Hearing Preservation in Retrosigmoid Approach of Small Vestibular Schwannomas: Prognostic Value of the Degree of Internal Auditory Canal Filling

Pathophysiology of Postoperative Hearing Disorders after Vestibular Schwannoma Resection: Insights from Auditory Brainstem Response and Otoacoustic Emissions

Background: In order to better understand the pathophysiology of surgically induced hearing loss after vestibular schwannoma (VS) surgery, we postoperatively analyzed the hearing status in a series of patients where hearing was at least partially preserved. Methods: Hearing was assessed through tonal audiometry, speech discrimination score, maximum word recognition score (dissyllabic word lists-MaxIS), otoacoustic emissions (OAEs), and auditory brainstem response (ABR). The magnetic resonance imaging (MRI) tumor characterization was also noted. Results: In a series of 24 patients operated on for VS over 5 years, depending on the results of this triple hearing exploration, we could identify, after surgery, patients with either a myelin alteration or partial damage to the acoustic fibers, others with a likely partial cochlear ischemia, and some with partial cochlear nerve ischemia. One case with persisting OAEs and no preoperative ABR recovered hearing and ABR after surgery. Long follow-up (73 ± 57 months) revealed a mean hearing loss of 30 ± 20 dB with a drastic drop of MaxIS. MRI revealed only 25% of fundus invasion. Conclusion: a precise analysis of hearing function, not only with classic audiometry but also with ABR and OEAs, allows for a better understanding of hearing damage in VS surgery.

Prognostic Factors for Hearing Preservation Surgery in Small Vestibular Schwannoma

OBJECTIVE

to evaluate recent contributions to the literature on prognostic factors of hearing preservation in small vestibular schwannoma microsurgery.

METHODS

review of the most recent studies.

RESULTS

factors such as tumor size, preoperative hearing status, tumor growth rate, tumor origin, surgical approach, radiological characteristics, results of preoperative neurophysiological tests, preoperative symptoms and demographic features have been investigated and some of them reported to be significant in the prediction of hearing preservation.

CONCLUSIONS

tumor size and preoperative hearing status are the most impactful factors and play a key role in patient selection for hearing preservation surgery. Other features such as fundal extension, tumor origin and impaired ABR could have prognostic value on hearing preservation. Tumor growth rate, preoperative impedance, cVEMPs and age have also recently been found to be significant, but more studies are needed. The role of preoperative tinnitus, vertigo and gender is lacking and controversial, whereas the differences between available surgical approaches have been smoothed out in recent years.

Factors Influencing Personalized Management of Vestibular Schwannoma: A Systematic Review

Management of vestibular schwannoma (VS) is a complex process aimed at identifying a clinical indication for fractionated stereotactic radiotherapy (sRT) or microsurgical resection or wait and scan (WS). The aim of the review was to clarify which patient and tumor parameters may lead to different therapeutic choices, with a view to a personalized VS approach. A systematic review according to Preferred Reporting Items for Systematic Review and Meta-Analysis criteria was conducted between February and March 2022. The authors defined six parameters that seemed to influence decision-making in VS management: 1-incidental VS; 2-tumor size; 3-tumor regrowth after sRT; 4-subtotal resection; 5-patients' age; 6-symptoms. The initial search yielded 3532 articles, and finally, 812 articles were included. Through a qualitative synthesis of the included studies, management strategies were evaluated and discussed. An individualized proposal of procedures is preferable as compared to a single gold-standard approach in VS decision-making. The most significant factors that need to be considered when dealing with a VS diagnosis are age, tumor size and hearing preservation issues.

Position of Retrosigmoid Craniotomy in Hearing Preservation Surgery for Vestibular Schwannoma

BACKGROUND

Surgical access to the internal auditory canal (IAC) fundus is a crucial aspect of the retrosigmoid approach for hearing preservation surgery in vestibular schwannoma. An appropriate positioning of the retrosigmoid craniotomy is necessary to obtain an adequate surgical corridor for full fundus exposure and labyrinth preservation.

OBJECTIVE

To describe how the position of the posterior edge of the access related to the probability of exposing the fundus and to propose novel criteria for positioning the retrosigmoid craniotomy.

METHODS

Data on fundus exposure were retrospectively collected in 33 consecutive cases of sporadic vestibular schwannoma, submitted to the retrosigmoid craniotomy in a park-bench position. Patients' computed tomography images were analyzed to calculate the position of the posterior edge of the craniotomy with reference to the fundus-labyrinth line (FLL), which starts at the fundus and, running just posterior to the labyrinth, reaches the occipital squama. A logistic regression model was used to correlate the craniotomy position with the probability of exposing the fundus.

RESULTS

The fundus exposure rate was significantly higher (P = .005) for craniotomies located posteromedially to the FLL. In a logistic regression model, the probability of exposing the fundus reached 95% for craniotomies located 11.3 mm posteromedially to the FLL.

CONCLUSION

This study showed a strong association between craniotomy position and fundus exposure rate. Our findings suggest that the posteromedial edge of the retrosigmoid craniotomy should lie approximately 11 mm posteromedially to FLL to maximize the chances of exposing the fundus.

Hearing Preservation Outcomes and Prognostic Factors in Acoustic Neuroma Surgery: Predicting Cutoffs

OBJECTIVE

To investigate the outcomes of hearing preservation surgery (HPS) for acoustic neuroma and quantify tumor and patient characteristics predictive of hearing preservation after surgery.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary referral center.

PATIENTS

A total of 100 consecutive patients diagnosed with acoustic neuroma from 2000 to 2012.

INTERVENTION

Hearing preservation surgery through microscopic retrosigmoid approach combined with a retrolabyrinthine meatotomy.

MAIN OUTCOME MEASURE

Pre- and postoperative hearing stratified according to the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) and the Tokyo classifications. The most accurate cutoff was identified for each tumor and patients' variable affecting the outcome by calculating the Youden index. A multivariable analysis was undertaken at these cutoffs to identify prognostic factors for hearing preservation.

RESULTS

Preoperative hearing class was preserved after surgery in 31% (AAO-HNS), and 39% (Tokyo classification) of patients. According to the AAO-HNS classification, the tumor size in the cerebello-pontine angle, pure-tone average (PTA), and speech discrimination score cutoffs for predicting good postoperative hearing function were 7 mm, 21 dB, and 90%, respectively. With the Tokyo classification, only the PTA cutoff differed, with 27 dB. On multivariable analysis, tumor size and PTA were independent prognostic factors for postoperative hearing with high model's goodness of fit (area under the curve  = 0.784; 95% CI = 0.68-0.88 and area under the curve  = 0.813; 95% CI = 0.72-0.90), according to both the hearing classifications.

CONCLUSIONS

The estimated cutoffs for tumor size and PTA were independently associated with HPS. These factors should be prospectively investigated before they are adopted as selection criteria for HPS.

Postoperative Hearing Preservation in Patients Undergoing Retrosigmoid Craniotomy for Resection of Vestibular Schwannomas: A Systematic Review of 2034 Patients

BACKGROUND

Vestibular schwannomas (VS) are benign tumors derived from Schwann cells ensheathing the vestibulocochlear nerve. The retrosigmoid (RS) surgical approach is useful to resect tumors of multiple sizes while affording the possibility of preserving postoperative hearing.

OBJECTIVE

To conduct a systematic review of published literature investigating hearing preservation rates in patients who underwent the RS approach for VS treatment.

METHODS

The PubMed, Scopus, and Embase databases were surveyed for studies that reported preoperative and postoperative hearing grades on VS patients who underwent RS treatment. Hearing preservation rates were calculated, and additional patient demographic data were extracted. Tumor size data were stratified to compare hearing preservation rates after surgery for intracanalicular, small (0-20 mm), and large (>20 mm) tumors.

RESULTS

Of 383 deduplicated articles, 26 studies (6.8%) met eligibility criteria for a total of 2034 patients with serviceable preoperative hearing, for whom postoperative hearing status was evaluated. Aggregate hearing preservation was 31% and 35% under a fixed and random effects model, respectively. A mixed effects model was used to determine hearing preservation rates depending on tumor size, which were determined to be 57%, 37%, and 12% for intracanalicular, small, and large tumors, respectively. Significant cross-study heterogeneity was found (I2 = 93%, τ2 = .964, P < .01; Q = 287.80, P = < .001), with rates of hearing preservation ranging from 0% to 100%.

CONCLUSION

Tumor size may have an effect on hearing preservation rates, but multiple factors should be considered. Discussion of a patient's expectations for hearing preservation is critical when deciding on VS treatment plans.

Long-Term Hearing Preservation Outcomes for Small Vestibular Schwannomas: Retrosigmoid Removal Versus Observation

OBJECTIVE

Management of small vestibular schwannomas (VSs) consists of three options: serial observation, radiosurgery, and microsurgery. The authors reported the long-term hearing outcomes after retrosigmoid tumor removal in 110 patients and hearing follow-up outcomes in 160 serial observation patients with small VSs to explore the appropriate management strategy and predictive factors of hearing preservation for small VSs.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary referral center.

PATIENTS

In this study, 110 patients with small VS (purely intracanalicular/cerebellopontine angle tumor ≤15 mm) during a 15-year period, from January 2001 to December 2015, were candidates for hearing preservation surgery through retrosigmoid approach, while 160 patients were candidates for serial observation. The main outcome measure was preservation of hearing under different hearing levels, assessed with the classification of American Academy of Otolaryngology-Head and Neck Surgery.

RESULTS

Preoperative hearing levels of the 110 study patients were Class A in 49 patients, Class B in 43 patients, and Class C in 18 patients. In all surgery patients (n = 110), 97.3% (107/110) patients maintained the same level during postoperative follow-up (mean follow-up time was 49.1 ± 28.2 mo) and 86 (78.2%) had complete radiologic and audiometric data at least 4 years follow-up for review. In the 4 years follow-up surgery group (n = 86), postoperative hearing levels were Class A, B, C, and D for 22, 11, 18, and 35 patients, and postoperative rates of preservation of serviceable and useful hearing were 59.3% (51/86) and 47.1% (33/70), respectively. In serial observation group, mean follow-up time was 35.2 ± 33.1 months; mean tumor size at presentation was 8.6 ± 4.3 mm; overall mean tumor growth rate was 1.08 ± 2.3 mm/yr; serviceable hearing preservation rate of 98 patients was 54.1% (53/98) at the 5-year end point and 48.7% (37/76) at the 7-year end point.

CONCLUSION

Tumor removal should be the first treatment option for patients with small VSs and preserved hearing, especially for young patients with good hearing; retrosigmoid approach is an effective and safe approach for small VSs removal with excellent functional outcomes; better preoperative hearing predicted a higher rate of postoperative hearing preservation; patients without fundal extension were more likely to achieve hearing preservation than those with fundal extension, but no difference had been detected when retrosigmoid removal assisted with endoscope was performed; patients with small tumors originating from SVN were more likely to achieve hearing preservation compared with those with IVN-originating tumors.

Hearing Response Following Internal Auditory Canal Decompression in Neurofibromatosis Type 2

BACKGROUND

Hearing response following an osteodural decompression of the internal auditory canal (IAC) is controversial.

OBJECTIVE

To evaluate the course of auditory brainstem responses (ABRs) and the early hearing response during the first year following IAC decompression for small to medium-sized vestibular schwannomas occurring in neurofibromatosis type 2 (NF2).

METHODS

Retrospective chart review of middle fossa craniotomy for IAC osteodural decompression in NF2-related vestibular schwannomas.

RESULTS

Twelve NF2 patients were operated on from 2011 to 2016 for IAC decompression. All had NF2 according to the Manchester criteria. All had a progressive change of their ABRs documented from the diagnosis of NF2 over a mean period of 6.25 [0.36;10.9] yr. Treatment was proposed to stop hearing progression based on the speech discrimination scores (SDSs; n = 4) or for hearing maintenance (n = 8). In patients with prior hearing progression, hearing responses were observed in 3 of the 4 patients during the first year. One patient kept on progressing. In the hearing maintenance group, the SDSs remained stable. SDSs improved from 85% [20-100] to 92.5% [60-100] on average (n = 12) and from 55% [20-80] to 77.5% [50-100] in the hearing progression group (n = 4). ABRs improved in 4 patients following decompression.

CONCLUSION

IAC decompression allows early objective hearing responses in select patients. We suggest that the procedure should be offered to patients with hearing progression based on their SDSs and/or associated progressive increases in their wave III and V latencies on ABRs.

Cochlear Dysfunction is not Common in Human Meningioma of the Internal Auditory Canal

HYPOTHESIS

Cochlear dysfunction is not common in human meningioma of the internal auditory canal.

BACKGROUND

Meningiomas arising from the cerebellopontine angle and internal auditory canal typically cause hearing loss. Cochlear dysfunction is known to contribute to sensorineural hearing loss induced by vestibular schwannoma, the most common tumor of the internal auditory canal. Detailed cochlear histopathology in meningioma has not been reported.

METHODS

Retrospective analysis of cochlear histopathology in five unoperated and five operated meningiomas of the internal auditory canal identified after screening human temporal bone collections from three academic medical centers.

RESULTS

While some dysfunction of all analyzed cochlear cell types was identified, a predominant or exclusive loss of hair cells was not observed in any meningioma. Only 14.3% of temporal bones showed significantly more hair cell damage on the side of the tumor when compared with the contralateral ear; cochlear neuronal damage was more prevalent in meningiomas. The incidence of hydrops, perilymphatic precipitate, or endolymphatic precipitate was low.

CONCLUSIONS

Substantial cochlear damage in human meningioma of the internal auditory canal is not common. This may explain the anecdotal hearing improvement observed after surgical resection of meningioma. Our findings underline the importance of developing therapeutic strategies to prevent cochlear neuronal degeneration due to tumors of the internal auditory canal.

Preserved Cochlear CISS Signal is a Predictor for Hearing Preservation in Patients Treated for Vestibular Schwannoma With Stereotactic Radiosurgery

BACKGROUND

Hearing preservation is a goal for many patients with vestibular schwannoma. We examined pretreatment magnetic resonance imaging (MRI) and posttreatment hearing outcome after stereotactic radiosurgery.

METHODS

From 2004 to 2014, a cohort of 125 consecutive patients with vestibular schwannoma (VS) treated via stereotactic radiosurgery (SRS) were retrospectively reviewed. MRIs containing three-dimensional constructive interference in steady state or equivalent within 1 year before treatment were classified by two radiologists for pretreatment characteristics. "Good" hearing was defined as American Academy of Otolaryngology-Head and Neck Surgery class A. Poor hearing outcome was defined as loss of good pretreatment hearing after stereotactic radiosurgery.

RESULTS

Sixty-one patients met criteria for inclusion. Most had tumors in the distal internal auditory canal (55%), separated from the brainstem (63%), oval shape (64%) without cysts (86%), and median volume of 0.85 ± 0.55 cm. Pretreatment audiograms were performed a median of 108 ± 173 days before stereotactic radiosurgery; 38% had good pretreatment hearing. Smaller tumor volume (p < 0.005) was the only variable associated with good pretreatment hearing. 49 (80%) patients had posttreatment audiometry, with median follow-up of 197 ± 247 days. Asymmetrically decreased pretreatment cochlear CISS signal on the side of the VS was the only variable associated with poor hearing outcome (p = 0.001). Inter-rater agreement on cochlear three-dimensional constructive interference in steady state preservation was 91%.

CONCLUSIONS

Decreased cochlear CISS signal may indicate a tumor's association with the cochlear neurovascular bundle, influencing endolymph protein concentration and creating an inability to preserve hearing. This important MRI characteristic can influence planning, counseling, and patient selection for vestibular schwannoma treatment.

Pediatric neurofibromatosis type 2: clinical and molecular presentation, management of vestibular schwannomas, and hearing rehabilitation

OBJECTIVE

This study aims to describe the clinical and molecular presentation of pediatric neurofibromatosis type 2 (NF2) and the subsequent management of vestibular schwannomas (VS) and hearing rehabilitation.

METHODS

This is a single-center retrospective study of neurofibromatosis type 2 diagnosed before the age of 18 years old from 1997. Natural history of vestibular schwannomas and surgical outcomes were evaluated using volumetric MRI, hearing, and facial nerve assessment. Patients included in chemotherapy protocols were excluded.

RESULTS

From a database of 80 patients followed up for NF2 on a regular basis, 25 patients were eligible (11 sporadic cases, 14 inherited in five families). The mean age at diagnosis was 11.6 years old. The average clinical follow-up was 6.5 years. NF2 mutation was identified in 81 % of the probands. The average growth rate based on the maximum linear diameter (DGR) was 1.68 mm/year (n = 33, average follow-up 4.22 years) and 545 mm3/year in volumetric assessment (VGR) for VS larger than 1 cm (n = 21, average follow-up 3.4 years). In unoperated ears, hearing was stable in about 50 % of ears. The mean change in dB HL was 9.5 dB/year for pure-tone average and 3.5 for speech-recognition threshold (n = 34, 5.5 years 1-12). Eight children required removal through a translabyrinthine approach (mean follow-up was 4.5 years), six patients were operated on for hearing preservation (mean postoperative follow-up 4.3 years). Six patients were eligible for hearing rehabilitation with cochlear implantation (I), and five received placement of an auditory brainstem implant.

CONCLUSION

Early diagnosis and treatment of small growing VS should be carefully discussed considering familial history and possible rehabilitation with a CI.

Use of supramaximal stimulation to predict facial nerve outcomes following vestibular schwannoma microsurgery: results from a decade of experience

Object

The goal of vestibular schwannoma surgery is tumor removal and preservation of neural function. Intraoperative facial nerve (FN) monitoring has emerged as the standard of care, but its role in predicting long-term facial function remains a matter of debate. The present report seeks to describe and critically assess the value of applying current at supramaximal levels in an effort to identify patients destined for permanent facial paralysis.

Methods

Over more than a decade, the protocol for stimulating and assessing the FN during vestibular schwannoma surgery at the authors' institution has consisted of applying pulsed constant-current stimulation at supramaximal levels proximally and distally following tumor resection to generate an amplitude ratio, which subtracted from 100% yields the degree to which the functional integrity of the FN “dropped off” intraoperatively. These data were prospectively collected and additional variables that might impact postoperative FN function were retrospectively reviewed from the medical record. Only patients with anatomically intact FNs and > 12 months of follow-up data were analyzed.

Results

There were 267 patients available for review. The average posterior fossa tumor diameter was 24 mm and the rate of long-term good (House-Brackmann Grade I–II) FN function was 84%. Univariate logistic regression analysis revealed that prior treatment, neurofibromatosis Type 2 status, tumor size, cerebellopontine angle extension, subjectively thinned FN at the time of operation, minimal stimulation threshold, percent dropoff by supramaximal stimulation (SMS), and postoperative FN function all correlated statistically (p < 0.05) with long-term FN function. When evaluating patients with significant FN weakness at the time of hospital discharge, only the percent dropoff by SMS remained a significant predictor of long-term FN function. However, the positive predictive value of SMS for long-term weakness is low, at 46%.

Conclusions

In a large cohort of patients, the authors found that interrogating intraoperative FN function with SMS is safe and technically simple. It is useful for predicting which patients will ultimately have good facial function, but is very limited in identifying patients destined for long-term facial weakness. This test may prove helpful in the future in tailoring less than gross-total tumor removal to limit postoperative facial weakness.

Current strategies in management of intracanalicular vestibular schwannoma

PURPOSE OF REVIEW

The current practitioner is more often managing intracanalicular vestibular schwannomas than in the past, as improved imaging and heightened awareness leads to earlier diagnosis of these tumors. The role of observation, microsurgery, and radiation treatment in the management of intracanalicular tumors continues to evolve. The goal of this article is to evaluate and summarize recent literature pertaining to the management of intracanalicular vestibular schwannomas.

RECENT FINDINGS

Watchful waiting is an important management option for patients with minimal symptoms. The literature on the natural history of small vestibular schwannomas continues to expand, with particular emphasis on the expected hearing outcomes. Microsurgical techniques also focus on hearing preservation. Presence of fundal fluid and good or normal hearing preoperatively are positive predictors of hearing preservation after surgery. Long-term follow-up after radiation therapy for vestibular schwannomas continues to demonstrate excellent tumor control rates, although hearing preservation rates are modest.

SUMMARY

Multiple factors, including status of hearing, presence of vestibular symptoms, patient age, medical comorbidities, institutional outcomes, and patient preferences, help determine the management strategy for patients with an intracanalicular vestibular schwannoma.

Dysfunction of the cochlea contributing to hearing loss in acoustic neuromas: an underappreciated entity

OBJECTIVE

Hearing loss is a common symptom in patients with cochleovestibular schwannoma. Clinical and histologic observations have suggested that the hearing loss may be caused by both retrocochlear and cochlear mechanisms. Our goal was to perform a detailed assessment of cochlear pathology in patients with vestibular schwannoma (VS).

STUDY DESIGN

Retrospective analysis of temporal bone histopathology.

SETTING

Multi-center study.

MATERIAL

Temporal bones from 32 patients with unilateral, sporadic VS within the internal auditory canal.

MAIN OUTCOME MEASURES

Sections through the cochleae on the VS side and opposite (control) ear were evaluated for loss of inner and outer hair cells, atrophy of the stria vascularis, loss of cochlear neurons, and presence of endolymphatic hydrops and precipitate within the endolymph or perilymph. Observed pathologies were correlated to nerve of origin, VS volume, and distance of VS from the cochlea. Hearing thresholds also were assessed.

RESULTS

VS caused significantly more inner and outer hair cell loss, cochlear neuronal loss, precipitate in endolymph and perilymph, and decreased pure tone average, when compared with the opposite ear. Tumor size, distance from the cochlea, and nerve of origin did not correlate with structural changes in the cochlea or the hearing threshold.

CONCLUSION

There is significant degeneration of cochlear structures in ears with VS. Cochlear dysfunction may be an important contributor to the hearing loss caused by VS and can explain certain clinically observed phenomena in patients with VS.