Copyright © 2004, Barrow Neurological Institute

Auditory Implantation ince 1979 auditory brainstem im- Gregory P. Lekovic, MD, PhD, JD Splants (ABIs) have provided pros- L. Fernando Gonzalez, MD thetic for patients deafened by † Mark J. Syms, MD neurofibromatosis-2 (NF-2). The first † C. Phillip Daspit, MD ABI was a comparatively primitive, sin- Randall W. Porter, MD gle-channel device that aided users by increasing awareness of environmental Auditory brainstem implants (ABIs) can restore meaningful hearing to patients sounds and lipreading. Contemporary deafened by neurofibromatosis type 2. These devices are similar to cochlear multichannel ABIs afford a level of per- implants on which their design is based. Current multichannel ABI technology formance comparable to that achieved affords a level of performance in aiding speech comprehension similar to that of- with single-channel cochlear implants, fered by single-channel cochlear implants. ABIs differ from cochlear implants in that is, the ability to discriminate envi- that the brainstem implants stimulate the cochlear nuclei directly, bypassing the ronmental sounds, marked improve- cochlear . Multichannel ABIs can be implanted at the time of first or second ment in lipreading, and limited open- side surgery for tumors involving the auditory nerve. Most surgeons favor a trans- set speech comprehension. Some ABI labyrinthine approach for ABI placement, because the stimulating leads need to users can even communicate on the be implanted within the of the . At this location, the telephone. This article reviews the de- ventral can be stimulated along its lateral to medial axis. Intra- velopment of ABIs, emphasizing rele- operative monitoring of brainstem auditory evoked potentials is essential and vant neuroanatomical and physiological helps confirm adequate positioning of the device. After programming, about 85% principles, intraoperative technique, re- of patients experience auditory percepts. Only a relatively rare, but significant, mi- lated surgical anatomy, clinical out- nority of patients is able to attain sound-only open-set speech comprehension with comes, and future directions for re- their ABI. Most experience a significant improvement in open-set speech com- search. prehension when used as an adjunct to lipreading. Speech comprehension con- tinues to increase as long as 8 years after device implantation. More than 90% of recipients use their ABI daily. Most are satisfied with their decision to obtain an History of ABIs ABI and would recommend the device to others. At the time of this writing, more than 400 ABIs have been placed world- Key Words: acoustic neuroma, auditory brainstem implantation, auditory wide.17 The first ABI implant was a sim- prosthesis, neurofibromatosis type 2, vestibular schwannoma ple ball electrode implanted into the pa- renchyma of the cochlear nucleus at the House Institute in 1979. This elec- trode migrated from its implantation site, and the design was soon modified into a pair of platinum plates with a syn- thetic mesh backing. Subsequent iter- ations of ABI design culminated in the development of multichannel implants composed of 8 to 21 platinum discs em- bedded in plastic with a synthetic mesh backing, depending on the manufac- Division of Neurological Surgery and †Section of Neurotology, Barrow Neurological Institute, St. turer or model. Joseph’s Hospital and Medical Center, Phoenix, Arizona In 1994 a clinical trial was begun in

40 BARROW QUARTERLY • Vol. 20, No. 4 • 2004 Lekovic et al: Auditory Brainstem Implantation the to evaluate the safety the ear above the canthomeatal line. A ing loss is not a deciding factor (i.e., and efficacy of multichannel ABIs. This second component consists of micro- there is no audiological cut-off for ABI trial was concluded in 2000 and culmi- phone, speech processor, and radio- placement). Other factors also distin- nated in the Food and Drug Adminis- transmitter coil that detects sound, con- guish optimal ABI candidates: good tration (FDA) approving the Nucleus verts it to a digital signal, and transmits overall health, acceptable vision (because 24 Contour (Cochlear Corporation, it to the receiver, respectively. The the ABI may aid most with lipreading), Englewood, CO) and Nucleus 22 (Co- transmitter attaches to the receiver-stim- high motivation, excellent family sup- chlear Corporation, Englewood, CO) ulator by a magnet. Once an ABI is im- port, acceptable anatomical status, and for implantation via the translabyrin- planted, monopolar cauterization is an interest in spoken communication. thine approach for the treatment of strictly forbidden from use for fear of Because the ABI creates an ‘unnatural’ deafness related to NF-2. Currently, the damaging the electrode, brain, or both. quality of sound, many users are disap- Nucleus 24 is the most widely implant- Recently, the magnet has been replaced pointed with it at first. High motiva- ed ABI in the world, including North with a nonmagnetic plug at surgery, and tion and excellent family support are America, , and the European the transmitter coil is fixed to the scalp important to ensure that users do not Union. Other available ABIs include the with adhesive. These changes permit drop out of the ABI program. MXM Digisonic (Laboratories MXM, MR imaging from the outset. These issues are exemplified in the Valaurious Cedex, France), Med-EL ABIs are not activated until a patient House experience with placing ABIs in (Med EL Corporation, Research Tri- recovers from surgery. Because of con- teenagers.17 Of 21 teens implanted, four angle Park, NC), and Clarion (Ad- cerns about the potential activation of dropped out of the program. One later vanced Bionics, Sylmar, CA). So far no brainstem structures, many centers pre- returned and has become an above av- evidence suggests that the efficacy of the fer that the electrode be activated in a erage ABI user as a result of strong fam- various multichannel ABIs differs. monitored setting. After successful ABI ily support and encouragement. Qual- implantation, medical and audiological ities most characteristic of program follow-up is performed at least every 3 dropouts included low motivation and Design of ABIs months for the first year and then an- poor family support. However, an im- All ABIs share certain features re- nually thereafter. portant lesson from the House experi- gardless of specifications (Fig. 1). The ence has been that the ideal candidate is basic electrode itself is placed within the self-motivated to hear again rather than lateral recess of the fourth ventricle and Indications for ABIs motivated for the benefit of family connected via a cable implanted into a The FDA has approved the ABI for members. groove in the temporal bone to a re- patients with NF-2 who are 12 years or The only absolute contraindication ceiver-stimulator. The latter is seated in older who have reasonable expectations to the placement of an ABI is an active the bone of the skull behind the helix of and motivation. The degree of hear- infection. Relative contraindications

Ground electrode

Paddle Microphone Speech processor- digitizer

Transmitter coil

A Receiver-stimulator B Figure 1. (A) The auditory brainstem implant consists of a radio receiver-stimulator that is implanted in the temporal bone. A ground electrode is inserted under the temporalis muscle, and the multichannel brainstem implant paddle is inserted into the lateral recess of the fourth ventricle. (B) Sound is picked up at the pinna by a microphone that sends the signal to a speech-processor/digitizer. The latter sends the signal to the brainstem implant receiver through the transmitter coil. Photographs courtesy of Cochlear Ltd.

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are rare and include patients who may on the first side. If the device is im- Marangos et al.15 examined 19 meet the formal criteria but who lack properly positioned within the lateral with promontory testing in patients adequate support or motivation, as out- recess of the fourth ventricle, does not with profound bilateral deafness. The lined above. As discussed later, if the co- elicit auditory sensations, or creates in- promontory tests were positive in five chlear nerve can be preserved intact after tolerable side effects that prevent its use, of six ears that had not undergone pre- resection of an acoustic neuroma, place- then the contralateral side can be im- vious surgery and in three other surgi- ment of a cochlear implant may be in- planted when surgery is performed on cally treated ears with residual tumor. dicated if promontory testing is positive. the second side. The patient thereby The patient who responded negatively The FDA has approved the use of has a second chance to obtain a func- on promontory testing but who had ABIs only in the setting of NF-2. How- tioning implant. Conversely, if the first undergone no previous surgery had bi- ever, off-label use of the device has been side is implanted and functions well, the lateral acoustic neuromas causing pro- reported (predominantly in Europe) for user can become accustomed to the de- found brainstem compression. A pa- other indications, including deafness re- vice while still able to hear with the tient presenting with deafness one year lated to bilateral skull base trauma,3 spo- other ear. This situation may help the after undergoing a subtemporal ap- radic acoustic neuroma in patients with patient to acclimatize to and interpret proach in which hearing was preserved only one hearing ear,4 the ABI sound. However, most patients had a positive promontory test. This hypoplasia or aplasia,2,5 cochlear ossifica- implanted during surgery on the first patient was fitted with a cochlear im- tion,11 bilateral auditory nerve deafness,22 side do not become daily users of ABI plant and had an excellent response. or involvement with other neoplastic until their deafness is bilateral. Marangos et al.15 concluded that the syndromes such as Bourneville’s disease goal of first-side surgery should be to pre- and von Hippel-Lindau disease.15 Promontory Testing serve hearing or at least the anatomical Since ABIs were approved by the Promontory testing is the direct stim- integrity of the auditory nerve to iden- FDA, they have been successfully im- ulation of the cochlear promontory via tify patients who will respond to cochle- planted at an increasing number of do- an electrode placed surgically in the mid- ar implantation. Preservation of the co- mestic and international centers. In Oc- dle ear. The procedure is performed un- chlear nerve depends on the size of the tober 2004, the first ABI was placed at der local anesthesia through a small tumor. Small tumors are usually found in our institution (Fig. 2). myringotomy and can distinguish be- patients with a known family history of tween cochlear and retrocochlear causes NF-2. In sporadic cases, the tumors are First Side vs. Second Side Surgery of deafness. In a negative promontory often diagnosed when too large for the Initially, ABIs were placed at the time test, pitch is not perceived in response to cochlear nerve to be preserved. They of second side surgery for tumor re- direct electrical stimulation of the co- further argued that ABI should be re- moval. Now more than a third of ABIs chlea. The finding implies a retroco- served for patients with a negative pre- are placed during the first surgery (i.e., chlear cause of deafness. Conversely, in operative promontory test, patients in while the patient still has serviceable a positive test, pitch is perceived in re- whom the cochlear nerve cannot be pre- hearing on the contralateral side).18 sponse to stimulation, indicating that the served, or patients whose deafness is both There are several advantages to plac- cochlear nerve is capable of transmitting cochlear and retrocochlear (e.g., related to ing the device during tumor removal tonal information centrally. tumor infiltration of the auditory nerve).

A B Figure 2. (A) Intraoperative views through the microscope as the auditory brainstem implant electrode paddle is positioned within the lateral recess and (B) as the receiver is secured to the temporal bone.

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Neuroanatomy and Phys- branch to the . recognize different pitches. Alterna- iology of Audition In contrast, low-frequency fibers bifur- tively, if improved speech comprehen- Sound is represented spatially in the cate superficially within the substance sion requires such ‘on’ and ‘off’ signals . This spatial relation- of the . All pri- or other more complicated stimuli, then ship, called , is maintained with mary afferent fibers bifurcate within the strategies such as penetrating ABIs that fidelity in ascending neuroanatomical ventral cochlear nucleus before termi- focus on the tonotopic organization of pathways from the peripheral auditory nating. the cochlear nuclei may not improve end organ (the organ of Corti in hu- If characteristic frequency is plotted speech comprehension. mans) to the primary . against position in the brainstem, the In the organ of Corti, hair cells line the cochlear nuclei are composed of isofre- quency laminae, or layers of neurons basal membrane of the in a Surgical Considerations (like the layers of an onion) (Fig. 3). In tonotopic fashion. Hair cells respond- and Techniques ing best (i.e., with a characteristic fre- this tonotopic organization, the super- quency) to high pitches are located at ficial regions of the cochlear nuclei (the Surgical Anatomy the basal turn of the cochlea, and hair lateral and anterior laminae of the ante- The surgical goal of ABI implantation cells responding best to low frequencies rior and posterior divisions of the ven- is to position the electrode array on the are located at the cochlear apex. tral cochlear nucleus) represent low fre- surface of the cochlear nuclei in the lat- In his theoretical work on the nature quency sounds, whereas the deeper eral recess of the fourth ventricle (Fig 4). of music, Tonemfindungen, Helmholtz regions of the nucleus represent higher The landmarks for proper identification proposed that sound delivers a standing frequencies. Unfortunately, the aspect of the lateral recess include the origins of wave to the basement membrane and of the cochlear nuclei accessible to sur- the facial, vestibulocochlear, glossopha- that regionalized movements of this face electrode stimulation is therefore ryngeal, and vagus ; the flocculus structure responded to specific frequen- restricted to a very narrow range of fre- of the , the choroid plexus cies to determine tonotopy in the co- quencies. This limitation is the moti- exiting the foramen of Luschka, and the chlea. This model predicts that the hair vation behind the development of pen- taenia. However, these landmarks can cells of the cochlea are passive transduc- etrating electrodes for implantation. be severely distorted by tumor. ers of frequency. Although still widely In addition to the tonotopic organi- The simplest way to identify the fo- taught, this view is now understood to zation of the cochlear nuclei, the rich ramen of Luschka is to follow the ves- be incomplete. In fact, hair cells are dy- constellation of neuronal cell types and tibulocochlear nerve proximally. When namic, and various adaptations, includ- interconnections is only partly under- the nerve is cut, its stump can be iden- ing active motor processes and electri- stood. Many ABI recipients are able to tified and similarly followed. In a study cal tuning, determine their characteristic perceive pitch. Most speech is compre- of the in 100 frequency. These adaptations tune the hensible over a relatively narrow band human specimens, the distance between hair cells, such that they preferentially of frequencies. Although pitch ranking the facial and vestibulocochlear nerves depolarize in response to their charac- of multiple channels is thought to facil- was 4.7 mm ± 0.9 mm.12 The distance teristic frequency. Loud sounds, how- itate speech comprehension, speech between the vestibulocochlear and glos- ever, flatten their tuning curve. comprehension may be improved with sopharyngeal nerves was 5.5 mm ± 1.0 To preserve this tonotopic relation- multiple channels even if pitch ranking mm. Thus, if the root of the vestibulo- ship, ascending primary afferents of the is impossible, and the extent of pitch cochlear nerve itself cannot be identi- must maintain fidelity to ranking does not necessarily correlate fied with confidence, its root lies in a the characteristic frequency of the inner with ABI performance outcomes.13 The triangle approximately 5 x 6 mm with- hair cells that they supply. Thus the co- cochlear nuclei are composed of many in the origins of the facial and glosso- chlear division of the vestibulocochlear different neuronal populations, includ- pharyngeal nerves. nerve is composed of afferent fibers, ing fusiform cells, globular and spheri- In the same study12 the dimensions each of which represents a specific cal bushy cells, and octopus cells, among of the foramen of Luschka were about pitch-place within the cochlea. As these others. Many neuronal cell types with- 3.4 mm x 2.0 mm. The foramen was fibers enter the brainstem, they termi- in the cochlear nuclei are specialized to wide open in only 24% of cases, open nate in regions of the cochlear nucleus respond to information other than only after incision of the arachnoid in that again reflect spatial segregation of strictly pitch. For example, some cells 53%, functionally closed (requiring ex- frequency encoding. Specifically, affer- respond best to the onset of a sound tensive dissection) in 18%, and anatom- ents with a high characteristic frequen- stimulus, others to the cessation of such ically occluded in 5%. The taenia of the cy (in humans the upper limit of hear- a stimulus. This specialization may ex- choroid was present in 92% of speci- ing is about 20 kHz) plunge deep into plain why multiple channels may im- mens, and it required incision to access the ventral cochlear nucleus before bi- prove speech comprehension even if the the lateral recess in 51%. furcating and sending a descending patient is unable to use the channels to Importantly, Matthies et al.16 analyzed

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the outcomes of ABI placement as a Vestibulocochlear function of the amount of dissection re- nerve quired to identify and open the foramen of Luschka. There was no relationship between the density of arachnoid adhe- sions involving the foramen of Luschka and outcomes with the ABI. Howev- er, these data were obtained from a small Low-frequency fiber sample (n = 8) and may lack the power to demonstrate such a relationship. The cochlear nucleus extends from High-frequency fiber the floor of the fourth ventricle medial- ly to the entry zone of the vestibuloco- chlear nerve at the ventrolateral brain- stem surface. In an anatomical study of the cochlear nuclei of humans, Quester 19,20 Ventral and coworkers made thread measure- cochlear ments of the length of the cochlear nu- nucleus cleus complex from the auditory tuber- cle (which overlies the dorsal cochlear nucleus) to the entry zone of the ves- tibulocochlear nerve. The length of the cochlear nucleus was 12.8 mm ± 1.2 mm. The length of the nucleus locat- ed within the lateral recess (i.e., primar- ily the ventral cochlear nucleus and site of ABI placement) was 7.6 mm ± 1.5 mm. Thus the dimensions of current Dorsal cochlear generations of ABI (i.e., about 3 x 8 nucleus mm) are well suited to placement of the device completely within the lateral re- cess.

Surgical Approach The original clinical trial protocol called for ABI placement via a translab- Figure 3. Schematic representation of the cochlear nucleus complex (comprising the ven- tral and dorsal cochlear nuclei) and surrounding structures. Alternating shaded bands yrinthine approach, which remains the represent isofrequency laminae of afferent fibers and second-order neurons tuned to most popular approach. The translaby- low-frequency (short dashed line) and high-frequency (long dashed line) sounds. Be- rinthine approach offers the most direct cause of the topography of the cochlear nucleus (tonotopy), a paddle electrode placed angle of attack to the lateral recess of the within the lateral recess tends to contact low isofrequency laminae. High-frequency neu- fourth ventricle. However, some sur- rons, of which the dorsal cochlear nucleus is primarily composed, are consequently only partially accessible to paddle electrode stimulation. geons, particularly in Europe, have ad- vocated for alternative approaches to ABI placement. Chief among these al- include difficulty in placing the lead ap- clude superior visualization of the floor ternatives is the retrosigmoid or lateral propriately. In one series, two of three of the fourth ventricle and the absence suboccipital approach.6,7 electrodes placed via the retrosigmoid of scarring of the surgical corridor. The main argument for use of the approach required revision for malpo- Some authors have asserted that the dor- retrosigmoid approach is the potential sitioning.23 sal cochlear nucleus, which can be ob- to preserve the cochlea and cochlear Other innovations to ABI placement served directly via a subtonsillar ap- nerve if promontory testing indicates include subtonsillar or telovelar ap- proach where it is found under the that the patient may benefit from a co- proaches via a midline suboccipital cra- auditory tubercle, is a superior target for chlear implant rather than an ABI.14 niotomy21 and ABI placement through ABI placement, because the ventral co- Other advantages include shorter oper- one of the standard approaches but with chlear nuclei are partially obscured by ative times and less risk of cerebrospinal endoscope-assisted technique.9 The ad- the cerebellar peduncle. However, the fluid (CSF) leakage. Its disadvantages vantages of a subtonsillar approach in- dorsal cochlear nucleus responds best to

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Facial nerve Stump of

Facial nerve Ventral cochlear nucleus Dorsal cochlear Vestibulocochlear nucleus nerve Ventral & dorsal cochlear nuclei Inferior cerebellar peduncle

Flocculus Choroid plexus Electrode in foramen of paddle Luschka in lateral recess A B

Figure 4. (A) Schematic representation of the right cerebellopontine angle. The ventral and dorsal cochlear nuclei border the lateral re- cess and extend from the anterolateral aspect of the brainstem to the floor of the fourth ventricle. Surgical landmarks for identifying the lateral recess include the flocculus of the cerebellum and the choroid plexus within the foramen of Luschka. (B) The auditory brainstem implant is placed within the lateral recess of the fourth ventricle. The leads of the paddle electrode are apposed to the dorsolateral sur- face of the ventral and dorsal cochlear nuclei. The electrode is held in place with a Teflon plug (not depicted). higher frequencies, including those out- endoscope can be wielded to excellent The auditory brainstem response side the normal range used in speech. effect in such situations because a 30- (ABR) is thought to reflect the sum- Regardless of the suitability of the degree angled endoscope gives the sur- mated activity of ascending portions of dorsal cochlear nucleus as a target for geon the ability to look ‘around the cor- the auditory system. Classically, five ABI, the telovelar approach, in which ner.’ Although theoretically appealing, ABR waves (i.e., waves I-V) are thought the inferior medullary velum is split and use of an endoscope is hindered by the to reflect the activity of the cochlea, co- the taenia are divided from their attach- necessity of holding the camera and ad- chlear nerve, cochlear nuclei, olivary ment to the floor of the fourth ventri- vancing the ABI paddle parallel to the nuclei, and nuclei of the lateral lemnis- cle, requires a midline suboccipital cra- scope before the device can be placed. cus, respectively. In the setting of ABI niotomy or craniectomy. However, an Advances in endoscopy may increase the placement, the cochlear or cochlear acoustic neuroma cannot be resected via use of endoscopically assisted proce- nerve waves of the ABR are not ex- such an approach. An ABI can only be dures. pected because the cochlear nuclear placed if the surgeon is willing to ex- complex is stimulated directly.24 tend a retrosigmoid craniotomy inferi- Intraoperatively, the first wave of the orly, possibly including a C1 laminec- Intraoperative Monitoring ABR seen would be wave III, that of tomy. Nevertheless, the telovelar or For several reasons intraoperative the cochlear nuclei. Ideally, three waves subtonsillar approach may be considered monitoring of evoked auditory poten- would be expected: those of the co- when the surgeon anticipates too much tials and monitoring of the trigeminal, chlear nuclei (III), olivary nuclei (IV), scarring or anatomical distortion relat- facial, and glossopharyngeal nerves is and nuclei of the (V). ed to the tumor to allow accurate place- crucial during ABI placement.1,10 Mon- In practice, anywhere between one and ment of the electrode through either a itoring auditory brainstem responses can three responses, termed P1-P3, are transpetrosal or lateral suboccipital ap- corroborate accurate electrode place- seen.24 proach (i.e., when an ABI is to be placed ment, whereas monitoring neighbor- The presence of one or more re- after the operation for tumor resection). ing may detect inadver- sponses helps corroborate proper elec- In a cadaveric study of endoscopical- tent stimulation of regional structures. trode placement. However, there are ly assisted translabyrinthine, retrosigmoid, When the labyrinth has not been drilled pitfalls in the interpretation of intraop- and even middle fossa approaches, Fried- and the cochlear nerve has been pre- erative responses, including the presence land and Wackym9 demonstrated that served, promontory testing also may be of motor contamination (i.e., motor re- visualization of the lateral recess is facil- useful to predict the possible benefit of sponses transmitted from inadvertent itated with the use of an endoscope. An cochlear implantation. stimulations of the trigeminal, facial,

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glossopharyngeal, or vagus nerves). auditory side effects, most commonly trials of Digisonix, Med-El, and the Motor responses can be differentiated paresthesias involving the ipsilateral body, Nucleus 24 ABIs). European centers from auditory responses by both laten- were common. They are attributed to have implanted the devices for more in- cy and amplitude. Higher amplitude stimulation of the inferior cerebellar pe- dications than have been used in the waves with longer latencies are indica- duncle, which lies close to the cochlear United States. European also have used tive of a motor response. nuclei (Fig. 4). the retrosigmoid approach more often ABR monitoring is best understood In the House Ear Institute experi- than the translabyrinthine approach. as an adjunct to anatomical means of lo- ence with the long-term follow-up of Nevertheless, the European experi- calizing the cochlear nuclei. Its role is 71 patients receiving an eight-electrode ence broadly mirrors the experience in simply to confirm that the ABI stimu- ABI, 10 patients did not participate in the United States in terms of rates of lates the auditory brainstem, with mini- follow-up.18 Of the remaining 61 pa- surgical morbidity and functional out- mal or no stimulation of other structures. tients, 6 detected no auditory sensations comes. Unfortunately, heterogeneity in No correlations between the number or after implantation. Two CSF leaks were audiological tests performed makes di- quality of waveform responses (i.e., P1, treated by pressure bandage and lumbar rect comparison of the audiological tests P2, P3) and the efficacy of ABI have drainage, and one patient developed impracticable. The combined results of been found. Moreover, as long as the . Eventually, 24% of the elec- the European Nucleus (i.e., 21-channel surgeon is confident of adequate elec- trodes were inactivated because of ABI) experience (n = 58), the Digisonix trode placement based on reliable ana- nonauditory perception. clinical trial results (n = 14), and the tomical landmarks, even the complete ABI patients benefited from significant MED-EL clinical trial results (n = 16) absence of ABR waves does not neces- qualitative and quantitative improvements yielded 88 patients. Three patients were sarily predict that the ABI will fail to in hearing, including awareness of envi- implanted for indications other than impart useful hearing. ronmental sounds and improved closed NF-2, including bilateral auditory neu- and open set speech recognition. Few ropathy and miscellaneous tumor syn- patients, however, demonstrated signif- dromes affecting the vestibulocochlear icant open-set speech recognition in the nerve bilaterally. Three patients died Surgical Results sound-only mode. Environmental sound and one wound infection required ex- American Experience discrimination was at or above 50% on plantation of the device. Of 24 patients The United States clinical trial of the closed-set tests. On a closed-set test of who underwent a retrosigmoid crani- multichannel ABI, composed of data col- word recognition (the MTS test), 87% otomy for electrode placement, three lected from 10 domestic centers, consti- of patients scored significantly higher required revision surgery. One patient tutes the largest published series. It in- than chance. Similar to the results of had transient but significant symptom- volved 92 patients receiving the Nucleus the clinical trial in the United States, the atic cerebellar swelling. Between 86 and 22 (Cochlear Corporation, Englewood, mean improvement in CUNY sentence 100% of patients experienced auditory CO), eight-electrode ABI, 85% of whom recognition scores over lipreading alone sensations, 63% to 100% of whom were reported receiving auditory sensations.8 was 26%. daily users. All patients who received At their six-month follow-up examina- Perhaps the most significant finding auditory percepts demonstrated im- tion, 93% of patients receiving auditory from the House experience, the largest proved speech recognition in conjunc- sensations demonstrated improved lip- single center experience in the world, tion with lipreading. A limited number reading, reflected in a mean improvement was that a significant proportion of pa- of patients achieved some open-set of 24% on the CUNY sentence test (an tients continued to show improvement sound-only speech recognition. open-set speech comprehension test) in audiological indices as long as 8 years over lipreading alone. Importantly, 85% after implantation. This finding testi- of patients reported satisfaction with their fies to the use-dependence of improving Future Directions ABI, and 74% would recommend it to speech recognition. In the last decade ABI research has others. Of patients who used the device focused on increasing the number of daily (97% of those patients implanted at European Experience available channels for stimulation. The the second surgery (i.e., deaf patients), The European experience with ABI ideal number of channels has not yet 65% reported using the device more than differs from the experience in the Unit- been established and whether more 8 hours a day. ed States in several significant ways. The channels necessarily correlate with bet- In 13 patients the failure of the device latter clinical trial primarily was per- ter chances of comprehending speech is to elicit auditory stimulation was attrib- formed with the Nucleus 22 eight-elec- unclear.13 The biggest innovation in uted to improper electrode placement trode ABI while in Europe 12-, 16- and ABI design has been the recent devel- related to distorted anatomy. There 21-electrode multichannel ABIs have opment of penetrating electrodes for were two deaths, although neither were been placed preferentially over eight- stimulation of regions of the ventral co- directly attributable to the ABI. Non- electrode models (including the clinical chlear nucleus complex that have been

46 BARROW QUARTERLY • Vol. 20, No. 4 • 2004 Lekovic et al: Auditory Brainstem Implantation inaccessible to surface electrodes. Such 14. Marangos N, Stecker M, Laszig R: Topodiagno- References sis of deafness: Strategy for treatment of neu- electrodes offer the potential of stimu- rofibromatosis type 2. J Laryngol Otol 114 1. Brackmann DE, Hitselberger WE, Nelson RA, et lating higher frequency cell populations (Suppl 27):3-7, 2000 al: Auditory brainstem implant: I. Issues in surgi- and may therefore increase the number cal implantation. Otolaryngol Head Surg 15. Marangos N, Stecker M, Sollmann WP, et al: Stim- of patients receiving ABI who are able 108:624-633, 1993 ulation of the cochlear nucleus with multichan- nel auditory brainstem implants and long-term 2. Colletti V, Carner M, Fiorino F, et al: Hearing to perform pitch scaling. Even though results: Freiburg patients. J Laryngol Otol 114 restoration with auditory brainstem implant in (Suppl 27):27-31, 2000 fewer electrodes are used, such an in- three children with cochlear nerve aplasia. Otol creased range of pitch sensation might Neurotol 23:682-693, 2002 16. Matthies C, Thomas S, Moshrefi M, et al: Audito- ry brainstem implants: Current neurosurgical ex- facilitate speech recognition. 3. Colletti V, Carner M, Miorelli V, et al: Auditory brain- periences and perspective. J Laryngol Otol 114 stem implant in posttraumatic cochlear nerve (Suppl 27):32-36, 2000 avulsion. Audiol Neurootol 9:247-255, 2004 17. Otto SR, Brackmann DE, Hitselberger W: Audi- 4. Colletti V, Fiorino F, Carner M, et al: Auditory brain- tory brainstem implantation in 12- to 18-year-olds. Conclusions stem implantation: The University of Verona ex- Arch Otolaryngol Head Neck Surg 130:656- perience. Otolaryngol Head Neck Surg 127:84- ABIs restore meaningful hearing to 659, 2004 96, 2002 patients deafened by NF-2. Almost all 18. 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Quester R, Schroder R, Klug N: Optimization of sigmoid approach for auditory brainstem implant. only speech comprehension to enable microsurgical operation technique to insert au- J Laryngol Otol 114 (Suppl 27):37-40, 2000 use of the telephone. ditory brainstem implants, taking into account Appropriate expectations and moti- 8. Ebinger K, Otto S, Arcaroli J, et al: Multichannel the results of a morphometric study [in German]. auditory brainstem implant: US clinical trial results. HNO 52:706-713, 2004 vation on the part of the patient is J Laryngol Otol 114 (Suppl 27):50-53, 2000 21. Seki Y, Samejima N, Kumakawa K, et al: Subton- mandatory. Many ABI patients are ini- 9. Friedland DR, Wackym PA: Evaluation of surgical sillar placement of auditory brainstem implant. tially discouraged by the quality of approaches to endoscopic auditory brainstem Acta Neurochir Suppl 87:85-87, 2003 implantation. Laryngoscope 109:175-180, 1999 sound heard with an ABI. They must 22. Sollmann WP, Laszig R, Marangos N: Surgical 10. Frohne C, Matthies C, Lesinski-Schiedat A, et al: understand that participation in their experiences in 58 cases using the Nucleus 22 Extensive monitoring during auditory brainstem multichannel auditory brainstem implant. J auditory rehabilitation program is cru- implant surgery. J Laryngol Otol 114 (Suppl Laryngol Otol 114 (Suppl 27):23-26, 2000 27):11-14, 2000 cial to continue to improve their profi- 23. Vincent C, Zini C, Gandolfi A, et al: Results of the ciency with the device. Such improve- 11. Grayeli AB, Bouccara D, Kalamarides M, et al: Au- MXM Digisonic auditory brainstem implant clini- ditory brainstem implant in bilateral and completely cal trials in Europe. Otol Neurotol 23:56-60, ment can be expected to continue over ossified cochleae. Otol Neurotol 24:79-82, 2003 2002 many years. 12. Klose AK, Sollmann WP: Anatomical variations of 24. Waring MD: Auditory brain-stem responses landmarks for implantation at the cochlear nucle- evoked by electrical stimulation of the cochle- us. J Laryngol Otol 114 (Suppl 27):8-10, 2000 ar nucleus in human subjects. Electroen- 13. Kuchta J, Otto SR, Shannon RV, et al: The multi- cephalogr Clin Neurophysiol 96:338-347, channel auditory brainstem implant: How many 1995 electrodes make sense? J Neurosurg 100:16- 23, 2004

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