Clinical UM Guideline

This document addresses cochlear implants, auditory brainstem implants, and replacement or upgrade of speech processor and controller components. This document does not address replacement parts other than as specifically described below.

A single- or multi-channel unilateral or bilateral cochlear implant is intended to restore a level of auditory sensation to an individual with unilateral or bilateral severe to profound sensorineural hearing loss by means of electrical stimulation of the auditory nerve. A unilateral hybrid cochlear implant is intended to restore a level of auditory sensation to an individual with residual low-frequency hearing sensitivity and bilateral high-frequency sensorineural hearing loss.

An auditory brainstem implant is a device designed to restore some hearing in an individual with neurofibromatosis type 2 (NF-2) who has been rendered deaf by the surgical removal of neurofibromas involving both auditory nerves.

Unilateral deafness and single-sided deafness both refer to the same condition. This document will refer to this condition as unilateral deafness.

Note: For a high-level overview of this document, please see “Summary for Members and Families” below.

I.  Cochlear Implants

Medically Necessary:

1. Cochlear implantation is considered medically necessary when both criterion 1 and criterion 2 listed below are met:
   1. The individual meets all the following criteria (a through c):
      1. Has received limited benefit from conventional hearing aids; and
      2. Is able to participate* in a post-cochlear implant rehabilitation program; and
      3. Absence of any of the following (i through iii):
         1. Active middle ear infections; or
         2. Cochlear nerve deficiency or other lesions in the auditory nerve confirmed by magnetic resonance imaging (MRI) (including cochlear nerve aplasia or hypoplasia); or
         3. Lesions in the central auditory pathway.
            and
   2. The individual has unilateral or bilateral sensorineural deafness with hearing loss in the ear(s) to be implanted greater than or equal to 70 decibels (dB).

Note: Implantation may be unilateral, bilateral-simultaneous [same session] procedures, or bilateral-sequential [different session] procedures. If bilateral-sequential, hearing tests do not need to be repeated between procedures.

*Note: For a young child, a parent or guardian may act as the surrogate for participation.

2. Upgrade to or replacement of an existing external speech processor, controller or speech processor and controller (integrated system) is considered medically necessary when the following criteria (1 and 2) are met:
   1. The existing components no longer meet the individual’s needs as demonstrated by either one of the following (a or b):
      1. Functional but inadequate to the point of interfering with the activities of daily living; or
      2. No longer functional.
         and
   2. The request is NOT for convenience or to upgrade to a newer technology when the current components remain functional.
3. Unilateral implantation of a hybrid cochlear implant device (for example, Nucleus^® Hybrid™ L24 Cochlear Implant System, Cochlear Americas, Lone Tree, CO) is considered medically necessary when all of the following criteria are met (1, 2, and 3 are required):
   1. Hearing requirements for the ear to be implanted (both a and b required):
      1. Hearing loss is 60 dB or lower at 125, 250, and 500 hertz (Hz); and
      2. Hearing loss is 75 dB or greater at 2000, 3000, and 4000 Hz.
         and
   2. Hearing loss in the contralateral (non-implanted) ear is 60 dB or greater at 2000, 3000, and 4000 Hz; and
   3. Preoperative Consonant-Nucleus-Consonant (CNC) word recognition (speech perception) scores show both of the following (both a and b required):
      1. Ear to be implanted CNC score is between 10% and 60%; and
      2. Contralateral (non-implanted) ear CNC score shows both of the following criteria (i and ii required):
         1. CNC score is 80% or lower in the best-aided condition; and
         2. CNC score is higher than the ear to be implanted.

Not Medically Necessary:

1. Upgrade to or replacement of an existing external speech processor, controller or speech processor and controller (integrated system) is considered not medically necessary when the criteria specified above are not met.
2. A cochlear implant is considered not medically necessary for all other indications when the above criteria are not met, including as a treatment for tinnitus in the absence of severe hearing loss (greater than or equal to 70 dB).

II.  Auditory Brainstem Implants

Medically Necessary:

1. An auditory brainstem implant is considered medically necessary in an individual when all of the following criteria are met:
   1. Is 12 years of age or older; and
   2. Diagnosed with neurofibromatosis type 2; and
   3. Is completely deaf as a result of bilateral neurofibromas of the auditory nerve.
2. Upgrade to or replacement of an existing external sound processor, remote assistant or both components is considered medically necessary for an individual whose response to existing components is inadequate to the point of interfering with the activities of daily living or when components are no longer functional.

Not Medically Necessary:

1. Upgrade to or replacement of an existing external sound processor, remote assistant, or both components is considered not medically necessary when the criteria specified above are not met, including as a treatment for tinnitus in the absence of severe hearing loss.
2. An auditory brainstem implant is considered not medically necessary for all other indications when the above criteria are not met.

This document describes clinical studies and expert recommendations and explains when the use of cochlear implants is clinically appropriate. The following summary does not replace the medical necessity criteria or other information in this document. The summary may not contain all of the relevant criteria or information. This summary is not medical advice. Please check with your healthcare provider for any advice about your health.

Key Information

The ear has three main parts: the outer ear, the middle ear, and the inner ear. Sound travels through the outer and middle ear to reach the inner ear, where a small, spiral-shaped structure called the cochlea is located. The cochlea contains tiny sensory cells that change sound vibrations into electrical signals. These signals are sent to the brain by the hearing (acoustic) nerve, which allows a person to recognize sounds and understand speech. When the cochlea or the hearing nerve does not work properly, it can lead to significant hearing loss.

A cochlear implant helps bypass parts of the inner ear that are not working properly. Instead of relying on the cochlea to convert sound into signals, the device picks up sound with an external microphone and processes it into electrical signals. These signals are then sent to an internal device placed in the cochlea, which directly stimulates the hearing (acoustic) nerve. The nerve carries these signals to the brain, where they are interpreted as sound. This allows some individuals with severe hearing loss to detect sounds and better understand speech.

A hybrid cochlear implant is a type of cochlear implant for people who can still hear some low-pitched sounds but have trouble hearing high-pitched sounds. It combines a hearing aid and a cochlear implant in one device.

An auditory brainstem implant is a device for people who have lost both hearing nerves. It sends sound signals directly to the brain, skipping the ear and the hearing nerve entirely. This device is used for a rare condition called neurofibromatosis type 2 (NF-2). In NF-2, tumors grow on the hearing nerves and can cause complete hearing loss.

What the Studies Show

Studies show that cochlear implants help people with severe or profound hearing loss hear speech better. People who receive cochlear implants often show improved ability to understand words and sentences, both in quiet settings and in noisy ones. Studies also show that cochlear implants improve quality of life. People report that they can take part in conversations more easily and feel less isolated.

Research has looked at whether getting cochlear implants in both ears is better than getting one. Studies show that people with two cochlear implants can often tell where sounds are coming from and understand speech in noisy places better than people with only one implant. Two implants can be placed at the same time or during separate surgeries.

Studies on hybrid cochlear implants show that many people who receive them can hear both low-pitched and high-pitched sounds. Research shows that most people keep their remaining natural hearing after surgery. People who use hybrid cochlear implants often understand speech better than they did with hearing aids alone.

For auditory brainstem implants, studies show that the device can help some people with NF-2 hear sounds and understand some speech after they lose both hearing nerves. The level of hearing benefit varies from person to person.

Cochlear implant surgery, like all surgery, has some risks. These include infection, dizziness, changes in taste, ringing in the ears, and, in rare cases, damage to the nerve that controls facial movement. For hybrid cochlear implants, there is a chance that remaining natural hearing in the implanted ear could be reduced or lost after surgery. Better studies are needed to know if cochlear implants improve health for some groups of people who are not included in the current recommendations.

When Are These Clinically Appropriate?

A cochlear implant may be clinically appropriate when all of the following are true:

• The person has received limited benefit from regular hearing aids.
• The person is able to take part in a hearing rehabilitation program after surgery. For young children, a parent or guardian may take part on the child’s behalf.
• The person does not have an active middle ear infection, an auditory nerve problem confirmed by magnetic resonance imaging (MRI), or a lesion in the central auditory pathway.
• The person has hearing loss of 70 decibels or more in the ear or ears to be implanted.

A cochlear implant may be placed in one ear or both ears. If placed in both ears, the surgeries can happen at the same time or at different times.

Replacing or upgrading a cochlear implant speech processor or controller may be clinically appropriate when the current parts no longer work or are so limited that they get in the way of daily activities. Replacing parts simply to get newer technology when the current parts still work is not clinically appropriate.

A hybrid cochlear implant may be clinically appropriate when all of the following are true:

• Hearing loss in the ear to be implanted is 60 decibels or lower at low-pitched sounds (125, 250, and 500 hertz) and 75 decibels or higher at high-pitched sounds (2000, 3000, and 4000 hertz).
• Hearing loss in the other ear is 60 decibels or higher at high-pitched sounds (2000, 3000, and 4000 hertz).
• A word recognition test score in the ear to be implanted is between 10% and 60%.
• A word recognition test score in the other ear is 80% or lower and is higher than the score in the ear to be implanted.

An auditory brainstem implant may be clinically appropriate when all of the following are true:

• The person is 12 years of age or older.
• The person has been diagnosed with neurofibromatosis type 2 (NF-2).
• The person is completely deaf because of tumors on both hearing nerves.

When Are These Not Clinically Appropriate?

A cochlear implant is not clinically appropriate when the requirements listed above are not met. This includes use as a treatment for ringing in the ears (tinnitus) when the person does not have severe hearing loss of 70 decibels or more.

An auditory brainstem implant is not clinically appropriate when the requirements listed above are not met.

Replacing or upgrading speech processor or controller parts is not clinically appropriate when it is done only for convenience or to get newer technology while the current parts still work.

(Return to Description)

The following codes for treatments and procedures applicable to this document are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

Cochlear Implants
When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met or for all other diagnoses not listed; or when the code describes a procedure or situation designated in the Clinical Indications section as not medically necessary.

Auditory Brainstem Implants
When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met or for all other diagnoses not listed; or when the code describes a procedure or situation designated in the Clinical Indications section as not medically necessary.

Summary

Peer-reviewed published literature, U.S. Food and Drug Administration (FDA) labeling, and specialty society recommendations and consensus guidance support cochlear implantation as medically necessary for appropriately selected individuals with severe to profound sensorineural hearing loss or other covered patterns of hearing loss who receive limited benefit from hearing aids and can participate in postoperative rehabilitation. The evidence also supports hybrid cochlear implantation for adults who meet the labeled criteria, including preserved low-frequency hearing with severe high-frequency loss and limited aided speech recognition, while recognizing the risk of postoperative loss of residual low-frequency hearing. Published evidence supports auditory brainstem implant (ABI) use for individuals aged 12 years or older with neurofibromatosis type 2 who are completely deaf due to bilateral auditory nerve tumors, while evidence for broader ABI indications remains limited and does not support expansion beyond the defined criteria. The literature does not support cochlear implant or ABI use for broader indications outside these criteria, including tinnitus alone without qualifying hearing loss, and replacement or upgrade of external components is medically necessary only when existing equipment is nonfunctional or functionally inadequate.

Discussion

Background Information and Description of the Technology

A person with normal hearing can perceive sounds in the 20 to 20,000 hertz (Hz) frequency range. The range between 500 and 4000 Hz is most important for understanding speech. Hearing loss is objectively assessed by pure-tone audiometry. While in a soundproof room, the subject is presented with a series of tones at different frequencies and at increasing decibel levels. Earphones are used to test air conduction hearing. A transducer is placed over bone to test bone conduction.

A decibel (dB) is a logarithmic unit used to describe sound level. The hearing threshold is defined as the lowest decibel level at which the subject perceives half of the presented tones. An individual’s thresholds typically differ at different frequencies. The American Speech-Language-Hearing Association classifies hearing loss as follows:

In addition to pure-tone testing in a quiet environment, a complete audiologic assessment will include testing perception in a noisy environment and specific testing of speech recognition. In the Hearing In Noise Test (HINT), sentences are presented from the front and then from each side, both with and without noise. The results are reported as the signal-to-noise ratio at which the tested individual correctly repeats 50% of the sentences. The consonant-nucleus-consonant (CNC) test is an open set word recognition test that is administered in quiet. It uses 10 recorded lists of 50 monosyllabic words to determine speech intelligibility.

This testing approach aligns with the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) Minimum Speech Test Battery, updated in 2024 (MSTB-3; Dunn, 2024), which provides consensus recommendations for assessing adult cochlear implant candidates and recipients.

In the evaluation for potential implantation of a cochlear implant, adults typically receive pure-tone and speech audiometric tests with or without an external hearing aid. Infants and young children receive other objective tests of auditory function. Visual reinforcement audiometry (VRA) is preferred for measuring hearing sensitivity in children between 6 and 24 months of age. VRA uses operant techniques to reward the child for turning their head toward a sound. Once the child is trained to turn their head, sound perception can be tested at different frequencies and intensities. This testing is not appropriate for infants who are less than 6 months old because they do not respond to sound with directed head turns (Holt, 2008). For very young infants, audiologists can assess the auditory system with other objective measures, including evoked otoacoustic emissions (OAE) testing, auditory brainstem response testing (ABR), and auditory steady-state response testing (ASSR).

After an initial diagnosis of hearing loss is made, a cochlear implant team will perform additional testing to determine whether the individual is suitable for cochlear implantation. This testing may include additional audiologic testing to fully characterize the type and degree of hearing loss. Psychological testing is done to assess the individual’s ability to accept a central nervous system implant and to participate in post-implant rehabilitation. A full medical history and physical examination are done to ensure that there is no active infection or other contraindication to anesthesia or the implant surgery. The process often involves advanced imaging techniques such as computed tomography or magnetic resonance imaging (MRI) to evaluate the inner ear anatomy.

Single- or Multi-Channel Cochlear Implantation

A cochlear implant directly stimulates the auditory nerve, bypassing the physiologic transduction of sound into neural impulses by a poorly functioning cochlea. A cochlear implant includes both external and internal components. The external components include a microphone, headpiece, an external sound processor, and an external transmitter/audio input selector. Internal components include an internal receiver implanted within the temporal bone and an electrode array that extends from the receiver into the cochlea through an opening created in the round window of the middle ear. The microphone picks up sounds, the external sound processor converts them into coded signals, and the external transmitter sends those signals through the skin to the implanted internal receiver. The receiver converts the incoming signals into electrical impulses that are sent through the electrode array to the auditory nerve.

Several U.S. Food and Drug Administration (FDA)-approved cochlear implant systems are commercially available in the United States.

The first cochlear implants used in the 1960s had limited utility because they could only provide stimulation at a single frequency. Devices in use since the 1970s can stimulate different areas of the cochlea separately to enable perception of different frequencies. Compared to earlier devices, currently marketed cochlear implants have improved electrode designs and speech processing capabilities. Furthermore, smaller devices and the accumulating experience with use of cochlear implants in children allow these devices to be used by children as young as 12 months of age. Specific criteria for use are different for each device. The FDA-labeled indications for each device are available on the FDA Premarket Approval (PMA) website (FDA, 2018).

Binaural hearing assists in localizing sound and understanding speech in a noisy environment. The auditory benefits enabled by binaural hearing include addressing “head shadow,” “binaural summation,” and “binaural squelch” (Tyler, 2002). Head shadow refers to the reduction in sound level at the ear opposite the sound source, which can improve the signal-to-noise ratio at the better-positioned ear and contribute to sound localization. The “signal” is the sound being focused on while the “noise” is the background sound. Binaural squelch is a central nervous system processing function that diminishes (squelches) background sound and accentuates perception of sound from the ear with the better signal-to-noise ratio. This is essential for focus in a noisy environment such as listening to one conversation in a room full of talking people.

Centers for Disease Control and Prevention (CDC) and Other Recommendations

Cochlear implant recipients should be up to date with age-appropriate pneumococcal conjugate and Haemophilus influenzae type b conjugate vaccinations in accordance with current CDC and Advisory Committee on Immunization Practices (ACIP) recommendations (CDC, 2023).

In 2010, the American Academy of Pediatrics (AAP) issued a policy statement on cochlear implants in children addressing surgical site infections and prevention and treatment of acute otitis media and meningitis. This statement was reaffirmed in 2018. The policy statement includes the following recommendations:

Children with profound deafness who are candidates for cochlear implantation should receive all age-appropriate doses of pneumococcal conjugate and Haemophilus influenzae type b conjugate vaccines. In addition, starting at 24 months of age, a single dose of 23-valent pneumococcal polysaccharide vaccine should be administered. Before implant surgery, primary care providers and cochlear implant teams should ensure that immunizations are up to date, preferably with completion of indicated vaccines at least 2 weeks before implant surgery. Imaging of the temporal bone/inner ear should be performed before cochlear implantation in all children with congenital deafness and all individuals with profound hearing impairment and a history of bacterial meningitis to identify those with inner-ear malformations/cerebrospinal fluid fistulas or ossification of the cochlea (Rubin, 2010).

Efficacy and Safety of Single or Multi-Channel Cochlear Implantation

When they were first developed, cochlear implants were typically implanted only in one ear, even for individuals with severe bilateral hearing loss. It is now common to provide implants to both ears to treat bilateral severe hearing loss. Early peer-reviewed literature included reports of individuals with bilateral cochlear implants, including the study by Tyler (2002). These early reports evaluated small numbers of individuals and provided limited outcome information. Most, but not all, individuals in these studies reported very slight to modest improvements in sound localization and speech intelligibility with bilateral cochlear implants. The benefit was more likely to be experienced in noisy backgrounds, but not necessarily in quiet environments. When reported, the combined use of binaural stimulation improved hearing by only a few decibels or percentage points. This improvement appeared marginal and was not believed to outweigh the significant risks of a second implantation.

Subsequent studies and later syntheses have shown that bilateral cochlear implants can provide some of the benefits of binaural hearing for sound localization and speech perception in both adults and children (Peters, 2007; Lammers, 2014; Kraaijenga, 2017). The largest and most complete of these early case studies included a case series of 30 U.S. children with sequentially placed bilateral cochlear implants (Peters, 2007).

Lammers (2014) summarized evidence of the effectiveness of bilateral cochlear implantation compared with unilateral implantation among children with sensorineural hearing loss. A total of 21 studies evaluated bilateral implantation in children, with no randomized controlled trials identified. The authors were unable to perform pooled statistical analysis due to a limited number of studies, heterogeneity in outcomes and comparison groups, and a high risk for bias in the studies. A “best-evidence synthesis” was performed, with results “…indicating the positive effect of the second implant for especially sound localization and possibly for preverbal communication and language development.” One study demonstrated improvements in language development, although other studies found no significant improvements. The currently available evidence consists solely of cohort studies that compare a bilaterally implanted group with a unilaterally implanted control group, with only one study providing a clear description of matching techniques to reduce bias.

Cochlear Implantation in Adults with Bilateral Severe-to-Profound Hearing Loss

Over the past several decades, studies have investigated the use of bilateral cochlear implantation in adults with severe postlingual hearing loss (Tyler, 2002; Kraaijenga, 2017). When viewed together, these studies show that bilateral cochlear implantation can improve sound localization in most adults and may improve speech perception in others when compared with unilateral implantation.

Kraaijenga (2017) conducted a multicenter randomized clinical trial at 5 tertiary referral centers. This study evaluated objective and subjective measures of simultaneous versus sequential bilateral cochlear implantation in 40 adults with postlingual severe to profound hearing loss and a maximum duration of 10 years without hearing aid use in both ears. The simultaneously implanted group received 2 cochlear implants during 1 surgical procedure, and another 19 participants were randomized to undergo sequential bilateral cochlear implants with an interval of 2 years between implants. The clinical and demographic characteristics of the groups were similar. A total of 3 participants in the sequential group did not receive a second cochlear implant and were unavailable for follow-up. At 1 year after simultaneous or sequential bilateral cochlear implants, similar outcomes were observed for speech intelligibility in noise from straight ahead (difference, 0.9 dB; 95% confidence interval [CI], -3.1 to 4.4 dB) and all secondary outcome measures except for localization with a 30° angle between loudspeakers (difference, -10%; 95% CI, -20.1% to 0.0%). In the sequential bilateral cochlear implant group, all participants performed significantly better after the bilateral cochlear implants on speech intelligibility in noise from spatially separated sources and on all localization tests. This was consistent with most of the participants' self-reported hearing capabilities. Speech intelligibility-in-noise results improved in the simultaneous bilateral cochlear implant group up to 3 years following implantation. This study shows comparable objective and subjective hearing results 1 year after receiving simultaneous bilateral cochlear implants and sequential bilateral cochlear implants with an interval of 2 years between implants. Significant additional improvement was seen after the second implant for those in the sequential bilateral cochlear implant group.

In summary, studies of cochlear implants in adults with severe-to-profound hearing loss who only receive limited or no benefit from amplification with conventional hearing aids show consistent clinical effectiveness in speech reception (especially in noise) and in sound localization with bilateral cochlear implants.

Recent evidence confirms that advanced age alone does not preclude meaningful benefit from cochlear implants. Zhan (2025) conducted a retrospective cohort study of 221 adults aged 80 years and older (171 aged 80 to 89, 50 aged 90 and older) with bilateral severe-to-profound sensorineural hearing loss undergoing cochlear implantation at a tertiary academic center. A total of 60.3% had abnormal preoperative cognitive screens. Mean 1-year postoperative speech scores for ages 80 to 89 versus 90 and older were: CNC words 50% versus 47%; AzBio sentences in quiet 54% versus 50%; and AzBio sentences at +10 dB signal-to-noise ratio 28% versus 23%. No statistically significant differences were found between the 2 age groups on any outcome measure. These findings indicate that advanced age and mild cognitive impairment should not be used as sole exclusion criteria for cochlear implant candidacy.

Cochlear Implantation for Asymmetric Hearing Loss and Bimodal Stimulation

A randomized controlled trial from a Danish research group, with companion analyses of audiologic and quality-of-life outcomes, provides Level 1 evidence that bimodal cochlear implant plus hearing aid significantly outperforms optimally fitted bilateral hearing aids in adults with asymmetric hearing loss and severe-to-profound loss in the poorer ear. In the primary analysis (n=63 randomized), Jakobsen (2026b) reported that 3 months of bimodal cochlear implant plus hearing aid yielded a 13.00 dB signal-to-noise ratio improvement in speech reception threshold at 70 dB compared with 0.23 dB signal-to-noise ratio in the hearing aid-only arm (p<0.001). Word recognition in quiet improved by 20.79% compared to 2.20% (p<0.001), and word recognition in noise improved by 31.10% compared to -1.22% (p<0.001). Replacement of older hearing aids with optimally fitted new hearing aids prior to cochlear implant referral did not produce statistically significant or clinically meaningful improvements at the group level, supporting referral for cochlear implant evaluation without requiring an extended additional hearing aid trial.

In a companion quality of life (QoL) analysis from the same trial, Jakobsen (2026a) reported that Nijmegen Cochlear Implant Questionnaire (NCIQ) total scores improved by 12.67 points in the bimodal cochlear implant plus hearing aid arm compared with 0.60 points in the hearing aid-only arm (p<0.001), with statistically significant gains across all 6 NCIQ subdomains: basic sound perception, advanced sound perception, speech production, self-esteem, activity limitation, and social interaction (all p<0.003).

Cochlear Implantation in Unilateral Deafness (with or without Tinnitus)

Earlier peer-reviewed evidence did not permit conclusions concerning the effect of cochlear implantation for the treatment of unilateral hearing loss (single-sided deafness), including cochlear implants for tinnitus relief in individuals with unilateral deafness. That evidence consisted of observational studies and case series with small sample sizes and heterogeneity in evaluation protocols and outcome measurements (Arndt, 2017; Dillon, 2017a; Dillon, 2017b; Mertens, 2017; van de Heyning, 2008).

Blasco (2014) published a systematic review and meta-analysis of studies evaluating cochlear implantation for improvement of tinnitus and speech comprehension in unilateral sudden deafness. In a pooled analysis of 9 studies with 36 participants, subjective improvement in tinnitus occurred in 96% of 27 assessed participants. Subjective improvement in speech understanding occurred in 100% of 16 assessed participants, and subjective improvement in sound localization occurred in 87% of 16 assessed participants. The meta-analyses demonstrated a high degree of inter-study heterogeneity among a small study population. The authors recommended additional study with follow-up longer than 24 months to compare symptoms and performance between unilateral cochlear implantation and more traditional strategies for hearing rehabilitation.

Van Zon (2015) published a systematic review of studies evaluating cochlear implantation for single-sided deafness or asymmetric hearing loss. A total of 9 studies (n=112 participants) were considered in the data review. The authors could find no high-quality studies of cochlear implantation in this population. They were unable to pool the data for meta-analysis due to high between-study heterogeneity in participants (classification of hearing loss, duration of deafness, and the indication for cochlear implantation [hearing loss versus tinnitus]), test conditions (pre-implant versus post-implant), follow-up duration, and outcome measurement methods. The authors concluded the “current literature suggests important benefits of cochlear implantation in this population regarding sound localization, quality of life, and tinnitus. Although results for speech perception in noise are promising as well, varying results between studies were reported for this outcome.”

Sladen (2017a) conducted a prospective repeated-measures study examining speech recognition and self-perceived health-related quality of life in a cohort of 20 adults and children who received a cochlear implant for unilateral hearing loss (> 6 months, but < 2 years). Hearing loss was attributed to idiopathic sudden sensorineural hearing loss (n=15), otosclerosis (n=2), vestibular schwannoma (n=1), cholesteatoma (n=1), and bacterial sepsis (n=1). A total of 15 (75%) participants reached the 6-month post-activation point and were included in the final data analysis. A significant improvement in speech recognition in both quiet and noise was reported at the 6-month post-activation point. Consonant-Nucleus-Consonant (CNC) scores improved from 4.8% in the preoperative period to 42.3% 6 months after activation. Limitations of this study include the small sample size, comprised of predominantly younger adults with a short duration of reported hearing loss prior to implantation, and the short follow-up period.

Sladen (2017b) retrospectively reviewed prospectively collected data of short-term outcomes for 23 adults and children who received a cochlear implant to treat single-sided deafness due to multiple etiologies. The most frequent causes of deafness were sudden sensorineural hearing loss (n=12) and congenital conditions (n=3). Participants had mild to severe sensorineural hearing loss with 40% or lower CNC word recognition on the affected side and normal hearing in the nonimplanted ear. CNC word recognition improved significantly from pre-implantation to 3 months post-activation (p=0.001), but not between the 3-month and 6-month intervals in 13 of the 20 evaluable participants. There was no significant improvement in 8 participants from pre-implantation to 6 months post-activation for AzBio sentence understanding in noise (+5 decibels signal-to-noise). A total of 12 of the 13 participants who reported tinnitus prior to surgery reported subjective improvement after implantation. Limitations of this study include its small sample size with retrospectively collected data from a variable number of participants at the 3- and 6-month intervals. Additionally, study outcomes were evaluated with different testing protocols at the 2 participating centers. Finally, the heterogeneous study population comprised children and adults with various hearing loss etiologies and duration of deafness, limiting conclusions regarding the net health benefit of cochlear implantation in individuals with unilateral sensorineural hearing loss.

A systematic review and meta-analysis of evidence for cochlear implantation to treat single-sided deafness in adults was published by Oh (2023). The review was conducted without commercial involvement and in full accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The analysts found 50 studies published between 2008 and 2020 that met their inclusion criteria. Of these, 41 (82%) were prospective cohort studies, 7 (14%) were retrospective cohort studies, and 2 (4%) were case series. The 674 participants in these studies ranged in age between 19 and 93 years and had an average duration of deafness between 0.8 and 68 years. The most recent outcomes reported in the included studies occurred less than 6 months after implant for 2 studies and 36 months post-implant for 3 studies, with most of the studies reporting at 12 months. Outcomes of the review and meta-analysis are summarized in the table below. Due to heterogeneity of methods and reporting, meta-analyses could only be conducted for a portion of the studies reporting each outcome.

Daher (2023) also performed a systematic review and meta-analysis on this topic. As for the work separately completed by Oh (2023), the Daher review was conducted in accordance with PRISMA and had no commercial involvement. This review found 36 studies reporting spatial hearing or quality of life (QoL) outcomes after cochlear implants for adults with severe-to-profound sensorineural hearing loss. All of these studies were retrospective or nonrandomized prospective cohort studies with small to medium sample sizes (10 to 100 participants). Speech recognition in noise was reported in 25 (69%) of the reviewed studies. Meta-analysis could be conducted with data from 19 of these studies. The aggregated results showed significant improvements in speech recognition in quiet and in noise. The greatest benefit was seen when both the signal and noise were presented from the side of the head with the implanted ear (SciNnh configuration, implant on versus implant off, mean difference [MD], -6.2 dB [95% CI, -7.7 to -4.8 dB]; p<0.00001). Sound source localization outcomes were reported in 17 (47%) of the reviewed studies. Twelve of these studies reported root-means-squared (RMS) values that could be combined in a meta-analysis. That analysis showed that cochlear implant use significantly improved the RMS error for sound localization (MD, -25.3 degrees; 95% CI, -35.9 to -14.6 degrees; p<0.001).

Tinnitus severity or loudness was reported in 12 of the 36 (33%) reviewed studies. Ten of these studies supported a meta-analysis of the tinnitus handicap index (THI). Compared to preoperative THI assessments, the postoperative THI was found to have been significantly improved (MD, -29.9; 95% CI, -43.9 to -16.1; p<0.001). Tinnitus loudness was assessed on a visual analog scale (VAS) in 5 studies. Meta-analysis of these 5 studies’ results showed significant postoperative loudness improvement (MD, -5.1; 95% CI, -6.5 to -4.16; p<0.001). Meta-analysis of data for QoL outcomes reported from 9 of the 36 (25%) studies also showed significant improvement (MD, 2.3; 95% CI, 1.7 to 2.8; p<0.001). The authors concluded that cochlear implantation to treat single-sided deafness resulted in significant improvements in speech recognition in noise, sound localization, tinnitus, and QoL. The authors noted that the small sizes of these studies and methodologic differences precluded control for potentially confounding factors such as duration of deafness prior to implantation, cause of deafness, or age at implantation.

Expanding on these findings, the American Cochlear Implant Alliance (ACIA) Task Force Guidelines (Dillon, 2022) reviewed evidence and provided expert consensus on cochlear implantation for adults with single-sided deafness (SSD; greater than 80 dB HL, 4-frequency pure-tone average [PTA]; less than or equal to 30 dB HL contralateral). The guidelines report significant improvements in spatial hearing, tinnitus reduction, and QoL, outperforming rerouting technologies (van de Heyning, 2008; Dillon, 2017a; Dillon, 2017b; Buss, 2018). Key clinical recommendations include waiting 3 to 6 months after sudden hearing loss before considering implantation, preoperative imaging, audiologic assessment isolating the affected ear, evaluating spatial hearing, and post-activation management with a minimum 8-hour daily device wear time and structured auditory training. These recommendations complement the medical necessity criteria outlined earlier in this document.

Building on this clinical framework, the AAO-HNS issued 2 position statements in April 2023. The adult statement highlights cochlear implantation’s ability to restore binaural hearing in adults with SSD or asymmetric hearing loss, improving speech perception in noise, sound localization, tinnitus, and QoL beyond conventional aids, as supported by several meta-analyses. A separate pediatric statement notes that cochlear implantation may mitigate developmental risks such as speech delay and academic challenges and supports timely implantation in appropriately selected children. Both statements advocate timely implantation, reinforcing cochlear implantation safety and efficacy.

Collectively, cohort studies, meta-analyses (Oh, 2023; Daher, 2023), clinical guidelines (Dillon, 2022), and AAO-HNS position statements issued in 2023 demonstrate that cochlear implantation for SSD enhances speech perception, sound localization, tinnitus relief, and QoL, supporting its use when audiologic and medical criteria are met. Further research is needed to refine candidacy.

Bernstein (2025) retrospectively reviewed outcomes for 27 adult cochlear implantation recipients with single-sided deafness (SSD; n=21) or asymmetric hearing loss (AHL; n=6) at a single center, including 11 individuals whose preoperative CNC word recognition exceeded the 5% candidacy criterion. Participants were divided into those meeting a preoperative CNC criterion of less than 5% and those exceeding it. At approximately 6 months post-implantation, both groups improved significantly on all 5 primary outcome measures (cochlear implant-alone CNC, cochlear implant-alone AzBio, binaural speech-in-noise, sound localization, and cochlear implantation quality of life). No statistically significant differences were found between groups in postoperative scores or in the magnitude of improvement. These results suggest that individuals with SSD and AHL who exceed the 5% CNC preoperative criterion may achieve benefit comparable to those meeting the criterion.

Smith (2025) retrospectively reviewed outcomes for 12 adults aged 60 and older (mean age 72.6 years) with single-sided deafness or asymmetric hearing loss who underwent unilateral cochlear implantation. In the implanted ear, median pure-tone average improved from 103.1 to 28.1 dB (p=0.002), CNC word scores improved from 0% to 42% (p=0.027), and AzBio sentence recognition improved from 0% to 48% (p=0.002). Interpretation is limited by the small sample size and retrospective design; however, the findings are consistent with broader evidence suggesting that older adults with SSD or AHL may derive meaningful benefit from cochlear implantation.

Cochlear Implantation in Children 12 Months of Age and Older

The early peer-reviewed literature concerning the use of bilateral cochlear implants in children is limited, but later reports and syntheses suggest improvement in speech discrimination in noise and other binaural outcomes with bilateral implants (Peters, 2007; Lammers, 2014). Sharma (2006) studied congenitally deaf children to establish the existence and time limits of a sensitive period for the development of central auditory pathways in humans. The authors reported that central auditory pathways are “maximally plastic” for a period of about 3½ years in children with cochlear implants. Stimulation delivered within this timeframe results in auditory evoked potentials that reach normal values in 3 to 6 months. However, when stimulation occurs after 7 years, changes occur within 1 month, but then have little to no subsequent change.

Peters (2007) reported experience with 30 children between 3 and 13 years old who were bilaterally implanted with sequential surgeries at least 6 months apart. All children received their first cochlear implant prior to 5 years of age. Children acquired speech perception in the second ear within 6 months. However, children under 8 years of age acquired speech perception in the second ear more rapidly and ultimately gained a higher level of speech understanding than older children. The authors reported that sequentially implanted children in all age groups showed better mean speech perception scores in background noise with bilateral implants than with a single implant. Speech performance in quiet was improved to a lesser degree, but this difference did not meet a level of statistical significance. In younger children, speech perception scores improved for 12 months following the second implant while scores for older children plateaued at 6 months. The rate of improvement in speech perception scores in the second ear was inversely related to the child’s age at the time of the second implant.

More recent evidence also supports bimodal hearing strategies that combine a cochlear implant in one ear with a hearing aid in the other in appropriately selected individuals with asymmetric hearing loss (Jakobsen, 2026a; Jakobsen, 2026b). These studies reported significant improvements in speech reception threshold, word recognition, and quality of life with bimodal cochlear implant plus hearing aid use compared with optimally fitted hearing aids alone. These findings support the clinical value of preserving and using contralateral acoustic input when appropriate.

Cochlear Implantation in Infants Younger than 12 Months of Age

In 2020, the AAO-HNS revised its position statement on cochlear implants to recommend that providers “Consider unilateral and bilateral cochlear implantation as appropriate treatment for adults and children over 9 months of age with moderate to profound hearing loss who have failed a trial with appropriately fit hearing aids.” They issued a position statement on pediatric cochlear implants, stating:

Cochlear implantation should occur as soon as practicable, including in infants between 6 and 12 months of age. The Academy states that implantation below 12 months of age is associated with better language outcome and as such, implantation should not be delayed by a hearing aid trial.

There are multiple small retrospective studies and small and large case series that suggest improved health outcomes in several objective measures in children implanted before 12 months of age. There are some data to suggest that earlier implantation leads to improved language acquisition during this critical period of development. It has been shown that the age at the time of auditory stimulation is a strong predictor of auditory and language outcomes (Harrison, 2005; Nicholas, 2006; Sharma, 2006; Tomblin, 2005). Cumulatively, published data indicate that cochlear implantation can be performed safely and successfully without serious complications in select children younger than 12 months of age with profound bilateral sensorineural deafness (Colletti, 2005b; Colletti, 2009; Dettman, 2007; Holman, 2013; Holt, 2008; Loundon, 2010; Roland, 2009; Tait, 2007; Valencia, 2008; Vlastarakos, 2010b; Waltzman, 2005).

In addition to information about children with congenital deafness, there are several small prospective and retrospective case reviews and a matched-pair analysis suggesting that children with profound bilateral sensorineural deafness secondary to bacterial meningitis may benefit from early cochlear implantation (El-Kashlan, 2003; Hehar, 2002; Johnson, 1995; Young, 2000). Philippon (2010) performed a descriptive analysis of data including the cause of meningitis, preoperative imaging evaluation, age at implantation, time lapse between meningitis and implantation, and relevant surgical findings, in an attempt to propose guidelines for the management of profound bilateral sensorineural hearing loss after bacterial meningitis. The mean age at implantation was 3 years 8 months; the mean time delay between meningitis and surgery was 2 years 1 month. A total of 18 children (67%) were implanted within a year. Labyrinthitis ossificans was seen at the time of surgery in 62% of the participants (children and adults). Open-set speech discrimination was achieved by 37% of the children (10 of 27). The authors recommended early cochlear implantation for individuals with bilateral profound deafness secondary to bacterial meningitis as an interventionist approach to avoid complications presented by labyrinthitis ossificans and to optimize hearing outcomes.

Vlastarakos (2010a) conducted a meta-analysis of prospective controlled studies, prospective and retrospective cohort studies, clinical guidelines, and review articles reporting the diagnostic challenges and safety considerations in cochlear implantation in 125 children younger than 12 months of age. Overall, no major anesthetic complication was reported; the rate of surgical complications was reported at 8.8% (3.2% major complications), similar to the respective complication rates in older implanted children (major complications ranging from 2.3 to 4.1%). The authors summarized that cochlear implantation can be performed in otherwise healthy infants, provided that the attending pediatric anesthesiologist is considerably experienced and appropriate facilities of pediatric perioperative care are readily available. A number of concerns, with regard to anatomic constraints, existing co-morbidities or additional disorders, tuning difficulties, and special phases of the developing child should be also taken into account. The meta-analysis did not find an increased rate of anesthetic or surgical complications in implanted infants, although it identified a lack of studies with long-term follow-up reporting improved health outcomes.

Colletti (2011) reported on the 10-year results of 19 children who received cochlear implants between the ages of 2 to 11 months, comparing them to 21 children implanted between 12-23 months and 33 children implanted between 24-35 months. Within the first 6 months post-implantation, there was no significant difference among groups in Category of Auditory Performance testing, but differences became significantly better in the infant group (early implantation) at the 12- and 36-month testing.

Sharma (2025) conducted a cross-sectional controlled cohort study of 90 children aged 7-10 years in India comparing cochlear implant recipients, hearing aid users, and unaided children with severe-to-profound hearing loss (n=30 per group). Cochlear implant users demonstrated the highest utility scores (Health Utilities Index Mark 3 [HUI-3] = 0.69; EuroQol 5-Dimension [EQ-5D] = 0.88) and the highest auditory performance scores on the Parents' Evaluation of Aural/Oral Performance of Children (PEACH) and Teachers' Evaluation of Aural/Oral Performance of Children (TEACH) scales. Strong correlations were found between utility scores and auditory performance across groups, supporting cochlear implantation as the intervention associated with the best quality of life and auditory outcomes in children with severe-to-profound sensorineural hearing loss.

Swami (2025) conducted a prospective observational study of 30 congenitally hearing-impaired children comparing simultaneous and sequential bilateral cochlear implantation at a single tertiary center in New Delhi, India. Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scores showed a statistically significant difference favoring simultaneous implants at 3 and 6 months; however, outcomes converged by 12 months. Parental satisfaction measures (Meaningful Auditory Integration Scale [MAIS], Meaningful Use of Speech Scale [MUSS]) favored sequential implants at all intervals. These findings support the clinical equivalence of simultaneous and sequential bilateral cochlear implantation when both approaches are offered.

In summary, given the strong evidence of benefit in children with profound hearing loss when cochlear implantation is performed after the age of 12 months, the additional evidence suggesting further benefit at ages under 12 months, and the lack of evidence that performing implantation at an earlier age is harmful, it is reasonable to perform cochlear implantation in children under 12 months of age.

Cochlear Implantation in Special Populations or Clinical Conditions

Several systematic reviews have evaluated outcomes after cochlear implantation for specific causes of deafness and in subgroups of the pediatric population. Eze (2013) published a systematic review comparing outcomes of cochlear implantation for children with developmental disability with those without developmental disability. The authors stated that while approximately 30% to 40% of children who receive cochlear implants have developmental disability, evidence about outcomes in this group is limited. A total of 13 studies met the inclusion criteria that compared receptive or expressive language outcomes in children with cochlear implants with and without developmental disability. A meta-analysis of pooled data was not performed as the studies were heterogeneous in terms of comparator groups and outcome measures. Seven of the eligible studies in the structured systematic review demonstrated significantly poorer cochlear implant outcomes in children with developmental disability, while the remaining 6 studies reported no significant difference in outcomes between the groups.

Humphriss (2013) published a systematic review evaluating outcomes after cochlear implantation in a pediatric population with auditory neuropathy spectrum disorder (ANSD), a sensorineural hearing disorder characterized by abnormal auditory brainstem response with preserved cochlear hair cell function as measured by otoacoustic emissions testing. A total of 27 observational studies were selected for review, including case studies, cohort studies, and comparison studies between children with ANSD and severe sensorineural hearing loss. Eleven of the 15 noncomparative studies did not include a measure of speech recognition before cochlear implantation. Among the comparative studies, those comparing cochlear implantation to usual care, typically a hearing aid, provided the most information about effectiveness of cochlear implantation among children with ANSD. A single small study that used this design found no significant differences between the groups.

Fernandes (2015) evaluated 18 published studies and 2 dissertations that reported hearing performance outcomes for children with ANSD and cochlear implants. A total of 5 studies were nonrandomized controlled trials considered high quality, 5 randomized controlled trials considered low quality, and 10 were clinical outcome studies. A total of 14 studies compared speech perception in children with ANSD and cochlear implants with speech perception in children with sensorineural hearing loss and cochlear implants. Most of the studies (n=13) concluded that children with ANSD and cochlear implants developed hearing skills similar to children with sensorineural hearing loss and cochlear implants.

In a subsequent small retrospective case series, Kontorinis (2014) retrospectively evaluated pre- and post-cochlear implantation hearing outcomes for 27 implanted children with ANSD. Cognitive disorders were found in 4 participants: 3 children were diagnosed with autism and another child with dyspraxia. Another child had hemiplegia. One of the autistic children became a non-user of her cochlear implant. The average age at implantation was 35.4 months (range, 19-68 months) with follow-up for an average of 63.1 months (range, 6-140 months). A total of 9 children were implanted bilaterally and 18 unilaterally. The mean preoperative CAP and Manchester spoken language development scale (MSLDS) scores with hearing aids were 2.5 (range, 0-5) and 2.5 (range, 0-6), respectively. The mean post-cochlear implant CAP and MSLDS scores were 5.8 (range, 2-9) and 7.7 (range, 3-10), respectively. The difference between the preoperative and post-cochlear implant scores was statistically significant for both CAP (p<0.001) and MSLDS (p<0.001). In 3 children the post-cochlear implant outcomes were fluctuating. The authors identified cognitive disorders as a significantly negative prognostic factor for cochlear implant outcome. Limitations of this study include the retrospective design and lack of information about how many children would have otherwise qualified for a cochlear implant without ANSD.

Current professional society guidelines support cochlear implantation for individuals with ANSD when clinical progress is inadequate with appropriately fitted amplification. The Joint Committee on Infant Hearing (2019) position statement states that cochlear implants are indicated for children older than 12 months of age with bilateral severe-to-profound sensorineural hearing loss, including auditory neuropathy, who fail to make expected progress with amplification. The ACIA Task Force Guidelines (Warner-Czyz, 2022) state that children with ANSD should be evaluated as potential cochlear implant candidates based on speech perception scores, parent questionnaires, and therapist reports even if audiometric threshold results do not meet typical candidacy guidelines, recognizing that ANSD characteristically presents with disproportionately poor speech recognition relative to the measured degree of hearing loss. The ACIA Task Force also established a 50/70+ referral threshold recommending evaluation for individuals with unaided pure-tone thresholds greater than 70 dB HL or word recognition scores less than 50% correct, consistent with the audiometric criteria applied in this policy.

In the largest management outcomes series to date, Morlet (2023) retrospectively reviewed 260 children with ANSD over a 15-year period. Among children with bilateral ANSD who underwent hearing aid trials, 89.2% did not benefit from conventional amplification. Only 5% of individuals derived significant benefit from hearing aids for speech and language development. Among those who received cochlear implants, mean post-implantation open-set word discrimination scores averaged 87.8% and sentence recognition scores were 91.2% in quiet. These findings were within the expected performance range for cochlear implant recipients with sensorineural hearing loss, although speech outcome data were not available for all individuals. These findings indicate that, while a trial of amplification is appropriate, conventional hearing aids are rarely sufficient to support speech and language development in most children with bilateral ANSD, and cochlear implantation represents the primary rehabilitative option when adequate progress is not achieved or when amplification benefit is absent.

The effect of age at implantation on the trajectory of outcomes was examined by Daneshi (2018) in a multicenter study of 136 children with ANSD. Children implanted at 24 months of age or younger demonstrated significantly greater CAP score improvement during the second year of follow-up compared with children implanted after 24 months (p<0.001), and significantly greater SIR improvement during the second year (p=0.003), consistent with the broader literature on the critical period for auditory development and the benefits of early cochlear implant activation.

Wu (2023) evaluated 75 unrelated individuals with auditory neuropathy who received cochlear implants and found that CN deficiency was the only candidate impact factor to reach statistical significance for poorer speech outcomes (p=0.008). Age at implantation, onset timing, presence of risk factors, and bilateral compared to unilateral implantation were not significantly associated with outcomes. Overall, 82.67% of individuals in this cohort benefited from cochlear implantation (SIR score 3 to 5, or maximum speech recognition score greater than 60%).

Lin (2022) reported multicenter retrospective outcomes in pediatric cochlear implant recipients with auditory neuropathy spectrum disorder and found that outcomes varied by etiology, with generally favorable results in otoferlin (OTOF)-related and certain other non-cochlear nerve deficiency (CND) etiologies, and poorer outcomes in cochlear nerve deficiency, supporting etiologic evaluation and preoperative MRI rather than exclusion based on ANSD diagnosis alone.

An umbrella review of 8 systematic reviews by Jafari (2023) synthesized data from 2 systematic reviews focused on CND and found that children with cochlear nerve hypoplasia achieved speech discrimination in approximately 65% of cases compared with 30% for cochlear nerve aplasia. Nonstimulation (deactivation of cochlear implant electrodes) was reported in 43.9% of individuals with CND and additional disabilities and in 8.8% of individuals without additional disabilities. The authors noted that MRI in the axial and sagittal planes allows precise differentiation of cochlear nerve aplasia from hypoplasia and is an essential component of candidacy evaluation for individuals with ANSD. These findings support the clinical utility of MRI-confirmed cochlear nerve deficiency as the operative exclusion criterion, rather than a blanket exclusion based on ANSD diagnosis alone.

Evidence has expanded understanding of cochlear implantation outcomes in children with ANSD, including pooled analyses and controlled comparative studies. A meta-analysis by Bo (2023), which included 15 observational studies (n=667), found no statistically significant differences between children with ANSD and those with non-ANSD sensorineural hearing loss across multiple outcome measures, including speech recognition, Categories of Auditory Performance (CAP), Speech Intelligibility Rating (SIR), and open-set speech perception. Similarly, an updated systematic review and meta-analysis by Tawakkul (2025), incorporating 14 studies (n=722), reported comparable outcomes between groups for CAP (mean difference [MD] -0.52; 95% CI, -1.34 to 0.29; p=0.21) and SIR (MD -0.26; 95% CI, -0.65 to 0.13; p=0.19).

These findings are further supported by a matched case-control study by Jafari (2024), in which 22 children with ANSD were matched 1:2 to 44 children with sensorineural hearing loss on sex, age, age at cochlear implant activation, and duration of follow-up. No statistically significant differences were observed between groups across 5 open-set speech perception measures, with mean scores ranging from approximately 88% to 96%. In regression analysis, ANSD diagnosis was not identified as a significant predictor of outcomes, while longer duration of implant use, younger age at activation, and bilateral implantation were associated with improved performance.

Taken together, this body of evidence suggests that children with ANSD may achieve speech perception outcomes comparable to those of children with sensorineural hearing loss following cochlear implantation. However, the overall evidence base is limited by reliance on observational studies, heterogeneity in ANSD etiology and diagnostic criteria, and potential selection bias, as outcomes are more favorable in individuals without cochlear nerve deficiency or with presumed presynaptic pathology. Additionally, individual studies, including the matched case-control analysis, are limited by small sample sizes and potential residual confounding. Accordingly, while current evidence supports the effectiveness of cochlear implantation in appropriately selected children with ANSD, these findings should be interpreted as supportive rather than definitive evidence of equivalence to outcomes observed in sensorineural hearing loss populations.

Otosclerosis

Al-Khateeb (2025) conducted a retrospective single-center study with 111 participants (114 ears) who had otosclerosis and received cochlear implants. Cochlear ossification was found in 57% of ears. Surgical challenges were common, with subtotal petrosectomy performed more often in ossified than non-ossified cochleae (63.1% vs. 28.6%); however, only 1 ear required scala vestibuli insertion and 4 ears had incomplete electrode insertion. Full scala tympani insertion was achieved in nearly all cases (96.5%). Auditory outcomes in ears with ossification were slightly better than those without ossification, but the difference was not statistically significant. These findings suggest that, despite frequent cochlear ossification and greater surgical complexity, cochlear implantation in otosclerosis can achieve favorable auditory outcomes, and ossification itself did not significantly worsen postoperative audiologic results.

Quatre (2025) conducted a retrospective case-control study comparing long-term cochlear implantation outcomes for 41 individuals with far advanced otosclerosis (FAO) and 73 matched postlingually deafened controls. Mean speech comprehension at 5 years was comparable between groups (48.63% vs. 48.17%; p=0.76). Cochleostomy was more common in the FAO group (63.4% vs. 38.4%; p=0.01), and prior stapedotomy negatively affected outcomes (mean 5-year speech comprehension 39.3% with prior stapes surgery vs. 57.52% without; p=0.02).

Meniere Disease

Boscke (2025) conducted a retrospective cohort study comparing cochlear implantation outcomes between individuals with Meniere disease who had received prior intratympanic gentamicin (ITG; n=14) and those who had not (n=22). ITG is sometimes used in advanced Meniere disease to control vertigo by selectively ablating vestibular hair cell function. Both groups showed significant improvement in word recognition scores over time; however, the ITG group had significantly inferior outcomes (relative treatment effect 0.38 versus 0.57; p<0.001). The finding suggests that prior ITG treatment may reduce, but does not eliminate, cochlear implantation benefit. The authors recommended counseling individuals about the potential adverse effects of ITG on cochlear implantation outcomes.

Objective Predictors of Cochlear Implant Outcomes

HabibAllah (2026) conducted a cross-sectional observational study of 54 cochlear implant recipients (33 pediatric ears, 21 adult ears) measuring electrically evoked cortical auditory evoked potentials (eCAEPs) recorded directly through the cochlear implant. Children showed significantly shorter P1 latencies (median 95 ms vs. 140 ms; p<0.001) and N1 latencies (150 ms vs. 185 ms; p<0.001) compared with adults. P1 latency strongly correlated with speech perception in noise (r=-0.751, p<0.0001) and in quiet (r=-0.632, p<0.0001). In regression analysis, age at cochlear implantation was a significant predictor of P1 latency (regression coefficient = 2.06, p=0.0013), while current age was not (p=0.60). These findings support the use of intracochlear eCAEP biomarkers as objective predictors of speech outcomes and reinforce the importance of early implantation in optimizing cortical auditory development.

Hybrid Cochlear Implantation

Background Information and Description of the Technology

On March 20, 2014, the FDA granted premarket approval (PMA) status to the Nucleus Hybrid L24 Cochlear Implant System (also referred to as “Hybrid L24”) as a unilateral cochlear implant system for individuals with residual low-frequency hearing sensitivity who have obtained limited benefit from bilateral conventional hearing aids. The Hybrid L24 is an electric-acoustic stimulation (EAS) cochlear implant system that consists of both internal and external components. The Hybrid L24 is designed to allow individuals to hear in 2 ways: electrically (similar to approved cochlear implants) for severe to profound hearing loss at mid and high frequencies, and acoustically (similar to hearing aids) for normal to moderate hearing loss at low frequencies. The Hybrid L24 includes an implant consisting of a receiver/stimulator and an intracochlear electrode array using short implant electrodes placed in the cochlea through a small cochleostomy or round window insertion to preserve low-frequency hearing. An externally worn sound processor can be fitted with an acoustic component, programming software/instruments, and various remote control options.

Using a small microphone, the sound processor picks up sound from the person’s surroundings and separates it into different groups of sounds by frequency (that is, the low or high "pitch" of a sound). The higher frequency information about the sound is sent to the receiver/stimulator and electrode array of the implanted part of the device. Since the electrode array is located inside the person’s cochlea, this sound-related information is relayed to the brain, allowing the person to hear. For people who have enough of their own acoustic low-frequency hearing after implantation, the sound processor also provides amplified low-frequency sound to the ear through the acoustic component. After implantation, some implanted individuals do not have enough low-frequency hearing to use the acoustic component so these individuals hear only electrically using the implant for all (lower and higher) sound frequencies (FDA, 2014).

The Hybrid L24 implant is intended for use in 1 ear by persons aged 18 years or older who obtain limited benefit from appropriately fitted conventional hearing aids in both ears and meet the following criteria (FDA, 2014):

• Typical preoperative hearing of candidates ranges from normal to moderate hearing loss in the low frequencies, with severe to profound loss in the mid to high frequencies; and
• The CNC word recognition score will be between 10% and 60%, inclusively, in the ear to be implanted in the preoperative aided condition and in the other ear will be equal to or better than that of the ear to be implanted but not more than 80% correct; and
• Previously have undergone a suitable hearing aid trial, unless already appropriately fit with conventional hearing aids.

The Hybrid L24 should not be used for individuals who have any of the following conditions:

• Deafness due to lesions of the acoustic nerve or central auditory pathway; or
• Active middle ear disease, with or without tympanic membrane perforation; or
• Absence of cochlear development; or
• Duration of severe to profound hearing loss of 30 years or greater.

Other hybrid hearing devices have been developed but do not have FDA 510(k) clearance or premarket approval for use in the U.S., including the Synchrony Electric Acoustic Stimulation (EAS) Hearing Implant System (MED-EL, USA, Durham, NC). The hybrid implant’s manufacturer states it is designed for use in individuals with “partial deafness,” that is, mild to moderate low-frequency hearing loss combined with profound hearing loss in the higher frequencies.

Efficacy and Safety of Hybrid Cochlear Implantation

The FDA approval of the Hybrid L24 was based on a multicenter, nonrandomized, unblinded single-subject study where participants served as their own control (so that post-implant performance was compared to each participant’s baseline or pre-implant performance) (Roland, 2016). According to the FDA PMA (P130016), criteria for study inclusion required that candidates be aged 18 years and older with preoperative hearing ranges from normal to moderate hearing loss in the low frequencies (thresholds no poorer than 60 decibels HL up to and including 500 hertz), with severe to profound mid-to-high frequency hearing loss (threshold average of 2000, 3000, and 4000 hertz 75 decibels HL or greater) in the ear to be implanted, and moderately severe-to-profound mid-to-high frequency hearing loss (threshold average of 2000, 3000, and 4000 hertz 60 decibels HL or greater) in the contralateral ear. A CNC word recognition test score was required to be between 10% and 60%, inclusively, in the ear to be implanted in the preoperative aided condition and in the contralateral ear, equal to or better than that of the ear to be implanted, but not more than 80% correct. Individuals with severe to profound high-frequency hearing loss for > 30 years’ duration or congenital hearing loss (onset prior to 2 years of age) were excluded from participation. Prospective candidates were required to go through a suitable 2-week hearing aid trial unless already appropriately fitted with conventional hearing aids.

The study was conducted at 10 United States sites, enrolled 50 participants (age at implantation, range: 23 to 86.2 years), and involved up to 9 visits before and after implantation for approximately a 1-year period. The Hybrid L24 was implanted in 1 ear and activated following a healing period of 2 to 4 weeks. Postoperative measurements included verification of hearing device functioning, unaided hearing thresholds and tympanometry, aided audiometric thresholds, aided CNC test in quiet, aided AzBio sentences-in-noise test, and adverse event reporting at 3-, 6-, and 12-month intervals. Co-primary effectiveness endpoints included CNC word-recognition scores and AzBio sentence-in-noise scores compared across 2 conditions: the baseline “Acoustic Alone” condition and the 6-month “post-activation Hybrid” condition. Success was defined as statistically significant improvement in both co-primary endpoint measures.

A total of 49 of the 50 enrolled participants (98%) completed all effectiveness outcome assessments at the 6-month interval, while 48 participants completed the audiometric testing for hearing sensitivity; 46 participants were evaluable at the 12-month interval. Based on data from 50 participants (including worst-case imputed scores for data missing for 1 participant), both co-primary effectiveness endpoints were met. Statistically significant improvements in mean CNC word score (35.7 percentage points; 95% CI, 27.8% to 43.6%; p<0.0001) and mean AzBio sentence-in-noise score (32.0 percentage points; 95% CI, 23.6% to 40.4%; p<0.0001) occurred from the baseline (Acoustic alone, hearing-aided) to the 6-month interval post-activation (Hybrid condition), respectively. Secondary effectiveness endpoints compared 6-month postoperative performance in the Hybrid condition to preoperative (ipsilateral) Acoustic Alone performance. All secondary endpoints were met as more than 75% of the participants performed similar to or better on each of the 3 specified measures: CNC words (96%), CNC phonemes (96%), and AzBio sentences (88%).

The primary safety endpoint was the number and proportion of participants experiencing an adverse event, defined as any surgical or device event. A total of 71 adverse events were reported to have occurred during the study. Of the 50 implanted participants, 34 (68%) experienced at least 1 adverse event, with multiple (2 to 4) adverse events experienced by 20 of 50 participants; 24 of 71 adverse events in 23 participants were unresolved during the study. The 2 most frequently observed adverse events that were reported as resolved included tinnitus-related issues and device-related open shorts experienced by 28% and 22% of participants, respectively. By May 31, 2013, 30 of 50 (60%) participants exhibited greater than 30 decibels loss in their residual low-frequency hearing. Unresolved adverse events observed included profound/total loss of residual low-frequency hearing occurring in 22 of 50 (44%) participants. As of February 10, 2014, 6 of 50 (12%) participants were subsequently explanted and reimplanted with a standard cochlear implant. Based on these results, the FDA stated “It is yet to be determined over the long-term how many additional subjects who experience profound loss will be explanted and re-implanted with a traditional cochlear implant array.”

Despite an improvement in speech recognition in terms of CNC words and AzBio sentences reported for the majority of the study population, the FDA concluded that the potential risks of profound and possibly total loss of low-frequency hearing, which occurred in 44% of the participants, were as follows:

 …is a known risk and renders the device usage to electrical (cochlear implant) stimulation only since the acoustic amplification is ineffective for these levels of hearing loss. For participants who lost low-frequency residual hearing to the profound/total level(s), the device showed benefit for only about half (9 of 17) or 53% of these participants. Furthermore, 6 of 50 participants who lost residual low-frequency hearing chose to undergo explantation of the Hybrid L24 and be reimplanted with an approved standard cochlear implant.

Considering the risks and benefits of the device, the FDA approved the hybrid implant only for unilateral use after a sufficient trial of conventional hearing aids, with an expiration date at 1 year. Continued approval of the PMA is contingent upon submission of periodic reports, which include reporting of device distribution in order to determine the frequency and prevalence of adverse events.

In 2016, Roland (2016) published the results of the multicenter clinical trial presented to the FDA (2014) as part of the Nucleus Hybrid L24 implant system PMA review process. The study evaluated 50 individuals aged 18 years or older with low-frequency hearing and severe-to-profound high-frequency sensorineural hearing loss who were implanted with the hybrid device at 10 clinical sites in the United States. Acoustic thresholds were measured for each ear preoperatively and postoperatively, at device activation, and 3, 6, and 12 months post-activation. The outcomes reported were consistent with the clinical trial data submitted to the FDA. Participants experienced a significant mean improvement (p<0.001) in both co-primary endpoints with the hybrid device compared to their preoperative hearing aid: CNC words (35.8 ± 27.9 percentage point change; 95% CI, 27.9 to 43.7) and AzBio sentences in noise (32.0 ± 29.4 percentage point change; 95% CI, 23.7 to 40.4). Secondary endpoints were met with the hybrid implant compared to performance with a hearing aid. Of the 17 participants that did not maintain functional acoustic hearing, 5 participants chose to have the hybrid implant explanted and replaced with a standard cochlear implant. A total of 65 adverse events were reported involving 34 of 50 participants. The most frequently occurring adverse events were profound/total hearing loss (22 events [33.8%] in 22 participants [40%]), open/short-circuited electrodes (11 events [16.9%] in 11 participants [22%]), and increased tinnitus or tinnitus not present preoperatively (6 events each [9.2%] in 6 participants [12%]). A total of 50 adverse events including tinnitus, vertigo, and other symptoms were considered to be medical or surgically associated with a mastoidectomy with the facial recess approach used in cochlear implantation. Limitations of this clinical trial include the nonrandomized design, small number of participants, and short duration of follow-up.

The results of a prospective study conducted at 16 European cochlear implant centers evaluated the performance benefits up to 1 year post-Hybrid L24 implantation in terms of speech recognition, sound quality, and quality of life (Lenarz, 2013). Postoperative performance using a Freedom Hybrid sound processor was compared with that of preoperative hearing aids in 66 individuals with bilateral severe-to-profound high-frequency hearing loss. The group median increase in air conduction thresholds in the implanted ear for test frequencies 125 to 1000 hertz was less than 15 decibels across the population, both immediately and 1 year postoperatively. A total of 88% of the participants used the Hybrid L24 processor at 1 year post-implantation. A total of 65% of the participants had significant gain in speech recognition in quiet, and 73% in noise (20 percentage points or greater per 2 decibel signal-to-noise ratio). The mean Speech Spatial Qualities (SSQ) of Hearing Questionnaire subscale scores were significantly improved (+1.2, +1.3, +1.8 points, p<0.001), as was the mean health utility-13 (HUI3) score (+0.117, p<0.01). Combining residual hearing with the hybrid device implantation gave a mean benefit of 22 to 26 percentage points in speech recognition scores over hybrid device implantation alone (p<0.01).

Partially preserved residual hearing was maintained in 89% of the participants within 1 month of follow-up; however, some degradation was reported over time, with 74% of the participants retaining residual hearing within 30 decibels of preoperative levels at 1 year, and approximately 50% retaining hearing within 15 decibels. There were 16 participants whose 500 hertz thresholds increased by > 30 decibels, with 4 of these 16 participants obtaining a large gain in speech recognition score for the implanted ear (55 to 65 percentage points). The remainder of the participants had limited benefit with either no change (8 of 16 participants) or a reduced score reported. One subject withdrew from the study after 1 month of follow-up due to non-device-related health problems, and 4 participants withdrew after 6 months of follow-up. The authors reported missing data and inconsistent data collection throughout the study, in particular at the 1-year primary endpoint for a total of 5 participants, so only 6-month speech recognition scores were used if available for the Hybrid L24 implanted ear and for best-aided preoperative-to-postoperative comparisons. Three adverse events may have been related to the device or surgery, including prickling pain below the eye/sinusitis, middle-ear infection, and dizziness. Two individuals required repositioning of the implant device due to poor fixation and confirmed partial extrusion of the electrode array.

Gantz (2016) reported the final outcomes of a multicenter, longitudinal, single-subject (3-stage) study conducted between 2002 and 2011 evaluating 87 individuals implanted with a Nucleus Hybrid S8 implant for high-frequency hearing loss. Speech perception in quiet (CNC words) and in noise (Bamford-Kowal-Bench Sentences-In-Noise [BKB-SIN]) were collected pre- and postoperatively at 3, 6, and 12 months. Subjective questionnaire data were also collected using the Abbreviated Profile for Hearing Aid Benefit (APHAB). The surgical implantation of the 10-mm electrode in the scala tympani resulted in some level of hearing preservation in 98% of participants, with 90% maintaining a functional low-frequency PTA at initial activation. A total of 2 participants experienced immediate postoperative total hearing loss. An additional 6 participants lost enough hearing in the low frequencies to be considered nonfunctional. At 3 months post-activation, a total of 14 participants experienced a total loss of hearing in the implanted ear and nonfunctional hearing. An additional 2 participants experienced total hearing loss at 12 months post-activation, resulting in 16 (18%) participants with nonfunctional hearing loss at 12 months. Data were available for 75 participants at the 12-month evaluation. A significant percentage of participants demonstrated improvement in speech perception as measured by CNC words: 82.5% of participants in the hybrid ear (that is, combined acoustic and electric in the same ear) and 87.5% of participants in the hybrid and combined condition (that is, acoustic plus electric combination when listening with both ears plus the Hybrid S8 device). In addition, all participants reported improvements in hearing in 3 of the 4 subscales of the APHAB. A total of 14 participants requested explantation of the Hybrid S8 implant for various reasons of dissatisfaction with the device and subsequently had placement of a standard length Nucleus Freedom cochlear implant. The authors concluded that combining acoustic plus electric speech processing has significant advantages for hearing-impaired individuals with residual low-frequency hearing. A limitation of this study is a lack of data to confirm the etiology of the decline in acoustic hearing sensitivity resulting in nonfunctional hearing loss in the 19% of the implanted individuals at 12 months.

Kelsall (2017) conducted a multicenter, prospective, nonrandomized, single-arm repeated measures, single-subject study of 50 adults (mean age 64.1 years) with severe to profound sensorineural hearing loss implanted with the Cochlear Nucleus Hybrid implant system. Participants had residual low-frequency hearing with aided word recognition scores between 10% and 60% in the ear to be implanted and 80% or greater in the contralateral ear. Self-reported outcomes were assessed using the Speech, Spatial and Qualities of Hearing Questionnaire (SSQ), a Device Use Questionnaire (DUQ), and the University of Washington Clinical Assessment of Music (UW-CAMP) questionnaire at preoperative intervals and after 6 and 12 months (SSQ and DUQ only) of hybrid cochlear implant use. Overall, significant improvements were reported at 6 and 12 months post-activation in mean SSQ ratings (p<0.0001) and in speech hearing, spatial hearing, and sound quality when compared with the bilateral hearing aid use preoperatively. Significant improvement was also reported in overall satisfaction on the DUQ in the following measures: 1) listening in speech in various 1:1 and group conversation and listening at a distance; 2) listening in a number of non-speech environments; 3) listening to live and recorded music with and without singing; 4) locating sounds; 5) sound quality of one’s own voice, naturalness and clarity of speech, and clarity of environmental sounds; and, 6) across specific listening situations including social engagement. UW-CAMP pitch discrimination and music perception abilities were retained postoperatively. Although some limitations of this study exist, including the non-randomized design, limited sample size, short duration of follow-up, and data collected from subjective measures, the authors stated the benefits reported by study participants were consistent with the objective benefits reported by Roland (2016) in the Hybrid L24 clinical trial.

The largest pooled analysis of Hybrid L24 outcomes to date was reported by Reinhart (2026). This study combined data from 2 prospective clinical trials and 1 retrospective cohort from the University of Iowa (n=150 ears). A total of 72.7% of recipients maintained functionally aidable thresholds (low-frequency pure-tone average < 80 dB HL) at 1 year, and 72.9% through 5 years. Threshold shifts occurred primarily at device activation (mean 15.4 dB shift) and stabilized by 1 year. CNC word scores and AzBio sentence-in-noise scores improved significantly at all postoperative timepoints compared with baseline (all p<0.0001). Younger recipients demonstrated better speech outcomes than older recipients, and electric-acoustic stimulation users (those who preserved aidable hearing) outperformed electric-only users on speech-in-noise tasks. Age at implantation was the only significant predictor of maintaining aidable hearing at 1 year (p=0.02). These data support durable hearing preservation in the majority of cochlear implant recipients and sustained improvement in speech perception over at least 5 years.

Auditory Brainstem Implantation

Background Information and Description of the Technology

An auditory brainstem implant (ABI) is a device designed to restore some hearing in individuals with neurofibromatosis type 2 rendered deaf by bilateral surgical removal of neurofibromas involving the auditory nerve. The device consists of an externally worn speech processor that converts auditory information into an electrical signal that is transferred to a receiver/stimulator implanted in the temporal bone. The receiver/stimulator is, in turn, attached to an electrode array implanted on the surface of the cochlear nucleus in the brainstem, thus bypassing the inner ear and auditory nerve. The electrode stimulates multiple sites on the cochlear nucleus, and the resulting signals are then processed by the brain. A total of 1 device has received FDA approval for auditory brainstem implantation, the Nucleus 24 Auditory Brain Stem Implant System (Cochlear Americas, Lone Tree, CO). The speech processor and receiver are similar to the devices used in cochlear implants; the electrode array placed on the brainstem is the novel component of the device.

Efficacy and Safety of Auditory Brainstem Implantation

The FDA approval of the Nucleus 24 Auditory Brain Stem Implant System was based on results of a case series of 90 individuals in which 28 complications occurred in 26 individuals. Of these 28 complications, 26 resolved without surgical or extensive medical intervention (Donaldson, 2001). Two individuals had infections of the postoperative flap requiring explantation of the device. Effectiveness outcomes were evaluated in 60 individuals with a minimum experience of 3 to 6 months with the device. Device benefit was defined as a significant enhancement of lip-reading or an above-chance improvement on sound-alone tests. Based on this definition, a total of 95% (57 of 60) derived benefit from the device. While the use of an ABI is associated with a modest improvement in hearing, this level of improvement is considered significant in this group of individuals with no other treatment options. Among the 90 individuals receiving the implant, 16 did not receive auditory stimulation from the device postoperatively. This was due to migration of the implanted electrodes or surgical misplacement. To place the electrode array on the surface of the cochlear nucleus, the surgeon must be able to visualize specific anatomical landmarks. Because large neurofibromas compress the brainstem and distort the underlying anatomy, it may be difficult or impossible for the surgeon to correctly place the electrode array. For this reason, individuals with large, longstanding tumors may not benefit from the device. Studies reported by Colletti (2005a, 2006, 2007) showed improvements in word and sentence recognition over a 1-year follow-up.

Merkus (2014) reported on a systematic review of ABIs for non-neurofibromatosis type 2 (non-NF-2) indications that included 144 non-NF-2 ABI cases from 31 publications. Non-NF-2 indications for which ABIs were evaluated included auditory neuropathy, autoimmune inner ear disease, bilateral traumatic cochlear nerve disruption, cochlear nerve aplasia, cochlear otosclerosis, temporal bone fractures, and vestibular schwannoma (in the only hearing ear). Cochlear implants generally resulted in better hearing than ABIs when the cochlea and cochlear nerve were intact. While comparative evidence is limited, cochlear implants appeared to demonstrate greater hearing benefits than ABI in individuals with non-NF-2 indications. It was suggested that ABI may only have potential for improved outcomes in bilateral complete cochlear and inner ear aplasia when imaging and electrophysiologic testing demonstrate that the cochlear nerve is absent. At this time, however, the available evidence in the peer-reviewed published literature does not support firm conclusions on the benefits of ABI for these individuals.

Sennaroglu (2016) reported on the long-term outcomes of 35 of 60 prelingually deaf children in Turkey who received 1 of 3 different ABI models implanted for severe inner ear malformations. A total of 19 children in the analysis were deaf due to cochlear hypoplasia. At regular follow-up, children were evaluated with the CAP, Speech Intelligibility Rate (SIR), Functional Auditory Performance of Cochlea Implantation (FAPCI), and Manchester scores. Approximately one-half of the children were in the CAP category 5 and could understand common phrases without lip reading. In the subgroup with better hearing thresholds (25-40 decibels), some children (17.6%) were able to understand conversation without lip reading, use the telephone with a known speaker (11.8%), and follow group conversation in a noisy room (5.9%). For children with higher hearing thresholds (> 50 decibels), none exceeded CAP category 5. SIR and Manchester scores were also better among children with lower hearing thresholds. Auditory performance measured with the FAPCI was in the 10th percentile for all groups and was worse compared to cochlear implantation. Children with additional nonauditory disabilities (for example, intellectual challenges) had worse outcomes. The authors reported that hearing progress was faster in the initial 2 years when compared with longer use of the ABI. Limitations of this study include the small number of participants in each hearing anomaly group, which resulted in a lack of certain statistical comparisons of outcomes. Additionally, as most children will have device failure at least two or three times over their lifespan, complications of revision surgery may result from fibrotic changes in the lateral recess of the ear channel.

de Cos (2024) reported a retrospective single-institution case series of 11 individuals with NF-2 who underwent ABI during vestibular schwannoma resection. Postoperatively, 9 of 11 (81%) showed improvement in pure-tone average. Of 7 individuals with Early Speech Perception testing, 5 (71%) achieved scores exceeding 75%, indicating auditory pattern perception through the ABI alone. Mild stimulation-associated side effects (dizziness, tinnitus, abdominal/lower extremity tingling) occurred in 7 individuals. No major complications were reported. Although limited by small sample size and lack of a comparator group, these findings are consistent with the broader evidence base indicating that ABI can provide meaningful auditory benefit in individuals with NF-2 undergoing tumor resection.

Asymmetric hearing loss (AHL): A condition characterized by a significant difference in hearing thresholds between ears, typically with severe-to-profound sensorineural hearing loss in one ear and better (but not necessarily normal) hearing in the contralateral ear. The better ear may range from normal hearing to moderate hearing loss and is often aidable with a conventional hearing aid.

Auditory brainstem implant (ABI): An implantable device that provides auditory input by directly stimulating the cochlear nucleus in the brainstem, bypassing both the cochlea and the auditory nerve, typically used in individuals with nonfunctional auditory nerves, such as those with neurofibromatosis type 2 (NF-2).

Auditory brainstem response (ABR): A neurologic test of auditory brainstem function in response to auditory (click) stimuli; the most common application of auditory evoked responses.

Auditory evoked potential: Evaluates the nerve pathways from the ear to the brain; consists of a very small electrical voltage originating from the brain recorded from the scalp in response to an auditory stimulus (for example, different tones, speech sounds).

Auditory neuropathy spectrum disorder (ANSD): A cause of sensorineural hearing loss in which outer hair cell function may be preserved, but auditory nerve signal transmission is impaired. Individuals with ANSD have normal otoacoustic emission tests. They characteristically have deficits in speech perception that do not correlate with the measured degree of hearing loss.

AzBio Sentences-in-Noise Test: A test to assess a cochlear implant recipient’s ability to understand sentences in the presence of background noise.

Binaural hearing: Hearing with both ears.

Central auditory pathway: Connections within the brain through which the auditory nerve transmits sensations for perception by the cerebral cortex. These include the cochlear nucleus, superior olivary complex, lateral lemnisci, inferior colliculi, medial geniculate nuclei, and the auditory cortex.

Cochlea: A spiral-shaped structure in the inner ear that converts sound vibrations into electrical signals that are transmitted to the brain via the auditory (acoustic) nerve.

Cochlear implant: An implantable electronic device that bypasses damaged structures of the inner ear by converting sound into electrical signals that directly stimulate the auditory (acoustic) nerve.

Conductive hearing loss (CHL): Hearing loss that occurs when sound is conducted inefficiently through the outer ear canal to the eardrum and the small bones (ossicles) of the middle ear; this disorder involves a reduction in sound level or the ability to hear faint sounds.

Consonant-Nucleus-Consonant Test (CNC): An open set word recognition test (administered in quiet) consisting of 10 recorded lists of 50 monosyllabic words used to determine speech intelligibility in listeners with hearing impairments.

Decibel (dB): A unit of measurement indicating the loudness of sound. The intensity relates to how loud or soft a sound is. Sound scales are based on either sound pressure level, expressed as dB SPL, or hearing level, expressed as dB HL.

Electrically evoked auditory brainstem response (EABR): A measurement of auditory brainstem response (ABR) integrity using an electrical stimulus with the purpose of determining if the auditory nerve responds as expected to electrical stimulation. The EABR test may be used presurgically in selected individuals to determine if cochlear implantation should be attempted and postsurgically to determine if the implant is working properly.

Evoked otoacoustic emissions (OAE): Sounds measured in the external ear canal that are a reflection of the working of the cochlea. OAE is used in the screening as well as the diagnosis of hearing impairments in neonates and young children. While the test is considered part of the standard battery of tests in infants, it is considered a specialized test in children and adults.

Hearing in Noise Test (HINT): A commonly used speech recognition test consisting of 250 sentences (25 lists of 10 sentences per list) performed in the evaluation of an individual’s ability to hear speech in quiet and in noise in the context of sentences.

Hearing loss: Loss of the sense of hearing due to loss of function of any part of the auditory system, including outer, middle, or inner ear, auditory nerves, or the part of the brain responsible for processing sound. Loss may be partial or entire, as well as uni- or bilateral.

Hybrid cochlear implant (electric-acoustic stimulation): A cochlear implant system designed for individuals with preserved low-frequency hearing and severe high-frequency hearing loss, combining acoustic amplification for low frequencies with electrical stimulation for higher frequencies.

Meningitis: Inflammation of the meninges, the membranes that surround the brain and the spinal cord. This condition may result in hearing loss or deafness.

Mixed hearing loss: Hearing loss that is both conductive and sensorineural, occurring in one or both ears. This term refers to a condition where conductive hearing loss coexists with sensorineural hearing loss.

Neural plasticity: Ability of the brain, certain parts of the nervous system, or both to adapt to new conditions, such as an injury.

Neurofibromatosis Type 2 (NF-2): A group of inherited disorders in which noncancerous tumors grow on several nerves that usually include the nerve involved with hearing.

Nonstimulation (also called electrode deactivation): The intentional turning off of specific electrodes in a cochlear implant array that are not providing useful auditory information or are causing problematic symptoms such as facial nerve stimulation, poor sound quality, or abnormal loudness perception.

Otitis externa: Inflammation or infection of the ear canal.

Otitis media: Inflammation of the middle ear caused by infection.

Postlingual deafness: Hearing loss that occurs after acquiring language or speech.

Prelingual deafness: Hearing loss that occurs before the development of language or speech.

Promontory/round window stimulation test (PST): The application of controlled electrical current to the promontory or round window niche of the middle ear. The current is delivered via an electrode that is inserted either through the tympanic membrane by myringotomy or puncture by the otolaryngologist. The test has been used to predict the electrical response of surviving spiral ganglion nerve fibers and has been thought to verify a functioning cochlear nerve.

Pure-tone average (PTA): The average hearing threshold, typically calculated at key speech frequencies (commonly 500, 1000, and 2000 Hz), used to quantify the degree of hearing loss.

Scala tympani: The lower tube of the cochlear canal extending from the opening in the medial wall of the middle ear leading into the cochlea.

Sensorineural hearing loss: A permanent hearing loss related to the sensory or neural structures responsible for hearing that involves a reduction in sound level or ability to hear faint sounds; this disorder affects speech understanding or the ability to hear clearly; the involved structures include, but are not limited to, the cochlea and the acoustic nerve.

Severity of hearing loss: Severity of hearing loss is defined in terms of decibels (dB HL) according to the American Speech-Language-Hearing Association classification shown earlier in this document.

Single-sided deafness (SSD): Significant or total hearing loss in one ear; this disorder is sometimes referred to as unilateral sensorineural hearing loss. SSD is defined as a unilateral severe-to-profound deafness (PTA greater than or equal to 70 dB HL), with a contralateral ear that has better, normal or near-normal hearing (PTA less than or equal to 30 dB HL). SSD may be a result of a congenital unilateral hearing loss, a sudden sensorineural hearing loss, significant head trauma affecting the ear(s), and surgery to treat acoustic neuroma or other tumors of the eighth cranial nerve.

Speech recognition test: A test frequently used to determine cochlear implant candidacy; currently used tests include the following:

• AzBio Sentences-in-Noise Test
• Central Institute for the Deaf (CID) Test
• City of New York (CUNY) Sentence Test
• Consonant-nucleus-consonant test
• Hearing in Noise Test (HINT)
• Lexical Neighborhood Test (LNT)
• Multi-syllabic Lexical Neighborhood Test (MLNT)
• Phonetically Balanced-Kindergarten (PBK) Test

Tinnitus: A sensation of ringing or other noises heard in one or both ears which is not caused by an external sound, and other people usually cannot hear it. Tinnitus is usually caused by an underlying condition, such as age-related hearing loss, an ear injury or a problem with the circulatory system. Tinnitus alone, in the absence of significant hearing loss, is not an established indication for cochlear implantation.

Unilateral hearing loss (UHL): A condition in which an individual has non-functioning hearing in one ear, receives little or no clinical benefit from amplification in that ear, and has normal or near-normal audiometric function in the contralateral ear. UHL includes single-sided deafness (SSD) and asymmetric hearing loss (AHL).

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49. Philippon D, Bergeron F, Ferron P, Bussieres R. Cochlear implantation in postmeningitic deafness. Otol Neurotol. 2010; 31(1):83-87.
50. Quatre R, Bonnard A, Wales J, Eklof M. Long-term cochlear implant sensitivity in patients with far advanced otosclerosis. Laryngoscope. 2025; 135(10):3885-3892.
51. Reinhart PN, Parkinson AJ, Dunn CC, Gantz BJ. Factors affecting audiometric and speech perception outcomes in Hybrid cochlear implant recipients. Laryngoscope. 2026; 136:1475-1486.
52. Roland JT Jr, Cosetti M, Wang KH, et al. Cochlear implantation in the very young child: long-term safety and efficacy. Laryngoscope. 2009; 119(11):2205-2210.
53. Roland JT Jr, Gantz BJ, Waltzman SB, Parkinson AJ; Multicenter Clinical Trial Group. United States multicenter clinical trial of the cochlear nucleus hybrid implant system. Laryngoscope. 2016; 126(1):175-181.
54. Sennaroglu L, Sennaroglu G, Yucel E, et al. Long-term results of ABI in children with severe inner ear malformations. Otol Neurotol. 2016; 37(7):865-872.
55. Sharma A, Dorman MF
56. Sharma A, Prinja S, Thakur R, et al. Comparison of utility measures and auditory performance in children with cochlear implants and hearing aids. Int J Pediatr Otorhinolaryngol. 2025; 189:112163.
57. Sladen DP, Carlson ML, Dowling BP, et al. Early outcomes after cochlear implantation for adults and children with unilateral hearing loss. Laryngoscope. 2017a; 127(7):1683-1688.
58. Sladen DP, Frisch CD, Carlson ML, et al. Cochlear implantation for single-sided deafness: a multicenter study. Laryngoscope. 2017b; 127(1):223-228.
59. Smith HJ, Takkoush S, Mendenhall TJ, et al. Hearing benefits of cochlear implantation in older adults with single-sided deafness and asymmetric hearing loss. Am J Otolaryngol. 2025; 46(2):104560.
60. Swami H, Kaur A, Kumari A, et al. Study to compare outcomes of bilateral sequential and bilateral simultaneous cochlear implant in congenitally hearing-impaired children. Indian J Otolaryngol Head Neck Surg. 2025; 77(1):1052-1060.
61. Tait M, De Raeve L, Nikolopoulos TP. Deaf children with cochlear implants before the age of 1 year: comparison of preverbal communication with normally hearing children. Int J Pediatr Otorhinolaryngol. 2007; 71(10):1605-1611.
62. Tawakkul Q, Alsanosi S, Alahmadi A, et al. Comparative outcomes of cochlear implantation in children with auditory neuropathy spectrum disorder and sensorineural hearing loss: a systematic review and meta-analysis. Audiol Neurotol. 2025; 30(6):545-555.
63. Tomblin JB, Barker BA, Spencer LJ, et al. The effect of age at cochlear implant initial stimulation on expressive language growth in infants and toddlers. J Speech Lang Hear Res. 2005; 48(4):853-867.
64. Tyler RS, Gantz BJ, Rubinstein JT, et al. Three-month results with bilateral cochlear implants. Ear Hear. 2002; 23(1 Suppl):80S-89S.
65. Valencia DM, Rimell FL, Friedman BJ, et al. Cochlear implantation in infants less than 12 months of age. Int J Pediatr Otorhinolaryngol. 2008; 72(6):767-773.
66. van de Heyning P, Vermeire K, Diebl M, et al. Incapacitating unilateral tinnitus in single-sided deafness treated by cochlear implantation. Ann Otol Rhinol Laryngol. 2008; 117(9):645-652.
67. van Zon A, Peters JP, Stegeman I, et al. Cochlear implantation for patients with single-sided deafness or asymmetrical hearing loss: a systematic review of the evidence. Otol Neurotol. 2015; 36(2):209-219.
68. Vlastarakos PV, Candiloros D, Papacharalampous G, et al. Diagnostic challenges and safety considerations in cochlear implantation under the age of 12 months. Int J Pediatr Otorhinolaryngol. 2010a; 74(2):127-132.
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70. Waltzman SB, Roland JT Jr. Cochlear implantation in children younger than 12 months. Pediatrics. 2005; 116(4):e487-e493.
71. Wu J, Chen J, Ding Z, et al. Outcomes of cochlear implantation in 75 patients with auditory neuropathy. Front Neurosci. 2023; 17:1281884.
72. Young NM, Hughes CA, Byrd SE, Darling C. Postmeningitic ossification in pediatric cochlear implantation. Otolaryngol Head Neck Surg. 2000; 122(2):183-188.
73. Zhan KY, Dizdar K, Kallogjeri D, et al. Cochlear implantation outcomes in older adults, ages 80-90+. Otol Neurotol. 2025; 46(4):381-387.

Government Agency, Medical Society, and Other Authoritative Publications:

1. American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Minimal test battery for cochlear implants. Reaffirmed April 21, 2021 (Reviewed: February 2026). Available at: https://www.entnet.org/resource/position-statement-minimal-test-battery-for-cochlear-implants. Accessed on March 26, 2026.American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Clinical practice guideline: Sudden hearing loss (update). April 19, 2021. Available at: https://www.entnet.org/quality-practice/quality-products/clinical-practice-guidelines/sudden-hearing-loss-update/. Accessed on March 26, 2026.
2. American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Position statement: cochlear implantation for single-sided deafness in adults. April 25, 2023. Available at: https://www.entnet.org/resource/position-statement-cochlear-implantation-for-single-sided-deafness-in-adults/. Accessed on March 26, 2026.
3. American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Position statement: cochlear implantation for single-sided deafness in children. April 25, 2023. Available at: https://www.entnet.org/resource/position-statement-cochlear-implantation-for-single-sided-deafness-in-children/. Accessed on March 26, 2026.
4. American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Position statement: pediatric cochlear implants candidacy. April 5, 2021. Available at: https://www.entnet.org/resource/position-statement-pediatric-cochlear-implantation-candidacy/. Accessed on March 26, 2026.
5. American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Position statement: cochlear implants. November 10, 2020 (Reviewed: August 2025). Available at: https://www.entnet.org/resource/position-statement-cochlear-implants.  Accessed on March 26, 2026.
6. Bond M, Mealing S, Anderson R, et al. The effectiveness and cost-effectiveness of cochlear implants for severe to profound deafness in children and adults: a systematic review and economic model. Health Technol Assess. 2009b; 13(44):1-330.
7. Centers for Disease Control and Prevention (CDC). Immunization Schedules. Available at: https://www.cdc.gov/vaccines/hcp/imz-schedules/. Accessed on March 26, 2026.
8. Centers for Disease Control and Prevention (CDC). Vaccines and preventable diseases: cochlear implants and meningitis vaccination. Reviewed November 20, 2023. Available at: https://www.cdc.gov/vaccines/vpd/mening/hcp/dis-cochlear-gen.html. Accessed on March 26, 2026.
9. Centers for Medicare and Medicaid Services (CMS). National Coverage Determination: cochlear implantation. NCD #50.3. Effective April 4, 2005. Available at: https://www.cms.gov/medicare-coverage-database/view/ncd.aspx?ncdid=245&ncdver=3&DocID=50.3&list_type=ncd&bc=gAAAABAAAAAA&=. Accessed on March 26, 2026.
10. Dillon MT, Kocharyan A, Daher GS, et al. American Cochlear Implant Alliance Task Force guidelines for clinical assessment and management of adult cochlear implantation for single-sided deafness. Ear Hear. 2022; 43(6):1605-1619.
11. Joint Committee on Infant Hearing. Year 2019 position statement: principles and guidelines for early hearing detection and intervention programs. J Early Hear Detect Interv. 2019; 4(2):1-44.
12. O'Connell BP, Holcomb MA, Morrison D, et al. Safety of cochlear implantation before 12 months of age: Medical University of South Carolina and Pediatric American College of Surgeons-National Surgical Quality Improvement Program outcomes. Laryngoscope. 2016; 126(3):707-712.
13. Rubin LG, Papsin B. Committee on Infectious Diseases and Section on Otolaryngology-Head and Neck Surgery. Cochlear implants in children: surgical site infections and prevention and treatment of acute otitis media and meningitis. Pediatrics. 2010; 126(2):381-391.
14. U.S. Food and Drug Administration (FDA). Summary of Safety and Effectiveness Data (SSED): MED-EL Cochlear Implant System (MED-EL Corp., Innsbruck, Austria). P000025/S104. July 19, 2019. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf/P000025S104B.pdf. Accessed on March 26, 2026.
15. U.S. Food and Drug Administration (FDA). Summary of Safety and Effectiveness Data (SSED): Nucleus 24 Cochlear Implant System (Cochlear Americas, Centennial, CO). P970051/S172. March 17, 2020. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf/P970051S172B.pdf. Accessed on March 26, 2026.
16. Warner-Czyz AD, Roland JT Jr, Thomas D, et al. American Cochlear Implant Alliance Task Force guidelines for determining cochlear implant candidacy in children. Ear Hear. 2022; 43(2):268-282.

1. National Institute on Deafness and Other Communication Disorders (NIDCD). Hearing, ear infections, and deafness. Available at: https://www.nidcd.nih.gov/health/hearing-ear-infections-deafness. Accessed on March 26, 2026.

Auditory Brainstem Implants
Cochlear Implants
MED-EL Cochlear Implant System
MED-EL COMBI 40+ Cochlear Implant System
Nucleus Hybrid L24 Implant System

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