Graeme Clark Collection
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ItemCochlear implantation in children: the risk of pneumococcal otitis media [Abstract]( 1992)Pneumococcal otitis media is most frequent in young children and is a matter of concern in cochlear implantation. In the course of the 'implantation surgery the physiological barrier between the middle ear and inner ear is broken down by incising the round window membrane or by fenestration of the cochlear wall. It is feared that the insertion of an electrode array into the scala tympani could provide a pathway for microorganisms and toxins to enter the cochlea, resulting in labyrinthitis. To assess the actual risk of, secondary inner ear infection post implantation we developed a cat animal model of otitis media. In addition we examined the, effectiveness of different sealing strategies compared to the alternative of leaving the electrode entry point unprotected. For sealing of the cochlea fibrous tissue or gelatine foam was wrapped around the electrode in the round window niche. 22 kittens (44 ears) were used for this study 32, ears were implanted at 2 months of age, and all 44 ears were inoculated after 2 months with a broth of, streptococcus pneumoniae and the animals sacrificed one week later. The bullae of the animals were swabbed and the cochleas processed and examined under light microscopy. Histological analysis of the cochleas showed ,the� highest incidence (45%) of labyrinthine spread of infection in the unimplanted control group. Suppurative or serous labyrinthitis was found in only one third (33.3%) of the implanted and unsealed cochleas. In contrast only one of 16 sealed cochleas, (6.2 %) showed labyrinthine signs of acute inflammation. Experimental pneumococcal otitis media could be reliably established in all animals and proved to be a valuable animal model for the testing of the intracochlear spread of infection. We conclude that a cochlear implant electrode inserted via the round window does not increase the risk of tympanogenic abyrinthitis. Our results indicate that grafting of the electrode entry point results in significant protection of the inner ear against labyrinthine spread of ototis media along the leadwire of the cochlear implant.
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ItemCochlear implantation in young children: studies on head growth, leadwire design and electrode fixation in the monkey model [Abstract]( 1992)For the safety of cochlear implantation in children under two, the implant assembly must not adversely effect the tissue of compromise head growth. Furthermore, growth changes and tissue responses should not impair functioning of the device. Dummy receiver-stimulators, interconnect plugs and leadwire-lengthening systems have been implanted for periods of 40 months in the young monkey to most effectively model the implantation of the young human child. The results show that implanting a receiver-stimulator package has no effect on skull growth or brain tissue under the package. The system for fixing the electrode at the fossa includes proved effective. There was marked osteoneogenesis in the mastoid cavity and this also resulted in fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young children.
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ItemCochlear implant safety studies [Abstract]( 1991)We have examined a number of safety issues associated with cochlear implantation in both adults and children and confirm that it is safe. The results of these studies may be summarized as follows: 1) The insertion of a free-fit scala tympani array into the human cochlea produces minimal damage to cochlear structures provided insertion is stopped at the point of first resistance. 2) Chronic intracochlear implantation and electrical stimulation using charge balanced biphasic current pulses does not result in neural degeneration or evoke an adverse tissue reaction within the cochlea. 3) The use of fascia to seal the implanted round window results in an effective barrier to the spread of infection into the cochlea. 4) Temporal bone studies have shown that the distance between the round window and the fossa incudis remains essentially unchanged from birth. Therefore, the fossa incudis provides a suitable fixation point for the electrode array in young children. This study also showed that the distance from the round window to the implanted receiver-stimulator undergoes significant change in children of up to two years of age. These children would require an expanding leadwire system. 5) Finally, long-term effects of cochlear implant surgery on skull growth have shown that this should not be a problem when implanting very young children. This work was supported by the NIH (NOI-NS-7-2342).