Hypoplastic Cochlear Nerve Research Articles

Congenital Unilateral Hearing Loss from Cochlear Nerve Canal Stenosis

A 2-month-old baby girl presented with a failed neonatal otoacoustic emission (OAE) hearing screening in the left ear. Combined Auditory Brainstem Response/Auditory Steady-State Response (ABR/ASSR) testing confirmed the presence of a unilateral left moderate to severe hearing loss. No Joint Committee on Infant Hearing (JCIH) risk factors for early childhood hearing loss1 were identified. She subsequently underwent computed tomography (CT) of the temporal bones to determine the presence of any inner ear malformation. No abnormalities of the internal auditory canal, cochlea, semicircular canals and ossicles were noted by the radiologist, and the study was officially reported as a “normal temporal bone CT scan.” Independent review of the CT imaging revealed the presence of a visually apparent disparity in the width of the cochlear nerve canals. (Figure 1) Measurement of the cochlear nerve canal width in the axial plane parallel to the infraorbitomeatal line2 using the length measurement tool in the DICOM imaging software (RadiAnt DICOM Viewer, Version 2024.1, Medixant) indicated a cochlear nerve canal width of 2.18 mm on the right and 1.02 mm on the left. (Figure 2) Applying the suggested cutoff point of 1.2 mm as described by Lin et al.,2 we identified the presence of left cochlear nerve canal stenosis as the etiology of the congenital unilateral hearing loss. The cochlear nerve canal, which has also been referred to as the bony canal for the cochlear nerve (BCNC), cochlear aperture, and cochlear fosette, is the bony transition point between the internal auditory canal and the cochlear modiolus. A relationship between a hypoplastic cochlear nerve canal and congenital sensorineural hearing loss was first suggested by Fatterpekar et al. in 2000.3 Subsequent studies confirmed the association between cochlear nerve canal stenosis and sensorineural hearing loss that ranges from near-normal to profound, with a statistically significant relationship between the degree of hearing loss and the degree of stenosis.4 Various cutoff points to define stenosis of the cochlear nerve canal have been identified in the medical literature. These cutoff points range from 1.2 mm to 1.7 mm when the canal width is measured in the axial plane.2 This particular case demonstrated clear-cut evidence of cochlear nerve canal stenosis, as it satisfied the smallest cutoff criteria (< 1.2 mm) seen in the medical literature. The identification of cochlear nerve canal stenosis as the cause of congenital sensorineural hearing loss is important not only from a diagnostic point, but also from a prognostic perspective. Cochlear nerve deficiency has been noted to be highly prevalent among pediatric patients with cochlear nerve canal stenosis,5 and this has significant negative implications in relation to rehabilitation with external hearing devices and cochlear implants.

Evaluation of Cochlear Implantation in Children With Cochlear Nerve Absence or Deficiency.

To identify associations between cochleovestibular anatomy findings and hearing outcomes found in children with imaging evidence of an absent or hypoplastic cochlear nerve treated with cochlear implantation (CI). retrospective review. Cochlear implant program at tertiary care center. A retrospective review was performed to identify children with imaging evidence of cochlear nerve absence or deficiency who underwent CI evaluation. High-resolution 3-dimensional T2-weighted magnetic resonance imaging in the oblique sagittal and axial planes were reviewed by a neuroradiologist to identify cochleovestibular anatomy. Hearing was assessed pre and postoperatively with Speech Perception Category scores. Seven CI recipients were identified (n = 10 ears) who had bilateral severe to profound sensorineural hearing loss with lack of auditory development with binaural hearing aid trial and imaging evidence of cochlear nerve aplasia/hypoplasia. All ears had 2 nerves in the cerebellopontine angle (100%, n = 10), half of the ears had evidence of 2 or less nerves in the internal auditory canal (IAC). All children showed large improvement in speech perception after CI. Our experience with CIs for children with absent or hypoplastic cochlear nerves demonstrates that CI can be a viable option in select patients who satisfy preoperative audiological criteria. Radiological identification of a hypoplastic or aplastic cochlear nerve does not preclude auditory innervation of the cochlea. CI recipients in this subgroup must be counseled on difficulty in predicting postimplantation language and speech outcomes, and cautioned about facial nerve stimulation.

Early cochlear implantation for children with single sided deafness

ObjectivesSingle-sided deafness (SSD) can have consequences for a child's language, educational, and social development. A cochlear implant (CI) is the only device which can restore true binaural hearing, yet they are only approved for children with (SSD) over the age of five in the United States. Reports on speech perception outcomes for children implanted at a younger age are limited. The present study aims to examine the effects of age at implantation, duration of deafness, hearing loss etiology, and presence of additional disabilities on device usage and speech perception outcomes. MethodsA retrospective chart review was used to examine demographics and speech perception outcomes for 18 children implanted at age five or younger. ResultsSpeech perception results were highly variable, with some children deriving significant benefit and others demonstrating no sound awareness through the implant alone. Age at implantation and duration of deafness did not have a clear impact on outcomes. Device usage was low in many children, often those with anatomical abnormalities such as a hypoplastic cochlear nerve. There are challenges to assessing speech perception in young children with SSD, leading to a lack of standardized outcome measures. ConclusionsEarly CI for children with SSD may improve speech perception, but benefit is not guaranteed. Candidacy evaluation should consider both medical and audiological factors, in addition to the degree of family support and realistic expectations. Caution is especially warranted in children with significant anatomical anomalies.

Cochlear Implantation in Very Young Children With Single-Sided Deafness.

Cochlear implants (CIs) for single-sided deafness (SSD) have only been approved for patients 5 years and older despite data supporting that younger children can also benefit from implantation. This study describes our institution's experience with CI for SSD in children 5 years and younger. Case series with chart review. Tertiary referral center. A case series with chart review identified 19 patients up to age 5 years who underwent CI for SSD between 2014 and 2022. Baseline characteristics, perioperative complications, device usage, and speech outcomes were collected. The median age at CI was 2.8 (range, 1.0-5.4) years, with 15 (79%) patients being below age 5 at implantation. Etiologies of hearing loss were idiopathic (n = 8), cytomegalovirus (n = 4), enlarged vestibular aqueduct (n = 3), hypoplastic cochlear nerve (n = 3), and meningitis (n = 1). The median preoperative pure-tone average was 90 (range, 75-120) and 20 (range, 5-35) dB eHL in the poorand better hearing ears, respectively. No patients had postoperative complications. Twelve patients achieved consistent device use (average, 9 h/d). Three of the seven who were not consistent users had hypoplastic cochlear nerves and/or developmental delays. The three patients with available preoperative and postoperative speech testing showed significant benefits, and five patients with available postoperative testing demonstrated speech recognition in the implanted ear when isolated from the better ear. CI can safely be performed in younger children with SSD. Patients and families accept early implantation, as evidenced by consistent device use, and derive notable benefits in speech recognition. Candidacy can be broadened to include SSD patients under age five years, particularly individuals without hypoplastic cochlear nerves or developmental delay.

Internal auditory canal volume in normal and malformed inner ears

PurposeA narrow bony internal auditory canal (IAC) may be associated with a hypoplastic cochlear nerve and poorer hearing performances after cochlear implantation. However, definitions for a narrow IAC vary widely and commonly, qualitative grading or two-dimensional measures are used to characterize a narrow IAC. We aimed to refine the definition of a narrow IAC by determining IAC volume in both control patients and patients with inner ear malformations (IEMs).MethodsIn this multicentric study, we included high-resolution CT (HRCT) scans of 128 temporal bones (85 with IEMs: cochlear aplasia, n = 11; common cavity, n = 2; cochlear hypoplasia type, n = 19; incomplete partition type I/III, n = 8/8; Mondini malformation, n = 16; enlarged vestibular aqueduct syndrome, n = 19; 45 controls). The IAC diameter was measured in the axial plane and the IAC volume was measured by semi-automatic segmentation and three-dimensional reconstruction.ResultsIn controls, the mean IAC diameter was 5.5 mm (SD 1.1 mm) and the mean IAC volume was 175.3 mm3 (SD 52.6 mm3). Statistically significant differences in IAC volumes were found in cochlear aplasia (68.3 mm3, p < 0.0001), IPI (107.4 mm3, p = 0.04), and IPIII (277.5 mm3, p = 0.0004 mm3). Inter-rater reliability was higher in IAC volume than in IAC diameter (intraclass correlation coefficient 0.92 vs. 0.77).ConclusionsVolumetric measurement of IAC in cases of IEMs reduces measurement variability and may add to classifying IEMs. Since a hypoplastic IAC can be associated with a hypoplastic cochlear nerve and sensorineural hearing loss, radiologic assessment of the IAC is crucial in patients with severe sensorineural hearing loss undergoing cochlear implantation.

Radiologic Findings in Pediatric Sudden Sensorineural Hearing Loss.

Pediatric sudden sensorineural hearing loss (pSSNHL) is a rare phenomenon. There is currently no consensus on the role of imaging in the work-up for this patient population. We aim to evaluate the efficacy of magnetic resonance imaging (MRI) and high-resolution computed tomography (CT) studies in determining the etiology of pSSNHL. Retrospective case review. Tertiary Hospital and Ambulatory Otolaryngology Clinic. Patients ≤18 years of age with sudden sensorineural hearing loss (SSNHL) and who had either MRI or CT imaging between January 2010 and May 2019 were included. Diagnostic imaging. Clinical characteristics and radiology impressions. A total of 11 patients were identified, and 10 had unilateral SSNHL. MRI was performed on all patients, five patients had additional CT imaging. Abnormal imaging findings relevant to SSNHL were observed in five patients (45.5%), which included enlarged endolymphatic duct and sac, labyrinthine ossification, apical petrositis, hypoplastic cochlear nerve, and arachnoid cyst in the internal auditory canal; one patient had unrelated findings (enlarged pituitary gland), all remaining imaging studies were normal. In our cohort, we found a higher imaging yield on pSSNHL than what has been reported for adult populations, indicating that the use of imaging in the diagnostic work-up is especially important in children.

Cochlear implantation versus auditory brainstem implantation in children with auditory nerve deficiencies.

Cochlear nerve deficiency is one of the known causes of congenital sensorineural hearing loss. Management of hearing loss in children with cochlear nerve deficiency poses a multidimensional challenge. The absent or hypoplastic cochlear nerve may prevent electrical stimulation from reaching the brainstem and the auditory cortex. A deficient cochlear nerve can be associated with other inner ear malformations, which may diminish the success of cochlear implantation in those children. Promising results in adults after auditory brainstem implantation led to the expansion of candidacy to include the pediatric populations who were contraindicated for CIs. To review the outcomes of cochlear implantation versus that of auditory brainstem implantation in children with various conditions of the auditory nerve. This retrospective chart review study comprised two pediatric groups. The first group consisted of seven ABI recipients with cochlear nerve aplasia and the second group consisted of another seven children with cochlear nerve deficiencies who underwent CI surgery. The participants' auditory skills and speech outcomes were assessed using different tests selected from the Evaluation of Auditory Responses to Speech (EARS) test battery. There were some individual variations in outcomes depending on the status of the auditory nerve. The mean CAP score of the ABI group was 2.87, while the mean SIR score was 0.62. On the other hand, the mean CAP score of the CI group was 1.29, while the mean SIR score was 0.42. Our results are in good agreement with the reported auditory perception and speech and language development outcomes of pediatric auditory brainstem implantation. We added to the growing body of literature on the importance of verifying and identifying the status of the cochlear nerve in the decision-making process of the surgical management of those pediatric groups.

Cochlear nerve anomalies in paediatric single-sided deafness - prevalence and implications for cochlear implantation strategies.

To determine the prevalence of cochlear nerve anomalies on magnetic resonance imaging in patients with unilateral or bilateral sensorineural hearing loss. A retrospective case series was conducted at a tertiary referral centre. The inclusion criteria were paediatric patients with bilateral or unilateral sensorineural hearing loss, investigated with magnetic resonance imaging. The primary outcome measure was the rate of cochlear nerve hypoplasia or aplasia. Of the 72 patients with unilateral sensorineural hearing loss, 39 per cent (28 cases) had absent or hypoplastic cochlear nerves on the affected side. Fifteen per cent (11 cases) had other abnormal findings on magnetic resonance imaging. Eighty-four patients had bilateral sensorineural hearing loss, of which cochlear nerve hypoplasia or aplasia was identified only in 5 per cent (four cases). Other abnormal findings were identified in 14 per cent (12 cases). Paediatric patients with unilateral sensorineural hearing loss are more likely to have cochlear nerve anomalies than those patients with bilateral sensorineural hearing loss. This has important implications regarding cochlear implantation for patients with single-sided deafness.

The Effect of Pulse Polarity on Neural Response of the Electrically Stimulated Cochlear Nerve in Children With Cochlear Nerve Deficiency and Children With Normal-Sized Cochlear Nerves.

This study aimed to (1) investigate the effect of pulse polarity on neural response of the electrically stimulated cochlear nerve in children with cochlear nerve deficiency (CND) and children with normal-sized cochlear nerves and (2) compare the size of the pulse polarity effect between these two subject groups. The experimental and control group included 31 children with CND and 31 children with normal-sized cochlear nerves, respectively. For each study participant, evoked compound action potential (eCAP) input/output (I/O) functions for anodic-leading and cathodic-leading biphasic stimuli were measured at three electrode locations across the electrode array. The dependent variables of interest included the eCAP amplitude measured at the maximum comfortable level of the anodic stimulus, the lowest level that could evoke an eCAP (i.e., the eCAP threshold), the slope of the eCAP I/O function estimated based on linear regression, the negative-peak (i.e., N1) latency of the eCAP, as well as the size of the pulse polarity effect on these eCAP measurements. Generalized linear mixed effect models were used to compare the eCAP amplitude, the eCAP threshold, the slope of the eCAP I/O function, and the N1 latency evoked by the anodic-leading stimulus with those measured for the cathodic-leading stimulus for children with CND and children with normal-sized cochlear nerves. Generalized linear mixed effect models were also used to compare the size of the pulse polarity effect on the eCAP between these two study groups. The one-tailed Spearman correlation test was used to assess the potential correlation between the pulse phase duration and the difference in N1 latency measured for different pulse polarities. Compared with children who had normal-sized cochlear nerves, children with CND had reduced eCAP amplitudes, elevated eCAP thresholds, flatter eCAP I/O functions, and prolonged N1 latencies. The anodic-leading stimulus led to higher eCAP amplitudes, lower eCAP thresholds, and shorter N1 latencies than the cathodic-leading stimulus in both study groups. Steeper eCAP I/O functions were recorded for the anodic-leading stimulus than those measured for the cathodic-leading stimulus in children with CND, but not in children with normal-sized cochlear nerves. Group differences in the size of the pulse polarity effect on the eCAP amplitude, the eCAP threshold, or the N1 latency were not statistically significant. Similar to the normal-sized cochlear nerve, the hypoplastic cochlear nerve is more sensitive to the anodic-leading than to the cathodic-leading stimulus. Results of this study do not provide sufficient evidence for proving the idea that the pulse polarity effect can provide an indication for local neural health.

Cochlear Nerve Aplasia and Hypoplasia: Predictors of Cochlear Implant Success.

Objective To identify factors predicting performance outcomes following cochlear implantation in patients with cochlear nerve aplasia or hypoplasia. Data Sources Individual patient data extracted from published case series and reports. Review Methods The MEDLINE database, Cochrane Library, Embase, Web of Science, and Google Scholar were queried for "cochlear implant" in conjunction with "aplasia" or "hypoplasia" between 1985 and 2015. Eighteen studies were included describing 97 subjects with individual postimplant auditory data. Postimplant performance was categorized as follows: level 1, nonstimulation/minimal detection; level 2, improved detection; level 3, closed-set speech perception; or level 4, open-set speech perception. The subjects achieving speech perception (levels 3 and 4) were descriptively compared with those who did not. Results Subjects with a hypoplastic cochlear nerve on magnetic resonance imaging had higher reported rates of achieving speech perception than those with an aplastic nerve. Subjects with syndromic medical comorbidities had higher reported rates of nonstimulation than nonsyndromic subjects. The data showed that some children with an aplastic cochlear nerve or those with partial electrode insertion could obtain levels of speech discrimination. Reporting of patient characteristics and auditory outcomes was extremely variable across studies. Conclusion As previously shown, cochlear implant in patients with cochlear nerve aplasia or hypoplasia can provide meaningful hearing for select patients. The current study suggests that presence of a cochlear nerve on magnetic resonance imaging and lack of comorbid medical syndrome are associated with better auditory outcomes in such patients. Future efforts to report individual data in a consistent manner may allow better determination of predictive factors.

Utility of MRIs in Adult Cochlear Implant Evaluations

To determine the prevalence of MRI abnormalities in adults undergoing cochlear implantation and to correlate abnormalities to audiology data. Case series. Academic medical center. Adult patients (>18 yr old) undergoing cochlear implant evaluation from January 2008 to December 2012 were identified based on CPT code search. Demographics, preoperative MRI findings, operative findings, and audiometric data were collected. The study included 188 patients. Seventeen (9%) patients had significant otic capsule or vestibulocochlear nerve pathologies: 5 vestibular schwannomas, 4 enlarged vestibular aqueducts, 2 hypoplastic cochlear nerves, 2 labyrinthitis ossificans, 1 cochlear aplasia, 1 posterior semicircular canal malformation, 1 calcified meningioma, and 1 cholesterol granuloma. MRI results were normal (65%) or with findings not directly related to hearing loss (incidental findings, 25%) in the remaining patients. Mean pure tone average (PTA) differences (between the implanted and contralateral ear) did not significantly vary between normal-incidental and abnormal MRI scans (-6.6 dB versus -6.7 dB, p = 0.99) nor did speech discrimination scores (SDS) scores (8.5% versus 8.4%, p = 0.99). No significant difference was found in HINT scores for patients with a normal versus an abnormal MRI (19% versus 16,%, p = 0.62). Although the majority of precochlear implantation MRIs were normal or demonstrated incidental findings, such as white matter changes, significant MRI findings affecting implantation site and patient counseling were found in almost 10% of patients. Audiogram findings did not correlate with abnormal findings on MRIs. Routine use of MRI in adult cochlear implant candidates may be warranted.

A new classification system for malformations of the internal auditory meatus, cochlear nerve canal and cochlear nerve

The present study aims to restudy the correlation between the internal auditory meatus (IAM), the cochlear nerve canal (CNC), the cochlear nerve (CN) and inner ear malformations. The abnormal diameter of the IAM, CNC and CN in patients with any kind of inner ear malformations were evaluated using multi-slice spiral computed tomography (MSCT) (37 patients) and magnetic resonance imaging (MRI) (18 patients). Of 37 MSCT-diagnosed patients, 2 had IAM atresia, 11 IAM stenosis, 22 enlarged IAM, and 2 normal IAM with an abnormal CN. MRI diagnoses of 18 patients revealed 8 cases of aplastic CN, 6 hypoplastic CN, and 4 normal CN. CNC stenosis was associated with CN hypoplasia ( P < 0.001). Patients with absent or stenotic IAM had less CN development than those with normal or enlarged IAM ( P = 0.001). We propose a modification of existing classification systems with a view to distinguishing malformations of the IAM, CNC and CN.

Restudy of malformations of the internal auditory meatus, cochlear nerve canal and cochlear nerve

The present study aims to restudy the correlation between the internal auditory meatus (IAM), the cochlear nerve canal (CNC), the cochlear nerve (CN) and inner ear malformations. In this retrospective study design, the abnormal diameter of the IAM, CNC and CN in patients with any kind of inner ear malformations was evaluated using multi-slice spiral computed tomography (MSCT) (37 patients) and magnetic resonance imaging (MRI) (18 patients). Of 37 MSCT-diagnosed patients, 2 had IAM atresia, 11 IAM stenosis, 22 enlarged IAM, and 2 normal IAM with an abnormal CN. MRI diagnoses of 18 patients revealed 8 cases of aplastic CN, 6 hypoplastic CN, and 4 normal CN. CNC stenosis was associated with CN hypoplasia (P < 0.001). Patients with absent or stenotic IAM had less CN development than those with normal or enlarged IAM (P = 0.001). We propose a modification of the existing classification systems with a view to distinguishing malformations of the IAM, CNC and CN.

BADANIE KLINICZNE ELEKTRYCZNIE WYWOŁANYCH KOROWYCH POTENCJAŁÓW SŁUCHOWYCH U DZIECI KORZYSTAJĄCYCH Z IMPLANTÓW DO PNIA MÓZGU

BackgroundCortical auditory evoked potentials (CAEPs) reflect the function of the auditory thalamo-cortical pathways and the auditory cortex, and so are a window to the ‘auditory brain’. They are a valuable prognosticator for predicting long-term outcomes in cochlear implantees. This preliminary study evaluated its use in pediatric auditory brainstem implant (ABI) who had bilateral Michel’s deformity with cochlear nerve hypoplasia.ObjectivesTo profile the aided CAEPs in children with ABI and to assess its efficacy as a tool for evaluating ABI outcomes.MethodThis prospective clinical study was performed in 3 pre-lingually deaf, non-syndromic children (aged 3–5 yrs) who had congenital bilateral hypoplastic cochlear nerves with Michel’s cochlear deformity who underwent ABI at our institute. All implantees underwent CAEP testing at 6 months and 1 year post-implantation and their results were compared. To compare responses between the various electrodes in contact with the brainstem the 12 ABI electrodes were divided into 4 groups (G1–G4). These groups were sequentially activated and the CAEPs recorded; the responses were compared to the overall CAEP response obtained by stimulating the entire electrode array. Testing comprised /m/, /g/, and /t/ acoustic stimuli and responses to them were recorded from each group of electrodes. Latency of P1, amplitude of P1 complex, and morphology of the responses were analyzed.ConclusionsResults from our preliminary study showed that CAEP can be successfully recorded in ABI, and CAEP profiling can be an objective method of analyzing the optimal placement and function of the ABI electrodes on the brainstem. Thus CAEP is an efficient adjunct to electrically evoked auditory brainstem response (EABR) for testing ABIs. When stimulated via the ABI, CAEP may reflect re-organization of higher auditory centers and hence may be a good prognosticator for long-term assessment of ABI performance.

The bony cochlear nerve canal in children with absent or hypoplastic cochlear nerves

Objective To correlate presence and size of the bony cochlear nerve canal [BCNC] with size of the internal auditory meatus [IAM] on CT in children with absent or hypoplastic cochlear nerves [CNs] as compared to age matched controls. Methods This retrospective case-notes review was based in the departments of Cochlear Implantation and Neuroradiology at a tertiary paediatric hospital. Twenty-five ears of fifteen children (subjects) with profound sensorineural deafness (SND) and absent or hypoplastic CN on MRI scan were compared to age matched controls. Two groups of controls were included; a control group of nineteen ears of twelve children with normal hearing or conductive hearing loss [control group 1] and a second control group of twenty one ears of eleven children with severe to profound hearing loss related to GJB2 mutations [control group 2]. Both control groups had evidence of the presence of the CN. Two neuroradiologists independently assessed presence and size of BCNC and IAM on CT and presence of CN on MRI in subjects and controls. The BCNC and IAM size was compared between subjects and both control groups. The presence of BCNC was correlated with the IAM size on CT, presence/absence of CN on MRI and audiological evaluation in subjects. Results The mean IAM width was significantly smaller in subjects as compared to controls. The BCNC was absent in 17/25 subject ears and present in all control ears. Absent BCNC correlated with a narrow IAM in 13/17 subject ears. Presence of the BCNC supported presence of a CN although this was not seen on MRI. However, BCNC absence may be associated with presence of a CN as was seen in two subject ears. Five subject ears out of 22 [22%] with absent CN on MRI had other evidence of a present cochlear nerve. Conclusions BCNC is an additional parameter to assess presence of the cochlear branch of the CN. Presence of the BCNC may indicate cochlear nerve presence. Caution should be used in assessing candidacy of cochlear implants based on MRI alone and a combination of imaging and audiological tests should be used to assess presence of the CN.

Temporal bone abnormalities in children with GJB2 mutations

To determine the incidence of temporal bone abnormalities in children with sensorineural hearing loss (SNHL) and pathogenic biallelic GJB2 mutations. Retrospective analysis of a large cohort of pediatric patients with biallelic GJB2 mutations and SNHL (observational case series). Blinded review of all available temporal bone computed tomographic (CT) and magnetic resonance imaging (MRI) studies in this cohort. Out of 158 patients with biallelic GJB2 mutations, 113 had CT and/or MRI studies available for review. Definite, although generally subtle, inner ear abnormalities were present in 12/113. There were malformations of the semicircular canals (SCC) in 4/12, of the internal auditory canal in 2/12, of the cochlear nerve canal (CNC) in 6, and unilateral cochlear malformation in 1/12. MRI in 1/5 showed mildly hypoplastic cochlear nerve. There was no correlation between SNHL severity and presence/absence/type of malformations or genotype. Our study of 113 biallelic GJB2 patients with SNHL and temporal bone imaging is the largest study to date. We found only 10% had any abnormalities, most subtle, and none had EVA. Additionally, there was no correlation between SNHL severity and presence/absence/type of malformations or genotype. Disparities between our group and previous reports may be due to differences in degree of hearing loss, types of mutations, populations studied, and radiologic factors for both image acquisition and interpretation.

Congenital Profound Hearing Loss: Management of Hypoplastic and Aplastic Vestibulocochlear Nerves

Cochlear implantation has become an established intervention for selected children with severe to profound deafness. As implant programmes have grown, an increasing number of children with congenital deafness have been identified with aplastic or hypoplastic cochlear nerves (Figure 1). These children pose a significant management challenge. Options for management include a cochlear implant, auditory brainstem implant, or no surgical intervention (Table 1).

Variable long-term outcomes from cochlear implantation in children with hypoplastic auditory nerves

This paper describes the outcomes in six children with hypoplastic cochlear nerves, demonstrated on magnetic resonance imaging who were selected for implantation because they had clear responses to sound, with hearing aids. In four of the six children the internal auditory canals were abnormally narrow; however in the remaining two the internal auditory canals were of normal width. After activation of their devices, all six children had auditory thresholds within the normal range for implanted congenitally deaf children. However the progress of all these children after 2 to 6 years of implant use turned out to be disappointing. Five of the children developed only the ability to detect the presence of sound, and were unable to discriminate accurately between speech sounds. They remain at Category of Auditory Performance (CAP) level 2: sign is their primary mode of communication. All five children also remain at Speech Intelligibility Rating (SIR) level 2, with unintelligible connected speech. The sixth child was able to develop some understanding of common phrases through listening alone, however he remains at CAP level 4 and his SIR level also remains at 2. The benefit of cochlear implantation in this group of children is likely to be considerably restricted. In specific cases it may be appropriate to offer a cochlear implant to a child with hypoplastic auditory nerves but careful counselling of the family about likely outcomes is essential. Copyright © 2008 John Wiley & Sons, Ltd.

Cochlear nerve size evaluation in children with sensorineural hearing loss by high-resolution magnetic resonance imaging

Purpose To determine differences in size of cochlear nerves among subjects with deafness due to connexin 26 (Cx26) mutations, subjects with deafness of unknown origin, and normal hearing subjects by sagittal high-resolution magnetic resonance (HRMR) imaging of the temporal bone. Materials and methods Cross-sectional and surface areas and volumetric measurements of the cochlear nerve and modiolus were made on HRMR images of the internal auditory canal (IAC) and inner ear in the 3 groups of children (groups 1, 2, and 3). Three-way comparisons of in vivo cochlear nerve measurements on HRMR imaging were made among 17 children with sensorineural hearing loss (SNHL) and no obvious etiology for the hearing loss (group 1), 7 children with profound SNHL due to a Cx26 mutation (group 2), and 10 normal hearing children (group 3). Results Children with profound SNHL of unknown cause and children with profound SNHL due to a connexin mutation displayed hypoplastic cochlear nerves as compared with normal controls. HRMR imaging of the temporal bone was accurately delineated potential problems with cochlear nerves in 2 of 17 instances where high-resolution computed tomography did not do so. Conclusions Accurate and specific measurements of the cochlear nerve and related structures is possible on HRMR imaging of the temporal bone. The size of the cochlear nerve is mildly hypoplastic in children with profound SNHL of unknown causes or children with a deafness-causing Cx26 mutation. HRMR imaging is superior to high-resolution computed tomography in the investigation of profound SNHL in children.

The Significance of a Hypoplastic Bony Canal for the Cochlear Nerve in Patients with Sensorineural Hearing Loss: CT and MRI Findings

Purpose: The purpose of this study is to evaluate the significance of the hypoplastic canal for the cochlear nerve in patients with sensorineural hearing loss (SNHL) and the relationship between the hypoplastic bony canal and aplasia or hypoplasia of the cochlear nerve. Materials and Methods: A retrospective review of high resolution temporal CT(HRCT) and MRI findings was conducted. The narrow bony canal of the cochlear nerve and the relative size of the internal auditory canal were correlated with the cochlear nerve deficiency on MRI. The comparative size of the component nerves (facial, cochlear, superior vestibular, inferior vestibular nerve), and the relative size of the internal auditory canal and the bony canal of the cochlear nerve were measured. The clinical history and the results of the clinical examination were reviewed for each patient. Results: High resolution MRI showed aplasia of the common vestibulocochlear nerve in one patient and a deficiency of the cochlear nerve in 9 patients. These abnormalities occurred in association with a prominent narrowing of the canal for the cochlear nerve and a stenosis of the internal auditory canal, which was observed on temporal bone CT in 9 patients with congenital SNHL. Three patients had normal IAC, despite the presence of a hypoplastic cochlear nerve on the side on which they had SNHL. In one patient, the narrowing of the canal for the cochlear nerve and internal auditory canal were not found to be associated with acquired SNHL. Conclusion: The hypoplastic bony canal for the cochlear nerve might be more highly indicative of congenital cochlear nerve deficiency than that of the narrow internal auditory canal, and the position of the crista falciformis should also be carefully.