听神经瘤术中连续听力监测的初步探讨

目的探讨听神经瘤外科术中连续听力监测的意义。方法采用乙状窦人路，在听性脑干反应（auditory brainstem response，ABR）和耳蜗电图（electrocochleogram，ECochG）监测下完成的听神经瘤切除术10例。对手术过程和术后听力结合术中监测进行分析。结果10例听神经瘤术前听力A级3耳，B级4耳，C级3耳（美国耳鼻咽喉头颈外科学会分级标准）。术前的ABR检查Ⅰ、Ⅲ、Ⅴ波存在者5耳（A级3耳，B级2耳），仅见Ⅰ波者5耳（B级2耳，C级3耳）。麻醉后手术前的监测显示：Ⅰ、Ⅲ、Ⅴ波存在者2耳，仅Ⅰ波存在者6耳，以复合动作电位（compound action potential，CAP）的N1波代替波Ⅰ；无波形者2耳。术后听力保留2耳，肿瘤均〈2cm，术前听力都为A级；连续听力监测显示1耳术中及术毕时Ⅰ、Ⅲ、Ⅴ持续存在，1耳Ⅰ、Ⅲ波存在，Ⅴ波消失；术后听力均为A级。听力未保留8耳，其中6耳术中监测时仅CAP的N1（波Ⅰ）存在，手术过程中夹内听动脉或处理内耳道处肿瘤时，4耳CAP波幅明显下降，甚至下降至0，术毕又恢复至术前的50％～60％或正常；1耳蜗神经与肿瘤一并切除，但CAP始终存在；1耳因牵拉脑干侧的耳蜗神经，CAP波幅降至0，手术结束亦未恢复。2耳为全身麻醉后术前监测中未引出任何波形者，其中1耳术中切除部分肿瘤后，出现CAP波，但波幅低，直至术毕；1耳始终未出现波形。结论联合应用ABR和ECochG术中监测，对提高听力保护率有积极意义，能及时反映术中与保留听力相关的敏感手术步骤，然而外科医师的熟练的解剖和精确的手术技巧是手术成功的最基本因素。     

两种听觉监护在听神经瘤术中的联合应用及评价

目的　探讨听神经瘤手术中听觉监护的意义。比较听性脑干反应（ABR）和蜗神经动作电位（cochlear nerve action potential,CNAP）在听觉监护应用中的价值。方法　回顾性分析我中心12例保留听力手术的听神经瘤患者资料及术中情况,患者术前均有实用听力（AAO-HNS分级A级、B级）,可引出ABR波形,V波分化可,所有手术均采取乙状窦后径路摘除肿瘤。所有患者均全程ABR监护,术中打开脑膜后联合监测CNAP。结果　手术过程中所有患者ABR波形较术前基线均有不同程度的变化,可记录到V波潜伏期均较基线延长（0.68±0.41）ms。CNAP波幅个体差异性较大,可记录到的P1潜伏期均较基线延长（0.25±0.16）ms。12例中有8例（66.7%）患者术后保留可用听力;另外4例（33.3%）术后达不到可用听力,此4例患者ABR表现为3例V波消失,1例V波潜伏期延长。CNAP表现为2例CNAP的P1消失,2例P1延长。电钻钻磨造成的震动和噪声、手术时神经被牵拉或热损伤后等急性损伤后ABR和CNAP波幅均出现短时间急剧下降,手术暂停5 min后,部分患者波幅可在一定程度恢复。结论　听神经瘤手术中ABR和CNAP对于听觉监护均有一定意义。ABR波形稳定可靠,但叠加时间相对较长;CNAP叠加快速,可提升监测灵敏度,但波形变异度较大。电钻钻磨造成的震动和噪声、操作过程中对神经组织的牵拉以及热损伤均被及时监控,两者联合应用可提升听神经瘤手术的听觉功能保留率。     

Preoperative, intraoperative, and postoperative auditory evaluation of patients with acoustic neuroma

This article is a concise clinical review of preoperative, intraoperative, and postoperative auditory evaluation of patients with acoustic neuroma. The author describes behavioral audiometry, auditory brainstem response, and otoacoustic emissions for preoperative evaluation; auditory brainstem and direct eighth-nerve intraoperative monitoring for intraoperative evaluation; and touches on postoperative auditory assessment.     

Hearing preservation using combined monitoring of extra-tympanic electrocochleography and auditory brainstem responses during acoustic neuroma surgery

The aim of this study was to evaluate the efficacy of an intraoperative monitoring hearing preservation strategy that includes simultaneous recordings of an auditory brainstem response (ABR) and non-invasive electrocochleography (ECochG). The combined ABR and tympanic membrane (TM) ECochG testing was performed in 74 patients undergoing acoustic neuroma (AN) surgery. In addition, EMG recordings were conducted to monitor the facial nerve function. Hearing was preserved in 19 of the 30 patients with residual hearing prior to surgery (63%), and facial nerve function was maintained in 89% of the patients. In most cases, the presence of both auditory brainstem and TM-ECochG responses at the end of surgery was associated with preservation of postoperative functional hearing; however, eight patients had a TM-ECochG response with a complete loss of the ABR, pointing to deafferentation of the auditory nerve. Tumour size and preoperative hearing thresholds significantly affected the postoperative hearing. The TM-ECochG response yielded large reproducible responses, which, in some patients, was the only way to monitor the auditory function. This auditory monitoring approach offers a valuable auditory tool that helps to improve the hearing preservation during AN surgery.     

Hearing preservation using combined monitoring of extra-tympanic electrocochleography and auditory brainstem responses during acoustic neuroma surgery

The aim of this study was to evaluate the efficacy of an intraoperative monitoring hearing preservation strategy that includes simultaneous recordings of an auditory brainstem response (ABR) and non-invasive electrocochleography (ECochG). The combined ABR and tympanic membrane (TM) ECochG testing was performed in 74 patients undergoing acoustic neuroma (AN) surgery. In addition, EMG recordings were conducted to monitor the facial nerve function. Hearing was preserved in 19 of the 30 patients with residual hearing prior to surgery (63%), and facial nerve function was maintained in 89% of the patients. In most cases, the presence of both auditory brainstem and TM-ECochG responses at the end of surgery was associated with preservation of postoperative functional hearing; however, eight patients had a TM-ECochG response with a complete loss of the ABR, pointing to deafferentation of the auditory nerve. Tumour size and preoperative hearing thresholds significantly affected the postoperative hearing. The TM-ECochG response yielded large reproducible responses, which, in some patients, was the only way to monitor the auditory function. This auditory monitoring approach offers a valuable auditory tool that helps to improve the hearing preservation during AN surgery.     

Physiological identification of the auditory nerve during surgery for acoustic neuroma

We report the design and clinical use of an electrode which can locate the acoustic nerve fibres in the normal eighth nerve and also in eighth nerves deformed by acoustic neuromas. The improvement in facial nerve preservation during acoustic neuroma surgery is partly due to the use of a facial nerve stimulator to anatomically locate the fibres. Our new acoustic nerve detector has the capability of anatomical location of cochlear fibres which may help to improve hearing preservation in selected cases of acoustic neuroma. The device functions by detecting the compound action potential evoked by no frequency auditory simulation at 500 Hz. The 500 Hz compound action potential is detected with a bipolar probe and then amplified and filtered. This results in a 500 Hz tone when the probe contacts the auditory nerve. Detection is virtually instantaneous. The acoustic nerve detector (AND) is demonstrated in a normal eighth nerve complex and its use is then described in the total removal of an acoustic neuroma with a 1 cm extracanalicular extension in which useful hearing was saved post-operatively. The present prototype may not be sensitive enough to detect the very low signals that may result when cochlear fibres are widely distorted around a large tumour or in cases where slight contusion of the nerve occurs during dissection. In all other cases the real time anatomical information is extremely helpful in guiding acoustic nerve dissection and also in monitoring the effects of petrous bone drilling.     

Cranioplasty in acoustic neuroma surgery

OBJECTIVES: To measure the incidence of postoperative headaches after retrosigmoid resections of acoustic neuromas and to evaluate the impact of cranioplasty on the prevention and management of these headaches. STUDY DESIGN: A prospective evaluation was performed on 30 consecutive patients who underwent a cranioplasty after retrosigmoid excision of their acoustic neuroma. The results were compared with 30 historical control patients who underwent the same procedure but did not have reconstruction with a cranioplasty. The patients were evaluated by review of office records and via telephone questionnaire. METHODS: One group of patients (30 patients) had no cranioplasty, and the other group of 30 patients had primary reconstruction with a titanium mesh-acrylic cranioplasty. All 60 patients were asked to report on the duration and severity of their headaches by means of a standard questionnaire, grading their symptoms on a scale of 1 to 4. The data were subjected to chi2 and Student t test statistical analyses. RESULTS: New-onset, postoperative headaches occurred in 27% of patients, 23% in the cranioplasty group compared with 30% in the group without cranioplasty (a difference that was not statistically significant [P = .158]). However, there was a statistically significant difference in the severity of the headaches (P<.03). The headaches in the cranioplasty group were less severe and were not disabling. There were no complications, infections, or extrusions related to the cranioplasty. CONCLUSIONS: Cranioplasty has not been able to eliminate postoperative headaches. However, the use of cranioplasty has significantly decreased the severity of postoperative headaches after retrosigmoid excision of acoustic neuromas.     

Contralateral auditory brainstem response abnormalities in acoustic neuroma

Contralateral Auditory Brainstem Response (ABR) findings in a series of 79 patients with unilateral acoustic neuroma are presented. Sixty-four patients (81 per cent) had a normal contralateral ABR, thirteen (16.4 per cent) had latency abnormalities contralaterally and in two patients (2.6 per cent) no consistent responses could be recorded despite good hearing. Abnormalities in the contralateral ABR were analysed and five patients had abnormal III-V interwave intervals, in seven patients the I-III intervals were abnormal and in one patient, only the fifth wave was present and of abnormal latency. The tumour size was assessed by computed axial tomography (CT) and the relationship between tumour size and contralateral ABR findings established. Large tumours (greater than 2.5 cm.) were associated with contralateral ABR abnormalities in 25.6 per cent of the patients, medium tumours (1.0-2.5 cm.) with ABR abnormalities in 14 per cent and there were no abnormalities in the small group (intracanalicular). The implications for interpretation of ABR recordings contralateral to an acoustic neuroma are discussed in relation to brainstem compression and its effect on the wave generator sites.     

Complications in acoustic neuroma surgery.

There has been a continuous lowering of mortality and morbidity rates in the 20th century, thanks to increasing experience and newer technology. Despite this, the readership should be aware of the hazards involved in this challenging field. Complications occur, and their incidence, mechanism, management, and prevention have been outlined here so physicians performing these procedures will be better prepared to manage them. We have found that the occurrence of complications can be greatly reduced through a team approach using the combined talents of a neurotologist, neurosurgeon, and frequently an internist. It is apparent from this article that the morbidity of removing larger tumors is significantly greater than the morbidity of removing small tumors. The recent introduction of MRI to the diagnostic armamentarium of the neurotologist may permit earlier detection and a further reduction of morbidity and mortality rates. Only continued study of prevention of complications will assure the improved quality of our results for patients undergoing microsurgical removal of acoustic neuromas.     

Hearing preservation in acoustic neuroma surgery

Hearing conservation in acoustic tumour surgery remains controversial. There have been few previous reports in the British literature. The senior author has managed 24 patients by retrosigmoid surgery with the intention of preserving hearing during the last 9 years. The clinical features, surgical technique and results are discussed with respect to pre-operative selection criteria, and post-operative quality of hearing. Hearing preservation has been achieved in 11 (78.6%) of 14 patients with small or intracanalicular tumours and a mean minimum auditory threshold of 35 dB and 70% speech discrimination, the majority (81.8%) above the 50 dB/50% level. Tumour filling the fundus of the internal auditory canal was found to be a significant adverse prognostic factor as regards successful hearing preservation. Tumour excision was complete in all patients. Nearly 90% of patients had normal facial function, and the remaining 10% grade II function. Associated morbidity was minimal. It is suggested that the potential for hearing conservation should be considered as a factor in the management of patients with small acoustic neuromas.     

Threshold monitoring of intraoperative auditory steady-state responses for ossiculoplasty surgery

Objective: The objective of this study is to establish a reliable intraoperative auditory threshold monitoring system for ossiculoplasty surgery.

Design: The chirp signal of self-designed sound field earphone (SFE) was calibrated physically and psychophysically. The interaural attenuation of the SFE was tested in patients with unilateral complete deafness and contralateral normal hearing (10 patients). Self-designed SFEs were used to measure the chirp-evoked auditory steady-state responses (Chirp-ASSR) threshold of patients (14 cases and 15 ears) with conductive hearing loss after anesthesia but before surgery.

Results: The response threshold of Chirp-ASSR under anesthesia displayed a strong correlation with the hearing threshold for pure tones: the Pearson coefficients at various frequencies (1, 2, and 4?kHz) were 0.56 (p?=?.03), 0.82 (p?p?p?=?0.02), 0.90 (p?p?Conclusions: By combining Chirp-ASSR with self-designed SFE, we obtained objective multi-frequency intraoperative auditory thresholds that correlate well with the pure tone audiometry threshold. This reliable system can be applied to future intraoperative auditory threshold monitoring for ossiculoplasty surgery.     

Suboccipital surgery for acoustic neuroma

A retrospective study was performed on 106 consecutive patients with an acoustic neuroma who underwent suboccipital surgery for the first time between 1980 and 1992. Complete follow-up data were available for all the patients, including regular imaging up to 1 January 1994. Incomplete removal of the tumours was chosen in preference to radical surgery in a large proportion of the patients, to avoid the risk of postoperative morbidity. The recurrence rate in this series was 20%. Comparison of the results of suboccipital surgery to those obtained using other surgical approaches, while taking the tumour size into consideration, showed that better results can be obtained after total removal of the tumour without any additional risk to post-operative facial nerve function. The long-term results of subtotal removal using the suboccipital approach were disappointing. It is therefore necessary to review the indications for non-radical surgery in patients with an acoustic neuroma.     

Intraoperative monitoring of facial and cochlear nerves during acoustic neuroma surgery.

The likelihood of successful preservation of facial and cochlear nerve function during acoustic neuroma surgery has been improved by the advent of intraoperative monitoring techniques. The facial nerve is monitored by recording EMG from facial muscles, with no muscle relaxants used; mechanical irritation of the nerve during surgery causes increased EMG activity, which can be detected in real time using a loudspeaker. Brief episodes of activity associated with specific surgical maneuvers aid the surgeon in avoiding damage to the nerve, whereas prolonged tonic EMG activity may reflect significant neural injury. Electrical stimulation with a hand-held probe elicits evoked EMG responses, which can be used to locate and map the nerve in relation to the tumor. The threshold for eliciting evoked EMG responses provides a rough indicator of the functional status of the nerve. Different nerves in the posterior fossa (trigeminal, facial, spinal accessory) can be identified in multichannel recordings by the spatial distribution and latency of responses to electrical stimulation. The ability to elicit EMG responses from low amplitude stimulation of the facial nerve at the brain stem after tumor removal is a reasonable predictor of postoperative facial function. Cochlear nerve function is assessed by recording the ABR from ear canal and scalp electrodes or the CNAP with an electrode placed directly on the nerve at the brain stem root entry zone. The ABR is a well-known, noninvasive technique that can be adapted to intraoperative use relatively easily but is of limited utility owing to the delay inherent in signal averaging. Direct CNAP recordings require placement of an intracranial electrode in such a way as to contact the cochlear nerve without interfering with surgical access but have the distinct advantage of rapid feedback on changes in cochlear nerve status.     

Normal auditory brainstem response in patients with acoustic neuroma

Auditory brainstem response testing has been a major breakthrough in audiologic screening for acoustic neuroma because of its high degree of sensitivity. Although it is not uncommon for other cerebellopontine angle masses to present with normal ABR findings, reports of eighth nerve tumors with false-negative auditory brainstem response tests are quite rare. A series of 120 acoustic neuromas resected at the University of Michigan was reviewed and revealed two such patients. These two patients presented with asymmetric sensorineural hearing loss and unilateral tinnitus and were found to have completely normal auditory brainstem response. The diagnosis of acoustic neuroma would have been delayed if a comprehensive evaluation had not been pursued.     

Hearing preservation in unilateral acoustic neuroma surgery

This paper reviews the principal English literature on hearing preservation in unilateral acoustic neuroma surgery. Seventeen case reports and 13 surgical series are included. In addition, we report ten cases of our own, two with successful hearing preservation. The purpose of this report is to study feasibility, success rate, and associated problems. Previous reports have been compared in terms of criteria that we have selected. A classification system similar to Silverstein's is used. The total number of cases under review is 621, with 221 reported successes. Cases limited to those having a unilateral acoustic neuroma, with valid supportive audiometry, were 394, with 131 successes. The approximate overall rate of success is 33%. There are five cases of hearing preservation with unilateral acoustic neuromas 3 cm or larger when supporting audiometric data are available, the largest being "4-5 centimeters." Problems included mixing of unilateral acoustic neuromas with other types of tumors and failure to include comprehensive data, particularly audiometry. We conclude 1) that hearing preservation is a reasonable goal in unilateral acoustic neuroma surgery, although the number of available candidates is relatively small and 2) that intelligent selection of patients and high quality surgical technique are the keys to success.     

Hearing preservation in acoustic neuroma surgery.

This article reviews the Montreal experience of hearing preservation in acoustic neuroma surgery. The medical records since 1995 of 36 patients who underwent acoustic neuroma extirpation with the intent to preserve hearing were examined. Intraoperative monitoring was conducted using auditory brainstem response measurement with electrocochleography via a transtympanic electrode. The role of intraoperative monitoring in guiding surgical technique and its correlation with postoperative hearing outcome are discussed. A review of the literature regarding hearing preservation in acoustic neuroma surgery is included.     

Hearing preservation in acoustic neuroma surgery.

With advances in imaging, intracanalicular acoustic neuromas are identified readily in patients including, oftentimes, those with serviceable hearing. Fourteen patients were operated on in an attempt to preserve hearing. Hearing was retained in 10 (71%) of the 14. Serviceable hearing was present in 7 (50%), borderline serviceable hearing in 2 (14%), and nonserviceable hearing in 1 (7%). The problems, advantages, and disadvantages of the differing approaches are discussed.