Discussion

With the goal of universal detection of hearing loss in infants by

3 months of age, and appropriate intervention (e.g., amplifica tion) by 6 months of age,50,51 it is likely that ever-increasing numbers of very young children will be identified as potential implant candidates. We know that early identification (i.e., by

6 months of age) and early intervention with hearing aids

(HAs) have a significant effect on language development in chil dren with hearing loss,52 but the spoken word recognition and receptive language benefits of early implantation in children with profound deafness have not been quantified, and critical age limits for cochlear implantation have not been identified.

Cochlear implantation earlier than the current FDA

accepted age of 12 months is feasible as the target organ, the cochlea, is adult size at birth. The small dimensions of the temporal bone must be accounted for, but the facial recess and mastoid antrum that provide access to the middle ear for electrode placement are adequately developed before the age of 1 year. In fact, several centers have chosen to implant children under

12 months of age. Furthermore, implanting children under the age of 12 months may have substantial advantages when the etiology of deafness is meningitis. Progressive intracochlear fibrosis and ossification may occur, which can preclude stan dard electrode insertion. A relatively short window exists during which this advancing process can be circumvented.

Nonetheless, implantation of the very young child remains controversial because the audiological assessment and management of this population is extremely challenging. Profound deafness must be substantiated and the inability to benefit from conventional hearing aids demonstrated. However, a compelling argument supporting implantation at the earliest possible time can be made because the development of speech perception, speech production, and language competence normally begins early in infancy. In addition, electrical stimulation has been shown to prevent at least some of the degenerative changes in the central auditory pathways caused by auditory deprivation.53

The extension of cochlear implantation to children with ever higher levels of preimplant residual hearing should be approached cautiously. Surgical implantation of the electrode array results in the loss of residual hearing in that ear. Thus, cochlear implantation should not be considered unless it seems likely that a given child will receive more benefit from this device than from conventional amplification. Recently, mounting evidence has been found to suggest that some children with severe hearing loss may derive as much or even more benefit from a cochlear implant than as from a well-fitted HA. In amplifying sound for an individual with hearing loss, an assumption is made that the acoustic-phonetic patterns of speech must be detected before they can be discriminated and recognized. To accomplish this goal, audibility across a broad frequency range is typically prescribed as a means of maximizing speech intelli-gibility.54 This, in fact, has been the goal of most standard HA prescriptions. For severe to profound losses, however, supplying adequate gain across a broad frequency range can present a special challenge to the clinician. Moreover, achieving this amount of amplification may cause acoustic feedback, necessitating a reduction in gain and audibility.55 Another issue concerns the risk of delivering high levels of sound to the impaired ear. According to Macrae,56,57 the sound pressure level required to achieve audibility for individuals with severe to profound hearing loss has the potential to destroy remaining hair cells due to excessive noise exposure. Thus, a trade-off may exist between providing audible speech and risking increased damage to inner ear structures. Lastly, there is some question as to the extent of benefit that may actually be realized by amplifying high frequencies to audible levels for this magnitude of loss. Recent research has suggested that provision of adequate audibility for losses of > 60 dB HL at > 3000 Hz does not improve speech recognition and may even degrade performance.58-60 Preliminary research has suggested that some children with cochlear implants obtain spoken word recognition abilities that surpass those of other children with severe hearing loss (i.e., pure tone averages (PTAs) of 70 to 90 dB HL) who use well-fit HAs.14'61'62 Given the limitations imposed in providing high levels of amplified speech to children with severe to profound hearing loss, the evidence suggests that a cochlear implant could provide added benefit for a select population of children with this magnitude of hearing loss.

The encouraging results obtained with younger children and those who have some useful hearing prior to implantation have led investigators to push the boundaries of cochlear implantation criteria further than ever before. With the continued evolution and expansion of cochlear implant candidacy it is crucial that we develop techniques to quantify hearing loss, to fit both hearing aids and cochlear implants, and to document the effects of implantation in these very young children.

REFERENCES

Miyamoto et al.—CHAPTER 80

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47. Waltzman S, Cohen NL, Gomolin R, et al. Perception and production results in children implanted between two and five years of age. In: Honjo I, Takahashi H, eds. Cochlear Implant and Related Sciences Update. Advances in Otorhinolaryngology, vol 52. Basel: Karger; 1997:177-180

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Cochlear Implants in Congenitally Deaf Children

Laura W. Kretschmer

CHAPTER 81

The history of cochlear implants is a somewhat recent one. The first experimental single-channel implant was provided to a child in 1980, and the first multichannel implant in a child was completed in Australia in 1985, with multisite trials begun with children in the United States the next year. Since the initial experimental work, it is estimated that about 12,000 to 15,000 persons worldwide have received implants, with approximately one-third of those being children. Most children with implants in the United States, in Australia, and in western Europe are deaf as a result of meningitis (45 to 64%). Those children with implants who are identified as having congenital onset of deafness is still a small subset. The push for early identification of hearing loss, and for early fitting of hearing aids, suggests that our attention will invariably be drawn to that subset of children with profound bilateral hearing loss who do not receive substantial benefit from conventional hearing aids, most of whom will have a congenital onset of deafness. It is readily accepted that any child who acquires deafness after the onset of spoken language and who receives limited benefit from amplification is a potential candidate for a cochlear implant. The analogous situation of an older child, adolescent, or adult who is deafened and is considered for an implant also causes little controversy. The question of an implant for the infant, toddler, or young child who has never had auditory experience should raise many cautions for the physician and implant teams, however.

The cochlear implant is not the end of habilitation in children with congenital deafness. Rather, it is just the beginning, constituting only one factor in the effort to promote the child's linguistic, educational, psychosocial, and intellectual development. Deafness may be considered a variation in the human condition by some, or a disability by others, but the most critical aspect of the deaf child's habilitation is the establishment of communication, whether or not an implant is involved. The heavy lifting of language acquisition is accomplished in normal hearing children by the fourth or fifth year of life. In view of the importance of these early years for language acquisition in general, it is an important goal to ensure that the first 4 or 5 years of life are primary language learning years for every child with congenital deafness as well.

The list of controversies surrounding the process of implantation in children with congenital deafness is substantial. The set of controversies discussed in this chapter, although not exhaustive, represents the most publicized and the most vexing issues:

(1) advisability of lowering the minimum age for implantation;

(2) deciding when benefit from conventional amplification is not sufficient to sustain communication development in a young child; (3) determining whether family and educational resources are sufficient to warrant and support implantation as part of the child's habilitation, including the question of which modes of communication (spoken versus sign language) seem to be most important to implant success; (4) the issue of deaf culture and how it should enter into parents' and professionals thinking about implantation; (5) whether or how the perspectives of the child might be taken into account; (6) the advisability of implantation in children with multiple neurologic and cognitive disabilities, including auditory neuropathy; (7) whether published data reflect the full range of outcomes for children who are implanted, to include those children who do not derive benefit or who voluntarily discard the implant; and (8) the implications of animal research on neural plasticity and cortical reorganization in regard to the use of implants in young children with congenital deafness. The best speech-processing schemes remain controversial among manufacturers and auditory researchers. (See comprehensive reports such as the 1997 Acta Otolaryngology supplement or the 1997 American Journal of Otology supplement for detailed information on cochlear implants in children, as well as Parkins1 for further information about processing schemes.)

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