Cochlear Implants to Treat Deafness Causedby Vestibular Schwannomas
*Payal Mukherjee, *James D. Ramsden, †Nick Donnelly, †Patrick Axon,‡Shakeel Saeed, §Paul Fagan, and kRichard M. Irving
*John Radcliffe Hospital, Oxford; ÞAddenbrookes Hospital, Cambridge; þUniversity College Hospital,National Hospital for Neurology and Neurosurgery, Royal National Throat, Nose and Ear Hospital, London,
U.K.; §St. Vincent’s Hospital, Sydney, Australia; and kQueen Elizabeth Hospital, Birmingham, U.K.
Objective: Rehabilitation of hearing is complicated in patientswith profound bilateral hearing loss in the presence of sporadicvestibular schwannoma (VS) or neurofibromatosis 2 (NF2), espe-cially if the tumor does not need to be removed. We present theoutcome of patients who have had a cochlear implant in the tumoraffected ear without removal of the primary tumor.Design: This is a retrospective multicentre study investigatingoutcomes of cochlear implantation in profoundly deaf patientswith vestibular schwannoma in the implanted ear.Materials and Methods: Out of 11 implanted patients, 5 re-quired no treatment for their tumor, whereas 6 had previouslyundergone radiotherapy. Nine patients experienced NF2, and 2had unilateral VS in the only hearing ear. Postoperative hearingwas assessed with open and closed set speech discrimination,
including City University of New York (CUNY) in noise andBamford, Kowal and Bench (BKB) sentence scores.Results: Patients with untreated lesions experienced markedimprovement in their BKB and CUNY scores in the implantedear and were daily cochlear implant users. The improvementwas less consistent in the patients who had radiotherapy whereonly 1 patient attained open set speech discrimination.Conclusion: Patients with unilateral VS (sporadic or those affectedwith NF2) whose tumor status was stable, benefited from co-chlear implantation in their tumor-affected ear. Patients who hadradiotherapy also benefited from CI, but their outcomes werevariable. Key Words: Cochlear implantsVHearing outcomeVObservationVRadiationVUntreatedVVestibular schwannoma.Otol Neurotol 34:1291Y1298, 2013.
Hearing rehabilitation in sporadic vestibular schwan-noma (VS) when it affects the only hearing ear poses manychallenges. Patients with neurofibromatosis 2 face an evenmore complex management dilemma. An auditory brain-stem implant (ABI) may be an option after tumor exci-sion; however, hearing results may be limited to detectionof environmental sounds or as an aid to lip reading, andonly a few patients get open set speech discrimination (1).A cochlear implant (CI) may be an option in those rarecases where the cochlear nerve has been left intact aftertumor resection or in those cases that have been treatedwith radiotherapy (2Y4). In addition, some authors advo-cate the use of a CI in preference to an ABI, not only be-cause of better open set speech discrimination with CI butalso because of the reduced surgical morbidity, risks, andtime associated with the operation (5).
The effectiveness of CI in untreated VS is unknown.Trotter and Briggs (2) cited case reports of 3 patients withNF2 who were implanted postradiotherapy. All 3 weredaily cochlear implant users. Lustig et al. (4) had alsoreported similar results in their experience of 2 patients.Neff et al. (3) in a large multicenter study reported a caseseries of 6 patients who underwent surgery of their tumorswith cochlear nerve preservation. All these patients re-ceived benefit from their cochlear implants. The studyshowed that, despite interruption of blood supply to thecochlear nerve and loss of postoperative hearing, a CI couldprovide significant improvement to hearing. An interestingobservation was made by Helbig et al. (6) who implanteda patient with sporadic VS that required no treatment forthe tumor. The contralateral ear was implanted first. Thetumor-affected ear was sequentially implanted. On 6-monthfollow-up, the patient attained 80% speech scores on mono-syllabylic testing, and the tumor side matched the resultsof the nontumor side.
One of the factors influencing the hearing outcome ofa cochlear implant is the length of time an ear has beendeaf (7). Therefore, a recently deafened ear with a tumormay give a good or better outcome than the long deafened
Address correspondence and reprint requests to Payal Mukherjee,M.S., FRACS (ORL-HNS), 42The Esplanade, Thornleigh, Sydney, NSW,Australia 2120; E-mail: [email protected] of Funding: No separate funding was used to finance this
study. None of the authors had any financial interests in the results of thestudy or any information presented in the manuscript.
Otology & Neurotology34:1291Y1298 � 2013, Otology & Neurotology, Inc.
contralateral nontumor ear, especially in light of findingsof equal outcome of hearing in tumor and nontumor side(6). NF2 patients are surgically often very challenging, andCI may provide an alternate safer rehabilitation.
METHODS
This is a retrospective multicenter study undertaken to in-vestigate hearing outcomes in patients implanted with CI intheir tumor-affected ear in 2 groups. First, patients whose tumorshave been stable and required no active treatment, and second,patients whose tumors have been implanted after they have beenstabilized after radiotherapy. The inclusion criteria were bilateralprofound sensorineural hearing loss in the setting of NF2 or asporadic vestibular schwannoma with a contralateral dead ear.All patients had stable tumors, with stable tumors being de-
fined as tumors that had no growth for at least 2 years. Patientswere assessed for CI candidacy only after this period, and hence, afurther period passed of observation before they were implanted.Patients with NF2 had a longer follow-up and observation period.They only became candidates for CI once their only hearing earlost hearing, but their total period of observation of the ipsilat-eral tumor would have been far longer as they would have beenregularly reviewed in the NF2 clinic for their bilateral VS as wellas other tumors.Postoperative hearing was assessed with open and closed set
speech discrimination, including City University of New York(CUNY) in noise and Bamford, Kowal and Bench (BKB) sen-tence scores. Follow-up audiogram was conducted at 3, 6, and12 months. Their average hearing threshold (referred to as puretone average or PTA) was also calculated as per American acad-emy guidelines (AAO-HNS) with average decibel hearing at0.5-, 1-, 2-, and 3-kHz frequency range.
RESULTS
There were 11 patients in the entire series, of which, 9were affected with NF2. None of the tumors were activelygrowing.
The results were stratified into 2 groups according tothe disease burden on the CI candidate ear. The first group,group A, were the untreated VS patients (5 patients), ofwhom, 2 had sporadic VS, and 3 had NF2. In this group,tumors that occupied the cerebellopontine angle (CPA)were all less than 1.5 cm in size. The second group, groupB (6 patients) were the ipsilaterally irradiated patientswho were all affected with NF2. These patients had a spec-trum of complexity but generally had tumors, which requiredtreatment to the ipsilateral side, patients with aggressivephenotypes, patients who presented in a pediatric age group,and patients with multiple comorbidities and other sensorydeficits.
All patients were managed in multidisciplinary teams.Patients with NF2 were managed in specialized NF2clinics, whereas sporadic patients were managed in a cra-nial base multidisciplinary team. Implant choice dependedmainly on individual patient preference and to a lesser ex-tent on the practice of different units. All patients were pre-viously deaf in the contralateral ear. The contralateral sidesof all the NF2 patients except 2 had been previously op-erated on and had no functional hearing. The 2 patients
who were exceptions had large tumors on the contralateralside and were awaiting urgent contralateral tumor removalon that side. The sizes were 5.4 and 4.5 cm, respectively(Patients 5 and 6; Table 2). They were implanted with a CIon the stable irradiated side, with a view that if unsuc-cessful, they would be considered for an ABI placementduring tumor removal on the contralateral side. These 2patients who were considered for ABIs were assessed in2 independent multidisciplinary specialized NF2 teams(one of these teams is a specialized ABI center) and prog-ressed to CI after consensus was reached.
There were some limitations to data collection. Be-cause this was a multicenter study and the data werecollected retrospectively, not all patients had PTA mea-sured. Some centers did not routinely measure hearingthresholds especially in situations where speech scoreswithout lip reading was zero anyway. Furthermore, wedid not have tumor measurements for 2 patients withintracanalicular tumors. Tumor measurements were rou-tinely made for the CPA component of tumors, as it is thismeasure that has been traditionally used to guide inter-vention. The intracanalicular size had therefore not beenroutinely documented. In the above 2 cases, it was alsodifficult to rectify this by reviewing the original films asthe imaging was recorded on hard copies and no longeravailable for review.
Group APatients in this group attained an improvement in open
set speech discrimination, although one had a languagedisorder as a result of NF2 and could perform audiometryeffectively but not speech testing.
The first patient (Table 1) had recently lost aidable hear-ing because of a 4-mm sporadic IAC tumor, and the con-tralateral ear had been deaf for more than 10 years. She hadsome usable hearing in that ear, so she was implanted inher tumor-affected side after promontory stimulation con-firmed a functioning nerve. She had the best result of theentire patient set with BKB scores at 12 months measuring99% in quiet without lip reading from 36% preoperatively.
The second patient was diagnosed with a small spo-radic CPA lesion when she presented for CI assessmentafter losing hearing in her only hearing ear. The contra-lateral ear had been deaf since childhood. Her tumor-free ear was implanted first, and she did poorly, whichresulted in implanting the tumor-affected side as this hadonly recently lost hearing. Although she did better in thisside compared with the other, her additive benefit whenshe used both implants was far greater than when using 1implant alone. This effect was sustained at 12 months.
The next 3 patients were NF2 patients whose implantedipsilateral ears had tumors that were untreated.
Patient 3 had an IAC lesion only with the contralateralear having no serviceable hearing after surgery 13 yearsago. The lesion was filling the IAC completely but notexpanding it. Her speech discrimination scores improvedpostoperatively, and when combined with lip reading, sheexperienced a great improvement to her overall commu-nication skills. She was able to return to bingo and win.
Patient 4 had a CPA lesion with no serviceable hearingin the contralateral ear after surgery 9 years ago. She wasdiagnosed with a language disorder secondary to the dis-ease. Her speech scores were therefore very poor, with BKBscores without lip reading being zero, although her postop-erative PTA improved to 30 dB from 100 dB preoperatively.
Patient 5 had a 10-mm CPA lesion with no serviceablehearing. The contralateral ear had partial resection of tumorin 1981 and had been stable. His BKB scores improved to98% in quiet and 68% in noise without lip reading. Hispreoperative scores were 44% aided with lip reading. Hewas a telephone user and was using an MP3 player throughhis implant when he presented for follow-up.
These patients were not considered for any form oftreatment on their ipsilateral side because their tumors werestable. This was despite the fact that some patients wererelatively young (Patients 1, 4, and 5 who were 58, 61, and65 yr old, respectively) as it was felt that they may not re-quire an intracranial procedure for treatment. Patient 1 hada small sporadic intracanalicular lesion, which was unlikelyto ever grow, although he was young. Patients 4 and 5, inaddition, were NF2 patients and had other comorbiditiesand preferred not to undergo surgery to the tumors if possible.
Group BOf the 6 NF2 patients, 3 had tumors 1.5 cm or less. The
others had lesions, although stable, measuring 1.9, 2.3,and 3.7 cm, respectively. These patients were also pediat-ric at age of presentation and had more aggressive pheno-types with multiple comorbidities and other sensory deficits.Three of the 6 patients had also lost their hearing eitherimmediately or within 12 months after radiotherapy. Ofthese, one was immediate, and this patient had stereotacticradiotherapy. The other 2 patients had gamma knife treat-ment and lost all aidable hearing during 12 months afterradiation.
Only 1 patient in this group attained open set speechdiscrimination. This patient had a 1.3-cm tumor in theCPA. The contralateral tumor had translabyrinthine removal10 years before and had no serviceable hearing. Her BKBscores were 82% in quiet and 52% in noise without LR(Table 2).
The other 5 patients could detect environmental soundonly. Those with vision improved their lip reading scores.Patient 5 (Table 2), for instance, was awaiting urgent re-moval of a contralateral 5.4 cm left VS, which was com-plicated by the fact that she also had a facial neuroma onthat side causing mild facial weakness. She also hadbilateral trigeminal, a right jugular foramen schwannoma, aright meningioma on posterior surface of temporal bone,and right ventriculoperitoneal shunt that was inserted be-fore radiation. Her ipsilateral (right) VS measured 2.3 cmand had been stable since irradiation, although she hadeventually lost all functional hearing in the months afterradiation. At the time of presentation and diagnosis, she al-ready had all these tumors. Within a few months of pre-sentation, she developed a right vagal palsy, and in viewof the fact that she had a left facial nerve schwannoma (and
so it was expected that she may lose some facial nervefunction on that side in due course), the patient preferredradiation for her ipsilateral VS. Her left VS grew within 6months of the radiation for her right VS and she also de-veloped left facial nerve palsy, so she was assessed for re-moval of her large Left VS and left facial nerve schwannoma.She was discussed in 2 separate specialized centers (ofwhich, one is an ABI center) with a view to either implanther with a cochlear implant on the ipsilateral side or anABI following tumor removal on the contralateral ear. Shehad a cochlear implant, and although she did not attainopen set speech discrimination postoperatively, she becamea more proficient lip reader. Her BKB scores with lip read-ing improved from 8% preoperatively to 36% postopera-tively at 6 months. She subsequently underwent surgery forher contralateral tumors and did not require an ABI.
Likewise, Patient 4 also improved her lip reading scores.She had lost her ipsilateral hearing after radiation of a 19-mmVS. She had multiple intracranial tumors, and her contra-lateral VS had been excised 3 years ago. She had a positiveresult on promontory stimulation preoperatively and wasimplanted 2 years after radiation. Although she did not at-tain open set speech scores, her BKB scores with lip readingimproved from 20% to 68% at 6 months.
Despite the fact that 5 of 6 patients did not attain openset speech discrimination, all patients found their implantsuseful and were daily users. One patient had device failure(Patient 6, Table 2). She was a 20-year-old woman with aleft-sided 3.7-cm tumor. Her tumor was irradiated 4 yearsago. A component of it had grown after irradiation but hadthen stabilized and had remained so. She was awaiting re-moval of a contralateral jugular foramen schwannoma and4.5-cm VS, which had recurred after a previous surgery.She already had nerve palsies of Cranial Nerves VII to Xand XII on this contralateral side. She was blind on this side(right) and slowly developing blindness in her left eye sec-ondary to pressure effects of her right CPA tumors. Becauseher left-sided facial and lower cranial nerves were the onlyfunctioning side, as her left eye was the only seeing eye,her left-sided tumor had been treated with radiotherapy,although it was on the larger side for radiation. This had pre-served the function of the cranial nerves on that side whilestabilizing the tumor and her management decision largelyinvolved further surgery to the right-sided lesions. Giventhe degree of brainstem distortion caused by the size of thetumors and particularly because this would be her third ope-ration on that side, the successful placement of an ABI wouldbe difficult. Her management rationale was the same asPatient 5. After discussion in 2 independent centers, she hada left-sided CI insertion (her left-sided tumor was stable)before her right-sided tumor removal. During operationforcochlear implantation, it was noted that she had intraco-chlear tumor, although this was unable to be visualized on thepreoperative MRI scan. She had good electrical responsespreoperatively. She derived no open set speech discrimi-nation from her CI but was able to hear the dog bark. Shefound this very useful, and although her device failed, shestrongly wanted the device replaced. Thus, although theoutcome of her CI was unquantifiable in terms of hearing
results, it made an important improvement in the patient’squality of life. She was incredibly sensory deprived, and theawareness of sound, although not enough to give her openset speech discrimination, made a dramatic difference to herlife. This patient had the most advanced disease in this series.
DISCUSSION
Management of sporadic and NF2-associated VS hasevolved over time with ‘‘wait and rescan,’’ an increasinglypopular treatment option for stable tumors. This is largelydue to better imaging, early detection, and increased aware-ness of the growth patterns of these lesions (8), with somestudies indicating that nearly two-thirds of tumors do notgrow (8). Studies also indicate that mean tumor growthrates range from 1.2 to 1.9 mm per year, that NF2 tumorsexhibit a higher annual growth rate (9Y12), and that intra-canalicular tumors do not exhibit significant growth com-pared with tumors occupying the CPA (13). Within these,there is a higher probability of growth if the tumor exceedsa size of more than 15 to 20 mm in the CPA (13Y15). The2 sporadic tumors in our series (tumor size intracanalicularand 1.2 cm at the CPA) were considered extremely unlikelyto grow beyond 2 years of observation for this reason.
Sporadic Tumors Affecting the Only Hearing EarSporadic VS with a bilateral profound loss, which is long
standing on the contralateral side creates a serious handi-cap. A high proportion of tumors are stable, whereas someothers may be stabilized with radiotherapy. These patients,who do not progress to surgical intervention for their tu-mors therefore, are not candidates for an ABI. If they haveno aidable hearing remaining, this group of patients hasno options for hearing rehabilitation apart from a cochlearimplant. This then creates debate over which side shouldbe implanted, the tumor-free side that has been deaf overa prolonged period or the side experiencing recent hear-ing loss but is occupied with tumor. In our series, 1 patientwas implanted in the nontumor side first. However, shedid poorly on that side and required implantation on thetumor-affected side. This is supported by historical data(7). Thus, the presence of an untreated VS is not a contra-indication for CI and provides new options for hearingrehabilitation with limited morbidity, to this subgroup ofpatients who would otherwise have no other options.
Patients Affected With NF2In NF2, treatment decisions are more complex. With
treatment of the first side, controversy surrounds the optionsof ‘‘wait and rescan’’ versus treating small tumors withhearing preservation surgery (2). Treatment of the secondside is usually advocated if there is hearing deteriorationor tumor enlargement and depends also on the hearingstatus of the first side (2,4).
NF2 patients form a spectrum in terms of their com-plexity in managing their hearing. On one hand, some
patients have small stable tumors, which do not requireactive treatment. On the other end of the spectrum arepatients who are incredibly complex, have multiple co-morbidities, large tumor bulk, and multiple intracranialtumors. They are increasingly sensory deprived, with pa-tients being blind and immobile as well as deaf and therebycan feel isolated from the world. This is more so the casein patients who are diagnosed in a pediatric age group.Many articles have reported that the most important pre-dictors of disease severity in NF2 are age at diagnosis andage at onset of symptoms (16Y19).
Regardless of where the individual patient lies on thespectrum, if their tumor does not require surgical interven-tion, CI offers them hearing rehabilitation without the needfor an intracranial procedure. ABI surgery carries highersurgical risks and morbidity (20), and in comparison, CIin many centers involves day case surgery (5). Moreover,having a CI does not preclude the opportunity for futureABI placement if required.
Factors Influencing Outcomes With CIIn our study, all patients who were implanted with no
treatment to their tumors received significant benefit andwere daily CI users. In the group of patients who were im-planted after having radiotherapy, only 1 of 6 patients re-ceived open set speech discrimination. It is likely that thisis because of advanced disease in these patients. Certainly,3 of 6 patients who had presented in a pediatric age grouphad large tumors, and one even had intracochlear tumor seenat the time of operation.
It is worthy to note that 3 patients lost their hearing afterradiotherapy. However, it was not possible to document thedosage of radiation to each tumor and in particular note thedosage of radiation exposure to the cochlea. The patientscame from different units, and each of these patients wentto different remote centers to have the radiation treatment.No information about their radiation was available at thecenters, and there were some significant logistical limitationsto accessing this retrospective data. There were not enoughdata, therefore, in this current article to derive conclusive ex-planations of the reason of hearing loss after radiotherapy,although some temporal bone studies have shown loss ofspiral ganglion cells after stereotactic radiotherapy (21).Likewise, studies evaluating the effect of hearing loss aftergamma knife (22) found that a change in PTA was signifi-cantly poor at 12 months in patients whose cochlea receiveddoses of 4.75 Gy or more. Linskey et al. (23) found a meanabsorption of 5.5 Gy at the inferior portion of the basal turnand 8.9 Gy at the modiolus of the basal turn after gammaknife treatment for vestibular schwannoma. Wakym et al.(24) found that the pattern of hearing loss was most con-sistent with cochlear damage as opposed to neural dam-age. Nevertheless, the effects of radiotherapy on hearingand its effect on cochlear implantation needs to be furtherstudied and perhaps as we acquire more patients who havebeen implanted without treatment, further comparisonscan be made.
In any case, this is a difficult area to study because weneed to first understand the mechanism of hearing loss
from the disease itself to then apply it to the effect of dif-ferent treatment variables. Hearing in VS may be lost be-cause of either cochlear ischemia or infarction. Alternatively,it may also be due to impairment of the cochlear nerve, and forlarger tumors, it may be due to effects on brainstem. It mayalso be due to a combination of some or all of these factors.Moreover, position of different tumors may be associatedwith different outcomes, such as a tumor, although small, ifwidening the IAC or extending into the cochlea through thehabenula perforata may predispose the cochlear nerve tomore trauma through pressure or devascularization and, al-though small, may pose a worse outcome from a CI.
In our study, there was quite a degree of heterogeneitywithin the individual groups as well as between the 2 groups,not only relating to differing cause of hearing loss but alsorelated to age difference in between patients, duration ofdeafness, and different implants used. Those affected withNF2 had different degrees of severity of disease and, there-fore, differing comorbidities, which were additional con-founding factors in the hearing outcome of CI. Because ofthe presence of so many confounding factors, it was ex-tremely difficult to subject these data to statistical analysis,and only observations regarding trends could be made.
Promontory stimulation using the golf club electrode mayprovide some prognostic information about the integrity ofthe pathway and the likelihood of success. This was cer-tainly used in some of the cases, and a positive promontorystimulation helped in the decision-making process to pro-ceed with implantation. Although there is much contro-versy about the role and value of this test (25), promontorystimulation in our patients using the golf club electrodeplayed a small but important role to aid the clinician andthe patient in what was sometimes a difficult decision-making and counseling process about CI candidacy.
A criticism of cochlear implantation in the setting ofvestibular schwannoma is follow-up imaging that is re-quired for their tumors. Where MRI is the gold standard,some patients can be continued to be followed up for theirtumor size with a CT scan. If the patient requires an MRI,it has been the experience of the centers participating in thisstudy that adequate images are able to be attained with anMRI scanner with 1.5 T magnet strength (Fig. 1). There is,however, an artifact, and some patients experience discom-fort at the site of the speech processor, requiring local an-esthetic at the site before imaging (26). There may be somelimited morbidity associated with this area in some patients,although if general precautions are taken, these can largelyminimized (26). Alternatively, a device without a magnetcan be used.
None of the units participating in this current study hadany patients where surgery to the tumor was required on theimplanted side. We were therefore unable to collect any dataor make any experience-based comments about the out-come of subtotal removal or cochlear nerve preservationsurgery and CI. Successful results of CI with cochlear nervepreservation surgery has already been reported (3), and withmany units now performing subtotal or near-total removalof VS (in preference to preserving facial nerve function),it is possible that future directions of implantation in these
patients may reveal promising results. From our experience,however, we are able to observe that a vestibular schwannomais not an absolute contraindication for cochlear implantation.
CONCLUSION
Although there is a great variability in terms of diseasespectrum and, therefore, confounding factors in our patients,it was apparent that if the vestibular schwannoma was smalland did not require treatment, cochlear implantation canattain good hearing results in the setting of NF2 or sporadiclesions despite the presence of tumor. If the tumor requiresradiotherapy, then the patients may still benefit from co-chlear implantation, although their outcome is more vari-able. Patients with very aggressive disease are less likely toattain open set speech discrimination, and their outcomemeasure may be better evaluated by a quality-of-life study.Most importantly, in this subgroup of patients who requireno surgical intervention for their tumor, cochlear implan-tation provides new hope for hearing rehabilitation. There
may be more advantages in cochlear implantation as opposedto an ABI, given the lower surgical risk and that the formerdoes not preclude the future possibility of the latter. Thebenefits noticed from the observations made from this studyhas moved the management paradigm of the units involvedfor considering CI as a treatment option at a much earlierstage in the planning and also considering it in preferencefor an ABI.
REFERENCES
1. Otto SR, Brackmann DE, Hitselberger WE, Shannon RV, Kuchta J.Multichannel auditory brainstem implant: update on performance in61 patients. J Neurosurg 2002;96:1063Y71.
2. Trotter M, Briggs R. Cochlear implantation in NF2 after radiationtherapy. Otology & Neurotology 2010;31:216Y9.
3. Neff B, Wiet M, Lasak J, et al. Cochlear implant in the NF2 patient:long term follow up. Laryngoscope 2007;117:1069Y72.
4. Lustig L, Yeagle J, Driscoll C, Blevins N, Francis H, Niparko J.Cochlear implant in NF2 and bilateral vestibular schwannoma. OtolNeurotol 2006;27:512Y18.
5. Vincenti V, Pasanisi E, Guida M, Di Trapani G, Sanna M. Hearingrehabilitation in neurofibromatosis type 2 patients: cochlear versusauditory brainstem implantation. Audiol Neurotol 2008;14:273Y80.
FIG. 1. T1-weighted images with gadolinium in a 1.5 Tesla magnet MRI scanner of bilateral vestibular schwannomas after right cochlearimplantation. Images A to D progress consecutively from the midbrain to the cerebellopontine angle.
6. Helbig S, Rader T, Bahmer A, Baumann U. A case of bilateral co-chlear implantation in single sided untreated acoustic neuroma. ActaOtolaryngol 2009;129:694Y96.
7. Ramsden R, Khwaja S, Green K, O-Driscoll M, Mawman D. Ves-tibular schwannoma in only hearing ear: CI or ABI? Otol Neurotol2005;26:261Y4.
8. Suryanarayan R, Ramsden R, Saeed S, et al. Vestibular schwannoma:role of conservative management. J Laryngol Otol 2010;124:251Y57.
9. Yoshimoto Y. Systematic review of the natural history of VestibularSchwannoma. J Neurosurgery 2005;103:59Y63.
10. Selesnick HS, Johnson G. Radiologic surveillance of acoustic neu-romas. Am J Otol 1998;19:846Y9.
11. Smouha EE, Yoo M, Mohr K, Davis RP. Conservative managementof acoustic neuroma: a meta-analysis and proposed treatment algo-rithm. Laryngoscope 2005;115:450Y4.
12. Yamakami I, Uchino Y, Kobayashi E, Yamaura A. Conservative man-agement, gamma-knife radiosurgery and microsurgery for acousticneurinomas: a systematic review of outcome and risk of three thera-peutic options. Neurol Res 2003;25:682Y90.
13. Suryanarayanan R, Lesser THJ. Growth rate of vestibular of vestibularschwannoma Y what the literature tells us. Otorhinolaryngologist 2007;1:66Y71.
14. Fucci MJ, Buchman CA, Brackmann DE, Berliner KI. Acoustictumour growth: implications for treatment choices. Am J Otol 1999;20:495Y9.
15. Martin TPC, Tzifa K, Kowalski C, Holder RL, Walsh R, Irving RM.Conservative versus primary surgical treatment of acoustic neuro-mas: a comparison of rates of facial nerve and hearing preservation.Clin Otolaryngol 2008;33:228Y35.
16. Mac Nally S, Rutherford S, King A, et al. Outcome from surgery forvestibular schwannomas in children. Br J Neurosurg 2009;23:226Y31.
noma growth in patients with neurofibromatosis type 2. J Neurosurg2002;96:217Y22.
18. Mautner VF, Baser ME, Thakkar SD, Feigen UM, Friedman JM,Kluwe L. Vestibular schwannoma growth in patients with neurofi-bromatosis type 2: a longitudinal study. J Neurosurg 2002;96:223Y8.
19. Otsuka G, Saito K, Nagatani T, Yoshida J. Age at symptom onsetand long-term survival in patients with neurofirmatosis type 2. JNeurosurg 2003;99:480Y3.
20. Celis-Aguilar E, Lassaletta L, Gavilan J. Cochlear implantation inpatients with neurofibromatosis type 2 and patients with vestibularschwannoma in the only hearing ear. Int J Otolaryngol 2012;2012:157497.
21. Hoistad DL, Ondrew C, Mutlu P, Schachern M, Paparella M,Adams GL. Histopathology of huma temporal bone after cis-platinum,radiation or both. Otolaryngol Head Neck Surg 1998;118:825Y32.
22. Lasak JM, Klish D, Kryzer TC, Hearn C, Gorecki JP, Rine GP.Gamma Knife radiosurgery for vestibular schwannoma: early hearingoutcomes and evaluation of the cochlear dose. Otol Neurotol 2008;29:1179Y86.
23. Linskey ME, Johnstone PAS, O’Leary M, Goetsch S. Radiation ex-posure of normal temporal bone structures during stereotactic guidedgamma knife surgery for vestibular schwannomas. J Neurosurg 2003;98:800Y6.
24. Wackym A, Runge-Samuelson CL, Nash JJ, et al. Gamma knifesurgery of vestibular schwannomas: volumetric dosimetry correla-tions to hearing loss suggest stria vascularis devascularisation as amechanism of early hearing loss. Otol Neurotol 2010;31:1480Y87.
25. Kuo SC, Gibson WPR. The role of the promontory stimulation testin cochlear implantation. Cochlear Implants Int 2002;3:19Y28.
26. Tam YC, Graves MJ, Black RT, et al. Magnetic resonance imagingin patients with cochlear implants and auditory brainstem implants.Cochlear Implants Int 2010;11:48Y51.
