The worldwide prevalence rate of cCMV infection ranges from 0.2% to 2.5%.52,53 Among all infected newborns, 80%‒90% will be asymptomatic.54,55 Approximately 10% of asymptomatic newborns will develop hearing impairment, with the majority having severe or profound levels of impairment. Approximately 42.6% of these patients will require hearing rehabilitation.53 Infection with cCMV may lead to a wide spectrum of dysfunctions that, in addition to sensorineural hearing loss, include blindness and neurodevelopmental delay.56

Time to the diagnosis of cCMV is short, approximately 2 to 3-weeks after birth. Available tests become undefined after this period. Failing the Universal Newborn Hearing Screening (UNHS) is twice as common in newborns with cCMV as in uninfected newborns.57 Hearing loss is 90 times more frequent in children infected with cCMV than in uninfected children. One-third of cases of bilateral sensorineural hearing loss and half of cases of UHL are associated with cCMV.

Sensorineural hearing loss occurred in 9.9% of asymptomatic children and 33% of symptomatic cases according to a systematic review conducted in 2014.53 Foulon et al.58 demonstrated that the incidence of sensorineural hearing loss in asymptomatic infected individuals is 22% and that 5% of the children had late-onset deafness at 10-years of follow-up. Fowler et al.59 showed that up to 40% of asymptomatic children with congenital infection had sensorineural hearing loss, with a late-onset sensorineural hearing loss rate of up to 50% in this group (mean onset at 44-months).

Asymptomatic disease can lead to silent lesions in the inner ear structures that may progress in severity over time, resulting in late-onset hearing loss.55 In a longitudinal study of 651 asymptomatic children, Dahle et al.55 found that 37.5% developed late-onset hearing loss at a median age of 44-months. Approximately 54% experienced progressive, fluctuating hearing loss in at least one frequency at a median age of 51-months. Approximately 10% of asymptomatic cases progressed to hearing loss over 48-months.

The diagnosis of cCMV is made by identifying viral particles in saliva and urine using a Polymerase Chain Reaction (PCR) technique up to the child’s third week of life,60 as sensitivity decreases over the days. In intrauterine life, after 20-weeks’ gestation, identification can be done via the amniotic fluid. This procedure is indicated in very specific situations. A PCR test for CMV in amniotic fluid can confirm cCMV infection (positive predictive value is close to 100%).61

While Dried Blood Spot (DBS)-PCR assays are used in newborn screening for other congenital diseases, their use in cCMV screening has shown low sensitivity (28%‒75%) in prospective studies compared with gold standard methods for detecting viral antigens in saliva and urine.61,62 A meta-analysis of 15 studies evaluated the performance of DBS-PCR assays used in cCMV screening and found a sensitivity of 62.3%.63 In cCMV infection, which has a low prevalence (0.2%‒2% of live births), low screening sensitivity is a limiting factor for the use of these assays.

PCR testing is most often performed in patients considered a target for the disease, such as symptomatic patients with a suggestive clinical status.60,64 Children who fail the UNHS or who present with sensorineural hearing loss of unapparent cause should be tested for cCMV regardless of age.60,64 The same applies to neonates born to mothers with a documented seroconversion during pregnancy. According to Cannon et al.,65 for cases of cCMV-induced sensorineural hearing loss, there is good evidence that routine newborn screening has a positive impact on communication-related outcomes and should be considered for all children.60,64

In children undergoing etiologic evaluation of sensorineural hearing loss over 3 weeks of age, cCMV infection can only be confirmed retrospectively, using stored newborn blood as a model source for PCR-based diagnosis. If cCMV infection is suspected, in addition to laboratory testing, brain imaging (cranial ultrasound or MRI), visual function assessment, and hearing assessment are required.57,66

Common findings suggestive of cCMV include central nervous system malformations, ventriculomegaly, microcephaly, and cortical and periventricular calcifications. Because these changes are present in 80% of patients with sensorineural hearing loss and symptomatic cCMV,58 they are relevant for the otolaryngologist providing hearing rehabilitation for these patients. Those with the most limited changes have demonstrated the best rehabilitation outcomes.

Given the impact of UHL and SSD on development, imaging should be performed to better assess the inner ear and guide clinical management decisions. Computed Tomography (CT) of the temporal bone or MRI of the brain are most commonly performed. Malformations have been diagnosed by CT and/or MRI in 25% to 67% of patients with UHL,67,68 with rates ranging from 3% to 50% in the literature evaluating only patients with SSD.67

CND presents on a spectrum ranging from complete aplasia to hypoplasia. The cochlear nerve is best assessed using high-resolution T2-weighted MRI,69 which has increased the rates of CND diagnosis. The cochlear nerve may be deficient on MRI even when there is a normal cochlear aperture or Internal Auditory Canal (IAC).70,71

While several studies have assessed CND in pediatric patients with UHL, the literature has reported widely variable prevalence of CND ranging from 9% to 50%.68,70,72,73 Assessment of CND in pediatric patients with UHL has been limited in the literature, with a range of 0%‒28% prevalence of CND.73,74 Of note, studies comparing the prevalence of CND in pediatric vs bilateral SSD have demonstrated significantly higher rates of CND in UHL (39%‒50%) than in bilateral hearing loss (5%).75,76

Assessment of hearing thresholds in patients with CND has also been limited in the literature. Patients with CND have profound hearing loss or no response on unaided or aided threshold testing.77–79 However, cases have been reported of ears with CND on imaging that demonstrate mild-to-moderate or moderate hearing loss.77,80 These reports suggest that hearing thresholds alone may not be a good predictor of good cochlear nerve integrity.

The diagnosis of CND has a significant impact on the clinical management of pediatric patients with SSD. The prognosis for open-set speech perception in ears with CND is poor compared with ears with normal nerves. However, many ears with CND demonstrate a benefit from CI surgery, and some even achieve speech recognition.78,79,81,82 Implanted ears with cochlear nerve hypoplasia achieve more positive outcomes than those with cochlear nerve aplasia.

Outcomes in patients with aplastic nerves typically show very limited sound perception with a CI, although there have been reports of post-implant speech recognition.83,84 In addition to traditional bilateral candidates, CI also provides benefits to pediatric patients with SSD.85 Because CI is contraindicated in cases of UHL or SSD with CND and outcomes may be more limited with certain types of inner ear malformations, there is a need to recognize how common CND and cochlear malformations are in this population. This will in turn allow for a more accurate determination of CI candidacy by alerting providers to the high risk of CND or malformations in this population.

While studies have emphasized the need for MRI to identify CND in contrast to CT, MRI is generally associated with higher cost, less availability, and longer image acquisition time.73,86,87 Furthermore, in pediatric populations, MRI may require procedural sedation or general anesthesia, which carries a possible risk of adverse neurodevelopmental effects, particularly in very young children.88 As such, there is benefit in identifying CT findings that can reliably predict CND.

One such finding is the width of the cochlear aperture, also known as the bony cochlear nerve canal, which can be stenotic in patients with UHL.89 The normal width of the cochlear aperture is estimated to be approximately 1.9 mm (SD = 0.24 mm) on CT, and the normal width of the cochlear nerve at the fundus of the IAC is estimated to be approximately 1.2 mm (SD = 0.2 mm).90 While there is no established cutoff value for CND, recent studies have shown a strong relationship between CND and cochlear aperture stenosis (CAS, defined as cochlear aperture widths ranging from <1.4 to <1.7 mm), and this suggests that CAS may be a predictor of CND.72,91

Dorismond et al.92 identified CND in 98.5% (64/65) of ears with CAS using a cutoff of < 1.4 mm. Komatsubara et al.93 found that 9/10 (90%) patients with cochlear aperture width <1.5 mm had CND, while Tahir et al.91 found CND in 53/59 (89%) patients with cochlear aperture width <1.6 mm. Clemmens et al.,72 based on MRI alone, determined that 27/29 (93.1%) patients with cochlear aperture width <1.7 mm had CND.

Some authors advocate for initial MRI due to the absence of radiation exposure, its ability to identify additional brain and cranial nerve abnormalities, and its status as the gold standard for detection of CND, which dictates CI candidacy.72,94 Others recommend obtaining an initial CT scan because of the high likelihood of yielding positive findings, possibility of identifying relevant anatomic variants, rapid image acquisition, cost-effectiveness, and feasibility of being performed without sedation.95 Ultimately, the decision for the optimal initial imaging modality requires consideration of multiple factors.

Patient comorbidities should also be considered when deciding on the best initial imaging modality. In patients with syndromes such as CHARGE syndrome, Trisomy 21 or 18, and VACTERL/VATER syndrome (an acronym for a disorder that can affect different organs and systems: V ‒ the Vertebrae [bones of the spinal column]; A ‒ Anus; C ‒ Cardiac anomalies; T ‒ Trachea; E ‒ Esophagus; R ‒ Renal [kidney] anomalies; L ‒ Limb differences), MRI is preferred to CT.92

In the absence of these patient-related factors, however, CT should be strongly considered for initial imaging. A meta-analysis of imaging features in patients with UHL found that CAS was the most common CT abnormality observed in patients with isolated UHL, present in approximately 44%.96 While there are cases in which the cochlear nerve can be deficient in the absence of CAS warranting subsequent MRI,91,97 an initial CT diagnosis of CAS may be predictive of CND and provide adequate information to determine CI candidacy in patients with UHL.

Shared decision-making should include a conversation about patient-specific factors as well as the risks and benefits of each imaging modality. In cases in which CT is initially obtained and CAS is observed, CT likely provides adequate information to determine CI candidacy and obviates the need for MRI to directly assess CND.98 This approach may ultimately lead to reduced cost, more timely diagnosis, and avoidance of sedation in these patients.

Recommendations

• I

  Children with a diagnosis of SSD should receive special attention. In the classroom, they should sit closer to the teacher, with their normal ear facing the teacher. Preferably in a room with good sound insulation. (Strong Recommendation – Low-Quality Evidence)

• II

  Speech assessment and therapy (if necessary) should be conducted as early as possible. (Strong Recommendation – Low-Quality Evidence)

• III

  Genetic testing in children with SSD without other clinical signs. (No Recommendation)

• IV

  Congenital UHL can cause a number of developmental problems in childhood and should be identified as early as possible. (Strong Recommendation – Moderate-Quality Evidence)

• V

  CND and cCMV are the main causes of congenital UHL and should be prioritized in investigation. (Strong Recommendation – Moderate-Quality Evidence)

• VI

  Patients with congenital SSD due to cCMV may develop late-onset bilateral hearing loss. Therefore, these patients should be monitored. (Strong Recommendation – Low-Quality Evidence)

• VII

  The diagnosis of cCMV can be made only by collecting samples up to 4 weeks after birth using a PCR assay (blood, saliva, or urine). Samples collected later have low diagnostic value. DBS has been an option, although not yet very sensitive, but it can be used for children with suspected cCMV who have not undergone other tests at the appropriate time. (Weak Recommendation – Moderate-Quality Evidence)

• VIII

  Imaging is critical for the diagnosis and treatment of children with SSD due to the high risk of CND. (Strong Recommendation – Moderate-Quality Evidence)

• IX

  The contralateral ear should always be monitored for the risk of late-onset hearing loss. (Strong Recommendation – Low-Quality Evidence)

• X

  Children with congenital SSD should undergo hearing assessment regularly or if there is any evidence of previously established language deterioration. (Strong Recommendation – Low-Quality Evidence)

Conventional treatments for hearing rehabilitation of patients with SSD typically involve rerouting the auditory signal from the affected ear to the unaffected ear. CROS systems are used when no benefit is expected from fitting amplification to the ear with hearing loss, which is the case of patients with SSD. These devices offer a non-surgical approach and represent the least invasive solution available. CROS hearing aids consist of a microphone and transmitter in a hearing aid worn on the impaired ear, which transmits sound to the functioning ear via a wire or wirelessly.101 In cases of asymmetric hearing loss (sensorineural, conductive, or mixed), the aid on the better hearing ear can also provide amplification in addition to the CROS input, creating a configuration known as bilateral CROS (BiCROS). BiCROS is recommended for individuals with mild-to-moderate hearing loss in the better hearing ear.102

Evidence suggests that CROS hearing aids are successful in reducing the negative effects of acoustic head shadow and improving sound awareness and signal-to-noise (S/N) ratio when sounds are directed toward the affected ear.103–105 The unobtrusive design of current wireless CROS and BiCROS hearing aids is certainly an additional advantage, influencing the acceptance of these solutions. These devices are also easy to handle, especially by patients with SSD, and do not require sophisticated programming or fitting strategies.104 However, CROS hearing aids do not restore binaural hearing and cannot improve tasks that require binaural cues, such as sound localization abilities on the horizontal plane.106,107 Furthermore, in listening situations where the signal of interest is in the better ear and noise is transferred through the CROS microphone from the affected side, there is a significant reduction in speech understanding.104,108

Children with mild-to-moderate UHL can be fitted with hearing aids. However, in children with SSD, the use of conventional hearing aids is contraindicated as they do not provide benefits.109,110 In the past, children with SSD were often observed without intervention if their school performance and language acquisition were unaffected. Pediatric CI users with bilateral deafness have an overall Health-Related QOL (HRQOL) similar to that of their peers with NH.111

BCDs are rerouting devices that transmit signals from the ear with SSD to the better ear via bone conduction, bypassing the air conduction pathway. Since the late 1970s, when the first hearing aids were implanted, many different implantable and non-implantable devices have been introduced. BCDs function similarly to CROS systems, but using a sound processor that is attached to the skull.

BCDs transform sound waves into mechanical vibrations through direct contact with the skull, facilitating transmission to the inner ear. Surgically implanted devices can be divided into 2 distinct types: percutaneous and transcutaneous. Transcutaneous devices can be further classified as passive or active. Percutaneous devices transmit vibrations through a percutaneous osseointegrated pin or abutment in the skull. This direct connection allows efficient signal transmission at all frequencies without skin or soft tissue impedance. However, complications such as skin reaction, granulation tissue formation, keloids, and soft tissue infection are not uncommon.112,113

Passive transcutaneous devices consist of a device, similar to a percutaneous device, and an external part held in place magnetically that transmits vibrations transcutaneously to the implanted device, keeping the skin intact. A major advantage of these devices is the lower rate of skin complications. However, sound attenuation caused by soft tissues may occur, reaching up to 25 dB at 6000–8000 Hz compared with percutaneous implants.114 They may also cause discomfort due to the magnetic force required to secure the processor in place.115 Symptoms can be relieved by reducing magnet pressure and limiting device use. However, excessive pressure can lead to skin necrosis.116

Active transcutaneous devices consist of an external audio processor (containing microphone, processor, and battery) and an internal system that houses the magnet, coil, and bone conduction transducer. Sound waves are transmitted electrically from the external device to the internal device using technology similar to that of CIs. Because the internal device is the one responsible for generating mechanical forces against the skull, skin attenuation is minimized, and the magnet power can be considerably reduced.117

BCDs are more effective than CROS hearing aids for sound discrimination in noise and quiet.118 Patients may have improved speech discrimination in noise, with results ranging from -3.8 to -4.8 dB S/N ratio, depending on the location of the sound source.119 Users often experience reduced hearing benefit and gain over time. The discontinuation rate has reached 14% over a 50-month period, approximately 3% per year.120

BCDs can alleviate the head shadow effect and improve sound awareness on the affected side.101,121 However, they cannot restore binaural hearing or improve sound localization ability.101,121,122 Stimulation of the contralateral auditory pathway is believed to play a role in suppressing tinnitus and may be an important factor for patients with this complaint.122–124

Discomfort with the device, concerns about sound quality, and subjective hearing impairment are among the main reasons for rejecting CROS hearing aids and BCDs.125,126 Reluctance to use rerouting devices is also linked to changes in self-perception, aesthetic concerns, and the presence of negative stereotypes. Despite counseling (habits, work/social environment, expectations) and extensive preoperative testing of non-implantable BCDs, they are less effective than osseointegrated systems because patients experience signal attenuation through the skin and soft tissues, especially at high frequencies, and their viable duration of use may be limited due to the discomfort caused by the force required to secure them in place.127

Comparing an adhesive hearing system with a CROS hearing aid in a prospective randomized crossover study, Mertens et al.128 evaluated 17 patients with SSD who used each of these devices for 2 weeks, divided into 2 groups. The results showed that 70% of participants with SSD considered the adhesive system to be partially useful or better, with satisfaction levels similar to those using the CROS system. While sound localization improved with the adhesive system, there was no significant improvement in speech perception in noisy environments. Another study of 9 patients with SSD evaluated a device that transmits vibrations through the palate and showed improved speech recognition and overall QOL in both quiet and noisy environments.129

Chandrasekar et al.130 found statistically significant improvements in hearing outcomes, as measured by Children’s Home Inventory for Listening Difficulties (CHILD) questionnaire scores and hearing thresholds for speech in noise, using a BCD compared with no amplification. Similar results were found by other authors.131,132 However, Chandrasekar et al. also observed a low level of adherence to BCD use. Despite improved audiological outcomes and CHILD scores, some patients chose not to use the devices. The major reason for rejection appears to be concern about cosmetic appearance and its impact on social acceptance.133

Surgically implantable BCDs with better sound quality are generally available for children over 5-years of age.134 The CROS system introduces an additional problem, which is the possible occlusion of the ear with NH.134 Very young children or those with a narrower External Auditory Canal (EAC) would have great difficulty using the CROS system. The auditory deprivation associated with SSD causes irreversible changes in the auditory cortex,135 which BCDs and CROS hearing aids cannot prevent because they do not provide hearing to the affected ear.98

Used since the 1960s, CIs provide the most effective treatment to restore useful hearing in profound deafness and represent an option for patients with SSD to restore binaural hearing. CIs can improve speech understanding in quiet and noise, sound localization, and QOL in those affected by SSD.136 Interest in restoring binaural inputs by using CIs in patients with SSD has grown during the last decade, with several studies reporting improvements in speech recognition in noise, sound localization, and tinnitus control.3,5,31,137,138

Initially suggested as a treatment for severe tinnitus in adults with SSD, CI indication has also been expanded to include rehabilitation of children and adults with SSD, regardless of tinnitus. In 2019, the Food and Drug Administration (FDA) approved CI for the treatment of SSD in children aged 5-years and older with profound sensorineural hearing loss in the compromised ear (PTA: 5, 1, 2, and 4 kHz of > 80 dB HL) and NH in the contralateral ear (PTA: 5, 1, 2, and 4 kHz ≤ 30 dB HL).98 Early evidence in children with SSD using a CI shows significant improvements in speech perception in quiet and noise, as well as in the accuracy of sound source localization.19 A systematic review of 119 children undergoing CI for SSD showed significant improvements in audiological and patient-reported outcomes after implantation.5 These results highlight the growing evidence supporting the subjective and objective benefits of binaural hearing in children with SSD after CI.

Children with bilateral hearing loss have better outcomes in language and speech recognition when they receive CI early than those who receive it later.139,140 Longer duration of deafness has a negative impact on speech recognition.141 However, these factors should not be considered a limitation to CI in children with SSD. Favorable HRQOL benefits have also been reported in children with an older age at the time of surgery and longer duration of deafness.142

Pediatric CI users report a worse HRQOL at school and in the social environment than their hearing peers.143 In the study by Zeitler et al.,142 children with bilateral CI reported higher mean QOL scores in the general functioning and social-relations domains than their peers with UHL. This may be explained by the fact that parents of children with bilateral hearing loss likely perceive their child’s initial disability as subjectively worse than parents of children with UHL, so the HRQOL benefits may be perceived more strongly in children with bilateral hearing loss. In both cases, it can be understood that a child with UHL, unlike a child with bilateral hearing loss, is not completely dependent on the implant due to the ear with NH. Furthermore, social isolation for children with bilateral hearing loss from being unable to hear at all may be more profound than for children with UHL.

Central neural adaptations after CI in patients with SSD may differ from those in patients with bilateral hearing loss, potentially enabling the integration of electric and acoustic signals.144 While the full extent of this signal integration is still under investigation, it supports the subjective evidence of improved hearing ability. It has been demonstrated that children with asymmetric hearing loss can benefit from the restoration of binaural hearing with CI, without detrimental effects on the unaffected ear.145 Children undergoing CI for profound SSD report substantial reductions in listening effort after implantation, with demonstrated reversal of cross-modal cortical reorganization even after long periods of pre-implant deafness.146,147

While single-word recognition with a CI alone is often used by clinicians as the primary outcome measure of CI benefit, the overall goal of CI in children with SSD is to provide benefits related to binaural hearing, specifically spatial hearing. While prospective studies of children with SSD receiving a CI are limited, case reports and retrospective studies have demonstrated the benefits of CI use for masked speech recognition.85,148,149 Long-term data suggest that the effects of CI use on hearing in noise for children with SSD are evident as early as 6-months after activation and are maintained for at least 24-months.19

CI is the only treatment for SSD that provides hearing to the affected ear and allows binaural auditory stimulation of the brain. Prospective clinical trials, case reports, and retrospective reviews have shown positive outcomes with CI use in this patient population. Studies have shown that children with SSD who listen with a CI experience improved speech recognition in noise19,150,151 and sound source localization19,148,152 compared with monaural listening or preoperative performance. Furthermore, studies of pediatric CI users with SSD generally report consistent device use.31,44,153

A study of children with UHL, using the Children With Cochlear Implants: Parental Perspectives Survey, found favorable responses toward CI in all 8 measured domains, with less strongly perceived benefits than children with sensorineural hearing loss undergoing CI only in the communication and general functioning domains.111 Furthermore, children with UHL and prolonged hearing loss or older age at implantation showed favorable benefits, which were similar to those of the younger cohort and the cohort with shorter duration of hearing loss.154

Assessing the benefits of CI (sound localization and speech perception in noise) in younger children with SSD can be difficult given limited cooperation and the need for an advanced level of task understanding. The identification of objective measures that do not require the active participation and cooperation of the child is desirable and necessary to better establish the benefits of CI in younger children. Therefore, the measurement of Cortical Auditory Evoked Potentials (CAEPs) for vocal stimuli could serve as a cortical biomarker of audibility and auditory processing efficiency in children with SSD who use a CI, which could be useful for management.155

Compared with their peers with NH, children with SSD are at a disadvantage with respect to word recognition in quiet, masked sentence recognition, and sound source localization. CIs can benefit children with SSD in unilateral and bilateral listening tasks, although their outcomes still lag behind those of their peers with NH. Patients with SSD have shown significant improvements in masked sentence recognition and sound source localization in the CI + NH condition, benefits that have been observed over 24-months of CI use.3

Consonant-Nucleus-Consonant (CNC) scores have been shown to stabilize after 6-months of CI use. After 24-months of CI use, word recognition in the CI ear ranges from 32% to 78% of correct words, with a mean of 58%.19 These findings are very similar to the results of Deep et al.,149 who reported a mean CI alone word recognition score of 56% correct for pediatric CI recipients with SSD and significant variability in scores (range, 4%‒88%). Beck et al.156 also found variable improvement in word recognition and attributed the variability to age at implantation.

Family counseling is a decisive step before CI indication in SSD, mainly because a certain proportion of these children have been shown to become nonusers. In addition to neurophysiological reasons, children may become nonusers due to other causes, such as lack of family support or emotional distress.149 The main feature linked to CI efficiency is represented by its daily use. Since optimal CI performance can only be achieved through relevant educational and family support,157 CI use may be negatively affected by the lack of such support, particularly if family expectations about CI outcomes are not met. Another factor that can eventually limit CI use (in terms of hours per day) is that children may experience subjective benefits from the device only in specific circumstances, such as at school.

In children with SSD who are at risk of progressive hearing loss in the better ear (eg, in cases of CMV), surgery before hearing deterioration in the better ear is recommended to minimize auditory deprivation and improve hearing outcomes. Children with SSD due to bacterial meningitis should be implanted promptly. CND is a contraindication to CI in SSD. Accurate diagnosis of CND is important given its high prevalence in children with SSD.98

Earlier age at implantation is beneficial in children with bilateral hearing loss.140,158,159 UHL begins to impact auditory development at very young ages, suggesting that early intervention may be necessary to mediate these effects. Yang et al.160 evaluated infants with UHL at a median age of 4.4-months and found delayed early prelingual auditory skills in infants with SSD compared with children with NH. Kishon-Rabin et al.161 reported delays in the auditory behavior of infants with UHL compared with infants with NH, and Fitzpatrick et al.162 observed delays in auditory function in preschool children with UHL.

Imaging and electrophysiologic data indicate that UHL can lead to marked cortical reorganization,163,164 and restoration of hearing can reverse some of these changes and restore binaural function.153 While restoration of binaural hearing can occur in listeners with long-standing hearing loss,165,166 hearing loss early in auditory development may be more detrimental than loss acquired later in development.167,168 Younger age at CI surgery takes advantage of auditory neuroplasticity, which declines after 7-years of age,169 and may prevent aural preference syndrome, which develops after years of unilateral hearing.3,146,167,169

A systematic review of children with UHL undergoing CI found that duration of hearing loss ranging from 4 to 7-years was associated with improvement in both audiologic and patient-reported outcomes.5 The duration of hearing loss that may determine outcomes is likely related to central auditory development, during which neural plasticity is at the highest. Auditory deprivation has been shown to result in delayed maturation of the auditory cortex and to affect a child’s neurocognition.170 A study using P1 latency as a measure of the maturity of central auditory pathways to evaluate children with congenital deafness using a CI169 found that the most sensitive period is up to 3.5-years of age, but neural plasticity exists up to 7-years of age, after which there is a marked decline.169

A systematic review assessed CI outcomes in children implanted for SSD, specifically addressing the child’s age at the time of surgery and duration of deafness, and found that the mean age of nonusers was higher than the mean age of daily device users.5 Also, a shorter duration of deafness was associated with improved outcomes. Beck et al.,156 in a series of 10 patients, determined that children with congenital deafness implanted after 4-years of age demonstrate poorer performance than children implanted before 4-years of age in SSD. Arndt et al.171 evaluated 36 children with SSD treated with CI – 20 had congenital, 7 had perilingual (0–4 years of age), and 9 had postlingual deafness (> 4-years of age). Children with congenital SSD showed better results with a shorter duration of deafness (< 3-years) than those with a longer duration of deafness.

Other studies have shown that children and adolescents with SSD who undergo CI can show significant improvement in speech recognition testing postoperatively despite age at implantation older than 7-years.151 Thomas et al.172 reported objective benefits in speech perception and sound localization in 21 patients with congenital SSD implanted up to 11-years of age and found no difference in Speech, Spatial, and Qualities of Hearing Scale (SSQ) scores in patients implanted before 6-years of age vs. those implanted after 6-years of age.

Park et al.,98 in children with SSD, suggested that the use of these devices at an earlier age could be beneficial given the importance of neuroplasticity in CI outcomes. Polonenko et al.153 demonstrated a rapid improvement in cortical reactivity, measured by electroencephalogram, after a few months of device use in children who received a CI before 3.6-years of age. In contrast, brain reorganization in response to SSD could hamper central binaural integration after CI, 2-years after the onset of hearing loss.170,173

Children with SSD are likely to benefit more from CI when surgery is performed early (<3-years of age)98,172 due to further maturation of the auditory pathway and myelination processes that have been reported to begin before birth and then continue up to the fourth year of life.144,174 However, data on these features remain inconsistent.

Huttunen et al.175 reported a lack of high-quality studies investigating the consequences and benefits of interventions for early-onset and congenital UHL. In a systematic review, Benchetrit et al.5 noted that the studies consist mainly of retrospective reviews and investigations with small, heterogeneous samples and inconsistent methods. Longitudinal, repeated-measures, controlled trials are needed to provide professionals and families with evidence-based information on how to care for children with SSD.

Arndt et al.137 described better performance in children with post-verbal UHL than in children with pre-verbal or congenital SSD, who had worse outcomes in verbal discrimination and sound localization. Rahne and Plontke176 demonstrated satisfactory results using CI in pre-verbal and congenital SSD. Central brain adaptations, which occur after CI in SSD, differ from those in individuals with bilateral hearing loss, and it remains unknown how patients with SSD and those rehabilitated by CI can integrate electric and physiological acoustic stimulation over time.177 Probst178 hypothesized the lack of development of central compensation mechanisms in children with SSD after CI. This fact, combined with the aforementioned considerations, makes the choice of CI rehabilitation in children with SSD quite complex.

Yaar-Soffer et al.155 assessed the neuroplasticity of the central auditory pathways after CI using CAEPs, demonstrating improved skills in these children. In particular, available data support the benefits of electric stimulation, including improved myelination and expanded neuronal connections within the auditory pathway.

Using electroencephalographic data, Sharma et al.146 demonstrated that, even after several years of unilateral auditory deprivation, children can eventually exhibit neuroplasticity patterns within the auditory cortex after CI. Therefore, late CI could eventually improve the processing of auditory information in the brain. Further studies are needed in this field.

Regarding potential effects of CI on tinnitus, the available data is still insufficient in the pediatric population;137,146,149,157 therefore, it is not possible to draw a conclusion on this specific topic.

Another factor that should be evaluated as it may affect the outcomes of CI users is the duration of device use. Daily device use has been shown to influence CI performance in children with bilateral hearing loss.179,180 Many studies have reported a mean of 7 h of device use per day in CI users.3,138,153,181 An important reason for performing CI surgery as early as possible would be for children and their environment to become accustomed to using the CI and to avoid the social stigma that can be a key factor in discontinuation of use when CI surgery occurs during adolescence.3,172 In addition to the difficulty of adjusting the adolescent’s expectations about surgical outcomes.182

Park et al.179 observed that, in children with SSD and CI, better word recognition was associated with more hours of daily CI use. Arndt et al.171 evaluated 36 children with congenital and acquired SSD treated with CI. After a mean follow-up of 4.75-years, 32 of the 36 children were using their CI regularly.

Magee et al.183 evaluated 27 children with SSD, with a mean age at CI of 7.8 years. The mean daily device use was 7.8 (SD = 3.0) hours/day, and 40.7% of children used Direct Audio Input (DAI) daily. There was no significant correlation between hours of CI use and CNC score. However, there was a significant improvement in CNC score associated with the use of DAI during rehabilitation (CNC 50.91% [yes] vs. 23.81% [no]), which remained significant when adjusting for age at CI, duration of deafness, and daily device use. Therefore, this study indicates that DAI may be a useful tool in the rehabilitation of these patients.

While the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) has attempted to find the optimal age at implantation for children with SSD, contraindicating surgery in children older than 3-years,98 a systematic review has suggested that findings are not yet robust enough to make recommendations.5 Park et al.3 found significant benefits of CI use for children implanted between 3.5- and 6.5-years of age. However, the age range of participants was quite narrow, limiting the ability to observe age effects. Almost half of the study population had an unknown onset of deafness, precluding a meaningful consideration of the impact of duration of deafness on CI outcomes. Unfortunately, this is not uncommon for children with UHL and SSD. If hearing loss is not present or detected on NHS, it may not be noted until hearing screening at elementary school enrollment. This is problematic because the incidence increases from 0.1% at birth to 3%‒6.3% in elementary school.184,185

Recommendations

• XI

  CROS hearing aids can successfully reduce the negative effects of acoustic head shadow and improve sound awareness and S/N ratio when sounds are directed toward the affected ear, being an option especially for patients unwilling to undergo surgery. (Strong Recommendation – Low-Quality Evidence)

• XII

  Given the risk of partial occlusion of the ear with NH, with loss of the monaural cues that are important for the child’s development, CROS hearing aids have limited indication in this age group. (Weak Recommendation – Low-Quality Evidence)

• XIII

  BCDs are more effective than CROS hearing aids for sound discrimination in noise and quiet, being particularly indicated in children. (Weak Recommendation – Low-Quality Evidence)

• XIV

  Sound localization abilities are largely dependent on binaural cues. CROS hearing aids and BCDs have restricted indications for these purposes because they do not rehabilitate the deaf ear. (No Recommendation)

• XV

  CIs provide the most effective treatment to restore useful hearing in profound deafness, being the only option for patients with SSD to restore binaural hearing. (Strong Recommendation – Low-Quality Evidence)

• XVI

  CIs can restore binaural hearing, producing significant improvements in speech perception, spatial localization of sound, tinnitus control, and overall QOL. (Strong Recommendation – Moderate-Quality Evidence)

• XVII

  There is low-quality evidence to suggest that CI for children with congenital SSD may be hardly beneficial to children older than 3-years. This should be evaluated on a case-by-case basis. (Weak Recommendation – Low-Quality Evidence)

• XVIII

  CI in children with SSD due to CND. (No Recommendation)

• XIX

  In children with SSD due to cCMV, CI is more appropriate due to the increased risk of contralateral hearing deterioration over time. (Strong Recommendation – Low-Quality Evidence)

• XX

  Family counseling is a decisive step before CI indication in SSD to adjust expectations and conduct therapy. (Strong Recommendation – Moderate-Quality Evidence)

The indication of CROS systems for adults is adopted worldwide212 because this modality can be used promptly, without the need for surgery. Despite the restricted indication in children, it has proven to be a viable option for adults.

Contralateral routing of sound was first achieved by connecting a hearing aid microphone on the side of the deaf ear to a hearing aid on the side of the NH ear.213 A similar result can now be achieved via wireless communication between 2 behind-the-ear devices.108 Evidence suggests that CROS hearing aids are successful in reducing the negative effects of acoustic head shadow and improving sound awareness and S/N ratio when sounds are directed toward the affected ear.100,213 In patients with tinnitus, the outcomes of their fitting are not encouraging.206 Patients may therefore need counseling to form appropriate expectations about situations in which benefit may be obtained and those in which the use of a rerouting device may be counterproductive to listening.

Regarding the effects of BCDs on QOL, a systematic review and meta-analysis found that BCDs are associated with significant improvements in hearing-related QOL in adult patients, whereas no difference was found in the measures of generic QOL as assessed by the HUI-3.214

Evidence suggests that rerouting devices can improve speech perception in noise. Statistically significant benefits to speech perception were found only when the S/N ratio was more favorable in the impaired ear than in the normal ear. In this situation, a rerouting device increases the S/N ratio in the normal ear by overcoming the head shadow effect.215 There is heterogeneity in the benefits of BCDs, with improvements in the S/N ratio ranging from 0.4215 to 4.4 dB.107 Therefore, uncertainty remains as to whether the magnitude of the benefit would be clinically meaningful.

Sound localization abilities are largely dependent on binaural cues,216 and rerouting devices do not restore 2-eared hearing. Some have speculated that these devices may provide cues that allow the listener to distinguish sounds on the left from sounds on the right (lateralization) by distorting the spectral content of sounds transmitted via the device. There is no evidence to suggest that devices that reroute sounds to the ear with NH provide reliable cues to support spatial hearing.206

Oh et al.217 conducted a systematic review and meta-analysis of 50 studies involving 674 adult patients with SSD undergoing ipsilateral CI and showed statistically significant improvements in speech perception, tinnitus reduction, sound localization, and global and disease-specific QOL. Similar results were found in other systematic reviews conducted by Van Zon et al.,218 Peter et al.,219 and Levy et al.220 Karoui et al.221 showed that restoration of binaural hearing results in reversal of the abnormal pattern of cortical lateralization in individuals with UHL, resulting in improved spatial hearing.

Adult CI users with SSD have shown significant improvements in their sound localization abilities within the first few weeks of activation, and this improvement has been sustained after 1-year of CI use. Furthermore, localization accuracy and consistency continued to improve over the 5-year follow-up period after activation.222 Advanced age is not a contraindication to CIs, which have risks and individual performance outcomes for patients of advanced age similar to those observed in younger adults.223

Several studies have demonstrated a clear negative correlation between duration of deafness and CI performance in individuals with SSD due to the effect of prolonged monaural hearing on the auditory pathways.224 However, in adults with SSD, prolonged deafness should not be the only contraindication to CI. Rader et al.,225 in a retrospective analysis of 36 adults with postlingual deafness, found a more favorable result in speech perception 12–36 months after CI activation in patients with duration of deafness < 400-months. For those with a longer duration, success is limited but still possible. Nassiri et al.226 found no difference in speech perception among patients with SSD using a CI, regardless of whether their deafness had lasted more or less than 10 years.

Studies comparing rerouting technologies vs CIs in adults with SSD have shown that CIs significantly improve sound localization and that CI users perform equally or significantly better on measures of speech recognition in noise and subjective benefit.227,228

The importance of intensive auditory training in CI users with SSD has been highlighted aiming to promote the perceptual integration of the electrically stimulated ear with the dominant ear, thus providing individuals with binaural hearing and optimizing outcomes.1,148,229 Further studies are needed to evaluate the effectiveness of optimal auditory training methods and to determine the recommended timing for individuals with SSD using CI.

CIs can also improve sound localization for individuals with contralateral residual hearing.230 Arnd et al.137 assessed sound localization before and after CI and identified a statistically significant improvement. Although CI undoubtedly restores some form of binaural hearing, it remains unclear whether it can restore spatial hearing in individuals with SSD and over what time scale.

Recommendations

• XXI

  The indication of CROS systems for adults is most commonly adopted because this modality can be used promptly, without the need for surgery, and most of these devices can be transformed into BiCROS hearing aids for use in cases of deterioration of an initially normal ear. (Weak Recommendation – Low-Quality Evidence)

• XXII

  BCDs are associated with significant improvements in hearing-related QOL in adult patients. (Strong Recommendation – Moderate-Quality Evidence)

• XXIII

  Adult patients with SSD undergoing ipsilateral CI have statistically significant improvements in speech perception, tinnitus reduction, sound localization, and QOL. (Strong Recommendation – Moderate-Quality Evidence)

• XXIV

  Despite the negative correlation between duration of deafness and CI performance in individuals with SSD due to the effect of prolonged monaural hearing on the auditory pathways, evidence is lacking to determine the threshold duration of auditory deprivation to indicate CI in this population. (Weak Recommendation – Low-quality Evidence)

CI may be useful in cases where the functional integrity of the cochlear nerve is preserved. Some surgeons rely only on the subjective assessment of the anatomical preservation of the cochlear nerve to decide whether CI could be performed. However, there are several objective measurement tools to assess cochlear nerve function, such as electrically evoked Auditory Brainstem Response (eABR). This monitoring can provide objective information on functional preservation of the cochlear nerve during tumor resection.

Electrical stimuli can be delivered using multiple methods. A rounded bent-tip (“hockey stick”) electrode can be placed in the round window niche and used to stimulate the cochlear nerve.231 This method is comparable to the promontory stimulation test. However, promontory stimulation relies on the subjective auditory sensations experienced by the patient in response to electrical stimulation and has been shown to have poor prognostic value considering speech performance with CI. The use of this method as a screening tool for CI was subsequently limited to cases of cochlear malformations. In contrast, eABR with the “hockey stick” electrode provides objective results and has proven to be much more useful in determining the excitability of the auditory nerve pathway – especially in patients with inconclusive preoperative audiological tests.232 Therefore, eABR with the “hockey stick” electrode can be performed in patients under local anesthesia, mainly to assess prognosis.

In addition to round window eABR, there is also the possibility of stimulating the auditory nerve via the cochlea. A test electrode can be used to provide appropriate stimuli for eABR measurements. In the case of CI after VS resection, the functional integrity of the cochlear nerve can be confirmed prior to CI insertion using an intracochlear test electrode.233 Unlike the CI, the intracochlear test electrode only has 3 contacts at an array length of 18 mm and a separate ground electrode. This device is subsequently removed and discarded after measurement. These evoked neural responses are measured using electrodes placed on the patient’s head. There is also the possibility of near-field ABR recordings using an electrode placed directly on the auditory nerve (cochlear nerve action potential) or using a surface electrode located on the dorsal cochlear nucleus (dorsal cochlear nucleus action potential).234 Despite these advances, there is no definitive evidence that eABR is a reliable tool for assessing cochlear nerve function during VS resection.235 Of all the various eABR features to be interpreted, in the case of VS resection, simply the presence of wave V has proven to be a reliable indicator of cochlear nerve function. A loss of wave V amplitude greater than 50% or an increase in wave V latency greater than 1 ms may act as warning signs, although no predictive value of these factors for postoperative hearing outcome has been confirmed in the literature. The presence of a clearly detectable eABR wave V after tumor resection may prompt consideration of CI. There are no general recommendations on what actions should be taken in cases where there is partial or complete loss of eABR signal. Systemic and local factors may influence the eABR signal during surgery. For example, systemic or local hypotension may contribute to a loss of amplitude and increase in wave latencies. When complete loss of an eABR wave V occurs, CI may not be successful. However, there are reports of patients with negative eABR responses undergoing CI who later achieve auditory perception.236 A few patients with a preserved eABR wave V may not achieve auditory perception following CI. It is essential to provide appropriate preoperative counseling and manage patients’ expectations, as well as to consider that the final decision should be well individualized for cases of sporadic VS and SSD.

The first prospective study assessing the audiological outcomes of CI after translabyrinthine resection of sporadic VS was conducted by Rooth et al.237 Seven patients met the inclusion criteria (small tumors, surgical feasibility, and willingness to participate in postoperative rehabilitation) and underwent simultaneous CI and VS resection; the main determinant for CI was the surgeon’s subjective perception of an intact cochlear nerve immediately after VS resection. Five patients had auditory perception at the time of activation, whereas 2 remained without auditory perception. All patients experienced subjective improvement in sound localization, speech perception in noise, and tinnitus severity. However, the study also demonstrated that patients with better outcomes achieved with VS have worse outcomes than patients undergoing CI for idiopathic UHL.

Sanna et al.238 conducted a prospective study with the largest series of patients with normal contralateral hearing undergoing CI insertion simultaneously to sporadic VS resection. A total of 13 individuals underwent VS resection by means of a modified translabyrinthine approach with cochlear nerve preservation and simultaneous CI and showed a slight improvement in the mean PTA at low frequencies, which was not statistically significant (p >  0.05). Furthermore, PTA, disyllabic word recognition, sentence recognition, and common phrase comprehension improved at the second control, but this improvement was also not statistically significant (p >  0.05). Regarding CI use, 90% of patients reported using the device between 5 and 7 days per week. The median subjective satisfaction score on a 10-point scale was 8. The main limitation of the study was failure to perform an intraoperative assessment of cochlear nerve function.

Conway et al.239 showed similar results in their prospective study in terms of improved speech discrimination in noise, improved sound source localization, and decreased tinnitus. Tadokoro et al.240 conducted a systematic review of 16 articles published from 1995 to 2017, including 45 patients. The postoperative auditory outcomes were as follows: Speech dDiscrimination Score (SDS) of 56.4% (SD = 27.6%) (vs. preoperative SDS of 30.0% [SD = 40.0%]); PTA of 28.8 (SD = 8.3) dB (vs. preoperative PTA of 79.8 [SD = 32.7] dB); and Arizona Biomedical Institute Sentence Test (AzBio) score of 75.0% (SD = 14.3%). Of the 7 patients with tinnitus complaints, 5 reported subjective improvement in symptoms. Thompson et al.241 conducted a systematic review of concurrent CI and resection of sporadic VS and Neurofibromatosis type 2 (NF2). Approximately 85% of patients had auditory perception with their CI and 75% had high-to-intermediate performance in terms of audibility (AzBio score of 72% in NF2 vs. 70% in sporadic VS). Most patients considered to be low performers still reported some subjective benefit from CI compared with preoperative measures. The main predictor of audiological outcome was tumor size (p = 0.018).

Longino et al.242 assessed CI outcomes in small, non-operated VS. Seven patients with VS volumes ranging from 0.11 to 1.02 cm3 were implanted. All patients were on imaging follow-up for 2-months to 7-years. Monosyllabic word recognition improved in all patients (from 6% to 55%), with stable performance at a follow-up of at least 12-months.

The level of evidence is low because, to date, only case series with small sample sizes are available. A few systematic reviews have been published in recent years on CI outcomes after sporadic VS resection, but the data from these studies are highly heterogeneous due to the large number of case reports included and the lack of standardized tools to assess hearing performance after implantation. There is likely publication bias in these successful cases. Only a few studies are prospective, and none have a comparative design. Furthermore, high variability in follow-up time, auditory test batteries, and preoperative measurements is responsible for meta-analyses with high heterogeneity.

The effectiveness of hearing rehabilitation with BCDs in patients with VS remains controversial. There are few published studies on hearing rehabilitation with BCDs in patients with SSD after VS resection. Bouček et al.243 assessed the audiological outcomes of 16 patients who accepted to undergo BCD implantation and found a significant improvement in sentence discrimination at both 6-week (64.0%) and 1-year (74.6%) follow-up. This improvement was noted in situations where the sentences came from the side of the affected ear, with contralateral noise of -5 dB S/N ratio. Another study evaluated subjective hearing handicap in patients with SSD after VS surgery and the effect of the BCD on the test band. Twenty-six patients were included and showed a mean improvement in speech discrimination in noise of 15%. However, only 50% of patients agreed to undergo BCD implantation after the test.107

Many studies comparing CROS and BCD technologies are available, but unfortunately none are specifically focused on patients with VS. Therefore, studies with long-term follow-up are lacking to determine the actual benefits in this population.

Aschendorff et al.244 published the results of 8 patients in a retrospective study. While no specific data on preoperative or postoperative hearing parameters were included, they reported that patients with simultaneous CI placement tend to have more favorable rehabilitation outcomes than those receiving a CI in two-stage, sequential surgery. Speech understanding obtained in their cohort of implanted patients was reported to be comparable to that of other patients with SSD of different etiologies.

Tian et al.245 conducted a systematic review of 14 studies of patients with sporadic VS and NF2, both irradiated. Hearing outcomes were considered poor in 27% and excellent in 19%, with a mean follow-up of 19-months. Outcomes were considered intermediate in 70% of patients.

Recommendations

• XXV

  CI is a treatment option for SSD associated with sporadic VS, especially in the presence of disabling tinnitus and preserved cochlear nerve function. (Strong Recommendation – Low-QualityEvidence)

• XXVI

  Intraoperative eABR measurements are suggested to help inform decision-making on CI candidacy after VS resection. (Weak Recommendation – Low-Quality Evidence)

• XXVII

  Despite not restoring binaural hearing, CROS systems and BCDs may be indicated in patients with VS-related SSD. It is recommended to perform preoperative tests with BCDs. (Strong Recommendation – Low-Quality Evidence)

After undergoing surgical resection with preservation of the EAC anatomy, patients may suffer from sensorineural, conductive, or mixed hearing loss and benefit from conventional personal hearing amplification devices.

In patients with SSD and maximal conductive hearing loss as a result of treatment, bone-anchored hearing aids may be a viable option. Patients undergoing subtotal petrosectomy with blind sac closure of the EAC have a large conductive hearing loss. These patients with maximal conductive hearing loss may benefit from BCDs.246 In these cases, considering imaging artifacts and a possible need for postoperative imaging monitoring, percutaneous hearing aids can be used.

Cases of profound unilateral sensorineural hearing loss due to temporal bone paragangliomas may occur for a variety of reasons. These situations are associated with intracochlear erosion secondary to tumor expansion, invasion of the IAC, or brainstem compression. In these situations, postsurgical patients are rarely CI candidates. However, in selected patients with progressive hearing loss and preserved cochlear anatomy, CI may be a viable option. CI was reported in a young patient treated surgically for bilateral paragangliomas. The implanted side was treated via canal-wall-up mastoidectomy without blind sac closure of the EAC. Despite good initial postoperative performance, the patient progressed with worsening of hearing due to cochlear ossification.247 A case of successful CI in patients with post-radiation paraganglioma has been reported.248

While CI is rarely indicated in patients operated on for paragangliomas, it may be feasible in well-selected cases.

Regardless of etiology, imaging follow-up is a consideration in all patients requiring assessment of CIs and transcutaneous bone-anchored hearing aids after treatment of temporal bone tumors.

While it is currently possible to perform MRI up to 3.0 T, distortion artifacts are present. There are methods to reduce these artifacts, especially so as not to impair lesion visualization, thus allowing regular imaging surveillance in patients receiving a CI. Proper head positioning, magnet placement at a distance greater than 6.5 cm from the EAC, use of spin-echo sequences, and fat suppression techniques can reduce the size and shape of MRI artifacts.249,250 In any case, it is important to take into account imaging artifacts with CIs and transcutaneous hearing aids and potential difficulties in MRI follow-up.

Recommendations

• XXVIII

  In patients with profound unilateral sensorineural hearing loss and neoplasms that require long-term imaging follow-up, the harm caused by the presence of imaging artifacts during follow-up should be considered when deciding on the use of CIs and transcutaneous bone-anchored hearing aids. (Weak Recommendation – Low-quality Evidence)