Auditory Neuropathy Characteristics in Children with Cochlear Nerve Deficiency

Clinical role of electrocochleography in children with auditory neuropathy spectrum disorder

OBJECTIVES

To assess electrocochleography (ECochG) to tones as an instrument to account for CI speech perception outcomes in children with auditory neuropathy spectrum disorder (ANSD).

MATERIALS & METHODS

Children (<18 years) receiving CIs for ANSD (n = 30) and non-ANSD (n = 74) etiologies of hearing loss were evaluated with ECochG using tone bursts (0.25-4 kHz). The total response (TR) is the sum of spectral peaks of responses across frequencies. The compound action potential (CAP) and the auditory nerve neurophonic (ANN) in ECochG waveforms were used to estimate nerve activity and calculate nerve score. Performance on open-set monosyllabic word tests was the outcome measure. Standard statistical methods were applied.

RESULTS

On average, TR was larger in ANSD than in non-ANSD subjects. Most ANSD (73.3%) and non-ANSD (87.8%) subjects achieved open-set speech perception; TR accounted for 33% and 20% of variability in the outcomes, respectively. In the ANSD group, the PTA accounted for 69.3% of the variability, but there was no relationship with outcomes in the non-ANSD group. In both populations, nerve score was sensitive in identifying subjects at risk for not acquiring open-set speech perception, while the CAP and the ANN were more specific.

CONCLUSION

In both subject groups, the TRs correlated with outcomes but these measures were notably larger in the ANSD group. There was also strong correlation between PTA and speech perception outcome in ANSD group. In both subject populations, weaker evidence of neural activity was related to failure to achieve open-set speech perception.

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.

Human Cochlear Histopathology Reflects Clinical Signatures of Primary Neural Degeneration

Auditory neuropathy is a significant and understudied cause of human hearing loss, diagnosed in patients who demonstrate abnormal function of the cochlear nerve despite typical function of sensory cells. Because the human inner ear cannot be visualized during life, histopathological analysis of autopsy specimens is critical to understanding the cellular mechanisms underlying this pathology. Here we present statistical models of severe primary neuronal degeneration and its relationship to pure tone audiometric thresholds and word recognition scores in comparison to age-matched control patients, spanning every decade of life. Analysis of 30 ears from 23 patients shows that severe neuronal loss correlates with elevated audiometric thresholds and poor word recognition. For each ten percent increase in total neuronal loss, average thresholds across patients at each audiometric test frequency increase by 6.0 dB hearing level (HL). As neuronal loss increases, threshold elevation proceeds more rapidly in low audiometric test frequencies than in high frequencies. Pure tone average closely agrees with word recognition scores in the case of severe neural pathology. Histopathologic study of the human inner ear continues to emphasize the need for non- or minimally invasive clinical tools capable of establishing cellular-level diagnoses.

Bony cochlear nerve canal and internal auditory canal measures predict cochlear nerve status

Objectives:

The bony cochlear nerve canal is the space between the fundus of the internal auditory canal and the base of the cochlear modiolus that carries cochlear nerve fibres. This study aimed to determine the distribution of bony labyrinth anomalies and cochlear nerve anomalies in patients with bony cochlear nerve canal and internal auditory canal atresia and stenosis, and then to compare the diameter of the bony cochlear nerve canal and internal auditory canal with cochlear nerve status.

Methods:

The study included 38 sensorineural hearing loss patients (59 ears) in whom the bony cochlear nerve canal diameter at the mid-modiolus was 1.5 mm or less. Atretic and stenotic bony cochlear nerve canals were examined separately, and internal auditory canals with a mid-point diameter of less than 2 mm were considered stenotic. Temporal bone computed tomography and magnetic resonance imaging scans were reviewed to determine cochlear nerve status.

Results:

Cochlear hypoplasia was noted in 44 out of 59 ears (75 per cent) with a bony cochlear nerve canal diameter at the mid-modiolus of 1.5 mm or less. Approximately 33 per cent of ears with bony cochlear nerve canal stenosis also had a stenotic internal auditory canal and 84 per cent had a hypoplastic or aplastic cochlear nerve. All patients with bony cochlear nerve canal atresia had cochlear nerve deficiency. The cochlear nerve was hypoplastic or aplastic when the diameter of the bony cochlear nerve canal was less than 1.5 mm and the diameter of the internal auditory canal was less than 2 mm.

Conclusion:

The cochlear nerve may be aplastic or hypoplastic even if temporal bone computed tomography findings indicate a normal cochlea. If possible, patients scheduled to receive a cochlear implant should undergo both computed tomography and magnetic resonance imaging of the temporal bone. The bony cochlear nerve canal and internal auditory canal are complementary structures, and both should be assessed to determine cochlear nerve status.

Audiological Profile of Adult Persons with Auditory Neuropathy Spectrum Disorders

BACKGROUND AND OBJECTIVES

The auditory profile of a large number of persons with late onset auditory neuropathy spectrum disorder (ANSD) is recently described in the Indian context. The purpose of study was 1) to profile data on routine audiological parameters, cortical evoked potentials, and temporal processing, 2) to analyze the benefit from hearing aids for persons with ANSD, and 3) to understand the association between benefit from hearing aids and auditory profile.

SUBJECTS AND METHODS

Thirty-eight adults with late onset ANSD and a matched group of 40 normally hearing adults participated in the study. Basic audiological tests, recording of cortical evoked potentials, and temporal processing tests were carried out on both groups of participant while only persons with ANSD were fitted with hearing aid.

RESULTS

Subjects in the two groups were significantly different on all the audiological parameters. ANSD group seemed to benefit from hearing aids variably. The mean amplitude of N2 was significantly different between normally-hearing participants and patients with ANSD.

CONCLUSIONS

Residual temporal processing, particularly amplitude modulation detection seems to be associated with benefit from hearing aids in patients with ANSD.

Assessment of cochlear nerve deficiency and its effect on normal maturation of auditory tract by diffusion kurtosis imaging and diffusion tensor imaging: A correlational approach

OBJECTIVE

The use of diffusion kurtosis imaging (DKI) and diffusion tensor imaging (DTI) was evaluated in assessing cochlear nerve deficiency (CND) and its effect on normal maturation of auditory tract.

METHODS

25 CND patients and 25 controls (age matched: 2months to 17years, gender matched) were evaluated by mean kurtosis (MK), axial kurtosis, and radial kurtosis and compared against fractional anisotropy (FA), axial and radial diffusivities in internal auditory canal (IAC), lateral lemniscus (LL) and inferior colliculus (IC). The age related changes of auditory tract were studied through Pearson correlation between estimated indices and age of both CND and control populations.

RESULTS

Significant loss of MK (IAC: 10.71%, IC: 10.87%, LL: 15.63%) was observed in CND cases as against moderate reduction in FA (IAC: 8.57%, IC: 10%, LL: 7.69%) in all three anatomical locations. Similarly, substantial decline is observed in radial kurtosis (IAC: 27.03%, IC: 33.33%, LL: 31.43%) in comparison to moderate increase in radial diffusivity (IAC: 13.46%, IC: 24.39%, LL: 24%) in CND cases. No statistically significant change was seen in both axial kurtosis and diffusivities. In control populations, MK (r=0.473, p=0.011) and radial kurtosis (r=0.418, p=0.016) correlate positively with age and had no correlation in case of CND cases. FA (r=0.356, p=0.019) minimally correlated with age in control population but showed no statistically significant correlation in CND cases (r=0.198, p=0.036).

CONCLUSION

DKI metrics performed better than DTI in assessing microstructural changes of CND. In particular, MK and radial kurtosis are found to be more sensitive enough to differentiate the normal maturation of cochlear nerve from CND cases.

Auditory neuropathy spectrum disorder (ANSD) in referrals from neonatal hearing screening at a well-baby clinic

Auditory neuropathy spectrum disorder (ANSD) is a particular kind of hearing disorder characterised by normal outer hair cell function and abnormal or absent auditory brain stem responses. Little data are available regarding the prevalence of this condition in healthy newborns. We performed a retrospective medical records review of 791 referrals from universal neonatal hearing screening (UNHS) at a well-baby clinic to investigate the prevalence of ANSD. Hearing screening was performed by automated auditory brain stem response (ABR) testing. A diagnosis of ANSD was established when ABR tracings were absent in the presence of otoacoustic emissions and/or a cochlear microphonic. Amongst 201 infants with confirmed congenital hearing loss, 13 infants were diagnosed with ANSD. The condition was unilateral in six and bilateral in seven infants. A risk factor for hearing loss could be identified in three infants. Abnormalities on magnetic resonance imaging were found in six infants; five of them had cochlear nerve deficiency.

CONCLUSION

The prevalence of ANSD was 6.5 % amongst well babies with confirmed congenital hearing loss identified through UNHS. The estimated incidence of ANSD in our population of newborns at the well-baby clinic was 0.09/1000 live births. Magnetic resonance revealed an underlying anatomical abnormality in about half of the patients.

WHAT IS KNOWN

• Auditory neuropathy dyssynchrony spectrum disorder (ANSD) is a particular form of hearing loss, mostly encountered in neonatal intensive care unit (NICU) graduates. • Little data are available on the prevalence and risk factors for ANSD in healthy newborns. What is new: • The estimated prevalence of ANSD in healthy newborns is 0.09/1000 live births. • In about half of the healthy newborns with ANSD, a structural abnormality was detected on magnetic resonance imaging of the posterior fossa/brain.

Diverse etiologies manifesting auditory neuropathy characteristics from infants with profound hearing loss and clinical implications

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder with impaired signal transmission from the inner ear to the brain. The electrophysiological characteristics of auditory neuropathy (AN characteristics) are marked with presence of otoacoustic emissions (OAE) or cochlear microphonics (CM) in the absence of auditory brainstem response (ABR). This study aimed to review etiologies related to AN characteristics from infants with profound hearing loss (HL), either unilaterally or bilaterally.

STUDY DESIGN

Prospective cohort study for thirty infants with prelingual profound HL.

METHODS

ABR, OAE, and/or CM were analyzed to identify electrophysiological characteristics. Temporal bone computed tomography and/or internal acoustic canal magnetic resonance imaging were reviewed to identify anatomical abnormalities. The electrophysiological characteristics and cochlear nerve status were analyzed according to the laterality of deafness (unilateral vs bilateral).

RESULTS

Among the total 41 ears (from 30 infants) with profound HL, 13 ears (7 (36.8%) of 19 ears with unilateral HL and 6 (27.3%) of 22 ears associated with bilateral HL) showed AN characteristics (37.1%), and 21 ears showed cochlear nerve deficiency (CND) (51.2%). AN characteristics was detected about two times more frequently in cases with CND (38.1%) than with anatomically normal cochlear nerve (20.0%), the difference not reaching a statistical significance probably due to a small sample size. Detection of AN characteristics did not differ between unilateral and bilateral profound HL, even though presence of CND was more frequently detected in cases with unilateral profound HL than with bilateral cases. There were at least five types of etiologies related to AN characteristics in 13 ears (from 10 infants) in our series depending on the laterality of deafness and presence of CND.

CONCLUSIONS

This study demonstrates that there were diverse etiologies related to AN characteristics from infants with unilateral or bilateral profound HL. Association between CND and AN characteristics is suggestive but not solid at this moment and AN characteristics is not a fully penetrant feature of CND.

The auditory characteristics of children with inner auditory canal stenosis

Conclusions This study shows that the prevalence of auditory neuropathy spectrum disorder (ANSD) in the children with inner auditory canal (IAC) stenosis is much higher than those without IAC stenosis, regardless of whether they have other inner ear anomalies. In addition, the auditory characteristics of ANSD with IAC stenosis are significantly different from those of ANSD without any middle and inner ear malformations. Objectives To describe the auditory characteristics in children with IAC stenosis as well as to examine whether the narrow inner auditory canal is associated with ANSD. Method A total of 21 children, with inner auditory canal stenosis, participated in this study. A series of auditory tests were measured. Meanwhile, a comparative study was conducted on the auditory characteristics of ANSD, based on whether the children were associated with isolated IAC stenosis. Results Wave V in the ABR was not observed in all the patients, while cochlear microphonic (CM) response was detected in 81.1% ears with stenotic IAC. Sixteen of 19 (84.2%) ears with isolated IAC stenosis had CM response present on auditory brainstem responses (ABR) waveforms. There was no significant difference in ANSD characteristics between the children with and without isolated IAC stenosis.

A Prospective Longitudinal Study of U.S. Children Unable to Achieve Open-Set Speech Recognition 5 Years After Cochlear Implantation

OBJECTIVE

To identify characteristics associated with the inability to progress to open-set speech recognition in children 5 years after cochlear implantation.

STUDY DESIGN

Prospective, longitudinal, and multidimensional assessment of auditory development for 5 years.

SETTING

Six tertiary cochlear implant (CI) referral centers in the United States.

PATIENTS

Children with severe-to-profound hearing loss who underwent implantation before age 5 years enrolled in the Childhood Development after Cochlear Implantation study, categorized by level of speech recognition ability.

INTERVENTION(S)

Cochlear implantation before 5 years of age and annual assessment of emergent speech recognition skills.

MAIN OUTCOME MEASURE(S)

Progression to open-set speech recognition by 5 years after implantation.

RESULTS

Less functional hearing before implantation, older age at onset of amplification, lower maternal sensitivity to communication needs, minority status, and complicated perinatal history were associated with the inability to obtain open-set speech recognition by 5 years.

CONCLUSION

Characteristics of a subpopulation of children with CIs associated with an inability to achieve open-set speech recognition after 5 years of CI experience were investigated. These data distinguish pediatric CI recipients at risk for poor auditory development and highlight areas for future interventions to enhance support of early implantation.

Nervus Intermedius Guides Auditory Brainstem Implant Surgery in Children with Cochlear Nerve Deficiency

OBJECTIVE

To investigate the anatomic features of the nervus intermedius and cranial nerve VII in children with cochlear nerve deficiency and to verify whether the nervus intermedius can provide an additional landmark to help guide placement of the auditory brainstem implant electrode.

STUDY DESIGN

Case series with chart review.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

High-definition video was captured during retrosigmoid surgery in 64 children (mean age, 3.91 ± 2.83 years) undergoing auditory brainstem implant placement. These videos were examined with particular reference to the number and variety of nervus intermedius bundles and any associated facial nerve anomalies.

RESULTS

Absence of cranial nerves VI, VII, and VIII was observed in 3, 6, and all 64 children, respectively. Fifteen children had several abnormalities of the facial nerve in the cerebellopontine angle. Anatomic identification of the facial nerve and the bundles composing the nervus intermedius was possible in 46 children. In 12 children, identification was possible with the assistance of intraoperative monitoring. The number of bundles composing the nervus intermedius varied from 1 to 6. The nervus intermedius and cranial nerve IX were useful landmarks for identifying the foramen of Luschka of the lateral recess.

CONCLUSION

The nervus intermedius provides an additional landmark during auditory brainstem microsurgery since it was identified in all subjects. The nervus intermedius anatomy and its topographic relationship with the neurovascular structures around the foramen of Luschka have been described for the first time in children with cochlear nerve deficiency.

Pathophysiological mechanisms and functional hearing consequences of auditory neuropathy

The effects of inner ear abnormality on audibility have been explored since the early 20th century when sound detection measures were first used to define and quantify 'hearing loss'. The development in the 1970s of objective measures of cochlear hair cell function (cochlear microphonics, otoacoustic emissions, summating potentials) and auditory nerve/brainstem activity (auditory brainstem responses) have made it possible to distinguish both synaptic and auditory nerve disorders from sensory receptor loss. This distinction is critically important when considering aetiology and management. In this review we address the clinical and pathophysiological features of auditory neuropathy that distinguish site(s) of dysfunction. We describe the diagnostic criteria for: (i) presynaptic disorders affecting inner hair cells and ribbon synapses; (ii) postsynaptic disorders affecting unmyelinated auditory nerve dendrites; (iii) postsynaptic disorders affecting auditory ganglion cells and their myelinated axons and dendrites; and (iv) central neural pathway disorders affecting the auditory brainstem. We review data and principles to identify treatment options for affected patients and explore their benefits as a function of site of lesion.

Auditory Neuropathy/Dys-Synchrony Disorder: Diagnosis and Management

Auditory neuropathy/dys-synchrony disorder affects neural responses, either directly or indirectly. Patients may demonstrate good ability to detect sound, but have significant difficulty listening in noise. Clinical auditory physiologic measures are used to characterize cochlear, eighth nerve, and brainstem function, and are needed to accurately identify this disorder. Cochlear implants provide benefit to many patients, and some patients derive benefit from amplification. This disorder can be identified and managed in infants, may have later onset, may be a part of a syndrome, and may include fluctuation in hearing ability.

Neural Response Telemetry Thresholds in Patients with Cochlear Nerve Canal Stenosis

Objective

To explore neural response telemetry (NRT) thresholds in patients with stenotic versus normal cochlear nerve canals.

Study Design

Case series with chart review.

Setting

Tertiary referral center.

Subjects and Methods

Thirty pediatric patients with profound sensorineural hearing loss in at least 1 ear and no benefit from amplification underwent computed tomography imaging of the temporal bones. They were divided into 3 groups according to the diameter of the cochlear nerve canal: group A, <1.5 mm; group B, 1.5 to 1.7 mm; group C, 1.8 to 2.1 mm. All patients underwent cochlear implantation with full insertion of all electrodes. NRT was performed both intraoperatively and 6 months postoperatively in all patients; thresholds of electrodes 1, 11, and 22 were compared.

Results

Per analysis of variance, intraoperative and 6-month postoperative NRT thresholds were both significantly different among groups A, B, and C at electrodes 1 and 22 but not at electrode 11. On intergroup analysis, group A showed statistically higher thresholds than those of groups B and C; however, no difference was found between groups B and C.

Conclusion

Cochlear nerve canal stenosis, defined as a canal diameter <1.5 mm, is associated with significantly increased NRT thresholds, which may play a role in postimplant performance.

Cortical development and neuroplasticity in Auditory Neuropathy Spectrum Disorder

Cortical development is dependent to a large extent on stimulus-driven input. Auditory Neuropathy Spectrum Disorder (ANSD) is a recently described form of hearing impairment where neural dys-synchrony is the predominant characteristic. Children with ANSD provide a unique platform to examine the effects of asynchronous and degraded afferent stimulation on cortical auditory neuroplasticity and behavioral processing of sound. In this review, we describe patterns of auditory cortical maturation in children with ANSD. The disruption of cortical maturation that leads to these various patterns includes high levels of intra-individual cortical variability and deficits in cortical phase synchronization of oscillatory neural responses. These neurodevelopmental changes, which are constrained by sensitive periods for central auditory maturation, are correlated with behavioral outcomes for children with ANSD. Overall, we hypothesize that patterns of cortical development in children with ANSD appear to be markers of the severity of the underlying neural dys-synchrony, providing prognostic indicators of success of clinical intervention with amplification and/or electrical stimulation. This article is part of a Special Issue entitled <Auditory Synaptology>.

Asymmetric and unilateral hearing loss in children

Asymmetric and unilateral hearing losses in children have traditionally been underappreciated, but health care practitioners are now beginning to understand their effect on development and the underlying pathophysiologic mechanisms. The common wisdom among medical and educational professionals has been that at least one normal-hearing or near-normal-hearing ear was sufficient for typical speech and language development in children. The objective of this review is to illustrate, to the non-otolaryngologist, the consequences of asymmetric and unilateral hearing loss in children on developmental and educational outcomes. Etiology, detection, and management are also discussed. Lastly, implications for further research are considered.

Bony cochlear nerve canal stenosis and speech discrimination in pediatric unilateral hearing loss

OBJECTIVES/HYPOTHESIS

To examine the relationship between bony cochlear nerve canal (BCNC) width, degree of hearing loss, and speech discrimination in children with unilateral sensorineural hearing loss (USNHL).

STUDY DESIGN

Retrospective chart review (case-control study).

METHODS

Audiometric database was cross-referenced with radiologic database at pediatric tertiary care facility to identify children with USNHL and temporal bone computed tomography. BCNC widths were measured independently by two radiologists blinded to affected ear. Regression analyses investigated associations among variables.

RESULTS

One hundred and sixty children with USNHL had temporal bone imaging. Mean BCNC width was significantly smaller in affected ears, P = 0.0001. Narrower width was associated with more severe hearing loss, P = 0.01. Among children who had narrower cochlear nerve canals in affected ears compared to unaffected ears, smaller width was associated with lower speech discrimination score, P = 0.03. Increasing asymmetry in BCNC width between affected and unaffected ears was associated with poorer discrimination scores, P = 0.02. Among ears with asymmetrically smaller cochlear nerve canals, a 1-mm reduction in cochlear canal width between the normal and affected ear was associated with 30.4% lower word recognition score percentage in the affected ear, P = < 0.001.

CONCLUSION

There is a significant association between BCNC stenosis and impaired speech discrimination, independent of degree of hearing loss. Further investigation is needed to determine whether BCNC stenosis is a poor prognostic factor for auditory rehabilitation.

Auditory neuropathy

Neural disorders of the auditory nerve are associated with particular disorders of auditory perceptions dependent on processing of acoustic temporal cues. These include: (1) speech perception; (2) localizing a sound's origin in space; and (3) identifying sounds in background noise. Auditory neuropathy (AN) is a consequence of: (1) presynaptic disorders affecting inner hair cell ribbon synapses; (2) postsynaptic disorders of auditory nerve dendrites; and (3) postsynaptic disorders of auditory nerve axons. The etiologies of these disorders are diverse, similar to other cranial or peripheral neuropathies. The pathologies cause attenuated and dyssynchronous auditory nerve discharges. Therapies and management of patients with AN are reviewed.

Does parental experience of the diagnosis and intervention process differ for children with auditory neuropathy?

OBJECTIVES

This study compared parental experience of the audiological diagnosis and intervention process in children with auditory neuropathy spectrum disorder and sensory neural hearing loss.

METHODS

A matched group survey was used with parents of children with auditory neuropathy spectrum disorder (ANSD) matched with a control group of parents and children with sensorineural hearing loss (SNHL). The two groups were matched in terms of the child's gender, age, amplifications used, social background and utilisation of private or public health care sectors. An interview questionnaire, consisting of 45 questions in six categories (1. biographic information, 2. experiences of audiological diagnosis, 3. hearing aid benefit, 4. parental experience of the rehabilitation decision making process, 5. parental needs for emotional support and 6. parental needs for information) using a 5-point Likert scale for categories 2-7, was administered by the same audiologist.

RESULTS

Children with ANSD experienced a significantly longer waiting period from diagnosis to hearing aid fitting (p=0.025) and/or cochlear implantation (p=0.036). Parents of children with ANSD reported significantly different experiences of the diagnostic process (p=0.001) with poorer understanding of the diagnosis and reporting insufficient time allowed for asking questions. During the rehabilitation decision-making process 47% of parents with ANSD children (vs. 0% of parents with SNHL children) reported receiving conflicting information. Parents of children with ANSD were also less likely to recommend hearing aids to other parents. Information needs were similar between groups.

CONCLUSIONS

Parents of children with ANSD have different experiences and greater uncertainty during the diagnostic and rehabilitation process. Providing regular consultation and structured timelines through the diagnostic process and decision-making process may facilitate this process with less uncertainty.

Cochlear implantation in unique pediatric populations

PURPOSE OF REVIEW

Over the last decade, the selection criteria for cochlear implantation have expanded to include children with special auditory, otologic, and medical problems. Included within this expanded group of candidates are those children with auditory neuropathy spectrum disorder, cochleovestibular malformations, cochlear nerve deficiency, associated syndromes, as well as multiple medical and developmental disorders. Definitive indications for cochlear implantation in these unique pediatric populations are in evolution. This review will provide an overview of managing and habilitating hearing loss within these populations with specific focus on cochlear implantation as a treatment option.

RECENT FINDINGS

Cochlear implants have been successfully implanted in children within unique populations with variable results. Evaluation for cochlear implant candidacy includes the core components of a full medical, audiologic, and speech and language evaluations. When considering candidacy in these children, additional aspects to consider include disorder-specific surgical considerations and child/caregiver counseling regarding reasonable postimplantation outcome expectations.

SUMMARY

Cochlear implants are accepted as the standard of care for improving hearing and speech development in children with severe-to-profound hearing loss. However, children with sensorineural hearing loss who meet established audiologic criteria for cochlear implantation may have unique audiologic, medical, and anatomic characteristics that necessitate special consideration regarding cochlear implantation candidacy and outcome. Individualized preoperative candidacy and counseling, surgical evaluation, and reasonable postoperative outcome expectations should be taken into account in the management of these children.

Unilateral cochlear nerve deficiency in children

OBJECTIVE

Cochlear nerve deficiency (CND) is increasingly diagnosed in children with sensorineural hearing loss (SNHL). We sought to determine the prevalence of CND, its imaging characteristics, and correlations with audiologic phenotype in children with unilateral SNHL.

DESIGN

Case series with chart review.

SETTING

Tertiary pediatric hospital.

SUBJECTS/METHODS

In 128 consecutive children with unilateral SNHL who underwent high-resolution magnetic resonance imaging, the diameters, area, and signal intensity of the cochlear nerve (CN) were measured and normalized to the ipsilateral facial nerve. Presence of CND was determined by comparison to normative data. Relationships among hearing loss severity, progression, and nerve size were investigated.

RESULTS

Cochlear nerve deficiency was present in 26% of children with unilateral SNHL. Its prevalence was higher (48%) in severe to profound SNHL, especially when in infants (100%). Width of the bony cochlear nerve canal (BCNC) correlated strongly with relative CN diameter, density, and area (R = 0.5); furthermore, a narrow BCNC (<1.7 mm) strongly predicted CND. Severity of hearing loss modestly correlated with nerve size, although significant variability was observed. Progression never occurred unless there were other inner ear malformations, whereas in the non-CND group, it occurred in 22%. Ophthalmologic abnormalities were very common (67%) in CND children, particularly oculomotor disturbances.

CONCLUSION

Cochlear nerve deficiency is a common cause of unilateral SNHL, particularly in congenital unilateral deafness. Width of the BCNC effectively predicts CND, a finding useful when only computed tomography imaging is available. In an ear with CND, hearing can be expected to remain stable over time. Diagnosis should prompt evaluation by an ophthalmologist.

Cochlear implant-evoked cortical activation in children with cochlear nerve deficiency

OBJECTIVE

To report the results of cochlear implant-elicited cortical auditory evoked potentials (eCAEP) in children with cochlear nerve deficiency (CND).

STUDY DESIGN

Case control series.

SETTING

Tertiary academic referral center.

PATIENTS

Seven children with CND that have a cochlear implant in their affected ear. Four children without CND served as controls.

INTERVENTION(S)

eCAEPs were elicited by activation of individual cochlear implant electrodes.

MAIN OUTCOME MEASURE(S)

Onset responses (P1-N1-P2 complex).

RESULTS

Three of 7 CND children demonstrated eCAEP responses across a broad range of electrodes despite having limited or no open set speech perception abilities using their implants. Two of these children had eCAEPs that were characterized by substantial variability in latency, amplitude, and number of electrodes with identifiable responses. The remaining 4 ears with CND and poor speech perception had multiphasic responses that are inconsistent with eCAEPs. Non-CND ears with excellent speech perception abilities demonstrated robust responses on all electrodes stimulated.

CONCLUSION

Abent eCAEP responses were indicative of poor open-set speech perception skills in all cases. However, eCAEP onset responses were measurable in some children with imaging evidence of CND, indicating probable cochlear nerve hypoplasia rather than aplasia. That some children with CND and poor speech perception had robust eCAEPs in some instances makes this particular measure of limited use for predicting good speech perception outcomes after cochlear implantation in these children. The origin of multiphasic responses remains to be determined but may be of somatosensory origin in some instances.

Speech processing disorder in neural hearing loss

Deficits in central auditory processing may occur in a variety of clinical conditions including traumatic brain injury, neurodegenerative disease, auditory neuropathy/dyssynchrony syndrome, neurological disorders associated with aging, and aphasia. Deficits in central auditory processing of a more subtle nature have also been studied extensively in neurodevelopmental disorders in children with learning disabilities, ADD, and developmental language disorders. Illustrative cases are reviewed demonstrating the use of an audiological test battery in patients with auditory neuropathy/dyssynchrony syndrome, bilateral lesions to the inferior colliculi, and bilateral lesions to the temporal lobes. Electrophysiological tests of auditory function were utilized to define the locus of dysfunction at neural levels ranging from the auditory nerve, midbrain, and cortical levels.

[Cases of pediatric hearing impairment with bilateral stenosis of the bony cochlear nerve canal: bilateral stenosis of bony cochlear nerve canal]

Cochlear nerve deficiency (CND) is diagnosed with magnetic resonance imaging (MRI) by an absent or small cochlear nerve. A small or absent bony cochlear nerve canal (BCNC) detected with computed tomography (CT) has been also considered as CND. We reviewed five bilateral hearing impaired children with BCNC. All patients were born maturely at full-term birth. Two of them had undergone newborn hearing screening (NHS), one passed and the other was referred in only one ear. Among five children, only one had a small internal auditory canal (IAC) diagnosed with CT. Two children with intracranial abnormalities also had cochlear anomalies without a small IAC. Hearing aids showed some effectiveness in two patients with normal-sized IACs, and they could communicate with normal speech using hearing aids. One with a small-sized IAC was unable to communicate with speech using hearing aids. The efficacy of hearing aids in the other 2 patients has not been evaluated yet. We concluded that patients with small or absent BCNCs showed various audiometorical findings and clinical courses.

Unilateral cochlear nerve hypoplasia in children with mild to moderate hearing loss

CONCLUSION

Even if hearing loss is mild to moderate, the presence of cochlear nerve (CN) hypoplasia associated with retrocochlear disorders should be considered.

OBJECTIVES

CN hypoplasia is a term that refers to an absent cochlear nerve on high-resolution magnetic resonance imaging (MRI). Most cases of CN hypoplasia are associated with profound hearing loss. The present study reports six pediatric cases of unilateral CN hypoplasia with mild to moderate hearing loss.

METHODS

Between May 2008 and April 2011, pure-tone hearing tests were performed in 17 patients who were diagnosed with CN hypoplasia on high resolution for evaluation of unilateral sensorineural hearing loss at the National Center for Child Health and Development. Of these, six patients had average hearing levels in the affected ears of < 60 dB and were therefore included in this study.

RESULTS

All six ears with CN hypoplasia were associated with CN canal stenosis. DPOAEs were present in one (17%) of the six affected ears. The ABR thresholds of the ears with CN hypoplasia were significantly elevated compared with 1-4 kHz pure-tone hearing levels in one of three cases. In two of five cases, the maximum word recognition scores of the affected ears were poor compared with pure-tone hearing levels.

Benefit of a commercially available cochlear implant processor with dual-microphone beamforming: a multi-center study

OBJECTIVE

Previous research shows that cochlear implant users experience significant difficulty with speech perception in noisy listening situations. There is a paucity of research evaluating the potential improvement in speech recognition in noise provided by a dual-microphone directional system in a commercial implant sound processor. The primary objective of this study was to compare speech recognition in quiet and in noise for the Nucleus Freedom and Nucleus 5 CP810 sound processors set to the manufacturer's default user programs for quiet and noisy environments.

RESEARCH DESIGN

Crossover with repeated-measures design.

SETTING

This multi-center study was conducted across four cochlear implant clinics in the United States.

PATIENTS

Thirty-five adults with unilateral Nucleus Freedom cochlear implants. All subjects had used their cochlear implant for at least 6 months and had substantial open-set word recognition as evidenced by a score of at least 40% correct on the Consonant-Nucleus-Consonant (CNC) monosyllabic word recognition test in quiet.

INTERVENTION

All subjects (previous users of the Nucleus Freedom sound processor) were fitted with the Nucleus 5 sound processor. Performance was assessed while these subjects used each sound processor in the default user program the manufacturer recommends for quiet and noisy conditions.

MAIN OUTCOME MEASURES

Speech recognition was assessed with CNC monosyllabic words in quiet and sentences in noise from the BKB-SIN (Bamford-Kowal-Bench Sentences in Noise) test. The data were analyzed with descriptive statistics and performance with each processor in each listening condition was compared using a repeated-measures analysis of variance.

RESULTS

Word recognition in quiet was significantly better with the Nucleus 5 sound processor when compared to performance with the Nucleus Freedom processor. In noise, the Nucleus 5 sound processor also provided a significant improvement in speech recognition relative to the performance with the Nucleus Freedom.

CONCLUSION

The results of the study suggest that the Nucleus 5 sound processor provides significantly better speech recognition in quiet and in noise when compared with performance with the Nucleus Freedom processor.

Plasticity in the developing auditory cortex: evidence from children with sensorineural hearing loss and auditory neuropathy spectrum disorder

The developing auditory cortex is highly plastic. As such, the cortex is both primed to mature normally and at risk for reorganizing abnormally, depending upon numerous factors that determine central maturation. From a clinical perspective, at least two major components of development can be manipulated: (1) input to the cortex and (2) the timing of cortical input. Children with sensorineural hearing loss (SNHL) and auditory neuropathy spectrum disorder (ANSD) have provided a model of early deprivation of sensory input to the cortex and demonstrated the resulting plasticity and development that can occur upon introduction of stimulation. In this article, we review several fundamental principles of cortical development and plasticity and discuss the clinical applications in children with SNHL and ANSD who receive intervention with hearing aids and/or cochlear implants.

Assessment of cochlear implant candidacy in patients with cochlear nerve deficiency using the P1 CAEP biomarker

OBJECTIVE

The goal of this report was to ascertain the efficacy of the P1 cortical auditory evoked potential (CAEP) biomarker as an objective tool to assist in the evaluation of cochlear implant (CI) candidacy in children with a radiological diagnosis of cochlear nerve deficiency (CND).

METHODS

Retrospective case study review of audiological and radiological findings was performed in four pediatric patients identified with CND and severe-to-profound sensorineural hearing loss. Cortical auditory evoked potential testing was conducted, and the presence and latency of the P1 component were analyzed.

RESULTS

Three out of four children demonstrated robust P1 CAEP responses, indicating activation of the central auditory pathways by auditory stimulation, despite the diagnosis of CND. These children were considered good candidates for cochlear implantation.

DISCUSSION

Although cochlear implantation in children is a fairly routine procedure, cases exist for which implant candidacy is questionable. Among these cases are children with CND. In these children, cochlear implantation may be contraindicated due to the likelihood that the implant electrodes may not stimulate the VIII nerve adequately. Magnetic resonance imaging (MRI) is considered the gold standard in the assessment of CND, but this measure is not always sufficient to determine CI candidacy in cases of CND. The addition of the P1 CAEP measurement to the usual electrophysiological, audiometric, and radiological test battery may prove to be useful in determining CI options for children with CND.

Unilateral auditory neuropathy caused by cochlear nerve deficiency

Objective. To explore possible corelationship between the cochlear nerve deficiency (CND) and unilateral auditory neuropathy (AN). Methods. From a database of 85 patients with unilateral profound sensorineural hearing loss, eight who presented with evoked otoacoustic emissions (EOAEs) or cochlear microphonic (CM) in the affected ear were diagnosed with unilateral AN. Audiological and radiological records in eight patients with unilateral AN were retrospectively reviewed. Results. Eight cases were diagnosed as having unilateral AN caused by CND. Seven had type "A" tympanogram with normal EOAE in both ears. The other patient had unilateral type "B" tympanogram and absent OAE but CM recorded, consistent with middle ear effusion in the affected ear. For all the ears involved in the study, auditory brainstem responses (ABRs) were either absent or responded to the maximum output and the neural responses from the cochlea were not revealed when viewed by means of the oblique sagittal MRI on the internal auditory canal. Conclusion. Cochlear nerve deficiency can be seen by electrophysiological evidence and may be a significant cause of unilateral AN. Inclined sagittal MRI of the internal auditory canal is recommended for the diagnosis of this disorder.

Characteristics of cochlear microphonics in infants and young children with auditory neuropathy

CONCLUSIONS

Cochlear microphonics (CMs) play an important role in the diagnosis of auditory neuropathy (AN). It is necessary and helpful to diagnose the sites-of-lesion in infants and children with AN by analyzing the patterns of CM amplitudes and I/O functions together.

OBJECTIVES

To investigate the characteristics and clinical significance of CMs in the diagnosis of AN among infants and children.

METHODS

A total of 36 infants and children (16 males and 20 females) were divided into two groups. Group A included 15 children (30 ears) with auditory brainstem response (ABR) absent and distortion product otoacoustic emissions (DPOAEs) present and group B included 21 children (30 ears) with ABR absent and DPOAEs absent. Fifteen normal-hearing infants (30 ears) made up the control group. Click eliciting CMs were recorded at stimulus levels of 100, 90, 80, and 70 dB nHL for each ear using a button electrode placed at the top of the forehead. A tube-clamping method was used to distinguish CMs from artifacts, and an averaging algorithm was used to obtain a clear CM waveform. The time delay and amplitude of CMs were measured in both children with AN and normal-hearing infants on (C-R)/2 waveforms, and an I/O function curve for each group was plotted with the stimulating level as input and the CM amplitude as output.

RESULTS

The largest identifiable CMs were generally found between 0.5 and 0.8 ms after stimulation with mean delay of 0.63 ± 0.04 ms in both group A and the control group, and 0.63 ± 0.07 ms in group B. There was no significant difference between the AN group and the control group in CM time delay. There was no significant difference (p > 0.05) between group A (AN with OAEs present, 0.47 ± 0.15 μV) and the control group (0.45 ± 0.13 μV) in CM amplitude, while CM amplitudes in children with AN with DPOAEs absent (0.24 ± 0.08 μV) were significantly lower than those in either the control group or group A (p < 0.01). The amplitude of CMs reduced with stimulus intensity in all the subjects. There was obvious nonlinearity in group A and the control group, while there was a more linear tendency in amplitude increasing on the I/O function curve in group B.

Unilateral auditory neuropathy spectrum disorder

CONCLUSIONS

The majority of the patients with unilateral auditory neuropathy spectrum disorder (UANSD) were pediatric and mostly showed a great degree of hearing loss when diagnosed. Abnormal auditory brainstem response (ABR) and preserved otoacoustic emissions (OAEs) and/or cochlear microphonics (CM) were important features to differentiate it from common sensorineural deafness and central nerve hearing loss.

OBJECTIVE

To identify the clinical characteristics of patients with UANSD.

METHODS

This was a retrospective study involving 14 patients diagnosed as having UANSD between 2004 and 2010 in the Chinese PLA Hospital.

RESULTS

In all, 50% of the cases were males (1:1 sex ratio) and the average age of onset was 4.1 years. Of the 14 affected ears with UANSD in these cases, 6 were left-sided, while 8 were right-sided. Of the 14 contralateral ears, 4 presented with sensorineural hearing loss, while the other 10 showed normal hearing. The degree of hearing loss in the 14 affected ears varied, including moderate in 1, moderately severe in 4, severe in 5, and profound in 4. ABRs were absent in the 14 affected ears, while the OAEs, and/or CM were present.

Audiologic management of auditory neuropathy spectrum disorder in children: a systematic review of the literature

PURPOSE

This review summarizes current evidence related to the audiologic management of children with auditory neuropathy spectrum disorder (ANSD).

METHOD

A systematic search of the literature was conducted in 25 electronic databases (e.g., PubMed, CINAHL, and ERIC) using key words such as auditory neuropathy, auditory neuropathy spectrum disorder, auditory neuropathy/dyssynchrony, and hearing loss. Eighteen studies met the inclusion criteria by addressing 1 or more of 8 clinical questions. Studies were evaluated for methodological quality, and data regarding participant, intervention, and outcome variables are reported.

RESULTS

Fifteen of the 18 studies addressed the use of cochlear implantation, and 4 addressed conventional acoustic amplification. All participants demonstrated improved auditory performance; however, all 18 studies were considered exploratory, and many had methodological limitations.

CONCLUSION

The clinical evidence related to intervention for ANSD is at a very preliminary stage. Additional research is needed to address the efficacy of acoustic amplification and cochlear implantation in children with ANSD and the impact of this disorder on developmental outcomes.

Cochlear implantation in children with labyrinthine anomalies and cochlear nerve deficiency: implications for auditory brainstem implantation

OBJECTIVES/HYPOTHESIS

Compare outcomes among children with inner ear malformations and/or cochlear nerve deficiency (CND) who have received a cochlear implant (CI).

STUDY DESIGN

Individual retrospective cohort study from 1993 to 2010.

METHODS

A select cohort of 76 children was identified. Imaging characteristics, operative findings, complications, mapping parameters, and performance were assessed. Comparisons among the different groups were undertaken.

RESULTS

Surgery was mostly uncomplicated. Nearly all children demonstrated behavioral responses to CI stimulation irrespective of inner ear morphology or the presence of CND. Children with CND had higher pure tone averages (PTAs) and required greater charge for stimulation than other malformation types. Open-set speech perception was achieved in 100% of children with incomplete partition-enlarged vestibular aqueduct (IP-EVA), 50% of those with hypoplastic malformations, and 19% of CND cases. Robust responses on eighth nerve compound action potential (ECAP) testing through the implant was associated with higher levels of speech perception. Manually supplemented communication strategies were more common among children with hypoplastic malformations (69%) and CND (95%) than those with IP-EVA (18%).

CONCLUSIONS

Children with IP-EVA malformations have an excellent prognosis for developing open-set speech perception and using oral communication modes following CI. On the contrary, children with severe malformations or CND may have elevated charge requirements for attaining sound detection alone. These children's prognosis for obtaining open-set speech understanding, using exclusive oral communication, and participating in mainstream education is more limited. These findings have important implications for considering alternative forms of intervention such as auditory brainstem implantation and/or supplementation with visually based communication strategies.

Auditory impairment in infants at risk for bilirubin-induced neurologic dysfunction

Classical and subtypes of kernicterus associated with bilirubin toxicity can be differentiated in part with physiological auditory measures that include auditory-evoked potentials and measures of cochlear integrity. The combination of these auditory measures suggests that bilirubin exposure results in auditory system damage initially at the level of the brainstem, progressing to the level of the VIII cranial nerve and then to greater neural centers. There is no evidence of neural damage at the level of the cochlea. Auditory neural damage from bilirubin toxicity ranges from neural timing deficits, including neural firing delays and dyssynchrony, to neural response reduction and even elimination of auditory neural responses. This condition is comprehensively described as auditory neuropathy spectrum disorder. Independent measures of cochlear function and auditory neural function up to the level of the brainstem can effectively diagnose auditory neural damage resulting from bilirubin neurotoxicity. Intervention, including cochlear implants can be effective.

Pediatric sensorineural hearing loss, part 1: Practical aspects for neuroradiologists

SNHL is a major cause of childhood disability worldwide, affecting 6 in 1000 children. For children with prelingual hearing loss, early diagnosis and treatment is critical to optimizing speech and language development, academic achievement, and social and emotional development. Cross-sectional imaging has come to play an important role in the evaluation of children with SNHL because otolaryngologists routinely order either CT or MR imaging to assess the anatomy of the inner ears, to identify causes of hearing loss, and to provide prognostic information related to potential treatments. In this article, which is the first in a 2-part series, we describe the basic clinical approach to imaging of children with SNHL, including the utility of CT and MR imaging of the temporal bones; we review the most recent proposed classification of inner ear malformations; and we discuss nonsyndromic congenital causes of childhood SNHL.