ABSTRACT
Objectives
Examine the incidence of one or more electrode contacts placed within the region of functional acoustic hearing and the potential influence of electrode positioning on speech recognition for pediatric cochlear implant (CI) recipients.
Methods
A retrospective review for pediatric CI recipients of straight electrode arrays with preserved low‐frequency hearing (an unaided threshold of ≤ 80 dB HL at 250 Hz) was conducted at a tertiary referral center. Intraoperative X‐rays were used to determine the angular insertion depth (AID) of each electrode. Proximity of contacts to the functional acoustic hearing region was calculated using AID and postoperative unaided thresholds. For electric‐acoustic stimulation (EAS) users, the association between proximity values and CNC word recognition in quiet was reviewed at 3‐, 6‐, and 12‐months post‐activation.
Results
Among 69 ears, 90% had at least one electrode contact within the functional acoustic hearing region. Proximity values ranged from −131° to 450° (mean: 100°, SD: 120°). For EAS users with speech recognition data (n = 29), proximity values were not significantly associated with post‐activation CNC scores (p ≥ 0.212).
Conclusions
Most pediatric CI recipients with hearing preservation had at least one electrode contact in the region of functional acoustic hearing. Proximity was not significantly associated with word recognition in quiet for EAS users, though this subgroup was limited in sample size. Further studies in pediatric EAS users are needed to understand the potential relationship with speech recognition in noise and to determine the benefits of individualizing array selection and/or EAS mapping.
Level of Evidence
3.
Keywords: angular insertion depth, electric‐acoustic stimulation, functional acoustic hearing, hearing preservation
This study reviewed the incidence of electrode contacts within the functional acoustic hearing region in pediatric cochlear implant recipients. Of 69 ears, 90% had at least one electrode contact in this region. For those with speech recognition data, word recognition in quiet was not significantly associated with proximity within the functional acoustic hearing region. Research is needed to understand the effects of electrode contact placement within this region on speech recognition in noise and the long‐term effects on hearing preservation.
1. Introduction
Pediatric cochlear implant (CI) recipients with low‐frequency hearing preservation have significantly improved speech recognition with an electric‐acoustic stimulation (EAS) device as compared to their preoperative performance [1, 2, 3]. However, individual outcomes vary widely, likely due to multiple factors including heterogeneous cochlear anatomy, duration of hearing loss, surgical technique, and postoperative low frequency thresholds [4, 5, 6]. An additional factor to consider is the potential interplay between electric and acoustic stimulation, which is influenced partly by positioning of the electrode array [7] and can negatively influence speech recognition with EAS [8]. Electrode array positioning in relation to the region of functional acoustic hearing likely contributes to the variability in outcomes for pediatric EAS users since angular insertion depth (AID) varies widely across CI recipients [5, 9], yet is not accounted for in traditional EAS mapping.
The incidence of contact placement in the region of functional acoustic hearing and the relationship between array placement and speech recognition with EAS was recently explored in adults by Nix and colleagues [5]. Angular insertion depth (AID) of the most apical electrode contact (EA) was determined from either intraoperative X‐ray or postoperative computed tomography (CT) imaging. In that sample, 60% had at least one electrode contact in the region of functional acoustic hearing [5]. Importantly, electrode array placement significantly influenced speech recognition in noise for EAS users 6 months following device activation. Specifically, the best scores were observed for cases where EA was in close correspondence to the upper border of the region of functional acoustic hearing [5]. EAS users with electrode arrays located either more basal or more apical to this region had poorer scores, which was thought to be due to stimulation gaps within the cochlea or electric‐on‐acoustic interference, respectively.
In pediatric CI recipients, the incidence of electrode contacts located in the region of functional acoustic hearing and the relationship between electrode array placement and EAS outcomes are unknown. The current study aimed to review the positioning of straight electrode arrays relative to the region of functional acoustic hearing for pediatric CI recipients and explore the association between electrode array placement and speech recognition for children using EAS.
2. Materials and Methods
A retrospective review was conducted for pediatric CI recipients with preserved low‐frequency hearing who received a MED‐EL straight electrode array (MED‐EL Corporation, Innsbruck, Austria) between 2016 and 2024. Inclusion criteria were an unaided acoustic threshold of ≤ 80 dB HL at 250 Hz at device activation, normal cochlear anatomy, ≤ 18.5 years of age at surgery, and intraoperative X‐ray of sufficient quality for visualization of electrode contacts. Exclusion criteria were cases of revision CI surgery, those with known or suspected cognitive delays, and those with inner ear malformations. Patients with enlarged vestibular aqueduct were included if cochlear anatomy was normal. Each ear was evaluated independently, and only ears meeting inclusion criteria were analyzed. Thus, device laterality does not necessarily equate to hearing status or hearing technology used in the contralateral ear. The study was approved by the site's Institutional Review Board.
Patients were recipients of a Flex24, Flex26, Flex28, or FlexSOFT electrode array. These 12‐channel flexible, straight arrays differ in length (24‐, 26‐, 28‐, and 31.5‐mm, respectively). The selection of the specific electrode array was based in part on the patient's unaided thresholds and the surgeon's preference. Typically, a shorter (24 mm) electrode array was selected for patients with low‐frequency thresholds that were either normal or in the mild hearing loss range; a longer (28 or 31.5 mm) electrode array was selected for patients with moderate to moderately severe thresholds in the low frequencies. Preoperative imaging was not used for device selection for this sample. At device activation (~4 week postoperatively), unaided acoustic thresholds for 125–8000 Hz were measured behaviorally with pulsed pure tone stimuli, presented via inserts. If no behavioral response was elicited, a value of 120 dB HL was recorded. The mean of the unaided thresholds at 125, 250, and 500 Hz was used to determine the low‐frequency pure tone average (LFPTA).
Clinical fitting procedures at the activation visit typically included the assignment of the most comfortable loudness (MCL) levels using behavioral measures or electrically‐evoked stapedius reflex threshold (ESRT), and estimation of threshold levels (e.g., 10% of MCL). At post‐activation visits, ESRT was typically used to assign MCL levels; behavioral measures were used if ESRT was not possible. Threshold levels were typically measured behaviorally at the post‐activation visits; thresholds remained at 10% of MCL when behavioral testing was not possible. At the study center, children with a postoperative unaided threshold of ≤ 65 dB HL at 250 Hz are typically recommended to be fit with an EAS device. Children with severe or profound unaided thresholds were typically fit with a CI alone device. For EAS users, the acoustic settings were programmed using real‐ear‐to‐coupler difference measurements and to fit DSL prescriptive targets. The maximum unaided threshold that can be fit with the MED‐EL EAS system is 80 dB HL [10], which is why this criterion was selected for inclusion in the present study.
The assessment of speech recognition was conducted in a sound booth using the consonant‐nucleus‐consonant (CNC) words in quiet [11]. Patients sat facing 0° azimuth, approximately 1 m from the loudspeaker. Recorded materials were presented at 60 dB SPL and a masker was presented to the contralateral ear via an insert when necessary.
Intraoperative X‐rays were analyzed to determine the AID for each electrode contact using a rotating 3‐D helical scala tympani model as described by Giardina et al. [12], which is the same procedure as used by Nix et al. [5] for intraoperative X‐rays. Two independent reviewers measured AID values for each case. Discrepancies of greater than 10° for the values calculated AID resulted in exclusion of the case.
The first aim was to determine the incidence of electrode contacts in the region of functional acoustic hearing, which was defined as ≤ 80 dB HL at 250 Hz. Unaided thresholds at activation and the AID values for each electrode contact were used to calculate proximity to the region of functional acoustic hearing, using the same procedure as described by Nix et al. [5]. Briefly, linear extrapolation with log‐transformed frequency was used to estimate the frequency at which unaided thresholds exceeded 80 dB HL and those frequencies were converted into AID values using the spiral ganglion frequency‐to‐place function [13]. Proximity values were calculated as the difference in the AID at EA and the AID at which unaided thresholds exceeded 80 dB HL. Positive values indicated EA placement within the region of functional acoustic hearing; negative values indicated a more basal placement. Figure 1 illustrates the determination of proximity from intraoperative X‐ray for two cases: one with an electrode array placed basal to the functional acoustic hearing region (negative proximity value) and one with the electrode array placed within the functional acoustic hearing region (positive proximity value). Both cases have the same boundary of the functional acoustic hearing region at an angular depth of 460°. Negative proximity values may be due to a shallow electrode array insertion depth (as a result of electrode array length and/or a larger cochlea size) as well as poorer residual hearing (smaller region of functional acoustic hearing region in the apex). Positive proximity values may be due to a deep electrode array insertion depth (due to the electrode array length and/or a smaller cochlea size) as well as more residual hearing (larger region of functional acoustic hearing region in the apex). Incidence refers to the percentage of patients in the sample with positive proximity values.
FIGURE 1.
Examples of proximity to the functional acoustic hearing region for two individuals with the same functional acoustic hearing and different electrode array angular insertion depths (AID). Proximity was defined as the difference between AID at EA and the AID at which unaided thresholds exceeded 80 dB HL. The angular depth corresponding to 80 dB HL (i.e., boundary of the functional acoustic hearing region) was 460° for both cases, as indicated by the blue line. (A) Electrode array placed at an AID of 400° (electrode array placed basal to the functional acoustic hearing region), resulting in a negative proximity value of −60°. (B) Electrode array placed at an AID of 720° (electrode array placed within the functional acoustic hearing region) resulting in a positive proximity value of 260°.[Color figure can be viewed in the online issue, which is available at www.laryngoscope.com]
An additional aim was to explore the relationship between proximity values and speech recognition for pediatric EAS users. We queried speech recognition data for pediatric EAS users from routine post‐activation visits (3, 6, and 12‐months). Only speech recognition data in quiet were included, as the available speech recognition in noise was insufficient for analysis. Data from children listening with a place‐based map were excluded since the place‐based mapping procedure accounts for the placement of the electrode array [14]. One‐tailed Pearson correlations computed in Prism 9 (GraphPad Software Inc., Boston, MA) were used to analyze associations between proximity values and CNC scores.
3. Results
Sixty‐nine (69) individual ears met inclusion criteria (45 unilateral, 12 bilateral). Age at surgery ranged from 1.3–18.4 years (mean 9.4, SD 4.6). Demographic information for the sample (41 female) is presented in Table 1. Most had a Flex24 electrode array (n = 45), followed by Flex28 (n = 18), FlexSOFT (n = 5), and Flex26 (n = 1). The mean AID of EA was 502° (SD: 80°), with a range of 372° to 752°. The preoperative LFPTA for the cohort ranged from 3.3 dB HL to 73.3 dB HL (mean 34.3, SD 17.4). The postoperative LFPTA ranged from 15 dB HL to 86.7 dB HL (mean 52.9, SD 17.9). The mean proximity of EA to the region of functional acoustic hearing was 100°, indicating an overlap of one or more electrode contacts and residual hearing region, with values ranging from −131° to 450°.
TABLE 1.
Data for demographics of pediatric cochlear implant recipients with residual low‐frequency hearing.
| Biological sex |
Female (n = 41) Male (n = 28) |
|
| Age at implantation (years) |
Min: 1.3 Max: 18.4 Mean: 9.4 SD: 4.6 |
|
| Etiology of hearing loss |
Unknown (n = 35) Suspected prematurity complications (n = 7) Suspected Hereditary (n = 5) Trauma (n = 4) Hypoxia (n = 4) Malformation (non‐syndromic) (n = 3) Brown–Vialetto–Van Laere (n = 2) Pendred Syndrome (n = 2) Cochlear nerve deficiency (n = 1) cCMV (n = 1) Infection (n = 1) Ototoxicity (n = 1) CLIC5 (n = 1) Kernicterus (n = 1) |
|
| Hearing loss onset age |
Congenital (n = 38) 1–3 years (5) 4–12 years (5) 13–18 years (3) Unknown (n = 18) |
|
| Electrode array |
Flex24 (n = 45) Flex26 (n = 1) Flex28 (n = 18) FlexSOFT (n = 5) |
|
| Angular insertion depth (degrees) |
Min: 372° Max: 752° Mean: 502° SD: 80° |
|
| Proximity to functional acoustic hearing region (degrees) |
Min: −131° Max: 450° Mean: 100° SD: 120° |
|
| Preoperative | 250 Hz unaided threshold (dB HL) |
Min: 0 Max: 65 Mean: 31.6 SD: 18 |
| Low frequency pure tone average (dB HL) a |
Min: 3.3 Max: 73.3 Mean: 34.3 SD: 17.4 |
|
| Postoperative | 250 Hz unaided threshold (dB HL) b |
Min: 10 Max: 80 Mean: 49.4 SD: 19.2 |
| Low frequency pure tone average (dB HL) b |
Min: 15 Max: 86.7 Mean: 52.9 SD: 17.9 |
|
Note: Each ear was treated as an individual.
Low‐frequency pure tone average was calculated as the mean of unaided thresholds at 125, 250, and 500 Hz.
Values calculated at the initial activation visit (~4 weeks post‐operatively).
Ninety percent (62/69) of patients had one or more electrode contacts in the region of functional acoustic hearing. Electrode contacts in this region were found across recipients of each electrode array type. Figure 2 illustrates AID and the number of electrode contacts in the region of functional acoustic hearing for each patient, stratified by electrode array. It was most common (30%) to have two electrode contacts in the region of functional acoustic hearing. It was more likely for a patient to have four or more electrode contacts in this region than it was for EA to be placed basal to this region (25% vs. 10%, respectively).
FIGURE 2.
Angular insertion depth for individual pediatric CI recipients stratified by electrode array. Symbol color indicates the number of electrode contacts within the functional acoustic hearing region, as defined in the legend. Each point represents one ear. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com]
For this sample, CNC word data were available for 20 EAS users at 3 months, 25 at 6 months, and 21 at 12 months post‐activation. Demographic information for this subset (21 female) is presented in Table 2. Figure 3 displays the distribution of CNC scores as a function of proximity to the functional acoustic hearing region at each post‐activation visit. An additional figure illustrating the relationship between the preoperative CNC scores and the post‐activation CNC scores at the reviewed follow‐up visits can be found in the Supporting Information file. There was an insufficient sample size to assess this relationship for patients with basal placement (negative values). For pediatric EAS users with electrode contacts placed in the region of functional acoustic hearing, there were no significant associations between proximity values and CNC scores at the 3‐month (r (17) = −0.32, p = 0.212), 6‐month (r (20) = −0.26, p = 0.263), or 12‐month visits (r (15) = 0.25, p = 0.361). While these data are exploratory considering the limited sample size of the subgroup, these data suggest that increased overlap of the electrode array with the region of functional acoustic hearing did not significantly diminish speech recognition in quiet.
TABLE 2.
Data for demographics of subset of pediatric EAS users with speech recognition data.
| Biological sex | Female (n = 21) Male (n = 8) | |
| Age at implantation (years) |
Min: 4.7 Max: 18.4 Mean: 9.8 SD: 3.9 |
|
| Etiology of hearing loss |
Unknown (n = 13) Suspected prematurity complications (n = 3) Suspected hereditary (n = 3) Malformation (non‐syndromic) (n = 2) CLIC5 (n = 2) CND—no known syndrome (n = 1) Trauma (n = 1) Infection (n = 1) cCMV (n = 1) Ototoxicity (n = 1) Hypoxia (n = 1) |
|
| Hearing loss onset age |
Congenital (n = 16) 1–3 years (2) 4–12 years (2) 13–18 years (2) Unknown (n = 7) |
|
| Hearing loss stability |
Unknown (n = 2) Progressive (n = 19) Stable (n = 6) Sudden (n = 2) |
|
| Electrode array |
Flex24 (n = 18) Flex28 (n = 10) FlexSOFT (n = 1) |
|
| Angular insertion depth (degrees) |
Min: 396° Max: 679° Mean: 499° SD: 76° |
|
| Proximity to functional acoustic hearing region (degrees) |
Min: −52° Max: 450° Mean: 115° SD: 109° |
|
| Preoperative | Low frequency pure tone average (dB HL) a |
Min: 3.3 Max: 60 Mean: 29.3 SD: 15.8 |
| Postoperative | Low frequency pure tone average (dB HL) b |
Min: 21.7 Max: 73.3 Mean: 48.0 SD: 14.6 |
Note: Each ear was treated as an individual participant.
Low‐frequency pure tone average was calculated as the mean of unaided thresholds at 125, 250, and 500 Hz.
Values calculated at the initial activation visit (~4 weeks postoperatively).
FIGURE 3.
Speech recognition in quiet (CNC words in percent correct) as a function of proximity of the most apical electrode contact (EA) to the functional acoustic hearing region. Positive proximity values indicate EA contact was positioned within the functional acoustic hearing region, while negative values indicate the EA contact was basal to this region. There was no significant association between speech recognition in quiet and proximity of EA at 3, 6, or 12 months post‐activation.[Color figure can be viewed in the online issue, which is available at www.laryngoscope.com]
4. Discussion
Several studies have investigated hearing preservation and outcomes with EAS in adults, with substantially fewer investigations of pediatric CI recipients. The benefits of EAS have been reported in children with functional acoustic hearing; however, not all eligible patients elect to be fit and others may discontinue use of EAS [15]. Spitzer et al. suggested that one key factor in why children may prefer a CI alone device over an EAS device may be lack of perceived benefit [15], which may be due to poor sound quality by not accounting for the position of the electrode array in EAS mapping. The present study reviewed the incidence of electrode contacts located within the region of functional acoustic hearing for pediatric CI patients. Remarkably, at least one electrode contact was found within the region of functional acoustic hearing for 90% of our sample—an incidence considerably higher than previously reported in adults (i.e., 60%) [5]. For this sample of pediatric EAS users, exploratory analyses revealed no significant relationship between CNC scores in quiet and proximity of EA within the region of functional acoustic hearing.
One possible explanation for the higher incidence of electrode contact placement within the region of functional acoustic hearing in children (90%) as compared to adults (60%) [5] is subtle differences in pediatric and adult cochleae. It has been established that the cochlea achieves adult size during gestation; however, changes occur in the skull base and temporal bone following birth that may contribute to age‐related variations in cochlear positioning [16, 17]. Such developmental variations have been described, such as a more obtuse angle of the basal turn [18] and close distance between the round window and the facial recess in younger children [19], which could potentially impact both array insertion depth and quantity of electrode contacts in the region of functional acoustic hearing. Additionally, it remains unclear whether children possess a more robust residual hearing region at baseline when compared to adults, which could be another explanation for the increased incidence. It may be that the greater inherent biological resilience of children, with higher resistance to cell death mechanisms, could explain a greater rate of preserved hearing area in the cochlea [20]. Further studies are warranted to elucidate effects of age on cochlear morphology with respect to preserved hearing regions.
Electrode array length did not appear to influence the presence of electrode contacts in region of functional acoustic hearing; electrode contacts were found across all electrode array lengths in this sample. Of note, the majority of the patients studied (45/69 or 65%) were implanted with the 24‐mm straight electrode array. The disproportionate representation of the 24‐mm array in the sample is likely a reflection of the surgical bias to opt for shorter electrode arrays in efforts to reduce trauma and preserve residual hearing.
In the present sample of pediatric EAS users, proximity of EA within the residual hearing region did not significantly influence speech recognition in quiet. This pattern in speech recognition aligns with the findings of Nix et al. in adult EAS users and suggests that proximity may not be a salient factor in performance in quiet [5]. Interestingly, Nix and colleagues found significant associations between speech recognition in noise and proximity (i.e., AzBio sentences in a 10‐talker masker, 10 dB SNR) [5]. In adults, EAS users with EA placed close to the upper edge of the region of residual hearing had better speech recognition in noise, suggesting an advantage in positioning EA in alignment with the upper border of residual hearing [5]. For our pediatric sample, speech recognition in noise data were limited at the reviewed post‐activation visits. Additional speech recognition testing in noise is warranted for more complete characterization of the impact of electrode contact placement on speech recognition for pediatric EAS users.
This study has limitations that merit discussion. First, the sample included recipients of a straight array from a single manufacturer. While this allows for control of variables such as electrode array design and number of electrode contacts, it limits the generalizability of the findings to recipients of other CI manufacturers. We acknowledge that the heterogeneity of factors inherent to pediatric CI populations such as age at implantation, hearing loss etiology, and cognitive function [21, 22] were not controlled for in the present study. Also, the use of X‐rays (rather than CT scans) for determination of AID and estimation of the functional acoustic hearing region may have influenced the precision of measurements. Additionally, speech recognition data in quiet were only available for some children in this sample. The small sample size may have limited the ability to detect a significant relationship between speech recognition and electrode array placement within the functional acoustic hearing region. Larger sample sizes are needed to better understand this relationship, as well as the relationship between speech recognition and negative proximity values (placement basal to the functional acoustic hearing region). Larger studies are needed to assess whether having electrode contacts in the area of functional acoustic hearing may predispose to delayed loss of residual hearing, and whether methods to limit electric‐on‐acoustic interference in EAS mapping support better speech recognition.
5. Conclusions
Among pediatric CI recipients with hearing preservation, 90% had one or more electrode contacts positioned in the region of functional acoustic hearing. Exploratory analyses suggested that proximity to the region of functional acoustic hearing may not significantly influence speech recognition in quiet for pediatric EAS users. Additional sentence‐in‐noise testing is needed to further understand the impact of electrode contacts within this region and the impact of potential electric‐on‐acoustic interference. More insight into the intricacies of electrode array placement and EAS mapping will help guide future development of preoperative planning (including device selection) and corresponding EAS mapping procedures.
Funding
M.T.D. and L.R.P. are supported by a research grant from MED‐EL Corporation provided to the university. K.D.B. serves on the Surgical Advisory Board for Advanced Bionics Corporation and MED‐EL Corporation and is a consultant for Cochlear Corporation. N.J.T. has received consulting fees from iotaMotion Inc.
Disclosure
The authors have nothing to report.
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Figure S1: Relationship of preoperative and post‐activation CNC scores (%) for individual EAS users. Reviewed post‐activation visits included 3, 6, and 12 months (left to right). Symbol color indicates the number of electrode contacts within the functional acoustic hearing region, as defined in the legend.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Figure S1: Relationship of preoperative and post‐activation CNC scores (%) for individual EAS users. Reviewed post‐activation visits included 3, 6, and 12 months (left to right). Symbol color indicates the number of electrode contacts within the functional acoustic hearing region, as defined in the legend.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.