling the angular acceleration during
turning and tilting motions of the head, rotatory body
movements, and turning movements during active and
passive locomotion.
Both the utricle and saccule are widened membranous
sacs in the bony vestibule. The utricle connects the ends
of each semicircular duct, whereas the saccule communicates with the utricle through a small duct and with the
CHAPTER 55 Disorders of Hearing and Vestibular Function
1345
Head rotation
B
Osseous labyrinth
(otic capsule)
Utricle
Utricle
Cupula
Ampulla
Saccule
Semicircular canals:
Anterior
(superior) canal
Hair cells
CN VIII
Posterior canal
Lateral
(horizontal) canal
Endolymphatic sac
Ampullae
A
C
FIGURE 55-8 (A) The osseous and membranous labyrinth of the left ear. (B) Location of the ampulla.
(C) The cupula and movement of hair bundles with head movement.
cochlear duct of the auditory apparatus through the ductus reuniens. The utricle and saccule house equilibrium receptors called maculae that respond to the pull of gravity
and report on changes in head position. Located at right
angles to the macula of the utricle, the macula of the saccule is oriented in the vertical plane. Small patches of hair
cells are located in the floor of the utricle (utricular macula),
in the sidewall of the saccule (saccular macula). Each hair
cell has several microvilli and one true cilium, called a
kinocilium. At the apical end of each inner hair cell is a projecting bundle of rodlike structures called stereocilia. The
stereocilia of the hair cells in both utricular and saccular
macula are embedded in a flattened gelatinous mass, the
otolithic membrane, which is studded with tiny stones (calcium carbonate crystals) called otoliths (Fig. 55-9). Although
small, the density of the otoliths increases the membrane’s
weight and its resistance to change in motion. When the
head is tilted, the gelatinous mass shifts its position because
of the pull of the gravitational field, bending the stereocilia
of the macular hair cells. Although each hair cell becomes
more or less excitable depending on the direction in which
the cilia are bending, the hair cells are oriented in all directions, making these sense organs sensitive to static or
changing head position in relation to the gravitational field.
Besides their static tilt reception function, the utricle
and saccule provide linear acceleration and deceleration reception. Differential movement between the head and the
otolithic membranes provides the basis for compensatory
reflex bracing of neck, trunk, and limbs. This happens
when the head is accelerated linearly, such as during the
initial or terminal phase of an elevator ride or during automobile acceleration or deceleration. The utricle and saccule
also provide the input data on which the air-righting re-
flexes are based. A cat dropped from an upside-down position lands on its feet and would do so even if blindfolded.
Most vestibular reflexes, including air-righting, are functional at birth. If a neonate is supported in the prone position and the support is momentarily (and with great care)
removed, the trunk and all four limbs are extended as
falling begins. In the supine position, the trunk is flexed
and the limbs are flexed as the fall progresses. However, the
head-on-body vestibular reflexes of the infant are not sufficiently operational during the first 6 weeks or so after
Otolithic membrane
Afferent
nerve
fiber
Otoliths
Supporting
Kinocilium
cell
Stereocilia
Sensory
hair
cell
FIGURE 55-9 The relation of the otoliths to the sensory cells in the
macula of the utricle and saccule. (Adapted from Selkurt F.D. [Ed.]
[1982]. Basic physiology for the health sciences [2nd ed.]. Boston: Little,
Brown)
1346
UNIT XIII
Special Sensory Function
birth to maintain head posture. This is why the neonate’s
head must be supported when the neonate is lifted in the
supine position.
Neural Pathways
Ganglion cells, homologous with dorsal root ganglion cells,
form afferent ganglia: the superior vestibular ganglion, which
innervates the hair cells of the utricular macula and the
cristae of the superior and horizontal semicircular ducts;
and the inferior vestibular ganglion, which innervates the saccular macula and the cristae of the inferior semicircular duct
(see Fig. 55-6). The central axons of these ganglion cells become the superior and inferior vestibular nerves.
Impulses from the vestibular nerves initially pass to one
of two destinations: the vestibular nuclear complex in the
brain stem or the cerebellum. The vestibular nuclei, which
form the main integrative center for balance, also receive
input from visual and somatic receptors, particularly from
proprioceptors in the neck muscles that report the angle or
inclination of the head. The vestibular nuclei integrate this
information and then send impulses to the brain stem centers that control the extrinsic eye movements (CN III, IV,
and VI) and reflex movements of the neck, limb, and trunk
muscles (via the vestibulospinal tracts). These reflexes include the vestibuloocular reflexes that keep the eyes still as
the head moves and the vestibulospinal reflexes that enable
the skeletomotor system to make the quick adjustments
needed to maintain or regain balance.
Neurons of the vestibular nuclei also project to the
thalamus, the temporal cortex, the somesthetic area
of the parietal cortex, and the chemoreceptor trigger zone.
The thalamic and cortical projections provide the basis
for the subjective experiences of position in space and of
rotation. Connections with the chemoreceptor trigger zone
stimulate the vomiting center in the brain. This accounts
for the nausea and vomiting that often are associated with
vestibular disorders.
rate, the image of the pencil is clearly defined. The eye
movements are the same in both cases. The reason that the
pencil image remains clear in the second situation is
because the vestibuloocular reflexes keep the image of the
pencil on the retinal fovea. When compensatory vestibuloocular reflexes carry the conjugate eye rotations to their
physical limit, a very rapid conjugate movement moves
the eyes in the direction of head rotation to a new fixation
point, followed by a slow vestibuloocular reflex as the
head continues to rotate past the new fixation point. This
pattern of slow–fast–slow movements is called nystagmus
(Fig. 55-10). Clinically, the direction of nystagmus is
named for the fast phase of nystagmus.
Nystagmus can be classified according to the direction
of eye movement: horizontal, vertical, rotary (torsional), or
mixed. If head rotation is continued, friction between endolymph and semicircular duct walls results in endolymph
Direction of
spin
Horizontal canals
Left ear
Right ear
Direction of
endolymph
movement
Hair
displacement
Nystagmus
The term nystagmus is used to describe the involuntary
rhythmic and oscillatory eye movements that preserve eye
fixation on stable objects in the visual field during angular
and rotational movements of the head.22 These vestibularcontrolled eye movements are initiated by impulses generated by the movement of the endolymph in the semicircular
ducts. This movement is transmitted to the vestibular nuclei
and relayed to the appropriate extraocular motor nuclei
for controlling conjugate eye movement.
The vestibuloocular reflexes produce slow compensatory conjugate eye rotations that occur in the direction
precisely opposite to ongoing head rotation and provide
for continuous, ongoing reflex stabilization of the binocular fixation point. This reflex can be demonstrated by
holding a pencil vertically in front of the eyes and moving
it from side to side through a 10-degree arc at a rate of approximately five times per second. At this rate of motion,
the pencil appears blurred because a different and more
complex reflex, smooth pursuit, cannot compensate quickly
enough. However, if the pencil is maintained in a stable
position and the head is moved back and forth at the same
Nerve
discharge
Slow
Slow
Nystagmus
Fast
Fast
FIGURE 55-10 Effect of spinning a subject clockwise. On acceleration,
the endolymph in the horizontal canals will lag behind with respect
to movement of the canal wall. The hairs of cristae will be displaced
to the left. In the left semicircular canal, hair displacement is away
from the kinocilium, leading to decreased nerve discharges below
the resting level. On the right, hair displacement is toward the
kinocilium, leading to an increase in nerve discharge above the
resting level. (Sekurt F.E. [1982]. Basic physiology for the health professions [2nd ed., p. 140]. Boston: Little, Brown)
CHAPTER 55 Disorders of Hearing and Vestibular Function
rotating at the same velocity as the head, and nystagmus
adapts to a stable eye posture. If rotation is suddenly
stopped, vestibular nystagmus reappears in the direction
precisely opposite to the angular accelerating nystagmus.
This results because the inertia of the endolymph is again
bending ampullar hair cells of a now stationary ampulla.
Nystagmus eye movements can be tested by caloric
stimulation (see Chapter 52) or rotation (discussed later).
Nystagmus always is abnormal if it occurs spontaneously
or is sustained. Nystagmus due to CNS pathology, in contrast to vestibular end organ or vestibulocochlear nerve
sources, seldom is accompanied by vertigo. If present, the
vertigo is of mild intensity.
Postural Reflexes
Sudden changes in balance or orientation, such as falling
to the right or left or backward or forward, result in powerful reflexes needed to maintain equilibrium and posture.
The vestibulospinal tract provides for the control of the
muscle tone of axial muscles, including the dorsal back
muscles. A rapidly conducting lateral vestibulospinal tract
descends in or within the spinal cord to provide powerful
vestibular control of the lower motoneurons of the upper
and lower limbs. As the head begins to tip (i.e., rotate) on
the neck or moves as part of general body tipping, the
vestibular system activates the appropriate extensor muscles of the neck, trunk, and limbs, opposing the direction
of the tilt. These powerful reflex adjustments in muscle
tone assist in maintaining stable head and therefore body
postural support during static posture and during passive
or active movement.
All the vestibular nuclei receive input from the cerebellum and the vestibular nerve. The cerebellar connections
of the vestibular system are necessary for adjustments of
temporally smooth, coordinated movements to ongoing
head movement, tilt, or angular acceleration. For instance,
accurate grasping can occur during a fall, indicating cerebellar adjustments based on vestibular information during
the performance of a smooth, accurate movement.
Vestibular reflexes are powerful, and considerable learning is required to inhibit or greatly modify them, as is nec-
TABLE 55-1
1347
essary for acrobatic pilots, divers, and gymnasts. Dancers
and skaters who engage in rapid spinning movements also
learn to use or at least partially inhibit these reflexes.
VERTIGO
Disorders of vestibular function are characterized by a condition called vertigo, in which an illusion of motion occurs.
With vertigo, the person may be stationary and the environment in motion (i.e., objective vertigo), or the person
may be in motion and the environment stationary (i.e., subjective vertigo). Persons with vertigo frequently describe a
sensation of spinning, “to-and-fro” motion, or falling.
Vertigo should be differentiated from light-headedness,
faintness, unsteadiness, or syncope (loss of consciousness)
44–46
(Table 55-1). Presyncope, which is characterized by a
feeling of light-headedness or “blacking out,” is commonly
caused by postural hypotension (see Chapter 25) or a
stenotic lesion in the cerebral circulation that limits blood
flow. An inability to maintain normal gait may be described as dizziness despite the absence of objective vertigo. The unstable gait may be caused by disorders of
sensory input (e.g., proprioception), peripheral neuropathy, gait problems, or disorders other than vestibular function and usually is corrected by touching a stationary
object such as the wall or a table.
Vertigo or dizziness can result from central or peripheral vestibular disorders. Approximately 85% of persons
with vertigo have a peripheral vestibular disorder, whereas
only 15% have a central disorder.45 Vertigo due to peripheral vestibular disorders tends to be severe in intensity and
episodic or brief in duration. In contrast, vertigo due to
central vestibular causes tends to be mild and constant
and chronic in duration.
MOTION SICKNESS
Motion sickness is a form of normal physiologic vertigo. It
is caused by repeated rhythmic stimulation of the vestibular system, such as is encountered in car, air, or boat
Differences in Pathology and Manifestations of Dizziness Associated With
Benign Positional Vertigo, Presyncope, and Disequilibrium State
Type of Disorder
Pathology
Symptoms
Benign positional
vertigo
Disorder of otoliths
Presyncope
Orthostatic hypotension
Disequilibrium
Sensory (e.g., vision,
proprioception) deficits
Vertigo initiated by a change in head
position, usually lasts less than a
minute
Light-headedness and feeling faint on
assumption of standing position
Dizziness and unsteadiness when
walking, especially when turning;
relieved by additional
proprioceptive stimulation such as
touching wall or table
1348
UNIT XIII
Special Sensory Function
travel. Vertigo, malaise, nausea, and vomiting are the principal symptoms. Autonomic signs, including lowered blood
pressure, tachycardia, and excessive sweating, may occur.
Hyperventilation, which commonly accompanies motion
sickness, produces changes in blood volume and pooling
of blood in the lower extremities, leading to postural
hypotension and sometimes to syncope. Some persons
experience a variant of motion sickness, complaining of
sensing the rocking motion of the boat after returning to
ground. This usually resolves after the vestibular system
becomes accustomed to the stationary influence of being
back on land.
Motion sickness can usually be suppressed by supplying visual signals that more closely match the motion signals being supplied to the vestibular system. For example,
looking out the window and watching the environment
move when experiencing motion sickness associated with
car travel provides the vestibular system with the visual sensation of motion, but reading a book provides the vestibular system with the miscue that the environment is stable.
Motion sickness usually decreases in severity with repeated
exposure. Anti–motion sickness drugs also may be used to
reduce or ameliorate the symptoms. These drugs work by
suppressing the activity of the vestibular system.
DISORDERS OF PERIPHERAL
VESTIBULAR FUNCTION
The peripheral vestibular system consists of a set of paired
inner ear sensory organs, each sending messages to brain
centers that interpret signals related to the body’s position
in space and control eye movement. Disorders of peripheral
vestibular function occur when these signals are distorted,
as in benign paroxysmal positional vertigo, or are unbalanced by unilateral involvement of one of the vestibular organs, as in Ménière’s disease. The inner ear is vulnerable to
injury caused by fracture of the petrous portion of the temporal bones; by infection of nearby structures, including the
middle ear and meninges; and by blood-borne toxins and
infections. Damage to the vestibular system can occur as an
adverse effect of certain drugs or from allergic reactions to
foods. The aminoglycosides (e.g., streptomycin, gentamicin) have a specific toxic affinity for the vestibular portion
of the inner ear. Alcohol can cause transient episodes of vertigo. The cause of peripheral vertigo remains unknown in
approximately half of the cases.
Severe irritation or damage of the vestibular end organs
or nerves results in severe balance disorders reflected by instability of posture, dystaxia, and falling accompanied by
vertigo. With irritation, falling is away from the affected
side; with destruction, it is toward the affected side. Adaptation to asymmetric stimulation occurs within a few days,
after which the signs and symptoms diminish and eventually are lost. After recovery, there usually is a slightly reduced acuity for tilt, and the person walks with a somewhat
broadened base to improve postural stability. The neurologic basis for this adaptation to unilateral loss of vestibular
input is not understood. After adaptation to the loss of
vestibular input from one side, the loss of function of the
opposite vestibular apparatus produces signs and symptoms
identical to those resulting from unilateral rather than bilateral loss. Within weeks, adaptation is again sufficient for
locomotion and even for driving a car. Such a person relies
heavily on visual and proprioceptive input and has severe
orientation difficulty in the dark, particularly when traversing uneven terrain.
Benign Paroxysmal Positional Vertigo
Benign paroxysmal positional vertigo (BPPV) is the most
common cause of pathologic vertigo and usually develops
after the fourth decade. It is characterized by brief periods
of vertigo, usually lasting less than 1 minute, that are precipitated by a change in head position.44,47 The most prominent symptom of BPPV is vertigo that occurs in bed when
the person rolls into a lateral position. It also commonly occurs when the person is getting in and out of bed, bending
over and straightening up, or extending the head to look
up. It also can be triggered by amusement rides that feature
turns and twists.
BPPV is thought to result from damage to the delicate
sensory organs of the inner ear, the semicircular ducts,
and otoliths (see Fig. 55-9). In persons with BPPV, the calcium carbonate particles (otoliths) from the utricle become dislodged and become free-floating debris in the
endolymph of the posterior semicircular duct, which is
the most dependent part of the inner ear.47 Movement of
the free-floating debris causes this portion of the vestibular system to become more sensitive, such that any movement of the head in the plane parallel to the posterior
duct may cause vertigo and nystagmus. There usually is a
several-second delay between head movement and onset
of vertigo, representing the time it takes to generate the
exaggerated endolymph activity. Symptoms usually subside with continued movement, probably because the
movement causes the debris to be redistributed throughout the endolymph system and away from the posterior
semicircular canal.
Diagnosis is based on tests that involve the use of a
change in head position to elicit vertigo and nystagmus.47,48
BPPV often is successfully treated with drug therapy to control vertigo-induced nausea. Nondrug therapies using habituation exercises and canalith repositioning are successful
in many people.47 Canalith repositioning involves a series
of maneuvers in which the head is moved to different positions in an effort to reposition the free-floating debris in the
endolymph of the semicircular canals.
Acute Vestibular Neuronitis
Acute vestibular neuronitis is characterized by an acute
onset (usually hours) of vertigo, nausea, and vomiting lasting several days and not associated with auditory or other
neurologic manifestations. Most persons experience gradual improvement over 1 to 2 weeks, but some develop recurrent episodes.49,50 A large percentage report an upper
respiratory tract illness 1 to 2 weeks before onset of symptoms, suggesting a viral origin. The condition also can occur
in persons with herpes zoster oticus. In some persons, attacks of acute vestibulopathy recur over months or years.
CHAPTER 55 Disorders of Hearing and Vestibular Function
There is no way to determine whether a person who experiences a first attack will have repeated attacks.
Ménière’s Disease
Ménière’s disease is a disorder of the inner ear due to distention of the endolymphatic compartment of the inner
ear, causing a triad of hearing loss, vertigo, and tinnitus.51–55
The primary lesion appears to be in the endolymphatic sac,
which is thought to be responsible for endolymph filtration
and excretion. A number of pathogenic mechanisms have
been postulated, including an increased production of endolymph, decreased production of perilymph accompanied
by a compensatory increase in volume of the endolymphatic sac, and decreased absorption of endolymph caused
by malfunction of the endolymphatic sac or blockage of
endolymphatic pathways.
Ménière’s disease is characterized by fluctuating episodes of tinnitus, feelings of ear fullness, and violent rotary vertigo that often renders the person unable to sit or
walk. There is a need to lie quietly with the head fixed in
a comfortable position, avoiding all head movements that
aggravate the vertigo. Symptoms referable to the autonomic nervous system, including pallor, sweating, nausea,
and vomiting, usually are present. The more severe the attack, the more prominent are the autonomic manifestations. A fluctuating hearing loss occurs with a return to
normal after the episode subsides. Initially, the symptoms
tend to be unilateral, resulting in rotatory nystagmus
caused by an imbalance in vestibular control of eye movements. Because initial involvement usually is unilateral
and because the sense of hearing is bilateral, many persons
with the disorder are not aware of the full extent of their
hearing loss. However, as the disease progresses, the hearing loss stops fluctuating and progressively worsens, with
both ears tending to be affected so that the prime disability becomes one of deafness.53 The episodes of vertigo
diminish and then disappear, although the person may be
unsteady, especially in the dark.
The cause of Ménière’s disease is unknown. A number
of conditions, such as trauma, infection (e.g., syphilis), and
immunologic, endocrine (adrenal-pituitary insufficiency
and hypothyroidism), and vascular disorders have been
proposed as possible causes of Ménière’s disease.53,54 The
most common form of the disease is an idiopathic form
thought to be caused by a single viral injury to the fluid
transport system of the inner ear. One area of investigation has been the relation between immune disorders and
Ménière’s disease.
Methods used in the diagnosis of Ménière’s disease
include audiograms, vestibular testing by electronystagmography, and petrous pyramid radiographs. The administration of hyperosmolar substances, such as glycerin
and urea, often produces acute temporary hearing improvement in persons with Ménière’s disease and sometimes is used as a diagnostic measure of endolymphatic
hydrops. The diuretic furosemide also may be used for
this purpose.
The management of Ménière’s disease focuses on attempts to reduce the distention of the endolymphatic
1349
space and can be medical or surgical. Pharmacologic management consists of suppressant drugs (e.g., prochlorperazine, promethazine, diazepam), which act centrally to
decrease the activity of the vestibular system. Diuretics are
used to reduce endolymph fluid volume. Histamine analogs,
which directly reduce inner ear fluid mainly by decreasing
cochlear blood flow, are being studied.52 A low-sodium
diet is recommended in addition to these medications. The
steroid hormone prednisone may be used to maintain satisfactory hearing and resolve dizziness. Gentamicin therapy
has been used for ablation of the vestibular system.53,54,56
Persons who are candidates for intratympanic gentamicin
infusion include those who have frequent attacks of
Ménière’s disease, disease that involves one ear, good contralateral vestibular function, or normal or near-normal
balance between episodes. This treatment is mainly effective in controlling vertigo and does not alter the underlying pathology.
Surgical methods include the creation of an endolymphatic shunt in which excess endolymph from the
inner ear is diverted into the subarachnoid space or
the mastoid (endolymphatic sac surgery) and vestibular
nerve section. Advances in vestibular nerve section have
facilitated the monitoring of CN VII and CN VIII potentials. These methods are used to prevent hearing damage.
In unilateral cases, vestibular nerve section has a success
rate of 90% to 95% in terms of providing complete relief
of vertigo at 2 years after surgery.53,54 The surgery, however, involves an intracranial procedure with possible
postoperative morbidity.
DISORDERS OF CENTRAL
VESTIBULAR FUNCTION
Abnormal nystagmus and vertigo can occur as a result of
CNS lesions involving the cerebellum and lower brain stem.
Central causes of vertigo include brain stem ischemia, tumors, and multiple sclerosis.57 When brain stem ischemia is
the cause of vertigo, it usually is associated with other brain
stem signs such as diplopia, ataxia, dysarthria, or facial
weakness. Compression of the vestibular nuclei by cerebellar tumors invading the fourth ventricle results in progressively severe signs and symptoms. In addition to abnormal
nystagmus and vertigo, vomiting and a broad-based and
dystaxic gait become progressively more evident. The central demyelinating effects of multiple sclerosis can present
with vertigo up to 10% of the time, and up to one third of
persons with multiple sclerosis experience vertigo and nystagmus some time in the course of the disease.57
Centrally derived nystagmus usually has equal excursion in both directions (i.e., pendular). In contrast to peripherally generated nystagmus, CNS-derived nystagmus is
relatively constant rather than episodic, can occur in any
direction rather than being primarily in the horizontal or
torsional (rotatory) dimensions, often changes direction
through time, and cannot be suppressed by visual fixation.
Repeated induction of nystagmus results in rapid diminution or “fatigue” of the reflex with peripheral abnormalities,
1350
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Special Sensory Function
but fatigue is not characteristic of central lesions. Abnormal
nystagmus can make reading and other tasks that require
precise eye positional control difficult.
DIAGNOSTIC TESTS OF
VESTIBULAR FUNCTION
Diagnosis of vestibular disorders is based on a description
of the symptoms, a history of trauma or exposure to agents
that are destructive to vestibular structures, and physical
examination. Tests of eye movements (i.e., nystagmus) and
muscle control of balance and equilibrium often are used.
The tests of vestibular function focus on the horizontal
semicircular reflex because it is the easiest reflex to stimulate rotationally and calorically and to record using
electronystagmography.
usually is performed in the dark without visual influence
and with selected light stimuli. Eye movements are monitored using ENG. The Bárány chair, a rotatable chair that
is much like a barber’s chair, can be used for assessing
postrotational vestibular reflexes. The person is strapped
into the chair with the head positioned so that the plane
of one pair of semicircular ducts is in the horizontal plane
(i.e., plane of rotation); each of the three primary planes of
the ducts is tested in turn. The person is rotated until a
steady rate of rotation is achieved. The chair is suddenly
stopped, and the ensuing postrotational reflex nystagmus
and the compensatory movements of the body and limbs
are observed. Vestibular reflexes are very powerful, and extreme caution is needed when rotational tests are used to
evaluate these reflexes.
Romberg Test
Electronystagmography
Electronystagmography (ENG) is a precise and objective
diagnostic method of evaluating nystagmus eye movements. Electrodes are placed lateral to the outer canthus of
each eye and above and below each eye. A ground electrode is placed on the forehead. With ENG, the velocity,
frequency, and amplitude of spontaneous or induced nystagmus and the changes in these measurements brought
by a loss of fixation, with the eyes open or closed, can be
quantified. The advantages of ENG are that it is easily administered, is noninvasive, does not interfere with vision,
and does not require head restraint.58
Caloric Stimulation
Caloric testing involves elevating the head 30 degrees and
irrigating each external auditory canal separately with 30 to
50 mL of ice water. The resulting changes in temperature, which are conducted through the petrous portion of
the temporal bone, set up convection currents in the endolymph that mimic the effects of angular acceleration. In
an unconscious person with a functional brain stem and intact oculovestibular reflexes, the eyes exhibit a jerk nystagmus lasting 2 to 3 minutes, with the slow component toward the irrigated ear followed by rapid movement away
from the ear (see Chapter 52, Fig. 52-11). With impairment
of brain stem function, the response becomes perverted and
eventually disappears. An advantage of the caloric stimulation method is the ability to test the vestibular apparatus on
one side at a time. The test should never be done on persons
who do not have an intact eardrum or who have blood or
fluid collected behind the eardrum.
Rotational Tests
Rotational testing involves rotation using a rotatable chair
or motor-driven platform. Unlike caloric testing, rotational
testing depends only on the inner ear and is unrelated to
conditions of the external ear or temporal bone. A major
disadvantage of the method is that both ears are tested
simultaneously.
Motor-driven platforms can be precisely controlled,
and multiple graded stimuli can be delivered in a relatively
short period. For rotational testing, the person is seated in
a chair mounted on the motor-driven platform. Testing
The Romberg test is used to demonstrate disorders of static vestibular function. The person being tested is requested to stand with feet together and arms extended
forward so that the degree of sway and arm stability can
be observed. The person then is asked to close his or her
eyes. When visual clues are removed, postural stability is
based on proprioceptive sensation from the joints, muscles, and tendons and from static vestibular reception.
Deficiency in vestibular static input is indicated by greatly
increased sway and a tendency for the arms to drift toward the side of deficiency.
If vestibular input is severely deficient, the subject
falls toward the deficient side. Care must be taken because
defects of proprioceptive projection to the forebrain also
result in some arm drift and postural instability toward
the deficient side. Only if two-point discrimination and
vibratory sensation from the lower and upper limbs are bilaterally normal can the deficiency be attributed to the
vestibular system.
TREATMENT OF VESTIBULAR DISORDERS
Pharmacologic Methods
Depending on the cause, vertigo may be treated pharmacologically. There are two types of drugs used in the treatment of vertigo.59 First, the drugs used to suppress the
illusion of motion include drugs such as antihistamines
(e.g., meclizine, cyclizine, dimenhydrinate, and promethazine) and anticholinergic drugs (e.g., scopolamine, atropine) that suppress the vestibular system. Although the
antihistamines have long been used in treating vertigo, little is known about their mechanism of action. The second
type includes drugs used to relieve the nausea and vomiting
that commonly accompany the condition. Antidopaminergic drugs (e.g., phenothiazines) and benzodiazepines commonly are used for this purpose.
Vestibular Rehabilitation Exercises
Vestibular rehabilitation, a relatively new treatment modality for peripheral vestibular disorders, has met with considerable success.60–62 It commonly is done by physical
therapists and uses a home exercise program that incorporates habituation exercises, balance retraining exercises,
CHAPTER 55 Disorders of Hearing and Vestibular Function
and a general conditioning program.60 The habituation exercises take advantage of physiologic fatigue of the neurovegetative response to repetitive movement or positional
stimulation and are done to decrease motion-provoked vertigo, light-headedness, and unsteadiness. The exercises are
selected to provoke the vestibular symptoms. The person
moves quickly into the position that causes symptoms,
holds the position until the symptoms subside (i.e., fatigue
of the neurovegetative response), relaxes, and then repeats
the exercise for a prescribed number of times. The exercises usually are repeated twice daily. The habituation effect is characterized by decreased sensitivity and duration
of symptoms. It may occur in as little as 2 weeks or take as
long as 6 months.62
Balance-retraining exercises consist of activities directed toward improving individual components of balance
that may be abnormal. General conditioning exercises, a
vital part of the rehabilitation process, are individualized to
the person’s preferences and lifestyle. They should consist
of motion-oriented activity that the person is interested in
and should be done on a regular basis, usually four to five
times per week.62
In summary, the vestibular system plays an essential role in
the equilibrium sense, which is closely integrated with the visual and proprioceptive (position) senses. Receptors in the
semicircular canals, utricle, and saccule of vestibular system,
located in the inner ear, respond to changes in linear and
angular acceleration of the head. The vestibular nerve fibers
travel in CN VIII to the vestibular nuclei at the junction of the
medulla and pons; some fibers pass through the nuclei to the
cerebellum. Cerebellar connections are necessary for temporally
smooth, coordinated movements during ongoing head movements, tilt, and angular acceleration. The vestibular nuclei also
connect with nuclei of the oculomotor (CN III), trochlear (CN IV),
and abducens (CN VI) nerves that control eye movement. Nystagmus is a term used to describe vestibular-controlled eye
movements that occur in response to angular and rotational
movements of the head. The vestibulospinal tract, which provides for the control of muscle tone in the axial muscles, including those of the back, provide the support for maintaining
balance. Neurons of the vestibular nuclei also project to the
thalamus, to the temporal cortex, and to the somesthetic area
of the parietal cortex. The thalamic and cortical projections
provide the basis for the subjective experiences of position in
space and of rotation and vertigo.
Vertigo, an illusory sensation of motion of either oneself or
one’s surroundings, tinnitus, and hearing loss are common
manifestations of vestibular dysfunction, as are autonomic
manifestations such as perspiration, nausea, and vomiting.
Common disorders of the vestibular system include motion
sickness, BPPV, and Ménière’s disease.
Benign paroxysmal positional vertigo is a condition believed
to be caused by free-floating particles in the posterior semicircular canal. It presents as a sudden onset of dizziness or vertigo
that is provoked by certain changes in head position. Ménière’s
disease, which is caused by an overaccumulation of endolymph,
is characterized by severe, disabling episodes of tinnitus, feelings of ear fullness, and violent rotary vertigo. The diagnosis of
1351
vestibular disorders is based on a description of the symptoms,
a history of trauma or exposure to agents destructive to vestibular structures, and tests of eye movements (i.e., nystagmus) and
muscle control of balance and equilibrium. Among the methods
used in treatment of the vertigo that accompanies vestibular
disorders are habituation exercises and antivertigo drugs. These
drugs act by diminishing the excitability of neurons in the
vestibular nucleus.
REVIEW EXERCISES
A mother notices that her 13-month-old child is fussy
and tugging at his ear and that he refuses to eat his
breakfast. When she takes his temperature it is 100°F.
Although the child attends day care, the mother has
kept him home and made an appointment with the
child’s pediatrician. In the physician’s office, the child’s
temperature is 100.2°F, he is somewhat irritable, and he
has a clear nasal drainage. His left tympanic membrane
shows normal landmarks and motility on pneumatic
otoscopy. His right tympanic membrane is erythematous, and there is decreased motility on pneumatic
otoscopy.
A. What risk factors are present that predispose this
child to the development of acute otitis media?
B. Are his signs and symptoms typical of otitis media in
a child of his age?
C. What are the most likely pathogens? What treatment would be indicated?
D. Later in the week, the mother notices that the child
does seem to hear as well as he did before developing the infection. Is this a common occurrence, and
should the mother be concerned about transient
hearing loss in a child of this age?
A granddaughter is worried that her grandfather is “losing his hearing.” Lately, he has been staying away from
social gatherings that he always enjoyed, saying everybody mumbles. He is defiant in maintaining that there
is nothing wrong with his hearing. However, he does
complain that his ears have been ringing a lot lately.
A. What are common manifestations of hearing loss in
the elderly?
B. What type of evaluation would be appropriate for
determining whether this man has a hearing loss
and the extent of his hearing loss?
C. What are some things that the granddaughter might
do so that her grandfather could hear her better
when she is talking to him?
A 70-year-old man complains that he gets this terrible
feeling “like the room is moving around” and becomes
nauseated when he rolls over in bed or bends over suddenly. It usually goes away once he has been up for
awhile. He has been told that his symptoms are consistent with benign paroxysmal positional vertigo.
1352
UNIT XIII
Special Sensory Function
A. What is the pathophysiology associated with this
man’s vertigo?
B. Why do the symptoms subside once he has been up
for awhile?
C. What methods are available for treatment of the disorder?
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