Cochlear implantation and auditory brainstem implantation in neurofibromatosis type 2.

OBJECTIVES/HYPOTHESIS: To report a series of patients with neurofibromatosis type 2 (NF2), where each patient underwent both cochlear implantation and auditory brainstem implantation for hearing rehabilitation, and to discuss factors influencing respective implant success. STUDY DESIGN: Retrospective case series. METHODS: Ten NF2 patients with both cochlear implantations and auditory brainstem implantations were retrospectively reviewed. Speech testing for auditory brainstem implants (ABIs) and cochlear implants (CIs) was performed separately. Scores at last follow-up were obtained for Iowa vowels and consonants, Northwestern University Children's Perception of Speech (NU-CHIPS), and City University of New York (CUNY) sentences. RESULTS: Mean age at time of implant was 37 years for cochlear implantation and 40 years for auditory brainstem implantation (P = .790, t test). Nine of 10 patients had a CI and ABI on contralateral sides, and one had both devices on the same side. Mean duration of deafness in the implanted ear was 4.3 years for both cochlear implantation and auditory brainstem implantation (P = .491, t test). Follow-up range was 1 to 28 years. CI performance on NU-CHIPS was 32% to 100%, and sound + lip-reading CUNY was 56% to 100%. Four patients experienced an eventual decline in CI function to unusable levels. ABI performance on NU-CHIPS was 40% to 80%, and sound + lip-reading CUNY was 38% to 94%. There was no notable decline in ABI function over time. CONCLUSIONS: If the cochlear nerve is intact, cochlear implantation can be an effective strategy for hearing rehabilitation in NF2. However, a significant proportion experience a decline in CI performance related to growing vestibular schwannoma or tumor treatment. Auditory brainstem implantation remains the standard option for surgical hearing rehabilitation in NF2, but peak performance is generally lower than that achievable with cochlear implantation. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:2163-2169, 2018.

Histopathological analysis of a 15-year user of an auditory brainstem implant.

Auditory brainstem implants (ABIs) can provide highly beneficial hearing sensations to individuals deafened by bilateral vestibular schwannomas (neurofibromatosis type 2). Relatively little is known about the status of stimulated neurons after long-term ABI use. Direct examination of the cochlear nuclear complex (CN) of one 5-year ABI user indicated no deleterious effect. Recently, we examined the brainstem of a patient who used his ABI daily for 15 years with excellent performance. There was good preservation of CN cell size, morphology, and packing density, a very favorable sign considering that a number of infants are now receiving ABIs.

Audiologic outcomes with the penetrating electrode auditory brainstem implant.

OBJECTIVE: The penetrating electrode auditory brainstem implant (PABI) is an extension of auditory brainstem implant (ABI) technology originally developed for individuals deafened by neurofibromatosis type 2. Whereas the conventional ABI uses surface electrodes on the cochlear nuclei, the PABI uses 8 or 10 penetrating microelectrodes in conjunction with a separate array of 10 or 12 surface electrodes. The goals of the PABI were to use microstimulation to reduce threshold current levels, increase the range of pitch percepts, and improve electrode selectivity and speech recognition. PATIENTS AND PROTOCOL: In a prospective clinical trial, 10 individuals, all with neurofibromatosis type 2, received a PABI after vestibular schwannoma removal via a translabyrinthine approach. All study participants met strict requirements for informed consent as part of a Food and Drug Administration clinical trial. Approximately 8 weeks after implantation, PABI devices were activated and tested at our tertiary clinical and research facility. Mean follow-up time was 33.8 months. STUDY DESIGN: Using a single-subject design, we measured thresholds and dynamic ranges, electrode-specific pitch percepts, and speech perception performance at regular intervals. RESULTS: Penetrating electrodes produced auditory thresholds at substantially lower charge levels than surface electrodes, a wide range of electrode-specific pitch sensations, and minimal cross-electrode interference and could be used in speech maps either alone or in combination with surface electrodes. However, less than 25% of penetrating electrodes resulted in auditory sensations, whereas more than 60% of surface electrodes were effective. Even after more than 3 years of experience, patients using penetrating electrodes did not achieve improved speech recognition compared with those using surface electrode ABIs. In patients with usable penetrating electrodes, City University of New York Sentence Test scores with sound and visual information were 61.6% in the PABI group and 64.7% in a surface ABI cohort (p = not significant). CONCLUSION: The PABI met the goals of lower threshold, increased pitch range, and high selectivity, but these properties did not result in improved speech recognition.

Auditory brainstem implants.

The development of cochlear implantation has allowed the majority of patients deafened after the development of language to regain significant auditory benefit. In a subset of patients, however, loss of hearing results from destruction of the cochlear nerves, rendering cochlear implantation ineffective. The most common cause of bilateral destruction of the cochlear nerves is neurofibromatosis type 2 (NF2). The hallmark of this genetic disorder is the development of bilateral acoustic neuromas, the growth or removal of which causes deafness in most patients. Patients with NF2 may benefit from direct stimulation of the cochlear nucleus. We describe the development, use, and results of the auditory brainstem implant (ABI), which is typically implanted via craniotomy at the time of tumor removal. Most patients with the implant have good appreciation of environmental sounds, but obtain more modest benefit with regard to speech perception. The majority of patients make use of the implant to facilitate lip reading; some can, to varying degrees, comprehend speech directly. We discuss future directions in central implants for hearing, including the penetrating ABI, the use of ABI in nontumor patients, and the auditory midbrain implant.

Auditory brainstem implants: surgical aspects.

Patients with neurofibromatosis type 2 often develop bilateral life-threatening vestibular schwannoma necessitating tumor removal, which results in deafness. We developed the auditory brainstem implant (ABI) in order to be able to electrically stimulate the cochlear nucleus complex in patients with bilateral cochlear nerve injury from bilateral schwannoma. After tumor removal, the electrode array of the ABI is inserted into the lateral recess of the fourth ventricle and placed over the surface of the ventral and dorsal cochlear nuclei. The ABI is designed to stimulate auditory neural structures within the cochlear nucleus in order to convey salient cues about the frequency, amplitude, and temporal characteristics of sounds. To date, more than 200 patients have received an ABI device at our institution. Recently, penetrating ABIs were introduced, and preliminary results of penetrating ABIs are discussed in this paper. The surgical anatomy of the nucleus and surgical placement of the ABI in patients with neurofibromatosis type 2 are described, and surgical considerations in this group of challenging patients are detailed.

Neural response telemetry and auditory/nonauditory sensations in 15 recipients of auditory brainstem implants.

Auditory brainstem implants (ABIs) provide a means of restoring some hearing sensations to individuals with neurofibromatosis type 2 (NF2) who are deaf after vestibular schwannoma removal. In this study, neural response telemetry (NRT) was used to record electrically evoked neuronal activity near the ABI electrode array in 15 such subjects. Our interest was to investigate whether NRT recordings from the brainstem might be useful in implanting or programming ABIs. We therefore sought relationships between postoperative NRT recordings and the sensations reported by the subjects in response to the test stimuli. However, no clear relationships among these variables were found, and it was not possible to differentiate recordings associated with auditory versus nonauditory sensations. The findings suggest that the categorization of NRT recordings used in this study is inappropriate for assisting with placement of an ABI electrode array intra-operatively or for programming the sound processor postoperatively.

Optimizing the clinical fit of auditory brain stem implants.

OBJECTIVE: To develop and implement a new audiological fitting procedure for auditory brain stem implants (ABIs), based on an efficient algorithm, and to compare it with two procedures presently used in clinical practice. DESIGN: First, the different procedures were compared by using computer models and simulations with normal-hearing subjects (N = 4). This allows for an analysis of the accuracy of the procedures in a way that is not possible when testing ABI users. The root-mean-square error between the order estimated by the procedure and the true order was calculated. In addition, ABI users (N = 2) were tested with the new procedure to see if it could be successfully applied in clinic. The degree of variability of their results across runs and sessions was analyzed. RESULTS: The tests of the normal-hearing subjects showed that our proposed procedure required significantly fewer trials (22 on average) than procedures presently used in clinic (with 76 and 234 trials on average for the two other procedures tested) to produce the same degree of accuracy. Computer modeling also demonstrated this advantage. Additional testing showed this advantage was maintained under a variety of conditions relevant to the clinic. The two patients tested were able to use this procedure with success, even though they were poor at discriminating the pitch of electrodes. The patients showed results consistent with having about 4 to 5 discriminable groups of electrodes with the 12 to 14 electrodes tested. CONCLUSIONS: The proposed procedure requires fewer trials to produce a clinically useful result and is well tolerated in the clinic. An additional advantage is that it allows testing to be broken down into several "blocks," each containing a small number of trials. If the variability between blocks is small, information can be combined across blocks to increase the accuracy of the result. If the variability is large, perhaps between blocks on different days, this may reflect a significant change in the percepts generated by the implant, and signal to the clinician that a significant alteration in the fitting is required. We recommend its use in ABI user fitting and in cochlear implant fitting when pitch ranking is problematic.

Auditory brainstem implantation in 12- to 18-year-olds.

OBJECTIVE: To assess the effects of the side of implantation (first-side vs second-side vestibular schwannoma); the presence of nonauditory sensations; the general health, expectations, and motivation of the patients; and a support group on the use of a multichannel auditory brainstem implant (ABI) in 12- to 18-year-old patients with neurofibromatosis 2. DESIGN: Since 1992, 21 individuals (age range, 12-18 years) who were deafened by neurofibromatosis 2 have undergone implantation with a multichannel ABI at the House Ear Institute, Los Angeles, Calif. The patients were categorized regarding side of implantation, presence of remaining hearing (in first-side implant recipients), incidence of nonauditory sensations, and ABI use or nonuse. They were also rated on factors of general health, personal motivation, expectations, and family support. RESULTS: Nineteen (95%) of 20 teenagers tested received hearing sensations from their ABIs. Eleven teenagers used their ABIs regularly, but 8 did not. Of the nonusers, 2 had good remaining hearing on the side with the second vestibular schwannoma, 2 had persistent nonauditory sensations, and 4 became program dropouts. None of the dropouts had remaining hearing, significant nonauditory sensations, or poor health; however, they generally rated poorly in terms of personal motivation, expectations, and family support. One patient with good family support returned with excellent ABI results after 4 years' absence. CONCLUSIONS: The multichannel ABI is an effective means of providing hearing sensations to young patients deafened by neurofibromatosis 2. Preoperative counseling regarding the importance of such factors as expectations, personal motivation, and family support is invaluable and can promote successful adaptation to the device. With patience and support, even young nonusers (including program dropouts) can become successful device users.

The multichannel auditory brainstem implant: how many electrodes make sense?

OBJECT: Development of multichannel auditory brainstem implant (ABI) systems has been based in part on the assumption that audiological outcome can be optimized by increasing the number of available electrodes. In this paper the authors critically analyze this assumption on the basis of a retrospective clinical study performed using the Nucleus 22 ABI surface electrode array. METHODS: The perceptual performances of 61 patients with neurofibromatosis Type 2 were tested approximately 6 weeks after an eight-electrode ABI had been implanted. Of eight implanted electrodes 5.57 +/- 2.57 (mean +/- standard deviation [SD] provided auditory sensations when stimulated. Electrodes were deactivated when stimulation resulted in significant nonauditory side effects or no auditory sensation at all, and also when they failed to provide distinctive pitch sensations. The mean (+/- SD) scores for patients with ABIs were the following: sound-only consonant recognition, 20.4 +/- 14.3 (range 0-65%); vowel recognition, 28.8 +/- 18% (range 0-67%); Monosyllable Trochee Spondee (MTS) word recognition 41.1 +/- 25.3% (range 0-100%); and sentence recognition, 5.3 +/- 11.4% (range 0-64%). Performance in patients in whom between one and three electrodes provided auditory sensation was significantly poorer than that in patients with between four and eight functional electrodes in the vowel, MTS word, and City University of New York (CUNY) sentence recognition tests. The correlation between performance and electrode number did not reach the 0.05 level of significance with respect to the sound effect, consonant, and MTS stress-pattern recognition tests, probably because a satisfactory performance in these tests can be obtained only with temporal cues, that is, without any information about the frequency of the sounds. In the MTS word and the CUNY sentence recognition tests, performance was optimal in the patients with eight functional electrodes. Although all top performers had more than three functional auditory electrodes, no further improvement (asymptotic performance) was seen in those with five or more active electrodes in the consonant, vowel, and sound effect recognition tests. CONCLUSIONS: A minimum of three spectral channels, programmed in the appropriate individual tonotopic order seem to be required for satisfactory speech recognition in most patients with ABI. Due to the limited access to the tonotopic frequency gradient of the cochlear nucleus with surface stimulation, patients with ABI do not receive a wide range of spectral cues (frequency information) with multielectrode (> 5) surface arrays.

Use of a multichannel auditory brainstem implant for neurofibromatosis type 2.

Neurofibromatosis type 2 (NF 2) typically results in deafness due to disruption of the cochlear nerves, making peripheral devices such as cochlear implants ineffective. Auditory brainstem implants (ABIs), for direct electrical stimulation of the cochlear nucleus, have been used to provide auditory stimulation in this group of patients. Currently, 141 patients have been implanted in our institution, most recently using an advanced multichannel device. We report results of a recent series of 86 patients who received ABIs. Of this group, 60 had successful implantation, recovered from surgery, responded successfully to stimulation and underwent a full course of device programming and audiologic testing. This group had significant improvement in scores on several audiologic tests compared to baseline. When used to augment lip reading, improvement was also seen. The degree of improvement varied considerably among patients. ABI is a useful device for deaf patients with NF 2. As measured by audiologic testing, many patients receive substantial benefit with regard to sound and speech comprehension.

Multichannel auditory brainstem implant: update on performance in 61 patients.

OBJECT: Neurofibromatosis Type 2 (NF2) has typically resulted in deafness after surgical removal of bilateral vestibular schwannomas (VSs). Cochlear implants are generally ineffective for this kind of deafness because of the loss of continuity in the auditory nerve after tumor removal. The first auditory brainstem implant (ABI) in such a patient was performed in 1979 at the House Ear Institute, and this individual continues to benefit from electrical stimulation of the cochlear nucleus complex. In 1992, an advanced multichannel ABI was developed and a series of patients with NF2 received this implant to study the safety and efficacy of the device. METHODS: At the time of first- or second-side VS removal, patients received an eight-electrode array applied to the surface of the cochlear nucleus within the confines of the lateral recess of the fourth ventricle. The device was activated approximately 6 weeks after implantation. and patients were tested every 3 months for the 1st year after the initial stimulation, and annually thereafter. The protocol included a comprehensive battery of psychophysical and speech perception tests. CONCLUSIONS: The multichannel ABI proved to be effective and safe in providing useful auditory sensations in most patients with NF2. The ABI improved patients' ability to communicate compared with the lipreading-only condition, it allowed the detection and recognition of many environmental sounds, and in some cases it provided significant ability to understand speech by using just the sound from the ABI (with no lipreading cues). Its performance in most patients has continued to improve for up to 8 years after implantation.