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1 Why Hearing Is Important in Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
a b
Fig. 1. 9 (a) Normal hearing cats and kittens who were implanted during the rst 3 months of life, showing normal activity observed at all layers of
the primary auditory cortex. (b) White deaf cats who received a cochlear implant after 5 months of age showed normal activity in layers I to IV but
reduced or no activity in the infragranular layers (V–VI).
a b
Fi g . 1.10 (a) Responses to sound measured in cortical layers of normal-hearing cats (on the left) and congenitally deafened late-implanted cats
(on the right).
cochlear implant at ages ranging from 1 year old to early adulthood. Note that children who received cochlear implants during the rst 2 to 3 years of
life had normal P1 latencies, while children who received their implants later typically did not.
32
(b) Latency of the P1 waveform of the cortical auditory evoked potential (P1-CAEP) in subjects who were born deaf and received a
31
In Kral’s studies of auditory brain development in congenitally
deafened white cats, the critical period of auditory brain devel-
opment was 4 to 5 months.
13,30
In other words, cochlear implan-
tation and subsequent access to meaningful auditory stimulation
had to be provided by 4 to 5 months of age to facilitate auditory
responsiveness in the infragranular layers of the primary auditory
cortex and consequential coupling of the primary and secondary
auditory cortices. When implantation was provided after the first
11
I Hearing Loss: Essential Information
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
few months of a cat’s life, the infragranular layers of the primary
auditory cortex and the connection to secondary auditory cortex
were irreparably impaired.
How does Kral’s research with cats apply to children with
hearing loss? The answer may partially reside in recent studies
examining auditory brain responses of children with various
durations of deafness. Anu Sharma measured the latency of the
P1 waveform of the cortical auditory evoked potential (P1-CAEP)
in subjects with normal hearing and in children who were born
deaf and received a cochlear implant at ages ranging from 1 year
old to early adulthood.31 Children who received cochlear implants
during the first 3 years of life had P1 latencies that were similar
to the P1 latencies of children with normal hearing (Fig. 1.10).32
In contrast, children who received their cochlear implants after
3 years of age generally had P1 latencies that fell outside of the
range for children with normal hearing. Sharma concluded that
the P1 latency was a biomarker of auditory brain development,
with delayed P1 latencies representing a decoupling between
primary and secondary auditory cortices. Sharma hypothesized
that this decoupling was similar to what Kral observed in his
late-implanted congenitally deafened cats.
The findings of Sharma and colleagues provided an electrophysiologic representation of the critical period of auditory and
spoken language development. Specifically, if early and sucient
access to meaningful auditory stimulation is not provided during
the early years of a child’s life, that child’s brain and auditory
brain function will be forever altered, and as a result, functional
auditory performance and spoken language development will also
suer, at least to some extent, for the rest of the child’s life.
with intelligible speech and a complex, high-level model of
spoken language and abstract language concepts.
of research shows that children who have hearing loss and are
exposed to greater amounts of total intelligible speech and complex language achieve higher spoken language outcomes than
their counter parts who are depr ived of access to a robust model of
high-level, complex language and intelligible speech.
Additionally, research has unequivocally shown that visual
stimulation (e.g, sign language) does not support spoken language
development. Although the secondary auditory cortex is particularly suited to process language, stimulation via visual input does
not prime the secondary auditory cortex to respond to intelligible
speech. Instead, the more a child is exposed to sign language at the
expense of exposure to intelligible speech, the more the secondary auditory cortex will be decoupled from the primary auditory
cortex. The less competent the secondary auditory cortex becomes
at processing auditory signals and distributing auditory information to the rest of the brain, the more susceptible the secondary
auditory cortex will be to colonization by the visual system.
Indeed, a large number of research studies also show poorer
listening, spoken language, and literacy outcomes for children
with hearing loss who use sign language or Total Communication
compared to children whose caregivers strive to provide a spoken
language–rich listening environment for their child’s auditory
brain development throughout the first few years of life.
Further, decades of clinical and anecdotal observations of persons
with congenital hearing loss suggest poor auditory and spoken
language outcomes for those who are deprived of sound during
the critical period, regardless of the child’s exposure to manual/
visual forms of communication.
33,34
A wealth
1,2,33,34,35,36,37
1,5,6,35,38
Pearl
Children with hearing loss must be appropriately tted with
hearing technology (e.g., hearing aids, bone conduction devices,
cochlear implants, remote microphone systems) as early as
possible in order to prevent auditory deprivation and irreparable
changes to the auditory brain and auditory neural network.
The implications of Kral’s and Sharma’s work on the outcomes
of children with hearing loss are obvious. Early fitting of technology is imperative to deliver the necessary stimulation to the
imary auditory cortex in order to promote synaptogenesis and
pr
functional connections/coupling between primary and secondary
auditory cortices.4 Inclusion of the secondary auditory cortex
in the system’s response to auditory stimuli is necessary for
the acoustic signal to be distributed throughout the brain (i.e.,
auditory connectome) and for sound to come to life and acquire
higher-order meaning.
1.4.4 Spoken Language Enrichment:
A Necessity for Auditory Brain
Development
It is also necessary for child’s caregivers to be equipped with
strategies to create an environment that inundates the child
Pearl
While discussing auditory brain development and related
research, such as the Kral and Sharma studies, it is important to
note that every day within the critical period is critical.
One may review Kral and Sharma’s work and erroneously
assume that an optimal outcome can be achieved as long as access
to a language-rich listening environment is provided by 3 years of
age. In reality, every month of auditory deprivation is likely to be
detrimental to the formation of functional synaptic connections
between the primary and secondary auditory cortices, resulting
in subsequently dysfunctional neural networks between the
secondary auditory cortex and the rest of the brain.
A landmark study by social scientists Betty Hart and Todd Risley
indicated that the language aptitudes of children who have normal
hearing and who were exposed to 46 million words during the
first few years of life far exceed those children who were exposed
to a smaller fraction (almost one-third, in fact) of words during
the critical period.
for those with hearing loss, the 46 million intelligible words serve
as the bedrock that supports functional pathways between the
primary and secondary auditory cortices and the establishment
of the auditory connectome necessary for sound to come to life
and possess higher-order meaning.
36
Both for children with normal hearing and
12
Every day, every week, and every month in which a child is
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
deprived of audible speech is lost time in which the child is
not working toward exposure to 46 million words by his or her
fourth birthday. As a result, every day is critical. Hearing aids and
cochlear implants must be provided as soon as hearing loss is
identified, and the audiologist must ensure that the child’s hearing technology provides satisfactory access to the wide repertoire
of sounds the child must hear to have access to 46 million words.
Recent studies have unequivocally established the critical
importance of early brain access to auditory information. In a
large prospective study of 468 children with congenital hearing
loss, Ching and Dillon showed a 0.5–standard deviation reduction
in language outcomes for children implanted at 12 months of age
compared to those implanted at 6 months of age.
Similarly, in a study of 207 children who had congenital hearing
loss and used cochlear implants, Dettman and colleagues found
normal vocabulary development in 81% of school-age children
who received cochlear implants prior to 1 year of age, while
only 52% of school-age children achieved normal vocabulary
development after receiving cochlear implants between 13 and
18 months of age.
Additionally, in a multicenter study of almost 300 children
with mild to severe hearing loss, children whose hearing aids
provided sucient audibility (as indicated by better aided Speech
Intelligibility Index [SII] scores) achieved two-thirds of a standard
deviation higher language outcomes compared to children with
poorer aided audibility.2 In the same study, children who used
their hearing aids more than 10 hours per day achieved mean
language scores that were almost one-half standard deviation
higher than children who used their hearing aids less than 10
hours per day.
Collectively, the studies just described provide great news!
When we do what it takes, great outcomes are possible for
children with hearing loss, regardless of their degree, type, or
configuration of hearing impairment.
35
1
Pearls
To achieve age appropriate spoken language outcomes, pediatric
audiologists must:
Oer the climate necessary for the auditory brain to develop
•
as intended
Identify hearing loss within the rst month of life
•
Provide the child with the hearing technology he or she needs
•
as soon as possible
Assist the child’s caregivers in creating an acoustically robust,
•
language-rich listening environment that provides 46 million
words during the rst few years of life
1 Why Hearing Is Important in Children
Fig . 1.11 PET scan imaging to evaluate activity in the left inferior
prefrontal cortex (LIPC) of cochlear implant recipients who listened
to running speech. Top right, circle: Activation of the LIPC requires
exposure to intelligible speech. High performers show activity in LIPC
(top right and left), while poor performers do not (bottom right and left).
phonologic or phonemic awareness, which is the explicit awareness of the speech sound structure of language units, forms the
b
asis for the development of literacy skills.
evidence of the importance of phonemic awareness for auditory
skill development, speech production, and literacy aptitude may
be found in a study in which Mortensen and colleagues used PET
scan imaging to evaluate activity in the LIPC of cochlear implant
recipients who listened to running speech.43 The LIPC, a region
often referred to as the Broca area, has been shown to be actively
involved in phonological processing, phonemic awareness,
speech production, and literacy aptitude. Indeed, lesions to the
Broca area typically impair a person’s ability to produce speech.
The Mortensen study included two groups of participants: one
that possessed a high level of open-set word recognition capacity
and another that possessed poor open-set word recognition
ability. The group with good word recognition aptitude showed
neural activity in the LIPC while listening to running speech, while
the group with poor speech understanding abilities showed little
to no activity in the LIPC (Fig. 1.11). In short, the Mortensen study
demonstrates the important link between the auditory areas of
the brain (e.g., secondary auditory cortex) and other areas related
to the auditory connectome. The link between the secondary
auditory cortex and other functionally related areas of the brain
is critical not only for the comprehension of spoken language but
also for speech production and literacy development. Clearly,
anything we can do to access and “program” those critical and
powerful auditory centers of the brain with acoustic detail will
expand children’s abilities to listen and learn spoken language.
8,39,40,41,42
Objective
1.5 Auditory Brain Development
and Literacy
Neural imaging has also demonstrated that the same areas in
the primary and secondary auditory cortex that are most active
when a child listens are also active when a child reads. That is,
1.6 New Context for the Word
“Deaf”
In this day and age, hearing aids, cochlear implants, and remote
microphone (RM) technology can provide brain access to the
entire speech spectrum to infants and children with even the
13
I Hearing Loss: Essential Information
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
most profound hearing losses as long as they have an intact
cochlea. Indeed, there is no degree of hearing loss that prohibits
brain access to sound if cochlear implants are available. Degree of
hearing loss as a limiting factor in auditory acuity is now an “old”
acoustic conversation. That is, when one uses the word “deaf,” the
implication is that a person’s brain has no access to sound, period.
The word “deaf” occurred in a very dierent context in 1970 or
even in 1990 than it does today. Today’s child who is “deaf” without
using technology may function like a child with a mild to moderate hearing loss when he or she is using hearing aids or a cochlear
implant because critical neural connectomes have been developed
through meaningful auditory stimulation. Therefore, the words
used today to express hearing loss may need to be reconsidered.
For this new generation of children with hearing loss, the degree
of hearing loss ought not determine their functional outcome;
performance with technology is what will determine functional
outcome. These are the new hearing children.
1.7 Hearing versus Listening
There is a distinction between hearing and listening. Hearing
is acoustic access to the brain; it includes improving the signalto-noise ratio by managing the environment and using hearing
technology. Listening, on the other hand, is focusing and attending to the acoustic events that are available.
Sequencing is important. Hearing must be made available
by audiologists before listening can be taught by parents, early
interventionists, speech-language pathologists, auditory-verbal
practitioners, teachers, and, of course, audiologists. That is, one
can reasonably focus on developing listening skills and strategies
only after acoustic events have been made available to the brain—
not before.
44
Pearl
Hearing must be made available by audiologists before listening
and language can be taught by parents, early interventionists,
speech-language pathologists, auditory-verbal practitioners,
and teachers.
How do we create a hearing brain and then teach it to be a
listening brain? In order to change the prefrontal cortex of the
brain, auditory attention and working memory must be fostered,
and training needs to commence in acoustically favorable con-
19
ditions.
foundation not only for spoken language and literacy skills but
also for age-appropriate social and cognitive skills.
Extensive auditory practice creates the neurobiologic
1.8 Conclusion
Pediatric audiologists have a key role in determining the future
opportunities of a child with a hearing loss. Sound/auditory
information has to reach the brain before auditory-based learning can occur.
All hearing losses in infants and children involve developmental
and educational issues requiring audiologic intervention. Some
hearing problems also involve medical issues.
Parents and other family members must understand the importance of auditory learning for language and literacy development
so that they can take an active part in building their children’s
skills. The purposes of audiologic environmental and technological management strategies are to enhance the reception of clear
and intact acoustic signals and auditory information to access,
develop, and organize the auditory centers of the brain.
Pitfall
Without clear detection of the entire speech spectrum, higher
levels of neural development and auditory processing are not
possible, and a baby’s or child’s listening, spoken language, and
literacy outcomes will be compromised.
The pediatric audiologist has a critical role in educating
families and, therefore, needs to be ever mindful of the desired
outcomes expressed by the family. The family’s vision for how
they want their child to communicate serves as the guide for the
technological and treatment recommendations that are made.
Because ~ 95% of children with hearing loss are born to hearing
and speaking families, listening and talking likely will be desired
outcomes for the vast majority of families we serve. For these
families, sign language would be a foreign language in which they
are not uent. Trying to teach a language they don’t know to their
child with hearing loss means the child will not be exposed to a
rich language environment.
In this day and age, the degree of hearing loss does not determine the functional outcome for infants and children who are
oung enough to have brain/neural plasticity; these children’s
y
auditory brain centers can be accessed, stimulated, and developed
through the early use of amplification or cochlear implant technologies and appropriate specialized intervention.
Someone once said, “Neglect the future, and no one will thank
you for managing the present.” Our job as pediatric audiologists is
to be visionary. How we audiologically diagnose and treat babies
from the beginning, and educate their families, lays the neurologic
foundation for the child’s entire life.
Discussion Questions
1. What is the relationship between the primary and secondary
auditory cortex?
2. How does auditory deprivation impact the development of
neural connectomes?
3. What is the relationship between hearing and listening?
4. How does auditory neuroplasticity relate to early tting of
hearing aids and cochlear implants?
5. What is the context for the word “deaf” in this day and age?
14
1 Why Hearing Is Important in Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
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Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
2 Hearing Disorders in Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
Brad A. Stach and Virginia Ramachandran
2 Hearing Disorders in Children
Summary
This chapter provides a comprehensive description of the
nongenetic causes of hearing loss in infants and children. Many
pathologic conditions, including disease, trauma, and developmental disturbance, cause hearing disorders during childhood.
The prevalence of hearing disorders in children is relatively high
compared with other childhood disorders. Hearing disorders are
customarily classified according to the site of the interruption in
sound transmission or encoding. Conductive hearing disorder
results from a problem with transmission of mechanical energy
to the cochlea, involving the structures of the outer and middle
ear. Conductive hearing disorders include congenital anomalies
and otitis media and its complications. Most conductive disorders
in children are acquired and transient. Sensory hearing disorder
results from problems involving the cochlea, including congenital
inner ear anomalies, maternal infections, such as cytomegalovirus
and toxoplasmosis, and acquired infections, such as meningitis and
mumps. They can also occur secondary to viral hemorrhagic fever
associated with infection from Ebola, Zika, or Lassa viruses. Neural
hearing disorder results from problems involving the auditory
nervous system, including neoplasms and hypoxia. The impact of
hearing disorder on speech and language development varies as a
function of degree, type, configuration, and stability of hearing loss
and when in the course of development hearing loss occurs.
Keywords
hearing, disorders, conductive, sensorineural, anomalies, otitis,
autoimmune, viral, ototoxicity, neuropathy
Key Points
Many pathologic conditions cause hearing disorders in childhood,
•
including disease, trauma, and developmental disturbance.
Some hear ing disorders are un ique to childhood; oth ers impact
•
children to a greater or lesser extent than they do adults.
Conductive hearing disorder results from problems involving
•
structures of the outer and middle ear, including congenital
anomalies and otitis media and its complications.
Sensory hearing disorder results from problems involving the
•
cochlea, including congenital inner ear anomalies, maternal
infections, such as cytomegalovirus and toxoplasmosis, and
acquired infections such as meningitis and mumps. They can
also occur secondary to viral hemorrhagic fever associated
with infection from Ebola, Zika, or Lassa virus.
Neural hearing disorder results from problems involving the
•
auditory nervous system, including neoplasms and hypoxia.
The impact of hearing disorder on speech and language
•
development varies as a function of hearing loss degree,
type, conguration, stability, and time of occurrence.
2.1 Introduction to Hearing
Disorders
A hearing disorder results from a disruption in function of
structures that transmit an acoustic signal from the outer ear to
the point of perception in the brain. Many pathologic conditions,
including disease, trauma, and developmental disturbance,
cause hearing disorders during childhood. In most cases, the
impacts on hearing sensitivity and suprathreshold perception
are predictable from the nature of the pathology.
The prevalence of hearing disorders in children is relatively high
compared with other childhood disorders. Approximately 1.5 to
2.5 in 1,000 infants are born with congenital hearing loss.1 Many
more infants and children have incidences of transient conductive
disorder.
Hearing disorders are customarily classified according to the site
of the interruption in sound transmission or encoding. Conductive
hearing disorder results from a problem with transmission of
mechanical energy to the cochlea, involving the structures of the
outer and middle ear. Conductive hearing disorders in children
are most commonly acquired and transient. Most respond well
to medical management and have negligible impact on longterm auditory function. There are two notable exceptions. First,
congenital disorders, which are primarily caused by structural
deformities or anomalies, can cause significant conductive
hearing loss and may not be readily treatable until the child is
older and skull growth is complete. Second, some children with
recurrent middle ear disorder and resultant uctuating hearing
sensitivity appear to be prone to suprathreshold dysfunction and
concomitant language/learning problems, presumably because of
the inconsistency of auditory input during the critical period of
language development.
Sensory, or sensorineural, hearing disorder is caused by a
failure in the cochlear transduction of sound from the mechanical
vibrations of the middle ear to neural impulses in the eighth
cranial nerve. Hearing sensitivity loss is the hallmark of a sensory
disorder and ranges from mild to profound. Sensorineural hearing
loss is usually permanent, although it can uctuate in some cases
and may be treatable in others. Depending on the cause, the loss
may also be progressive. Disorders of cochlear processes result
in reduced sensitivity of the cochlear receptor cells, reduced
frequency resolution, and reduced dynamic range. These complex
changes in cochlear function can have a significant negative
impact on suprathreshold hearing. The cause of most congenital
hearing loss is genetic and is described in Chapter 3.
Neural hearing disorder results from a problem with the
transmission of the electrical signal to and throughout the brain,
involving the eighth cranial nerve and the auditory central nervous
system pathways. Neural hearing disorders tend to be classified
into two groups: retrocochlear disorders and auditory processing
disorders. When a disorder is caused by an active, measurable
disease process, such as a neoplasm, or from damage caused by
2
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copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
trauma or stroke, it is often referred to as a retrocochlear disorder.
That is, retrocochlear disorders result from structural lesions of
the nervous system. Neural hearing disorders in children from
retrocochlear pathology are relatively rare. When they do occur,
they are characterized by patterns of abnormality consistent with
those found in adults with similar lesions,3 although some chil-
dren with central nervous system lesions have auditory deficits
that are more generalized and less severe than in adults with
similar lesions. Regardless, the morbidity and mortality of tumors
in young children is significantly greater than in adults. When an
impairment is due to developmental disorder or delay, it is often
referred to as an auditory processing disorder (APD). That is, APDs
result from more diuse, functional lesions of the nervous system.
The term APD is also used to describe the functional consequence
of a retrocochlear disorder. Auditory processing disorders are
discussed in detail in Chapter 16.
Pearl
When a neura l disorder is caused by an ac tive, measurable disease
process, such as a neoplasm, or from damage caused by trauma
or stroke, it is often referred to as a retrocochlear disorder. When
an impairment is due to developmental disorder or delay, it is
often referred to as an auditory processing disorder (APD).
mesodermal layer. Development of the auditory system begins
in the third week of gestation. At 7 to 8 weeks, the semicircular
canals are formed. The cochlea is adultlike by 25 weeks of gesta-
tion, while the middle ear continues to develop until the end of
estation. The auditory system develops alongside all other body
g
systems, and developmental abnormalities that aect one body
system can readily impact the developmental sequence of other
systems. Genetic anomalies can cause embryological abnormalities, as can factors external to the developing fetus, such as
drugs and alcohol. The timing of development of auditory system
structures is highly specific, and the relative timing of genetic
or environmental insults is critical to the ultimate anatomic and
functional outcomes. Depending on the causative factor and its
timing, other body systems that are undergoing similarly critical
development may also be aected, resulting in a constellation of
symptoms, known as a syndrome.
The remainder of this chapter will focus on the characteristics
of hearing disorders related to specific exogenous etiologies,
which have factors that are not necessarily intrinsic to the genetic
makeup of the individual. Endogenous conditions, which are
inherited, are discussed in Chapter 3.
2.3 Conductive Hearing Disorders
Causes of conductive hearing disorders a re summarized in Tab le 2 .1.
Some hearing disorders are unique to childhood; others aect
children to a greater or lesser extent than they do adults. Several
factors, including type of disorder, severity, and time of onset,
interact to determine the impact of childhood hearing disorders
on speech and language development. Disorders that uctuate or
are transient tend to have a more subtle impact on overall hearing
ability than do permanent disorders. Similarly, disorders that
are unilateral are likely to have far less impact than those that
are bilateral. In general, the more severe the hearing disorder,
the more likely it will be to aect normal speech and language
acquisition. Interacting with type and severity of the disorder is
the age of onset. Some hearing disorders are present at birth, or
congenital; others occur after birth, or are acquired. The onset of
a hearing disorder is also often described in relation to birth. A
hearing disorder can occur before (prenatal), during (perinatal),
or after (postnatal) birth. Furthermore, the onset of hearing disorder can be described in relation to the development of speech
guage. Hearing disorder can occur before (prelinguistic),
and lan
during (perilinguistic), or after (postlinguistic) the acquisition of
substantial speech and language skills.
2.2 Embryologic Development and
Hearing Disorders
Prenatal disorders are typically caused by abnormal embryologic
development. The auditory system arises from two of the three
germ cell layers that dierentiate shortly after fertilization. The
outer and inner ear systems develop primarily from the ectodermal tissues; the middle ear components develop from the
2.3.1 Acquired Prenatal Conductive
Disorders
Outer Ear Anomalies
Atresia is the absence of an opening of the ear or external audi-
tory meatus. It is not uncommon, occurring in ~ 1 in 6,000 births.
Bony atresia is the congenital absence of the ear canal caused by
a wall of bone separating the external ear from the middle ear.
Membranous atresia is the absence of a canal caused by a dense
soft tissue plug obstructing the canal. Atresia is unilateral in ~ 70
to 90% of cases. Atresia can cause maximum conductive hearing
loss (~ 60 dB) depending on the density of the blockage.
Other congenital anomalies of the ear canal and outer ear
can also cause conductive disorders. An abnormally small or
malformed ear is known as microtia. Although microtia does not
necessarily cause hearing disorder, it is often associated with
abnormalities of the ear canal, including stenosis or narrowing of
the ear canal. Stenosis may or may not cause a hearing disorder,
but it can cause additional complications, including excessive
cerumen accumulation and even cholesteatoma formation.
Table 2.1 Some causes of conductive hearing disorder
Acquired prenatal disorders Acquired postnatal disorders
Atresia
Middle ear anomalies
Otitis media with eusion
Tympanic membrane perforation
Cholesteatoma
Excessive cerumen
Otitis externa
4
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Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
Middle Ear Anomalies
Middle ear anomalies are often associated with abnormalities of the ear canal and auricle,4 although they can occur in
isolation. Middle ear anomalies include ossicular dysplasia
(abnormal development of the bones of the middle ear),
fenestral malformations (malformation of the oval window),
and congenital cholesteatoma. Ossicular dysplasia can result
in fixation, deformity, and disarticulation of the bones,
especially the incus and stapes. In congenital stapes fixation,
a fenestral malformation, the stapes footplate is fixed into
the bony wall of the cochlea at the oval window. Lack of oval
window development is also an example of fenestral malformation. Congenital cholesteatoma is a cyst that is present in
t
he middle ear space without any evidence of causative factors
such as otitis media.
Causes of Prenatal Outer and Middle Ear
Anomalies
Congenital outer and middle ear anomalies are often a result
of genetic causes. Genetic causes of hearing loss in the pediatric population are addressed in Chapter 3 of this text. In
many cases, these anomalies may be one of a constellation
of symptoms occurring as part of a syndrome or sequence.
Often, prenatal outer and middle ear anomalies may occur
with other craniofacial anomalies and/or sensorineural hearing loss. Some of the more common syndromes associated
with prenatal outer and middle ear anomalies are Treacher
Collins syndrome,5 branchio-oculo-facial (BOF) syndrome,6
Hutchinson-Gilford progeria syndrome,7 Down syndrome,
Townes-Brocks syndrome,8 lacrimo-auriculo-dento-digital
(LADD) syndrome,9 oculoauriculovertebral dysplasia
(Goldenhar syndrome),10 Klippel-Feil syndrome,11 Cornelia de
Lange syndrome,12 and CHARGE (coloboma of the eye, heart
anomaly, choanal atresia, retardation, genital and ear anomalies) syndrome.
13
2.3.2 Acquired Postnatal Conductive
Disorders
Otitis Media with Eusion
Otitis media is a general term to describe inammation of the
middle ear mucous membrane and tympanic membrane. Otitis
media is the most common diagnosis in patients who make
oce visits to physicians in the United States. Estimates are that
76 to 95% of all children have one episode of otitis media by 6
years of age. The prevalence is highest during the first 2 years
and declines with age. Approximately 60% of those children who
have otitis media before the age of 1 year will have six or more
bouts within the ensuing 2 years.
14
Pearl
Otitis media is the most common diagnosis in patients who make
oce visits to physicians in the United States.
The growing use of pneumococcal conjugate vaccines holds
promise for reducing rates of otitis media. The most commonly
associated microbial contributions to otitis media are Haemophilus
inuenzae and Streptococcus pneumoniae, with Moraxella catarrhalis
and others contributing to a lesser extent. Vaccination has been
associated with a decrease in the percentage of cases of otitis media
due to H. inuenzae and a resultant increase in the relative number
of cases of S. pneumoniae.
Risk factors for otitis media include young age, Native American
or Inuit heritage, Down syndrome, human immunodeficiency
virus (HIV)/acquired immunodeficiency syndrome (AIDS),
anatomic defects such as cleft palate, exposure to smoke in the
household, male sex, crowded living conditions, poor sanitation,
inadequate medical care, eating in prone position, obesity, and
day care.16 There is also increasing evidence of genetic susceptibility to otitis media.
Otitis media is typically caused by eustachian tube dysfunction
secondary to upper respiratory tract infection. Swelling of the
nasopharynx results in failure of the eustachian tube to protect,
clear, and equalize the pressure of the middle ear space, permit-
ting reux of infectious secretions from the nasopharynx into the
middle ear.
Otitis media is usually defined by the presence or absence of
eusion in the middle ear space, the type of eusion, and the
time course of the disorder. Otitis media with eusion (OME) is
the common term used to describe the disorder. The uid may
be referred to as serous (thin, watery, sterile), suppurative (containing pus), purulent (suppurative), mucoid (thick, viscid), or
sanguineous (containing blood). Adhesive otitis media involves
severe retraction of the tympanic membrane into the middle ear
space.
Acute otitis media with eusion is the term describing rapid
onset of symptoms of middle ear inammation, including redness of the tympanic membrane and otalgia. It is usually referred
to as acute if it lasts shorter than 3 weeks or as subacute if it lasts
shorter than 3 months. Middle ear eusion is signaled by bulging
and limited mobility of the tympanic membrane, otorrhea, or a
uid level behind the tympanic membrane. Other nonspecific
symptoms in an infant or toddler may include fever, excessive
crying, or pulling on the ears. Vertigo, dizziness, and imbalance
are also common in children with otitis media. Recurrent acute
OME consists of repeated episodes of acute otitis media with
normal middle ear examinations between episodes. Persistent
middle ear eusion is an asymptomatic eusion that persists following treatment for acute OME. The term chronic OME is used
to describe a condition that lasts longer than 3 months. Chronic
suppurative otitis media is a chronic infection of the middle ear
and mastoid air cells with a perforation of the tympanic membrane and otorrhea.
OME may resolve spontaneously or may require treatment with
antibiotics or pressure equalization tubes, with varying eects
on recurrence rates. Hearing loss uctuates with the presence or
absence of uid. Untreated OME can lead to several complications,
including cholesterol granuloma, adhesive otitis media, facial
paralysis, labyrinthitis, acute mastoiditis, petrositis, meningitis,
sigmoid sinus thrombosis, extradural abscess, brain abscess, otic
hydrocephalus, and sensorineural hearing loss.18 In rare cases
otitis media can result in death.
15
17
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copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
Among the more common complications are tympanic mem-
brane perforation, tympanosclerosis, and cholesteatoma.
Complications of Otitis Media with Eusion
The tympanic membrane may become perforated as a result of
OME because of increased pressure from uid in the middle ear
space, or it may be perforated from barotrauma, trauma, myringotomy, or tympanostomy tube placement. Although perforations generally heal spontaneously, they may require surgical
intervention to repair the damaged membrane. Drainage from
perforation may cause a secondary infection of the external
auditory canal or auricle. A perforation may or may not result in
hearing loss, depending on its size and location.
Tympanosclerosis is a degeneration of collagenous fibrous tis-
sues of the tympanic membrane and is a common sequela of OME,
occurring in ~ 10% of cases.19 Calcification or ossification may
occur and spread to the ossicles in rare cases. Tympanosclerosis
can often be observed as a horseshoe-shaped plaque on the
tympanic membrane. Tympanosclerosis is not associated with
significant hearing loss unless it also involves the ossicular chain.
Cholesteatomas are cysts that contain keratinizing squamous
epithelium and are found in the middle ear, mastoid, external
auditory canal, or petrous bone.20 Congenital cholesteatomas are
present behind an intact tympanic membrane with no history of
significant otitis media or eustachian tube dysfunction. Acquired
cholesteatomas are more common and are usually a consequence
of chronic otitis media. Cholesteatomas can be destructive, as
they grow and compete for space with the normal structures
of the areas they occupy. Conductive hearing loss varies as a
function of the structures involved. Allowed to grow unchecked,
a cholesteatoma can erode the middle ear ossicles and cause
ossicular discontinuity, creating additional conductive hearing
loss. In advanced cases, sensorineural hearing loss can also occur
because of cochlear erosion.
Excessive Cerumen
Excessive cerumen (ear wax) in the ear canal occurs in ~ 10% of
children, and it may have an even greater incidence, up to 28 to
36%, in children with developmental delays. A high-frequency
conductive hearing loss can occur when the ear canal is 80 to
95% occluded. A low-frequency conductive loss occurs with total
occlusion of the ear canal.
Otitis Externa
Otitis externa is the broad term for inammation or infection
of the external auditory canal and auricle. Otitis externa rarely
causes hearing disorder, except in cases where it causes stenosis
of the external auditory meatus. Acute diuse otitis externa, also
known as swimmer’s ear, is one example of otitis externa. It is a
bacterial infection that causes itching, tenderness, and pain and
may include hearing loss and aural fullness as the external auditory canal decreases in size with swelling. Several fungal, viral,
and bacterial infections of the external ear have been reported.
Complications of otitis externa may include ear canal stenosis,
myringitis, and tympanic membrane perforation. Ototoxicity
from topical otic preparations for treatment of external otitis
can also occur.
21
2.4 Sensory Hearing Disorders
Causes of sensory hearing disorders are summarized in Table 2.2.
2.4.1 Acquired Prenatal Sensory
Disorders
Inner Ear Anomalies
Inner ear malformations occur when development of the membranous and/or bony labyrinth is arrested during fetal development.22 Although in many cases the arrest of development
is genetic, some cases are the result of teratogenic inuences
during pregnancy, including viral infections such as rubella,
drugs such as thalidomide, and fetal radiation exposure.
Inner ear malformations can be divided into those in which
both the osseous and membranous labyrinths are abnormal and
those in which only the membranous labyrinth is abnormal. The
former anomalies are better understood, because they can be
readily identified with scanning techniques, although magnetic
resonance imaging (MRI) has become a useful tool for imaging of
the soft tissue structures as well.
Included in the malformations of both membranous and osseous labyrinths are complete labyrinthine aplasia (Michel deformity), common-cavity defect, cochlear aplasia and hypoplasia,
and Mondini defect. Michel deformity is a very rare malformation
characterized by complete absence of membranous and osseous
inner ear structures, resulting in total deafness. Common-cavity
malformation comprises about one-fourth of all cochlear malformations. It is a membranous and osseous malformation in
which the cochlea is not dierentiated from the vestibule, usually
resulting in substantial hearing loss. Cochlear aplasia is a rare
malformation consisting of complete absence of the membranous
and osseous cochlea and no auditory function, but presence of
semicircular canals and vestibule. Cochlear hypoplasia is a malformation in which less than one full turn of the cochlea is developed.
Cochlear hypoplasia accounts for ~ 15% of cochlear malformations.
Mondini malformation, an incomplete partition of the cochlea, is
a relatively common inner ear malformation in which the cochlea
contains only ~1.5 turns and the osseous spiral lamina is partially
or completely absent. The resulting hearing loss is highly variable.
Other abnormalities of both the osseous and membranous labyrinth include anomalies of the semicircular canals, the internal
auditory canals, and the cochlear and vestibular aqueducts. One
example of the latter is large vestibular aqueduct syndrome, a
Table 2.2 Some causes of sensory hearing disorder
Acquired prenatal disorders Acquired perinatal and postnatal
Inner ear anomalies
Cytomegalovirus
Syphilis
Rubella
Toxoplasmosis
disorders
Persistent pulmonary hypertension of
the newborn (PPHN)/extracorporeal
membrane oxygenation (ECMO)
Meningitis
Autoimmune inner ear disease
Mumps
Measles
Hemorrhagic fever
Ototoxicity
20
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