Download Cochlear implantation in patients with vestibular schwannoma

The Laryngoscope
C 2013 The American Laryngological,
V
Rhinological and Otological Society, Inc.
Cochlear Implantation in Patients With Vestibular Schwannoma:
A Single United Kingdom Center Experience
Irumee Pai, MSc, FRCS; Vikram Dhar, FRCS; Catherine Kelleher, BA; Terry Nunn, MSc;
Steve Connor, MRCP, FRCR; Dan Jiang, PhD, FRCS; Alec Fitzgerald O’Connor, FRCS
Objectives/Hypothesis: To evaluate the outcome of cochlear implantation (CI) in patients with vestibular
schwannoma (VS).
Study Design: A retrospective case series from a tertiary auditory implant center.
Methods: A retrospective case note review was carried out to evaluate patients with bilateral profound hearing loss and
VS who underwent unilateral CI within the Auditory Implant Centre at St. Thomas’ Hospital, London, between 2000 and
2012. This included both bilateral VS with neurofibromatosis type 2 (NF2) and unilateral sporadic VS. Outcome measures
included speech perception with Bamford-Kowal-Bench and City University of New York sentences, sound-field thresholds
with warble tones, and the subjective benefits reported by patients.
Results: The study included five patients with NF2 and bilateral VS and two patients with sporadic unilateral VS. The
standard preoperative audiologic assessment for CI often could not be carried out in NF2 patients. Preoperative testing was
more complete in the two patients with sporadic VS. The audiologic outcome was variable. Open-set speech perception was
achieved in three out of five NF2 patients, and another reported significant improvement in environmental sound perception
and ease of communication. The outcome was overall better in patients with sporadic VS, both of whom were able to use the
telephone in their implanted ear.
Conclusions: Good speech perception can be achieved in some cases, and CI should be considered as an option for auditory rehabilitation in patients with VS.
Key Words: Cochlear implants, vestibular schwannoma, neurofibromatosis type 2.
Level of Evidence: 4.
Laryngoscope, 123:2019–2023, 2013
INTRODUCTION
Auditory rehabilitation for profound sensorineural
hearing loss in patients with bilateral vestibular
schwannoma (VS) associated with neurofibromatosis
type 2 (NF2), or those with sporadic VS and profound
hearing loss in their contralateral ear, poses a great
therapeutic challenge. This is particularly the case in
patients with NF2, who often have other medical comorbidities and eventually develop multiple disabilities
including blindness.
There are a number of potential pathophysiologic
mechanisms by which hearing loss occurs in VS. In a
cadaveric study by Roosli et al.,1 a number of changes
were found in the cochlea in association with unilateral
From the Auditory Implant Centre (I.P., V.D., C.K., T.N., D.J., A.F.O.),
Department of Diagnostic Imaging (S.C.), St Thomas’ Hospital, London,
United Kingdom
Editor’s Note: This Manuscript was accepted for publication
January 28, 2013.
This study was an oral presentation at the joint 6th International
Congress of the World Federation of Skull Base Societies and 10th
European Skull Base Society Congress, Brighton, United Kingdom, May
16, 2012.
The authors have no funding, financial relationships, or conflicts
of interest to disclose.
Send correspondence to Dan Jiang, PhD, FRCS, Auditory Implant
Department, St. Thomas’ Hospital, Westminster Bridge Road, London
SE1 7EH, United Kingdom. E-mail: [email protected]
DOI: 10.1002/lary.24056
Laryngoscope 123: August 2013
sporadic VS, including loss of inner and outer hair cells,
spiral ganglia degeneration, and precipitates in the
endolymph and perilymph. The cochlea may also be
directly invaded by the tumor.2 The cochlear nerve function can be compromised, usually through compression,
but it may be directly infiltrated by tumor.3
Hearing may deteriorate further following treatment of VS. Even with hearing-preservation surgical
techniques such as middle fossa and retrosigmoid
approaches, retention of useful hearing is not always
possible. If the cochlear nerve is structurally preserved
during surgical resection, hearing loss may still occur,
probably due to direct neuronal disruption and/or compromise of the vascular supply to the cochlea.4 A number
of studies have shown a correlation between hearing loss
following stereotactic radiotherapy and radiation dose
delivered to the cochlea, in both single and fractionated
doses.5–7
Until recently, active intervention for profound sensorineural hearing loss in these two groups of patients
was limited to auditory brainstem implant (ABI) following tumor removal. Whilst ABI can provide useful auditory percepts and improve communication especially in
conjunction with lip reading, open-set speech recognition
is uncommon.8 Of late, there has been a growing interest in cochlear implantation (CI) as an alternative option
for auditory rehabilitation in patients with VS who have
residual cochlear nerve function. Although reported
Pai et al.: CI in Vestibular Schwannoma
2019
audiologic outcomes are variable,9–11 a recent review by
Celis-Aguilar et al. suggests that CI is a reasonable
option for these patients.12
In this article, we present the experience from our
single tertiary referral center with CI both for bilateral
VS with NF2 and for unilateral sporadic VS and discuss
the management considerations for the two unique
groups of patients.
MATERIALS AND METHODS
A retrospective case note review was carried out to evaluate patients with bilateral profound hearing loss and VS who
underwent unilateral CI within the Auditory Implant Centre at
St. Thomas’ Hospital, London, between 2000 and 2012. This
included both sporadic and NF2-associated VS patients. The
study was reviewed by the institutional clinical governance
review board and was exempted from the formal ethical approval process.
Preoperative audiologic assessment included pure-tone audiometry, sound-field with warble tones, and speech perception
testing using Bamford-Kowal-Bench (BKB) sentences and City
University of New York (CUNY) sentences with lip reading at
70 dBA sound presentation level. In patients who had no auditory perception, transtympanic electrical promontory stimulation (EPS) was performed to determine gap detection as a
surrogate measure of the cochlear nerve function (starting at a
pulse rate of 50 Hz and gap length of 250 ms).
Radiologic evaluation by serial magnetic resonance imaging (MRI) was carried out by a single consultant neuro-otology
radiologist, with particular attention to the rate of tumor
growth and detailed assessment of the tumor involvement of
the cochlea.
Intraoperative findings including electrode insertion depth
and neural response telemetry were recorded, as well as any
postoperative complications.
Outcome measures included sound-field thresholds, BKB,
CUNY, and the subjective benefits reported by patients.
RESULTS
Over the 10-year period, seven patients with VS
and bilateral profound hearing loss received a unilateral
cochlear implant. Five patients had NF2 with bilateral
tumors. Of the two patients with unilateral sporadic VS,
one had a 30-year history of profound sensorineural
hearing loss of unknown etiology in the contralateral
ear, which had never been aided. The other patient had
identified the nontumor ear as the better hearing ear,
still deriving some benefits from an acoustic hearing aid,
but overall fell within the CI criteria and was unwilling
to receive an implant in his better hearing (nontumor)
ear. Both sporadic VS patients therefore received an
implant in the tumor ear. The mean age at implantation
was 35.0 years in the NF2 group (range, 18.2–49.8) and
82.4 years in the sporadic group (range, 76.3–88.4).
The management of VS in the ear to be implanted
was variable and had included surgical resection only
(n 5 3), surgery followed by interval gamma knife radiotherapy for control of further growth (n 5 1), gamma
knife radiotherapy only (n 5 1), fractionated stereotactic
radiotherapy (n 5 1), and observation with serial imaging and no intervention (n 5 1). All four patients who
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2020
had had surgery were NF2 patients, and the resection
was via the retrosigmoid approach in all cases.
As can be seen in Table I, the standard preoperative
audiologic assessment for CI was largely impossible to
carry out in NF2 patients, and testing often had to be
abandoned, as they found the tests unmanageable. All
five NF2 patients underwent EPS testing, of which four
had positive gap detection. The other patient had a negative response with a needle electrode on the promontory
but had a positive response with a ball electrode in the
round window. Some preoperative audiologic testing was
possible in the two patients with sporadic VS. Tumor
invasion of the cochlea was evident on MRI in four of five
NF2 patients but not in either sporadic VS patient.
Implanted
devices
were
Advanced
Bionics
(Advanced Bionics AG Laubisr€
utistrasse 28, 8712 St€
afa,
Switzerland) Clarion AB-5100H, Cochlear Nucleus Freedom CI24RE(ST), Cochlear (Cochlear Headquarters,
University Avenue, Macquarie University NSW 2109
Australia) Nucleus CI422, and Advanced Bionics HiRes
90K. No attempt was made to remove intracochlear tumor before insertion of the electrode in any of the cases.
Full insertion was achieved in all patients except one
NF2 patient (patient 3), where the electrode buckled at
180-degree insertion because of obstruction of the scala
tympani adjacent to the internal auditory canal. In only
two NF2 patients (patients 4 and 5) did intraoperative
neural response telemetry display a compound action
potential. There were no surgical complications, and all
patients made an uneventful recovery.
Two of the NF2 patients (patients 2 and 3) had no
open-set speech perception postoperatively. Nonetheless,
patient 3 was highly satisfied with the implant and
reported that he was able to recognize familiar music
and identify some words without lip reading (follow-up,
11 months). Patient 2 had no auditory perception postimplantation. Patient 1 performed very well initially,
with BKB score of 78% and CUNY score of 93% at 1
week after switch-on. However, his medical condition
deteriorated steadily over the following few months with
rapid progression of visual impairment and worsening
implant performance, and he died 28 months after implantation. Patient 4 had a good outcome, with BKB and
CUNY scores of 63% and 94%, respectively, at 3 months.
He reported that he was able to have group conversations with family members and listen to audio books.
Patient 5, who was the latest patient to receive an
implant, also performed well, with BKB and CUNY
scores of 89% and 94%, respectively, at 3 months. He
was able to have a one-to-one conversation in a quiet
restaurant and enjoy music again. All NF2 patients who
are alive wear their device all day.
Both sporadic VS patients had significant improvement in sound-field thresholds. One had no appreciable
change on either speech perception test, and the other
showed improvement in the CUNY score only. Nevertheless, both patients are highly satisfied CI users; despite
the relatively low open speech perception scores postimplantation, they are able to use the telephone in their
implanted ear and wear their implant all day (mean
follow-up, 31 months).
Pai et al.: CI in Vestibular Schwannoma
TABLE I.
Demographics, Preoperative Audiologic Assessment, and Postoperative Outcome.
Patient 1
Patient 2
Patient 3
Patient 4
Patient 5
Patient 6
Age at CI, yr
28.7
36.1
18.2
42.1
49.8
88.4
76.3
Etiology
Visual impairment
NF2
Yes
NF2
No
NF2
Yes
NF2
Yes
NF2
No
Sporadic
No
Sporadic
No
Treatment for VS
before CI
Surgery
Surgery then
interval GK
Surgery
Fractionated
radiotherapy
Surgery
Monitoring only
GK
Tumor size in implanted
ear before CI, mm
16 3 7
Unknown
26 3 19
20 3 12
332
433
23 3 15
Preoperative AC, dBHL
EPS
NR
Yes
NR
No*
NR
Yes
NR
Yes
NR
Yes
90
Not performed
90
Not performed
Preoperative BKB, %
NA
NA
NA
NA
0
Postoperative BKB, %
78 at 1 wk
NR
2 at 3 mo
11 at 1 wk,
63 at 3 mo
0
50 at 1 wk,
89 at 3 mo
14
28 at 3 mo
24
10 at 1 wk,
54 at 3 mo
Patient 7
0
13 at 1 wk,
0 at 9 mo
9
Preoperative CUNY, %†
NA
NA
0
Postoperative CUNY, %†
93 at 1 wk,
28 at 1 yr
NR
10 at 3 mo
62 at 1 wk,
94 at 3 mo
85 at 1 wk,
94 at 3 mo
Preoperative sound
field, dBA
NA
NA
NR
NA
NA
Postoperative sound
field, dBA
Deceased
NT
NT
35 at 3 mo
30 at 1 wk
36 at 1 wk
40 at 3 mo
36 at 3 mo
28 mo
after CI
47 mo
after CI
No
No
No
No
No
52
64
22 at 1 wk,
61 at 9 mo
51
*Positive round window stimulation.
†
With lip reading.
AC 5 air conduction (averaged over 0.5, 1, 2, and 4 kHz); BKB 5 Bamford-Kowal-Bench; CI 5 cochlear implantation; CUNY 5 City University of New
York; EPS 5 electrical promontory stimulation; GK 5 gamma knife; NA 5 unable to perform test; NF2 5 neurofibromatosis type 2; NR 5 no response; NT 5 not
tested; VS 5 vestibular schwannoma.
In patients 1 and 2, progressive growth of all NF2associated tumors was observed, including the VS in the
implanted ear, and they died 28 and 47 months after implantation, respectively. In patient 3, there has been no
further tumor growth since implantation (follow-up, 16
months). The other two NF2 patients who received their
implant in the last 12 months have not had repeat imaging to date (patients 4 and 5). There has been no change
in the tumor size in either sporadic VS patient.
DISCUSSION
With advances in our understanding of NF2 and VS
molecular biology, a number of novel therapeutic agents
are emerging13,14 that may potentially control tumor
progression and improve quality of life. It is hoped that
these will in turn facilitate a more active management
of the associated disabilities such as profound hearing
loss and provide a longer window of opportunity for
interventions.
In our experience, it was largely impossible to implement the standard audiologic CI assessment protocol preoperatively, particularly in NF2 patients. Whilst it is
likely that the preoperative assessment will always
require some degree of modification, especially when
there are other comorbidities such as visual impairment,
our findings emphasize the importance of working closely
with the NF2 multidisciplinary team and encouraging an
early referral to the implant team, even if the patients
are not yet meeting the criteria for CI. More comprehenLaryngoscope 123: August 2013
sive audiologic assessment and closer monitoring of the
inevitable deterioration in their hearing will aid better
counseling concerning their options and the optimal timing of interventions that may maximize improvement in
quality of life. Furthermore, thorough preoperative
assessment when patients are still able will facilitate further refinement of implant candidacy criteria, which may
lead to a better and more consistent outcome.
When there was no auditory percept preoperatively
(all five NF2 patients), EPS was performed to assess the
functional integrity of the cochlear nerve. To date only
those with positive electrical promontory or round window stimulation have received a cochlear implant in our
unit. However, the literature suggests that the absence of
EPS responses does not necessarily preclude CI. There
have been reported cases of successful CIs in NF2
patients, despite negative EPS response.11,15 Nonetheless,
it should also be borne in mind that evidence from CI in
non-VS patients suggests a correlation between no EPS
response and poorer speech perception outcome.16 Until
the precise implication of the absent EPS response can be
established, or a more reliable predictor of the cochlear
nerve function found, the decision whether or not to
implant in its absence will need to be made on a case-bycase basis after a full discussion with the patient.
Thorough radiologic evaluation is crucial when CI
is being considered in VS patients. A combination of
thin-section T2-weighted (T2w) and gadoliniumenhanced imaging is required to assess the status of the
cochlea. The presence of fibrosis or calcification
Pai et al.: CI in Vestibular Schwannoma
2021
subsequent to previous surgery results in loss of the
increased T2w signal of the cochlea lumen, with possible
increased T1w signal and minor enhancement. Transmodiolar extension of schwannoma is associated with loss
of the increased T2w signal of the cochlea lumen and
similar enhancement characteristics to an intracanalicular tumor. Each scenario may impede the advancement
of the electrode, thus influencing electrode choice and
route of insertion. The presence of schwannoma in the
middle ear may represent transotic extension or be emanating from the tympanic segment of the facial nerve.
The postsurgical distortion of the internal auditory meatus (IAM) makes it difficult to assess the anatomy and
integrity of the nerves within the IAM or the location of
any residual intracanalicular tumor.
The timing of CI surgery is another subject of interest. There are reported cases of simultaneous translabyrinthine excision of VS and CI.17–19 This approach has
the obvious advantage of sparing the patient another
major surgery. In addition, it avoids the potential pitfall
of cochlear fibrosis or ossification, which may follow labyrinthectomy.18 However, the main concern about this
strategy is that, even if the cochlear nerve is structurally intact following removal of VS, it may not necessarily be functioning.
One of the important considerations following CI
surgery is radiologically monitoring the tumor growth.
Although a number of devices are deemed to be MRI
compatible up to 1.5 T, there are potential risks, including device damage, magnet displacement, and migration.
Alternative options are removal of the magnet and the
use of a magnetless device. There is also a significant artifact (shadow) surrounding the implanted cochlear stimulator. Our current policy is to perform full intracranial
and whole spine MRI just before implantation. Subsequent monitoring is usually with computed tomography
for the brain and temporal bone, and, if there is a specific indication for MRI, a CI-compatible protocol is used
with a compression head bandage, leaving the magnet in
place if in keeping with the manufacturer’s guidelines.
The audiologic outcomes were variable in our series
of patients with VS undergoing CI. Open-set speech perception was achieved in three of five NF2 patients, and
another reported significant improvement in environmental sound perception and ease of communication.
The outcome was overall better in patients with sporadic
VS, both of whom were able to use the telephone in their
implanted ear. At present, all five surviving patients are
consistent and satisfied users of their device.
It is uncertain which speech perception tests are
the most appropriate outcome measures in these
patients. In our experience, patients often found it difficult to complete postoperative testing in one session due
to fatigue, and the scores obtained may not necessarily
be representative of their abilities. It is also possible
that the standard CI assessment battery used in our
study was not always sensitive enough for detecting the
small but significant improvement in speech perception
in these specific subgroups of CI patients. This may
explain, at least in part, the discrepancy between the
scores obtained and the subjective improvement in real
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life reported by some patients. Careful consideration
should therefore be given to the choice of outcome measures in future studies.
Direct comparisons between the efficacy of CI for
auditory rehabilitation in these patients and that of ABI
are difficult due to the differences in the patient populations and outcome criteria used for reporting of the
results, and the available evidence is limited to small
case series. Nonetheless, the audiologic outcome is likely
to be better with CI than with ABI, as the electrical
stimulus is presented accurately to the acoustic pathway
as long as the cochlear nerve is functioning. In a study
by Vincenti et al.,15 patients with NF2 performed better
with CI than ABI, although the outcome was variable in
both groups. Two recently published review articles on
the subject reached a similar conclusion.8,12 With CI
becoming the favored option, there is increasing emphasis placed on preservation of the cochlear nerve, where
possible, during surgical resection.
CONCLUSION
In our experience, although there is variability in
outcome, speech perception can be achieved in some
cases, and CI should be considered as an option for auditory rehabilitation in patients with VS. Some modification of the standard CI assessment protocol is likely to
be necessary, and highly specific radiologic evaluation is
essential. We recommend early referral to the auditory
implant team for more comprehensive assessment and
monitoring of hearing loss progression, so that more
appropriate and timely patient selection for intervention
can be achieved.
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