Cochlear Implantation After Labyrinthectomy or a Translabyrinthine Surgical Approach

The treatment for cases of vestibular schwannoma or Meniere's disease may require a
translabyrinthine surgical approach. This surgical approach results in a complete loss of
hearing in the surgical ear, leaving the patient with a unilateral hearing loss. Though
assistive hearing technologies exist to route signals from the poorer hearing ear to the
better hearing ear, affected patients continue to have limitations with localization and
speech perception in noise. An alternative hearing device is a cochlear implant, which would
provide the signal to the affected ear. This could potentially offer binaural cues, thus
improving localization and speech perception in noise. Since the surgical procedures for a
translabyrinthine approach parallel those for cochlear implantation, insertion of the
cochlear implant could occur within the same surgery.

A vestibular schwannoma is a benign tumor on cranial nerve VIII that affects the vestibular
and auditory systems. Hearing loss on the side of the vestibular schwannoma may result from
degeneration of hair cells and spiral ganglia or growth of the schwannoma into the cochlear
space. Treatment options include observation from routine imaging, radiation therapy, or
surgical removal of the tumor. Despite treatment for the vestibular schwannoma, auditory
sensitivity may be further reduced on the affected side as a result of the radiation therapy
or compromises to the inner ear or cranial nerve VIII from surgical removal. Thus, in cases
of unilateral vestibular schwannoma the patient is often left with a unilateral profound
hearing loss.

Patients who are scheduled to undergo labyrinthectomy for intractable Meniere's disease are a
second population with resulting unilateral profound hearing loss. These patients typically
have non-functional hearing on the affected ear prior to the procedure. The main indication
for the surgery is intractable vertigo and thus the loss of already non-functional hearing is
typically well accepted.

Though hearing on the contralateral ear may be within normal limits, unilateral hearing loss
is known to result in reduced speech perception in noise, variable abilities on localization
tasks, increased report of hearing handicap, and reduced quality of life. Due to the severity
of the hearing loss, these patient populations cannot utilize conventional amplification that
would offer auditory input to the affected ear. The current hearing device options for this
patient population include contralateral routing of signal (CROS) hearing aids and
bone-conduction devices. With a CROS hearing aid, a microphone positioned near the affected
ear picks up the signal and sends it to a hearing aid placed on the contralateral ear to
present the signal to the unaffected side. Bone-conduction devices transmit the signal from
the affected ear to the contralateral ear via transcutaneous vibrations. Though CROS hearing
aids and bone-conduction devices provide the patient with auditory information from both
sides, the ability to use binaural cues for localization and speech perception in noise is
variable.

It is of interest as to the potential benefit of cochlear implantation in these populations
considering the profound hearing loss resulting from surgical intervention. A cochlear
implant is a two-part system, including the internal electrode array and external speech
processor. The internal electrode array is surgically implanted into the affected cochlea.
The external speech processor receives sounds and transmits this signal to the internal
portion. The electrode array presents the signal via electrical pulses within the cochlear
space, which is interpreted by the brain as sound.

Cochlear implantation has been reported as a viable treatment option in other cases of
unilateral hearing loss, including sudden sensorineural hearing loss, and severe tinnitus.
Further, cochlear implantation has been shown to offer superior speech perception in noise,
localization abilities, and subjective report in cases of unilateral sensorineural hearing
loss as compared to CROS hearing aids and bone-conduction devices.

There is limited evidence as to the success of cochlear implantation in patients with
unilateral profound hearing loss resulting from vestibular schwannoma. One study reported
variable speech perception outcomes in five cochlear implant recipients with a history of
vestibular schwannoma due to neurofibromatosis type 2 (NF2) or sporadic growth. Limitations
of this study are the subjects underwent a range of treatments prior to cochlear implantation
and the cases reviewed had profound hearing loss in both ears. A second study reported on a
case study of unilateral vestibular schwannoma removal and simultaneous cochlear
implantation. This subject reportedly experienced an improvement in speech perception
abilities and quality of life postoperatively. Determining the preferred treatment option for
patients suffering from unilateral vestibular schwannoma is still needed.

Further, there is limited evidence of the preferred treatment option for patients suffering
from unilateral profound hearing loss after undergoing a labyrinthectomy for intractable
Meniere's disease. One study reported on a patient who underwent bilateral labyrinthectomies
for Meniere's disease. They reported an improvement in speech perception abilities and
subjective benefit; however, there was a delay between the two surgeries. Allowing for a
waiting period between the two surgeries is not ideal as cochlear ossification may occur,
limiting the ability to successfully insert the electrode array. Another study also reported
successful outcomes from cochlear implantation in subjects with bilateral Meniere's disease.
However, there is no published report investigating whether cochlear implantation improves
speech perception and/or localization abilities in unilateral cases of Meniere's disease.

The goal of this project is to determine whether subjects who have undergone labyrinthectomy
or a translabyrinthine surgical approach as the treatment for vestibular schwannoma or
Meniere's disease benefit from cochlear implantation on speech perception and localization
tasks. If the auditory nerve is able to transmit this signal effectively, then these two
populations may be able to utilize the combination of electric (in the affected ear) and
acoustic (in the non-affected ear) information for improved speech perception in noise and
localization as reportedly experienced in other unilateral sensorineural hearing loss
populations.

Inclusion Criteria:

1. Scheduled to undergo a surgical procedure that will result in profound hearing loss in
the surgical ear [unilateral vestibular schwannoma wtih planned translabyrinthine
surgery or unilateral Meniere's disease with planned labyrinthectomy] [diagnosed by
UNC investigators]

2. Pure-tone average (PTA) less than or equal to 35 decibels Hearing Level (dB HL) in the
contralateral ear [no evidence of retrocochlear dysfunction]

3. Unaided consonant-nucleus-consonant (CNC) words score greater than or equal to 80% in
the contralateral ear

4. Greater than 18 years of age at implantation

5. Realistic expectations

6. Willing to obtain appropriate meningitis vaccinations

7. No reported cognitive issues [pass the Mini Mental State Examination screener]

8. Able and willing to comply with study requirements, including travel to
investigational site

9. Obtain Centers for Disease Control and Prevention (CDC) recommended meningitis
vaccinations prior to surgery

Exclusion Criteria:

1. History of implantable technology in either ear, such as a bone-conduction implant

2. Non-native English speaker [speech perception materials presented in English]

3. Inability to participate in follow-up procedures (unwillingness, geographic location)