Download Active Middle Ear Implants in Patients Undergoing Subtotal

Otology & Neurotology
30:41Y47 2008, Otology & Neurotology, Inc.
Active Middle Ear Implants in Patients Undergoing
Subtotal Petrosectomy: New Application for the
Vibrant Soundbridge Device and Its Implication for
Lateral Cranium Base Surgery
Thomas Linder, Christoph Schlegel, Nicola DeMin,
and Stephan van der Westhuizen
Department of Otorhinolaryngology, Head and Neck Surgery, Kantonsspital Luzern, Luzern, Switzerland
Objective: The functional outcome of ossiculoplasties in
chronic ear and lateral cranium base surgery depends on the
presence of a ventilated middle ear space and is guided by the
existence or absence of ossicular remnants. In patients with
poorly ventilated middle ears, after multiple previous operations, missing stapes suprastructure, or after partial temporal
bone resection for tumor removal, restoration of conductive
hearing is not possible. The direct placement of a vibrating
floating mass transducer (FMT) onto the round window membrane with obliteration of the surgical cavity is a new option.
Patients and Intervention: Starting in January 2006, five
patients underwent a subtotal petrosectomy to control their
chronically discharging ear, to remove residual cholesteatoma,
or to revise previous incompletely exenterated cavities. Four
patients underwent a simultaneous placement of a Vibrant
Soundbridge (VSB) onto the round window membrane; one
patient had a staged reconstruction after initial Bone-Anchored
Hearing Aid rehabilitation. In all operations, the external ear
canal and the eustachian tube were closed, and the cavity was
obliterated using abdominal fat.
Main Outcome Measures: Preoperative and postoperative
pure tone audiograms were analyzed in respect to deterioration
of inner ear function, aided and unaided (hearing aid, VSB, and
Bone-Anchored Hearing Aid) speech audiograms were com-
pared to verify improvements in communication skills, functional gains were calculated at comfortable level settings, and
postoperative computed tomographic scans were used to exclude recurrent disease and to confirm the position of the
FMT onto the round window membrane. Patient’s satisfaction
was measured using a standardized questionnaire.
Results: All patients were very satisfied daily users of their
middle ear implant and had complete eradication of their middle ear pathology. Bone conduction worsened at 2 kHz, with
preservation of inner ear function in the other frequencies.
Whereas none of the patients had any unaided speech discrimination before the surgery at conversational levels, all patients
obtained 95 to 100% correct monosyllabic scores at 70 to 80 dB
using the VSB. The functional gain was highest at higher
frequencies.
Conclusion: Patients with combined hearing loss undergoing
subtotal petrosectomy with complete fat obliteration of the middle ear and mastoid area can be safely rehabilitated, placing the
FMT of a VSB onto the round window membrane, either at the
time of primary surgery, or as a staged secondary procedure.
Key Words: Chronic otitis mediaVMiddle ear implantV
Round windowVSurgical technique.
The goals of temporal bone surgery for chronic otitis
media have not changed over the last 50 years; however,
new techniques have evolved to improve the outcome.
Eradication of the disease, achieving a dry and selfcleaning ear, and preserving or restoring hearing are
the 3 most important principles. In patients with recurrent
disease, poor ventilation of the middle ear space, multiple
previous operations, and missing middle ear ossicles, restoration of conductive hearing may not be possible. In
patients undergoing lateral cranium base approaches,
ossiculoplasties are not feasible because no ventilated
middle ear space is left. Subtotal petrosectomy (SP) is
the first surgical step for the infratemporal fossa approaches types A to C and can be used as a primary
procedure in patients with extensive cholesteatomas or
chronic draining ears after previous operations with
poor ventilation properties. Because the external ear
canal is closed and the operative cavity is filled with abdominal fat, the fitting of a conventional hearing aid is
Otol Neurotol 30:41Y47, 2009.
Address correspondence and reprint requests to Thomas Linder,
M.D., Department of Otorhinolaryngology, Kantonsspital Luzern,
Spitalstrasse, CH-6000 Luzern, Switzerland; E-mail: Thomas.Linder@
kls.ch
41
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
42
T. LINDER ET AL.
not possible. Bone conductive hearing aids, mainly as a
BAHA device, were the only alternative. However, new
developments in the application of implantable hearing
aids had brought up new options.
We share our experience with the use of the Vibrant
Soundbridge (VSB) active middle ear implant directly
stimulating the round window membrane in 5 patients
undergoing SP for chronic otitis media, present our
intermediate-term results (more than 2 yr), and speculate on its application for hearing rehabilitation in lateral cranium base surgery.
PATIENTS AND METHODS
Between January 2006 and July 2007, five patients with
chronic otitis media and conductive or mixed hearing loss underwent an SP. The patients were informed on all options of hearing rehabilitation and opted for the implantation of a Vibrant
Soundbridge during a 1- or 2-stage surgery. Fisch and Mattox
(1) have described the surgical steps of an SP. In brief, an Sshaped retroauricular approach was used, the external ear canal
was closed in 2 layers, all tympanomastoid air cells were exenterated, the eardrum and middle ear mucosa and any ossicular
remnantsVexcept the stapes footplateVwere removed, and the
eustachian tube was obliterated using bone wax. Before closure,
the bony bed of the implant was drilled behind the sinus-dura
angle, and the clip of the floating mass transducer (FMT) was
removed using strong scissors. A dummy device was used to
measure the size of the round window opening, and the natural
round window niche was enlarged using diamond drills at low
speed, avoiding any contact with the round window membrane.
Once the bone margins were wide enough, a small and thin piece
of temporal fascia was used to cover the membrane, and the FMT
was introduced perpendicular to the round window membrane.
The FMT was tightly fitted into the round window niche, and an
additional temporal fascia was secured around the FMT to prevent dislodgement. The rather stiff cable of the electrode lead
was bent over the skeletonized mastoid portion of the facial nerve
and secured in 2 patients with bone wax to avoid displacement.
The cavity was carefully filled with abdominal fat, and a temporalis muscle flap. No drain was placed, and the wound was
closed in 2 layers. A pressure bandage was applied for 1 day, and
the first fitting of the patients was scheduled 4 weeks postoperatively. One patient with an SP and a previous BAHA implantation lost the BAHA screw and was scheduled for a second-stage
Vibrant Soundbridge implantation.
Pure-tone audiometries were performed preoperatively and at
repeated visits postoperatively. The Freiburger syllable and
number test was used for speech discrimination. The implant
was tested in the free field, with the contralateral ear closed
FIG. 1. Preoperative and postoperative pure tone audiograms
of all the 5 patients. AC indicates air conduction; BC, bone conduction. Preoperative audiogram (left): preoperative AC right ()),
preoperative AC left (x), BC not-masked right (G), BC not-masked
left (9), BC masked right ([ ), BC masked left ( ] ). Postoperative
audiogram (right): preoperative AC right ()), postoperative AC
right (•), preoperative AC left (x), postoperative AC left (* ), postoperative AC aided with VSB (h).
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
MIDDLE EAR IMPLANTS IN SUBTOTAL PETROSECTOMY
and the loudspeakers in front of the patient. A standardized questionnaire, the Glasgow Benefit Inventory (GBI) by Gatehouse
et al. (2), was administered to all patients between 12 and
18 months after the surgery.
Indications, Case Histories, and Preoperative
Hearing Status
Case 1 (M.W.)
A 66-year-old woman presented with discharge and underwent multiple ear operations between 1948 and 1999. Computed tomographic (CT) scans confirmed an expansile lesion
within the operative cavity with complete obliteration of the
remaining mastoid and middle ear cleft. Audiometry revealed
a combined profound hearing loss on the left side and low frequency hearing loss on the right side (Fig. 1). Speech audiometry
showed no left side discrimination. Intraoperatively, a cholesterol granuloma cyst was filling the mastoid cavity, the middle
ear was scarred with granulation tissue, and residual squamous
epithelium was covering the footplate. An SP was performed,
and the FMT was placed on the round window membrane. The
postoperative course was uneventful. First fitting occurred
8 weeks later and continued with 2 more sessions within
3 months. The retired patient is a frequent user of the implant,
subjectively enjoys the improved conversation skills and consistently wears the implant during musical concerts. She has
the longest follow-up of 2 years 4 months. The patient does
not wear the implant while playing with the grandchildren
because of the fear of loosing the implant.
Case 2 (M.D.)
A 45-year-old woman presented with dizziness at temperature fluctuations and intermitting otorrhea of the right ear.
Between 1970 and 1989, multiple ear operations were performed elsewhere because of recurrent cholesteatoma formation. Otoscopic examination revealed a dry crust filling a
modified radical cavity with an atelectatic eardrum. Audiometry revealed a predominantly conductive hearing loss on the
right and a slight conductive hearing loss on the left side
43
(Fig. 1). Intraoperative findings confirmed an incomplete radical mastoid cavity with residual squamous epithelium and multiple regions with fibrous and chronic inflammatory tissue. The
cavity was converted to an SP. Postoperative wound healing was
prolonged, possibly because of the multiple previous operations.
First fitting occurred at 6 weeks. She experienced a base noise
disturbance produced by the speech processor itself. An aluminum sheet measuring 28 mm by 40 Km was fitted underneath
the processor to reduce the electromagnetic field of the processor. Interestingly, the patient experienced an unpleasant auditory
sensation when passing certain alarm checkpoints, when using
household devices like the microwave, and before takeoff when
sitting near the cockpit. Two years after the surgery, the patient is
a daily user of her implant up to 17 hours a day. She got well
accustomed to the occasional unpleasant interferences. Fitted
with a strong magnet, she occasionally complains of discomfort
at the implant site after a long day of continuous usage. However,
there is no skin irritation visible.
Case 3 (H.I.)
A 56-year-old woman, after radiochemotherapy for a nasopharyngeal carcinoma, presented with a recent history of acute
mastoiditis complicated by otogenic meningitis. A left mastoidectomy was subsequently performed elsewhere. A preoperative computed tomography showed bony destruction in the
antrum and the mesotympanum and into the external auditory
canal. Audiometry revealed a severe combined hearing loss on
the left and a moderate combined hearing loss on the right.
Speech audiometry confirmed the bilateral loss of discrimination, which was moderately improved by bilateral conventional
hearing aid fitting (Fig. 2). The recent otogenic meningitis made
this patient an excellent candidate for an SP. Intraoperatively, a
defect in the tegmen tympani was observed, and the entire temporal bone was fragile and hyperemic after the previous irradiation. The ossicles were intact, however, surrounded by scar tissue
and chronic effusion. The closed cavity was converted into an
SP, and after placement of the implant, the defect was filled with
abdominal fat and a vascularized temporalis muscle flap. The
first fitting took place 5 weeks later. One year and 7 months
after surgery, the patient is still impressed by the improvement
FIG. 2. Preoperative and postoperative speech audiogram. Comparison of unfitted preoperative (x) scores, preoperative aided with
hearing aid (r), and postoperative using VSB (h).
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
44
T. LINDER ET AL.
FIG. 3. Postoperative axial (A) and coronal (B) CT scan confirming the complete obliteration of the operative cavity with abdominal fat
and the correct position of the FMT at the round window membrane.
in sound quality (attending classical concerts) and speech understanding, which could be confirmed by comparing the previous
discrimination scores of the conventional hearing aid and the
implant (Fig. 2). She predominantly relies on the implant
(even on the telephone) and uses the contralateral hearing aid
only as support.
Case 4 (J.S.)
A 64-year-old man presented with a long-standing history of
bilateral chronic draining ears combined with hearing loss. An
initial right atticoantrotomy was followed by several revision
operations elsewhere. Conventional hearing aid fittings were
unsuccessful because of chronic drainage. Otoscopy showed a
retracted tympanic membrane with humid and partially opened
mastoid air cells. CT findings revealed the total opacification of
the surgical cavity and missing ossicles. Audiometry revealed a
mixed bilateral hearing impairment. Intraoperatively, the middle ear was filled with granulomatous tissue, and only a partial
stapes suprastructure was present. A residual cholesteatoma sac
in the supralabyrinthine space was removed, and an SP with
placement of the middle ear implant and fat obliteration of the
cavity was performed. A local retroauricular wound infection
2 weeks postoperatively was treated with intravenous antibiotics.
First fitting took place at 9 weeks. As with Case 2, a metal foil
was necessary to damp any base noise. After an initial marked
hearing improvement, the hearing worsened 6 months later. A
CT scan revealed that the FMT is still tightly within the round
window niche, no air within the obliterated cavity and no sign
of recurrent disease (Fig. 3, A and B). Further testings confirmed
a malfunctioning of the outer speech processor, which was subsequently replaced with complete restoration of the initial functional improvement. The patient predominantly relies on the
implant 17 months after surgery because of intermittent drainage
of the opposite ear.
Case 5 (B.E.)
Because of persistent infection after multiple ear operations
including a radical mastoidectomy for cholesteatoma removal,
a 45-year-old woman eventually underwent an SP in 2004. The
clinical course and postoperative imaging confirmed successful
eradication of the disease. The patient was subsequently fitted
with a BAHA device but experienced recurrent skin infections
FIG. 4. Preoperative and postoperative speech audiogram. Comparison of unfitted preoperative (x) scores, preoperative aided with
hearing aid (r), postoperative aided with BAHA (0), and postoperative using VSB (h).
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
MIDDLE EAR IMPLANTS IN SUBTOTAL PETROSECTOMY
45
after the surgery. The GBI examines the impact of the benefit
derived from an otologic procedure in general, physically, and
socially. All the patients reported a substantial positive impact
of the treatment, scoring 80% in the general subcategory and
85% in physical health score, whereas no change was mentioned
in the social support score (50%).
Audiometric Summary
FIG. 5. Analysis of average and minimal/maximal inner ear
deterioration after round window fitting for individual frequencies.
in the region of the BAHA screw and eczema of her scalp. The
BAHA screw loosened 36 months after implantation and was
removed. Instead of a new BAHA screw fixation, the placement
of the active middle ear implant was scheduled. Intraoperatively,
the fat was, in part, replaced by fibrous tissue. The bony surfaces
were easily identified, the fat was removed, the bony rim of
the round window was enlarged, and the FMT was placed onto
the round window membrane with a thin coverage of fascia. The
original healthy fat was replaced, and additional fat was supplemented. The postoperative course was uneventful, and first fitting occurred 4 weeks later. As previously described, a damping
foil was needed. The patient immediately enjoyed the benefit
of her hearing improvement and mentioned an improvement
in the quality of sound, which was confirmed audiologically
(Fig. 4). Nine months postoperatively, she uses the implant daily
up to 14 hours and favors the sound quality over the previous
devices.
Postoperative Speech Processor Fitting
The speech processors were fitted between 30 and 63 days
after surgery. The fitting software for the Vibrant audioprocessor was modified based on the bone conductive values.
The optimal calibration was achieved by feedback preference
of the patient. This was again optimized at follow-up visits. In 2
of the 5 patients with bone conduction thresholds lower than
30 dB, a base noise disturbance produced by the speech processor was experienced even in minimal settings. An aluminum
sheet measuring 28 mm by 40 Km was fitted underneath the
external processor to reduce the electromagnetic field transmission. This metal sheet causes a linear attenuation of approximately 10 dB of base noise and the audio signal. This loss in
signal was compensated by increasing the adjustment values.
Comparing unaided preoperative and postoperative measures, all patients with some degree of conductive hearing loss
preoperatively had a complete conductive block after surgery
(Fig. 1). We carefully analyzed the bone conduction thresholds
to evaluate any impairment of inner ear function after extensive
drilling and the placement of the FMT onto the round window
membrane (Fig. 5). Three patients had a temporary threshold
shift of less than 5 dB in the low frequencies. All 5 patients
had a persistent worsening of the bone conduction at 2 kHz
between 10 and 30 dB, with preservation of inner ear function
in the other frequencies. One patient had an additional impairment of 15 dB at 4 kHz. However, this high-frequency change
was overpowered by the remarkable output of the transducer at
2 and 4 kHz.
The aided postoperative measures revealed the following results: all patients had a remarkable gain of 40 dB (Fig. 6) calculated from the differences of the preoperative air-conduction
(AC) thresholds and the postoperative aided AC thresholds. For
individual frequencies, the average functional gain was 34 dB
at 500 Hz, 43 dB at 1 kHz, 35 dB at 2 kHz, and 46 dB at 8 kHz,
respectively. Therefore, higher gains were achieved at higher
frequencies.
Aided AC thresholds using the implant setting at comfortable levels were between 25- and 35-dB hearing loss, whereas
the unaided thresholds were typically above 60-dB hearing loss.
After optimized fitting, the aided speech reception threshold
at 50% intelligibility was between 19 and 32 dB. Preoperatively,
the speech reception threshold at 50% intelligibility was not
measurable in 2 patients and between 50 and 60 dB for the
remaining patients. All patients were able to obtain 95 and
100% correct speech discrimination scores at 70 to 80 dB
after proper adjustments. Preoperatively, none of the patients
had any speech discrimination for monosyllabic words at the
conversational level of 65 dB.
Postoperative Results
All the ears were dry, and the patients were allowed to swim
without any precautions starting 6 weeks after surgery. No
recurrence of the initial disease was observed because of
the radical exenteration of the tympanomastoid air cells. All
patients receive a postoperative CT scan routinely at 12 months
and 3 years after SP to verify no recurrence of the disease.
Computed tomography also demonstrates the correct positioning of the FMT within the round window niche.
A standardized questionnaire, the GBI by Gatehouse et al. (2),
was administered to all the patients between 12 and 18 months
FIG. 6. Postoperative mean and minimal/maximal functional
gain of the VSB for individual frequencies.
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
46
T. LINDER ET AL.
DISCUSSION
Since the first implantation of a Vibrant Soundbridge
by Fisch in 1996, more than 2,000 patients worldwide
have received this active middle ear implant for the treatment of moderate sensorineural hearing loss. Classic use
requires a well-ventilated middle ear space and an intact
and vibrating ossicular chain. This conventional fitting
of the VSB onto the incus in patients with sensorineural
hearing loss was challenged in recent years by marked
improvements of conventional hearing aids, including
open fitting options for high-frequency Bski-slope[ hearing impairments. Ten years after the first multicenter
study (3), the application has now been extended. Laboratory and clinical investigations have focused on various sites to position the FMT. Direct stapes stimulation,
fitting onto a partial ossicular replacement prosthesis,
and direct round window stimulations have been studied
(4Y6). A first series of 7 patients was reported by Colletti
et al. (7), applying the VSB’s FMT onto the round window
membrane. The audiologic success was measured immediately after surgery. Recently, further reports have been
published on small case series, expanding the indications
for middle ear implants to patients with aural atresia (5,6).
In all these patients, the middle ear space was preserved.
We are now reporting on its application for patients with
chronic ear discharge due to otitis media or osteoradionecrosis and mixed hearing loss. In our patients, the fitting
of conventional hearing aids was limited or impossible
because of the chronic drainage or the anatomic disturbance of the ear canal after previous operations. An
ossiculoplasty was impossible because of the lack of a
ventilated middle ear space and missing ossicles. An alternative could have been the implantation of a percutaneous
BAHA screw and the fitting of a BAHA speech processor.
All our patients with sufficient cochlear reserve tested the
BAHA device using a headband. The patients declined a
BAHA fitting because they were disturbed by the hollow
sound quality or refused the BAHA implantation because
they were afraid of local skin infections, having experienced otorrhea over many years. Patient 5 already had
worn a BAHA device, which failed because of the loosening of the screw after multiple skin infections. SP provides
the ideal surgical concept to accomplish a dry and safe ear.
Typically, the chorda tympani is resected; however, in
most patients, the chorda is already missing because of
previous operations or its function is impaired because of
chronic infection or cholesteatoma formation. In our series, 2 patients reported initially some sort of taste disturbance, which completely subsided and was not reported
on the GBI forms. The technique of SP has been used for
more than 20 years by Fisch and Mattox (1). In 1998,
Bendet et al. (8) described the application of SP and
cochlear implantation in patients with chronic ear infections or possible CSF leaks. Our experience with more
than 80 SP and a dozen SP with cochlear implantations
led us to its application for middle ear implants. In patients
undergoing SP, any residual conductive hearing is totally
blocked; therefore, the functional gain is completely de-
pendent on the round window stimulation by the FMT.
Recently, the exact anatomy of the round window niche
has been reexplored for its application in cochlear
implantation (9,10). The round window membrane is
conical in shape, and the round window recess is highly
variable in its morphology, at times obscured by a mucosal fold. The opening of the niche has been measured
between 0.48 and 2.7 mm in width; the surface area of
the vertical segment of the round window membrane was
found to vary from 0.8 to 1.75 mm2 (9). The dimensions
of the FMT measure 2 mm in length and 1.5 mm in
diameter for the coupling part. Drilling of the overhang
is therefore mandatory to tightly fit the FMT onto the
membrane itself. Low-speed drilling with constant irrigation should avoid acoustic damage to the inner ear and
injury to the membrane itself. A test dummy device of
the FMT was helpful in judging the correct amount of
bone removal before inserting the original implant. We
reinforced the connection using a thinned tiny piece of
fascia between the surface of the FMT and the round
window membrane. The clip portion was easily trimmed
off with large scissors, and the FMT was tightly
squeezed into the enlarged round window niche by prebending the electrode lead over the facial ridge. An additional piece of the temporal fascia was used to cover the
FMT within the hypotympanum, and small pieces of
abdominal fat were placed to fill the cavity. Therefore,
any dislocation of the FMT was thought to be avoided. In
Patient 5, the FMT was placed in a second stage after
previous SP. Blunt removal of the fat was an easy task as
long as all the bony margins of the cavity were preserved. Any previous exposure of soft tissue structures
(e.g., sigmoid sinus, dura, or facial nerve) would induce
strong scar formation and necessitates sharp dissection.
The technique of skeletonizing structures and avoiding
their exposure should be familiar to all otologic surgeons
(11). In all 5 patients, the FMT remained in a stable
position over time, and no dislocation was observed.
Complete removal of the disease is of paramount
importance before obliterating the cavity in SP. The personal experience of the senior author (T. L.) has not
encountered recurrent disease in a vast number of SP.
CT scans are routinely performed after 1 year and preferentially 3 years. The signal intensity of fat and muscle
can clearly be distinguished on CT scans. In case of
a suspected cholesteatoma recurrence, magnetic resonance imaging (MRI) with diffusion sequence would be
advisable. However, MRI of implantable ferromagnetic
hearing devices could cause implant heating, current
induction, implant demagnetization, image degradation,
acoustic trauma, and implant dislocation because of mechanical forces. Therefore, MRI scans are not recommended after VSB implantation. A recent case review of
2 patients conventionally implanted with the VSB who
underwent a 1.5-Tesla head MRI scan showed no adverse
effects noted by the patients other than transient hyperacusis resulting from loudness during the procedure. Puretone thresholds remained unchanged after MRI scanning,
fixation of the FMT and its attachment on the incus
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
MIDDLE EAR IMPLANTS IN SUBTOTAL PETROSECTOMY
remained stable, and there was no evidence of implant
demagnetization (12). Studies on round window placement and MRI scanners are still lacking, and patients
necessitating repeated MRI scans (e.g., tumor follow-up)
are hitherto a contraindication for a round window
insertion.
Our first interest in the audiometric evaluation was the
impact on inner ear function. In all the patients, the
stapes footplate remained mobile. All our patients had
a loss of bone conduction thresholds at 2 kHz. A noiseinduced hearing impairment is quite unlikely because the
other frequencies remained stable. Based on the work of
Tonndorf (13), it seems tempting that our observation
reflects a Carhart notch peaking at 2,000 Hz because of
the loss of the middle ear component close to the resonance frequency of the ossicular chain. A similar shape of
the bone conduction is found in otosclerosis or in isolated
round window atresia (14). Previous reports on round
window placements have not specifically addressed this
issue (5Y7). The impact of this isolated deterioration at
2 kHz was fully compensated by the functional gain of
the device.
von Békésy (15) demonstrated that, regardless of the
location of the stimulation of the cochlea, the waves on
the basilar membrane always travel from the stiffer part
toward the more compliant one (i.e., from the base of the
cochlea toward the helicotrema). Studies dating back to
1950 by Wever and Lawrence (16) showed equivalent
generated cochlear potentials evoked by either round or
oval window stimulation. In theory and in practice, round
window stimulation allows a powerful stimulation of the
inner ear. The marked increase in functional gain and
aided threshold levels was confirmed by the remarkable
improvement in speech understanding. Some patients
were emotionally overwhelmed once the implant was
activated in an ear, which was Buseless[ to them for
many years or even decades. Therefore, the group of
patients with mixed hearing loss and chronic middle
ear disease may become increasingly popular for the
application of implantable hearing devices. It is worth
mentioning that one of the first piezoelectric middle ear
implants by Yanagihara et al. (17) already addressed
patients with mixed hearing loss 20 years ago.
Patients undergoing lateral cranium base surgery with
preservation of the functioning cochlea, but removal of
the middle ear, may also become candidates for round
window stimulation. Limitations may be the excessive
temporal bone removal limiting the proper fixation of
the FMT as well as the necessity for MRI scans postoperatively in case of initial tumor removal.
CONCLUSION
Patients with severe and chronic middle ear disease
necessitating revision surgery may become candidates
47
for an SP. The conductive or mixed hearing loss can
be compensated by placing the FMT of a Vibrant Soundbridge onto the round window membrane. The functional
gain allows remarkable improvements of aided thresholds and speech understanding scores. Patients are satisfied by the dry ear, allowing even water sports without
precautions, and by the quality of sound amplification.
Our intermediate-term results with a mean follow-up of
19 months (ranging from 9 mo to 2 yr 4 mo) do not show
a dislocation of the FMT from the enlarged round window niche.
REFERENCES
1. Fisch U, Mattox D, eds. Microsurgery of the Skull Base. Stuttgart,
Germany: Georg Thieme Verlag, 1988.
2. Gatehouse S, Robinson K, Browning GC. Measuring benefit
from otorhinolaryngological surgery and therapy. Ann Otol Rhinol
Laryngol 1996;105:415Y22.
3. Fisch U, Cremers CW, Lenarz T, et al. Clinical experience with
the Vibrant Soundbridge implant device. Otol Neurotol 2001;22:
962Y72.
4. Huber AM, Ball GR, Veraguth D, Dillier N, Bodmer D, Sequeira
D. A new implantable middle ear device for mixed hearing loss: a
feasibility study in human temporal bones. Otol Neurotol 2006;
27:1104Y9.
5. Kiefer J, Arnold W, Staudenmaier R. Round window stimulation
with an implantable hearing aid (Soundbridge) combined with
autogenous reconstruction of the auricle-a new approach. ORL J
Otorhinolaryngol Relat Spec 2006;68:378Y85.
6. Wollenberg B, Beltrame M, Schonweiler R, et al. Integration of the
active middle ear implant Vibrant Soundbridge in total auricular
reconstruction. HNO 2007;55:349Y56.
7. Colletti V, Soli SD, Carner M, Colletti L. Treatment of mixed
hearing loss via implantation of a vibratory transducer on the
round window. Int J Audiol 2006;45:600Y8.
8. Bendet E, Cerenko D, Linder TE, Fisch U. Cochlear implantation
after subtotal petrosectomies. Eur Arch Otorhinolaryngol 1998;
255:169Y74.
9. Roland PS, Wright CG, Isaacson B. Cochlear implant electrode
insertion: the round window revisited. Laryngoscope 2007;117:
1397Y402.
10. Li PMMC, Wang H, Northrop C, Merchant SN, Nadol JB. Anatomy of the round window and hook region of the cochlea with
implications for cochlear implantation and other endocochlear surgical procedures. Otol Neurotol 2007;28:641Y8.
11. Fisch U, May J, Linder T, eds. Tympanoplasty, Mastoidectomy and
Stapes Surgery. Stuttgart, Germany: Georg Thieme Verlag, 2008.
12. Todt I, Seidl RO, Mutze S, Ernst A. MRI scanning and incus fixation in Vibrant Soundbridge implantation. Otol Neurotol 2004;
25:969Y72.
13. Tonndorf J. Bone conduction: studies in experimental animals.
Acta Otolaryngol 1966;213:1Y132.
14. Linder TE, Ma F, Huber A. Round window atresia and its effect on
sound transmission. Otol Neurotol 2003;24:259Y63.
15. von Békésy G. Paradoxical direction of wave travel along the
cochlear partition. J Acoust Soc Am 1955;27:137Y45.
16. Wever EG, Lawrence M. Physiological Acoustics. Princeton, NJ:
Princeton University Press, 1954:240.
17. Yanagihara N, Yamanaka E, Gyo K. Implantable hearing aid using
an ossicular vibrator composed of a piezoelectric ceramic bimorph:
application to four patients. Am J Otol 1987;8:213Y9.
Otology & Neurotology, Vol. 30, No. 1, 2009
Copyright @ 2008 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.