**Cochlear Implants in Children: A Review**

Julia Sarant *The University of Melbourne Australia* 

#### **1. Introduction**

In 1980, the first child in the world was implanted with the single-channel House cochlear implant device (Eisenberg & House, 1982). Children who initially received cochlear implants during this first paediatric clinical trial were quite old compared to current ages (the average age in the first House clinical trial was 8 years, whereas children are now being implanted as young as 6 months of age), and the majority communicated using sign language (Eisenberg & Johnson, 2008). It is now known that implanting older children who do not communicate orally gives little chance of speech perception or spoken language development. In 1985, the first children received a multichannel cochlear implant in Australia (Clark et al., 1987). This clinical trial selected children who had a higher potential for success, including shorter duration of deafness and a commitment to oral communication both at home and in their educational programs. At this time, it was unknown whether the speech processing schemes used with adults who had lost their hearing after developing language (ie. post-lingually deafened) would be appropriate for facilitating the speech perception and language development of young children with immature auditory systems. It is important also to note that the desired outcomes for adults and children differed; while the goal for adults was to improve auditory skills and communication using previously acquired cognitive, spoken language, and social skills, the goal for children was to develop these skills using the auditory information provided by the cochlear implant, having had no useful auditory experience (and therefore presumably no neural development of their auditory system) until they received their cochlear implant. The implantation of children was also highly controversial. For many years, cochlear implantation in children was opposed by the Deaf Community, on the grounds that deafness in children should be considered as a cultural and linguistic difference rather than as a disability that could be remediated by a cochlear implant. Over time, this view has changed such that in 2000, a position paper of the National Association of the Deaf in the U.S. stated that "cochlear implantation is a technology that represents a tool to be used in some forms of communication, and not a cure for deafness" (National Association of the Deaf, 2000).

It is now well documented that children with severe-profound hearing loss receive significant benefits from cochlear implants in terms of speech perception and language development (Blamey et al., 2006; Geers et al., 2008; Moog, 2002; Nicholas & Geers 2007). Cochlear implants are becoming the standard of care for children with severe-profound hearing loss, with increasing uptake of simultaneous bilateral implants over recent years. There is a large variation in implementation of cochlear implant technology around the

Cochlear Implants in Children: A Review 333

speech perception scores for children with cochlear implants who are matched according to language ability (Blamey & Sarant, 2002). While this approach is helpful for older children with some language ability, it is not suitable for use with very young children whose speech perception, production and language skills are undeveloped, independent of their degree of hearing loss, and for whom, due to behavioural and cognitive developmental issues, it is

Since the 1990's, several researchers have proposed alternate methods of determining suitability for a cochlear implant in children. Osberger et al. (1991) classified children using hearing aids into 'gold', 'silver' and 'bronze' categories, based on their unaided pure tone thresholds (PTA) averaged across 0.5, 1, and 2 kHz. Initially, it was predicted that only children in the 'bronze' category (mean >110dbHL and >110dbHL at two of the three frequencies) were suitable candidates for a cochlear implant. These categories were revised when it became apparent that children with cochlear implants were outperforming not only hearing aid users in the bronze, but also in the silver (mean = 104dbHL and 101-110 dbHL at two of the three frequencies) and gold (mean = 94dbHL and 90-100 dbHL in two of the three frequencies) categories. A further methodology that compared speech perception results for children using hearing aids and cochlear implants in order to determine criteria for suitability used the concept of 'equivalent hearing loss' (EHL). Boothroyd and Eran (1994) compared the abilities of children using hearing aids with those using a cochlear implant on an imitative test of phonetic (speech sound) contrasts, and derived EHL by plotting speech perception results against the three-frequency unaided PTA for each ear. Linear regression statistical analysis was used to transform the speech perception scores of the children into EHL values. Although the EHL for the children using cochlear implants suggested that their potential for speech perception was similar to that of children with a severe hearing loss using hearing aids, there were still children using cochlear implants whose speech perception skills were no better than those of children with a profound hearing loss using hearing aids. In 1997, Boothroyd reported that children with cochlear implants who were educated mostly in oral communicative environments achieved speech perception scores equivalent to those of children using hearing aids with a hearing loss in the 70-89 dbHL (severe) range (Boothroyd, 1997). Similar results have been reported more recently

Throughout the current decade, several studies of large numbers of children with cochlear implants have reported speech perception results that are comparable to those achieved by post-lingually deafened adults using cochlear implants, and even to those achieved by children with a moderate hearing loss using hearing aids (Geers et al., 2003; Svirsky et al., 2004; Tajudeen et al. 2010; Wie et al. 2007). In response to these achievements, the criteria for suitability have again changed such that even very young children with a severe to severeprofound hearing loss are now deemed suitable recipients for cochlear implants, and children with significant, or useable, residual hearing are currently being implanted in centers not under the jurisdiction of the United States FDA (Geers & Moog, 1994; Leigh et al., 2011; Svirsky & Meyer, 1999; Zwolan et al., 1997). Currently, the more conservative FDA guidelines approve cochlear implantation in children aged 12-23 months with bilateral profound sensorineural hearing loss (>90dbHL) and in children aged 2 years and older with severe-profound hearing loss (greater than or equal to 90dBHL in the better

very difficult to assess speech perception ability.

(Davidson, 2006; Eisenberg et al., 2004).

hearing ear).

world, and also within regions in some countries. Bilateral implantation is becoming the standard of care for children in developed countries, such as Germany, England and the United States, while in developing countries it is very infrequent. In less developed countries, many children are still receiving unilateral single-channel cochlear implants, which are cheaper to manufacture, and many are not able to access the technology at all due to high cost. For example, of the estimated 1 million children with profound hearing loss in India, only approximately 5000 are reported to have cochlear implants. It is difficult to estimate how many children worldwide have received cochlear implants to date, as reports vary widely. However, in December 2010, the U.S. Food and Drug Administration (FDA) reported that approximately 219,000 people worldwide had received implants (National Institute on Deafness and other Communication Disorders, 2011). Despite variations in estimates, it is generally accepted that approximately half of the number of cochlear implant recipients are children.

#### **2. Suitability for a cochlear implant**

#### **2.1 Criteria for candidature**

In the early days of cochlear implantation in children, children were only considered as suitable recipients for a cochlear implant when they had no useable aided hearing, and therefore had nothing to lose if the outcome were not good, as cochlear implantation damages the inner ear such that acoustic hearing is not usually possible post-operatively. As technological improvements in electrode design, speech processing strategies, receiver/stimulator design and programming have gradually facilitated improving outcomes with cochlear implants, the clinical perspective has changed.

Determining suitability in children is a more complicated process than it is for post-lingually deafened adults, whose speech production and language skills are fully developed. Whereas for adults it can be assumed that the ability to perceive speech is limited by hearing ability alone, for children, speech perception is limited by language knowledge and speech production skills as well as by residual hearing quality and quantity (DesJardin et al., 2009; Sarant et al., 1997). Unsurprisingly, speech perception scores (obtained from measuring the number of sounds, words, or sentences perceived correctly on a test) in children are more highly correlated with spoken language abilities than with any other factor (Blamey et al., 2001a), and are also influenced by speech production skills (Paatsch et al., 2004). Therefore, basing decisions about cochlear implant candidature for children on speech perception scores alone could risk implanting some children who have sufficient aided hearing to develop spoken language through hearing aids, but who are limited in their speech perception ability by their undeveloped spoken language skills. This risk has increased over time as the age at which children receive cochlear implants has decreased. Further, as speech perception results with cochlear implants have improved, the amount of hearing being risked in order to achieve the potential benefits of a cochlear implant has increased. Given this increasing risk, accurate prediction of a particular child's potential to benefit from a cochlear implant has become even more important.

Blamey and Sarant (2002) proposed a method of combining speech perception and language assessment scores to calculate an objective criterion for cochlear implant suitability, so that a child's pre-operative aided speech perception performance is compared to a distribution of

world, and also within regions in some countries. Bilateral implantation is becoming the standard of care for children in developed countries, such as Germany, England and the United States, while in developing countries it is very infrequent. In less developed countries, many children are still receiving unilateral single-channel cochlear implants, which are cheaper to manufacture, and many are not able to access the technology at all due to high cost. For example, of the estimated 1 million children with profound hearing loss in India, only approximately 5000 are reported to have cochlear implants. It is difficult to estimate how many children worldwide have received cochlear implants to date, as reports vary widely. However, in December 2010, the U.S. Food and Drug Administration (FDA) reported that approximately 219,000 people worldwide had received implants (National Institute on Deafness and other Communication Disorders, 2011). Despite variations in estimates, it is generally accepted that approximately half of the number of cochlear implant

In the early days of cochlear implantation in children, children were only considered as suitable recipients for a cochlear implant when they had no useable aided hearing, and therefore had nothing to lose if the outcome were not good, as cochlear implantation damages the inner ear such that acoustic hearing is not usually possible post-operatively. As technological improvements in electrode design, speech processing strategies, receiver/stimulator design and programming have gradually facilitated improving

Determining suitability in children is a more complicated process than it is for post-lingually deafened adults, whose speech production and language skills are fully developed. Whereas for adults it can be assumed that the ability to perceive speech is limited by hearing ability alone, for children, speech perception is limited by language knowledge and speech production skills as well as by residual hearing quality and quantity (DesJardin et al., 2009; Sarant et al., 1997). Unsurprisingly, speech perception scores (obtained from measuring the number of sounds, words, or sentences perceived correctly on a test) in children are more highly correlated with spoken language abilities than with any other factor (Blamey et al., 2001a), and are also influenced by speech production skills (Paatsch et al., 2004). Therefore, basing decisions about cochlear implant candidature for children on speech perception scores alone could risk implanting some children who have sufficient aided hearing to develop spoken language through hearing aids, but who are limited in their speech perception ability by their undeveloped spoken language skills. This risk has increased over time as the age at which children receive cochlear implants has decreased. Further, as speech perception results with cochlear implants have improved, the amount of hearing being risked in order to achieve the potential benefits of a cochlear implant has increased. Given this increasing risk, accurate prediction of a particular child's potential to benefit from

Blamey and Sarant (2002) proposed a method of combining speech perception and language assessment scores to calculate an objective criterion for cochlear implant suitability, so that a child's pre-operative aided speech perception performance is compared to a distribution of

outcomes with cochlear implants, the clinical perspective has changed.

a cochlear implant has become even more important.

recipients are children.

**2.1 Criteria for candidature** 

**2. Suitability for a cochlear implant** 

speech perception scores for children with cochlear implants who are matched according to language ability (Blamey & Sarant, 2002). While this approach is helpful for older children with some language ability, it is not suitable for use with very young children whose speech perception, production and language skills are undeveloped, independent of their degree of hearing loss, and for whom, due to behavioural and cognitive developmental issues, it is very difficult to assess speech perception ability.

Since the 1990's, several researchers have proposed alternate methods of determining suitability for a cochlear implant in children. Osberger et al. (1991) classified children using hearing aids into 'gold', 'silver' and 'bronze' categories, based on their unaided pure tone thresholds (PTA) averaged across 0.5, 1, and 2 kHz. Initially, it was predicted that only children in the 'bronze' category (mean >110dbHL and >110dbHL at two of the three frequencies) were suitable candidates for a cochlear implant. These categories were revised when it became apparent that children with cochlear implants were outperforming not only hearing aid users in the bronze, but also in the silver (mean = 104dbHL and 101-110 dbHL at two of the three frequencies) and gold (mean = 94dbHL and 90-100 dbHL in two of the three frequencies) categories. A further methodology that compared speech perception results for children using hearing aids and cochlear implants in order to determine criteria for suitability used the concept of 'equivalent hearing loss' (EHL). Boothroyd and Eran (1994) compared the abilities of children using hearing aids with those using a cochlear implant on an imitative test of phonetic (speech sound) contrasts, and derived EHL by plotting speech perception results against the three-frequency unaided PTA for each ear. Linear regression statistical analysis was used to transform the speech perception scores of the children into EHL values. Although the EHL for the children using cochlear implants suggested that their potential for speech perception was similar to that of children with a severe hearing loss using hearing aids, there were still children using cochlear implants whose speech perception skills were no better than those of children with a profound hearing loss using hearing aids. In 1997, Boothroyd reported that children with cochlear implants who were educated mostly in oral communicative environments achieved speech perception scores equivalent to those of children using hearing aids with a hearing loss in the 70-89 dbHL (severe) range (Boothroyd, 1997). Similar results have been reported more recently (Davidson, 2006; Eisenberg et al., 2004).

Throughout the current decade, several studies of large numbers of children with cochlear implants have reported speech perception results that are comparable to those achieved by post-lingually deafened adults using cochlear implants, and even to those achieved by children with a moderate hearing loss using hearing aids (Geers et al., 2003; Svirsky et al., 2004; Tajudeen et al. 2010; Wie et al. 2007). In response to these achievements, the criteria for suitability have again changed such that even very young children with a severe to severeprofound hearing loss are now deemed suitable recipients for cochlear implants, and children with significant, or useable, residual hearing are currently being implanted in centers not under the jurisdiction of the United States FDA (Geers & Moog, 1994; Leigh et al., 2011; Svirsky & Meyer, 1999; Zwolan et al., 1997). Currently, the more conservative FDA guidelines approve cochlear implantation in children aged 12-23 months with bilateral profound sensorineural hearing loss (>90dbHL) and in children aged 2 years and older with severe-profound hearing loss (greater than or equal to 90dBHL in the better hearing ear).

Cochlear Implants in Children: A Review 335

aspects of each disability and its impact on communication development after implantation

The few studies of children with cochlear implants and additional disabilities have generally reported poorer performance on speech perception, production and language assessments, particularly when higher level speech processing abilities are required. For example, in one of the first studies of these children, (Pyman et al., 2000) found that although 90% of 75 children with motor and/or cognitive delays could discriminate consonants and vowels after four years of cochlear implant use, only around 60% of the children were able to use this information to perceive open-set sentences (those presented with no context), compared to over 80% of children without additional disabilities. Similarly, a further study of children with a variety of disabilities, such as attention-deficit disorder, cerebral palsy, central auditory processing disorder, dyspraxia and autism, showed some speech perception skill development at a slower rate than for the general population (Waltzman et al., 2000). Children whose additional disability is mild can derive significant benefit from cochlear implants, whereas children with more severe disabilities have much less favourable outcomes, with some showing almost no progress (Edwards, Frost & Witham, 2006; Filipo et al., 2004; Hamzavi et al., 2000; Holt & Kirk, 2005; Meinzen-Derr et al., 2011; Vlahovic & Sindija, 2004). Most studies have highlighted that children with additional disabilities require longer periods of implant use before demonstrating any benefit, and as for children in the general cochlear implant population, variation in outcomes is wide for children with additional disabilities (Hamzavi et al., 2000; Waltzman et al., 2000). It was reported for some children that the assessment tasks were too difficult to complete (Donaldson et al., 2004; Waltzman et al., 2000), which is a factor that has added to the difficulty of determining

Children with autistic spectrum disorders (ASD) have historically been considered poor cochlear implant candidates, but as the age at which children are being implanted has decreased, there are now a number of children who have been implanted before their diagnosis of ASD. The single published study of progress in a group of children with ASD reported that smaller gains on tests of speech perception and language had been made in comparison to those reported for the cochlear implant general population, but that parent reports suggested positive improvements in their children's functioning and responsiveness

In summary, although the degree of benefit obtained from cochlear implants is often lower for children with additional disabilities, many children still receive measurable benefit from their devices, and this benefit adds to their quality of life. Some of the observed benefits cannot be quantified on standardised tests, and have been instead reported anecdotally, with observations of improvements in social interaction and responsiveness to the environment, behaviour, vocalization, self-help skills, motor skills and the ability to follow instructions (Donaldson et al., 2004; Filipo et al., 2004; Fukuda et al., 2003; Waltzman et al., 2000; Wiley et al., 2005). There is still a need to determine the impact of additional disabilities on post-operative benefit with cochlear implants, and to define more clearly what benefits might reasonably be expected for children with different additional disabilities. The point at which a cochlear implant will not be beneficial also needs to be determined with regard to the degree of severity of additional disabilities, and the definition of benefit should be carefully explored, with improved psychological well-being, children's

has been difficult.

outcomes for this population.

(Donaldson et al., 2004).

The introduction of neonatal hearing screening programs in developed countries over the past decade has meant that hearing loss is now identified in babies as young as a few days or months old, and there is earlier referral and diagnosis than ever before (Dalzell, 2000; White & Maxon, 1995; Yoshinaga-Itano, 2003a). Very young infants and toddlers now represent the majority of paediatric cochlear implant candidates in these countries, and for these children, decisions about candidacy must currently be based solely or primarily on audiometric information if cochlear implants are to be given early, as there are limited tools available to measure speech perception or language abilities in this age group. The audiometric information is usually objective data obtained from the transient evoked auditory brainstem response (ABR) used in hearing screening, otoacoustic emissions, or auditory steady state responses (ASSR). These results may be combined with behavioural data derived from testing conducted by audiologists, depending on the protocol of individual cochlear implant programs. Most recently, an "equivalent PTA" model was derived to be applied to audiometric data for very young children from a comparison of the open-set speech perception scores of preschool and elementary school-aged children using cochlear implants and hearing aids. The model gives equivalent PTA for a 75% through to 95% chance of improvement in speech perception outcomes in 5% steps. Using a less conservative 75% chance of improvement criterion (as opposed to the 95% criterion that has until now been applied), the model recommends that children with bilateral profound hearing loss through to children with unaided pure tone average thresholds of 75 to 90 dBHL are suitable recipients for cochlear implants, while children with lesser hearing loss than 75dbHL are encouraged to continue with hearing aid use (Leigh et al., 2011).

#### **2.2 Children with additional disabilities: Implications for candidacy**

It is well established that 30-40% of children with severe-profound hearing loss also have an additional physical and/or cognitive disability, such as visual impairment, cognitive impairment, learning disabilities, autistic spectrum disorders (ASD) or developmental delay (Archbold & O'Donoghue, 2009; Edwards, 2007; Holt et al., 2005). Often, the additional disability is related to the cause of deafness, and is part of a syndrome or other grouping of disabilities. Children with additional disabilities present a further challenge with regard to determining suitability for cochlear implants, because the degree of benefit derived by the 'average' child with hearing loss is unlikely to be experienced by these children due to the effects of their additional disabilities. For this reason, children with additional disabilities were not considered suitable cochlear implant candidates for many years. Although excluded from FDA clinical trials in the past (Holt et al., 2005), small numbers of children with additional disabilities have received cochlear implants. Little is known about the degree of benefit children with hearing loss and additional disabilities derive from cochlear implants with regard to speech perception and spoken language development, for several reasons. Firstly, much of the research effort around cochlear implants has been directed at identifying outcomes and predictive factors for the majority of children with cochlear implants who do not have additional disabilities. Secondly, due to the fact that there are smaller numbers of children with additional disabilities, and many are unable to complete standardised assessment procedures, quantitative analysis of outcomes has been difficult. A further challenge is that there are a large number of additional disabilities spread across a relatively small population of children, therefore obtaining sufficient numbers to define the

The introduction of neonatal hearing screening programs in developed countries over the past decade has meant that hearing loss is now identified in babies as young as a few days or months old, and there is earlier referral and diagnosis than ever before (Dalzell, 2000; White & Maxon, 1995; Yoshinaga-Itano, 2003a). Very young infants and toddlers now represent the majority of paediatric cochlear implant candidates in these countries, and for these children, decisions about candidacy must currently be based solely or primarily on audiometric information if cochlear implants are to be given early, as there are limited tools available to measure speech perception or language abilities in this age group. The audiometric information is usually objective data obtained from the transient evoked auditory brainstem response (ABR) used in hearing screening, otoacoustic emissions, or auditory steady state responses (ASSR). These results may be combined with behavioural data derived from testing conducted by audiologists, depending on the protocol of individual cochlear implant programs. Most recently, an "equivalent PTA" model was derived to be applied to audiometric data for very young children from a comparison of the open-set speech perception scores of preschool and elementary school-aged children using cochlear implants and hearing aids. The model gives equivalent PTA for a 75% through to 95% chance of improvement in speech perception outcomes in 5% steps. Using a less conservative 75% chance of improvement criterion (as opposed to the 95% criterion that has until now been applied), the model recommends that children with bilateral profound hearing loss through to children with unaided pure tone average thresholds of 75 to 90 dBHL are suitable recipients for cochlear implants, while children with lesser hearing loss

than 75dbHL are encouraged to continue with hearing aid use (Leigh et al., 2011).

It is well established that 30-40% of children with severe-profound hearing loss also have an additional physical and/or cognitive disability, such as visual impairment, cognitive impairment, learning disabilities, autistic spectrum disorders (ASD) or developmental delay (Archbold & O'Donoghue, 2009; Edwards, 2007; Holt et al., 2005). Often, the additional disability is related to the cause of deafness, and is part of a syndrome or other grouping of disabilities. Children with additional disabilities present a further challenge with regard to determining suitability for cochlear implants, because the degree of benefit derived by the 'average' child with hearing loss is unlikely to be experienced by these children due to the effects of their additional disabilities. For this reason, children with additional disabilities were not considered suitable cochlear implant candidates for many years. Although excluded from FDA clinical trials in the past (Holt et al., 2005), small numbers of children with additional disabilities have received cochlear implants. Little is known about the degree of benefit children with hearing loss and additional disabilities derive from cochlear implants with regard to speech perception and spoken language development, for several reasons. Firstly, much of the research effort around cochlear implants has been directed at identifying outcomes and predictive factors for the majority of children with cochlear implants who do not have additional disabilities. Secondly, due to the fact that there are smaller numbers of children with additional disabilities, and many are unable to complete standardised assessment procedures, quantitative analysis of outcomes has been difficult. A further challenge is that there are a large number of additional disabilities spread across a relatively small population of children, therefore obtaining sufficient numbers to define the

**2.2 Children with additional disabilities: Implications for candidacy** 

aspects of each disability and its impact on communication development after implantation has been difficult.

The few studies of children with cochlear implants and additional disabilities have generally reported poorer performance on speech perception, production and language assessments, particularly when higher level speech processing abilities are required. For example, in one of the first studies of these children, (Pyman et al., 2000) found that although 90% of 75 children with motor and/or cognitive delays could discriminate consonants and vowels after four years of cochlear implant use, only around 60% of the children were able to use this information to perceive open-set sentences (those presented with no context), compared to over 80% of children without additional disabilities. Similarly, a further study of children with a variety of disabilities, such as attention-deficit disorder, cerebral palsy, central auditory processing disorder, dyspraxia and autism, showed some speech perception skill development at a slower rate than for the general population (Waltzman et al., 2000). Children whose additional disability is mild can derive significant benefit from cochlear implants, whereas children with more severe disabilities have much less favourable outcomes, with some showing almost no progress (Edwards, Frost & Witham, 2006; Filipo et al., 2004; Hamzavi et al., 2000; Holt & Kirk, 2005; Meinzen-Derr et al., 2011; Vlahovic & Sindija, 2004). Most studies have highlighted that children with additional disabilities require longer periods of implant use before demonstrating any benefit, and as for children in the general cochlear implant population, variation in outcomes is wide for children with additional disabilities (Hamzavi et al., 2000; Waltzman et al., 2000). It was reported for some children that the assessment tasks were too difficult to complete (Donaldson et al., 2004; Waltzman et al., 2000), which is a factor that has added to the difficulty of determining outcomes for this population.

Children with autistic spectrum disorders (ASD) have historically been considered poor cochlear implant candidates, but as the age at which children are being implanted has decreased, there are now a number of children who have been implanted before their diagnosis of ASD. The single published study of progress in a group of children with ASD reported that smaller gains on tests of speech perception and language had been made in comparison to those reported for the cochlear implant general population, but that parent reports suggested positive improvements in their children's functioning and responsiveness (Donaldson et al., 2004).

In summary, although the degree of benefit obtained from cochlear implants is often lower for children with additional disabilities, many children still receive measurable benefit from their devices, and this benefit adds to their quality of life. Some of the observed benefits cannot be quantified on standardised tests, and have been instead reported anecdotally, with observations of improvements in social interaction and responsiveness to the environment, behaviour, vocalization, self-help skills, motor skills and the ability to follow instructions (Donaldson et al., 2004; Filipo et al., 2004; Fukuda et al., 2003; Waltzman et al., 2000; Wiley et al., 2005). There is still a need to determine the impact of additional disabilities on post-operative benefit with cochlear implants, and to define more clearly what benefits might reasonably be expected for children with different additional disabilities. The point at which a cochlear implant will not be beneficial also needs to be determined with regard to the degree of severity of additional disabilities, and the definition of benefit should be carefully explored, with improved psychological well-being, children's

Cochlear Implants in Children: A Review 337

connecting and communicating with the world, so it is very important that these children are diagnosed and receive their cochlear implants early in order to establish communication through audition prior to the loss of vision. Usher syndrome is one of the 20% of causes of deafness that involve abnormalities in cochlea-vestibular anatomy. These abnormalities increase the potential for surgical difficulties and complications, such as damage to the facial nerve and incomplete insertion of the implant electrode array in the cochlea (Bauer et al.,

Some other children with congenital deafness also have cochlear abnormalities, often due to a range of genetic causes, another of which is CHARGE syndrome. Children with this rare genetic syndrome have deafness, visual problems, and a variety of other physical abnormalities, including serious heart defects, colobomas (or holes) in one or both eyes, growth retardation, genital abnormalities and external and internal ear malformations. Anatomical abnormalities in the structure of the cochlea can also create difficulties for programming, with reduced dynamic ranges for children with more severe cochlear abnormalities (Papsin, 2005). For these reasons, malformation of the cochlea was considered a contra-indication to cochlear implant surgery in the early years of cochlear implantation in children, and it is still not possible to implant some of these children (Bamiou et al., 2001). Despite these difficulties, initial results for small numbers of children with cochlear anomalies have shown that implantation is possible, with some children achieving speech perception and language results similar to those without anatomical abnormalities (Chadha et al., 2009; Dettman et al., 2011). Children with a common cavity anomaly (a single cavity in the cochlea) and other more severe syndromic anomalies have achieved much poorer results (Bauer et al.,

2002; Chadha et al., 2009; Lanson et al., 2007; Loundon et al., 2003; Young et al., 1995).

Children with viral causes of deafness such as rubella, cytomegalovirus (CMV), toxoplasmosis and meningitis also require special consideration, as these viruses can cause developmental neurological deficits, including learning and cognitive difficulties (Edwards, 2007; Grimwood et al., 2000; Isaacson et al., 1996). A significant difference between children with deafness caused by meningitis and that caused by the other viruses is that while CMV, toxoplasmosis and rubella are contracted perinatally, children who have had meningitis will have experienced sound prior to infection and may have developed some spoken language skills. A further complication of meningitis is ossification (bone growth) within the cochlea, which is usually bilateral and can commence within four weeks of the illness (Durisin et al., 2010). This makes it imperative that children who have had meningitis are diagnosed with hearing loss and receive cochlear implants as soon as possible, before ossification limits both the potential for a full insertion and for benefit. Again, limited reports of post-operative benefit for children with these causes of deafness show a wide range of speech perception skills, intelligibility and language outcomes, with some children doing well (Francis et al., 2004; Lee et al., 2005) and others doing poorly (Isaacson et al., 1996; Ramirez Inscoe &

At the most basic level, cochlear implants provide children with an auditory awareness of their environment. Through their cochlear implant, children can hear many environmental

2002; Chadha et al., 2009).

Nikolopoulos, 2004; Wie et al., 2007).

**3.1 Environmental awareness** 

**3. Benefits of unilateral cochlear implants** 

maximum potential, and quality of life being taken into consideration in addition to quantitative outcomes on tests.

#### **2.3 Candidacy and selected aetiologies/pathologies of deafness**

A further group of children for whom candidacy issues are more complex are those with selected pathologies that not only cause severe-profound hearing loss but may also impact on outcomes with cochlear implants. Although there are many such pathologies, the most common of these will be discussed as examples of the impact aetiology, or cause of hearing loss, may have on post-implantation outcomes.

In the 1990's, auditory neuropathy (AN) was defined as a distinct type of hearing disorder that disrupts neural activity in the central and peripheral auditory pathways (Starr et al., 1996). Auditory neuropathy is characterised by normal outer hair cell function in the cochlea (which enables many babies to pass newborn hearing screening if otoacoustic emission testing is used), and a retro cochlear lesion (dysfunction in the inner hair cells or auditory [eighth] nerve), which manifests as an absent or abnormal response to auditory brainstem response (ABR) testing. Features of this pathology include poorer than expected speech perception abilities in relation to degree of hearing loss in the majority of children, with some children who have only a mild hearing loss demonstrating a severely impaired ability to use their hearing for speech understanding (Rance et al., 2007). This pathology affects approximately 0.23% of at-risk children (Rance et al., 1999). Given the unusual pattern of perceptual deficits that characterises AN, much of the research in this area has focused on whether or not a cochlear implant can assist these children to understand speech through their hearing. The few published investigations on speech perception have varied widely, reporting no benefit (Miyamoto et al., 1999; Teagle et al., 2010) through to benefit comparable to that received by the general population of children with cochlear implants (Buss et al., 2002; Peterson et al., 2003; Rance & Barker, 2008; Trautwein et al., 2000). For the children who demonstrated significant benefit, it was noted that electrical stimulation via the cochlear implant elicited ABR responses, which suggests that the implant was able to enable greater neural synchrony and therefore to overcome the desynchronization thought to underlie AN. Studies of language and speech production outcomes for these children are again limited, and results are similar to those for speech perception, with wide variation in outcomes, but also with some children demonstrating the same level of development as the general population of children with cochlear implants (Jeong et al., 2007; Madden, 2002; Rance et al., 2007). For parents of children with this pathology, there is reasonable evidence to suggest that children may benefit from a cochlear implant, although expectations may need to be lower than for the general population of children with sensorineural hearing loss.

Usher syndrome is the most common condition that affects both hearing and vision, and its major symptoms are congenital or progressive deafness resulting in severe-profound hearing loss, and progressive loss of vision due to retinitis pigmentosa, an eye disorder which causes night blindness and a loss of peripheral vision. Many children with Usher syndrome also have significant balance problems, which can delay walking in very young children. Approximately 6-12% of children with hearing loss, or 4 in every 100,000 births in the United States (Boughman et al., 1983) and 6 per 100,000 births in England (Hope et al., 1997) have Usher Syndrome, which is a genetic condition. Once children have lost their vision, the auditory information provided by a cochlear implant is their only means of

maximum potential, and quality of life being taken into consideration in addition to

A further group of children for whom candidacy issues are more complex are those with selected pathologies that not only cause severe-profound hearing loss but may also impact on outcomes with cochlear implants. Although there are many such pathologies, the most common of these will be discussed as examples of the impact aetiology, or cause of hearing

In the 1990's, auditory neuropathy (AN) was defined as a distinct type of hearing disorder that disrupts neural activity in the central and peripheral auditory pathways (Starr et al., 1996). Auditory neuropathy is characterised by normal outer hair cell function in the cochlea (which enables many babies to pass newborn hearing screening if otoacoustic emission testing is used), and a retro cochlear lesion (dysfunction in the inner hair cells or auditory [eighth] nerve), which manifests as an absent or abnormal response to auditory brainstem response (ABR) testing. Features of this pathology include poorer than expected speech perception abilities in relation to degree of hearing loss in the majority of children, with some children who have only a mild hearing loss demonstrating a severely impaired ability to use their hearing for speech understanding (Rance et al., 2007). This pathology affects approximately 0.23% of at-risk children (Rance et al., 1999). Given the unusual pattern of perceptual deficits that characterises AN, much of the research in this area has focused on whether or not a cochlear implant can assist these children to understand speech through their hearing. The few published investigations on speech perception have varied widely, reporting no benefit (Miyamoto et al., 1999; Teagle et al., 2010) through to benefit comparable to that received by the general population of children with cochlear implants (Buss et al., 2002; Peterson et al., 2003; Rance & Barker, 2008; Trautwein et al., 2000). For the children who demonstrated significant benefit, it was noted that electrical stimulation via the cochlear implant elicited ABR responses, which suggests that the implant was able to enable greater neural synchrony and therefore to overcome the desynchronization thought to underlie AN. Studies of language and speech production outcomes for these children are again limited, and results are similar to those for speech perception, with wide variation in outcomes, but also with some children demonstrating the same level of development as the general population of children with cochlear implants (Jeong et al., 2007; Madden, 2002; Rance et al., 2007). For parents of children with this pathology, there is reasonable evidence to suggest that children may benefit from a cochlear implant, although expectations may need to be lower than for the general population of children with sensorineural hearing loss. Usher syndrome is the most common condition that affects both hearing and vision, and its major symptoms are congenital or progressive deafness resulting in severe-profound hearing loss, and progressive loss of vision due to retinitis pigmentosa, an eye disorder which causes night blindness and a loss of peripheral vision. Many children with Usher syndrome also have significant balance problems, which can delay walking in very young children. Approximately 6-12% of children with hearing loss, or 4 in every 100,000 births in the United States (Boughman et al., 1983) and 6 per 100,000 births in England (Hope et al., 1997) have Usher Syndrome, which is a genetic condition. Once children have lost their vision, the auditory information provided by a cochlear implant is their only means of

**2.3 Candidacy and selected aetiologies/pathologies of deafness** 

quantitative outcomes on tests.

loss, may have on post-implantation outcomes.

connecting and communicating with the world, so it is very important that these children are diagnosed and receive their cochlear implants early in order to establish communication through audition prior to the loss of vision. Usher syndrome is one of the 20% of causes of deafness that involve abnormalities in cochlea-vestibular anatomy. These abnormalities increase the potential for surgical difficulties and complications, such as damage to the facial nerve and incomplete insertion of the implant electrode array in the cochlea (Bauer et al., 2002; Chadha et al., 2009).

Some other children with congenital deafness also have cochlear abnormalities, often due to a range of genetic causes, another of which is CHARGE syndrome. Children with this rare genetic syndrome have deafness, visual problems, and a variety of other physical abnormalities, including serious heart defects, colobomas (or holes) in one or both eyes, growth retardation, genital abnormalities and external and internal ear malformations. Anatomical abnormalities in the structure of the cochlea can also create difficulties for programming, with reduced dynamic ranges for children with more severe cochlear abnormalities (Papsin, 2005). For these reasons, malformation of the cochlea was considered a contra-indication to cochlear implant surgery in the early years of cochlear implantation in children, and it is still not possible to implant some of these children (Bamiou et al., 2001). Despite these difficulties, initial results for small numbers of children with cochlear anomalies have shown that implantation is possible, with some children achieving speech perception and language results similar to those without anatomical abnormalities (Chadha et al., 2009; Dettman et al., 2011). Children with a common cavity anomaly (a single cavity in the cochlea) and other more severe syndromic anomalies have achieved much poorer results (Bauer et al., 2002; Chadha et al., 2009; Lanson et al., 2007; Loundon et al., 2003; Young et al., 1995).

Children with viral causes of deafness such as rubella, cytomegalovirus (CMV), toxoplasmosis and meningitis also require special consideration, as these viruses can cause developmental neurological deficits, including learning and cognitive difficulties (Edwards, 2007; Grimwood et al., 2000; Isaacson et al., 1996). A significant difference between children with deafness caused by meningitis and that caused by the other viruses is that while CMV, toxoplasmosis and rubella are contracted perinatally, children who have had meningitis will have experienced sound prior to infection and may have developed some spoken language skills. A further complication of meningitis is ossification (bone growth) within the cochlea, which is usually bilateral and can commence within four weeks of the illness (Durisin et al., 2010). This makes it imperative that children who have had meningitis are diagnosed with hearing loss and receive cochlear implants as soon as possible, before ossification limits both the potential for a full insertion and for benefit. Again, limited reports of post-operative benefit for children with these causes of deafness show a wide range of speech perception skills, intelligibility and language outcomes, with some children doing well (Francis et al., 2004; Lee et al., 2005) and others doing poorly (Isaacson et al., 1996; Ramirez Inscoe & Nikolopoulos, 2004; Wie et al., 2007).
