Graeme Clark Collection
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ItemAssessment of intracochlear ossification by three-dimensional reconstruction of computerised scans( 1995)The aim of the study was to investigate whether the three-dimensional (3-D) images from computed tomography (CT) scans of the ears could adequately define the site and extent of new bone in the cochlea, and how these images compared with those created by magnetic resonance imaging (MRI). The patients whose investigations were used in the study were being assessed for a cochlear implant and were selected on the basis of their history and the appearance of their two-dimensional (2-D) CT scans. Four patients had progressive mixed deafness, a family history of deafness, and stapedectomies. They were considered to be deaf from otosclerosis and needed further assessment because their scans showed either obstructed cochleas from new bone, or demineralized otic capsules to the point that we could not determine whether new bone was present or not. The fifth patient was being assessed within 3 months of suffering deafness from meningitis. In one ear he had extensive ossification, and in the other the degree of opacification shown in axial and coronal cuts of the basal turn was inconsistent. Essentially the problem is that at the magnification used in examination of the inner ear, the resolution of 2-D CT scans gives indistinct borders between bone and water. Magnetic resonance imaging has commonly been used in these cases. The study showed that it is now possible to confirm whether or not there is new bone and to demonstrate the site and extent of new bone with both 3-D and MRI images. It is not possible to give a degree of sensitivity and specificity for this observation because of the small group of subjects in the study. It should be worth applying the reconstruction software to scans from helical scanners with a view to assessing whether the resolution of the 3-D images can be improved further.
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ItemThe progress of children using the multichannel cochlear implant in Melbourne( 1995)Multi-channel cochlear implantation in children began in Australia in 1985 and there are now close to 4000 profoundly deaf children and adolescents using the Australian implant system around the world. The aim of the implant procedure is to provide adequate hearing for speech and language development through auditory input. This contrasts with the situation for adults with acquired deafness where the cochlear implant aims to restore hearing for someone with well-developed auditory processing and language skills. As with adults, results vary over a wide range for children using the Multi-channel implant. Many factors have been suggested that may contribute to differences in speech perception for implanted children. In an attempt to better understand these factors, the speech perception results for children implanted in Melbourne were reviewed and subjected to statistical analysis. This has indicated that the amount of experience with the implant and the length of sensory deprivation are strongly correlated with perceptual results. This means that younger children are likely to perform better with an implant and that a number of years of experience are required for children to reach their full potential. The results have also indicated that educational placement and management play a crucial role in children reaching their potential. Overall, 60% of the children and adolescents in the study have reached a level of open-set speech understanding using the cochlear implant without lipreading.
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ItemChronic middle ear disease and cochlear implantation( 1995)Profound or total hearing loss can occur in the setting of chronic suppurative otitis media (CSOM), either coincidentally or secondary to the disease process. Obviously, inserting a foreign body through a potentially infected field into a space that communicates intracranially presents a challenging management problem. This paper presents the experience from the Melbourne Cochlear Implant Clinic (CIC) in implanting patients with bilateral CSOM. This is certainly not a common problem, as there have been only 3 cases from 121 implanted adults. However, we feel that it is an important issue with potentially devastating consequences. In addition, there are many countries in which bilateral CSOM is a more common problem and cause of profound or total hearing loss.
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ItemSurgical considerations for the placement of the new Cochlear Pty Limited micro-multiple-channel cochlear implant for research studies( 1995)A new micro-receiver-stimulator for research studies on very young children as well as adults has been developed by Cochlear Pty Limited. The dimensions of the device are length 58 mm and width at front 18 mm. The width starts to increase 19 mm from the front, and the back section, which has the receiver coil and magnet, has a maximum diameter of 33 mm. The depth or thickness of the front portion of the electronic package is 5.7mm, and the remainder of the package 4.0 mm. The antenna section is 3.5 mm thick. The other dimensions of the front section of the electronic package are length 9.5 mm and width 13.7 mm. There is an angle of 160° between the titanium electronic package and the receiver coil. The dimensions of the receiver-stimulator were arrived at after anatomic studies on the temporal bones of children ranging in age from 2 to 11 months.
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ItemCochlear pathology following reimplantation of a multichannel scala tympani electrode array in the macaque( 1995)The histopathologic consequence of removing and reimplanting intracochlear electrode arrays on residual auditory nerve fibers is an important issue when evaluating the safety of cochlear prostheses. The authors have examined this issue by implanting multichannel intracochlear electrodes in macaque monkeys. Macaques were selected because of the similarity of the surgical technique used to insert electrodes into the cochlea compared to that in humans, in particular the ability to insert the arrays into the upper basal turn. Five macaques were bilaterally implanted with the Melbourne/Cochlear banded electrode array. Following a minimum implant period of 5 months, the electrode array on one side of each animal was removed and another immediately implanted. The animals were sacrificed a minimum of 5 months following the reinsertion procedure, and the cochleas prepared for histopathologic analysis. Long-term implantation of the electrode resulted in a relatively mild tissue response within the cochlea. Results also showed that inner and outer hair cell survival, although significantly reduced adjacent to the array, was normal in 8 of the 10 cochleas apicalward. Moreover, the electrode reinsertion procedure did not appear to adversely affect this apical hair cell population. Significant new bone formation was frequently observed in both control and reimplanted cochleas close to the electrode fenestration site and was associated with trauma to the endosteum and/or the introduction of bone chips into the cochlea at the time of surgery. Electrode insertion trauma, involving the osseous spiral lamina or basilar membrane, was more commonly observed in reimplanted cochleas. This damage was usually restricted to the lower basal turn and resulted in a more extensive ganglion cell loss. Finally, in a number of cochleas part of the electrode array was located within the scala media or scala vestibuli. These electrodes did not appear to evoke a more extensive tissue response or result in more extensive neural degeneration compared with electrodes located within the scala tympani. In conclusion, the present study has shown that the reimplantation of a multichannel scala tympani electrode array can be achieved with minimal damage to the majority of cochlear structures. Increased insertion trauma, resulting in new bone formation and spiral ganglion cell loss, can occur in the lower basal turn in cases where the electrode entry point is difficult to identify due to proliferation of granulation and fibrous tissue.
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ItemThe development of the Melbourne/Cochlear multiple-channel cochlear implant for profoundly deaf children( 1992)In 1978-79, a speech processing strategy which extracted the voicing (FO) and second formant (F2) frequencies and presented these as rate and place of stimulation respectively to residual auditory nerve fibres was developed for the University of Melbourne's prototype multiple-channel receiver-stimulator (Clark et aI1977, Clark et a11978, Tong et aI1980). This speech processing strategy was shown to provide post linguistically deaf adults with some open-set speech comprehension using electrical stimulation alone, and considerable help when used in combination with lipreading (Clark et al 1981).
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ItemSurgical complications with the cochlear multiple-channel intracochlear implant: experience at Hannover and Melbourne( 1991)The surgical complications for the first 153 multi-channel cochlear implant operations carried out at the Medizinische Hochschule in Hannover and the first 100 operations at The University of Melbourne Clinic, The Royal Victorian Eye and Ear Hospital, are presented. In the Hannover experience the major complications were wound breakdown, wound infection, electrode tie erosion through the external auditory canal, electrode slippage, a persistent increase in tinnitus, and facial nerve stimulation. The incidence of wound breakdown requiring removal of the package was 0.6% in Hannover and 1.0% in Melbourne. The complications for the operation at both clinics were at acceptable levels. It was considered that wound breakdown requiring implant removal could be kept to a minimum by making a generous incision and suturing the flap without tension.