Hearing Preservation After Translabyrinthine Vestibular Schwannoma Excision: Audiometry and Electrocochleography Results

Intraoperative brainstem auditory evoked potential monitoring during cerebellopontine angle surgery via retrosigmoid approach

OBJECTIVES

Brainstem auditory evoked potential (BAEP) monitoring was used to identify the influence of auditory function during cerebellopontine angle (CPA) surgery for cranial neuropathy via the retrosigmoid approach.

METHODS

This prospective study included 20 patients who underwent CPA surgery for cranial neuropathy via the retrosigmoid approach with intraoperative BAEP monitoring and pure tone audiometry (PTA). The latency and interpeak latency were analyzed at each surgical step in combination with the pre- and postoperative PTA.

RESULTS

Follow-up data were available for 17 patients. The mean pre- and postoperative PTA values were 25.65 dB and 20.70 dB, respectively. Two patients (2/17, 11.76%) developed hearing loss postoperatively. The latency of wave І significantly changed during direct auditory nerve manipulation and at the end of the surgery, while that of wave III only changed during direct auditory nerve manipulation. The appearance of wave V peak was delayed during CPA surgery.

CONCLUSIONS

CPA surgery for cranial neuropathy via the retrosigmoid approach can cause hearing loss to varying degrees, and intraoperative BAEP monitoring can reduce the occurrence of hearing loss. Intraoperative hearing function can be estimated by the latency of wave I. Hearing loss due to stretching of the brainstem can be estimated by the latency of wave III, and wave V is an early indicator of intraoperative hearing loss. Waves I and III remained stable both pre- and postoperatively, whereas wave V was unstable despite no surgery. Therefore, a precise operation and well-defined operative steps for surgeons during CPA surgery could facilitate maximal preservation of the anatomical structure and function.

A case series shows independent vestibular labyrinthine function after major surgical trauma to the human cochlea

Background

The receptors for hearing and balance are housed together in the labyrinth of the inner ear and share the same fluids. Surgical damage to either receptor system was widely believed to cause certain permanent loss of the receptor function of the other. That principle, however, has been called into question because there have been anecdotal reports in individual patients of at least partial preservation of cochlear function after major surgical damage to the vestibular division and vice versa.

Methods

We performed specific objective vestibular function tests before and after surgical trauma (partial or subtotal cochlear removal) for treatment of intracochlear tumors in 27 consecutive patients in a tertiary referral center. Vestibular function was assessed by calorics (low-frequency response of the lateral semicircular canal), vestibulo-ocular reflex by video head impulse test (vHIT) of the three semicircular canals, cervical and ocular vestibular evoked myogenic potentials (cVEMP, saccule and oVEMP, utricle). Preoperative and postoperative distributions were compared with paired t-tests.

Results

Here we show that there was no significant difference between pre- and post-operative measures for all tests of the five vestibular organs, and that after major surgical cochlear trauma, the vestibular receptors continue to function independently.

Conclusions

These surprising observations have important implications for our understanding of the function and the surgery of the peripheral auditory and vestibular system in general and open up new possibilities for the development, construction and evaluation of neural interfaces for electrical or optical stimulation of the peripheral auditory and vestibular nervous system.

Plontke et al. report data on the preservation of vestibular function in a series of patients undergoing surgical removal of intracochlear tumors. Using objective clinical tests, the authors show that in most patients the vestibular system can function normally despite major surgical trauma to the cochlea.

Receptors for the hearing and balance systems are located in the inner ear. These are very delicate structures that convert sound and movement into nerve signals to control hearing and balance. Surgical damage to either system was widely believed to cause loss of function in the other. Here, we investigated the function of the balance receptors before and after severe damage to the part of the inner ear which is responsible for hearing (the cochlea) due to surgical removal of tumurs. We show that despite the close proximity of both types of receptors and the severe trauma to the cochlea, in most patients the balance system can still function normally. This observation may have important implications for how we treat patients with inner ear surgery and for the techniques we use to treat hearing and balance disorders.

Hearing Preservation in Patients Who Undergo Labyrinthectomy and Translabyrinthine Procedures: A Case Report and Systematic Review

Importance

Preservation of endolymphatic fluids, maintenance of a fluid-filled vestibule, and preservation of the cochlear nerve and its vasculature are believed to be necessary to retaining hearing after an inner-ear operation. However, some studies have reported no hearing loss despite the violation of the vestibule, questioning the importance of maintaining a fluid-filled vestibule in preserving hearing.

Objective

To report on the preservation of hearing after a complete labyrinthectomy for Meniere disease and after disruption of the vestibule.

Evidence Review

This systematic review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines. A search of PubMed, Scopus, Ovid, and Cochrane Library databases was conducted to identify English-language articles on hearing preservation after labyrinthectomy, published from 1947 through December 11, 2019. The search strategy used a combination of boolean operators and included the following Medical Subject Heading terms and keywords: hearing preservation, labyrinth surgery, labyrinthectomy, vestibule violation, vestibule disruption, translabyrinthine approach, schwannoma removal, and semicircular canal ablation. Studies that included disruption of the vestibule and hearing preservation were included.

Findings

This systematic review identified 10 studies with 10 patients who underwent surgical removal of cholesteatoma or vestibular schwannoma and displayed postoperative hearing preservation. This study also reported on 1 patient with Meniere disease who retained hearing after undergoing a complete labyrinthectomy. Among these 11 patients, the mean (range) age was 45.1 (27-55) years, and 8 patients (73%) were women. Multiple theories exist that explain the mechanism behind hearing preservation, such as sealing of the ductus reuniens or closure of the remaining vestibule.

Conclusions and Relevance

This systematic review describes a set of patients who did not experience hearing loss after a labyrinthectomy or surgical violation of the vestibule, which seems to contradict prevailing principles for retaining hearing after inner-ear surgical procedures. This finding suggests that hearing preservation is possible after labyrinthine destruction despite the absence of a fluid-filled vestibule and that other mechanisms, such as occlusion of the ductus reuniens with granulation tissue or bone dust, may be sufficient to achieve that outcome.

Improving facial nerve outcome and hearing preservation by different degrees of vestibular schwannoma resection guided by intraoperative facial nerve electromyography

BACKGROUND

Facial nerve (FN) outcome has been improved by deciding upon the degree of vestibular schwannoma (VS) resection guided by intraoperative facial nerve monitoring (IOFM). This study aimed to evaluate hearing and FN outcomes following IOFM-guided VS removal through a retrosigmoid approach (RS).

METHODS

Between January 2015 and August 2017, 77 patients undergoing VS resection through RS, regardless of their preoperative hearing or tumor size, were included in this monocentric retrospective study. Total or near-/subtotal resection was decided intraoperatively according to IOFM. Partial resection was planned preoperatively. Pre- and postoperative FN function (House-Brackmann) and hearing level (AAO-HNS and Gardner-Robertson (GR) scales) were reported. Predictive factors for hearing preservation were analyzed according to a score developed to take into account pre-/postoperative hearing evolution.

RESULTS

The mean extrameatal diameter was 17 ± 8.5 mm. VS resection was total, near-/subtotal, and partial in 71%, 21%, and 8% of cases, respectively. Postoperative grade I and II FN function was achieved in 91% of patients. Serviceable (A+B or GR I+II) hearing and hearing with intelligibility (A+B+C or GR I-III) were preserved in 30% and 43% of cases, respectively. In multivariate analysis, preoperative synchronized auditory brainstem responses (ABR) were the only predictive factor (p = 0.006) imparting a five times greater chance of hearing preservation.

CONCLUSION

IOFM-guided VS excision through RS, whatever the VS size and hearing level, achieved a high rate of good postoperative FN function together with significant hearing preservation, and it should be used if hearing with some intelligibility is still present preoperatively, even in large VS.

Therapy of Sporadic and NF2-Related Vestibular Schwannoma

Vestibular schwannoma (VS) is a benign primary brain tumor that occurs sporadic or as part of a genetic syndrome. The most common cause is the mutation of the NF2 tumor suppressor gene that is involved in the production of the protein merlin. Merlin plays a role in cell growth and cell adhesion. In patients with NF2, the VSs arise bilaterally and coincide with other brain tumors. In sporadic VS, the tumor is typically unilateral and does not coincide in combination with other tumors. MRI is the standard imaging technique and can be used to assess the size and aspect of the tumor as well as the progression of disease. The preferred management of large VS in both VS types is surgery with or without adjuvant radiation. The management for the medium- or small-sized VS includes wait and scan, radiotherapy and/or surgery. This choice depends on the preference of the patient and institutional protocols. The outcomes of surgical and radiotherapy treatments are improving due to progress in surgical equipment/approaches, advances in radiation delivery techniques and dose optimizations protocols. The main purpose of the management of VS is preserving function as long as possible in combination with tumor control.

Intraoperative Monitoring of Auditory Function During Lateral Skull Base Surgery

OBJECTIVE

We present a unique case of a patient with a jugular foramen tumor with serviceable hearing. This study discusses the audiometric results and intraoperative electrocochleographic (ECochG) findings recorded during tumor removal to illustrate the potential utility of this technique in skull base surgery.

PATIENTS

A 22-year-old female patient presented with a jugular foramen schwannoma and associated symptoms of right-sided otalgia, mild hearing loss, and blurry vision.

INTERVENTIONS

Intraoperative ECochG responses during an infratemporal fossa approach: click and tone burst (1, 2, 4 kHz) stimuli were used and presented at 90 dB nHL.

MAIN OUTCOME MEASURES

Intraoperative ECochG testing using frequency-specific tone bursts and clicks before and after tumor resection.

RESULTS

The compound action potential magnitudes, cochlear microphonic, and summation potential were recorded pre- and post-tumor removal. For statistical analysis, a paired t test with significance set at p < 0.05 was used. The compound action potential magnitudes increased at all test frequencies (p < 0.01) while the summation potential and cochlear microphonic remained relatively stable (p > 0.05). Audiometric testing demonstrated an improvement of the preoperative mild right-sided hearing loss after tumor resection (pure-tone average for 0.5, 1, 2, and 4 kHz of 30 dB HL preoperation and 7.5 dB HL after tumor resection).

CONCLUSIONS

Intraoperative ECochG may allow for real-time monitoring during complex skull base surgery.