2012 Vol.7 No.2

JOURNAL OF

OTOLOGY

ADVANCES IN SURGICAL TREATMENT OF ACOUSTIC NEUROMA

HAN Dongyi ,CAI Chaochan

Affiliation:Department of Otolaryngology Head and Neck Surgery, PLAGeneral Hospital, Beijing 100853

Acoustic Neuroma (AN) arises from the eighth cranialnerve. It primarily involves the vestibular branch of thenerve and is therefore also called vestibular schwannoma(VS). To the date, diagnosis and surgical treatment ofAN have advanced significantly. Along with advancesin audiology and imaging technologies, cases of diag-nosed AN have been increasing, making it a commonneurotologic disease. Currently, management is basedupon the patient’s age, tumor size, hearing in the dis-eased and contralateral ears and overall health, althoughsurgical removal remains the primary treatment. As thesurgical approaches and intraoperative monitoring of thefacial and auditory nerves improve, outcomes of surgicaltreatment in AN have greatly improved. Ideally, surgeryin AN would achieve complete tumor excision whileminimizing complications for improved post-operativequality of life. Facial nerve protection and hearing pres-ervation have been among the important focuses in surgi-cal treatment in AN.

The Department of Otolaryngology Head and NeckSurgery, PLA General Hospital, started surgical treat-ment for patients withAN in 1983, starting with intra-capi-sule debulking, partial and subtotal excision to save life,and now manages complete resection with preservationof facial function in most cases and even hearing preser-vation in some patients. This writing reports the au-thors'experiences with 241 AN cases surgically treatedbetween January 1999 and August 2012 and the authors'thoughts on issues related to protection of facial nerveand hearing preservation.

Yearly distribution of surgically treatedAN cases

AN has been reported to comprise 6% to 9% of intra-cranial tumors and 80% to 90% of cerebellopontine angle

(CPA) tumors. Annual AN incidence in the US is about1/100,000 [1]. To the date, there has not been large se-ries-based epidemiological data on AN in China. Fromthe authors' 241 cases between January 1999 and August2012, the yearly distribution appears to have progressive-ly increased (Figure 1). Between January 2009 and Au-gust 2012, 129 of the 241 cases (54%) were treated, indi-cating a significant increase in case number over recentyears. This increase may be related to advances in diag-nostic technologies such as auditory brainstem respons-es (ABRs) and magnetic resonance imaging (MRI), al-though it may also be a result of increasing demand onthe patient's part as surgical treatment outcomes haveimproved dramatically along with improvement in surgi-cal approaches and techniques.

History of surgical approaches for AN re-section

Corresponding authors:HAN Dongyi, Email:hdy301@263.net

SPECIAL PAPER IN CELEBRATION OF PROF.YANG'S 50 YEARS CAREER IN MEDICINE

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手术量

Volume ofsurgical cases

Figure 1. Yearly distribution of surgically treated AN cases

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Most frequently used approaches in otological surger-ies so far are translabyrinthine, post-sigmoid and mid-cra-nial fossa approaches. Selection of these approaches de-pends mainly on hearing levels in the disease ear and tu-mor size. The approaches can be classified as hearingpreserving and non-hearing preserving.Translabyrinthineapproach is non-hearing preserving and used when aver-age speech frequency hearing threshold is over 50 dBHL (deemed as non-useful). In contrast, post-sigmoidapproach is a hearing preserving approach and usedwhen average speech frequency hearing threshold is betterthan 50 dB HL with speech discrimination better than50% and a tumor size smaller than 2 cm (considered opti-mal for hearing preservation). Mid-cranial fossa ap-proach is also a hearing preserving approach and usedwhen tumor is limited to the internal auditory canal(IAC) or tumor outside the IAC is smaller than 1 cm.Among the authors' 241 cases, post-sigmoid approachwas used in 135 cases (59%), translabyrinthine approachin 96 cases (37%) and mid-cranial fossa approach in 10cases (4% ). Before facial nerve monitoring became aroutine intraoperative test modality in 2003, the translab-yrinthine approach was used more often due to its advan-tage in possible visualizing and protecting the facialnerve at the early stage of the procedure. Along with in-troduction of neuromonitoring and endoscopy technolo-gies and as the number of patients requesting hearingpreservation increases, use of the post-sigmoid approachhas increased significantly (Figure 2).

Endoscopy in AN surgeries

Endoscopy has gained broad applications in otologicmicrosurgeries. The authors pioneered using endoscopictechnology in AN surgeries in China in 2004 [2-4]. In ANsurgeries, endoscopy can be used for: 1) guidance andmonitoring in microsurgery; 2) assistance in completing

part of the procedure; and 3) main visualization for theentire procedure. Its advantages include: 1) early visual-ization of the entire CPA area; 2) providing different visualangles to identify structures on the surface of tumor,including nerves (VIIth and VIIIth nerves) and importantblood vessels (anteroinferior cerebellar artery, etc); and3) determination of residual tumor after removal of mini-mal posterior wall of the IAC. Figure 3 shows images ofendoscopy assisted AN resection.

Among the cases treated via the post-sigmoid approachin this series, endoscopy was applied in 3 cases to eradi-cate residual tumor in the IAC with preservation offacial function. The most useful feature of endoscopy insuch cases is that it helps overcome the notorious disad-vantage of this approach, ie, difficulty in visualizingstructures in the IAC. The 30 degree endoscope allowsremoval of residual tumor in the IAC while better pro-tecting involved nerves and blood vessels. An innate dis-advantage of endoscopy, however, is that it limits opera-tion to one hand. Also visual field through the endoscopeis easily obscured when there is bleeding and there lacksa sense of depth. All these limit its broader use anddevelopment of an endoscopic system that allows biman-ual operation and provides three dimensional views is ingreat need.

Preservation of facial nerve function inAN surgeries

One of the purposes of AN surgeries is minimizingcomplications to provide best post-operative quality oflife possible, in addition to tumor removal.Facial nervefunction preservation is an important index in assessingtreatment outcomes. Literature indicates that facial nervefunction is preserved in 60% to 95% of AN surgeries and

Figure 2. Yearly distribution of surgical approach selection for ANsurgeries

Figure 3. Endoscopic views of the IAC before and after AN resec-tion

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that post-operative facial function is dependent on tumorsize and some of its biological characteristics besidessurgeon's expertise. Regardless of selected surgical ap-proaches, intraoperative facial nerve monitoring is thekey to improving facial nerve preservation. Advantagesof facial nerve monitoring include early identification oflocation of facial nerve and its relation to the tumor forbetter protection. The early works by the authors showedthat facial nerve was anatomically intact during surgeryin as many as 98% (47/48) of cases and facial functionreached H-B I or II levels in 83% (40/48) of cases within7 days. Post-operative facial function did not appear tobe affected by surgical approach. In this series, H-B gradeI or II facial function at Day 7 was 84% (21/25) forpost-sigmoid approach, 83% (15/18) for translabyrin-thine approach and 80% (4/5) for mid-cranial fossa ap-proach [5]. Obviously, facial function preservation duringAN surgeries has greatly improved as a result of the in-troduction of facial nerve monitoring,although it remainsa challenge to otologists when attempting complete re-section of large solid AN with tight relation to the facialnerve. From the authors' experiences, when anatomy ofthe facial nerve is compromised, two strategies may beused to repair the nerve: 1) end-to-end anastomosis withbiological glue. This was used in one of the authors’cases and yielded H-B grade II facial function one yearafter surgery with significantly improved facial move-ment (Figure 4); and 2) facial-hypoglossal nerve anasto-mosis when stumps cannot be located. Shown in Fig-ures 5A-C is a case in which the facial nerve was com-promised due to the large size and tight tumor relation tothe facial nerve, and stumps could not be located aftertumor resection.Facial-hypoglossal nerve anastomosiswas performed and facial function reached H-B II oneyear later.

Hearing preservation in AN surgeries

AN arises primarily from the vestibular branch of theeighth cranial nerve, mostly within the IAC. As the tumorincreases and extends from the IAC to the CPA, the sup-plying vessels to the inner ear and the cochlear nerve arecovered by the arachnoid membrane on the surface ofthe tumor. Such tumor development patterns provide thepossibility of preservation of the cochlear nerve andhearing during AN surgeries [5, 9]. In addition, along with

Figure 4. Facial function after AN resection via translabyrinthineapproach with end-to-end facial nerve anastomosis

Figure 5C. Two years after facial-hypoglossal nerve anastomosis

a bFigure 5A. a) Pre-operative MRI. b) MRI one year after surgicalresection

Figure 5B. Facial-hypoglossal nerve anastomosis and incision

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improvement in imaging diagnosis, detection of earlyAN with minimal clinical symptoms has increased.These plus application of endoscopy and monitoring ofauditory function during surgery have provided increas-ing opportunities of hearing preservation. We can saythat surgical treatment for AN has moved rapidly fromtumor resection for saving life in the early days to pro-tecting facial and auditory functions in addition to safetumor resection these days. However, preserving hear-ing in resecting tumors greater than 2 cm remains a seri-ous challenge to be further studied. The authors startedusing intraoperative compound action potentials (CAP)and ABR monitoring in some cases in 2003, in an at-tempt to preserve hearing while attempting complete tu-mor resection

From March 2000 to April 2012, there were 32 casesoperated upon by the same surgeon in which hearingpreservation was attempted with complete clinical data.The post-sigmoid approach was adopted in all 32 cases.The part of tumor outside the IAC was removed underthe microscope and the posterior wall of IAC was drilledaway to remove tumor inside the IAC. Endoscopy wasused to assist resection of residual tumor inside the IACin 6 cases. Pre- and post-operative hearing was evaluatedusing the AAO-HNA (1995) criteria (Table 1). Hearingpreservation was assessed using the criteria recommend-ed by Brackmann et al, i.e. post-operative deteriorationof pure tone average (PTA) is less than 15 dB and speechdiscrimination score (SDS) improves by 15% or more.

Hearing preservation was successful in 14 of the 32cases (43.8%), of which post-operative hearing was rat-ed A in 5 cases, B in 5 cases, C in 3 cases and D in 1case. In cases with pre-operative grade A hearing, hear-ing remained as A in 62.5% (5/8) and deteriorated to Bin 25% (2/8) and to C in 12.5% (1/8) of the cases. In cas-es with pre-operative grade B hearing, hearing remainedas B in 21.4% (3/14) and deteriorated to C in 14.3% (2/14), to D in 7.1% (1/14) of the cases and was lost in theremaining cases. Figures 6 A-E shows a case in whichthe AN was completely resected via the post-sigmoid ap-proach with successful preservation of the facial nerveand hearing.

Table 1 AAO-HNS Hearing Classification Criteria

*PTA over 0.5, 1, 2 and 3 kHz.

GradeABCD

PTA (dB)*

Less than 30>30 -50

>50Any

SDS (%)70 or better50 or better50 or better

<50

a b cFigure 6A. a) Exposure of tumor. b) Removal of IAC posteriorwall and tumor resection. c) Preserved nerves and blood vesselsafter tumor resection

Figure 6B. CPA tracings at closing

Figure 6C. a) Pre-operative MRI. b) MRI at 1 year after surgery

Figure 6D. Hearing before and after surgery

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Summary

To summarize, along with advances in microsurgerytechnology and especially with application of intraopera-tive facial nerve and hearing monitoring and endoscopy,preservation of facial and auditory functions during ANsurgery has greatly improved. In another word, surgicaltreatment for AN has rapidly advanced from safe resec-tion to save life into a stage of preserving facial and audi-tory function in addition to tumor resection. However,in patients with AN of mid-size or greater sizes, future ef-forts should aim at further improving preservation of fa-cial function and hearing.

References

[1] Lessser THJ, Pollak A. Acoustic schwannoma of traumatic ori-gin ? A temporal bone study . J Otolaryngol Otol 1990,104:270-4.[2] Han Dong-Yi ,Yu Li-Min,Yang Shi-Ming,et al. Hearing protec-tion during the operation of acoustic neurinoma. Chinese JournalOtology ,2004,03:174-178.[3] Yang Shi-Ming,Han Dong-Yi,Yang wei-yan. Endoscope-assist-ed cerebellopontine angle surgery Chinese Journal Otology,2005,02:81-85.[4] Yu Li-Min,Han Dong-Yi . Hearing preservation in acousticneuroma surgery.Journal of Clinical Otorhinolaryngology Headand Neck Surgery,2005,10:474-477.[5] Han Dong-Yi,Yang Shi-Ming,Wu Wen-Ming,et al. Resectionof acoustic neurinoma and preservation of function of the facialnerve. Chinese Journal Otology,2004,01:1-3.[6] Yu Li-Min,Yang Shi-Ming,Han Dong-Yi,et al. Preliminarystudy of intraoperative auditory monitoring techniques in acousticneuroma surgery. Chinese Journal of Otorhinolaryngology Headand Neck Surgery ,2006,05:335-340.[7] Committee on Hearing and Equilibrium guidelines for the eval-uation of hearing preservation in acoustic neuroma (vestibularschwannoma). American Academy of Otolaryngology-Head andNeck Surgery Foundation, Inc. Otolaryngol Head&Neck Surg1995;113:179-80.[8] Brackmann DE , Owens RM , Friedman RA , et al. Prognosticfactors for hearing preservation in vestibular schwannoma surgery.Am J Otol ,2000 ,21 :417-424.[9] Han DY, Yu LM, Yu LM, et al. Acoustic neuroma surgery forpreservation of hearing: technique and experience in the ChinesePLA General Hospital. Acta Otolaryngol. 2010 ,130(5):583-92.

（Rrceived September 27,2012）

Figure 6E. Post-operative facial function (1 month and 2 years af-ter surgery)

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