Bilateral Cochlear Nerve Aplasia Research Articles

Functional Outcomes of Cochlear Implantation in Children with Bilateral Cochlear Nerve Aplasia.

Background and Objectives: Many otologists face a dilemma in the decision-making process of surgical management of patients with cochlear nerve (CN) aplasia. The goal of this study is to provide fresh evidence on cochlear implantation (CI) results in patients with CN aplasia. Materials and Methods: We scrutinized functional outcomes in 37 ears of 21 children with bilateral CN aplasia who underwent unilateral or bilateral CI based on cross-sectional and longitudinal assessments. Results: The Categories of Auditory Performance (CAP) scores gradually improved throughout the 3-year follow-up; however, variable outcomes existed between individuals. Specifically, 90% of recipients with a 1-year postoperative CAP score ≤1 could not achieve a CAP score over 1 even at 3-year postoperative evaluation, while the recipients with a 1-year postoperative CAP score >1 had improved auditory performance, and 72.7% of them were able to achieve a CAP score of 4 or higher. Meanwhile, intraoperative electrically evoked compound action potential was not correlated with postoperative CAP score. Conclusions: Our results further refine previous studies on the clinical feasibility of CI as the first treatment modality to elicit favorable auditory performance in children with CN aplasia. However, special attention should be paid to pediatric patients with an early postoperative CAP score ≤1 for identification of unsuccessful cochlear implants and switching to auditory brainstem implants.

Temporal bone and cranial nerve findings in pontine tegmental cap dysplasia.

Pontine tegmental cap dysplasia (PTCD) is a recently described brain malformation associated with multiple cranial neuropathies, most commonly congenital sensorineural hearing loss. The purpose of this study is to systematically characterize the cranial nerve and temporal bone findings in a cohort of children with this rare condition. Sixteen patients with PTCD and diagnostic quality imaging were retrospectively reviewed. All patients had high-resolution MR of the brain and/or internal auditory canals, and seven patients had additional high-resolution CT of the temporal bones. Studies were evaluated by two pediatric neuroradiologists for cranial nerve and temporal bone anomalies. Fifteen of 16 patients (94%) had duplication of one or both internal auditory canals. Of the 24 total duplicated internal auditory canals, all 24 (100%) demonstrated stenosis or atresia of the vestibulocochlear nerve canal, as well as ipsilateral vestibulocochlear nerve aplasia. Of the non-duplicated internal auditory canals, 63% (5/8) were atretic or stenotic. Thirty-eight percent (3/8) were associated with absent vestibulocochlear nerve, and 38% (3/8) demonstrated isolated cochlear nerve aplasia. Twenty-five percent (2/8) demonstrated normal vestibulocochlear nerves, both in the same patient. Fifteen of 16 patients overall (94%) demonstrated bilateral cochlear nerve aplasia. Of the 32 total temporal bones, 4 (13%) demonstrated facial nerve aplasia. Seventy-nine percent (22/28) of facial nerves that were present demonstrated an aberrant origin or course. Patients with PTCD have highly characteristic temporal bone and cranial nerve findings on both CT and MR. Recognition of these findings is important for improved diagnosis of this rare disorder, particularly by CT.

Auditory brainstem implant candidacy in the United States in children 0–17 years old

ObjectivesThe auditory brainstem implant (ABI) is an option for hearing rehabilitation in profoundly deaf patients ineligible for cochlear implantation. Over the past decade, surgeons have begun implanting ABIs in pediatric patients who are unable to receive cochlear implants due to congenital or acquired malformations of the inner ear. No study has examined the potential population-level demand for ABIs in the United States (US). Herein, we aim to quantify the potential need for pediatric ABIs. MethodsA systematic literature review was conducted to identify studies detailing the rates of congenital cochlear and/or cochlear nerve (CN) anomalies. Absolute indications for ABI include bilateral cochlea or CN aplasia (Group A), and relative indications for ABI include bilateral cochlea or CN hypoplasia (Group B). Data was subsequently correlated to the US Census Bureau, the National Health Interview Survey, and the Gallaudet Research Institute to provide an estimation of pediatric ABI candidates. ResultsEleven studies documented rates of bilateral findings. Bilateral cochlea aplasia was identified in 0–8.7% of patients and bilateral CN aplasia in 0–4.8% of patients (Group A). Bilateral cochlea hypoplasia was identified in 0–8.7% of patients and bilateral CN hypoplasia in 0–5.4% of patients (Group B). Using population-level sensorineural hearing loss data, we roughly estimate 2.1% of potential implant candidates meet absolute indications for an ABI in the United States. ConclusionCongenital cochlear and cochlear nerve anomalies are exceedingly rare. This study provides the first preliminary estimate of cochlea and CN aplasia/hypoplasia at the population level albeit with limitations based on available data. These data suggest the need for dedicated ABI centers to focus expertise and management.

Auditory Brainstem Implants

AbstractAuditory brainstem implants (ABIs) are currently indicated for patients with neurofibromatosis type 2 (NF-2) tumors involving both vestibulocochlear nerves. The ABI helps bypass the damaged cochlear nerves and stimulates the cochlear nucleus in the brainstem directly thereby restoring auditory sensation. The implant is usually placed in the lateral recess of the fourth ventricle after tumor resection. The indications for ABI have recently expanded onto even nontumoral cases, such as congenital bilateral cochlear nerve aplasia. In such cases, the ABI helps bypass the nonfunctioning hypoplastic or absent cochlear nerves and stimulates the cochlear nucleus directly thereby restoring auditory sensation. This article reviews the nuances of this sophisticated implant, shares our experience with auditory brainstem implantation and its current status in world literature.

Beneficial auditory and cognitive effects of auditory brainstem implantation in children

Conclusion: This preliminary study demonstrates the development of hearing ability and shows that there is a significant improvement in some cognitive parameters related to selective visual/spatial attention and to fluid or multisensory reasoning, in children fitted with auditory brainstem implantation (ABI). The improvement in cognitive paramenters is due to several factors, among which there is certainly, as demonstrated in the literature on a cochlear implants (CIs), the activation of the auditory sensory canal, which was previously absent. The findings of the present study indicate that children with cochlear or cochlear nerve abnormalities with associated cognitive deficits should not be excluded from ABI implantation. Objectives: The indications for ABI have been extended over the last 10 years to adults with non-tumoral (NT) cochlear or cochlear nerve abnormalities that cannot benefit from CI. We demonstrated that the ABI with surface electrodes may provide sufficient stimulation of the central auditory system in adults for open set speech recognition. These favourable results motivated us to extend ABI indications to children with profound hearing loss who were not candidates for a CI. This study investigated the performances of young deaf children undergoing ABI, in terms of their auditory perceptual development and their non-verbal cognitive abilities. Patients and methods: In our department from 2000 to 2006, 24 children aged 14 months to 16 years received an ABI for different tumour and non-tumour diseases. Two children had NF2 tumours. Eighteen children had bilateral cochlear nerve aplasia. In this group, nine children had associated cochlear malformations, two had unilateral facial nerve agenesia and two had combined microtia, aural atresia and middle ear malformations. Four of these children had previously been fitted elsewhere with a CI with no auditory results. One child had bilateral incomplete cochlear partition (type II); one child, who had previously been fitted unsuccessfully elsewhere with a CI, had auditory neuropathy; one child showed total cochlear ossification bilaterally due to meningitis; and one child had profound hearing loss with cochlear fractures after a head injury. Twelve of these children had multiple associated psychomotor handicaps. The retrosigmoid approach was used in all children. Intraoperative electrical auditory brainstem responses (EABRs) and postoperative EABRs and electrical middle latency responses (EMLRs) were performed. Perceptual auditory abilities were evaluated with the Evaluation of Auditory Responses to Speech (EARS) battery – the Listening Progress Profile (LIP), the Meaningful Auditory Integration Scale (MAIS), the Meaningful Use of Speech Scale (MUSS) – and the Category of Auditory Performance (CAP). Cognitive evaluation was performed on seven children using the Leiter International Performance Scale – Revised (LIPS-R) test with the following subtests: Figure ground, Form completion, Sequential order and Repeated pattern. Results: No postoperative complications were observed. All children consistently used their devices for >75% of waking hours and had environmental sound awareness and utterance of words and simple sentences. Their CAP scores ranged from 1 to 7 (average =4); with MAIS they scored 2–97.5% (average =38%); MUSS scores ranged from 5 to 100% (average =49%) and LIP scores from 5 to 100% (average =45%). Owing to associated disabilities, 12 children were given other therapies (e.g. physical therapy and counselling) in addition to speech and aural rehabilitation therapy. Scores for two of the four subtests of LIPS-R in this study increased significantly during the first year of auditory brainstem implant use in all seven children selected for cognitive evaluation.

Perceptual outcomes in children with auditory brainstem implants

In previous studies, only patients with neurofibromatosis type 2 older than 12 years have been considered as candidates for an auditory brainstem implant (ABI). Our study now extends the potential criteria to include children with other cochlear or cochlear nerve malfunctions who either would not benefit at all from a cochlear implant (e.g. cochlear nerve aplasia or avulsion) or would receive only severely compromised benefit (e.g. cochlear ossification). In our department, over the period from April 1997 to April 2004, 10 children were fitted with ABIs. Their ages ranged from 14 months to 16 years. Two children had neurofibromatosis type 2, and five bilateral cochlear nerve aplasia, 2 of whom with associated unilateral facial nerve agenesia. One of these children had previously been fitted twice with a cochlear implant in the same ear during the same session. One child was suffering from auditory neuropathy and had previously been fitted with a cochlear implant that yielded no benefit. One child showed complete cochlear ossification, one had cochlear malformations and one had profound hearing loss following a head injury. A retrosigmoid-transmeatal approach was used in the tumor patients and a retrosigmoid approach in the non-tumor patients. Correct implantation was achieved in all patients. No complications due to implantation surgery or related to ABI activation or long-term use were observed. Auditory sensations were induced in all 10 patients with various numbers of electrodes (from 5 to 15). The indications for ABI can be extended to include children with severe cochlear and/or cochlear nerve abnormalities, such as cochlear nerve aplasia, cochlear malformation or complete ossification of the cochlea, or cochlear nerve disruption due to head injury.

Advantages of the Retrosigmoid Approach in Auditory Brain Stem Implantation

From April 1997 to December 1999, six patients (five men and one woman), ranging in age from 22 to 37 years with neurofibromatosis type 2 (NF2) were operated on via the classic retrosigmoid-transmental (RS-TM) approach for removal of a vestibular schwannoma (VS) (tumor size from 12 to 40 mm) and for auditory brain stem implantation (ABI). After tumor removal, the floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleos were reached, and the ABI was inserted. More recently, an ABI was implanted via the retrosigmoid approach in a 4-year-old boy with a cochlear malformation (common cavity) associated with cochlear nerve aplasia. Electrically evoked auditory brain stem responses (EABRs) and neural response telemetry (NRT) were performed to verify the correct positioning of the inserted electrodes. No major complications related to ABI were observed. ABI has been activated to date in five of the NF2 patients. Auditory sensations with various numbers of electrodes were evoked in all patients. We consider the RS-TM approach the route of choice for ABI insertion in patients with NF2 and good hearing, offering a chance of hearing preservation, and in patients with complete cochlear ossification, severe head trauma and cochlear fracture, or nerve disruption, or a combination of these. A new indication for ABI implantation via the RS approach is presented by patients with bilateral cochlear nerve aplasia.