Hearing preservation and improvement of auditory brainstem response findings after acoustic neuroma surgery

Comparing Auditory Brainstem Responses evoked by Click and Sweep-Tone in Normal-Hearing Adults

Auditory brainstem response (ABR) is an objective method via which hearing loss could be detected. ABR induced by click, a broadband signal, is generally considered as the gold standard. However, due to the inherent delay of the cochlear traveling wave, click cannot excite the entire cochlear basement membrane at the same time, leading to the attenuation of the induced ABR waveform. In order to resolve this limitation, a sweep-tone-based stimulus that reconstructs the arrival time of different frequency components with respect to the delay characteristics of cochlear basement membrane was designed and used to induce ABR in this study. Subsequently, we compared the performance of the proposed sweep-tone-induced ABR method and the commonly adopted click induced ABR at different test levels and different stimulus rates. And the obtained results showed that the waveform morphology of sweep-tone-induced ABR was significantly better than that of click induced ABR across different test levels and stimulus rates. Moreover, compared to the click induced ABR at different sweeps, we found that the proposed sweep-tone-induced ABR effectively induced the ABR waveform at a relatively faster rate. Hence, the proposed sweep-tone-induced ABR approach provides a new method to improve the sensitivity of ABR detection in hearing loss.

Preservation of facial nerve function after resection of vestibular schwannoma

OBJECTIVE

Most data regarding facial nerve function in patients undergoing microsurgical resection of vestibular schwannomas predominantly include series performed at a single institution. In an effort to minimise individual surgeon or institutional bias, we performed an analysis of the published literature on facial nerve outcomes following microsurgical resection of vestibular schwannomas. The objective of this study was to provide a comprehensive assessment of reported outcomes for facial nerve preservation after VS surgery.

MATERIALS AND METHODS

We identified a total of 296 studies involving over 25,000 patients that included outcome data for facial nerve function of vestibular schwannoma patients treated surgically. Data regarding surgical approach, tumour size, patient age, and use of intra-operative monitoring were extracted and correlated with facial nerve function after surgery. Patients with preoperative facial nerve dysfunction (House-Brackmann score 3 or higher) were excluded and 'facial nerve preservation' was defined as grade I or II House-Brackmann function at last follow-up visit.

RESULTS

A total of 79 articles reporting on 11,873 patients met our inclusion criteria contributing to our analysis. Patients treated with the middle cranial fossa approach had a trend towards higher overall facial nerve preservation rate (85%), compared to the translabyrinthine approach (81%, p = 0.07) , and did statistically better than the retrosigmoid approach (78%, p < 0.0001). Patients with an average tumour size <20 mm had significantly improved facial nerve preservation rates, compared to larger tumours (90% vs. 67%, p < 0.0001). Patients under 65 years of age had a lower facial nerve preservation rate (71% vs. 84%, p < 0.001). Finally, the use of intra-operative monitoring improved the facial nerve preservation rate (76% vs. 71%, p < 0.001).

CONCLUSION

Factors that appear to be associated with facial nerve preservation after microsurgical resection of a vestibular schwannoma include tumour size <20 mm, use of the middle fossa approach and use of neuromonitoring during surgery. These data provide a summary assessment of the published literature regarding facial nerve preservation after microsurgical resection of vestibular schwannoma.

Mapping clinical outcomes expectations to treatment decisions: an application to vestibular schwannoma management

OBJECTIVE

Complex medical decision making obligates tradeoff assessments among treatment outcomes expectations, but an accessible tool to perform the necessary analysis is conspicuously absent. We aimed to demonstrate methodology and feasibility of adapting conjoint analysis for mapping clinical outcomes expectations to treatment decisions in vestibular schwannoma (VS) management.

STUDY DESIGN

Prospective.

SETTINGS

Tertiary medical center and US-based otologists/neurotologists.

SUBJECTS

Treatment preference profiles among VS stakeholders-61 younger and 74 older prospective patients, 61 observation patients, and 60 surgeons-were assessed for the synthetic VS case scenario of a 10-mm tumor in association with useful hearing and normal facial function.

MAIN OUTCOME MEASURE

Treatment attribute utility.

METHODS

Conjoint analysis attribute levels were set in accordance to the results of a meta-analysis. Forty-five case series were disaggregated to formulate microsurgery facial nerve and hearing preservation outcomes expectations models. Attribute utilities were computed and mapped to the realistic treatment choices of translabyrinthine craniotomy, middle fossa craniotomy, and gamma knife radiosurgery.

RESULTS

Among the treatment attributes of likelihoods of causing deafness, temporary facial weakness for 2 months, and incurable cancer within 20 years, and recovery time, permanent deafness was less important to tumor surgeons, and temporary facial weakness was more important to tumor surgeons and observation patients (Wilcoxon rank-sum, p < 0.001). Inverse mapping of preference profiles to realistic treatment choices showed all study cohorts were inclined to choose gamma knife radiosurgery.

CONCLUSION

Mapping clinical outcomes expectations to treatment decisions for a synthetic clinical scenario revealed inhomogeneous drivers of choice selection among study cohorts. Medical decision engines that analyze personal preferences of outcomes expectations for VS and many other diseases may be developed to promote shared decision making among health care stakeholders and transparency in the informed consent process.

Preventing internal auditory artery vasospasm using topical papaverine: an animal study

BACKGROUND

Internal auditory artery (IAA) spasm is thought to be one of the causes of postoperative sensory hearing loss after attempted hearing preservation removal of an acoustic neuroma. The use of topical papaverine, a nonspecific vasodilator, to prevent vascular insufficiency to the inner ear and to improve hearing outcomes has been suggested but not proven.

MATERIALS AND METHODS

Vasospasm was mechanically induced by compressing the IAA in the control ears of six rabbits after application of topical saline. The subsequent reduction of cochlear blood flow (CBF) was measured using a laser-Doppler (LD) flow-monitoring technique. Functional loss of cochlear activity was verified with distortion product otoacoustic emissions (DPOAE). The contralateral experimental ears were treated with the topical application of papaverine directly to the IAA and cochleovestibular nerve complex. CBF and DPOAE were compared between the control and papaverine treated ears for 3-minute and 5-minute IAA compressions.

RESULTS

Every control ear demonstrated some degree of postcompression IAA vasospasm (i.e., reduced CBF) and reduction of DPOAE. Nearly complete recovery of CBF and DPOAE to baseline was observed in all of the papaverine treated ears.

CONCLUSIONS

An animal model of IAA vasospasm was described. Mechanically induced vasospasm of the IAA was prevented by the topical application of papaverine. These findings have clinical implications for surgical procedures involving the internal auditory canal/cerebellopontine angle such as acoustic neuroma removal.

Acuteness of preoperative factors to predict hearing preservation in acoustic neuroma surgery

OBJECTIVES

To determine in patients with acoustic neuromas the predictive factors of hearing preservation according to clinical, radiological, and electrophysiological parameters and to evaluate, for each of these predictive factors, the percentage of patients with preserved hearing.

STUDY DESIGN

The study involved 107 candidates for hearing preservation attempt. Mean age was 49.7 +/- 11.4 years. Quantitative and qualitative parameters were prospectively studied. Quantitative parameters were age, duration of functional complaints, hearing loss assessed by pure tone and speech audiometry, and auditory brainstem responses (ABRs). Qualitative parameters (expressed in percentage of presence) were sex, functional complaints, vestibular deficit revealed by vestibular testings, well-shaped ABRs, wave I, III, or V of ABRs, and transient evoked otoacoustic emissions (TEOAEs).

METHODS

Patients were divided into two groups according to whether their hearing was preserved (52.3%) or not preserved (47.7%). First, quantitative and qualitative factors were compared between both groups to identify predictive factors. Second, all patients were considered together and the percentage of hearing preservation was determined according to the presence of each predictive factor.

RESULTS

The results confirmed the predictive value of classic parameters such as preoperative hearing level, radiological data, and trace of ABRs. They also emphasized the predictive role of other parameters such as short duration of hearing loss, presence of wave III in ABRs, and presence of TEOAEs.

CONCLUSIONS

The size of the tumor and the preoperative hearing levels are longstanding predictive factors of hearing preservation in acoustic neuroma surgery, and candidates for hearing preservation are therefore now selected according to these factors. This study added more recent predictive factors and, among the 10 factors identified as predictive, the most relevant to hearing preservation were the presence of TEOAEs (69.7%), short duration of hearing loss (66.7%), and presence of wave III in ABRs (66.7%).

Cochlear microphonics for hearing preservation in vestibular schwannoma surgery

OBJECTIVES

To determine whether cochlear function is beneficial in decision-making concerning the selection of hearing preservation surgery for vestibular schwannoma.

STUDY DESIGN

Retrospective review of 44 patients undergoing tumor resection with a middle fossa approach.

METHODS

Cochlear microphonics in electrocochleography together with tumor size, pure-tone average (PTA), speech discrimination score (SDS), auditory brainstem response (ABR), and compound action potentials were examined. As acoustic stimuli, short tone-bursts with frequencies of 0.5, 1, and 2 kHz were employed to measure cochlear microphonics and a click was used to obtain compound action potentials. We determined detection thresholds of cochlear microphonics and action potentials.

RESULTS

The overall rate of preservation of serviceable hearing was 59.1% (26/44). There were significant differences between patients with and without serviceable postoperative hearing in PTA, SDS, finding of ABR, compound action potential detection threshold, and mean cochlear microphonic detection threshold (at 0.5, 1, and 2 kHz). However, tumor size was unrelated to hearing outcome. Serviceable hearing was preserved in 23 (76.7%) of 30 patients, with a mean cochlear microphonic detection threshold of 40 dB nHL or less, suggesting normal or slightly impaired cochlear function. Hearing recovery was recognized in three patients, who also had a mean cochlear microphonic detection threshold of 40 dB nHL or less. Of the three patients, two had lower cochlear microphonic detection thresholds than audiometric thresholds, demonstrating the existence of a retrocochlear component in their hearing loss.

CONCLUSIONS

The cochlear microphonic detection threshold predicts not only hearing preservation but also hearing improvement in patients with vestibular schwannomas.

Acoustic neuroma surgery: absent auditory brainstem response does not contraindicate attempted hearing preservation

OBJECTIVE

Absence of auditory brainstem response (ABR) waveforms has been associated with a poor likelihood of hearing preservation following resection of acoustic neuromas. Our experience is reviewed for patients with absent preoperative ABR regarding hearing preservation, hearing improvement, and return of ABR.

STUDY DESIGN

Retrospective review of 22 cases of acoustic neuroma resection. Nine patients with absent preoperative ABR were identified. All underwent tumor resection utilizing intraoperative cochlear nerve action potential (CNAP) monitoring. Postoperative hearing results and ABR waveforms were examined.

METHODS

Charts were reviewed and tabulated for age, sex, tumor side, tumor size, preoperative and postoperative audiometric and ABR results, intraoperative monitoring results by ABR and CNAP, and surgical complications.

RESULTS

Hearing preservation was achieved in seven of nine patients (78%) with absent preoperative ABR, as well as six of seven patients (86%) with tumors less than or equal to 20 mm in greatest dimension. Although intraoperative ABR monitoring was not possible in any of these patients, CNAP monitoring was successful in all. Return of ABR waveforms was observed in four of the six patients (67%) tested from 3 to 22 months postoperatively. Four of the seven patients (57%) enjoyed improvement in hearing class as defined by the guidelines of the American Academy of Otolaryngology-Head and Neck Surgery.

CONCLUSIONS

Absent ABR waveforms have not been a negative prognostic sign regarding hearing preservation. CNAP monitoring is possible in these patients and likely helps to minimize iatrogenic cochlear nerve trauma. Patients with no ABR waveforms have hope of hearing preservation and even improvement following acoustic neuroma resection performed utilizing CNAP monitoring and hearing preservation surgical techniques.

Is the presence of transient evoked otoacoustic emmissions in ears with acoustic neuroma significant?

One hundred sixty-eight patients admitted for acoustic neuroma removal were involved in this study. In all cases, the size of the tumor and the presence or absence of tinnitus and vertigo or dizziness were evaluated. Investigated functional procedures included bilateral measures of pure-tone audiometry (PTA), auditory brainstem response (ABR), electronystagmography (ENG), and transient evoked otoacoustic emissions (TEOAEs). Thirty-five patients (21%) had normal preoperative TEOAEs in the affected ear, whereas 133 patients (79%) failed to show reproducible responses. The aims of this study were 1. to evaluate what distinguishes patients with preoperative TEOAEs in the pathological ear (group A) from those who had no TEOAE (group B); and 2. to determine in cases of attempted hearing preservation whether preoperative TEOAE presence in the neuroma ear (group C) was predictive of postoperative hearing preservation compared with the group of patients without TEOAEs (group D). The presence of vertigo or dizziness was significantly less frequent, the age was lower, and preoperative mean PTA loss in both ears was lower in group A compared with group B. Frequency of the other studied parameters and ABR threshold were similar in both groups. When hearing preservation was attempted, the mean preoperative PTA loss of group C patients was lower in both ears compared with group D. However, postoperative mean PTA loss did not significantly differ in the two groups. In group C, the percentage of hearing preservation (66.6%) was significantly higher than the percentage of deafness (33.4%), whereas in group D the percentage of postoperative preserved audition and deafness did not significantly differ (respectively 44.4% and 55.6%). The findings suggest that 1. TEOAEs in ears with acoustic neuromas are found in younger patients with a lower preoperative mean PTA loss and are accompanied by fewer functional complaints, perhaps because preserved TEOAEs indicate a better preservation of inner ear vasculature; and, 2. along with radiological and electrophysiological investigations, TEOAE presence in the pathological ear could provide an additional criterion or predictive factor for the successful outcome of attempted hearing-conservation surgery in ears with acoustic neuromas.