Cochlear Implants

Chih-Hung Wang, MD, PhDDepartment of Otolaryngology-Head & Neck Surgery

Tri-Service General Hospital, National Defense Medical Center

王智弘

三軍總醫院耳鼻喉部 國防醫學院耳鼻喉學科

Photo source: U. S. Food and Drug Administration

Biologic Application of Electricity

has driven the development of a wide range of medical treatments, past and present,use electricity.

Outer Ear Structure

Middle Ear Structure

Middle Ear Structure

Middle Ear Function

Middle Ear Function

What Is A Cochlear Implant?

A surgically implanted medical device that bypasses the damaged part of the inner ear to electrically stimulate the remaining neural fibers of the auditory nerve

Electrical current stimulates the remaining auditory nerve fibers in the damaged inner ear to generate sensations of hearing

What are the potential benefits of CI? Access to sound

Environmental sounds Speech sounds High frequency sounds Soft sounds

Development of speech recognition and speech communication

1790, when Alessandro Volta (the developer of the electric battery)placed metal rods in his own ears and connected them to a 50-voltcircuit, experiencing a jolt and hearing

a noise "like a thick boiling soup".

Djourno and Eyries(1957) - direct stimulation by placing a wire on the auditory nerve

House and Doyle(1961) – approaching the auditory nerve through scala tympani electrode implantation tympani approach( hearing sensation that were “pleasant and useful”)

Simmons(1964) - modiolar stimulation

House and Michelson - implantation of electrodes driven by implantable receiver-stimulators

History of Cochlear Implants

House(1972) - first speech processor was developed to interface with the House 3M single-electrode implant, 1972~1980: > 1000 implanted, In 1980, age criteria were lowered form 18 to 2 years )

1984 – multiple-channel devices, enhanced spectral perception and speech recognition capabilities (Australia, Nucleus)

1990s – changes in implant technology and in clinical approaches, speechprocessor designs have evolved to produce higher performance levels strategies

1995 - Clarion CI, ABC applied in USA

1998 – MedEl, Austria entered the US market

History of Cochlear Implants (cont.)

How many people are implanted? 1980 - 1,000

1990 - 5,000, 90% adults

1997 - 20,000

2002 - 45,000, 50% children

2006 - >100,000

2009 - >188,000 approximately 6,000 procedures take place annually in the

United States. (adult/child: 41,500/25,500) Approximately 100 cases annually in Taiwan

Van Naarden et al: An overall prevalence rate of serious hearing impairment of 1.1

cases per 1000 children aged 3-10 years. By age 75 years, 360 of 1000 adults have a disabling hearing

loss.

1996, National Institute on Deafness and Other Communications Disorders survey

More than 28 million Americans are deaf or hearing impaired. This statistic may reach 40 million by the year 2020.

+ + + ++ + +

The indication for cochlear implantation

Congenital hearing loss and prelingual deafness

Acquired hearing loss and postlingual deafness

Severe hearing loss that can be aided and that deteriorates to profound loss in childhood, adolescence, or adulthood (perilingual) and coexists with various degrees of language development

The contraindication for cochlear implantation deafness due to lesions of the eighth cranial nerve or brain stem

chronic infections of the middle ear and mastoid cavity or tympanic membrane perforation

The absence of cochlear development as demonstrated on CT scans remains an absolute contraindication

Certain medical conditions that preclude surgery (eg, specific hematologic, pulmonary, and cardiac conditions) also may be contraindications

The lack of realistic expectations regarding the benefits of cochlear implantation and/or a lack of strong desire to develop enhanced oral communication skills poses a strong contraindication for implantsurgery

Evolving Audiologic CriteriaMay, 1995 NIH Consensus Development Conference on Cochlear Implants

Profound bilateral sensorineural hearing loss (>90dB)

Minimal speech perception under best aided conditions.

April, 2001: Balkany T, et al: Cochlear Implants in Children.Otolaryngologic Clinics of North America 34:455-62.

Severe (70-90dB) or profound bilateral sensorineural hearing loss

Those with some residual amplified hearing are still candidates

Expanding Age CriteriaMay, 1995 NIH Consensus Development Conference on Cochlear Implants

Minimum age of 2 years

April, 2001: Balkany T, et al: Cochlear Implants in Children.Otolaryngologic Clinics of North America 34:455-62.

Recommend minimum age to be 12 months.

Provides child with auditory input during critical period of language development

Candidacy- ADULTS Health adult over 18 Y/O Severe to profound hearing loss in both ears

(PTA 70 dBHL) Post-lingual onset of severe to profound hearing loss

(after age 6 y/o) Limited benefit from hearing aids

(SDS 50%) Desire to improve hearing and realistic expectations No medical contraindications

12 months to 17 years of age Bilateral profound hearing loss

(PTA 90 dBHL) Negligible functional hearing aid benefit

(6 months at least) In USAChildren 4 y/oPBK word score 0-12% or HINT-C score 30%Children 4 y/oMLNT word score 20% or IT-MAIS score 2 on questions 3, 5, 6

Candidacy- CHILDREN

January 2005

Medicare guidelines as of January 2005 allow for cochlear implantation in patients with 50% aided sentence discrimination scores and allow for 60% sentence scores in clinical trials.

Clearly, the trend over time is that relaxed guidelines are better, and better implant performance and outcome have been demonstrated.

How to evaluate the candidate Measures the patient's hearing with and without hearing aids. Evaluation with pure-tone audiometry (PTA) and auditory brainstem

response (ABR) testing (in the case of children) often is performed. Otoacoustic emission (OAE) testing complements these studies; OAE results often indicate the need for a trial of newer and sometimes stronger hearing aids.

A CT scan is obtained to evaluate the status of the cochlea and to establish the presence of a patent (nonossified) cochlea or to identify a common cavity, Mondini dysplasia, enlarged vestibular aqueduct, or an ossified cochlea.

In children and young adults, speech and language evaluation andeducational placement discussions are performed next.

Finally, a psychosocial evaluation is completed. Once a patient has been evaluated, a team meeting commences to recommend implantation advice.

If the patient is cleared for implantation, the patient proceeds with preoperative medical clearance, chooses an implant device, and proceeds with surgery

How many surviving neuron should be left

The number of surviving neuron populations needed for successful implantation remains unclear.

In 1991, Linthicum et al:successful speech understanding in a patient who demonstrated less than 10% of the normal complement of neurons via a temporal bone study

Speech Audiometry

1950, USA: Speech sound , words or sentences

Speech reception threshold (SRT):spondee words: 50% repeatSRT-PTA< 6~8 dB, if >12 dB, repeat SRT or PTASRT-speech detection threshold< 8 dB

Speech discrimination score(SDS):phonetically balanced words: SRT + 40 dB=PB-MAX

Speech discrimination score(SDS)

Score Disability90-100% Normal 75-90% Mild 60-75% Moderate 50-60% Severe<50% Profound

The Cochlear Implantation Team

Interdisciplinary team Otologist

Audiologist

Aural rehabilitation specialist

Speech pathologist

Clinical psychologist

Age & Outcomes

Younger age at implantation is generally associated with better outcomes.

Children implanted after age 5 show improvement over those with hearing aids, but less improvement than children implanted under age 5.

Children over age 10 should be screened carefully, as they are more likely to have poorer outcomes.

Central Neural Plasticity

Children older than 7 y/o with prelingual hearing loss are typically not considered as good candidates for CI

Radiologic Evaluation

Computed tomography of the temporal bones Mastoid aeration

Facial nerve position

Patency of cochlea

Middle ear status

Evaluate IAC

Mondini Dysplasia

Radiologic Evaluation Indications for Magnetic Resonance Imaging

IAC <1.5mm on CT Evaluate presence of cochlear nerve

Hx of Meningitic Deafness Evaluate degree of cochlear ossification

Cochlear aplasia or auditory nerve aplasia are contraindications to cochlear implantation

High-resolution T2-weighted fast spin echo MRI is complementing and even replacing CT scanning because of its increased ability to reveal cochlear ossification

Normal Cochlear CT

Psychosocial Factors

Patient and family motivation are critical

Must be prepared for extensive period

of aural rehabilitation

Initial postoperative rehabilitation may require daily sessions for up to two weeks.

Realistic expectations

Cochlear Implantation Procedure

2-3 hours under general anesthesia The internal device is placed under the skin

behind the ear into a well created in the mastoid bone

The electrode array is inserted into the cochlea

Patient usually discharged the following day

Device is activated 4 weeks later

Determine the side of the implant Implanting the better-hearing ear, allows for

a greater population of surviving spiral ganglion cells to receive electrical stimulation and, hence, potentially results in a better outcome.

However, some patients, especially those who have progressive bilateral sensorineural hearing loss and are experiencing asymmetric deafness bilaterally , the poorer-hearing ear may be implanted

• Headpiece (HP) with Microphone (and Transmitter Antenna), Cable

• Speech Processor (SP)• Internal Cochlear Stimulator

(ICS) Package (with Receiver Antenna)

• Electrode Array

Components of All Cochlear Implant Systems

HP

HP

SP

SP

ICS ICS

Cochlear Implant Components

Internal Device Surgically implanted under the

skin Electronics package (receiver-

stimulator) with magnet Electrode array placed inside the

cochlea

External Device Worn on the body or at ear level Sound/speech processor Microphone Coil with magnet

The external components of the CI system pick up sounds, analyze them, and convert them into an electrical signal that is sent to the internal device located under the skin

Internal and external components are held close to each other by a pair of magnets and communicate via transcutaneous transmission of a radio-frequency signal

The internal device decodes the signal and sends electrical current to each electrode

When the electrodes stimulate the nerve fibers of the auditory nerve, the signal is received by the brain and interpreted as sound

Nucleus 24 Contour Array

Facial Recess Width

Oval Window: 5.4 0.9 mmRound Window: 4.5 1.3 mm

Robert H.R. Bettman et al. ORL 2003

Dr. Wang’s Lab 2006

RW

cochleostomy

Basilar membrane

Medel

人工電子耳 帶來一線「聲」機三總耳鼻喉頭頸外科部部主任 王智弘

說人工電子耳是現代醫學中的一項”奇蹟”，一點也不為過，它不僅實現聽障患者對於聆聽聲音的渴望，也破解了亙古以來老祖宗們所謂“聾即是啞”的一貫魔咒，為先天性聽障孩童與後天性失聰的患者，帶來了一線「聲」機。

人工電子耳的原理是利用植入的電極線，纏繞於我們已經受損的聽覺接受器官-耳蝸，進而取代受損的耳蝸器官並發揮其刺激聽覺神經纖維的功能; 當環境中的聲音訊息透過掛在耳朵上微小麥克風的接收與語言處理器的信號轉換後，這些聲音的編碼信號就會傳輸到耳蝸的電極線，就如同正常的耳蝸器官接受到聲音訊號的刺激一般，植入的電極線收到訊號後立即執行其刺激聽覺神經纖維的功能，聲音的接收從此不再受限於耳蝸的罷工而中止傳遞，這就是人工電子耳的奧妙，而這樣的巧思竟是來自1790年代左右，有人嘗試將鐵線放入耳道後給予電壓通電，竟然聽到猶如濃湯煮沸的噪音聲所揭櫫。

值得注意的是，有兩項新進的發展讓整個植入系統的表現有了重大提升: 一是兩耳均植入人工電子耳；另一為合併助聽器使用與人工電子耳植入所產生的效應。 兩耳植入有助於將兩耳間的音量差與時間差作某種程度的恢復，提供植入者分辨聲音方向的線索，有了兩耳的刺激，頭影效應(head shadow effect)的存在會讓兩耳感受到不同的音量，於是加強了音源位置的辨識。至於合併助聽器與電子耳的使用，是讓戴助聽器的低頻殘存聽力得以保存，結合電子耳所提供的高頻聽力，整體的頻率辨識度表現將更趨理想。

如果聽障患者配戴助聽器能得到助益，人工電子耳的植入就不太必要，這是最簡單的分辨與取捨方式，畢竟人工電子耳的植入是一項需要開刀的侵入性治療模式，不過，手術的安全性很高，經術前評估的適合植入者，都可藉由這項醫學科技產品來重新體驗“聆聽聲音”的感覺。

人工電子耳手術術前評估

人工電子耳手術雖然可恢復聽障患者的聽力，但是術前的評估卻必須小心謹慎。不良的術前溝通和評估，可能會造成手術本身成功、但是個案失敗的情況。是以對於醫療團隊來說，完善的術前評估常需耗費心力、花上數個月的時間，經醫師綜合考量檢查的結果、預期的成效和家屬及病人的期望值等因素後，才能了解患者是否真的適合。

術前評估包括了許多檢查，可分為以下幾類：

病史詢問：透過詳細的病史詢問來初步排除罹患遺傳疾病或智能障礙的孩童個案，使之儘早接受早期療育。後天性失聰患者則須了解其病因以及聽障發生的時間。

聽力檢查：包含了純音聽力圖、聽性腦幹反應與耳聲傳射檢查。並非所有聽障個案都需要人工電子耳手術，若評估透過助聽器輔助後可使個案聽力進步、語言發展獲得改善，或是對成年案例的生活品質有所助益者，則以助聽器輔助改善聽力即可。

身體檢查：包含全身理學檢查、耳鼻喉科方面的檢查以及放射影像學的檢查。透過這些檢查，醫師才能知道患者是否可以進行全身麻醉、有無影響電子耳手術的非適應症或疾病。藉由影像檢查才能得知患者的內耳構造是否適合植入電極，包括耳蝸發育不全、前庭大腦導水管擴大等畸形變化。

語言評估：對於幼兒來說，術前評估語言的發展極為重要，因為改善聽力即是為了能發展健全的語言。定期的觀察幼兒語言發展情況，且互相對照語言評估和聽能評估的結果，可得知患者對於人工電子耳的需求。

其他支持系統的評估：人工電子耳手術前後的聽語評估及復健，對於患者日後聽力的改善有很大影響。故此必須有詳盡的聽語復健計畫和日後患者家庭對於教育的安排等後續的支持體系，方能收得最大療效。三總耳鼻喉部目前均有專業合格的聽力師與語言治療師，來專責評估並訓練幼兒的聽能與語言復健。

人工電子耳適應症及禁忌症人工電子耳的植入，目前健保並未給付此品項，以下為適應症的說明。

成年聽障者：1. 年齡大於18歲以上、且身體狀況無明顯開刀禁忌症的患者。2. 兩側重度到極重度的感音性聽力障礙。3. 經傳統式助聽器輔助效果不佳、或語言辨識能力不足者。4. 若患者語言發展前即失聰、且未曾配戴助聽器輔助者，不建議接受植入手術。

幼兒聽障者：1. 雙耳極重度聽障確定者，經配戴適當之助聽器六個月以上，語言發展仍無明

顯進步時，建議3歲前進行植入。2. 若因腦膜炎引起之聽障，為避免發炎後耳蝸骨化增加此手術的困難度，更可儘早施行手術。3. 無其他接受手術之禁忌症或無法配合術後復健訓練者。4. 有完整的術後教育計劃。

若重度聽障患者有以下情況，則為人工電子耳植入的禁忌症，不建議接受此手術：

（1）持續進行之中耳炎。

（2）併有自閉症。

（3）併有重度智障。

（4）中樞聽覺系統病變 (如: 核黃疸所致的聽神經病變) 。 （5）上全身麻醉可能有風險者，如：嚴重之心臟疾病。

（6）內耳畸形(如耳蝸發育不全)、經評估後不適合手術者。

人工電子耳手術後照護

接受人工電子耳手術後，術後一週即可拆線，於術後三至四週，確定手術傷口癒合良好時，聽力師即可透過電腦、為患者量身訂作出一套個人的「電子耳音量與舒適度的調整圖」。這個過程通常不會一次就決定好，大約三個月內需每個禮拜一次回門診進行調整。若患者是幼兒，還必須透過聽語治療師一系列課程，配合語言復健，如聽音訓練、讀唇技巧、發聲方法等課程，方能使聽障幼童開始辨識新的語音訊息。由此可見，人工電子耳植入術的成功，不單是指手術的順利完成，更需配合術後聽能復健的完整課程。

另外人工電子耳的手術亦有併發症的可能，故術後必需注意是否有如下的症狀出現，並做好傷口照護。併發症包括：

（1）傷口皮瓣發炎、感染，嚴重時需移除人工電子耳植入物。（2）腦膜炎。（3）植入電極放置不當或折壓傷。（4）術後持續頭暈疑有外淋巴液漏或廔管時。