Abstract
Objective
The objective of this study was to investigate the audiological characteristics of children with cochlear nerve deficiency (CND) and their correlation with cochlear implantation (CI) prognosis.
Methods
The records of 48 patients (24 with bilateral CND and 24 with no inner ear malformations (IEMs)) who underwent unilateral CI were reviewed. Preoperative audiometric, postoperative electrical stimulation auditory brainstem response (EABR), and auditory performance measures were also assessed.
Results
CND patients demonstrated a significantly higher positive wave detection rate (41.67%) compared with controls (0%, p < 0.001). Ears with isolated cochlear nerve canal stenosis (CNCs) had higher positive wave detection rates (62.5%) than those with additional semicircular canal/vestibular abnormalities (0%). Ears with positive waves demonstrated better multiple frequency steady-state response and postoperative EABR thresholds than those without positive waves. The categories of auditory performance (CAP) scores at the 2-year follow-up were significantly higher in patients with positive waves than in those without positive waves (4.17 ± 0.58 vs. 3.58 ± 0.51).
Conclusions
The presence of a distinctive positive waveform in auditory brainstem response (ABR) testing may indicate preserved residual auditory pathway integrity in CND patients. This characteristic may serve as a prognostic indicator for CI outcomes, warranting further investigation in larger, longitudinal cohorts.
Keywords: Cochlear nerve deficiency, auditory brainstem response, positive wave, cochlear implantation, electrically evoked auditory brainstem response
KEY MESSAGES
The presence of positive waves in auditory brainstem response tests is helpful for the diagnosis of cochlear nerve deficiency (CND) and is associated with better hearing ability.
Normal vestibular and semicircular canal structures may facilitate positive wave generation in CND patients.
Introduction
Cochlear nerve deficiency (CND), encompassing both cochlear nerve aplasia and hypoplasia, represents a significant structural malformation affecting approximately 15.4% of children with severe to profound sensorineural hearing loss (SNHL) [1,2]. Cochlear implantation (CI) employs the conversion of acoustic signals to electrical stimuli, directly activating spiral ganglion neurons to facilitate auditory signal transmission through cochlear nerve fibers to brainstem auditory nuclei. This intervention represents the gold standard treatment for patients with bilateral severe to profound SNHL [3–5]. Patients with CND have reduced spiral ganglion neuron (SGN) fiber density, which consequently impairs neural substrate availability for electrical stimulation. This patient population presents unique therapeutic challenges attributable to their diminished spiral ganglion cell populations, which fundamentally compromise the neural interface required for effective auditory signal processing [6–9]. Although technological advances have expanded CI eligibility criteria to include younger patients and those with various inner ear malformations, pediatric CND patients consistently demonstrate variable and often suboptimal outcomes following CI [10–12]. This variability underscores the critical importance of precise preoperative evaluation and outcome prediction. However, this area remains a substantial research gap in the field.
The current diagnostic paradigm for CND relies predominantly on noninvasive imaging techniques, particularly magnetic resonance imaging (MRI). A comprehensive analysis at a tertiary academic center examining 69 ears with cochlear nerve anomalies highlighted significant limitations in current imaging methodologies [13]. While imaging can identify gross anatomical abnormalities, it often fails to provide a detailed functional assessment of the cochleovestibular nerve and accurate prediction of CI outcomes. This diagnostic challenge is particularly pronounced in pediatric cases, where anatomical structures are smaller and more difficult to evaluate, creating a pressing need for more reliable and clinically feasible evaluation methods.
Preoperative auditory brainstem response (ABR) testing in CND patients typically yields no measurable thresholds because of severely compromised residual hearing. Electrical stimulation auditory brainstem response (EABR) testing has emerged as a valuable diagnostic tool for evaluating neural function in CI recipients [14,15]. However, comprehensive analyses of audiological profiles in CND patients and their predictive value for CI outcomes remain limited. Previous studies have documented a significant negative deflection (3–4 ms latency) in the ABR results of large vestibular aqueduct syndrome (LVAS) patients, with an acoustically evoked short latency negative response (ASNR) dependent on proper saccular function [16,17]. In our research group’s study, ASNR was elicited in more than 60% of the LVAS ears. This investigation aimed to evaluate the diagnostic significance of specific ABR waveform characteristics in CND patients. The response of interest manifests as a reproducible positive deflection within a latency period of 4–5 ms after the appearance of a high-intensity sound. By identifying reliable prognostic indicators, this research seeks to optimize preoperative assessment protocols and refine patient selection criteria for CI in CND patients.
Current diagnostic approaches rely heavily on MRI-based anatomical criteria, which may not fully capture the functional capacity of residual neural elements. There is a critical clinical need for physiological biomarkers that can predict CI outcomes and guide therapeutic decision-making on the basis of functional rather than purely morphological assessments.
Methods
Participants
Prior to enrollment, their legal representatives provided informed consent. We thoroughly examined data from 24 pediatric patients with bilateral CND who received CI at our institution between January 2021 and November 2023. A control group of 24 participants without inner ear malformations (IEMs) was selected via frequency matching on the basis of age at implantation, gender, and presurgical auditory and speech capabilities (Table 1). The participants were selected according to the following criteria: (1) bilateral severe-to-profound sensorineural hearing impairment prior to implantation and (2) receipt of a unilateral CI via a straight electrode array via round window insertion to minimize damage to the cochlear structure. The exclusion criteria included patients (1) presenting with additional deafness-related syndromes and (2) declining CI use or speech rehabilitation. The inner ear structure was assessed via high-resolution computed tomography (CT) and MRI. Cochlear nerve canal stenosis (CNCs) was diagnosed if the diameter of the cochlear nerve canal was less than 1.5 mm (Figure 1) [10,18,19]. All the children in our study received professional auditory–verbal training independently or accompanied by their parents for 4–8 h per day in the rehabilitation center. Auditory–verbal rehabilitation courses include auditory discrimination and identification and speech comprehension and repetition.
Table 1.
Demographic information of 48 patients.
| Variable | Bilateral CND | No IEMs |
|---|---|---|
| N | 24 (48 ears) | 24 (48 ears) |
| Sex (F/M, N) | 9/15 | 11/13 |
| Age at CI (mean ± SD, months) | 19.25 ± 8.56 | 14.25 ± 3.61 |
| ABR threshold (>95/≤90 dB nHL) | 43/5 | 46/2 |
| Inner ear structure | 0/16/2/1/5 | 24/0/0/0/0 |
| (Normal/CNCs/CNCs & SCCMs/CNCs & VMs/CNCs & SCCMs & VMs) | ||
| Side of CI (L/R, N) | 12/12 | 10/14 |
ABR, auditory brainstem response; CI, cochlear implantation; CND, cochlear nerve deficiency; CNCs, cochlear nerve canal stenosis; F, female; L, left; M, male; R, right; SCCMs, semicircular canal malformations; VMs, vestibule malformations.
Figure 1.
High-resolution computed tomography (CT) and magnetic resonance imaging (MRI) of two patients. (A) A patient with cochlear nerve deficiency (CND). (B) A patient without inner ear malformations (IEMs). CN: cochlear nerve; CNC: cochlear nerve canal; FN: facial nerve; VN: vestibular nerve (red arrow).
Preoperative audiological assessment
Prior to implantation, all patients underwent comprehensive audiometric evaluations, including tympanometry, distortion product otoacoustic emission (DPOAE), ABR, and multiple frequency steady-state response (MSSR).
All the subjects were tested for tympanometry via the Titan IMP440 middle ear impedance device (Interacoustics, Denmark, Version 3.4). According to the classification of Jerger, all the patients had type A tympanograms for tympanometry at 226 Hz [20]. DPOAE testing was conducted via Capella equipment (GN Otometrics, Denmark). The samples were collected in response to pairs of primary tones f1 and f2; f2/f1 = 1.22. Primary tones were presented at sound pressure levels of L1 = 65 dB SPL and L2 = 55 dB SPL. Seven test frequencies were selected: 750, 1,000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz. The criteria for a successful DPOAE test were a signal-to-noise ratio (S/N) ≥ 6 dB and at least four of the seven test frequencies eliciting a response.
The evaluation of ABR and MSSR was performed using ICS Chart EP equipment (GN Otometrics, Denmark) within a soundproof environment. Patients underwent testing while sedated with chloral hydrate. For electrode placement, the recording electrode was positioned at the forehead midline, the ground electrode at the nasal base, and reference electrodes on the left and right mastoid processes. Throughout testing, the electrode impedance was kept under 5 kΩ. For ABR assessment, alternating clicks were delivered through ER-3A insert earphones, starting with 95 dB nHL intensity and progressively decreasing in 10 dB steps. The positive wave in the ABR was identified manually by two audiologists blinded to the information of each participant. When this positive component was identified in ABR recordings, the following criteria were applied [21]:
Response evoked by sounds with high intensities (≥95 dB nHL)
A reproducible positive wave should appear 4–5 ms after the onset of stimulation
Absence of preceding negative deflection
Became absent after external auditory canal occlusion
The latency of a wave V was longer (>5.5 ms) and more likely to shorten as the stimulation intensity increased than that of a positive wave [22]. These differences could be used to discriminate the two waves (Figure 2A). MSSR testing utilized amplitude-modulated stimuli at 500, 1,000, 2,000, and 4,000 Hz. The absence of a response at the maximum intensity was recorded as the 120 dB nHL threshold.
Figure 2.
The identification of characteristic auditory brainstem response (ABR) waveforms in cochlear nerve deficiency (CND) patients.
Postoperative EABR and auditory scale assessment
Compared with intraoperative recordings, postimplantation EABR measurements provide more stable stimulation conditions. The 24 patients with bilateral CND underwent EABR testing one-month post-implantation (Table 2). We performed EABR recordings via a Neuro-Audio device (Neurosoft, Ivanova, Russia). Electrical stimulation was delivered via a MAX programming interface and controlled through Maestro software (MED-EL, Innsbruck, Austria). The implant array comprised 12 channels (C1-C12), with C1 and C12 positioned apically and basally, respectively. We selected four representative channels for stimulation: C2, C5, C8, and C11. Wave V demonstrated optimal reproducibility across channels and was utilized as the primary metric for EABR threshold determination and extraction rate calculation. We defined the EABR threshold as the minimum stimulation level eliciting wave V, with an established upper limit of 1,200 cu [23].
Table 2.
Demographic information of 24 patients with CND.
| Subject | Gender | Age at CI (months) | ABR threshold at test (dB nHL) | First side of CI | Implant type and Electrode type | Ear(s) with positive wave | Inner ear structure |
|---|---|---|---|---|---|---|---|
| 1 | M | 11 | >95 | R | SONATAti100(Flex28) | Bi | CNCs |
| 2 | F | 10 | >95 | R | SONATAti100(Flex28) | R | CNCs |
| 3 | F | 14 | >95 | R | SONATAti100(Flex28) | Bi | CNCs |
| 4 | M | 24 | >95 | L | SONATAti100(Flex28) | Bi | CNCs |
| 5 | M | 24 | >95 | L | SONATAti100(Flex28) | Bi | CNCs |
| 6 | M | 30 | L:90 R:90 | L | SONATAti100(Flex28) | Bi | CNCs |
| 7 | M | 36 | >95 | R | SONATAti100(Flex28) | / | CNCs |
| 8 | F | 36 | L:70 R:>95 | R | SONATAti100(Flex28) | R | CNCs |
| 9 | F | 12 | >95 | L | SONATAti100(Flex28) | Bi | CNCs |
| 10 | M | 12 | >95 | R | CONCERTO(Flex28) | L | CNCs |
| 11 | F | 12 | >95 | R | CONCERTO(Flex28) | L | CNCs |
| 12 | M | 32 | >95 | L | SONATAti100(Flex28) | Bi | CNCs |
| 13 | F | 23 | >95 | R | CONCERTO(Flex28) | / | CNCs |
| 14 | F | 24 | L:>95 R:90 | L | CONCERTO(Flex28) | / | CNCs,SCCMs |
| 15 | F | 11 | >95 | R | CONCERTO(Flex28) | / | CNCs,VMs |
| 16 | M | 30 | L:80 R:>95 | R | CONCERTO(Flex28) | / | CNCs,SCCMs |
| 17 | M | 13 | >95 | L | SONATAti100(Flex28) | Bi | CNCs |
| 18 | M | 15 | >95 | R | SONATAti100(Flex28) | / | CNCs,SCCMs,VMs |
| 19 | M | 10 | >95 | L | SONATAti100(Flex28) | / | CNCs,SCCMs,VMs |
| 20 | M | 12 | >95 | R | SONATAti100(Flex28) | / | CNCs,SCCMs,VMs |
| 21 | M | 15 | >95 | L | SONATAti100(Flex28) | / | CNCs,SCCMs,VMs |
| 22 | M | 23 | >95 | L | SONATAti100(Flex28) | / | CNCs,SCCMs,VMs |
| 23 | F | 17 | >95 | L | CONCERTO(Flex28) | / | CNCs |
| 24 | M | 16 | >95 | L | SONATAti100(Flex28) | / | CNCs |
ABR, auditory brainstem response; Bi, bilateral; CI, cochlear implantation; CND, cochlear nerve deficiency; CNCs, cochlear nerve canal stenosis; F, female; L, left; M, male; R, right; SCCMs, semicircular canal malformations; VMs, vestibule malformations.
During the subsequent follow-up process (pre-operation, one year after CI, and two years after CI), we utilized categories of auditory performance (CAP) and speech intelligibility rating (SIR) to assess the children’s auditory perception ability and speech intelligibility [24].
Categories of Auditory Performance (CAP): An eight-level classification system assessing daily auditory function (7 = highest capability; 0 = lowest capability)
Speech intelligibility rating (SIR): A five-point scale evaluating speech comprehensibility (5 = optimal performance; 1 = minimal intelligibility)
Statistical data analysis
We conducted the statistical analyses via SPSS software (version 17.0 for Windows; SPSS Inc., USA). For patients with CND, we assessed the differences in EABR thresholds and latencies between ears with and without positive waves via the nonparametric Mann–Whitney U test. We evaluated hearing outcomes in CND patients via two-way analysis of variance (ANOVA), with test frequencies (500, 1,000, 2,000, 4,000 Hz and average MSSR) used as within-subject factors and response groups used as between-subject factors. The postoperative mean CAP and SIR scores between the two groups (with/without positive waves) were analyzed by a nonparametric Mann–Whitney U test. Given the limited sample size, Fisher’s exact test was employed to assess relationships between variables (positive wave detection rates with different inner ear structures, DPOAE extraction rates, and EABR extraction rates), with statistical significance set at p < 0.05. When a zero cell was present, the Haldane–Anscombe correction (adding 0.5 to each cell) was employed to estimate the odds ratio (OR) and its confidence interval for Fisher’s exact test.
Results
Auditory brainstem response analysis: positive wave detection
Among the 48 ears in the CND patients, five demonstrated distinct wave V responses at 95 dB nHL, with ABR thresholds ranging from 70 to 90 dB nHL (individual values: 90, 90, 70, 90, and 80 dB nHL). The remaining 43 ears (89.58%) presented no discernible wave V at maximum stimulation.
Ears with CND had a significantly higher positive wave detection rate than those without IEMs did (41.67% vs. 0%, p < 0.001, OR = 69.77, 95% confidence interval [4.063, 1198.136]). Within the bilateral CND cohort (n = 24), eight patients presented bilateral positive waves, whereas four presented unilateral responses. The mean latency in the 20 ears with this ABR characteristic (n = 20) was 4.91 ± 0.20 ms (Figure 2).
Among the 48 ears, 16 ears (33.33%) had both cochlear nerve canal stenosis (CNCs) and semicircular canal/vestibular malformations (SCCMs/VMs). Compared with ears with CNCs and SCCMs/VMs, ears with isolated CNCs presented a higher positive wave detection rate (62.5% vs. 0%, p < 0.001, OR = 54.120, 95% confidence interval [2.978, 983.659]) (Table 3).
Table 3.
The extraction rate of a positive wave from ears with CND.
| Group | Total ears | Positive wave | No positive wave |
|---|---|---|---|
| CNCs | 32 | 20/32** | 12/32 |
| CNCs + SCCMs/VMs | 16 | 0/16 | 16/16 |
CNCs, cochlear nerve canal stenosis; SCCMs, semicircular canal malformations; VMs, vestibule malformations. **p < 0.001 versus ears with CNCs + SCCMs/VMs.
Other preoperative audiometric results
The failure rate of DPOAE testing for 20 ears with positive waves was 85% (17/20), whereas the failure rate of DPOAE testing for 28 ears without positive waves was 82.14% (23/28). There was no significant difference between the two groups (p > 0.999, OR = 1.232, 95% confidence interval [0.258, 5.878]) (Figure 3A).
Figure 3.
Distortion product otoacoustic emission (DPOAE) and multiple frequency steady-state response (MSSR) in ears with cochlear nerve deficiency (CND).
For MSSR testing, two-way ANOVA revealed a significant effect on groups [F (1,34) = 7.523, p = 0.009, ηp2 = 0.181] but no significant effect on test frequencies [F (4,136) = 2.138, p = 0.079, ηp2 = 0.059] or interaction between the two effects [F (4,136) = 0.274, p = 0.894, ηp2 = 0.008]. Multiple comparisons with the Fisher LSD correction showed lower thresholds at 500 Hz, 1,000 Hz, 2,000 Hz and average MSSR for ears with positive waves than for ears without positive waves (500 Hz: mean difference = −9.381, p = 0.044, 95% confidence interval [−18.495, −0.267]; 1,000 Hz: mean difference = −11.037, p = 0.014, 95% confidence interval [−19.704, −2.370]; 2,000 Hz: mean difference = −8.700, p = 0.027, 95% confidence interval [−16.360, −1.039]; 4,000 Hz: mean difference = −7.183, p = 0.111, 95% confidence interval [−16.102, 1.737]; average MSSR: mean difference = −9.075, p = 0.010, 95% confidence interval [−15.799, −2.351]). The mean MSSR values were 103.16 ± 9.95 dB nHL and 112.24 ± 9.87 dB nHL for ears with and without positive waves, respectively (Figure 3B).
EABR extraction rates, thresholds, and latency analysis
Statistical comparisons between patients exhibiting positive waves (n = 12) and those without positive waves (n = 12) revealed no significant differences in EABR extraction rates across channels (C2: p > 0.999, OR = 1.400, 95% confidence interval [0.279, 7.016]; C5: p > 0.999, OR = 1.000, 95% confidence interval [0.197, 5.068]; C8: p = 0.220, OR = 4.000, 95% confidence interval [0.733, 21.838]; C11: p = 0.414, OR = 2.800, 95% confidence interval [0.532, 14.735]). The EABR thresholds (mean ± SD) for patients with positive waves were 642.9 ± 237 µV, 685.7 ± 241.0 µV, 737.5 ± 159.8 µV and 775.0 ± 128.2 µV for C2, C5, C8 and C11, respectively. The EABR thresholds for patients without positive waves were 766.6 ± 265.8 µV, 742.9 ± 181.3 µV, 950.0 ± 100.0 µV and 960.0 ± 89.44 µV for C2, C5, C8 and C11, respectively. The EABR thresholds were significantly lower for ears with positive waves than for those without positive waves at C11 (C2: U = 14.5, p = 0.421, r = 0.246; C5: U = 21, p = 0.642, r = 0.110; C8: U = 4.5, p = 0.085, r = 0.571; C11: U = 5.5, p = 0.048, r = 0.618) (Figure 4A). The eV latencies (mean ± SD) for patients with positive waves were 3.99 ± 0.50 ms, 3.85 ± 0.41 ms, 3.69 ± 0.33 ms and 3.80 ± 0.21 ms for C2, C5, C8 and C11, respectively. The eV latencies for patients without positive waves were 3.72 ± 0.30 ms, 3.77 ± 0.29 ms, 3.91 ± 0.25 ms and 3.95 ± 0.32 ms for C2, C5, C8 and C11, respectively. No significant difference in the eV latencies was found between the two groups across all channels (C2: U = 29, p = 0.269, r = 0.302; C5: U = 32, p = 0.364, r = 0.239; C8: U = 10.5, p = 0.388, r = 0.246; C11: U = 14.5, p = 0.468, r = 0.204) (Figure 4B).
Figure 4.
Threshold and latency analysis of the electrically evoked auditory brainstem response (EABR). The EABR thresholds (mean ± SD) were significantly lower for ears with positive waves than for those without positive waves at C11 (C2: 642.9 ± 237 vs. 766.6 ± 265.8 µV, p = 0.421; C5: 685.7 ± 241.0 vs. 742.9 ± 181.3 µV, p = 0.642; C8: 737.5 ± 159.8 vs. 950.0 ± 100.0 µV, p = 0.085; C11: 775.0 ± 128.2 vs. 960.0 ± 89.44 µV, p = 0.048) (Figure 4A). No significant difference in the eV latencies was found between the two groups across all channels (C2: 3.99 ± 0.50 vs. 3.72 ± 0.30 ms, p = 0.269; C5: 3.85 ± 0.41 vs. 3.77 ± 0.29 ms, p = 0.364; C8: 3.69 ± 0.33 vs. 3.91 ± 0.25 ms, p = 0.388; C11: 3.80 ± 0.21 vs. 3.95 ± 0.32 ms, p = 0.468) (Figure 4B).
Clinical outcome assessment
Postoperative performance evaluation of 24 CND patients revealed distinctive patterns in auditory outcomes. One year after CI, patients with positive waves achieved a mean CAP score of 3.17 ± 0.58, whereas those without the waves scored 2.92 ± 0.67. Speech intelligibility assessment through the SIR test revealed scores of 2.00 ± 0.60 and 1.58 ± 0.67 for the groups with and without positive waves, respectively (CAP: U = 57.50, p = 0.410, r = 0.198; SIR: U = 47.00, p = 0.160, r = 0.329). However, these differences did not reach statistical significance for either measure. Two years after CI, patients with positive waves demonstrated higher scores than those without the positive deflection in the CAP tests did (CAP: U = 37.50, p = 0.045, r = 0.473; SIR: U = 42.00, p = 0.089, r = 0.449) (Figure 5).
Figure 5.
Categories of auditory performance (CAP) and speech intelligibility rating (SIR) scores in cochlear nerve deficiency (CND) patients with and without a positive wave at different time points.
Discussion
Auditory brainstem response (ABR) testing at 95 dB nHL revealed a distinctive positive wave in 15% of the examined ears (22/144). In patients with bilateral CND (24 patients, 48 ears), 20 ears presented a positive wave with latencies between 4–5 ms, falling between typical wave III and V measurements [22]. This wave exhibits amplitude reduction and latency prolongation with decreasing stimulus intensity, appearing exclusively at high intensities. In contrast, subjects without inner ear anomalies presented no positive waves. However, the origin and mechanism of this positive deflection remain poorly understood and sparsely documented. Statistical analysis revealed a strong correlation between the occurrence of this ABR component and CND. Among the 48 CND-affected ears, 32 presented with isolated cochlear nerve canal stenosis, whereas 16 displayed additional semicircular canal and/or vestibular abnormalities. A positive wave appeared in 20/32 ears with isolated CNCs. Notably, none of the 16 ears with combined CNCs and semicircular canal malformations/vestibular malformations presented this ABR characteristic, suggesting that concurrent vestibular system abnormalities may influence their manifestations. The specificity of this waveform to CND cases, which are absent in other inner ear malformations or sensorineural hearing loss, may be explained by vestibular–auditory neural pathway interconnections. An intact vestibular system might preserve these neural connections, thereby influencing ABR characteristics. Research indicates that approximately one-third of pediatric CND patients present with concurrent vestibular abnormalities [25]. When evaluating patients with sensorineural hearing loss and cochlear nerve canal stenosis, careful assessment of semicircular canal integrity is essential [26]. The presence of normal semicircular canal and vestibular structures may be a prerequisite for generating this distinctive positive wave in CND patients. The Tullio phenomenon demonstrates that high-intensity sound stimulation can affect saccule function [27]. Another negative wave from the ABR evoked high-intensity sound is the ASNR. The ASNR is generally found in patients with large vestibular aqueduct and is likely to originate from the saccule [28–30]. Although the findings of this study suggest that vestibular system integrity may influence the generation of positive waves, this relationship requires further investigation in future studies.
Our examination of 48 ears from 24 patients with CND revealed clear wave V responses in 5 ears at 95 dB nHL testing levels, with the lowest auditory brainstem response (ABR) sensitivity threshold at 70 dB nHL. While CND typically manifests as severe-to-profound hearing deficits [18], recent evidence has revealed cases of moderate hearing impairment in pediatric patients with radiologically confirmed CND [31]. This variability likely stems from two factors: current imaging technology limitations in detecting minute nerve fibers and anatomical configurations that impede MRI visualization of the cochlear nerve. Our assessment of hearing capabilities revealed no consistent audiological patterns across various cochleovestibular nerve configurations, underscoring the necessity for individualized patient evaluation. Cochlear implants function by converting acoustic signals into electrical stimuli via a processor, which then activates cochlear nerve fibers to generate auditory sensations. The evidence indicates that postimplantation outcomes correlate directly with the integrity of both the cochlear nerve and the auditory pathway [32–34]. Historically, CND patients were considered poor candidates for CI because of their suboptimal outcomes [35]. Studies indicate substantially reduced implant efficacy in CND patients, necessitating comprehensive discussions with families regarding realistic expectations [36]. However, patients demonstrating functional auditory pathways through diagnostic testing may achieve favorable outcomes, independent of their MRI-based diagnosis. The preimplantation evaluation protocol typically combines monitored hearing aid usage with professional audiological assessment, including ABR or MSSR measurements, to predict potential outcomes. Our findings revealed that ears exhibiting positive ABR responses presented better hearing thresholds than those without positive waves according to the MSSR. This observation raises the crucial research question of whether there is a correlation between positive ABR waves and subsequent CI success rates.
EABR plays a crucial role in assessing auditory nerve function and ascending pathway integrity. Recent evidence has demonstrated its predictive value for hearing outcomes in patients with prolonged hearing loss, particularly those with cochlear nerve hypoplasia and aplasia [37]. EABR assessment has become instrumental in clinical decision-making between CI and auditory brainstem implantation for treating profound hearing loss [38]. The combination of preoperative magnetic resonance imaging and EABR measurements enhances the prediction of CI performance, especially in patients with cochlear nerve abnormalities [39]. Current research indicates that pediatric patients with CNCs have lower EABR detection rates and higher thresholds than do patients without inner ear malformations (IEMs) [23]. This finding aligns with the observed elevated EABR thresholds in patients with cochlear nerve hypoplasia [31]. A comparison between patients with and without a positive wave revealed significant differences in the EABR thresholds for two channels (C8 and C11). In our study of 24 CND patients, researchers found no significant variations in EABR extraction rates or latency per channel between patients with and without positive waveforms. While the EABR has prognostic value, its utility remains constrained by the substantial impact of postimplantation rehabilitation on CI outcomes in CND patients [40,41].
The evaluation of hearing outcomes in 24 CI patients with CND revealed notable trends in auditory performance post-surgery. Statistical analysis revealed that these differences in auditory scale scores were not significant at the one-year follow-up. However, at the 24-month follow-up, participants who reported positive responses demonstrated significantly greater CAP scores than did those who lacked such responses. Long-term monitoring indicated that CND patients who scored below 1 on the CAP scale within the first year rarely improved beyond this threshold during subsequent three-year evaluations. In contrast, individuals who achieved CAP scores exceeding 1 in the initial year demonstrated significant improvement, with approximately 73% reaching CAP scores of 4 or higher during follow-up assessment [42]. Research indicates that neither implantation age nor residual hearing level significantly influences postoperative CAP and SIR measurements in CND patients [43].
There is still a methodological limitation in this study. A retrospective design was used here and the sample size of 24 CND patients was relatively small, which may limit the statistical power and generalizability across the broader CND population. Our study might have been underpowered to detect smaller, yet potentially meaningful, effects. In addition, the variability in device type, implantation age, and follow-up time introduced potential confounding factors that might influence the study results independently of the variables we examined. Future studies should validate these findings across diverse patient populations with a prospective cohort design.
Conclusion
This study identified a distinctive positive waveform in the ABR testing of CND patients, which may indicate preserved auditory pathway integrity. Patients exhibiting this characteristic demonstrated better hearing levels than those without positive waves. While the observed improvements in auditory and speech outcomes did not reach statistical significance in the first postoperative year, the trend observed in longer-term follow-up warrants further investigation in larger cohorts to determine whether this waveform may have potential prognostic value for CI success in CND patients. Future studies should avoid methodological limitations and validate these preliminary findings with a larger-scale, multicenter, and prospective cohort design.
Acknowledgments
The authors thank all the subjects and their families involved in this study. RG collected and analyzed data and approved the final version of this paper. WL collected data and approved the final version of this paper. WZh analyzed data and approved the final version of this paper. JS designed this study, provided critical comments, and approved the final version of this paper. JS analyzed data and approved the final version of this paper. CL designed this study, analyzed data, and approved the final version of this paper. XG designed this study, provided critical comments, and approved the final version of this paper.
Funding Statement
This work was supported by the National Natural Science Foundation of China (Grants 82301299, 82471172, 82271180, 82471179, 82201278, and 82471162), the Excellent Young Scientists Fund of the Natural Science Foundation of China (Grant 82322020), and the National Key R&D Program of China (Grant 2024YFC2418105).
Ethical statement
This study adheres to the Declaration of helsinki and was approved by the ethics committee of the University of Science and Technology of China (No. 2020-KY-211). Written informed consent to participate in this study was obtained from the participants’ guardians.
Disclosure statement
No potential competing interest was reported by the authors.
Data availability statement
The datasets are available from the corresponding author, Guo XT, on reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets are available from the corresponding author, Guo XT, on reasonable request.