Kevin D. Brown

Benefits of bilateral cochlear implantation: a review.

Purpose of reviewAlthough unilateral cochlear implantation generally provides good speech understanding under quiet conditions, cochlear implantation patients frequently report difficulty understanding speech when exposed to background noise and with sound localization. Since these two listening functions require binaural stimulation for normal individuals and hearing aid recipients, it is not surprising that there is growing interest in binaural implants. This update reviews the basics of binaural listening and the advantages and disadvantages of binaural cochlear implantation. Recent findingsAlthough the psychoacoustic literature has long demonstrated the benefits of binaural hearing, only recently have studies shown improvement in speech intelligibility with bilateral implants compared with unilateral implants. Of the three known binaural mechanisms, the head shadow effect provides greater benefit than binaural squelch or summation. In addition, binaural cochlear implants improve the ability to localize sound. SummaryBilateral implantation provides multiple benefits to patients with severe to profound hearing loss. Research is currently directed at improving speech intelligibility by utilizing evolving technologies in speech-processing strategies.

Incidence and indications for revision cochlear implant surgery in adults and children

To identify the incidence of and common causes for cochlear implant revision.

The temporalis pocket technique for cochlear implantation: an anatomic and clinical study.

Objective: To describe the surgical anatomy and clinical outcomes of a technique for securing cochlear implant receiver/stimulators (R/S). Receiver/stimulators are generally secured by drilling a custom-fit seat and suture-retaining holes in the skull. However, rare intracranial complications and R/S migration have been reported with this standard method. Newer R/S designs feature a low profile and larger, rigid flat bottoms in which drilling a seat may be less appropriate. We report a technique for securing the R/S without drilling bone. Study Design: Anatomic: Forty-eight half-heads were studied. Digital photography and morphometric analysis demonstrated anatomic boundaries of the subpericranial pocket (t-pocket). Clinical: Retrospective series of 227 consecutive Cochlear implant recipients implanted during a 2-year period using either the t-pocket or standard technique. The main outcome measures were rates of R/S migration and intracranial complications. Minimum follow-up was 12 months. Results: The t-pocket is limited anteriorly by dense condensations of pericranium anteriorly at the temporal-parietal suture, posteroinferiorly at the lamdoid suture, and anteroinferiorly by the bony ridge of the squamous suture. One hundred seventy-one subjects were implanted using the t-pocket technique and 56 using the standard technique, with a minimum follow-up of 12 months. There were no cases of migration or intracranial complications in either group. Conclusion: The t-pocket secures the R/S with anatomically consistent strong points of fixation while precluding dural complications. There were no cases of migration or intracranial complication noted. Further trials and device-specific training with this technique are necessary before it is widely adopted.

Lipid raft localization of ErbB2 in vestibular schwannoma and schwann cells.

Hypothesis: ErbB2 resides in lipid rafts (regions of receptor regulation) in vestibular schwannoma (VS) cells. Background: ErbB2 is a growth factor receptor critical for Schwann cell (SC) proliferation and development. ErbB2 localization and activity may be regulated by merlin, an adaptor protein deficient in VS. Lipid rafts are microdomains in the plasma membrane that amplify and regulate receptor signaling. Persistence of erbB2 in lipid rafts in VS due to merlin deficiency may explain increased VS cell growth. Methods: Protein extracts from VS or rat sciatic nerve (proximal or distal to a crush injury) were isolated into lipid raft and nonraft fractions and immunoblotted for erbB2, phosphorylated erbB2, and merlin (for sciatic nerve). Cultured VS cells were probed with anti-erbB2 antibody and a lipid raft marker, cholera toxin B (CTB). Results: ErbB2 moves to lipid rafts in proliferating SCs and is persistently localized to lipid rafts in VS cells. ErbB2 is phosphorylated (activated) in lipid rafts. ErbB2 colocalized with CTB in cultured VS cells, confirming raft targeting. Merlin also persistently localized to lipid rafts in SCs, and its relative phosphorylation increased in proliferating cells. Conclusion: Lipid raft localization of erbB2 in proliferating SCs and in VS cells supports a critical role for lipid rafts in amplifying/regulating erbB2 signaling. Merlin resides in lipid rafts in SCs, and its phosphorylation increases in proliferating SCs, suggesting it regulates cell proliferation within lipid rafts. The absence of merlin in VS may therefore lead to persistent erbB2 localization to lipid rafts and increased cell proliferation.

Cochlear Implantation in Cases of Unilateral Hearing Loss: Initial Localization Abilities

Objectives: The present study evaluated early auditory localization abilities of cochlear implant (CI) recipients with normal or near-normal hearing (NH) in the contralateral ear. The goal of the study was to better understand the effect of CI listening experience on localization in this population. Design: Twenty participants with unilateral hearing loss enrolled in a prospective clinical trial assessing outcomes of cochlear implantation (ClinicalTrials.gov Identifier: NCT02203305). All participants received the MED-EL Standard electrode array, were fit with an ear-level audio processor, and listened with the FS4 coding strategy. Localization was assessed in the sound field using an 11-speaker array with speakers uniformly positioned on a horizontal, semicircular frame. Stimuli were 200-msec speech-shaped noise bursts. The intensity level (52, 62, and 72 dB SPL) and sound source were randomly interleaved across trials. Participants were tested preoperatively, and 1, 3, and 6 months after activation of the audio processor. Performance was evaluated in two conditions at each interval: (1) unaided (NH ear alone [NH-alone] condition), and (2) aided, with either a bone conduction hearing aid (preoperative interval; bone conduction hearing aid + NH condition) or a CI (postoperative intervals; CI + NH condition). Performance was evaluated by comparing root-mean-squared (RMS) error between listening conditions and between measurement intervals. Results: Mean RMS error for the soft, medium, and loud levels were 66°, 64°, and 69° in the NH-alone condition and 72°, 66°, and 70° in the bone conduction hearing aid + NH condition. Participants experienced a significant improvement in localization in the CI + NH condition at the 1-month interval (38°, 35°, and 38°) as compared with the preoperative NH-alone condition. Localization in the CI + NH condition continued to improve through the 6-month interval. Mean RMS errors were 28°, 25°, and 28° in the CI + NH condition at the 6-month interval. Conclusions: Adult CI recipients with normal or near-normal hearing in the contralateral ear experienced significant improvement in localization after 1 month of device use, and continued to improve through the 6-month interval. The present results show that binaural acclimatization in CI users with unilateral hearing loss can progress rapidly, with marked improvements in performance observed after only 1 month of listening experience.

The Compound Action Potential in Subjects Receiving a Cochlear Implant.

Hypothesis: The compound action potential (CAP) is a purely neural component of the cochleas response to sound, and may provide information regarding the existing neural substrate in cochlear implant (CI) subjects that can help account for variance in speech perception outcomes. Background: Measurement of the “total response” (TR), or sum of the magnitudes of spectral components in the ongoing responses to tone bursts across frequencies, has been shown to account for 40 to 50% of variance in speech perception outcomes. The ongoing response is composed of both hair cell and neural components. This correlation may be improved with the addition of the CAP. Methods: Intraoperative round window electrocochleography (ECochG) was performed in adult and pediatric CI subjects (n = 238). Stimuli were tones of different frequencies (250 Hz–4 kHz) at 90 dB nHL. The CAP was assessed in two ways, as an amplitude and with a scaling factor derived from a function fitted to the response. The results were correlated with consonant-nucleus-consonant (CNC) word scores at 6 months post-implantation (n = 51). Results: Only about half of the subjects had a measurable CAP at any frequency. The CNC word scores correlated weakly with both amplitude (r2 = 0.20, p < 0.001) and scaling factor (r2 = 0.25, p < 0.01). In contrast, the TR alone accounted for 43% of the variance, and addition of either CAP measurement in multiple regression did not account for additional variance. Conclusions: The underlying pathology in CI patients causes the CAP to be often absent and highly variable when present. The TR is a better predictor of speech perception outcomes than the CAP.

Surveillance after resection of vestibular schwannoma: measurement techniques and predictors of growth.

Objectives To compare different methods of measuring tumor growth after resection of vestibular schwannoma and to identify predictors of growth. Study Design Retrospective case review. Setting Tertiary referral center, inpatient surgery with ambulatory follow-up. Patients All patients who underwent vestibular schwannoma resection by the senior author from September 1991 to April 2012 and had two or more postoperative MRI scans. Interventions Vestibular schwannoma resection. Measurement of tumor size and enhancement pattern on postoperative magnetic resonance imaging scans. Main Outcome Measures Tumor size as measured in one (linear), two (planar), and three (volumetric) dimensions using standard radiology workstation tools versus time elapsed since surgical resection. Results Eighty-eight patients were included with mean follow-up of 3.9 years. Linear measurement of tumor size was found to have modest correlation with planar and volumetric measurements. Excellent correlation was found between the planar and volumetric methods. Nodular enhancement increased risk for tumor growth (OR 6.25, p = 0.03 on planar analysis). If there was growth, tumors with nodular enhancement typically showed increase in size beginning 2 years postoperatively, whereas those with linear or no enhancement were typically stable in size through 5 years. Younger age and larger preoperative tumor size were also risk factors for growth (OR 0.9/p = 0.01 and OR 1.09/p = 0.02). Conclusion Simple planar measurement is an efficient method that correlates well with the more time-consuming volumetric method. The major risk factor for tumor growth is nodular enhancement on a baseline scan, a finding that warrants annual MRI beginning 2 years postoperatively. Younger age and larger preoperative size minimally increased risk of growth.

The effect of interdevice interval on speech perception performance among bilateral, pediatric cochlear implant recipients

To determine if prolongation of the interdevice interval in children receiving bilateral cochlear implants adversely affects speech perception outcomes.

Preserved low-frequency hearing following 20-mm cochlear implantation

Objective To determine the preservation of pure tone thresholds for a series of cochlear implant patients who underwent atraumatic round window insertion with a new thin 22-mm electrode to a 20-mm depth. Study Design Retrospective, within-subject repeated measures design. Setting Tertiary care hospital. Patients Nine sequential cochlear implant patients with functional preoperative acoustic hearing (defined as low-frequency pure tone average thresholds ⩽90 dB). Intervention Therapeutic. Main Outcome Measure Pure tone thresholds after cochlear implantation. Results Low-frequency hearing preservation was achieved in all cases. Less than 10 dB average change was seen for low-frequency pure tone average measures (125, 250, 500, and 1,000 Hz) at 6 and 12 months following cochlear implantation. Conclusions Atraumatic round window insertion with a thin 22-mm electrode to a 20-mm depth results in dramatically high levels of acoustic hearing preservation among CI patients.

Intraoperative electrocochleographic characteristics of auditory neuropathy spectrum disorder in cochlear implant subjects

Auditory neuropathy spectrum disorder (ANSD) is characterized by an apparent discrepancy between measures of cochlear and neural function based on auditory brainstem response (ABR) testing. Clinical indicators of ANSD are a present cochlear microphonic (CM) with small or absent wave V. Many identified ANSD patients have speech impairment severe enough that cochlear implantation (CI) is indicated. To better understand the cochleae identified with ANSD that lead to a CI, we performed intraoperative round window electrocochleography (ECochG) to tone bursts in children (n = 167) and adults (n = 163). Magnitudes of the responses to tones of different frequencies were summed to measure the “total response” (ECochG-TR), a metric often dominated by hair cell activity, and auditory nerve activity was estimated visually from the compound action potential (CAP) and auditory nerve neurophonic (ANN) as a ranked “Nerve Score”. Subjects identified as ANSD (45 ears in children, 3 in adults) had higher values of ECochG-TR than adult and pediatric subjects also receiving CIs not identified as ANSD. However, nerve scores of the ANSD group were similar to the other cohorts, although dominated by the ANN to low frequencies more than in the non-ANSD groups. To high frequencies, the common morphology of ANSD cases was a large CM and summating potential, and small or absent CAP. Common morphologies in other groups were either only a CM, or a combination of CM and CAP. These results indicate that responses to high frequencies, derived primarily from hair cells, are the main source of the CM used to evaluate ANSD in the clinical setting. However, the clinical tests do not capture the wide range of neural activity seen to low frequency sounds.