청각재활 - 와우이식 이준호 http://dx.doi.org/10.7599/hmr.2015.35.2.108 pissn 1738-429X eissn 2234-4446 서울대학교병원이비인후과 Auditory Rehabilitation Cochlear Implantation Jun Ho Lee Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Hospital, Seoul, Korea The first cochlear implant was approved about 30 years ago. It just provided a limited sensation of sound and facilitated lip-reading based communication. Recent advances in the cochlear implant system and surgical techniques have enabled the majority of recipients to communicate orally without visual cues. The cochlear implantation has become a standard means of auditory rehabilitation for profound sensorineural deafness. To evaluate candidacy for cochlear implantation, an objective and behavioural audiological test, imaging and functional studies to identify the status of the cochlea and the auditory nerve, and evaluation of additional medical conditions are needed. Although the cochlear implantation can restore auditory function, sound perceived with the cochlear implant is different from normal hearing. Therefore postoperative rehabilitation is crucial for good speech performance. Nowadays, the indications for cochlear implantation have been extended. Hearing loss patients with residual low-frequency hearing could be candidates for cochlear implantation. Therefore, residual hearing preservation during cochlear implantation has been an important issue. In addition, bilateral cochlear implantation, cochlear implantation for single-sided deafness and fully implantable cochlear implant systems have been receiving more attention. The purpose of this article is to review current knowledge concerning the cochlear implantation. Correspondence to: Jun Ho Lee 우 110-744, 서울시종로구대학로 101, 서울대학교병원이비인후과 Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul 110-744, Korea Tel: +82-2-2072-2445 Fax: +82-2-745-2387 E-mail: junlee@snu.ac.kr Received 3 March 2015 Revised 7 March 2015 Accepted 16 March 2015 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Key Words: Cochlear Implants; Deafness; Rehabilitation; Hearing Loss, Sensorineural 서론감각신경성난청은흔히발생하는감각기관질환으로, 500명의신생아중약 1명의신생아에서발생한다 [1-3]. 난청의유병률은나이가증가함에따라더증가하여 65세이상에서는 50% 이상의유병률을보이고, 80세이상에서는 95% 의유병률을보인다 [4-6]. 경도및중등도의감각신경성난청의경우보청기를통해이득을얻을수있으나, 고도난청의경우보청기를통해서는큰이득을얻을수없고, 와우이식을통해청각재활을할수있다. 인공와우는소리자극을전기자극으로바꾸어유모세포를거치지않고, 나선신경절세 포나말초청신경을직접자극하여대뇌청각중추에서소리를인지하도록한다. 지난 10년간와우이식은혁신적인발전을이룩하여많은난청환자들의청각재활수단으로사용되고있다. 여기에서는와우이식의전반에대해살펴보고, 최근이슈가되고있는양측와우이식, 와우이식술중잔존청력보존에대해대해기술하였다. 와우이식의역사인공와우는 1790년이탈리아의 Alessandro Volta 가자신의귀에전극을삽입하고, 전기자극을가한후소리를느낄수있음을발견 108 2015 Hanyang University College of Medicine Institute of Medical Science http://www.e-hmr.org
이준호 청각재활 - 와우이식 함으로써그역사가시작되었다. 이후 1957년프랑스의 Djournio와 Eyrices는청력이완전히소실된환자의내이에전극을삽입하고전기자극을주어전농환자가음을감지한것을보고하였다 [7]. 이후본격적인인공와우개발이진행되어미국의 House는 1961년단일채널을이용한와우이식수술을처음으로시행하였고, 1972년에는단일채널인공와우에사용할수있는언어처리기를개발하였다 [8]. 이후인공와우기술은더발전하여 1978년호주의 Clark는 10개채널을가진인공와우를이식하여전극의위치에따라인지되는음의높이가달라짐을보고하였다 [9]. 그후 1984년에는 House 3M의단채널인공와우, 1985년에는 22채널인공와우, 그리고 1998년에는 Nucleus 24채널인공와우가 FDA로부터인가를받았다. 인공와우의구성및작동인공와우는크게머리에부착하는외부장치와머리속에이식되는내부장치로이루어져있다. 외부장치는소리를처음받아들이는송화기 (microphone), 소리를전기신호로바꾸어내부장치로전달하는어음처리기 (speech processor) 로구성되어있다. 내부장치는외부장치에서보내는전기신호를받아들여와우에삽입된전극으로신호를보내는수신기 / 자극기 (receiver/stimulator), 전기신호를받아와우의나선신경절을직접자극하는전극 (electrode) 으로이루어져있다. 따라서인공와우는소리자극을전기자극으로변환시켜나선신경절을자극하고이는청신경을통해뇌로전달되어소리로인지된다. 따라서인공와우는정상와우를대신하여소리를증폭하고와우내적절한위치에서전기신호를발생시킴으로써다양한세기와주파수의소리를인지할수있도록한다. 하지만이렇게인지되는소리는정상와우를통해전달되는소리에비해한계를가지고있어, 소리의세기와주파수를인지하는데있어제약점이있다. 이를극복하기위해여러가지 sound processing strategy가사용되고있다. 와우이식대상자양측청력이 70-90 db 이상의고도감각신경성난청환자는와우이식의대상자가될수있으며, 와우이식을시행할수있는병원에서검사를받아야한다. 검사에는객관적청력검사, 주관적청력검사, 내이, 청각신경에대한영상검사그리고와우이식에문제가없는지에대한내과적, 신경과적, 정신과적검사가포함된다. 와우기원의양측감각신경성난청으로와우이식에관한청력기준을만족하며기존의보청기로는만족할만한청각재활을할수없는경우와우이식의대상자가된다. 와우이식의결과에대한현실적인기대를가지게하고, 수술후원활한언어치료를하기위해서는수술전검사와충분한상담이필요하다. 와우이식대상자에대한수 술전검사와상담은이비인후과의사뿐만아니라청각사, 언어치료사, 사회사업사, 언어병리학자, 교육전문가가팀을이루어진행되어야한다. 와우이식의목표는와우이식전에사용하던기존의보청기를사용할때보다인공와우를통해언어를더잘이해하고의사소통이가능하도록하는것이다 [10]. 인공와우시스템이발전하고와우이식의결과가좋아짐에따라와우이식대상자의기준도넓어지고있다. 최근에는저음부 (1 khz 이하 ) 에잔존청력이있는난청환자에게도 electro-acoustical stimulation (EAS) 라는와우이식이시행되고있다. EAS는고음부의청력저하는와우이식을통해청력을복구하고, 잔존청력이있는저음부는기존의보청기를이용하는시스템이다. 이외에도 2008년부터일측에정상청력을가지고있고일측만전농인환자에게도와우이식술이시행되고있으며, 초기결과는뇌가양측귀로부터의정보를효과적으로통합할수있음을보였다 [11]. 수술전평가와우이식전평가는환자의난청정도와의학적상태뿐만아니라사회 / 경제적상태, 교육, 가족 / 환경에대한여러가지요소를평가하여야한다. 1. 청력검사청력검사는주관적청력검사와객관적청력검사로나누어진다. 대표적인주관적청력검사는순음청력검사이며, 환자가보청기를착용하는경우에는보청기를착용한상태에서도검사를시행하여야한다. 환자가소아인경우는행동반응검사 (behavioral audiometry) 나시각강화청력검사 (visual reinforcement audiometry) 를시행하게된다. 객관적청력검사로는청성뇌간유발반응검사 (auditory brainstem response audiometry) 나청성지속반응검사 (auditory steady state response) 를시행하게된다. 이외에도와우이식후결과예측을위해전기자극청성뇌간유발반응검사 (electrically evoked auditory brainstem response audiometry) 나와우갑각검사 (promontory stimulation test) 를시행하기도한다. 2. 언어평가언어평가는환자의소리자극에대한인지능력을측정하는검사로, 와우이식전환자의상태를평가하고와우이식후청각재활의기초자료로이용하게된다. 언어평가방법은여러개의보기가주어진상태에서진행되는말소리변별능력검사 (closed set speech perception test) 와보기가주어지지않은상태에서시행되는말소리이해능력검사 (open set speech perception test) 가있다. 언어평가는와우이식후에도환자의언어능력발달을평가하기위해정기적으로시행되어야힌다. http://www.e-hmr.org 109
Jun Ho Lee Auditory Rehabilitation Cochlear Implantation 3. 영상의학적검사와우이식전시행하는영상검사로는측두골고해상도단층촬영과자기공명영상이있다. 고해상도단층촬영은와우이식수술을시행함에있어필요한기본적인해부학적정보를제공해주고, 난청을유발한내이기형이있는지확인할수있다. 자기공명영상은청신경을비롯한청각전도로에대한해부학적인정보를제공해준다. 대한인지능력을향상시키고, 이를통해인공와우를이용한듣기능력및구어의사소통능력을최대화하고자한다. 언어재활치료를통하지않을경우는청각재활의효과가미미하며인공와우이식후청각재활훈련의필요성은많은연구에서입증되어있다 [22-26]. 와우이식의발전 수술및합병증와우이식은대개전신마취하에서진행되며, 피부절개의경우과거에는역 U형이나 C형의절개를많이사용했으나최근에는귀뒤 1 cm 정도에최소한의피부절개만가하는경우가점점많아지고있다. 피부절개후폐쇄형유양동절제술을시행하고수용 / 자극기의밑부분이위치할공간을만든다. 이후안면신경과고삭신경사이의공간인안면신경와 (facial recess) 를개방하여정원창에이르는통로를확보한다. 과거에는정원창을노출시킨후정원창의전하방에구멍을뚫는와우개창술 (cochleostomy) 을시행하고이구멍을통해인공와우전극을삽입하였다. 하지만최근에는잔존청력보존을위해와우개창술을시행하지않고정원창으로전극을직접삽입하는방법이주로이용되고있다. 이후절개선을봉합하고수술을마친다. 수술중기기의이상유무를확인하기위하여임피던스검사, electrical stapedial reflex test (ESRT), electrical compound action potential (ECAP) 검사등을하기도한다. 와우이식후발생하는합병증은수술적치료가필요한중한합병증 (major complication) 과보존적치료만필요한경한합병증 (minor complication) 으로분류된다 [12]. 중한합병증으로는기기고장, 술후감염등이있으며발생률은 2.3% 에서 6.6% 정도로보고되어있다 [13-19]. 경한합병증으로는어지러움증, 이명, 미각변화등이있으며발생률은 10.3% 에서 18% 정도로보고되어있다 [14,15,20,21]. 인공와우조율 (Mapping) 및언어재활치료수술후 5주부터인공와우를사용하게되는데최상의소리를들을수있도록언어처리기의프로그램을조절하여야한다. 소리자극을감지할수있는가장작은소리자극의크기인최소가청역치 (Tlevel) 와불쾌감을느끼지않는최대자극강도인최적가청역치 (Clevel) 를조절하게되는데이를조율 (mapping) 이라고한다. 조율은한번시행하는것으로끝나지않고정기적으로반복하여최소가청역치와최적가청역치를재조정하여야한다. 조율과더불어와우이식후에정기적인언어재활치료를시행하여야한다. 청각의회복은인공와우장치이식만으로끝나는것이아니라, 장치이식후 3-4년간의반복적인언어재활치료를통해서만가능하다. 언어재활치료는다양한방법을이용하여말소리에 1. Electroacoustic Stimulation 과잔존청력보존저음역에는잔존청력이있지만고음역에는고도난청을가진환자의경우, 기존의보청기로충분한청각재활을얻을수없음에도불구하고와우이식수술중발생하게되는저주파수대청력소실로인해일반적인와우이식의대상이되지못했다 [27-29]. 하지만최근들어잔존청력을보존하며와우이식을시행하여, 잔존청력이있는저음부는보청기를이용하여잔존청력을사용하고, 잔존청력이없는주파수대는전극을통한전기자극으로청력을이용하려는 EAS가개발되어시행되고있다. 따라서 EAS를시행함에있어잔존청력을보존하는것이중요한데, 와우이식에서사용하는일반적인길이와두께의전극을기존의방식대로와우에삽입하게되면와우의기저막과유모세포가파괴되어잔존청력을보존할수없음이알려져있다 [30,31]. 그래서기존인공와우의전극보다짧고가는전극이개발되어 EAS에이용되고있다. EAS에사용되는전극의최적길이에관해서는아직논란이있다. 전극의길이가길수록전극삽입시저음부의잔존청력이손상될가능성이높아지지만, 긴전극을사용할경우저음부의잔존청력이손상되더라도 EAS를기존의인공와우처럼사용하여잔존청력을대체할수있다. 하지만짧은전극을사용할경우전극이와우의기저부에만닿아고음부에만전기자극을가할수있고와우의저음부대에전기자극을가할수없다. 따라서전극삽입시저음부잔존청력이손상될경우저음부청력을복구할방법이없다. 하지만짧은전극을사용한 EAS에서전기자극만을이용하여소리들었을때도자음인식에있어서는긴전극을사용한경우와비슷한결과를얻었다는연구가있었다 [23]. 이에반해짧은전극을사용하였을때는소리인지가좋아지기까지 12개월이상이걸렸고, 긴전극을사용하였을경우 6-12 개월정도의시간이걸렸다는연구도있었다 [32,33]. 긴전극사용을주장하는또다른근거는전극삽입당시는저음부의잔존청력이보존되었더라도이후에저음부청력이서서히저하될수있기때문이다. 하지만 Yao 등은짧은전극을사용하였을경우저음부청력저하가 1년에 1.05 db에불과함을보고하여처음전극삽입당시저음부청력이보존된다면저음부청력저하는심하지않을것이라고예측하였다 [34]. EAS에사용되는전극의최적길이에대해서는추가적인연구가필요하다. 110 http://www.e-hmr.org
이준호 청각재활 - 와우이식 2. 양측와우이식청각재활에있어양측와우이식이일측와우이식보다우수한결과를얻을수있음이알려져있다 [35]. 특히양측인공와우를시행하였을경우소리의위치파악능력이향상됨은여러연구에서일관되게입증되었다 [36-39]. 그뿐만아니라언어발달에있어서도양측인공와우가도움이됨이알려졌고 [40,41], 소음상황에서의언어인지도향상됨이보고되었다 [38,42-44]. 조용한환경에서의언어인지도향상됨이보고되었는데, 양측인공와우를사용한경우가일측인공와우를이용하는경우에비해단음절단어인지가평균적으로 10% 향상되었다 [45]. 이에많은나라에서양측고도난청치료에있어양측와우이식을표준치료로지정하고있다 [42]. 양측와우이식은양측을동시에시행할수도있고, 순차적으로시행할수도있다. 순차적으로시행할경우와우이식간격을최대한짧게하는것이좋고 1년을넘기지않는것이좋다 [46]. 3. 일측고도난청환자에서의와우이식최근여러연구에서반대측에정상청력을가지고있는일측고도난청환자에서도와우이식이많은도움을줄수있음이밝혀지고있다 [11,47,48]. 일측고도난청환자에서와우이식을시행받은환자는 contralateral routing of signal (CROS) 보청기나 bone-anchored hearing aid (BAHA) 를사용하는환자에비해소음환경에서의언어인지와소리의위치파악에있어우수한결과를보였다. CROS 보청기나 BAHA의경우난청이있는귀를사용하지않고모든소리를정상청력의귀로보내지만, 와우이식을시행하게되면소리를들을수있는새로운귀가생기므로청각재활에있어더우수한결과를얻을수있는것으로생각된다 [46]. 4. 완전이식형인공와우완전이식형인공와우는환자의미용과편이성면에서커다란도움을줄수있다. 하지만완전이식형인공와우개발에있어가장큰문제는신체의잡음에영향을받지않는이식형마이크로폰개발이다. 현재식약처의승인을받은완전이식형인공와우는없으나, 시제품이임상시험중에있다 [49]. 결론와우이식은전농환자들의청각재활을위한훌륭한수단으로자리잡았다. 현재의인공와우는전농환자들이시각적도움없이도언어를이해할수있을정도로청력을회복시킬수있게되었다. 따라서인공와우가환자들의삶에미치는영향은막대하다. 또한와우이식수술도커다란부작용없이안전하게시행될수있게되었다. 하지만인공와우에는완전이식형인공와우개발등아직발전되어야할부분이남아있어앞으로도더많은연구가진행되어야할것이다. REFERENCES 1. Marazita ML, Ploughman LM, Rawlings B, Remington E, Arnos KS, Nance WE. Genetic epidemiological studies of early-onset deafness in the U.S. school-age population. Am J Med Genet 1993;46:486-91. 2. Morton NE. Genetic epidemiology of hearing impairment. Ann N Y Acad Sci 1991;630:16-31. 3. Smith RJ, Bale JF Jr, White KR. Sensorineural hearing loss in children. Lancet 2005;365:879-90. 4. Mazelova J, Popelar J, Syka J. Auditory function in presbycusis: peripheral vs. central changes. Exp Gerontol 2003;38:87-94. 5. Olusanya BO. The right stuff : the global burden of disease. PLoS Med 2007;4:e84. 6. Stach BA, Spretnjak ML, Jerger J. The prevalence of central presbyacusis in a clinical population. J Am Acad Audiol 1990;1:109-15. 7. Djourno A, Eyries C. Auditory prosthesis by means of a distant electrical stimulation of the sensory nerve with the use of an indwelt coiling. Presse Med 1957;65:1417. 8. House WF. Cochlear implants. Ann Otol Rhinol Laryngol 1976;85 suppl 27:1-93. 9. Tong YC, Black RC, Clark GM, Forster IC, Millar JB, O Loughlin BJ, et al. A preliminary report on a multiple-channel cochlear implant operation. J Laryngol Otol 1979;93:679-95. 10. Eisenberg LS, House WF. Initial experience with the cochlear implant in children. Ann Otol Rhinol Laryngol Suppl 1982;91:67-73. 11. Arndt S, Aschendorff A, Laszig R, Beck R, Schild C, Kroeger S, et al. Comparison of pseudobinaural hearing to real binaural hearing rehabilitation after cochlear implantation in patients with unilateral deafness and tinnitus. Otol Neurotol 2011;32:39-47. 12. Cohen NL, Hoffman RA. Complications of cochlear implant surgery in adults and children. Ann Otol Rhinol Laryngol 1991;100:708-11. 13. Arnold W, Brockmeier SJ. Medical, surgical, and technical complications with the COMBI-40. Am J Otol 1997;18:S67-8. 14. Bhatia K, Gibbin KP, Nikolopoulos TP, O Donoghue GM. Surgical complications and their management in a series of 300 consecutive pediatric cochlear implantations. Otol Neurotol 2004;25:730-9. 15. Cohen NL, Waltzman SB, Roland JT, Jr., Staller SJ, Hoffman RA. Early results using the nucleus CI24M in children. Am J Otol 1999;20:198-204. 16. Gibbin KP, Raine CH, Summerfield AQ. Cochlear implantation--united Kingdom and Ireland surgical survey. Cochlear Implants Int 2003;4:11-21. 17. Johnson IJ, Gibbin KP, O Donoghue GM. Surgical aspects of cochlear implantation in young children: a review of 115 cases. Am J Otol 1997; 18:S69-70. 18. Kempf HG, Johann K, Lenarz T. Complications in pediatric cochlear implant surgery. Eur Arch Otorhinolaryngol 1999;256:128-32. 19. Kronenberg J, Migirov L, Dagan T. Suprameatal approach: new surgical approach for cochlear implantation. J Laryngol Otol 2001;115:283-5. 20. Fayad JN, Wanna GB, Micheletto JN, Parisier SC. Facial nerve paralysis following cochlear implant surgery. Laryngoscope 2003;113:1344-6. 21. Kempf HG, Stover T, Lenarz T. Mastoiditis and acute otitis media in children with cochlear implants: recommendations for medical management. Ann Otol Rhinol Laryngol Suppl 2000;185:25-7. 22. Fu QJ, Galvin JJ, 3rd. Perceptual learning and auditory training in cochlear implant recipients. Trends Amplif 2007;11:193-205. 23. Fu QJ, Galvin JJ, 3rd. Maximizing cochlear implant patients performance with advanced speech training procedures. Hear Res 2008;242:198-208. 24. Nogaki G, Fu QJ, Galvin JJ 3rd. Effect of training rate on recognition of http://www.e-hmr.org 111
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