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Audiology Review: Preparing for the Praxis and Comprehensive Examinations
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n
Frequency allocation of the electric stimulation is adjusted based on the resulting audiogram
of the recipient.
Better hearing preoperatively makes it more likely that the recipient will have hearing preservation.
There can be some reduction of hearing thresholds post implantation.
Hearing Assistive Technology
Despite using advanced pre- and post-hoc signal processing (e.g., directional microphones, digital
noise reduction) to improve speech-in-noise performance, CI recipients still experience poorer performance in noise than individuals with normal hearing. Adding hearing assistive technology (HAT)
is particularly useful for recipients. With all CI orders, recipients can choose accessory devices. These
can be waterproof options, additional wearing options, extra batteries, or HAT in the form of remote
microphones and others such as television connectors.
Special Populations
Bilateral and Bimodal
When a user has one HA and one CI, it is referred to as bimodal. When a user has a CI on each ear, it
is referred to as bilateral implantation.
n
If a patient is unilaterally implanted, better performance and satisfaction with hearing status
can be achieved by adding a HA on the contralateral ear, regardless of degree of hearing loss.
This is due to improved access to low-frequency sounds, which has a positive correlation with
sound quality.
CASE EXAMPLE
An adult HA user has been experiencing progressive hearing loss over the previous
10 years. She has recently had a bilateral change in hearing that qualifies her
for bilateral cochlear implantation. She is concerned about undergoing surgery
and inquires with the CI team if they would consider bilateral, simultaneous
implantation. The team ultimately decides to recommend her for unilateral
implantation with the option to consider a sequential implant. This patient is
ultimately counseled on a few key considerations as part of their recommendation. The first is insurance reimbursement. Many insurance providers will only
approve one CI for adult users, despite significant evidence to support the use of
two. It is possible she would be approved for a second CI in the future. Another
consideration is time without sound. Cochlear implantation involves the risk
of loss of residual hearing, healing time of 1 to 4 weeks prior to activation,
and extended habilitation of weeks to months before the user can experience
significant improvements in word recognition. Implanting one ear at a time may
allow for an easier acclimation period where she can still utilize residual hearing
in her contralateral ear with a HA.
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n
For adults, the recipient’s insurance may preclude them from obtaining a second CI; however,
it should be considered for a few reasons. When deciding on adding a second CI or a
contralateral HA, the following considerations should be made:
Both bimodal and bilateral CI users have better performance on speech-in-noise compared
to recipients who only utilize one CI.
Bilateral CI users experience better localization compared to unilateral CI and bimodal
users.
Bimodal users may have better music perception and sound quality due to improved fine
temporal structure provided by the low frequencies from the HA.
n
Bilateral CI use is much more widely accepted and approved in pediatrics and is preferred to
unilateral use for patients with bilateral profound SNHL. It has significant implications for
language and educational outcomes.
Optimal performance is achieved when there are <2 years between implantation (Gordon
etal., 2010).
Single-Sided Deafness
463
Since 2019, CIs have been FDA approved for single-sided deafness (SSD) and asymmetric hearing
loss for patients 5 years of age and over for MED-EL and, more recently, Cochlear recipients. Before
that, CIs were provided in an off-label capacity and for research purposes for recipients for whom more
traditional interventions were not sufficient or for those who had incapacitating tinnitus.
n
The only way to restore hearing in unilateral deafness is a CI.
n
CIs for people with SSD can improve speech understanding in quiet and in noise, localization,
music appreciation, quality of life, and potentially speech and language development for
pediatrics as compared to more traditional interventions of CROS, BCHD, and proactive
environmental management.
Bone-Conduction Devices
Introduction
Conductive hearing losses may be medically managed by an otologist/neurotologist, but not all are
medically manageable and/or not all patients desire surgical intervention. Even with surgical management, there may be a residual hearing loss for which audiologic management is recommended.
n
Traditional bone-conduction devices function similarly to air-conduction devices until the last
stage, which is when the signal is transduced to the patient. Instead of an acoustic signal, it is a
vibratory signal that directly stimulates the inner ear, bypassing the outer and middle ear.
Candidacy
Bone-conduction devices have two indications: conductive hearing losses and SSD as a transcranial
routing of signal device. These are also divided into implanted and nonimplanted devices.
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Candidacy Evaluations
Candidacy evaluations include a comprehensive audiologic evaluation with air- and bone-conduction
thresholds, speech recognition thresholds, word recognition testing, and subjective measures. Considerations for candidacy will be made based on the patient’s bone-conduction thresholds and lifestyle. To
help the patient decide on a device (nonimplantable or implantable), the audiologist should consider
completing aided testing with a clinical demo device on a hard headband. Aided measures of functional
gain, including soundfield thresholds and aided word recognition in quiet and in noise, may be performed. The patient may also undergo an at-home trial and wear a nonsurgical device for 2 to 6 weeks.
CASE EXAMPLE
A 65-year-old patient presents with a moderately severe conductive hearing
loss in his right ear secondary to a failed ossicular chain reconstruction. He
has an otherwise normal ear canal and no history of significant cerumen occlusion or drainage. His left ear presents with normal hearing. This patient has
significant complaints of hearing in background noise. He has been trialing
an air-conduction HA for his right ear for 1 month and is dissatisfied with the
sound quality. At this time, it may be more appropriate to recommend a trial
with a bone-conduction device. Since this patient has an air-bone gap greater
than 35 to 45 dB HL, he will likely achieve better aided outcomes and better
satisfaction with a bone-conduction device. He can trial a nonsurgical option
first with counseling regarding the possibility of improved sound quality and
gain characteristics with a surgically implanted device.
Bone-conduction devices may be implanted or nonimplanted. Uses, advantages, and disadvantages are reviewed in Table 9–11.
n
Nonimplanted coupling methods
Hard headband: this resembles the traditional headband used for bone-conduction
audiometric testing.
Soft headband: an elastic band that surrounds the head
SoundArc™: a hard headband that sits behind the head
Sticker (ADHEAR™): an adhesive that can be placed on the mastoid by which to affix the
sound processor to the head
n
Implanted coupling methods
Transcutaneous: vibratory communication occurs across the skin via an internal magnet
that is affixed to the skull.
Percutaneous: vibratory communication occurs via a screw affixed to the skull that
protrudes the skin.
Active transcutaneous bone-conduction implants: a semi-implanted device with the
vibratory component being surgically implanted and the sound processor serving as the
external component, which communicates through radiofrequency code across the skin to
the internal component.
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TAB LE 9 –11. Implanted Versus Nonimplanted Bone-Conduction Devices
TYPE USES ADVANTAGES DISADVANTAGES
465
Nonimplanted People that cannot
undergo surgery based
on age or surgical
risks factors
Trial devices prior to
deciding on surgery
Those who do not
want to undergo
surgery
Interim use prior to
medical management
of hearing loss
Implanted Adults and children
over 5 years of age;
other indications are
device-specific
Temporary, may be used in
interim scenarios
Access to sound immediately,
no osseointegration or surgical
healing
Easy to discontinue if hearing
improves or management
changes
No internal components Higher incidence of feedback
More likely to be covered by
insurance than nonsurgical; no
pressure from headband; less
feedback and distortion, better
high-frequency transmission
depending on coupling
method; stable position; can be
more optimally programmed;
surgery is reversible without
affecting patient hearing
High cost of device compared
to traditional amplification,
may not be covered by
insurance if not implanted
Consistent pressure needed,
can cause discomfort and/
or headaches; if consistent
pressure not achieved, gain is
not optimal
Aesthetics
any coupling method
and distortion
used to accommodate for
placement
High frequencies not
transmitted as effectively
Limitations based on patient
age; patient needs to undergo
surgery; others (discussed in
chapter)
— not optimal for
— higher gain
Nonimplanted Bone-Conduction Devices
Nonimplanted devices are in the same regulatory class as HAs and can be fit according to audiologic
need and recommendations from the audiologist. Guidelines may help the clinician decide whether
to choose an air-conduction or bone-conduction device for a patient with a conductive or mixed
hearing loss.
n
For patients with conductive or mixed hearing loss who have an intact ear canal,
air-conduction HAs may be an option. The managing audiologist should consider the
following:
Available gain: as discussed in the first section of this chapter, when there is an air-bone
gap, the patient requires more gain than with a SNHL (to overcome the attenuation caused
by the conductive component) with the same air-conduction thresholds.
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Drainage that occurs in the ear canal
●
Frequent or persistent drainage can cause numerous challenges with traditional HA use,
including damage to the internal components of the device, possible reinfection, and
increased incidence of drainage with an occluded ear.
Comfort of the patient
●
Some patients find air-conduction HAs to be uncomfortable and dislike having to wear a
device in the ear canal.
Size of air-bone gap (de Wolf et al., 2011)
●
Patients perform better on audiometric tasks with a bone-conduction device compared
to traditional amplification when their air-bone-gap is >35 dB HL. Patients report
improvements in their performance on subjective ranking on the APHAB when the
air-bone gap is >45 dB HL.
n
Based on these data, a bone-conduction device should be recommended when the air-bone
gap is 35 to 45 dB HL.
n
Patients may be candidates for bone-conduction devices if the audiologist cannot occlude the ear
canal, they have a congenital malformation of the external ear, or a large air-bone gap is present.
n
Audiologic bone-conduction thresholds should be normal to near-normal if the patient is
being chosen for a nonimplanted bone-conduction device for optimal performance. If the
device is going to be implanted, they can have poorer bone-conduction thresholds as there will
be more available gain. This is discussed in more detail below.
Normal high-frequency bone-conduction thresholds are of primary importance. All
nonimplanted bone-conduction devices have suboptimal transmission of high-frequency
sounds due to the dampening of high frequencies by the skin. Reduced transmission and
Q & A
Question: A 6-month-old with bilateral microtia and ear canal stenosis arrives
for a follow-up visit. The patient has received an ABR, which suggested maximum
(moderate to moderately severe) conductive hearing loss in both ears. The family
asks if a watch-and-wait approach can be utilized as they believe the ear canals
are likely to grow. What is the most appropriate audiologic management and
what counseling should be provided to the family?
Answer: Timely intervention, with management of hearing loss by age 6months,
is critical to maximal spoken language outcomes. A traditional HA is not appropriate for this patient due to infant ear canal stenosis. Various bone-conduction
devices can be presented to the family as options. Bone-conduction devices
should not be implanted for children younger than age 5 years due to skull
thickness. Therefore, nonimplanted coupling methods should be discussed.
Counseling should also include a discussion of frequent audiologic reevaluation
and adjustment of the management strategy with age, ear canal growth, and
changes in hearing status.
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perception of high-frequency speech sounds will have an adverse effect on the perception
of speech.
n
Nonimplanted device coupling
Cochlear Baha™ processor can be used on a Soundarc™ or Softband™.
Oticon Medical Ponto™ processor can be used on a soft headband or a hard traditional
headband for trial purposes.
MED-EL ADHEAR™ processor does have a soft headband option for certain situational
needs but is designed specifically to be connected to an adhesive that is placed on the
mastoid. There is no surgical version of the ADHEAR™.
●
While the Baha and Ponto can be used in a nonsurgical capacity with up to 45 dB HL
bone conduction thresholds, the ADHEAR™ processor should only be utilized if bone-
conduction thresholds are in the normal range.
Implanted Bone-Conduction Devices
Implanted devices undergo FDA approval in the same regulatory class as CIs (III). Typical candidacy
evaluations involve the otologist/neurotologist and the audiologist. Candidacy requirements are based
on bone-conduction thresholds, air-bone gaps, patient goals, and suitability for surgery. Devices may
be chosen based on lifestyle factors considering the pros and cons mentioned in the description of the
internal devices earlier in this chapter.
n
Transcutaneous and percutaneous devices have similar candidacy profiles.
FDA indicates patients need to be ≥5 years of age.
Hearing loss can be conductive, mixed, or SSD.
●
For SSD, normal hearing is required in the contralateral ear.
For bilateral surgical placement, symmetrical bone-conduction thresholds (no more than
10-dB difference on average between ears) are required.
As with CIs, other FDA indications are manufacturer specific.
Cochlear offers both transcutaneous and percutaneous devices.
●
Baha Connect™— percutaneous
●
Baha Attract™— transcutaneous
●
Sound processors can accommodate bone-conduction thresholds of up to 65 dB HL,
depending on the coupling.
Oticon Medical offers percutaneous devices.
●
Ponto™ sound processors can accommodate up to 65 dB HL bone-conduction thresholds.
Medtronic Sophono™ is a transcutaneous device and is technically a bone fixture device
as it attaches to the skull without osseointegration. It is the only device on the market that
does not require osseointegration but is a traditional vibratory external device.
n
Active transcutaneous bone-conduction implants
FDA indications are age 12 and older with conductive, mixed, or SSD.
●
Individuals between the ages of 5 and 12 may undergo placement of these devices in an
off-label capacity.
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MED-EL BONEBRIDGE™
●
●
●
Cochlear Osia™
●
●
●
Surgery
For mixed or conductive hearing losses, the pure-tone average bone-conduction
thresholds should be better than 55 dB HL.
For SSD, the implanted ear needs to have profound SNHL and the contralateral ear
pure-tone average bone-conduction thresholds should be better than 20 dB HL.
Patient should have experience with air-conduction or bone-conduction HAs as a trial,
with length of time not specified.
For mixed or conductive hearing losses, the pure-tone average bone-conduction
thresholds should be better than 55 dB HL.
For SSD, the implanted ear needs to have profound SNHL and the contralateral ear
pure-tone average bone-conduction thresholds should be better than 20 dB HL.
Patient should have experience with air-conduction or bone-conduction HAs as a trial,
with length of time not specified.
Transcutaneous and percutaneous implanted devices, with the exception of the Sophono™ device,
undergo osseointegration, which is the bonding of the implanted device to living tissue. This is a
natural process that occurs when titanium is placed into bone.
Internal Devices
n
Percutaneous
The titanium screw protrudes through the skin, and the abutment (connection point of the
bone-conduction device to the osseointegrated component) is directly connected to the screw.
Advantages
●
High signal fidelity as there is no dampening from the skin and it is directly transmitted
to the bone and therefore the cochlea.
●
Because the only surgically implanted component is the titanium screw, this is beneficial
for people who need to undergo MRIs as it is approved for up to 3.0 Tesla (3T) with
minimal shadow caused by the screw.
●
Retention is optimal.
Disadvantages
●
Skin overgrowth, infection, loss due to head trauma, extrusion of device, granulation tissue
●
Cannot be activated until osseointegration takes place, which on average takes 3 months
Percutaneous devices should not be used in cases of psychiatric concerns, poor hygiene, or
diseases that impact wound healing.
n
Transcutaneous
A titanium screw is still placed into skull with an additional magnetic plate placed under
the skin.
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Bone-conduction device is attached to an internal magnet component.
Vibration of internal magnet + screw component occurs through the connection of the
internal and external magnets, across the skin.
Advantages
●
Lower complications and less wound care required compared to percutaneous
●
More aesthetically pleasing
●
Can be activated before full osseointegration has taken place, as soon as 4 weeks after
surgery
●
Less risk of damage secondary to head trauma
●
May be easier to place by recipients
Disadvantages
●
Dampening of high-frequency sounds by the skin
●
May be more susceptible to feedback due to higher gain needed to provide stimulation
across the skin
●
Can only undergo MRI up to 1.5 Tesla (1.5T) and may have greater shadow if MRI is of
the head
●
Poorer retention if recipient has an active lifestyle
●
Skin aggravation secondary to pressure of magnet external component
n
Active transcutaneous bone-conduction implants
469
These devices are more similar to CIs in that the vibratory device is affixed to the skull
and a receiver stimulator is underneath the skin. The external device communicates via
an electromagnetic signal to the internal device. Vibration is not generated in the external
component, unlike the abovementioned bone-conduction devices. The vibration occurs at
the level of the internal fixation point.
MED-EL BONEBRIDGE™
●
Utilizes a bone-conduction floating mass transducer that is placed in a bone bed in the
skull
Cochlear Osia™
KNOWLEDGE CHECKPOINT
Bone-conduction devices may be surgical or nonsurgical. Patients of any age can
obtain a nonsurgical bone-conduction device and only patients 5 years of age or
older can receive transcutaneous and percutaneous devices, with patients 12years
of age being indicated for active transcutaneous bone-conduction implants. Some
patients may choose to defer surgery and utilize a bone-conduction device in a
nonsurgical capacity. These patients should be counseled regarding significant
benefits to surgical placement, including comfort, consistent device placement,
available gain before feedback, and transmission of high-frequency sounds.
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●
Utilizes the same internal B300™ implant used for the Connect™ and Attract™, which is
screwed into the skull, but physical location of the implant will be different. The B300™
implant is affixed to a piezoelectric transducer.
Both of these devices have the benefit of being transcutaneous but without the limitations
of skin dampening. There is superior high-frequency output and more useable gain before
feedback, as such, that it is comparable to a percutaneous device.
Post-Implantation and Device Management
Verification is a challenge with bone-conduction devices as there is a not a currently acceptable, standardized method for verification as there is with air-conduction devices. The Verifit
artificial mastoid with which verification of electroacoustic device can be completed; however, the only
available prescriptive targets are DSL-BCD, which should only be used with percutaneous devices.
Other considerations are skin thickness, skull shape, and individual cochlear differences. Depending
on the coupling of the device, the patient’s skin and hair thickness, and placement, the gain will vary
from that which would be recommended by connection to an artificial mastoid.
n
Nearly all bone-conduction devices are programmed with in-situ audiometric measures,
meaning the clinician identifies the patient’s threshold via direct stimulation of the processor.
As of the time of this writing, the only device that does not allow for in-situ measurement is
the MED-EL ADHEAR™.
n
This device comes preprogrammed with the sole intention of converting the auditory signal
into mechanical transduction. Minor adjustments can be made to overall gain, but it is not
meant to be individually programmed to a recipient’s bone-conduction thresholds.
n
Validation can be completed via aided audiologic measures of threshold detection, speech-in-
quiet, and speech-in-noise.
® system offers an
Auditory Brainstem Implants
Introduction
Certain individuals may not benefit from the implantable options discussed above. These individuals
may benefit from an auditory brainstem implant (ABI). The primary goal of an ABI is sound awareness
and potential assistance in speech reading (Wong et al., 2019).
An ABI uses the same external components as the CI. The internal components consist of a
receiver-stimulator and a paddle electrode, which communicates directly with the cochlear nucleus,
located in the brainstem, using electrical pulses.
Candidacy
The only current FDA indication for use of an ABI is for patients with neurofibromatosis type 2 (NF2)
who are 12 years of age and older. These individuals do not receive benefit from a CI due to the site
of lesion being at the level of the auditory nerve, and the success of a CI is dependent on the status of
the auditory nerve. In the United States, there are a few centers that will implant ABIs off-label. Those
who may be considered for off-label candidacy include cases of a temporal bone fracture that severs the
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auditory nerve, congenital cochlear nerve aplasia, cochlear aplasia, or complete cochlear ossification.
Outside of the United States, there is a wider recipient base of ABI devices.
Children may also receive ABIs. They may be required to undergo and fail cochlear implantation
prior to receiving an ABI, if they have an intact cochlea. Below is a list of conditions that would make
a person a potential off-label candidate (Wolfe, 2020):
n
Congenital cochlear nerve aplasia or cochlear aplasia
n
Bilateral profound hearing loss
n
Age 18 months to 5 years
n
Realistic expectations and family dedication
ABI Team
The ABI team is more extensive than the CI team. An ABI team includes an otologist, a neurosurgeon,
a neuroradiologist, an audiologist, an electrophysiologist, and a SLP. It is imperative that the potential
candidate and/or family understand that a small percentage of recipients achieve open-set word understanding secondary to ABI (Colletti & Shannon, 2005). As a result, children who are possible ABI
candidates should be exposed to signed/manual language to ensure language development.
Candidacy Evaluations
Candidacy evaluations include the traditional test battery for cochlear implantation, MRI imaging,
possible CT imaging, and extensive counseling regarding risks of surgery and potential outcomes.
Counseling may include:
n
Many of the same outcome predictors for performance with a CI can be applied to
performance with an ABI. Additional factors for consideration include if there has been neural
degeneration within the brainstem and placement of the electrode array.
n
Individuals with NF2 have been identified as the poorest performers with an ABI, and
recipients who do not have NF2 typically perform better (Colletti & Shannon, 2005).
n
A small subset of people achieves open-set word understanding. More often, “good” outcomes
include the ability to detect environmental sounds and slightly improved performance on
speech tasks with visual cues.
Surgery
n
Insertion of the auditory brainstem implant is completed via a craniotomy and therefore
requires a comprehensive team with more specialty providers than a CI surgery. These
providers are present during the surgery and may also be involved in candidacy evaluation.
Due to the placement within the brainstem (at the cochlear nucleus), the surgical team also
needs to ensure the integrity of the cranial nerves remains intact.
Patients are usually admitted to the hospital for multiple days after surgery to ensure
adequate recovery.
Internal Devices
n
Cochlear is the only ABI device in use in the United States at the time of this publication.
Cochlear’s ABI device utilizes the same external processor as their CI device. The primary
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