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Optimal electrode design: Straight versus perimodiolar
European Annals of Otorhinolaryngology, Head and Neck diseases 133S (2016) S63–S65
Available online at
ScienceDirect www.sciencedirect.com
Mini review
Optimal electrode design: Straight versus perimodiolar P. Gibson a,∗ , P. Boyd b a b
Global Head of Professional, Surgical & Clinical Strategy, Cochlear Limited, Macquarie University, 1 University Avenue, 2109 Sydney, NSW, Australia The Wilmslow Hospital, Wilmslow, United Kingdom
a r t i c l e
i n f o
Keywords: Cochlear implant Perimodiolar electrode Design Hybrid stimulation
a b s t r a c t The electrode in a cochlear implant (CI) system is a key factor in hearing performance as it is the interface between the device and the auditory pathway of the recipient. The first CI electrodes were straight and thus adopted a lateral wall position. Subsequent innovations include: perimodiolar electrodes designed to lie adjacent to the modiolar wall and thus to provide more spatially-focused stimulation of the spiral ganglion cells; shorter atraumatic straight electrodes for combined electric and acoustic (hybrid) stimulation. This paper explores the relative merits of straight and perimodiolar electrodes in the search for the optimal electrode design with reference to electrodes from Cochlear® . © 2016 Elsevier Masson SAS. All rights reserved.
The electrode in a cochlear implant (CI) system is a key factor in hearing performance as it is the interface between the device and the auditory pathway of the recipient. The first multichannel research electrode revolutionised our understanding of how to effectively stimulate the cochlea [1] and Cochlear® ’s first commercial system with the straight 22 channel Nucleus® electrode achieved performance beyond all expectations at the time. Electrode technology continues to be a strong focus of innovation in CIs and a wide range of electrode designs have been studied. Two notable innovations are the introduction of perimodiolar electrodes in the late 1990s and, more recently, shorter straight electrodes for combined electric and acoustic stimulation. Fig. 1 shows examples of current straight and perimodiolar electrodes produced by Cochlear® Limited. This paper explores the relative merits of straight and perimodiolar electrodes in the search for the optimal electrode design with reference to electrodes from Cochlear® .
1. Benefits of straight electrodes Straight electrodes have been developed by all CI manufacturers and implanted in research subjects and clinical recipients for over three decades. The longevity and number of implanted electrodes are evidence of the clinical efficacy and reliability of straight electrodes. By mid-2015, over 84,000 people had been implanted with various designs of Nucleus® straight electrodes.
∗ Corresponding author. Tel.: +61 9428 6367. E-mail address: [email protected] (P. Gibson). http://dx.doi.org/10.1016/j.anorl.2016.04.014 1879-7296/© 2016 Elsevier Masson SAS. All rights reserved.
The benefits of combined electric and acoustic (hybrid) stimulation have also been established [2,3], for which electrode design is critical for preservation of residual hearing. Prof Gantz began researching the Hybrid S electrode in Iowa in the mid 1990s [3] and a number of electrodes suited to hybrid hearing have been developed over the past 20 years. These electrodes have been straight with limited length to avoid the intracochlear trauma associated with very deep insertion [2]. Straight electrodes have also been used in a substantial population of recipients with a variety of anatomical variations and pathology, particularly when the structure of the cochlea is not suitable for a perimodiolar electrode placement [4,5]. The Slim Straight electrode used with the CI422 and CI522 implants is the most recent lateral wall design in Nucleus® technology and has demonstrated useful preservation of residual hearing, thereby facilitating benefits from Hybrid stimulation. Several studies have demonstrated long-term low-frequency hearing preservation within 20 dB of preoperative levels in cohorts of up to 41 subjects with usable acoustic hearing [6,7]. Significant improvement in speech understanding in both quiet and noise has been reported in a study of 35 subjects with useful residual preoperative hearing [8]. The subjects were assessed 12 months after implantation with the CI422 device and used the Hybrid Sound Processor to provide acoustic combined with electrical stimulation. 2. Benefits of perimodiolar electrodes The scientific foundations of perimodiolar placement were established by Shepherd et al. [9], who demonstrated reduced EABR thresholds in a cat model. Over 15 years of experience with precurved perimodiolar electrodes and in excess of 200,000 recipients
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P. Gibson, P. Boyd / European Annals of Otorhinolaryngology, Head and Neck diseases 133S (2016) S63–S65
Fig. 1. Slim Straight and Contour Advance® Electrodes. Bone histology courtesy The HEARing CRC, Melbourne.
Fig. 2. Indications: the primary criteria for electrode choice. Group 1: perimodiolar electrodes optimise electric stimulation for traditional CI candidates; Group 2: straight electrodes optimise Hybrid Hearing; Group 3: perimodiolar or straight electrodes chosen on the anatomical and medical conditions in each case. *PTA loss of moderately severe to profound degree. Image courtesy of Cochlear® Ltd.
of Nucleus ContourTM technology provide extensive evidence of the efficacy and reliability of these electrodes which aim to bring the electrode contacts closer to the neural elements of the cochlea. Subsequent clinical studies on the Contour array have demonstrated narrower spread of excitation, reduced behavioural and electrically-evoked compound action potential (ECAP) thresholds and wider dynamic range [10–12]. Significant improvements in listening performance have also been reported with perimodiolar placement [12,13,16]. In a prospective study of 59 subjects, Holden et al. [13] reported a significant relationship between CNC word scores in quiet and the “wrapping factor” (a measure of distance from the modiolus). Contour electrodes have also been successfully used in a range of anatomical variations and patient conditions as presented in a number of publications [5,14,15]. 3. A strong case for straight AND perimodiolar electrodes The question is not whether all people should be implanted with either straight or perimodiolar electrodes. Rather, there is a strong case based on patient indications that it is essential to have both. We can group potential CI recipients into three broad indication categories which pose different clinical challenges and require different treatment options (Fig. 2). 3.1. Group 1 People with severe to profound sensorineural hearing loss. These are the “traditional” CI candidates and still the largest group actually implanted.
3.2. Group 2 People with mild-moderate low-frequency hearing loss who seek a better solution than that available from surgical intervention or hearing aids. A characteristic of this group is the clinical diversity with large differences in residual hearing thresholds, hearing function and the frequency range affected. 3.3. Group 3 People with a wide range of special conditions. This group includes: • congenital anatomical abnormalities such as common cavity, incomplete partition, hypoplastic cochlea and Large Vestibular Aqueduct Syndrome; • conditions that cause fibrosis or ossification of the cochlea (e.g. otosclerosis); • tumor patients with conditions such as Neurofibromatosis Type II. Considering these three indication groups there is a strong argument to include both perimodiolar and straight electrodes in the armament available for treatment. Group 1 require optimal electrical stimulation which is best provided by perimodiolar electrodes; Group 2 may benefit from functional residual hearing combined with electrical stimulation, and so are candidates for straight, hybrid electrodes; and Group 3 may require either a perimodiolar or straight electrode depending on the anatomical and medical conditions in individual cases.
P. Gibson, P. Boyd / European Annals of Otorhinolaryngology, Head and Neck diseases 133S (2016) S63–S65
The future in electrodes is to combine the best of both worlds, i.e. a perimodiolar electrode that preserves hearing at the same rate as current straight electrodes. This would add further subtlety to the treatment options available to the implanting surgeon. Disclosure of interest Peter Gibson is an employee of Cochlear® Ltd., the manufacturer of the devices described in this article. Paul Boyd performs some consultancy work for Cochlear® Europe Ltd. References [1] Clark GM. The multi-channel cochlear implant: multi-disciplinary development of electrical stimulation of the cochlea and the resulting clinical benefit. Hear Res 2015;322:4–13. [2] Lenarz T, Stöver T, Buechner A, Lesinski-Schiedat A, Patrick J, Pesch J. Hearing conservation surgery using the Hybrid-L electrode. Results from the first clinical trial at the Medical University of Hannover. Audiol Neurootol 2009;14(Suppl. 1):22–31. [3] Gantz BJ, Turner CW. Combining acoustic and electrical hearing. Laryngoscope 2003;113(10):1726–30. [4] Graham JM, Phelps PD, Michaels L. Congenital malformations of the ear and cochlear implantation in children: review and temporal bone report of common cavity. J Laryngol Otol Suppl 2000;25:1–14. [5] Sennaroglu L. Cochlear implantation in inner ear malformations - a review article. Cochlear Implants Int 2010;11(1):4–41.
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[6] Jurawitz MC, Büchner A, Harpel T, et al. Hearing preservation outcomes with different cochlear implant electrodes: Nucleus® HybridTM -L24 and Nucleus FreedomTM CI422. Audiol Neurootol 2014;19(5):293–309. [7] Hassepass F, Aschendorff A, Bulla S, et al. Radiologic results and hearing preservation with a straight narrow electrode via round window versus cochleostomy approach at initial activation. Otol Neurotol 2015;36(6):993–1000. [8] Skarzynski H, Lorens A, Matusiak M, Porowski M, Skarzynski PH, James CJ. Cochlear implantation with the nucleus slim straight electrode in subjects with residual low-frequency hearing. Ear Hear 2014;35(2):e33–43. [9] Shepherd RK, Hatsushika S, Clark GM. Electrical stimulation of the auditory nerve: the effect of electrode position on neural excitation. Hear Res 1993;66(1):108–20. [10] Cohen LT. Practical model description of peripheral neural excitation in cochlear implant recipients: 2. Spread of the effective stimulation field (ESF), from ECAP and FEA. Hear Res 2009;247(2):100–11. [11] van Wermeskerken GK, van Olphen AF, Graamans K. Imaging of electrode position in relation to electrode functioning after cochlear implantation. Eur Arch Otorhinolaryngol 2009;266(10):1527–31. [12] Gordin A, Papsin B, James A, Gordon K. Evolution of cochlear implant arrays result in changes in behavioral and physiological responses in children. Otol Neurotol 2009;30(7):908–15. [13] Holden LK, Finley CC, Firszt JB, et al. Factors affecting open-set word recognition in adults with cochlear implants. Ear Hear 2013;34(3):342–60. [14] Bille J, Fink-Jensen V, Ovesen T. Outcome of cochlear implantation in children with cochlear malformations. Eur Arch Otorhinolaryngol 2015;272(3):583–9. [15] Loundon N, Rouillon I, Munier N, Marlin S, Roger G, Garabedian EN. Cochlear implantation in children with internal ear malformations. Otol Neurotol 2005;26(4):668–73. [16] Dowell R. Evidence about the effectiveness of cochlear implants for adults. In: Lena Wong, Louise Hickson, editors. Evidence-Based Practice in Audiology. Plural Publishing; 2012. p. 141–65.
Available online at
ScienceDirect www.sciencedirect.com
Mini review
Optimal electrode design: Straight versus perimodiolar P. Gibson a,∗ , P. Boyd b a b
Global Head of Professional, Surgical & Clinical Strategy, Cochlear Limited, Macquarie University, 1 University Avenue, 2109 Sydney, NSW, Australia The Wilmslow Hospital, Wilmslow, United Kingdom
a r t i c l e
i n f o
Keywords: Cochlear implant Perimodiolar electrode Design Hybrid stimulation
a b s t r a c t The electrode in a cochlear implant (CI) system is a key factor in hearing performance as it is the interface between the device and the auditory pathway of the recipient. The first CI electrodes were straight and thus adopted a lateral wall position. Subsequent innovations include: perimodiolar electrodes designed to lie adjacent to the modiolar wall and thus to provide more spatially-focused stimulation of the spiral ganglion cells; shorter atraumatic straight electrodes for combined electric and acoustic (hybrid) stimulation. This paper explores the relative merits of straight and perimodiolar electrodes in the search for the optimal electrode design with reference to electrodes from Cochlear® . © 2016 Elsevier Masson SAS. All rights reserved.
The electrode in a cochlear implant (CI) system is a key factor in hearing performance as it is the interface between the device and the auditory pathway of the recipient. The first multichannel research electrode revolutionised our understanding of how to effectively stimulate the cochlea [1] and Cochlear® ’s first commercial system with the straight 22 channel Nucleus® electrode achieved performance beyond all expectations at the time. Electrode technology continues to be a strong focus of innovation in CIs and a wide range of electrode designs have been studied. Two notable innovations are the introduction of perimodiolar electrodes in the late 1990s and, more recently, shorter straight electrodes for combined electric and acoustic stimulation. Fig. 1 shows examples of current straight and perimodiolar electrodes produced by Cochlear® Limited. This paper explores the relative merits of straight and perimodiolar electrodes in the search for the optimal electrode design with reference to electrodes from Cochlear® .
1. Benefits of straight electrodes Straight electrodes have been developed by all CI manufacturers and implanted in research subjects and clinical recipients for over three decades. The longevity and number of implanted electrodes are evidence of the clinical efficacy and reliability of straight electrodes. By mid-2015, over 84,000 people had been implanted with various designs of Nucleus® straight electrodes.
∗ Corresponding author. Tel.: +61 9428 6367. E-mail address: [email protected] (P. Gibson). http://dx.doi.org/10.1016/j.anorl.2016.04.014 1879-7296/© 2016 Elsevier Masson SAS. All rights reserved.
The benefits of combined electric and acoustic (hybrid) stimulation have also been established [2,3], for which electrode design is critical for preservation of residual hearing. Prof Gantz began researching the Hybrid S electrode in Iowa in the mid 1990s [3] and a number of electrodes suited to hybrid hearing have been developed over the past 20 years. These electrodes have been straight with limited length to avoid the intracochlear trauma associated with very deep insertion [2]. Straight electrodes have also been used in a substantial population of recipients with a variety of anatomical variations and pathology, particularly when the structure of the cochlea is not suitable for a perimodiolar electrode placement [4,5]. The Slim Straight electrode used with the CI422 and CI522 implants is the most recent lateral wall design in Nucleus® technology and has demonstrated useful preservation of residual hearing, thereby facilitating benefits from Hybrid stimulation. Several studies have demonstrated long-term low-frequency hearing preservation within 20 dB of preoperative levels in cohorts of up to 41 subjects with usable acoustic hearing [6,7]. Significant improvement in speech understanding in both quiet and noise has been reported in a study of 35 subjects with useful residual preoperative hearing [8]. The subjects were assessed 12 months after implantation with the CI422 device and used the Hybrid Sound Processor to provide acoustic combined with electrical stimulation. 2. Benefits of perimodiolar electrodes The scientific foundations of perimodiolar placement were established by Shepherd et al. [9], who demonstrated reduced EABR thresholds in a cat model. Over 15 years of experience with precurved perimodiolar electrodes and in excess of 200,000 recipients
S64
P. Gibson, P. Boyd / European Annals of Otorhinolaryngology, Head and Neck diseases 133S (2016) S63–S65
Fig. 1. Slim Straight and Contour Advance® Electrodes. Bone histology courtesy The HEARing CRC, Melbourne.
Fig. 2. Indications: the primary criteria for electrode choice. Group 1: perimodiolar electrodes optimise electric stimulation for traditional CI candidates; Group 2: straight electrodes optimise Hybrid Hearing; Group 3: perimodiolar or straight electrodes chosen on the anatomical and medical conditions in each case. *PTA loss of moderately severe to profound degree. Image courtesy of Cochlear® Ltd.
of Nucleus ContourTM technology provide extensive evidence of the efficacy and reliability of these electrodes which aim to bring the electrode contacts closer to the neural elements of the cochlea. Subsequent clinical studies on the Contour array have demonstrated narrower spread of excitation, reduced behavioural and electrically-evoked compound action potential (ECAP) thresholds and wider dynamic range [10–12]. Significant improvements in listening performance have also been reported with perimodiolar placement [12,13,16]. In a prospective study of 59 subjects, Holden et al. [13] reported a significant relationship between CNC word scores in quiet and the “wrapping factor” (a measure of distance from the modiolus). Contour electrodes have also been successfully used in a range of anatomical variations and patient conditions as presented in a number of publications [5,14,15]. 3. A strong case for straight AND perimodiolar electrodes The question is not whether all people should be implanted with either straight or perimodiolar electrodes. Rather, there is a strong case based on patient indications that it is essential to have both. We can group potential CI recipients into three broad indication categories which pose different clinical challenges and require different treatment options (Fig. 2). 3.1. Group 1 People with severe to profound sensorineural hearing loss. These are the “traditional” CI candidates and still the largest group actually implanted.
3.2. Group 2 People with mild-moderate low-frequency hearing loss who seek a better solution than that available from surgical intervention or hearing aids. A characteristic of this group is the clinical diversity with large differences in residual hearing thresholds, hearing function and the frequency range affected. 3.3. Group 3 People with a wide range of special conditions. This group includes: • congenital anatomical abnormalities such as common cavity, incomplete partition, hypoplastic cochlea and Large Vestibular Aqueduct Syndrome; • conditions that cause fibrosis or ossification of the cochlea (e.g. otosclerosis); • tumor patients with conditions such as Neurofibromatosis Type II. Considering these three indication groups there is a strong argument to include both perimodiolar and straight electrodes in the armament available for treatment. Group 1 require optimal electrical stimulation which is best provided by perimodiolar electrodes; Group 2 may benefit from functional residual hearing combined with electrical stimulation, and so are candidates for straight, hybrid electrodes; and Group 3 may require either a perimodiolar or straight electrode depending on the anatomical and medical conditions in individual cases.
P. Gibson, P. Boyd / European Annals of Otorhinolaryngology, Head and Neck diseases 133S (2016) S63–S65
The future in electrodes is to combine the best of both worlds, i.e. a perimodiolar electrode that preserves hearing at the same rate as current straight electrodes. This would add further subtlety to the treatment options available to the implanting surgeon. Disclosure of interest Peter Gibson is an employee of Cochlear® Ltd., the manufacturer of the devices described in this article. Paul Boyd performs some consultancy work for Cochlear® Europe Ltd. References [1] Clark GM. The multi-channel cochlear implant: multi-disciplinary development of electrical stimulation of the cochlea and the resulting clinical benefit. Hear Res 2015;322:4–13. [2] Lenarz T, Stöver T, Buechner A, Lesinski-Schiedat A, Patrick J, Pesch J. Hearing conservation surgery using the Hybrid-L electrode. Results from the first clinical trial at the Medical University of Hannover. Audiol Neurootol 2009;14(Suppl. 1):22–31. [3] Gantz BJ, Turner CW. Combining acoustic and electrical hearing. Laryngoscope 2003;113(10):1726–30. [4] Graham JM, Phelps PD, Michaels L. Congenital malformations of the ear and cochlear implantation in children: review and temporal bone report of common cavity. J Laryngol Otol Suppl 2000;25:1–14. [5] Sennaroglu L. Cochlear implantation in inner ear malformations - a review article. Cochlear Implants Int 2010;11(1):4–41.
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[6] Jurawitz MC, Büchner A, Harpel T, et al. Hearing preservation outcomes with different cochlear implant electrodes: Nucleus® HybridTM -L24 and Nucleus FreedomTM CI422. Audiol Neurootol 2014;19(5):293–309. [7] Hassepass F, Aschendorff A, Bulla S, et al. Radiologic results and hearing preservation with a straight narrow electrode via round window versus cochleostomy approach at initial activation. Otol Neurotol 2015;36(6):993–1000. [8] Skarzynski H, Lorens A, Matusiak M, Porowski M, Skarzynski PH, James CJ. Cochlear implantation with the nucleus slim straight electrode in subjects with residual low-frequency hearing. Ear Hear 2014;35(2):e33–43. [9] Shepherd RK, Hatsushika S, Clark GM. Electrical stimulation of the auditory nerve: the effect of electrode position on neural excitation. Hear Res 1993;66(1):108–20. [10] Cohen LT. Practical model description of peripheral neural excitation in cochlear implant recipients: 2. Spread of the effective stimulation field (ESF), from ECAP and FEA. Hear Res 2009;247(2):100–11. [11] van Wermeskerken GK, van Olphen AF, Graamans K. Imaging of electrode position in relation to electrode functioning after cochlear implantation. Eur Arch Otorhinolaryngol 2009;266(10):1527–31. [12] Gordin A, Papsin B, James A, Gordon K. Evolution of cochlear implant arrays result in changes in behavioral and physiological responses in children. Otol Neurotol 2009;30(7):908–15. [13] Holden LK, Finley CC, Firszt JB, et al. Factors affecting open-set word recognition in adults with cochlear implants. Ear Hear 2013;34(3):342–60. [14] Bille J, Fink-Jensen V, Ovesen T. Outcome of cochlear implantation in children with cochlear malformations. Eur Arch Otorhinolaryngol 2015;272(3):583–9. [15] Loundon N, Rouillon I, Munier N, Marlin S, Roger G, Garabedian EN. Cochlear implantation in children with internal ear malformations. Otol Neurotol 2005;26(4):668–73. [16] Dowell R. Evidence about the effectiveness of cochlear implants for adults. In: Lena Wong, Louise Hickson, editors. Evidence-Based Practice in Audiology. Plural Publishing; 2012. p. 141–65.