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110 Disorders of the Auditory System
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and electrophysiologic central auditory
tests, which were corroborated by the
imaging test results.
Computed tomography and MRI
often play complementary roles in the
evaluation of various auditory conditions, with each having relative advantages in characterizing a particular component of the disease process. Although
not absolute, and certainly subject to
change with continued advances in imaging techniques, Table 3–7 provides a tem-
Table 3 –7. Disorders of the Auditory System and the Respective
Roles of Computerized Tomography and Magnetic Resonance
Imaging in Their Diagnoses
Pathologic Process CT MRI
Congenital hearing loss ++ +
Progressive/acquired hearing loss + ++
plate as to which imaging study should
be performed in the initial evaluation
of suspected auditory pathology. The
previous discussion provides an overview of the foundations of two radiologic procedures (CT and MRI) and their
specific applications in the assessment
of the peripheral and central auditory
systems. The reader interested in more
detailed information about these imaging procedures is referred to Dunnebier
(2011).
Vestibular-cochlear dysplasias ++ +
External auditory canal atresia ++ −
Otosclerosis ++ −
Superior canal dehiscence ++ −
Cholesteatoma (preoperative) ++ +
Recurrent cholesteatoma (postoperative) + ++
Trauma ++ −
Schwannomas (e.g., vestibular, facial) − ++
Meningioma + ++
Epidermoid and arachnoid cysts + ++
Paragangliomas (glomus tumors) ++ ++
Petrous apex cholesterol granulomas + ++
Vascular abnormalities/anomalies + ++
Note. ++ Modality of choice, + Alternative Modality, − Limited Utility.
3. Audiologic, Vestibular, and Radiologic Procedures 111
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summaRy
This chapter is intended to provide the
reader with a basic orientation with respect to the tools available to the clinician to aid in the diagnosis of disorders
of the auditory system. Even the simplest
measure, such as tympanometry, provides
key information regarding auditory system function or dysfunction. In addition,
radiologic procedures and vestibular system evaluation tests are often included
in the evaluation of an auditory system
disorder. Therefore, a brief overview of
these procedures was also included in
this chapter. One cannot stress enough
how important these audiologic, vestibular, and radiologic measures are in guiding audiologists and otolaryngologists in
making the correct diagnosis in order to
aid in appropriate audiologic and medical
management and rehabilitation.
Acknowledgments. The authors grate-
fully acknowledge the contributions of
Curtis A. Given, II, MD, Director of Neurointerventional Services, Central Baptist
Hospital, Lexington, Kentucky to this
chapter.
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4
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Outer and Middle Ear
Disorders
intRoduction
The outer (external) and middle ear comprise the receptive and transformer structures for the auditory system. The external
ear includes the auricle (also referred to as
the pinna) and the external auditory canal.
The external auditory canal is a skin-lined
opening that ends at the eardrum or tympanic membrane. The subcutaneous support of the outer third of the external
canal is cartilage, whereas the medial twothirds of the canal (i.e., the portion adjacent to the tympanic membrane) is bony.
The tympanic membrane has three cellular layers: the lateral squamous cell layer,
the middle fibrous layer, and the medial
respiratory epithelial layer. The tympanic
membrane is held in position by a bony
trough located at the medial end of the
external auditory canal in which a fibrous
ligament called the annulus resides. The
superior portion of the membrane contains a higher proportion of elastin within
its fibrous layer and is referred to as the
pars flaccida; the rest of the membrane is
referred to as the pars tensa.
The middle ear is an aerated space
that begins laterally with the tympanic
membrane and ends medially with the
bony encasement of the cochlea and
the vestibule. The middle ear space is
divided into separate regions based on
their relationships to the tympanic membrane annulus. The protympanum is the
anterior-most space of the middle ear and
contains the opening of the Eustachian
tube, which connects the middle ear to
the nasopharynx. The mesotympanum is
on the same plane as the tympanic membrane and it contains the handle of the
malleus, the long process of the incus,
the stapes, the oval and round windows,
and the tympanic segment of the facial
nerve. The hypotympanum is inferior to
the annulus and is the typical location
of the bony covering of the jugular bulb;
however, this bulb may lack a bony covering, creating a risk of jugular bulb injury
115
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during middle ear surgery. The epitympanum is above the tympanic membrane
and is closely related to the pars flaccida
portion of the tympanic membrane. This
space contains the head of the malleus
and the short process of the incus and is
confluent with the air cells of the mastoid
portion of the temporal bone by an opening called the additus ad antrum. The
external and middle ears are surrounded
by vital neural and vascular structures
that can become involved in the disease
processes that affect the ear. (For more
information on the anatomy and physiology of the outer and middle ears, see
Musiek and Baran, 2020, and Chapter 2,
“Structure and Function of the Auditory
and Vestibular Systems.”)
A wide variety of diseases, both congenital and acquired, can affect this portion of the auditory system, resulting in
significant hearing dysfunction. As a
whole, diseases of the external and middle
ears are quite prevalent and account for
a large portion of health care resources.
This chapter examines a selection of the
diseases and conditions that affect the
external and/or middle ears.
auRal atResia
Introduction
Aural atresia is a condition in which the
external auditory canal (EAC) fails to
develop properly, resulting in an abnormally closed or absent canal (see also
Chapter 9, “Hereditary and Congenital
Hearing Loss”). Any interruption of the
embryologic development of the EAC
can result in atresia with varying degrees
of severity. This condition is usually congenital in nature; however, acquired atre-
sia can also occur and is most commonly
related to chronic infections or trauma of
the external auditory canal.
Symptoms
Atresia of the external auditory canal is
typically discovered during a newborn
screening examination. The condition is
characterized by the absence of an external
auditory canal or the presence of a blind
pouch in the canal, and it may involve one
or both ears. Microtia, which is the malformation or absence of the pinna, is frequently present with aural atresia; however, the pinna is normal in many patients
with atresia. The middle ear may also be
involved in individuals with aural atresia.
In these cases, the tympanic membrane is
typically absent and the ossicles may be
significantly malformed or completely
absent. In addition, the inner ear may be
malformed; however, this condition is less
common than external and/or middle ear
malformations due to the separate and
distinct embryologic development of the
inner ear. When the EAC is shallow or
blunted, the atresia may not be identified
at birth and diagnosis is often delayed
until entrance into school. In these cases,
a routine hearing screening test administered in school may identify hearing loss
and ultimately lead to the medical diagnosis of aural atresia.
The absence of an external canal
results in a conductive hearing loss. In
the event that the condition is bilateral
and left untreated, the patient is likely
to experience significant speech and language delays. The external canal, if not
completely absent, may be as small as a
pinpoint in size. This narrowing, or stenosis, of the ear canal may lead to the collection of epithelial skin cells in the exter-
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nal auditory canal — a condition known
as an external canal cholesteatoma that
can result in inflammation, pain, and/or
aural discharge (otorrhea). Other systemic
congenital anomalies may be present, but
special attention should be paid to craniofacial anomalies, such as cleft palate,
which may be an important consideration
during perioperative airway management
(see Schuknecht, 1989).
Incidence and Prevalence
Congenital aural atresia generally occurs
in 1 out of 10,000 to 20,000 live births.
Typically, males are affected more than
females and unilateral atresia is approximately three times more common than
bilateral atresia (De la Cruz & Chandrasekhar, 1994). Also, the right ear tends
to be involved slightly more frequently
than the left ear, and the atretic portion
of the external canal is more frequently
bony rather than membranous (Jahrsdoerfer, 1978).
Etiology and Pathology
This condition is primarily a congenital
malformation of the external ear canal that
may occur in conjunction with a number of
syndromes (e.g., Pierre Robin, CHARGE,
VATER, Goldenhar, and Treacher Collins).
Anomalies of the ear tend to develop
along with other craniofacial malformations during the early stages of fetal development due to their common embryologic origins. Five branchial arches and
their associated structures form the major
structures of the head and neck. The
ossicles begin to develop in the 4th gestational week and this process continues to
the 16th gestational week when the ossi-
cles reach adult size. During the 8th gestational week, the first branchial groove
forms a plug of cells that migrates medially to oppose the developing middle ear
cleft. The plug of cells begins to hollow
out to form an epithelial-lined external
auditory canal during the 6th month of
gestation. Any interruption during this
external and middle ear development
typically results in ossicular malformation
or atresia of the canal (see Lambert, 1998).
Site of Lesion
The severity and location of aural atresia
can be classified in a number of ways.
commonly used classification system was
A
described by Schuknecht (1989). Type A,
or meatal atresia, involves the lateral
cartilaginous portion of the canal, which
is extremely narrowed in the atretic ear,
preventing sloughing skin cells and cerumen from exiting the external canal. These
sloughing skin cells can form a cyst, which
then can erode soft tissue and bony structures. Type B, or partial atresia, involves a
narrowing of the cartilaginous and bony
portions of the canal. In this condition,
the narrowed ear canal typically allows
visualization of the tympanic membrane,
but malformations of the ossicles are common. Type C, or total atresia, involves
complete atresia of the cartilaginous and
bony portions of the canal; however, the
mastoid and middle ear are aerated. The
bone adjacent to the middle ear is referred
to as the atretic plate. The tympanic membrane is typically absent, and the ossicles
are fused and frequently adherent to the
atretic plate. Type D, or hypopneumatic
atresia, is similar to type C; however, the
mastoid is poorly pneumatized and the
facial nerve has an aberrant course within
the temporal bone.
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Audiology
The audiologic evaluation of an individual with atresia can be difficult, but it
is a critical component of the diagnostic
workup, especially in the case of pediatric
patients. Audiologic evaluation is accomplished through two different approaches
(routine threshold test procedures or
threshold auditory brainstem response
[ABR] tests) that are dependent on the
presence of either unilateral or bilateral
atretic involvement (see discussion that
follows). Either way, when evaluating an
infant or a very young child, the recommended approach is through the use of
the auditory brainstem response (ABR)
evaluation.
Most individuals with atresia present
with a significant conductive hearing loss
on the involved side. If a patient presents
with involvement of only one ear, auditory sensitivity should be determined
initially for the normal or nonatretic ear.
This may be accomplished using standard
audiometric test procedures, if feasible.
However, in cases of infants, young children, or difficult to test patients, an ABR
procedure may be used. It is recommended
that a frequency-specific ABR (tone-bursts)
be used in order to establish the level of
hearing sensitivity across a range of frequencies. Once air-conduction hearing
thresholds have been established, it is
recommended that bone-conduction testing be performed on the atretic side with
masking delivered to the uninvolved ear.
In cases of bilateral atresia, boneconduction ABR is critical in determining
serviceable hearing; however, it is nearly
impossible to determine with any degree
of certainty which ear is the better hearing ear due to the presence of the bilateral conductive loss and related masking
dilemmas.
Medical Examination
Atresia of the external auditory canal is
typically found during a routine neonatal screening examination shortly after
birth, as it may be heralded by microtia.
The examination of aural atresia begins
with inspection and palpation of the head
and neck. The patient may have dysmorphic features or craniofacial anomalies
that may require further workup and
intervention prior to addressing the aural
atresia (e.g., as in the case of Pierre Robin
sequence syndrome with cleft palate). Otologic examination involves inspection and
palpation of the auricle with careful photographic documentation of any degree
of microtia. One must also examine facial
nerve function as the facial nerve may
have a highly variable course in atretic
ears. Examination of the external auditory
canal may be limited, but an attempt to
evaluate the canal must be made. The use
of a microscope to inspect the canal may
uncover a stenotic or narrowed meatus
and allow for cleaning of cerumen and
squamous debris. Computed tomography
(CT) scanning is vital in determining the
location and severity of the compromise,
as well as to aid in preoperative planning.
The gold standard imaging procedure is
a high-resolution CT scan of the temporal
bone with 1- to 2-mm slices.
Audiologic Management
Audiologic management in cases of atresia varies depending on a variety of factors (i.e., unilateral versus bilateral atresia,
hearing sensitivity of the nonatretic ear in
cases of unilateral atresia, the extent of the
atresia, the age of the patient, etc.). If serviceable hearing is documented through
pure-tone testing, a bone-conduction hear-
4. Outer and Middle Ear Disorders 119
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ing aid is often a viable option in many
cases (Declau, Cremers, & Van de Heyning, 1999). Keeping in mind, however,
that in cases of unilateral atresia, if the
nonatretic ear demonstrates any degree of
hearing loss, this should be managed with
traditional amplification or medically if
indicated. For preschool and school-age
children, utilization of an FM system in
the classroom should be considered in
order to provide them with the best possible signal-to-noise ratio in an effort to
maximize their speech understanding and
academic success.
Medical Management
The type of treatment utilized for aural
atresia is based on the severity of disease. Documentation of audiologic function must occur early in the evaluation
of these patients, whether by boneconduction audiometry or evoked auditory responses. Careful examination of the
CT scan must be performed. Lack of sensorineural function and/or the presence
of a malformed inner ear are contraindications for surgical intervention. Jahrsdoerfer and colleagues developed a 10-point
grading scale of temporal bone anatomy
that is used commonly today in determining candidacy for surgical intervention
(Jahrsdoerfer, Yeakley, Aguilar, Cole, &
Gray, 1992). The grading scale is based on
a system that awards points for the normal radiographic appearance of specific
temporal bone structures. Specifically,
2 points are awarded for the presence of a
stapes and 1 point is awarded for the presence of a normal finding for each of the
following structures: open oval window,
middle ear space, facial nerve, malleus/
incus complex, pneumatized mastoid,
incus-stapes connection, round window,
and the appearance of the external ear.
A score of 10 would suggest an excellent
candidate, whereas a score of 5 or less is
considered poor and disqualifies a patient
for surgical intervention.
Surgical correction of the atretic ear
canal is difficult and requires a combination of skill and experience. Typically,
microtia is surgically addressed by a
reconstructive surgeon prior to the creation of a new external auditory canal.
Microtia repair usually occurs when the
child reaches 6 or 7 years of age and aural
atresia repair is performed 1 to 2 years
later. Patients with incomplete atresia or
stenotic ear canals require careful cleaning of the canal and close follow-up to
prevent cholesteatoma formation and/
or canal restenosis. If the canal cannot be
cleaned adequately, then surgical correction becomes necessary.
Repair of the atretic canal involves a
postauricular incision and the drilling of
a new external auditory canal within the
temporal bone while carefully avoiding
the mastoid air cells, the middle cranial
fossa dura mater, and the facial nerve.
Once the middle ear is reached, careful
inspection of the ossicles is performed.
A tympanic membrane graft is fashioned
from temporalis fascia and draped over
the ossicles. A skin graft is then carefully
placed into position to provide the lining for the newly created canal. Patients
are followed closely as outpatients, and
debridement of the canal is performed frequently in the clinic using a microscope.
Patients who are poor reconstructive
surgical candidates based on their scores
on the Jahrsdoerfer grading scale may be
candidates for amplification using a softband bone-anchored device or a surgically implanted osseointegrated device.
The softband option involves attaching a
bone-conduction device to a headband by
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