Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients

Facial Nerve Tractography Using Diffusion MRI: A Comparison of Acquisition b -Values and Single- and Multifiber Tracking Strategies

HYPOTHESIS

This study investigates the impact of different diffusion magnetic imaging (dMRI) acquisition settings and mathematical fiber models on tractography performance for depicting cranial nerve (CN) VII in healthy young adults.

BACKGROUND

The aim of this study is to optimize visualization of CN VII for preoperative assessment in surgeries near the nerve in the cerebellopontine angle, reducing surgery-associated complications. The study analyzes 100 CN VII in dMRI images from the Human Connectome Project, using three separate sets with different b values ( b = 1,000 s/mm 2 , b =2,000 s/mm 2 , b =3,000 s/mm 2 ) and four different tractography methods, resulting in 1,200 tractographies analyzed.

RESULTS

The results show that multifiber and free water (FW) compartment models produce significantly more streamlines than single-fiber tractography. The addition of an FW compartment significantly increases the mean streamline fractional anisotropy (FA). Expert quality ratings showed that the highest rated tractography was the 1 tensor (1T) method without FW at b values of 1,000 s/mm2.

CONCLUSIONS

In this young and healthy cohort, best tractography results are obtained by using a 1T model without a FW compartment in b =1,000 diffusion MR images. The FW compartment increased the contrast between streamlines and cerebrospinal fluid (higher mean streamline FA). This finding may help ongoing research to improve CN VII tractography results in tumor cases where the nerve is often stretched and thinned by the tumor.

Functional outcomes after retrosigmoid approach to the cerebellopontine angle: Observations from a single-center experience of over 13 years

Introduction

Accessing the posterior base of the skull is complex because of the vital neurovascular structures in the area. However, the retrosigmoid approach (RSA) offers a solution to this challenge.

Research question

To analyze surgical outcome of RSA.

Material and methods

This study involved a retrospective review of patient charts from a single center, focusing on the surgical procedure and outcomes following the operation.

Results

The study included 517 patients suffering from conditions like vestibular schwannomas (VS), metastatic cancers, and trigeminal neuralgia. The most frequent symptoms reported were balance disorders (42.7%), hearing loss (36.5%), walking difficulties (21.2%), headaches (18.9%), facial pain (17.1%), issues with trigeminal nerve function (14.1%), cerebellar dysfunction (13.5%), and facial nerve paralysis (10.2%). The rate of complications stood at 21.1%, with 11.3% of patients needing revision surgery. The median score on the Clavien-Dindo scale was 2, and the rate of mortality related to surgery was 1.0%. Permanent symptom improvement was seen in 72.1% of cases. Temporary new deficits occurred in 43.2% of patients, with facial nerve paralysis being the most common (14.1%). No significant correlation was found between the size of the craniotomy and the extent of tumor resection (p = 0.155), except in the case of VS (p = 0.041). Larger craniotomy sizes were associated with higher rates of complications (p = 0.016), especially CSF leaks (p = 0.006). Complications significantly affected the likelihood and number of new deficits (p < 0.001 for both), particularly postoperative bleeding (p = 0.019, p = 0.001), CSF leaks (p = 0.026, p = 0.039), and hydrocephalus (p = 0.050, p = 0.007).

Conclusions

The potential for complications related to the surgical approach cannot be overlooked. The size of the tumor should not dictate larger surgical approaches due to the associated increase in postoperative complications; a tailored approach that considers the precise tumor location and pathology is crucial for optimizing postoperative outcomes.

Subtotal resection of vestibular schwannoma with subsequent Gamma Knife irradiation - tumor growth control, facial and cochlear nerve outcome - preliminary results

<b>Introduction:</b> The choice of treatment of vestibular schwannoma (VS) depends on several factors, including the tumor size, the patient's age and overall health, and the presence and severity of symptoms.<b>Aim:</b> The aim of the study was to assess the effectiveness of intentional subtotal resection (STR) of tumor followed by Gamma Knife surgery (GKS) in patients with larger VS (Koos 3 and 4).<b>Materials and methods:</b> The retrospective analysis was performed on 18 patients. Data of VS volumes measured in MRI, the facial nerve function assessed in the House-Brackmann scoring system (HB), and the results of audiological examination expressed on the Gardner-Robertson scale (GR) were collected preoperatively, postoperatively, and post-GKS.<b>Results:</b> Preoperatively, the main symptom was hearing loss observed in 13 out of 18 patients. The facial nerve function was assessed as HB 1 in 16, whereas HB 2 in 2 patients. The mean volume of the tumor in the initial MRI amounted to 16.81 cm³ . Postoperatively, the facial nerve was assessed as HB 1 or 2 in 16, whereas HB 3 in 2 patients. Serviceable hearing was presented by only 4 persons. The Mean diameter of the tumor after subtotal surgery amounted to 3.16 cm³ , 1.83 cm³ after GKS, and 1.58 cm³ at the last follow-up. The facial nerve function and hearing level remained the same as before GKS in all patients.<b>Conclusions:</b> STR followed by GKS can be a safe and effective method of treatment of large VS concerning the functional outcome of the facial nerve and the tumor volume growth control.

Retrosigmoid versus middle fossa approach for hearing and facial nerve preservation in vestibular schwannoma surgery: A systematic review and comparative meta-analysis

BACKGROUND

Vestibular schwannomas (VS) are benign tumors arising from vestibular nerve's Schwann cells. Surgical resection via retrosigmoid (RS) or middle fossa (MF) is standard, but the optimal approach remains debated. This meta-analysis evaluated RS and MF approaches for VS management, emphasizing hearing preservation and Cranial nerve seven (CN VII) outcomes stratified by tumor size.

METHODS

Systematic searches across PubMed, Cochrane, Web of Science, and Embase identified relevant studies. Hearing and CN VII outcomes were gauged using the American Academy of Otolaryngology-Head and Neck Surgery, Gardner Robertson, and House-Brackmann scores.

RESULTS

Among 7228 patients, 56 % underwent RS and 44 % MF. For intracanalicular tumors, MF recorded 38 % hearing loss, compared to RS's 54 %. In small tumors (<1.5 cm), MF showed 41 % hearing loss, contrasting RS's lower 15 %. Medium-sized tumors (1.5 cm-2.9 cm) revealed 68 % hearing loss in MF and 55 % in RS. Large tumors (>3cm) were only reported in RS with a hearing loss rate of 62 %.

CONCLUSION

Conclusively, while MF may be preferable for intracanalicular tumors, RS demonstrated superior hearing preservation for small to medium-sized tumors. This research underlines the significance of stratified outcomes by tumor size, guiding surgical decisions and enhancing patient outcomes.

Facial nerve electrical motor evoked potential in cerebellopontine angle tumors for its anatomical and functional preservation

Background

Among the technical measures to preserve facial nerve (FN) function, intraoperative neuromonitoring has become mandatory and is constantly being scrutinized. Hence, to determine the efficacy of FN motor evoked potentials (FNMEPs) in predicting long-term motor FN function following cerebellopontine angle (CPA) tumor surgery, an analysis of cases was done.

Methods

In 37 patients who underwent CPA surgery, FNMEPs through corkscrew electrodes positioned at C5-C6 and C6-C5 (C is the central line of the brain as per 10-20 EEG electrode placement) were used to deliver short train stimuli and recorded from the orbicularis oculi, oris, and mentalis muscles.

Results

In 58 patients, triggered electromyography (EMG) was able to identify the FN during resection of tumor, but 8 out of these (4.64%) patients developed new facial weakness, whereas 3 out of 38 (1.11%) patients who had intact FN function MEP (decrement of FN target muscles - CMAPs amplitude peak to peak >50-60%), developed new facial weakness (House and Brackmann grade II to III).

Conclusion

The FNMEP has significant superiority over triggered EMG when tumor is giant and envelops the FN.

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.

Wireless facial biosensing system for monitoring facial palsy with flexible microneedle electrode arrays

Facial palsy (FP) profoundly influences interpersonal communication and emotional expression, necessitating precise diagnostic and monitoring tools for optimal care. However, current electromyography (EMG) systems are limited by their bulky nature, complex setups, and dependence on skilled technicians. Here we report an innovative biosensing approach that utilizes a PEDOT:PSS-modified flexible microneedle electrode array (P-FMNEA) to overcome the limitations of existing EMG devices. Supple system-level mechanics ensure excellent conformality to the facial curvilinear regions, enabling the detection of targeted muscular ensemble movements for facial paralysis assessment. Moreover, our apparatus adeptly captures each electrical impulse in response to real-time direct nerve stimulation during neurosurgical procedures. The wireless conveyance of EMG signals to medical facilities via a server augments access to patient follow-up evaluation data, fostering prompt treatment suggestions and enabling the access of multiple facial EMG datasets during typical 6-month follow-ups. Furthermore, the device's soft mechanics alleviate issues of spatial intricacy, diminish pain, and minimize soft tissue hematomas associated with traditional needle electrode positioning. This groundbreaking biosensing strategy has the potential to transform FP management by providing an efficient, user-friendly, and less invasive alternative to the prevailing EMG devices. This pioneering technology enables more informed decision-making in FP-management and therapeutic intervention.

Comparison of Postoperative Outcomes in Cystic Versus Solid Vestibular Schwannoma in a Multi-institutional Cohort

OBJECTIVE

Cystic vestibular schwannomas (cVSs) have more variable and less favorable clinical outcomes after microsurgical resection compared with solid VS (sVS). This study compares the preoperative presentation and postoperative outcomes between cVS and sVS.

STUDY DESIGN

Retrospective cohort study.

SETTING

Two tertiary skull base referral centers.

METHODS

Consecutive adult patients who underwent VS resection from 2016 to 2021 were included. Univariate and multivariate analyses compared differences in baseline symptoms and postoperative outcomes between cVS and sVS.

RESULTS

There were a total of 315 patients (64% female; mean age, 54 yrs) and 46 (15%) were cystic. cVS were significantly larger than sVS (maximum diameter, 28 vs. 18 mm, p < 0.001) and had higher rates of dysphagia and dysphonia preoperatively (p < 0.02). cVSs were more likely to undergo translabyrinthine resection (76 vs. 50%, p = 0.001) and have a higher rate of subtotal resection (STR) compared with sVS (30 vs. 13%, p = 0.003). At latest follow-up, fewer cVS achieved good facial nerve (FN) outcome (House-Brackmann [HB] I/II) (80 vs. 90%, p = 0.048). Subanalysis of cVS and sVS matched in tumor size, and surgical approach did not show differences in the rate of STR or FN outcomes (HB I/II, 82 vs. 78%, p = 0.79).

CONCLUSION

In this large multi-institutional series, cVSs represent a distinct entity and are characterized by larger tumor size and higher incidence of atypical symptoms. Although cVSs were more likely to undergo STR and portend worse FN outcomes than sVSs, this may be due to their larger tumor size rather than the presence of the cystic component.

[Our approach to the treatment of vestibular schwannomas with arachnoid dissection of the facial nerve]

Preserving the function of the facial nerve is extremely important in surgery for vestibular schwannomas. Two methods of arachnoid dissection are described for resection of vestibular schwannoma via retrosigmoid approach (from the brain stem and internal auditory canal).

OBJECTIVE

To evaluate the results of arachnoid dissection of the facial nerve from internal auditory canal when resecting the vestibular schwannoma.

MATERIAL AND METHODS

We analyzed 61 patients with vestibular schwannomas. Patients were divided into 2 groups depending on surgical technique. We estimated facial nerve function before and after surgery, preoperative dimension of vestibular schwannoma and extent of resection. The influence of various factors on extent of resection and postoperative facial nerve function was studied.

RESULTS

Vestibular schwannoma resection from the brain stem was performed in 30 patients, arachnoid dissection - in 31 patients. There was no significant between-group difference. Gross total resection was performed in 78.7% of cases. Both techniques demonstrated similar results regarding extent of resection. Arachnoid dissection showed the advantage regarding facial nerve function immediately after surgery (p=0.012) and 6 months later (p<0.001). Normal facial nerve function in 6 months after arachnoid dissection was observed in 80.7% of patients. Preoperative dimension of tumor influenced facial nerve function in addition to technique of resection (p=0.001).

CONCLUSION

We identified the factors influencing facial nerve function after resection of vestibular schwannoma. Surgical technique was the most significant factor. These data expand and popularize arachnoid dissection in surgery of vestibular schwannomas.

Two-Stage Surgical Management for Acutely Presented Large Vestibular Schwannomas: Report of Two Cases

The surgical management of vestibular schwannomas should be based on their presentation, neuro-imaging findings, surgeons' expertise, and logistics. Multi-stage surgery can be beneficial for large-sized lesions with acute presentations. Herein, we highlighted the indications for two cases managed initially through the retrosigmoid and, subsequently, translabyrinthine approaches. The first case presented with acute balance and gait issues and a long history of hearing loss and blurred vision. Neuroimaging findings revealed a cerebellopontine angle lesion, resembling a vestibular schwannoma, with significant brainstem compression and hydrocephalus. Due to the rapidly deteriorating clinical status and large-sized tumor, we first proceeded with urgent decompression via a retrosigmoid approach, followed by gross total resection via a translabyrinthine approach two weeks later. The second case presented with gradually worsening dizziness and hemifacial numbness accompanied by acute onset severe headaches and hearing loss. Neuroimaging findings showed a large cerebellopontine angle lesion suggestive of a vestibular schwannoma with acute intratumoral hemorrhage. Given the acute clinical deterioration and large size of the tumor, we performed urgent decompression with a retrosigmoid approach followed by gross total resection through a translabyrinthine approach a week later. Post-surgery, both patients showed excellent recovery. When managing acutely presented large-sized vestibular schwannomas, immediate surgical decompression is vital to avoid permanent neurological deficits.

Vestibular Schwannoma: Long-term Outcome of the Vestibular Function After Stereotactic Radiosurgery

Objective

Evaluation at long term of the impact of the stereotactic surgery (SRS) on the vestibular function in vestibular schwannoma (VS) patients.

Study design and setting

Retrospective study in a tertiary referral center.

Patients

Fifty-one VS patients were included (34 females;17 males), aged from 41 to 78 years treated exclusively with SRS.

Intervention

Vestibular function was assessed before SRS and with median time interval of 14 (FU1) and 25 (FU2) months after treatment. Vestibular evaluation included: history, clinical vestibular examination, videonystagmography, head impulse test (v-HIT) and cervical vestibular evoked myogenic potentials (c-VEMPS).

Results

Before SRS, caloric testing (Caloric) was impaired in 77%; after treatment, in 92% (FU1) and 77% (FU2). Lateral HIT was decreased in 22% before SRS, in 39% at FU1 and FU2. C-VEMPS were absent in 50% before SRS, in 76% at FU1 and, FU2. Before SRS, no statistically significant association was found between asymptomatic and symptomatic patients with respect to the results of Caloric, v-HIT and c-VEMPS. This lack of association was also seen after SRS, at FU1 and FU2.

Conclusion

Our study showed that the impairment of the vestibular function might be attributed to the VS itself as well as to the radiation of the inner ear during SRS. The lateral SSC at low frequencies and the saccular function seem to be more involved with the time.

Significance of Preoperative Nerve Reconstruction Using Diffusion Tensor Imaging Tractography for Facial Nerve Protection in Vestibular Schwannoma

OBJECTIVE

The facial nerve trace on the ipsilateral side of the vestibular schwannoma was reconstructed by diffusion tensor imaging tractography to identify the adjacent relationship between the facial nerve and the tumor, and to improve the level of intraoperative facial nerve protection.

METHODS

The clinical data of 30 cases of unilateral vestibular schwannoma who underwent tumor resection via retrosigmoid approach were collected between January 2019 and December 2020. All cases underwent magnetic resonance imaging examination before operation. Diffusion tensor imaging and anatomical images were used to reconstruct the facial nerve track of the affected side, so as to predict the course of the nerve and its adjacent relationship with the tumor, to compare the actual trace of the facial nerve during operation, verify the degree of coincidence, and evaluate the nerve function (House-Brackmann grade) after surgery.

RESULTS

The facial nerve of 27 out of 30 cases could be displayed by diffusion tensor imaging tractography, and the tracking rate was 90% (27/30). The intraoperative locations of facial nerve shown in 25 cases were consistent with the preoperative reconstruction results. The coincidence rate was 92.6% (25/27). The facial nerves were located on the anterior middle part of the tumor in 14 cases, anterior upper part in eight cases, anterior lower part in seven cases, and superior polar in one case. Intraoperative facial nerve anatomy was preserved in 30 cases. Among the 30 patients, total resection was performed in 28 cases and subtotal resection in two cases. The facial nerve function was evaluated 2 weeks after operation, and the results showed grade I in 12 cases, grade II in 16 cases and grade III in two cases.

CONCLUSION

Preoperative diffusion tensor imaging tractography can clearly show the trajectory and adjacent position of the facial nerve on the side of vestibular schwannoma, which is beneficial to accurately identify and effectively protect the facial nerve during the operation, and is worthy of clinical application and promotion.

Preservation of the integrity of facial nerve in vestibular schwannoma microsurgery: A consecutive study of 127 clinical cases focusing on nervus intermedius

Background

Nervus intermedius (NI) injuries are not given enough attention by neurosurgeons during vestibular schwannoma (VS) surgery. Preservation of NI function is essential for the integrity and continuity of the facial nerve, although this can be challenging. We identified the risk factors for NI injury and proposed our experience for optimizing NI preservation based on our cases.

Methods

We retrospectively analyzed clinical data from a consecutive series of 127 patients with VS who underwent microsurgery via the retrosigmoid approach from 2017 to 2021 at our institution. The baseline characteristics of the patients were collected from the medical records, and the incidence of NI dysfunction symptoms was obtained by outpatient and online video follow-up 6 months after surgery. The surgical procedures and techniques used were described in detail. The data were analyzed in relation to sex, age, tumor location (left or right), Koos grading scale, internal acoustic canal (IAC) invasion (TFIAC Classification), brainstem adhesion, tumor characteristics (cystic or solid), tumor necrosis, and preoperative House-Brackmann (HB) grading by univariate and multivariate analyses.

Results

Gross tumor removal was achieved in 126 (99.21%) patients. Subtotal removal was performed on one patient (0.79%). Twenty-three of our cases exhibited facial nerve palsy preoperatively; 21 patients had HB grade II facial palsy, and two had HB grade III. Two months after surgery, 97 (76.38%) patients had normal function of the motor portion of the facial nerve; 25 (19.69%) patients had HB Grade II facial palsy, five had Grade III (3.94%), and zero (0%) had Grade IV. Postoperatively, 15 patients experienced newly gained dry eyes (11.81%), whereas 21 cases of lacrimal disturbances (16.54%), nine of taste disturbances (7.09%), seven of xerostomia (5.51%), five of nasal hypersecretions (3.94%), and seven of hypersalivation (5.51%) were identified in our cases. Univariate and multivariate analyses revealed that the Koos grading scale and tumor characteristics (solid or cystic) were correlated with NI injury (p <0.01).

Conclusion

The data in this study demonstrate that although the motor function of the facial nerve is well preserved, NI disturbance is still common after VS surgery. Maintaining the integrity and continuity of the facial nerve is key to NI function. Performing bidirectional and subperineurium dissection based on even and adequate debulking is beneficial for NI preservation in VS surgery. Higher Koos grading and cystic characteristics of VS are associated with postoperative NI injuries. These two parameters can be used to guide the delineation of surgical strategy and predict the prognosis of NI function preservation.

Management of Vestibular Schwannoma with Normal Hearing

INTRODUCTION

This work aimed to study the management of vestibular schwannoma (VS) patients with normal hearing (NH).

METHODS

A retrospective study was undertaken in a Quaternary referral center for skull base pathologies. Among 4,000 VS patients 162 met our strict audiological criteria for NH. These patients were divided into 2 management groups, wait and scan (W&S) (45/162, 25%) and operated patients (123/162, 75%), and 6 patients were included in both groups.

RESULTS

Our management strategy achieved the goals for treatment of VS. First goal, all tumors were completely removed except for 2 intentional residuals. Second goal, facial nerve (FN) function preservation (House Brackmann I, II, and III) was 95.9%. Third goal, possible hearing preservation (HP) attempts occurred in (50/122) (40.9%) with an HP rate in 44% of the patients. Additionally, there were only 2 cases of postoperative complications with no CSF leakage. The prospect of HP in NH patients did not differ with respect to tumor size. However, patients with normal preoperative ABR seemed to have better chances of HP and good FN function and vice versa. HP rate was superior for the MCFA as opposed to the RS + RLA. W&S group demonstrated hearing stability in 88.9% of the patients and FN function stability of HB I in 100% of the patients.

CONCLUSIONS

Surgical resection is a reasonable and definitive management option for VS with NH. Nevertheless, choosing to manage cases with observation remains an appropriate management option for NH patients. ABR might be considered as an adjuvant tool indicating better prognosis for HP.

Hearing Preservation, Facial Nerve Dysfunction, and Tumor Control in Small Vestibular Schwannoma: A Systematic Review of Gamma Knife Radiosurgery Versus Microsurgery

BACKGROUND AND PURPOSE

Vestibular schwannoma (VS) is the most common type of tumor found in the cerebellopontine angle that accounts for 8% of all intracranial tumors. VS management is currently a challenge due to the unpredictable nature of the tumor. Few studies have compared the results and complications of various therapeutic approaches to VS. Therefore, as a treatment option for VSs smaller than 25 mm, we conducted a systematic review to compare Gamma Knife radiosurgery (GKRS) with conventional surgery.

METHODS

Literature searches were conducted of four online databases (PubMed, Google Scholar, Cochrane, and ScienceDirect) using the following keyword search: ("vestibular schwannoma" OR "acoustic neuroma") AND ("gamma knife" OR "gamma knife radiosurgery") AND ("resection" OR "open surgery") AND ("hearing preservation" OR "facial nerve" OR "tumor growth").

RESULTS

We identified six retrospective cohort studies, five of which were of fair-to-good quality. All studies showed that GKRS was superior to surgery in hearing preservation. Two studies indicated that surgery was superior to GKRS in maintaining tumor control, one indicated that GKRS was superior, and the remainder indicated that there was no significant difference in maintaining tumor control between GKRS and microsurgery.

CONCLUSIONS

Based on the three outcomes chosen for this review, GKRS was superior to microsurgery in small VS.

A comparative study of microsurgery and gamma knife radiosurgery in vestibular schwannoma evaluating tumor control and functional outcome

Background

Both stereotactic radiosurgery (SRS) and microsurgical resection (SURGERY) are available as treatment options for sporadic vestibular schwannoma (VS). There are very few direct comparative studies comparing both treatment modalities in large cohorts allowing detailed subgroup analysis. This present study aimed to compare the nuances in the treatment of VS by SURGERY and SRS in 2 highly specialized neurosurgical centers.

Methods

This is a retrospective bicentric cohort study. Data from patients treated between 2005 and 2011 were collected retrospectively. Recurrence-free survival (RFS) was assessed radiographically by contrast-enhanced magnetic resonance imaging.

Results

The study population included N = 901 patients with a mean follow-up of 7 years. Overall, the incidence of recurrence was 7% after SURGERY, and 11% after SRS with superior tumor control in SURGERY in the Kaplan-Meier-analysis (P = 0.031). In small tumors (Koos I and II), tumor control was equivalent in both treatment arms. In large VS (Koos III and IV), however, RFS was superior in SURGERY. The extent of resection correlated with RFS (P < .001). Facial and hearing deterioration was similar in both treatment arms in small VS, but more pronounced in SURGERY of large VS. Tinnitus, vertigo, imbalance, and trigeminal symptoms were more often improved by SURGERY than SRS.

Conclusions

SRS can achieve similar tumor control compared to SURGERY in smaller VS (Koos I and II)-with similar postinterventional morbidities. In large VS (Koos III and IV), long-term tumor control of SRS is inferior to SURGERY. Based on these results, we suggest that if combination therapy is chosen, the residual tumor should not exceed the size of Koos II.

Schwannomas of Brain and Spinal Cord

Schwannomas are benign tumors originating from the Schwann cells of cranial or spinal nerves. The most common cranial schwannomas originate from the eight cranial nervevestibular schwannomas (VS). VS account for 6-8% of all intracranial tumors, 25-33% of the tumors localized in the posterior cranial fossa, and 80-94% of the tumors in the cerebellopontine angle (CPA). Schwannomas of other cranial nerves/trigeminal, facial, and schwannomas of the lower cranial nerves/are much less frequent. According to the World Health Organization (WHO), intracranial and intraspinal schwannomas are classified as Grade I. Some VS are found incidentally, but most present with hearing loss (95%), tinnitus (63%), disequilibrium (61%), or headache (32%). The neurological symptoms of VSs are mainly due to compression on the surrounding structures, such as the cranial nerves and vessels, or the brainstem. The gold standard for the imaging diagnosis of VS is MRI scan. The optimal management of VSs remains controversial. There are three main management options-conservative treatment or "watch-and-wait" policy, surgical treatment, and radiotherapy in all its variations. Currently, surgery of VS is not merely a life-saving procedure. The functional outcome of surgery and the quality of life become issues of major importance. The most appropriate surgical approach for each patient should be considered according to some criteria including indications, risk-benefit ratio, and prognosis of each patient. The approaches to the CPA and VS removal are generally divided in posterior and lateral. The retrosigmoid suboccipital approach is a safe and simple approach, and it is favored for VS surgery in most neurosurgical centers. Radiosurgery is becoming more and more available nowadays and is established as one of the main treatment modalities in VS management. Radiosurgery (SRS) is performed with either Gamma knife, Cyber knife, or linear accelerator. Larger tumors are being increasingly frequently managed with combined surgery and radiosurgery. The main goal of VS management is preservation of neurological function - facial nerve function, hearing, etc. The reported recurrence rate after microsurgical tumor removal is 0.5-5%. Postoperative follow-up imaging is essential to diagnose any recurrence.

Is Preoperative Facial Palsy a Deterrent to Facial Nerve Preservation after Gross-Total Removal of Giant Vestibular Schwannomas?

Background Although rare in small vestibular schwannomas, preoperative facial nerve paresis is often present in giant schwannomas. Preserving facial nerve function in these cases remains a herculean task. This study evaluates the facial functions after complete tumor removal and whether preoperative facial nerve involvement affects postoperative functional status.

Methods This retrospective study from January 2014 to August 2021 excluded nongiant tumors (< 4 cm), neurofibromatosis type 2 cases, incomplete removals, redo surgeries, deaths, and cases done without nerve monitoring. These were grouped into preoperative facial palsy present (PFP) and no preoperative facial palsy (NFP). Facial nerve functions were assessed on first postoperative day, at the time of discharge, and at last follow-up and dichotomized into two groups: nondisfiguring (House–Brackmann [HB] grades I–III) and disfiguring (HB grades IV–VI). The cohort outcomes of patients with nondisfiguring PFP (HB grades I–III) were also analyzed.

Results There were 88 cases (PFP, n = 57; NFP, n = 31). Facial nerve was preserved anatomically in 62 (70.45%) patients (PFP, n = 38; NFP, n = 24) without any statistical difference (p = 0.29). Statistically significant disfiguring facial outcomes (HB IV, V, VI) were seen in patients with preoperative facial palsy (p = 0.01); however, a comparison of facial functions in patients with only nondisfiguring PFP with those in NFP group did not show the statistical difference (p = 0.12).

Conclusions Facial nerve palsy present before surgery does not seem to be a deterrent to intraoperative preservation of facial nerve during complete removal of giant vestibular schwannomas. Patients with nondisfiguring facial palsies have postoperative facial functions comparable to those without facial palsy.

The Learning Curve in Skull Base Surgery Part 1–From Historical-Philosophical Concepts to Microsurgical Lab Training

The learning curve reflects surgeons' experience in managing several patients with the same disease. In skull base surgery, the professional's place on the curve could be related to the number of times the same procedure was performed. Where does curve begin? What amount of training is necessary prior to its application in surgical settings? What were the results of the first few skull base tumor surgeries performed by a surgeon who goes on to produce excellent results, and how is reflected in the start of their learning curve? The only way for neurosurgeons to improve their results from the start is with prior training in the microsurgery laboratory. This learning technique is essential to maximize the chance of success of a neurosurgical procedures, minimizing the morbidity rate to which patients are subjected by less experienced neurosurgeons. This article is divided in two parts, and its purpose is to show how training in the microsurgical laboratory fits into the construction of knowledge about skull base surgery, based on authors' experience and reflections. This first part discusses the technical, psychological, and philosophical aspects of medical knowledge, primarily addressing those training in skull base surgery, the principles of some selected philosophical currents, and their influence on the development of current medical knowledge.

Surgical management of skull base meningiomas and vestibular schwannomas

PURPOSE OF REVIEW

The aim of this study is to discuss surgical management of meningiomas and schwannomas of skull base.

RECENT FINDINGS

Meningiomas and schwannomas are typically benign neoplasm with a good prognosis after surgery. Patients should be treated individually related to several features: size and localization of tumor and its proximity with deep critical neurovascular structures, neurological status, age and comorbidity. Also, the widespread use of neuroimaging and the progressive and constant aging of the populations inevitably result in the increase of detection rate of incidental (asymptomatic) neoplasm.Nowadays, there are still controversies about the correct management strategy.

SUMMARY

Surgery represents the gold standard treatment, with the objective of gross total resection; however, it is not always feasible due to localization, encasement of neuro-vascular structure, invasion of cranial nerve and brain parenchyma. Stereotactic radiosurgery and radiation therapy are important to achieve a satisfactory functional outcome and tumor control in case of residue or recurrence. A multidisciplinary approach is pivotal.

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.

Presence of a fundal fluid cap on preoperative magnetic resonance imaging may predict long-term facial nerve function after resection of vestibular schwannoma via the retrosigmoid approach

OBJECTIVE

Preservation of neurological function is a priority when performing a resection of a vestibular schwannoma (VS). Few studies have examined the radiographic value of a fundal fluid cap—i.e., cerebrospinal fluid in the lateral end of a VS within the internal auditory canal—for prediction of postoperative neurological function. The aim of this study was to clarify whether the presence of a fundal fluid cap on preoperative magnetic resonance images has a clinical impact on facial nerve function after resection of VSs.

METHODS

The presence of a fundal fluid cap and its prognostic impact on long-term postoperative facial nerve function were analyzed.

RESULTS

A fundal fluid cap was present in 102 of 143 patients who underwent resection of sporadic VSs via the retrosigmoid approach. Facial nerve function was acceptable (House-Brackmann grade I–II) immediately after surgery in 82 (80.4%) patients with a fundal fluid cap and in 26 (63.4%) of those without this sign. The preservation rate of facial nerve function increased in a time-dependent manner after surgery in patients with a fundal fluid cap but plateaued by 3 months postoperatively in those without a fundal fluid cap; the difference was statistically significant at 12 months (96.1% vs 82.9%, p = 0.013) and 24 months (97.1% vs 82.9%, p = 0.006) after surgery. The presence of a fundal fluid cap had a significantly positive effect on long-term facial nerve function at 24 months after surgery when tumor size and intraoperative neuromonitoring response were taken into account (OR 5.55, 95% CI 1.12–27.5, p = 0.034).

CONCLUSIONS

Neuromonitoring-guided microsurgery for total resection of VSs is more likely to be successful in terms of preservation of facial nerve function if a fundal fluid cap is present. This preoperative radiographic sign could be helpful when counseling patients and deciding the treatment strategy.

Early Translabyrinthine Surgery for Small- and Medium-Sized Vestibular Schwannomas: Consecutive Cohort Analysis of Outcomes

OBJECTIVE

Reappraisal of the role of translabyrinthine (TLAB) surgery in small- and medium-sized vestibular schwannomas (VSs).

STUDY DESIGN

Retrospective study.

SETTING

Tertiary referral center.

PATIENTS

A total of 330 consecutive patients diagnosed between 1973 and 2019 with small- and medium-sized VS up to 20 mm in the extrameatal portion submitted to surgical treatment.

INTERVENTIONS

VS removal through microscopic TLAB approach.

MAIN OUTCOME MEASURES

Facial nerve function according to the House-Brackmann scale at 12-month follow-up, postoperative complications and entity of tumor resection assessed with postoperative MRI. A comparative analysis of outcomes between two groups of patients was further conducted, according to tumor size: Group A, small-sized (intrameatal or ≤10 mm extrameatal tumors) and Group B, medium-sized VSs (extrameatal between 11 and 20 mm).

RESULTS

Complete tumor removal was achieved in all cases. The overall complication rate was 5.5%, being cerebrospinal fluid leak the most frequent. Patients with small-sized VS (n = 121) presented a significantly better facial nerve function than patients with medium-sized tumors (n = 209), showing House-Brackmann Grades I to II in 92.6% versus 73.6% of cases, respectively ( p < 0.001). A nearly 4.5-fold higher risk of poor facial nerve function at 12 months affects patients with medium-sized tumors (odds ratio, 4.473; 95% confidence interval, 2.122-9.430; p < 0.001).

CONCLUSION

In the current scenario of multioptional VS management, when hearing preservation is not feasible, early TLAB approach as first-line treatment for small-sized VSs showed favorable results. Factors supporting such proactive surgical treatment include long-term definitive cure, no major complications, good facial nerve outcomes, and the possibility of simultaneous hearing rehabilitation with a cochlear implant.

The Bigger the Better? Analysis of Surgical Complications and Outcome of the Retrosigmoid Approach in 449 Oncological Cases

Introduction

Exposure of the posterior skull base and the cerebellopontine angle is challenging due to important neurovascular structures. The retrosigmoid approach (RSA) has become the standard method used in surgery. We report our experiences with RSAs regarding technical obstacles, complications, and approach-related outcomes.

Materials and Methods

We performed a retrospective chart review at a tertiary neurosurgical center between January 2007 and September 2020. We included all patients undergoing surgery for oncologic lesions through RSAs, concentrating on surgical technique, postoperative outcome, and complications.

Results

A total of 449 RSAs were included. The median age at the time of surgery was 58 years; 168 (37.4%) were male and 281 (62.6%) were female. The median approach surface was 7.8 cm². The median tumor volume was 5.9 cm³. The median Clavien–Dindo grade was 2, the total complication rate was 28.7%, and gross total resection (GTR) was 78.8%. Findings revealed that tumor volume had no significant impact on postoperative complications in general (p = 0.086) but had a significant impact on postoperative hemorrhage (p = 0.037) and hydrocephalus (p = 0.019). Tumor volume was significant for several preoperative symptoms (p < 0.001). The extent of the approach had no significant impact on complications in general (p = 0.120) but was significant regarding postoperative cerebrospinal fluid (CSF) leaks (p = 0.008). Craniotomy size was not significant regarding GTR (p = 0.178); GTR rate just missed significant correlation with tumor volume (p = 0.056). However, in the case of vestibular schwannomas, the size of craniotomy was important for GTR (p = 0.041).

Conclusion

Tumor volume has an important impact on preoperative symptoms as well as on postoperative complications. Although the extent of the craniotomy barely missed significance regarding GTR, a correlation can be assumed. Thus, the extent of craniotomy should be taken into presurgical consideration, especially in the case of postoperative CSF leaks. Regarding vestibular schwannomas, craniotomy size plays an important role in achieving satisfactory oncological outcomes. Different approaches should be selected where necessary regarding superior resection rates.

The 100 Most Highly Cited Publications on Hearing Preservation for Vestibular Schwannomas

OBJECTIVE

Vestibular schwannomas are benign, slow-growing tumors that often reduce patient quality of life by compressing nearby nerves. Neurological function preservation is one of the indicators of treatment success, with hearing preservation being the most difficult to obtain. This paper provides a bibliometric analysis of hearing preservation in treating acoustic neuromas and a greater understanding of the most highly cited articles, which have enhanced our understanding of this topic.

METHODS

Key terms of "acoustic neuroma," "vestibular schwannoma," and "hearing preservation" were queried through Web of Science. Articles were sorted by citation frequency, and the top 100 articles were recorded for title, name of first author, journal title, year of publication, total number of citations (and associated rank), average number of citations per year, country of the first author's associated institution, and type of study.

RESULTS

The top 100 cited articles were published from 1980 to 2014. The United States had the highest involvement as a country (55%), the University of Pittsburgh as an institution (13%), and The Journal of Neurosurgery as a publishing source (27%). Fourteen were reviews, and 86 were clinical papers. Of the 86, 73 were retrospective studies.

CONCLUSION

Bibliometric analyses summarize and assess potential areas of strength and knowledge gaps within the literature. Studies on hearing preservation in vestibular schwannomas mostly consist of retrospective reviews that assess postoperative outcomes of microsurgery and radiosurgery. Prospective studies and novel treatment options for hearing preservation in vestibular schwannomas are needed to increase current literature diversity.

How to Precisely Open the Internal Auditory Canal for Resection of Vestibular Schwannoma via the Retrosigmoid Approach

Objective

The aim of this study was to investigate how to precisely expose the intrameatal portion of vestibular schwannomas (VSs) without damaging the labyrinth.

Methods

This was a retrospective study of patients who had undergone retrosigmoid resection of a VS in our institution from April 2018 to December 2021. The patients were divided into microsurgery (MS) and navigation endoscopic-assisted (combined surgery, CS) groups and the effects of image guidance and endoscopy evaluated. The tumors in the CS group were then divided into medial and lateral types by fusion imaging and the differences between the two types analyzed.

Results

Data of 84 patients were analyzed. Residual tumor was detected by postoperative MRI at the fundus of the internal auditory canal in 5 of the 31 patients in the MS group and 1 of the 53 in the CS group. The labyrinth was damaged in four patients in the MS group but was not damaged in any of the CS group patients. The CS group included 29 lateral type and 24 medial type schwannomas. Endoscopic-assisted resection of residual tumor in the IAC was performed significantly more often on medial than on lateral tumors.

Conclusion

Navigation and endoscopy are useful in assisting the exposure of the intrameatal portion of VSs. Preoperative MRI/CT fusion imaging is helpful in preoperative evaluation and surgical planning in patients undergoing VS surgery. Tumors of the medial type require endoscopic assistance for resection.

The effects of different surgical positions (semi-sitting and lateral position) on the surgical outcomes of large vestibular schwannoma: study protocol for a randomized controlled trial

Background

There is an ongoing discussion about the advantages and disadvantages of different surgical positions (semi-sitting and lateral position) for vestibular schwannoma surgery. Each position has its advantages, disadvantages, challenges, and risk profiles. The objectives of this study are to compare the effects of different surgical positions (semi-sitting and lateral position) on the outcomes of large vestibular schwannoma, primarily including effectiveness and safety.

Methods

In this single-centre, open, randomized controlled trial, we will recruit a total of 116 participants according to the inclusion and exclusion criteria who will be randomized to an experimental group or control group. Patients will undergo operations in semi-sitting and lateral positions. The primary endpoint will be the percentage of gross total resection. The secondary endpoints will include the facial nerve function, hearing preservation, surgical position placement time, time of operation (skin-to-skin surgical time), hospital stay, total hospitalization fee, and complications. The follow-up period will be at least 12 months, during which time patients will be evaluated both clinically and radiologically.

Discussion

This issue is still debated after 30 years since the first large comparative study was published in 1989, so the study will be useful. Therefore, more high-quality studies are required to compare clinical outcomes, complications, and other factors associated with these two positions.

Trial registration

Chinese Clinical Trial Registry ChiCTR1900027550. Registered on 17 November 2019

Vestibular Schwannomas

Vestibular Schwannomas are well treated by GKNS. This can be used alone for tumors up to 20cm³. For larger tumors subtotal, intracapsular resection followed by GKNS a few months later would seem to give the best results. While there remain disagreements relating to optimal treatment for VSs among colleagues using different techniques, there are indications that these are becoming less confrontational. The evidence in this chapter suggests that early GKNS intervention results in better hearing preservation and tumor control in small tumors. The evidence in favor of "wait and see" depends on series reporting on changes in tumor size using suboptimal measurements. It is more important to record the fate of hearing, and this would seem to be better preserved following early GKNS. The results of GKNS for NF2 are by no means as good as could be wished but would seem to be superior to those of microsurgery. The importance of screening of family members cannot be over emphasized.

Endoscope-Assisted Retrosigmoid Approach for Vestibular Schwannomas With Intracanalicular Extensions: Facial Nerve Outcomes

Objective

To explore the role of neuroendoscope assistance during surgical resection of the intracanalicular portion of vestibular schwannomas via the retrosigmoid approach and the subsequent early facial nerve outcomes.

Methods

Patients of vestibular schwannoma with intracanalicular extensions undergoing retrosigmoid dissection at a single institution were retrospectively analyzed in this study. Several surgical techniques were applied to ensure maximal and safe removal of tumors. Tumors extending less than 10 mm into the internal acoustic canal (IAC) were classified as Grade A, while those extending over 10 mm into IAC were taken as Grade B. Neuroendoscope was applied at the end of microscopic phase to search for potential remnants for Grade B tumors. Absolute tumor extension was defined and measured. House and Brackmann (HB) scale was used to evaluate immediate CN VII outcomes.

Results

Of the 61 patients, there were 38 females and 23 males. A total of 18 (29.51%) cases were Koos Grade II, 12 (19.67%) cases Koos Grade III, and 31 (50.82%) cases Koos Grade IV. There were 38 cases (62.30%) of Grade A and 23 cases (37.70%) of Grade B. Gross total resection was achieved in 60 cases (98.36%). Four cases of intracanalicular remnants were detected and completely removed under endoscopic visualizations. There was a significantly higher proportion (17%, p = 0.02) of intracanalicular remnants in Grade B than Grade A. CN VII and VIII were anatomically preserved in all cases. A total of 55 cases (90.16%) retained good (HB Grades 1 and 2) facial nerve outcomes.

Conclusions

In Grade B vestibular schwannomas, after maximal microsurgical removal, endoscopic evaluation of the intracanalicular portion revealed residual tumors in 17% of the patients. Hence endoscopic evaluation of the potential intracanalicular remnants for tumor extending over 10 mm within IAC (Grade B) is recommended.

Modified Skin Incision and Location of Burr-Hole Surgery via a Retrosigmoid Approach: An Anatomical Study

Objective  This study aims to reduce the tissue damage during craniotomy with retrosigmoid approach. A modified sickle-shaped skin incision was developed, and a new burr-hole positioning method was proposed. Methods  Five adult cadaveric heads (10 sides) were used in this study. The sickle-shaped skin incision was performed during craniotomy. The nerves, blood vessels, and muscles were observed and measured under a microscope. Additionally, 62 dry adult skull specimens (left sided, n  = 35; right sided, n  = 27) were used to measure the distance between the most commonly used locating point (asterion [Ast] point) and the posteroinferior point of the transverse sigmoid sinus junction (PSTS) (Ast-PSTS), as well as the distance between the new locating O point and the PSTS (O-PSTS). Then, the reliability of the new locating O point was validated on the same five adult cadaveric heads (10 sides) used for the sickle-shaped skin incision. Results  The sickle-shaped skin incision reduced the damage to the occipital nerves, blood vessels, and muscles during the surgery via a retrosigmoid approach. The dispersion and variability of O-PSTS were smaller than those of Ast-PSTS. Conclusion  The sickle-shaped skin incision of the retrosigmoid approach can reduce the tissue damage and can completely expose the structures in the cerebellopontine angle. The modified O point is a more reliable locating point for a burr-hole surgery than the Ast point.

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.

Preoperative Facial Nerve Palsy in Patients With Vestibular Schwannoma: Clinical Features and Postoperative Functional Prognosis in a Case Series of 34 Among 1228 Consecutive Patients

BACKGROUND

Facial nerve palsy is a rare presenting symptom of vestibular schwannomas and has not been investigated in detail.

OBJECTIVE

To investigate the incidence, clinical features, and postoperative long-term outcomes of facial nerve function in patients with vestibular schwannomas causing preoperative facial nerve palsy.

METHODS

After excluding patients with neurofibromatosis type 2 and those with prior treatment, 1228 consecutive patients who underwent vestibular schwannoma surgery were retrospectively investigated. Patients with and without preoperative facial nerve palsy were compared statistically to clarify their clinical features.

RESULTS

Preoperative tumoral facial nerve palsy was seen in 34 patients (2.8%). Their clinical features included older age, having large cystic tumors with significant meatal extension, and showing abnormal electrogustometric responses, compared with patients without preoperative facial nerve palsy. Owing to the frequent insufficient intraoperative responses on facial nerve electromyography, the tumor resection rate was lower in the group with preoperative facial nerve palsy (mean: 95.2%). Among the 33 patients with sufficient follow-up data (mean: 63.9 mo), additional treatment was required only in 1 patient and facial nerve function improved in 25 patients (75.8%) within 2 yr postoperatively.

CONCLUSION

Facial nerve palsy is a rare preoperative symptom that occurs in less than 3% of patients with vestibular schwannoma. Tumor resection in such patients tends to be challenging owing to their advanced age, having large cystic tumors with significant meatal extension, and difficulties in intraoperative facial nerve monitoring, but surgical decompression of the facial nerve can assist in the improvement of their long-term functions.

EMG monitoring

While most neurophysiologists are familiar with electromyography (EMG) for the purpose of clinical diagnostics, this technique also has a long tradition for neuro-monitoring. In short, intra-operative use of EMG can be divided into stimulated EMG on the one hand and monitoring of the free-running EMG and its spontaneous activity on the other hand. Methods for utilization of stimulated EMG are covered elsewhere in this book. This chapter focuses on the monitoring of spontaneous, or, more correctly, "surgically evoked" EMG. The history and underlying physiologic principles of intra-operative EMG are covered in this chapter as well as a detailed overview of the methodology. Building up from the basis of this background, we describe examples of how EMG can be used to help in intra-operative detection of adverse events and also in the prediction of postoperative outcomes. In the opinion of the authors, EMG should not be used as a "standalone" technique in contemporary neuro-monitoring. Most of its significant potential may be realized when it is used in a complementary way together with other modalities, mainly motor evoked potentials. Bearing this in mind, we sketch out how such a complementary setup may be used for improved neuro-monitoring.

Accuracy and outcomes of diffusion tensor imaging tractography in resection for vestibular schwannoma for facial nerve preservation

BACKGROUND

Impairment of facial nerve (FN) function is a common postoperative complication in surgical resections of Vestibular Schwannomas (VS). Diffusion tensor imaging (DTI) tractography creates in vivo imaging of the anatomical location of white matter tracts that can be preoperatively used to visualize the displaced FN. We present an analysis of patients who underwent DTI tractography imaging prior to VS resection.

METHODS

Patient charts were reviewed from March 2012 to April 2015 who underwent DTI tractography prior to surgical resection for VS. Reliability of this measure was compared to the intraoperative FN location as determined by the surgeon. House Brackmann (HB) score was used to assess facial nerve function.

RESULTS

A total of 11 patients were included with a mean age of 43 years (range: 19-64) and mean follow-up length of 11.9 months (range: 3.1-34.2). The average maximum tumor diameter was 2.82 cm (range: 1.7-4.2). DTI tractography was accurate in 90.9% (10/11) of patients. Postoperatively, 72.7% (8/11) had a HB score of I or II, 18.2% (2/11) had a HB score of III, and 9.1% (1/11) had a HB score of IV.

CONCLUSIONS

Facial nerve visualization for VS resection can be accurately visualized using DTI tractography. This modality may lead to reduction of postoperative FN damage.

Suboccipital Transhorizontal Fissure Approach for Posterior Cranial Fossa Lesions: A Cadaveric Study and First Clinical Experience

BACKGROUND

Surgical treatment of pathological lesions in the deep cerebellar hemisphere, cerebellopontine angle (CPA), and fourth ventricle of the posterior cranial fossa (PCF) is challenging. Conventional neurosurgical approaches to these lesions are associated with risk of various complications. Mastery of efficient fissure dissection is imperative when approaching deep-seated lesions. The horizontal fissure (HF) is the largest and deepest fissure of the cerebellum.

OBJECTIVE

To conduct an anatomical study and introduce a novel suboccipital trans-HF (SOTHF) approach to access lesions of the deep cerebellar hemispheres, CPA, and upper fourth ventricle of the PCF.

METHODS

We performed a cadaveric dissection study focusing on anatomical landmarks and surgical feasibility of the SOTHF approach then implemented it in 2 patients with a deep cerebellar hemispheric tumor.

RESULTS

Anatomical feasibility of the SOTHF approach was demonstrated and compared with conventional approaches in the cadaveric study. Opening the suboccipital surface of the HF to create medial, intermediate, and lateral surgical corridors provided optimal viewing angles and wide access to the deep cerebellar hemispheres, CPA, and upper fourth ventricle without heavy cerebellar retraction. Sacrificing cerebellar neural structures and complex skull base techniques were not required to obtain adequate exposure. The SOTHF approach was successfully applied without complication in 2 patients with a deep cerebellar hemispheric tumor.

CONCLUSION

The HF is an important cerebellar fissure that provides a gateway to deep areas of the PCF. Further studies are needed to define and expand applications of the SOTHF approach.

Hearing Preservation in a Vestibular Schwannoma Patient via a Retrosigmoid Approach

Vestibular schwannoma(s) (VS) are benign tumors of the cerebellopontine angle comprising the Schwann cells that line the vestibular branch of cranial nerve VIII. Treatment goals focus on the preservation and improvement of facial nerve and hearing function as well as tumor control. The retrosigmoid (RS) approach is associated with lower hearing preservation rates compared to the middle cranial fossa (MCF) approach. A 60-year-old male was diagnosed with right-sided cystic VS and subsequently underwent surgical resection via a RS approach. Although his preoperative hearing function was quite low, with a right-sided speech reception threshold of 35 dB and a right-sided word recognition score of 48%, he experienced a drastic improvement in his hearing postoperatively with stable residual tumor. Although the RS approach for VS resection is not considered to be as effective at preserving hearing function compared to the MCF approach, we present a case where it resulted in significantly improved hearing function. Additionally, in cases where preoperative hearing function is severely diminished, hearing preservation is not typically an outcome that is considered. However, this case suggests that improvement of hearing in these patients may be attainable, particularly with the RS approach.

Endoscope-assisted microsurgical retrosigmoid approach to the lateral posterior fossa: Cadaveric model and a review of literature

Background:

The advancement of endoscopic techniques in the past decade has improved the surgical management of cerebellopontine angle (CPA) tumors. Endoscope-assisted microsurgery improves the ability to evaluate the extent of resection, achieve safe tumor resection and reduce the risk of surgery-related morbidity.

Methods:

In this study, we used a cadaveric model to demonstrate a step by step endoscope-assisted microsurgery of the retrosigmoid approach to the lateral posterior fossa.

Results:

Retrosigmoid craniotomies were performed on four latex-injected cadaver heads (eight CPAs). Microsurgical exposures were performed to identify neurovascular structures in each segment. 0° and 30° rigid endoscope lenses were subsequently introduced into each corridor and views were compared in this manner. The endoscopic images were compared with the standard microscopic views to determine the degree of visualization with each technique. In each case, better visualization was provided by both the 0° and 30° endoscope lenses. Endoscopic views frequently clarified neurovascular relationships in obscured anatomic regions.

Conclusion:

Endoscope-assisted microsurgery could allow better visualization of various regions of the posterior fossa. Surgical planning for posterior fossa lesions should include consideration of this combined approach.

Evolution in Surgical Treatment of Vestibular Schwannomas

Purpose of Review

Management of vestibular schwannomas (VSs) is multimodal and include watchful observation, radiation treatment, and surgery. Over the past decades, a shift in treatment strategy toward radiation treatment has gradually displaced surgery from the main treatment option for VS. In recent years, however, surgery has been further refined by developments of microsurgical and endoscopic techniques and advances in intraoperative application of neuroprotective drugs. This article presents outcomes of modern surgical treatment of VS in the era of radiosurgery and reviews recent published advancements relevant to VS management.

Recent Findings

Following VS surgery, excellent tumor resection rates and cranial nerve outcomes were achieved in a consecutive series of 572 adult patients with mean postoperative follow up of 4 years. Innovations in surgical technique include endoscopic technique as additional tool to microsurgery, exploration of semi-sitting position for large tumors, and intraoperative use of vasoactive agents as neuroprotective strategy.

Summary

Despite great developments in radiation treatment of VS, surgery remains the key solution for the majority of the cases in order to achieve cure of the disease, long-term tumor control, and preservation of cranial nerve function at long-term.

Bone Cement Internal Auditory Canal Reconstruction to Reduce CSF Leak After Vestibular Schwannoma Retrosigmoid Approach

OBJECTIVE

To describe rates of cerebrospinal fluid (CSF) rhinorrhea after reconstruction of the IAC with calcium phosphate bone cement during retrosigmoid resections of vestibular schwannomas.

METHODS

A retrospective chart review of 177 patients who underwent retrosigmoid craniotomy and opening of the internal auditory canal for resection of a vestibular schwannoma between January 2016 and September 2019 at a tertiary referral center. Patients with other cerebellopontine angle tumor histology, neurofibromatosis type II, or those undergoing revision surgeries were excluded.

RESULTS

Out of 177 patients, six patients (3.4%) developed postoperative rhinorrhea. Four patients (2.3%) were taken back to the OR for mastoidectomy and repair of CSF leak. Three of these patients were noted to have a CSF leak from the peri-labyrinthine air cells, and one was found to have a leak from the craniotomy site communicating with the mastoid air cells. Two patients were conservatively managed with diuretics and had resolution of their CSF leak. Six patients (3.4%) were readmitted for postoperative infection. Two patients were diagnosed with meningitis (1.1%), one aseptic and one H. Influenza, and three patients developed surgical site infections (1.6%). One patient was empirically treated with antibiotics and ultimately had a negative CSF culture.

CONCLUSIONS

Our results demonstrate that the use of calcium phosphate bone cement for IAC closure in retrosigmoid resection of vestibular schwannomas is a safe and effective technique with low rates of postoperative CSF rhinorrhea.

Hearing loss and volumetric growth rate in untreated vestibular schwannoma

OBJECTIVE

In this study, the authors aimed to clarify the relationship between hearing loss and tumor volumetric growth rates in patients with untreated vestibular schwannoma (VS).

METHODS

Records of 128 treatment-naive patients diagnosed with unilateral VS between 2012 and 2018 with serial audiometric assessment and MRI were reviewed. Tumor growth rates were determined from initial and final tumor volumes, with a median follow-up of 24.3 months (IQR 8.5-48.8 months). Hearing changes were based on pure tone averages, speech discrimination scores, and American Academy of Otolaryngology-Head and Neck Surgery hearing class. Primary outcomes were the loss of class A hearing and loss of serviceable hearing, estimated using the Kaplan-Meier method and with associations estimated from Cox proportional hazards models and reported as hazard ratios.

RESULTS

Larger initial tumor size was associated with an increased risk of losing class A (HR 1.5 for a 1-cm3 increase; p = 0.047) and serviceable (HR 1.3; p < 0.001) hearing. Additionally, increasing volumetric tumor growth rate was associated with elevated risk of loss of class A hearing (HR 1.2 for increase of 100% per year; p = 0.031) and serviceable hearing (HR 1.2; p = 0.014). Hazard ratios increased linearly with increasing growth rates, without any evident threshold growth rate that resulted in a large, sudden increased risk of hearing loss.

CONCLUSIONS

Larger initial tumor size and faster tumor growth rates were associated with an elevated risk of loss of class A and serviceable hearing.

Depression and ability to work after vestibular schwannoma surgery: a nationwide registry-based matched cohort study on antidepressants, sedatives, and sick leave

BACKGROUND

In patients with vestibular schwannomas (VS), tumor control is often achieved, and life expectancy is relatively good. The main risks of surgical treatment are hearing loss and facial nerve function. The occurrence of mood and sleeping disorders in relation to surgery is an important aspect of health that has rarely been studied. Similarly, only limited data exist on the rate of sick leave for patients with VS. In this nationwide registry-based study, we define the use of antidepressants and sedatives and the sick leave pattern before and after VS surgery.

METHODS

Adult patients with histopathologically verified VS were identified in the Swedish Brain Tumor Registry (SBTR) and clinical data were linked to relevant national registries after assigning five matched controls to each patient. We studied patterns of dispensed antidepressants and sedative drugs as well as patterns of sick leave compared to respective controls at 2 years before and 2 years following surgery.

RESULTS

We identified 333 patients and 1662 matched controls. The rate of antidepressant use was similar between patients and controls 2 years before surgery (6.0% vs 6.3%) and 2 years after surgery (10.1% vs 7.5%). The rate of sedative use was also similar 2 years before surgery (3.9% vs 4.3%) and 2 years after surgery (4.8% vs 5.3%). The rate of sick leave was similar at baseline between patients and controls, but at 2 years after surgery, 75% of patients vs 88% of controls (p < 0.01) had no registered sick leave. Long-term sick leave after surgery was predicted by use of sedatives (OR 0.60, 95% CI 0.38-0.94, p = 0.03), more preoperative sick leave (OR 0.91, 95% CI 0.89-0.93, p < 0.001), and new-onset neurological deficits after surgery (OR 0.42, 95% CI 0.24-0.76, p = 0.004).

CONCLUSION

This nationwide study shows no significant differences in the use of antidepressants and sedatives between patients and controls, while the rate of postoperative sick leave was higher in patients than in controls after VS surgery. Our findings underpin the importance of avoiding surgical sequelae and facilitating return to normal professional life.

Is salvage surgery for large vestibular schwannomas after failed gamma knife radiosurgery more challenging?

In order to verify whether a previous gamma knife surgery (GKS) treatment could influence the oncological and functional outcome in large vestibular schwannoma (VS) surgery, we have compared group of patients operated on for large VS after failed GKS to a group of genuine VS that underwent the same functional nerve-sparing resection technique regimen in the same period. Single center retrospective cohort study of 23 consecutive GKS failure and 170 genuine VS patients operated on between April 2003 and March 2019. After resection, patients were allocated to a Wait-&-rescan or an upfront GKS policy. At last follow-up examination, the facial nerve function was good (House-Brackmann grades I or II) in 95% of the GKS failure and 84% of the genuine VS patients (p = .25). The median volume of tumor residue was .56 cc in the GKS failure group and .62 cc in the genuine VS group (p = .70). Tumor control was achieved in 91% and 83% of cases with a mean follow-up of 74 and 63 months in the GKS failure and the genuine VS populations, respectively. The 1-, 5-, and 7-year progression-free survival were 100%, 95%, and 85% respectively in the GKS failure group and 97%, 80%, and 81% in the genuine VS group (p = .27). Despite significant modifications of the microsurgical environment associated to salvage surgery after GKS failure, a functional nerve-sparing resection is an effective strategy to optimize the results on facial nerve function, with similar long-term tumor control to those observed in the genuine VS population.

[Trigeminal radiculopathy in vestibular schwannomas]

OBJECTIVE

To evaluate the correlation of trigeminal radiculopathy with anatomical relationships of trigeminal nerve root, brainstem, tumors and vessels in patients with vestibular schwannomas.

MATERIAL AND METHODS

A retrospective analysis included 153 patients (106 females and 47 males aged 22-82 years) with vestibular schwannomas who underwent surgery via retromastoid approach. Preoperative trigeminal radiculopathy (facial pain and sensory disturbances) was examined after microsurgical resection. Brainstem compression was analyzed by comparison of transverse size of contralateral to vestibular schwannoma half of brainstem and ipsilateral side.

RESULTS

Tumor-induced brainstem and trigeminal nerve compression was found in 115 cases. Sixty-four of these patients had trigeminal radiculopathy symptoms. Degree of brainstem compression was significantly higher in trigeminal radiculopathy group. Facial hypoesthesia was found in 61patients, trigeminal neuralgia - in 5 cases, neuropathic pain - in 3 patients. Thirty-seven patients without brainstem compression had no trigeminal nerve involvement. One patient had trigeminal neuralgia following compression by superior cerebellar artery. Total resection with brainstem and trigeminal nerve decompression were performed in all cases. Isolated or combined compression of trigeminal nerve root was noted in 9 patients with trigeminal neuralgia and neuropathic pain, in 2 with facial numbness and in 2 patients without trigeminal symptoms. In case of trigeminal neuralgia following compression by superior cerebellar artery, vascular decompression was performed only in patients with facial pain and numbness. Facial pain completely resolved in all patients. Complete or partial sensory restoration was noted in 25 cases. No facial sensory disorders were noted in 26 cases, transient sensory deterioration - in 10 patients.

CONCLUSION

Trigeminal radiculopathy is caused by severe brainstem compression following vestibular schwannomas and usually results sensory disturbances and rarely facial pain. The impact of tumor on trigeminal nerve root and brainstem trigeminal pathways can be accompanied by vascular compression by superior cerebellar artery. Regression of trigeminal radiculopathy symptoms after resection of vestibular schwannoma is caused by decompression of trigeminal nerve root and brainstem. In case of concomitant neurovascular syndrome, vascular decompression is indicated.

Outcomes after semisitting and lateral positioning in large vestibular schwannoma surgery: A single-center comparison

OBJECTIVE

The semisitting position (SSP) and lateral position (LP) in vestibular schwannoma (VS) surgery each have advantages and disadvantages, and which position is superior overall is debatable. Our objective was to determine the optimal position for surgical treatment of VSs with a diameter ≥3 cm.

METHODS

We retrospectively evaluated consecutive patients with a large VS treated between January 2010 and July 2020. Patients were grouped by surgical position and analyzed.

RESULTS

We enrolled 259 patients (LP group, n = 156; SSP group, n = 103). The resection extent was not significantly different between the SSP (gross-total resection [GTR], n = 89 [88.1%], near-total resection [NTR], n = 10 [9.9%], subtotal resection [STR], n = 2 [2.0%]) and LP (GTR, n = 125 [80.1%]; NTR, n = 24 [15.4%]; STR, n = 7 [4.5%]) groups. The rate of GTR with facial nerve (FN) functional preservation was higher in the SSP group than in the LP group (P = 0.014) at eight days after the operation. However, during follow-up (SSP group median, 31.5 months; LP group median, 19.5 months), there was no significant between-group difference in FN functional preservation. Two patients in the SSP group required conversion to the LP due to severe intraoperative venous air embolism (VAE).

CONCLUSION

Compared with the LP, the SSP did not produce significantly better FN outcomes in patients with a large VS. The duration of surgery was significantly longer in SSP cases than in LP cases. Given the risk of VAE associated with the SSP, the selection of the optimal surgical position should be made with caution on an individual basis.

Clinical Studies and Pre-clinical Animal Models on Facial Nerve Preservation, Reconstruction, and Regeneration Following Cerebellopontine Angle Tumor Surgery-A Systematic Review and Future Perspectives

Background and purpose: Tumorous lesions developing in the cerebellopontine angle (CPA) get into close contact with the 1st (cisternal) and 2nd (meatal) intra-arachnoidal portion of the facial nerve (FN). When surgical damage occurs, commonly known reconstruction strategies are often associated with poor functional recovery. This article aims to provide a systematic overview for translational research by establishing the current evidence on available clinical studies and experimental models reporting on intracranial FN injury.

Methods: A systematic literature search of several databases (PubMed, EMBASE, Medline) was performed prior to July 2020. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. Included clinical studies were reviewed and categorized according to the pathology and surgical resection strategy, and experimental studies according to the animal. For anatomical study purposes, perfusion-fixed adult New Zealand white rabbits were used for radiological high-resolution imaging and anatomical dissection of the CPA and periotic skull base.

Results: One hundred forty four out of 166 included publications were clinical studies reporting on FN outcomes after CPA-tumor surgery in 19,136 patients. During CPA-tumor surgery, the specific vulnerability of the intracranial FN to stretching and compression more likely leads to neurapraxia or axonotmesis than neurotmesis. Severe FN palsy was reported in 7 to 15 % after vestibular schwannoma surgery, and 6% following the resection of CPA-meningioma. Twenty-two papers reported on experimental studies, out of which only 6 specifically used intracranial FN injury in a rodent (n = 4) or non-rodent model (n = 2). Rats and rabbits offer a feasible model for manipulation of the FN in the CPA, the latter was further confirmed in our study covering the radiological and anatomical analysis of perfusion fixed periotic bones.

Conclusion: The particular anatomical and physiological features of the intracranial FN warrant a distinguishment of experimental models for intracranial FN injuries. New Zealand White rabbits might be a very cost-effective and valuable option to test new experimental approaches for intracranial FN regeneration. Flexible and bioactive biomaterials, commonly used in skull base surgery, endowed with trophic and topographical functions, should address the specific needs of intracranial FN injuries.