Letter to the Editor: Save the nerve

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TO THE EDITOR: We read with keen interest the article by Yamakami and associates27 regarding the resection of small acoustic neuromas through the retrosigmoid approach (Yamakami I, Ito S, Higuchi Y: Retrosigmoid removal of small acoustic neuroma: curative tumor removal with preservation of function. J Neurosurg 121:554–563, September 2014). We commend the authors for the excellent outcome they achieved with their technique and believe that their article is a decisive one with regard to the preference of surgical removal of small vestibular schwannomas, particularly in younger patients, over other options. Although their emphasis was on preserving serviceable hearing, the success in preserving any hearing, regardless of how poor it might be, indicates the viability of the cochlear nerve. Preserving the hearing anatomy (the inner ear and cochlear nerve) in all patients for preservation of hearing or potential functional restoration has been our avid interest and has incited us to rethink the management of all acoustic tumors, regardless of the size or the patient’s hearing status.

The remarkable success of cochlear implants in restoring hearing in patients with postlingual deafness is, in our opinion, a “game-changer” in the management of all vestibular schwannoma. In postlingual deaf patients, cochlear implants offer 70%–100% word recognition and 65%–80% sentence recognition.17,20,21 Modern cochlear implants have the far more ambitious goal of restoring speech perception for patients. In favorable hearing conditions and with auditory training, implantation of these devices can lead to an appreciation of more complex sound, including aspects of music perception.14 Impressive results have been obtained with cochlear implantation in patients with neurofibromatosis Type 2, as long as the nerve is kept intact.4,6,21 Thus, the prospect of restoring functional hearing must necessarily influence today’s management and approach to patients with unilateral acoustic neuromas.

The translabyrinthine approach inescapably sacrifices hearing, even though some pathological studies have suggested that some spinal ganglion cells might still be alive after labyrinthectomy.7 The middle fossa approach puts the facial nerve at higher risk.12,15,19,23 Although the middle fossa approach might be equal to the posterior fossa approach in preserving serviceable hearing,23 it might risk the cochlea and the part of the nerve near the fundus. In particular, this approach might involve dissection distally in the fundus, and reports show that a distal extension into the meatus is a significant adverse factor in preserving hearing.16 In addition, it was thought that a posterior fossa approach is more advantageous as far as complications are concerned.23,27 In the quest to preserve the cochlear nerve and function, we believe that the posterior fossa approach should be the approach of choice to all acoustic tumors. To alleviate the inherent risk of cerebellar retraction, which is associated with the retrosigmoid approach, we use the transmastoid approach and finesse it with endoscopic techniques.1,2

Decreasing the prescribed radiosurgery dose to 12–13 Gy has been reported, with a rate of 61%–78% early hearing preservation of patients with small tumors.10,18,26 Undeniably, however, there have been definitive, progressive, and permanent declines of hearing over the years after radiosurgery, to a very low level of hearing.5,8,11,22 The damage appears on the cochlear nerve, at the cochlear level, and the salient, identifying factor is a cochlear dose higher than 3 Gy.11,26 In one study, the only patients who maintained hearing were those who received a cochlear dose of less than 2 Gy.3 Exceeding such a dose is expected in all radiosurgery patients, with rare exceptions. Linskey and colleagues13 calculated the doses that different parts of the cochlea receive during radiosurgery for acoustic tumors, and found a range of 5–8 Gy. These facts suggest that radiation-induced injury would compromise the potential for hearing restoration through a cochlear implant, and that radiosurgery is disadvantageous for long-term preservation or potential restoration of hearing.

Preserving hearing, the cochlea, and the cochlear nerve is highly achievable in patients with tumors of all sizes, including giant ones, through the retrosigmoid approach.9,24 The cochlear nerve was preserved in 84% of a recent series of 200 patients reported by Samii et al.25 Most patients would be candidates for hearing restoration even if useful hearing was not preserved. Admittedly, the value and experience in applying a cochlear implant in the presence of another good hearing ear has yet to be determined, but the potential is vast.

Hence, as Yamakami and his colleagues recommended for the small tumors, we advocate curative tumor removal with the preservation of the cochlear nerve for potential hearing restoration in all surgically fit patients, regardless of the tumor size or the hearing status.

References

  • 1

    Abolfotoh MBi LWHong CAl-Mefty KBoskoviz ADunn IF: The combined microscopic endoscopic approach to increase the radical resection of CPA tumor. J Neurosurg epub ahead of printApril242015.

  • 2

    Abolfotoh MDunn IFAl-Mefty O: Transmastoid retrosigmoid approach to the cerebellopontine angle: surgical technique. Neurosurgery 73:1 suppl operativeons16ons232013

  • 3

    Baschnagel AMChen PYBojrab DPieper DKartush JDidyuk O: Hearing preservation in patients with vestibular schwannoma treated with Gamma Knife surgery. J Neurosurg 118:5715782013

  • 4

    Carlson MLBreen JTDriscoll CLLink MJNeff BAGifford RH: Cochlear implantation in patients with neuroflbromatosis type 2: variables affecting auditory performance. Otol Neurotol 33:8538622012

  • 5

    Carlson MLJacob JTPollock BENeff BATombers NMDriscoll CL: Long-term hearing outcomes following stereotactic radiosurgery for vestibular schwannoma: patterns of hearing loss and variables influencing audiometric decline. J Neurosurg 118:5795872013

  • 6

    Celis-Aguilar ELassaletta LGavilán J: Cochlear implantation in patients with neuroflbromatosis type 2 and patients with vestibular schwannoma in the only hearing ear. Int J Otolaryngol 2012:1574972012

  • 7

    Chen DALinthicum FH JrRizer FM: Cochlear histopathology in the labyrinthectomized ear: implications for cochlear implantation. Laryngoscope 98:117011721988

  • 8

    Chopra RKondziolka DNiranjan ALunsford LDFlickinger JC: Long-term follow-up of acoustic schwannoma radiosurgery with marginal tumor doses of 12 to 13 Gy. Int J Radiat Oncol Biol Phys 68:8458512007

  • 9

    Dunn IFBi WLErkmen KKadri PAHasan DTang CT: Medial acoustic neuromas: clinical and surgical implications. J Neurosurg 120:109511042014

  • 10

    Franzin ASpatola GSerra CPicozzi PMedone MMilani D: Evaluation of hearing function after Gamma Knife surgery of vestibular schwannomas. Neurosurg Focus 27:6E32009

  • 11

    Hasegawa TKida YKato TIizuka HYamamoto T: Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing. J Neurosurg 115:107810862011

  • 12

    Hillman TChen DAArriaga MAQuigley M: Facial nerve function and hearing preservation acoustic tumor surgery: does the approach matter?. Otolaryngol Head Neck Surg 142:1151192010

  • 13

    Linskey MEJohnstone PAO'Leary MGoetsch S: Radiation exposure of normal temporal bone structures during stereotactically guided gamma knife surgery for vestibular schwannomas. J Neurosurg 98:8008062003

  • 14

    Looi VGfeller KDriscoll V: Music appreciation and training for cochlear implant recipients: a review. Semin Hear 33:3073342012

  • 15

    Mangham CA Jr: Retrosigmoid versus middle fossa surgery for small vestibular schwannomas. Laryngoscope 114:145514612004

  • 16

    Mohr GSade BDufour JJRappaport JM: Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling. J Neurosurg 102:152005

  • 17

    Møller AR: History of cochlear implants and auditory brain-stem implants. Adv Otorhinolaryngol 64:110

  • 18

    Niranjan AMathieu DFlickinger JCKondziolka DLunsford LD: Hearing preservation after intracanalicular vestibular schwannoma radiosurgery. Neurosurgery 63:105410632008

  • 19

    Noudel RGomis PDuntze JMarnet DBazin ARoche PH: Hearing preservation and facial nerve function after microsurgery for intracanalicular vestibular schwannomas: comparison of middle fossa and retrosigmoid approaches. Acta Neurochir (Wien) 151:9359452009

  • 20

    Peterson NRPisoni DBMiyamoto RT: Cochlear implants and spoken language processing abilities: review and assessment of the literature. Restor Neurol Neurosci 28:2372502010

  • 21

    Roehm PCMallen-St Clair JJethanamest DGolfinos JGShapiro WWaltzman S: Auditory rehabilitation of patients with neurofibromatosis Type 2 by using cochlear implants. J Neurosurg 115:8278342011

  • 22

    Roos DEPotter AEBrophy BP: Stereotactic radiosurgery for acoustic neuromas: what happens long term?. Int J Radiat Oncol Biol Phys 82:135213552012

  • 23

    Sameshima TFukushima TMcElveen JT JrFriedman AH: Critical assessment of operative approaches for hearing preservation in small acoustic neuroma surgery: retrosigmoid vs middle fossa approach. Neurosurgery 67:6406452010

  • 24

    Samii MGerganov VSamii A: Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients. J Neurosurg 105:5275352006

  • 25

    Samii MMatthies C: Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections. Neurosurgery 40:2482621997

  • 26

    Tamura MCarron RYomo SArkha YMuraciolle XPorcheron D: Hearing preservation after gamma knife radiosurgery for vestibular schwannomas presenting with high-level hearing. Neurosurgery 64:2892962009

  • 27

    Yamakami IIto SHiguchi Y: Retrosigmoid removal of small acoustic neuroma: curative tumor removal with preservation of function. J Neurosurg 121:5545632014

Response

We greatly appreciate Dr. Al-Mefty and colleagues’ interest in our article concerning the retrosigmoid curative removal of small acoustic neuroma with functional preservation.

Dr. Al-Mefty advocates the curative removal of tumor with hearing and cochlear nerve preservation in all patients with acoustic neuroma, regardless of the tumor’s size or the patient’s hearing status. We agree that, even in the large acoustic neuroma, the optimum goal is curative tumor removal with preservation of the facial nerve and hearing, and that surgeons must make every effort to accomplish this goal. Actually, during the same study period of 1998–2012 as our article, we accomplished curative tumor removal with facial nerve and hearing preservation in 8 patients with large acoustic neuroma (30- to 50-mm tumor diameter; our unpublished data). We have the possibility to accomplish both curative tumor removal and hearing preservation, even in large acoustic neuromas. However, the possibility is much smaller than 84% in small acoustic neuromas with preoperative hearing, which our article reported.

Expressing the possibility of hearing restoration by the future development of cochlear implants, Dr. Al-Mefty points out the importance of anatomical preservation of the cochlear nerve. Using continuous monitoring of cochlear nerve compound action potential (CNAP) during removal of small acoustic neuromas with hearing preservation, we found out that mechanical injury of the cochlear nerve by surgical manipulation was the most common cause of postoperative hearing loss, and that the hearing did not recover in spite of the anatomical preservation of cochlear nerve.1 Once the cochlear nerve loses the function of nerve conduction intraoperatively, the nerve preserved anatomically may not restore the nerve conduction and hearing function years after tumor removal. We are not so optimistic for future hearing restoration by the cochlear implant in acoustic neuroma patients postoperatively.

We agree with Dr. Al-Mefty and associates that the retrosigmoid approach is the surgical approach of choice to all acoustic neuromas in the quest for hearing preservation. Our published article showed that, compared with the middle fossa approach, the retrosigmoid approach accomplished better facial function and the same hearing preservation. However, we emphasize that even in the retrosigmoid approach, the surgical manipulations near the fundus of the internal auditory canal (IAC) are most critical for preserving the nerve function. Continuous CNAP monitoring during acoustic neuroma removal showed that patients with tumor dissection near the fundus of the IAC frequently developed a stepwise decrease of CNAP amplitude and latency elongation.1

We believe that the most critical point for preservation of hearing and facial function is sharp dissection performed using microscissors and microknives, and therefore we very frequently use microscissors during tumor debulking as well as tumor dissection. The frequent usage of microscissors is practiced without difficulty under the direct surgical field by using the microscope. Although the endoscopic microsurgical instrumentation is being progressively refined, blunt dissection is the predominant surgical technique under the endoscope at present.

Reference

1

Yamakami IYoshinori HSaeki NWada MOka N: Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach. J Neurol Neurosurg Psychiatry 80:2182272009

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Article Information

INCLUDE WHEN CITING Published online July 10, 2015; DOI: 10.3171/2014.12.JNS142826.

DISCLOSURE The authors report no conflict of interest.

© AANS, except where prohibited by US copyright law.

Headings

References

  • 1

    Abolfotoh MBi LWHong CAl-Mefty KBoskoviz ADunn IF: The combined microscopic endoscopic approach to increase the radical resection of CPA tumor. J Neurosurg epub ahead of printApril242015.

  • 2

    Abolfotoh MDunn IFAl-Mefty O: Transmastoid retrosigmoid approach to the cerebellopontine angle: surgical technique. Neurosurgery 73:1 suppl operativeons16ons232013

  • 3

    Baschnagel AMChen PYBojrab DPieper DKartush JDidyuk O: Hearing preservation in patients with vestibular schwannoma treated with Gamma Knife surgery. J Neurosurg 118:5715782013

  • 4

    Carlson MLBreen JTDriscoll CLLink MJNeff BAGifford RH: Cochlear implantation in patients with neuroflbromatosis type 2: variables affecting auditory performance. Otol Neurotol 33:8538622012

  • 5

    Carlson MLJacob JTPollock BENeff BATombers NMDriscoll CL: Long-term hearing outcomes following stereotactic radiosurgery for vestibular schwannoma: patterns of hearing loss and variables influencing audiometric decline. J Neurosurg 118:5795872013

  • 6

    Celis-Aguilar ELassaletta LGavilán J: Cochlear implantation in patients with neuroflbromatosis type 2 and patients with vestibular schwannoma in the only hearing ear. Int J Otolaryngol 2012:1574972012

  • 7

    Chen DALinthicum FH JrRizer FM: Cochlear histopathology in the labyrinthectomized ear: implications for cochlear implantation. Laryngoscope 98:117011721988

  • 8

    Chopra RKondziolka DNiranjan ALunsford LDFlickinger JC: Long-term follow-up of acoustic schwannoma radiosurgery with marginal tumor doses of 12 to 13 Gy. Int J Radiat Oncol Biol Phys 68:8458512007

  • 9

    Dunn IFBi WLErkmen KKadri PAHasan DTang CT: Medial acoustic neuromas: clinical and surgical implications. J Neurosurg 120:109511042014

  • 10

    Franzin ASpatola GSerra CPicozzi PMedone MMilani D: Evaluation of hearing function after Gamma Knife surgery of vestibular schwannomas. Neurosurg Focus 27:6E32009

  • 11

    Hasegawa TKida YKato TIizuka HYamamoto T: Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing. J Neurosurg 115:107810862011

  • 12

    Hillman TChen DAArriaga MAQuigley M: Facial nerve function and hearing preservation acoustic tumor surgery: does the approach matter?. Otolaryngol Head Neck Surg 142:1151192010

  • 13

    Linskey MEJohnstone PAO'Leary MGoetsch S: Radiation exposure of normal temporal bone structures during stereotactically guided gamma knife surgery for vestibular schwannomas. J Neurosurg 98:8008062003

  • 14

    Looi VGfeller KDriscoll V: Music appreciation and training for cochlear implant recipients: a review. Semin Hear 33:3073342012

  • 15

    Mangham CA Jr: Retrosigmoid versus middle fossa surgery for small vestibular schwannomas. Laryngoscope 114:145514612004

  • 16

    Mohr GSade BDufour JJRappaport JM: Preservation of hearing in patients undergoing microsurgery for vestibular schwannoma: degree of meatal filling. J Neurosurg 102:152005

  • 17

    Møller AR: History of cochlear implants and auditory brain-stem implants. Adv Otorhinolaryngol 64:110

  • 18

    Niranjan AMathieu DFlickinger JCKondziolka DLunsford LD: Hearing preservation after intracanalicular vestibular schwannoma radiosurgery. Neurosurgery 63:105410632008

  • 19

    Noudel RGomis PDuntze JMarnet DBazin ARoche PH: Hearing preservation and facial nerve function after microsurgery for intracanalicular vestibular schwannomas: comparison of middle fossa and retrosigmoid approaches. Acta Neurochir (Wien) 151:9359452009

  • 20

    Peterson NRPisoni DBMiyamoto RT: Cochlear implants and spoken language processing abilities: review and assessment of the literature. Restor Neurol Neurosci 28:2372502010

  • 21

    Roehm PCMallen-St Clair JJethanamest DGolfinos JGShapiro WWaltzman S: Auditory rehabilitation of patients with neurofibromatosis Type 2 by using cochlear implants. J Neurosurg 115:8278342011

  • 22

    Roos DEPotter AEBrophy BP: Stereotactic radiosurgery for acoustic neuromas: what happens long term?. Int J Radiat Oncol Biol Phys 82:135213552012

  • 23

    Sameshima TFukushima TMcElveen JT JrFriedman AH: Critical assessment of operative approaches for hearing preservation in small acoustic neuroma surgery: retrosigmoid vs middle fossa approach. Neurosurgery 67:6406452010

  • 24

    Samii MGerganov VSamii A: Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients. J Neurosurg 105:5275352006

  • 25

    Samii MMatthies C: Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections. Neurosurgery 40:2482621997

  • 26

    Tamura MCarron RYomo SArkha YMuraciolle XPorcheron D: Hearing preservation after gamma knife radiosurgery for vestibular schwannomas presenting with high-level hearing. Neurosurgery 64:2892962009

  • 27

    Yamakami IIto SHiguchi Y: Retrosigmoid removal of small acoustic neuroma: curative tumor removal with preservation of function. J Neurosurg 121:5545632014

  • 1

    Yamakami IYoshinori HSaeki NWada MOka N: Hearing preservation and intraoperative auditory brainstem response and cochlear nerve compound action potential monitoring in the removal of small acoustic neurinoma via the retrosigmoid approach. J Neurol Neurosurg Psychiatry 80:2182272009

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