Widespread universal newborn hearing screening programs and increased general awareness of cochlear implants have resulted in increasing numbers of children younger than 12 mo of age being diagnosed and referred to implantation centers. The “earlier is better” argument as it relates to cochlear implants is supported by evidence from physiological studies and from studies of children using hearing aids. A younger age at implantation is also associated with optimum communication outcomes for children with cochlear implants.
Auditory perception, that is, learning to listen, in hearing children as well as children with hearing loss, is associated with the regular occurrence of speech events coupled with the features of attention, memory, and meaning. If listening is not developed during the critical language learning years, a child's potential to use speech input is likely to deteriorate. The key feature of the developing auditory system is plasticity, which is present at birth and decreases with age (Ruben & Rapin, 1980). Evidence suggests that the myelination occurs early in life and enables stable neural connections to form so that memory and learning can develop (Ryugo, Limb, & Redd, 2000). The earlier that a child receives the cochlear implant, the greater is the child's potential to benefit from these critical periods of neural development.
Studies regarding the human fetus' ability to detect sound, neonates' preferences for their native language, fundamental frequency and prosodic cues (of the primary caregiver), coupled with a curtailing of perceptual discrimination skills toward the end of the first 12 mo suggest a phonological critical period from the 6th mo of fetal life to 12 mo chronological age (Ruben, 1997). So, from a neurolinguistic perspective, it appears possible that if phonological distinctions are not made in the first year post-implantation, long-term language processing difficulties will result. Ruben (1997) suggested “insufficient early phonological input results in flawed semantic and syntactic capacities” (p. 204).
There is also evidence from animal models and investigations of brain plasticity that suggests that auditory stimulation can facilitate preservation of auditory structures and reverse the effects of auditory deprivation (Matsushima, Shepherd, Seldon, Xu, & Clark, 1991; Shepherd, Hartmann, Heid, Hardie, & Klinke, 1997).
Children Younger than 6 Mo Using Hearing Aids
For children using hearing aids, many of the negative effects of hearing loss on communication development can be prevented, or at least substantially minimized, if intervention and training are initiated early in life (Hayes & Northern, 1997; Yoshinaga-Itano, Sedey, Coulter, & Mehl, 1998). Studies have shown that early diagnosis and appropriate intervention for infants with hearing aids is associated with improvements in receptive and expressive language skills (Apuzzo & Yoshinaga-Itano, 1995; Markides, 1986; Robinshaw, 1995; White & White, 1987; Yoshinaga-Itano et al., 1998). Apuzzo and Yoshinaga-Itano (1995) demonstrated that children who were identified and aided in the first 2 mo of life had significantly better language development than children identified between 3 and 12 mo of age, despite significant hearing loss.
Children Using Cochlear Implants
For children using cochlear implants, a younger age at surgery is associated with optimum speech perception, speech intelligibility (Dowell, Blamey, & Clark, 1995; Nikolopoulos, O'Donoghue, & Archbold, 1999; Waltzman & Cohen, 1998) and language outcomes (Hammes, Novak, Rotz, Wills, Edmondson, & Thomas, 2002; Kirk, Miyamoto, Lento, Ying, O'Neill, & Fears, 2002; Svirsky, Teoh, & Neuburger, 2004).
Risks versus Benefits
Cochlear implants for infants younger than 12 mo should only be considered if the potential benefits outweigh the potential risks of the procedure. Objections to elective surgery in very young infants are sometimes raised with regard to the safety of general anesthesia in this age group. Outpatient anesthetic studies reported mortality rates of zero in healthy children for ophthalmological surgery (Petruscak, Smith, & Breslin, 1973; Romano, 1981); however, other studies reported that the risk of cardiac arrest increased with decreasing age (Cohen, Cameron, & Duncan, 1990; Tiret, Nivoche, Hatton, Desmonts, & Vourc'h, 1988). A history of anesthesia, emergency procedures, and/or fasting of less than 8 hr were risk factors for anesthetic complications (Tiret, Nivoche, Hatton, Desmonts, & Vourc'h, 1988). Initial findings of the Pediatric Perioperative Cardiac Arrest Registry* suggested that, of all cardiac arrests, 55% occurred in infants younger than 12 mo, and 43% occurred in infants younger than 5 mo. When data were analyzed according to the American Society of Anesthesiologist's physical status classification system, it was found that emergency procedures, not age alone, were predictive of infant mortality (Morray et al., 2000). Pediatric anesthesiologist's expertise was suggested as a possible factor in the incidence of critical pediatric perioperative events (Keenan, Shapiro, & Dawson, 1991), but the Pediatric Perioperative Cardiac Arrest Registry data, being from larger university-based and children's hospitals, not smaller and community hospitals, did not add support to this finding.
Waltzman and Cohen (1998) reported on the safe implantation of children between the ages of 12 and 24 mo. No additional surgical risk was reported for the younger children. The authors, however, acknowledged the difficulties inherent in documenting speech perception improvement with this young group due to the nature of the assessment materials. It was not possible to make valid comparisons with older children due to the differences in linguistic knowledge. Nikolopoulos et al. (1999) stated the need for long-term follow-up as children who were older at implantation initially performed tests better due to advanced cognitive skills, longer exposure to language, and greater familiarity with test conditions. This advantage gradually diminished over time as the children who were younger at implantation gradually overtook and outperformed them. Lesinski-Schiedat, Illg, Heermann, Bertram, and Lenarz (2004) reported there was no higher incidence of surgical complications, and higher mean speech perception scores for 27 children who were implanted under 12 months compared to 89 children implanted between 12 and 24 months (both group being tested at 2½ yr of age). The problem with reporting results in this way is that the younger group had, on average, 18 to 24 mo of device experience, whereas the older group had, on average, less than 12 mo and in some cases only 6 mo of device experience. Cochlear implantation was reported to be safe and facilitated normalization of babbling in 10 infants who underwent implantation before 12 mo (Colletti, Carner, Miorelli, Guida, Colletti, & Fiorino, 2005). Full insertions without perioperative or immediate postoperative surgical complications, and the development of auditory perception (Infant-Toddler Meaningful Auditory Integration Scale, open-set words and sentences) was reported for 18 children who received implants before 12 mo of age (Waltzman & Roland, 2005). One child underwent successful reimplantation after wound breakdown (thought to be due to eyeglass frame irritation) after 12 mo of device use. Anecdotal reports from parents and teachers indicated good development of speech production and language skill, but formal tests of language were not yet reported for this group.
For children who were old enough to complete formal test procedures, language data are customarily reported in terms of the difference between the child's chronological and equivalent language age, gap index (El-Hakim, Levasseur, Blake, Papsin, Panesar, Mount, Steven, & Harrison, 2001), rate of growth over time, and/or developmental trajectory (Svirsky, Teoh, & Neuburger, 2004). Studies suggest that for children receiving cochlear implants during the critical language period, deficits associated with profound hearing loss may be minimized (Bollard, Shute, Popp, & Parisier, 1999; El-Hakim, Levasseur, Blake, Papsin, Panesar, Mount, Steven, & Harrison, 2001; Novak, Firszt, Rotz, Hammes, Reeder, & Willis, 2000; Robbins, Bollard, & Green, 1999; Robbins, Svirsky, & Kirk, 1997; Svirsky, Teoh, & Neuburger, 2004; Truy, Lina-Granade, Jonas, Martinon, Maison, Girard, Porot, & Morgon, 1998). Language outcomes for children with cochlear implants, however, vary considerably, and there are complex interactions between preexisting child and family characteristics, child intelligence, hearing thresholds, device used, mode of communication, and age (Connor, Hieber, Arts, & Zwolan, 2000; Dowell, Dettman, Blamey, Barker, & Clark, 2002; Geers, Nicholas, & Sedey, 2003; Musselman, Lindsay, & Wilson, 1988).
Studies examining the impact of the cochlear implant on language development need to select appropriate early indicators of language progress, rather than wait for the child to perform formal test procedures. Nott, Cowan, Brown and Wigglesworth (2003) used the Rossetti Infant-Toddler Language Scale (RI-TLS) (Rossetti, 1990) in addition to the MacArthur Communicative Developmental Inventories and parental diary entries to chart early lexical development in young children with profound hearing loss using cochlear implants and/or hearing aids. Good correlations were found between the diary entries, RI-TLS, and the Communicative Developmental Inventories.
The aim of the present study was to examine the receptive and expressive language growth of children who received implants before 12 mo of age compared to children who received them between 12 and 24 mo of age and to determine the prevalence of surgical and/or anesthetic complications. As most cochlear implantation centers do not routinely proceed with children younger than 6 mo, it is not yet possible to replicate the studies by Apuzzo and Yoshinaga-Itano (1995) or Yoshinaga-Itano et al. (1998), but it is possible to examine children using cochlear implants from 6 mo onward. Accurate records regarding prevalence of mapping and/or device problems are required as preverbal children may be unable to report changes in their hearing. Given potentially greater surgical and anesthetic risks in those younger than 12 mo of age, improved dissemination of appropriate evidence is required for parents trying to decide whether to proceed with cochlear implantation.
There were 106 children who received the Cochlear Ltd. multichannel implant at the Melbourne Cochlear Implant Clinic before the age of 24 mo. Each had profound bilateral sensorineural hearing loss, used the ACE or SPEAK speech-processing strategy with SPrint, ESPrit 3G, or Freedom speech processors, and used a range of communication modes. There were 19 children in group 1 (mean age at implantation, 0.88 yr; range, 0.61–1.07; SD 0.15) and 87 toddlers in group 2 (mean age at implantation, 1.60 yr; range, 1.13–2.00; SD 0.24). Individual demographic and developmental features for the 19 children who underwent implantation at younger than 12 mo of age are given in Table 1. Statistical comparisons between groups 1 and 2 for hearing level and cognitive status are given in Table 2.
All children completed a standardized psychological, cognitive, and motor evaluation by an educational psychologist, using a range of assessment materials suitable for the age and developmental level of each child. There was one group 1 child with severe global delay (after meningitis), and eight group 2 children who had mild, moderate, or severe cognitive delay.
The RI-TLS (Rossetti, 1990) uses a combination of author observations, developmental hierarchies, and behaviors recognized by leading authorities in the field of infant/toddler assessment to assess the language skills of children from birth to 36 mo of age. The RI-TLS differs from other rating scales as it is appropriate for use from birth through to 3 yr of age and examines mastery or emergence of important aspects of preverbal and verbal interaction such as interaction-attachment, pragmatics, gesture, and play, in addition to 76 language comprehension and 93 language expression milestones. These milestones may be observed, elicited, or reported by the clinician and/or the primary caregiver within an interview/play interaction session.
It was desirable to obtain at least one test administration of the RI-TLS pre-implantation and at yearly intervals post-implantation, but this was not always achieved. All six subscales including Interaction-Attachment, Pragmatics, Gesture, Play, Language Comprehension (LC), and Language Expression (LE) were administered. Results are reported for 11 group 1 children and 36 group 2 children who completed two or more RI-TLS over time. The slope of the linear regression lines through the available data points for the subscales LC and LE were derived.
Computed tomography, magnetic resonance imaging, anesthetic, and surgical records for all 106 children were reviewed. In all cases, a minimally invasive surgical approach was used similar to that described by O'Donoghue and Nikolopoulos (2003). Before reversal of anesthesia, a plain radiograph of the mastoid was taken to check the position of the electrode. The functional status of the implant was tested with impedance and neural response telemetry. A head bandage was applied.
Rate of Language Growth
For the 11 group 1 subjects, the individual rates of growth for LC and LE are given in Figures 1 and 2, respectively. There was a significant difference between the average rate of growth for LC for group 1 (1.12) and group 2 (0.71) (t = 3.50, p < 0.001) (Table 2). There was also a significant difference between the rate of growth for LE for group 1 (1.01) and group 2 (0.68) (t = 3.38, p < 0.002) (Table 2). When data from all children with cognitive delay were removed from the analysis, the difference between the rates of growth remained statistically significant (Table 2).
Surgical and Programming Considerations
Most children were discharged from the hospital 1 d after surgery and reviewed in the clinic after 1 wk. Activation of the device usually took place 2 to 3 wk after surgery. A number of children had a preimplantation history of ear infections that required careful management. One group 1 child presented with mastoiditis 6 d after discharge that resolved after readmission for intravenous antibiotics. There were three group 2 children who underwent explantation: one for infection after trauma (fall from a child's seat) at 4 mo post-implantation, one due to an unknown cause of device failure at 9 mo post-implantation, and one due to device failure (after a blow to the head) at 3 yr post-implantation. All three children underwent successful reimplantation and attended regular otological and audiological reviews.
Appropriate threshold levels were obtained for all children using visual reinforcement audiometry (Moore, Thompson, & Thompson, 1975; Moore & Wilson, 1978) and/or play audiometry (Wilson & Thompson, 1984) depending on the age, developmental stage, and response state of the child. Maximum comfort levels were obtained using language that was appropriate for each child's comprehension and were checked by eliciting an auropalpebral reflex (eye blink in response to a loudness discomfort level) and subsequently reducing levels by 30% (Rance & Dowell, 1997).
This study demonstrated that children who received the cochlear implant who were younger than the age of 12 mo could demonstrate language comprehension and expressive development comparable to that of their hearing peers. The rate of growth was significantly better than the rate of comprehension and expressive growth demonstrated by a group of children who received the implant between 12 and 24 mo of age.
The relationship between cognitive status and communication outcomes in previous literature suggests that children with cochlear implants who also demonstrate cognitive delays tend to progress more slowly than other children in the areas of speech perception (Dowell, Dettman, Blamey, Barker, & Clark, 2002; Isaacson, Hasenstab, Wohl, & Williams, 1996; Pyman, Blamey, Lacy, Clark, & Dowell, 2000; Tomov, Dettman, Barker, Dowell, Williams, & Hughes, 2002; Waltzman, Scalchunes, & Cohen, 2000) and language (Dettman, Tomov, Dowell, Barker, Hughes, Williams, & Saldic, 2003). As cognitive delays could potentially reduce the average rate of growth for the group 2 children, the language data from children who demonstrated mild, moderate, or severe delay were removed from the analysis. This had the effect of improving the group 2 mean rate of LC from 0.71 to 0.78 and LE from 0.68 to 0.73, but these rates were still statistically significantly poorer than the rates demonstrated by group 1 children. The poorest group 1 rates of development of LC (case 18, 0.78) and LE (case 4, 0.73) were coincidentally the same as the average group 2 rates (LC = 0.78, LE = 0.73).
Reporting of the language results in terms of the slope of the child's receptive and expressive development over a consistent time interval proved useful in this study. Making comparisons with normalized data for hearing children then enables clinicians to determine whether the gap between the children's chronological and equivalent language age is decreasing or increasing over time.
The finding that children who receive a cochlear implant at a younger age demonstrate better postimplantation language outcomes is consistent with previous research (Brackett & Zara, 1998; Hammes et al., 2002; Miyamoto, Houston, Kirk, Perdew, & Svirsky, 2003; Robbins, 2000; Yoshinaga-Itano et al., 1998). It must be noted that the average age at hearing aid fitting was also significantly different for group 1 (0.41 yr) and group 2 (0.92). Future research may consider cohorts of children matched for cognitive status, who variously receive hearing aids early/undergo implantation early, receive hearing aids late/undergo implantation early, and receive hearing aids late/undergo implantation late to examine the relative influence of these variables. It was not within the scope of this article to report on speech perception outcomes for this group of children; speech perception and emerging babble production will be the focus of subsequent publications.
These preliminary comprehension and expression results obtained from this group of children, coupled with the absence of anesthetic and/or surgical complications, provides support for the consideration of cochlear implants for children younger than 12 mo of age. The children who underwent implantation at younger than 12 mo of age achieved mean rates of receptive (1.12) and expressive (1.01) language growth that were comparable to their normally hearing peers and were significantly greater than the rates achieved by children who underwent implantation between 12 and 24 mo of age. If normal rates of language acquisition can be maintained in this group, earlier cochlear implantation represents a cost benefit to the community due to improved employment opportunities and reduced reliance on specialized psychosocial and educational support.
The authors acknowledge the Speech Pathologists and Audiologists at the Cochlear Implant Clinic, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
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*The Pediatric Perioperative Cardiac Arrest Registry is an U.S.-based registry that was established to collect data regarding pediatric cardiac arrests and deaths in the perioperative and immediate postoperative period and analyze causal relationships.