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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4446_Библиотеки_им_академика_М_И_Перельмана
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20 Cochlear Implant and Other Implantable Hearing Devices
Fig. 20.3 Total absence of the right inner ear structures is noted with a attening of the medial wall of the right inner
cavity in a patient with Michel anomaly
219
Fig. 20.4 Axial HRCT of the right temporal bone show-
ing marked hypoplasia of the right cochlea associated
with small malformed vestibule and semicircular canals
Prophylactic antibiotics intra- and
postoperative.
Immunization against Streptococcus pneu-
moniae and Haemophilus inuenzae if not taken
in the immunization schedule.
Fig. 20.5 Axial and coronal HRCT of the temporal bones
showing tight stenosis of the right internal auditory canal
with normal appearing osseous labyrinth
20.11.2 Surgical Therapy
Cochlear implant surgery is the treatment of
choice for patient with moderate-to-profound
sensorineural hearing loss without benet from
hearing aids.
Unilateral versus bilateral implant has always
been a debate regarding the benets versus cost.
Bilateral implants showed benets in the
aspects of improved speech perception, allowed
better hearing in conditions with signicant
background noise, and enhanced sound localization [11, 12].
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H. Abdulkarim et al.
a
b
Fig. 20.6 T2 axial cut of temporal bone MRI showing
internal auditory canal and inner ear structures
20.12 Procedure
20.12.1 Step 1: Flap Marking
andIncision Design
Facial nerve monitoring is recommended.
Hair shaving is optional according to the sur-
geon’s preference.
Using the dummies (or mock ups) and specic
implant templates, marking of the location of the
external and internal devices is made.
Incision is in or at a parallel line to the postauricular crease according to the surgeon preference up to 2cm posterior to the crease.
Elevation of anterior and posterior aps.
Periosteum elevation anteriorly and posteriorly.
Fig. 20.7 Transorbital x-ray postoperatively showing
inner device (red asterisk) and the electrodes array turn
inside the cochlea (white asterisk)
20.12.2 Step 2: Mastoidectomy
andPosterior
Tympanotomy
A cortical mastoidectomy is done till reaching
the mastoid antrum by identifying the short process of incus and lateral semicircular canal.
Thinning of posterior canal wall is done.
Thinning of facial nerve surrounding bone is
done with generous irrigation till hue of the facial
nerve is seen.
Posterior tympanotomy is done to enter the
facial recess enough to visualize the round window (Fig.20.8a).
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20 Cochlear Implant and Other Implantable Hearing Devices
221
20.12.3 Step 3: Cochlear Implant
Receiver Well Drill Out
withTie- Down Holes
Using internal device’s templates, the receiver
well is drilled usually superior and posterior to
the mastoidectomy area.
Holes are drilled around the well to be used
for xation after device placement.
20.12.4 Step 4: Cochleostomy
Size of cochleostomy is variable according to
cochlear implant manufacturer recommendations.
Location is over the basilar turn of the cochlea
anteroinferior to the round window.
Some surgeons including author prefer to do
cochleostomy through round window
(Fig.20.8b).
20.12.5 Step 5: Implant Tie Down
andElectrode Insertion
a
b
c
The electrode is inserted through the cochleostomy to the maximum length possible.
Once inserted, the device is xed to the well
by sutures or tie.
Cochleostomy is sealed by subcutaneous tissue (Fig.20.8c).
20.12.6 Step 6: Telemetry, Closure,
andRadiograph
Telemetry, impedance, and NRT (neural response
telemetry) testing are done.
Closure of the layers and wound is done.
Mastoid pressure bandage is applied for
24–72h.
20.12.7 Postoperative Details
Observe for nystagmus and facial weakness.
Radiological testing as preferred (Fig.20.7).
Fig. 20.8 Surgical steps of cochlear implant surgery. (a)
Cortical mastoidectomy and posterior tympanotomy.
Showing the short process of incus (white asterisk) and
chorda tympani (red asterisk) and the shadow of round
window niche (black arrow). (b) Cochleostomy made
through the round window (white arrow). (c) Insertion of
electrodes array through the cochleostomy
20.12.8 Follow-Up
Visit within 5–7days to check for hematoma and
wound, to be repeated at the 2 weeks
postoperative.
Arrange a visit within 3–5weeks postoperatively with the audiologist for device
stimulation.
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H. Abdulkarim et al.
20.13 Complications
• Same as mastoidectomy [13, 14]
1. Postoperative infection
2. Facial paralysis or facial spasm (treated by
deactivating offending electrode)
3. Cerebrospinal uid (CSF) leakage
A CSF/perilymph gusher through the
round window or cochleostomy is common
in patients with cochlear anomalies (like
enlarged vestibular aqueduct syndrome,
common cavity, and wide internal auditory
canal syndrome). Leak is best managed by
packing the round window with fascia or
muscle after implant insertion.
4. Meningitis. Usually prevented by preoperative vaccine, and treated by antibiotics.
5. Flap complications
(a) Seroma formation best avoided by use
of a mastoid compressive dressing for
at least 2days. If developed, it can be
evacuated using large bore needle aspiration with mastoid pressure dressing
applied for another 2–3days.
(b) Implant migration: good xation of the
device to the well and sealing the
cochleostomy area with tissue or
muscle.
(c) Necrosis of the ap: sometimes clo-
sure under tension will affect the blood
supply of the skin and subcutaneous
tissue causing necrosis.
Can be prevented by good supraand subperiosteal aps and closed in
different directions.
6. Device failure: perform telemetry and consider communication with the implant
manufacturer before explanation and
reimplantation.
20.14 Outcome andPrognosis
• The overall prognosis for hearing improvement and improved quality of life in the properly selected patient is excellent.
20.15 Future andControversies
• The future of cochlear implantation is exciting
and is now upon us.
• Bilateral cochlear implantation has demonstrated
signicant benets for patients in a number of
areas, which include hearing in noise, speech perception outcomes, and sound directionality.
• In the future, patients can expect faster and
better coding strategies, which result in better
speech perception.
• Improvement in chip design and battery design
will likely pave the way for totally implantable
cochlear implants as microphones become inte-
grated to middle- or external-ear structures.
• Nanotechnology is rapidly providing hope for
smaller, more robust, electrode array designs
with a virtually endless number of electrode
contact sites.
• Image-guided minimally invasive cochlear
implantation
20.16 Conclusion
• Team-based approach for selection of cochlear
implant candidates.
• Cochlear implants are surgically implanted
devices to convert sound to electrical impulse
through the cochlear nerve.
• Thorough evaluation makes better hearing
results.
• Bilateral cochlear implantation showed better
hearing results and sound localization.
20.17 Implantable Hearing Aids
The majority of cases of SNHL require only acoustic amplication to address communication skills.
This is generally accomplished with conventional
air conduction hearing aids. Despite improvements
in conventional hearing aid technology, only 15%
of the 20 million hearing-impaired people in the
United States who could benet from amplication
utilize these devices [15].
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20 Cochlear Implant and Other Implantable Hearing Devices
223
The development of semi-implantable and
totally implantable hearing aids has in part been
an attempt to compensate for limitations of conventional hearing aids.
Implantable hearing aids comprise two types:
middle ear aids and bone-anchored devices.
20.17.1 Middle Ear Implantable
Hearing Aids
Given the costs and risks of surgical placement,
an implantable hearing aid (IHA) should ideally
provide signicant benets over conventional
hearing aids, including
1. Better appearance
2. Improved delity
3. Broader frequency response
4. Less distortion
5. Reduction or elimination of feedback
6. Better speech understanding
The devices should not
1. Interfere with residual hearing
2. Limit patient activities
3. Predispose patients to infection
Several IHA designs are currently under investigation and development, with at least few already
receiving approval by the FDA for clinical use.
However, despite many potential advantages
over conventional aids, IHAs have met with limited success to date.
Conventional hearing aids work by amplifying
airborne sound prior to its reaching the middle ear.
Microphone converts an incoming acoustic signal
into an electrical signal that is amplied, ltered,
processed to adjust dynamic range, and then transduced by a speaker back into airborne sound
waves that then drive the middle ear and inner ear
in the normal physiologic manner. Though usually
adequate, this approach has many limitations.
First, nonlinearities in the transduction process cause distortion and limit the useful dynamic
range of the aid.
Second, because the impedance mismatch
between the air-lled external auditory canal and
uid-lled cochlea is only partly compensated by
the middle ear mechanism, much of the amplied
airborne sound is reected back from the tympanic membrane. This limits the acoustic power
and perceptual loudness a hearing aid can generate, and increases problems with hearing aid
“squeal” due to feedback of sounds reaching the
hearing aid’s microphone.
The potential for feedback limits the useful
amplication of a conventional hearing aid and
mandates a tight hearing aid mold t in the ear
canal or placement of the microphone outside the
canal, resulting in discomfort, otitis externa,
autophony, ear fullness (the occlusion effect),
and visibility of the hearing aid. All of these factors conspire to reduce patient acceptance of conventional aids.
In contrast to conventional air-conducting hearing aids, middle ear IHAs are designed to directly
drive the ossicular chain, reducing impedance
mismatch, feedback, autophony, and distortion of
the amplied signal while offering increased functional gain. Some IHA designs require no ear
canal components, averting the risk of otitis
externa and reducing autophony and ear fullness.
There is also a cosmetic advantage to not having a visible apparatus within the ear, though
most IHAs do require an external processor that
is visible behind the ear.
Middle ear IHAs may be completely or partially implantable.
Partially implantable devices consist of an
external microphone and speech processor,
which is connected to an inductive transmitter
with an external coil that transmits electrical
energy transcutaneously to the internal device.
Batteries to power the system are contained
within the external device.
The internal device consists of a receiving
coil, processing electronics, and mechanical
driver (Fig.20.9).
A fully implantable system houses all of these
components within the implanted portion of the
device and is periodically recharged via a transcutaneous inductive link (Fig.20.10).
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Fig. 20.9 Partially
implantable IHA
components (Vibrant
Med-El (formerly
Vibrant Soundbridge))
Audio
Processor
receiver
Conductor
Link
H. Abdulkarim et al.
Vibrating Ossicular Prosthesis
(VORP) implant
Fig. 20.10 Fully
implantable IHA
components (the Totally
Implantable
Communication
Assistance aid, or
®
TICA
)
Ossicles
Transducer
Ear drum
Most IHAs employ either piezoelectric or
electromagnetic actuators for converting electrical signals to mechanical movement of the ossicular chain.
20.17.2 Bone-Anchored Hearing
Devices
Conductive and mixed hearing losses are highly
prevalent disorders that often may be addressed
with standard tympanoplasty and/or ossiculoplasty techniques or rehabilitated with traditional
hearing aids.
However, there remains a large subset of these
patients who are unsuitable surgical candidates
Floating Mass
Transducer
Mastoid
Bone Bowl
Microphone
Detail of Floating
Mass Transducer
Sound
Processor
for correction of their decit or who are unable to
tolerate a traditional hearing aid.
This group includes patients with
1. Chronically draining ears.
2. Discomfort from the sound levels required
from a traditional hearing aid.
3. Patients unable to tolerate a hearing aid
because of a large mastoid bowl or meatoplasty following chronic ear surgery.
4. Patients with otosclerosis, tympanosclerosis, or
canal atresia and who have a contraindication
to surgical repair may defy traditional
approaches.
5. Patients who have undergone external auditory canal closure following extensive skull
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20 Cochlear Implant and Other Implantable Hearing Devices
225
base surgery also are not amenable to traditional hearing aids.
6. Single-sided deafness also are candidates.
Application of osteointegration technology to
bone-anchored hearing aids represents a renement of conventional bone-conducting hearing
aids.
The utility of conventional bone-conducting
devices is now considered limited.
The bone conductor must be applied with
steady pressure to the mastoid cortex (usually via
a headband or eyeglasses). Patients often experience pain, headache, and skin irritation at the
contact site. Furrowing of the skull due to pressure is not unusual in children who use bone conductors. Further, sound delity is limited by soft
tissue attenuation, variable placement of the
vibrator, and accidity of the securing device
(e.g., eyeglass frames).
The success of this technology relies on two
basic principles: the creation of a permanent percutaneous connection and the placement of an
osseointegrated titanium abutment upon which a
transducer is coupled.
Titanium is the most notable among several
materials that have found clinical application in
anchoring dental prostheses. This is because of
its ability to create a corrosion-resistant oxide
layer on the surface of the implant that confers
osseointegration potential. Because the implant
may be worn for several decades or longer, the
toxicity and carcinogenicity of the oxide coating
take on particular importance.
To date, pure titanium appears free of the adverse
sequelae seen with other metals and thus continues
to represent an ideal implant material [16–18].
Currently, the only commercially available
osseointegrated hearing aid is the Bone-Anchored
Hearing Aid (the BAHA™, manufactured by
Cochlear Corporation, formerly by Entic and
Nobel Biocare).
The BAHA™ consists of a pure titanium
implant and a sound processor. The processor
couples directly to the titanium implant via a skin
penetrating abutment, utilizing a force-t, plastic
coupling) (Fig.20.11).
In addition to implantation for purely conductive or mixed hearing losses, emerging data indicate the value of BAHA amplication for patients
Fig. 20.11 BAHA
components
Sound processor
Abutment
Titanium Implant
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H. Abdulkarim et al.
Fig. 20.12 BAHA sound waves pathways to both ipsilateral and contralateral ears
with unilateral profound SNHL.The BAHA on
the deafened ear effectively expanded the sound
eld for the patient and improved the patient’s
speech understanding in noise, much like a contralateral routing of sound (CROS) hearing aid or
He recommended placing a new implant 7mm
above or below the rst site as a short outpatient
procedure under a local anesthesia, removing
only a small circle of skin and leaving the former
surgical site otherwise intact.
transcranial CROS system (Fig.20.12) [19, 20].
However, in contrast to CROS, BAHA does
not require the placement of an earmold in the
better hearing ear.
BAHA hearing results show subjective
improvement in both sound quality and speech
understanding in noise [21]. The main drawback of BAHA is the possibility for the implant
to dislodge from the skull after apparent successful, complete osseointegration, unrelated to
trauma or other obvious cause. Tjellstrom (personal communication, September 2005)
reported the rate was 6.0% in adults and 5.7%
Take Home Messages
• Cochlear implant surgery is the main
surgical treatment for severe SNHL
after the failure of hearing aid.
• Surgery itself is the main step of the treatment, but results depend mainly on the
postoperative rehabilitation program.
• Future technological advances will
make a signicant development in the
cochlear implant’s devices, surgery, and
results.
in children.
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20 Cochlear Implant and Other Implantable Hearing Devices
Question
Which is the absolute contraindication for
9. Basura GJ, Eapen R, Buchman CA.Bilateral cochlear
cochlear implant surgery?
(a) Mondini displasia
10. Bichey BG, Miyamoto RT. Outcomes in bilateral
(b) Cochlear ossication
(c) Cochlear aplasia
(d) Otosclerosis
Answer
11. Smulders YE, van Zon A, Stegeman I, et al.
12. National Institute on Deafness and Other
(c)
13. Tambyraja RR, Gutman MA, Megerian CA.Cochlear
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Part III
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Rhinology/Allergy
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