Electrical stimulation of the vestibular nerve: evaluating effects and potential starting points for optimization in vestibular implants.

PURPOSE OF REVIEW: Oscillopsia and unsteadiness are common and highly debilitating symptoms in individuals with bilateral vestibulopathy. A lack of adequate treatment options encouraged the investigation of vestibular implants, which aim to restore vestibular function with motion-modulated electrical stimulation. This review aims to outline the ocular and postural responses that can be evoked with electrical prosthetic stimulation of the semicircular canals and discuss potential approaches to further optimize evoked responses. Particular focus is given to the stimulation paradigm. RECENT FINDINGS: Feasibility studies in animals paved the way for vestibular implantation in human patients with bilateral vestibulopathy. Recent human trials demonstrated prosthetic electrical stimulation to partially restore vestibular reflexes, enhance dynamic visual acuity, and generate controlled postural responses. To further optimize prosthetic performance, studies predominantly targeted eye responses elicited by the vestibulo-ocular reflex, aiming to minimize misalignments and asymmetries while maximizing the response. Changes of stimulation parameters are shown to hold promise to increase prosthetic efficacy, together with surgical refinements and neuroplastic effects. SUMMARY: Optimization of the stimulation paradigm, in combination with a more precise electrode placement, holds great potential to enhance the clinical benefit of vestibular implants.

Popularizing Surgical Cures: Walter Dandy and the Vestibular Neurectomy for Menière's Disease at the Johns Hopkins Hospital.

OBJECTIVES: To uncover the context that allowed for the vestibular neurectomy to grow in favor and practice at the Johns Hopkins Hospital in the early 20th century, and the reasons for its broad abandonment since. METHODS: The Walter E. Dandy (1905-1946) and Samuel J. Crowe collections (1905-1920) at the Alan Mason Chesney Medical Archives were reviewed, as well as the Samuel J. Crowe and Stacy Guild Temporal Bone Collection. RESULTS: Speculation on the etiology of Menière's disease (MD) has been countless, as have the medical and surgical interventions aimed at treating it. At the Johns Hopkins Hospital, Walter Dandy popularized the neurectomy for MD and performed 692 procedures from 1924 to 1946, believing it to be a curative therapy for vertigo. When he later modified the procedure from a total cranial nerve section to a partial vestibular neurectomy preserving auditory function, surgical candidacy expanded to include nearly any patient with vestibular symptoms. After his passing, trainees' attention shifted to traumatic injuries, likely influenced by WWII. This left the procedure scarcely used until third parties rekindled interest decades later. CONCLUSIONS: Neurectomy as the preferential treatment for MD at the Johns Hopkins Hospital was not driven by pure scientific reasoning but was rather contingent on historical context and sponsorship by a prominent figure like Walter Dandy. Appreciation of MD's natural history has since curtailed the favorability of destructive procedures in preference for conservative management.

Multiple Intracranial Schwannomas of the Vestibular and Trigeminal Nerves: A Technical Note.

BACKGROUND: A schwannoma is a nerve sheath tumor that is formed by Schwann cells. Vestibular schwannomas are thought to account for the majority of intracranial schwannomas. Nonvestibular schwannomas account for about 10%, about half of which are trigeminal schwannomas. Multiple intracranial schwannomas originating from different cranial nerves are extremely rare. METHODS: We describe the clinical case of a 42-year-old female patient with vestibular schwannoma and multiple trigeminal schwannomas. RESULTS: That case shows how multiple trigeminal schwannomas were identified intraoperatively during elective surgery for vestibular schwannoma removal, most of which were resected. No new neurological deficits were observed in the patient. CONCLUSIONS: The presence of multiple intracranial schwannomas is extremely rare in neurosurgical practice and can change the intraoperative strategy and the course of the surgery.

How I do it: hearing preservation in large vestibular schwannomas using vestibular nerve fiber preservation technique.

BACKGROUND: To improve hearing function after resection of large vestibular schwannomas, we describe a strategy of vestibular-nerve-fiber preservation. Anatomical considerations and stepwise dissection are described. METHOD: Steps include locating the vestibular nerve at the brainstem and identifying a dissection plane between nerve fibers and tumor capsule. Using this plane to mobilize and resect tumor reduced manipulation and maintained vascularity of underlying cochlear and facial nerves. CONCLUSION: Preservation of hearing function is feasible in large vestibular schwannomas with vestibular-nerve-fiber preservation. Reducing manipulation and ischemic injury of underlying cochlear and facial nerves thereby helped facilitate hearing preservation, even in large tumors.

Prosthetic Stimulation of the Vestibular Nerve Can Evoke Robust Eye and Head Movements Despite Prior Labyrinthectomy.

HYPOTHESIS: Prosthetic electrical stimulation can evoke compensatory eye and head movement despite vestibular implant electrode insertion occurring years after prior labyrinthectomy. BACKGROUND: Vestibular implants sense head rotation and directly stimulate the vestibular nerve, bypassing damaged end organs. Animal research and current clinical trials have demonstrated the efficacy of this approach. However, candidacy criteria for vestibular implants currently require presence of a patent labyrinth in the candidate ear and at least aidable hearing in the opposite ear, thus excluding patients who have undergone prior labyrinthectomy for unilateral Menière's disease that later progressed to bilateral vestibular hypofunction. METHODS: Eight years after right unilateral labyrinthectomy, we implanted stimulating electrodes in the previously exenterated right ear ampullae of a rhesus macaque monkey. The left labyrinth had long-standing hypofunction due to intratympanic gentamicin injection and surgical disruption. We used three-dimensional video-oculography to measure eye movement responses to prosthetic electrical stimulation. We also measured head-movement responses to prosthetic stimulation with the head unrestrained. RESULTS: Bilateral vestibular hypofunction was confirmed by absence of vestibuloocular reflex responses to whole-body rotation without prosthetic stimulation. For a subset of the implanted electrodes, prosthetic vestibular stimulation evoked robust compensatory eye and head movements. One electrode reliably elicited responses aligned with the implanted ear's anterior canal nerve regardless of the return electrode used. Similarly, a second electrode also elicited responses consistent with excitation of the horizontal canal nerve. Responses grew quasilinearly with stimulation rate and current amplitude. CONCLUSION: Prosthetic electrical stimulation targeting the vestibular nerve can be effective years after labyrinthectomy, if at least some parts of the vestibular nerve's ampullary branches remain despite destruction or removal of the membranous labyrinth.

Preoperative vestibular evoked myogenic potentials (VEMPs), caloric test, and pure tone audiometry to identify the vestibular nerve branch of schwannoma origin: preliminary results in a series of 26 cases.

Vestibular schwannoma (VS) is a benign tumor which develops in the internal auditory canal and the cerebellopontine angle, potentially diminishing hearing or balance. Most VS tumors arise from one of two vestibular branches: the superior or inferior vestibular nerve. Determining the specific nerve of origin could improve patient management in terms of preoperative counseling, treatment selection, and surgical decision-making and planning. The aim of this study was to introduce a preoperative testing protocol with high accuracy to determine the nerve branch of origin. The nerve of origin was predicted on the basis of preoperative vestibular evoked myogenic potentials (VEMPs), caloric stimulation test, and pure tone audiometry on 26 recipients. The acquired data were entered into a statistic scoring system developed to allocate the tumor origin. Finally, the nerve of origin was definitively determined intraoperatively. Receiver operating characteristic (ROC) curves analysis of preoperative testing data showed the possibility of predicting the branch of origin. In particular, ROC curve of combined VEMPs absence, nystagmus detectable at caloric stimulation, and PTA < 75 dB HL allowed to obtain high accuracy for inferior vestibular nerve implant of the tumor (area under the curve-AUC = 0.8788, p = 0.012). In 24 of 26 cases, the preoperatively predicted tumor origin was the same as the origin determined during surgery. Preoperative audiological and vestibular evaluation can predict the vestibular tumor branch of origin with high accuracy. Despite the necessity of larger prospective cohort studies, these findings may change preoperative approach, possible functional aspects, and counseling with the patients.

Transcanal Transvestibular Endoscopic Neurectomy: First Experience.

OBJECTIVE: Ménière's disease is an idiopathic inner ear disorder characterized by recurrent vertigo, fluctuating sensorineural hearing loss, and persistent tinnitus. In 10% to 30% of cases, conservative therapy fails, and Ménière's disease is defined as intractable. In these patients, ablative techniques with unilateral vestibular deafferentation are mandatory. Several approaches for vestibular neurectomy, which preserve hearing capability, are described. In patients presenting severe dizziness associated with high-grade sensorineural hearing loss, surgical labyrinthectomy, or selected vestibular neurectomy through a translabyrinthine approach are the treatments commonly considered. This study reports the first application of transcanal transvestibular endoscopic neurectomy in two patients with frequent disabling vertigo and high-grade sensorineural hypoacusia. METHODS: This was a retrospective chart review including patients with intractable Ménière's disease who underwent vestibular neurectomy, performed in our ENT department between January 2017 and January 2020, selecting patients with disabling vertigo and high-grade sensorineural hypoacusia. We describe step-by-step the surgical technique of transcanal transvestibular endoscopic neurectomy. RESULTS: Overall, two patients underwent transcanal transvestibular endoscopic neurectomy. We performed transcanal transvestibular neurectomy in all cases. No intraoperative complications were observed. On the 2nd postoperative day, one patient presented CSF leak, leading to surgical revision. A complete resolution of vertigo attacks was observed 6 months after surgery. CONCLUSION: Even though this study presents a limited number of cases, transcanal transvestibular neurectomy is a promising, safe, and effective procedure in selected cases.

Retrosigmoid Vestibular Neurectomy for Meniere Disease: A Technical Note.

BACKGROUND: Meniere disease (MD) is an idiopathic peripheral pathology involving the acoustic apparatus. One of the most critical challenges in managing MD is intractable vertigo. In this context, retrosigmoid vestibular neurectomy has been described as a safe and effective technique to manage this symptom when it is resistant to first- and second-line treatments. This article analyzed the alternative treatment options, specific surgical anatomy, and relevant details of vestibular neurectomies performed for intractable MD. METHODS: Relevant neurovascular landmarks, critical surgical steps, adequate indications, and potential pitfalls of retrosigmoid vestibular neurectomy were analyzed based on an illustrative clinical case of intractable MD. RESULTS: The illustrative case demonstrated how early recognition of the facial nerve and the vestibulocochlear plane is fundamental to performing retrosigmoid vestibular neurectomy. This procedure is indicated in cases of resistant MD with preoperative hearing integrity. Potential pitfalls of this technique are incomplete neurotomy, nerve regeneration, comorbidities in the contralateral ear, adverse anatomy, the possibility of nonotologic vertigo, and incomplete vestibular compensation. CONCLUSIONS: Vestibular neurectomy represents a safe and effective technique to manage MD that is resistant to medical treatment, allowing symptom control and hearing preservation. Nevertheless, detailed knowledge of surgical anatomy and possible pitfalls is of paramount importance to achieve a good outcome.

Gangliformis Intumescentia and Beyond: Antonio Scarpa and His Core Contribution to Neuroanatomy, Neurosurgery, and Otoneurosurgery.

Nearly 250 years ago, Antonio Scarpa became a professor of anatomy and surgery only 2 years after he graduated from the University of Padua. The young lecturer soon became one of the most renowned anatomists in Italy and a director of the Faculty of Medicine at the University of Pavia. He worked in the fields of general surgery and ophthalmology. Several anatomic structures have been named after him, mainly Scarpa fascia and Scarpa triangle. His interest in neuroanatomy was ardent, despite being occasionally neglected. Scarpa's contributions to the fields of neurosciences have been significant. He was the first to describe the round window and the secondary tympanic membrane, and he eventually focused on the auditory and olfactory organs. Notably, the vestibular ganglion is now known as Scarpa ganglion. Scarpa's magnum opus was the book Tabulae Neurologicae, in which he described the path of several cranial nerves including the vagus nerve and innervation of the heart. Since his death in 1832, Scarpa's head has been preserved at the University History Museum of the University of Pavia. In this historical vignette, we aim to describe Antonio Scarpa's troubled life and brilliant career, focusing on his core contributions to neuroanatomy, neurosurgery, and otoneurosurgery.

Effects of vestibular neurectomy and neural compensation on head movements in patients undergoing vestibular schwannoma resection.

The vestibular system is vital for maintaining balance and stabilizing gaze and vestibular damage causes impaired postural and gaze control. Here we examined the effects of vestibular loss and subsequent compensation on head motion kinematics during voluntary behavior. Head movements were measured in vestibular schwannoma patients before, and then 6 weeks and 6 months after surgical tumor removal, requiring sectioning of the involved vestibular nerve (vestibular neurectomy). Head movements were recorded in six dimensions using a small head-mounted sensor while patients performed the Functional Gait Assessment (FGA). Kinematic measures differed between patients (at all three time points) and normal subjects on several challenging FGA tasks, indicating that vestibular damage (caused by the tumor or neurectomy) alters head movements in a manner that is not normalized by central compensation. Kinematics measured at different time points relative to vestibular neurectomy differed substantially between pre-operative and 6-week post-operative states but changed little between 6-week and > 6-month post-operative states, demonstrating that compensation affecting head kinematics is relatively rapid. Our results indicate that quantifying head kinematics during self-generated gait tasks provides valuable information about vestibular damage and compensation, suggesting that early changes in patient head motion strategy may be maladaptive for long-term vestibular compensation.

The Relationship of Vestibulo-Ocular Reflex With Self-Reported Dizziness Handicap in Patients With Vestibular Deafferentation.

The relationship between objective vestibular tests and subjective vestibular tests is a controversial topic. In this study, to contribute to this issue, the vestibulo-ocular reflex features and their relationship with balance perception at long-term follow-up in vestibular neurectomy (VN) and total labyrentectomy patients were evaluated. Prospectively, 19 VN and 18 labyrinthectomy patients were enrolled in this study. Patients underwent video head impulse test (VHIT) as objective vestibular test and dizziness handicap inventory (DHI) as subjective vestibular test when they attended to their control visit follow-up between March and September 2017. Lateral canal corrective saccades were classified as organized pattern and deorganized (scattered) pattern. In our results, the saccade pattern analysis (between organized and deorganized saccades) regarding the DHI scores gave P value as .039 for covert saccade pattern and .050 for overt saccade pattern. Therefore, we conclude that the presence of saccades, their patterns, and amplitudes provide extra information at assessing the results of the VHIT test, and the organized pattern of saccades is related to a stable vestibular system and better balance perception.

Surgical techniques and functional evaluation for vestibular lesions in the mouse: unilateral labyrinthectomy (UL) and unilateral vestibular neurectomy (UVN).

OBJECTIVE: Unilateral labyrinthectomy (UL) and unilateral vestibular neurectomy (UVN) are two surgical methods to produce vestibular lesions in the mouse. The objective of this study was to describe the surgical technique of both methods, and compare functional compensation using vestibulo-ocular reflex-based tests. METHODS: UL and UVN were each performed on groups of seven and ten mice, respectively. Main surgical landmarks were the facial nerve, the external auditory canal and the sternomastoid and digastric muscles. For UL, the sternomastoid muscle was elevated to expose the mastoid, which was drilled to destroy the labyrinth. For UVN, the bulla was drilled opened and a transcochlear approach enabled the identification of the vestibulo-cochlear nerve exiting the brainstem, which was sectioned and the ganglion of Scarpa suctioned. Behaviour and vestibular function were analysed before surgery and at 1, 4, 7 days and at 1 month postlesion using sinusoidal rotation, off-vertical axis rotation, static head tilts and angular velocity steps. RESULTS: UL is a faster and safer procedure than UVN (operative time 16.3 vs 20.5 min, p = 0.19; survival rate 86% vs 60%, p = 0.25). UVN was more severe with significantly worse behavioural scores at day 4 and day 7 (p < 0.001). Vestibular compensation was overall similar during the first week and at 1 month (non-statistically significant difference). CONCLUSION: Both UL and UVN procedures can routinely be performed in the mouse with similar post-operative recovery and behavioural compensation. The operative risk of vascular or neurological damage is smaller in UL compared to UVN. UVN may be required for specific research protocols studying central cellular process specifically related to the destruction of the ganglion of Scarpa and following vestibular nerve degeneration.

Clinical outcomes of resecting scarpa's ganglion during vestibular schwannoma surgery.

Vestibular schwannomas are slow-growing tumors arising from the Schwann cells of the vestibular nerve. Scarpa's ganglion, the vestibular nerve ganglion, is located within the internal auditory meatus. Surgical treatment of vestibular schwannomas carries the potential of resecting Scarpa's ganglion along with the tumor. No prior studies have evaluated outcomes based on the presence of Scarpa's ganglion within tumor specimens. The neurosurgery patient records were queried for patients who underwent surgical resection of vestibular schwannomas at the University of Missouri Healthcare between January 1, 2008 and December 31, 2018. Inclusion criteria consisted of minimum age of 18, imaging demonstrating an eighth nerve tumor, surgical resection thereof, and a final pathological diagnosis of WHO grade I schwannoma. Data were collected retrospectively. The histological slides of the tumors were reviewed, and the presence or absence of the ganglion was noted. Outcomes analyzed included postoperative dizziness, hearing, and facial nerve function. Fifty-two patients met inclusion criteria. Ten (19%) resected tumors contained portions of the ganglion. No difference in risk of resection of ganglion occurred based on the surgical approach (p = 0.2454). Mean follow-up duration was 24.6 months ± 26.2 standard deviation. No differences in postoperative hearing or dizziness (p = 0.8483 and p = 0.3190 respectively) were present if Scarpa's ganglion was resected. House-Brackmann classification of facial nerve function at last follow-up was similar (p = 0.9190). Resection of Scarpa's ganglion with vestibular schwannomas does not increase risk of post-operative dizziness, facial nerve weakness, or hearing loss.

Vestibular Implantation and the Feasibility of Fluoroscopy-Guided Electrode Insertion.

Recent research has shown promising results for the development of a clinically feasible vestibular implant in the near future. However, correct electrode placement remains a challenge. It was shown that fluoroscopy was able to visualize the semicircular canal ampullae and electrodes, and guide electrode insertion in real time. Ninety-four percent of the 18 electrodes were implanted correctly (<1.5 mm distance to target). The median distances were 0.60 mm, 0.85 mm, and 0.65 mm for the superior, lateral, and posterior semicircular canal, respectively. These findings suggest that fluoroscopy can significantly improve electrode placement during vestibular implantation.

European Position Statement on Diagnosis, and Treatment of Meniere's Disease.

Meniere Disease keeps challenges in its diagnosis and treatment since was defined by Prosper Meniere at the beginning of 19th Century. Several classifications and definition were made until now and speculations still exist on its etiology. As the etiology remains speculative the treatment models remain in discussion also. The European Academy of Otology and Neurotology Vertigo Guidelines Study Group intended to work on the diagnosis and treatment of Meniere's disease and created the European Positional Statement Document also by resuming the consensus studies on it. The new techniques on diagnosis are emphasized as well as the treatment models for each stage of the disease are clarified by disregarding the dilemmas on its treatment. The conservative, noninvasive and invasive therapeutic models are highlighted.

Transcanal endoscopic infracochlear vestibular neurectomy: A pilot cadaveric study.

PURPOSE: Effective operative approaches for the treatment of refractory vertigo in Meniere's disease are invasive. Vestibular neurectomy can preserve hearing and has been shown to be effective; however, current approaches require an extensive craniotomy. Transcanal endoscopic approaches to the internal auditory canal (IAC) with cochlear preservation have been recently described and may offer a minimally invasive approach to selectively sectioning the distal vestibular nerves while preserving residual hearing. MATERIALS AND METHODS: Three cadaveric human heads were imaged using high resolution computed tomography (CT). Anatomic analysis of preoperative CT scans showed adequate diameters (>3 mm) of the infracochlear surgical corridor for access to the IAC. A transcanal endoscopic approach was attempted to section the vestibular nerve. Post-operative CT scans were assessed to define the operative tract, determine cochlear preservation and assess cochlear and facial nerve preservation. RESULTS: Transcanal endoscopic approach was successfully performed (n = 3) using 3 mm-diameter, 14 cm-length 0°, 30°, and 45° endoscopes and microsurgical drills. In all cases the tympanomeatal flap and ossicular chain remained intact. Internal auditory canalotomy was performed using angled instruments and confirmed in real time via lateral skull base navigation. The vestibular nerves were readily identified and sectioned with preservation of the facial and cochlear nerves. Post-procedure CT showed no violation of the cochlea. CONCLUSION: A transcanal, infracochlear approach to the IAC may permit a minimally invasive approach to distal vestibular neurectomy in cadavers with appropriate anatomy.

Comparison of VEMPs, VHIT and caloric test outcomes after vestibular neurectomy in Menière's disease.

OBJECTIVE: Selective unilateral vestibular neurectomy (VN) is considered a reliable surgical treatment in case of recurrent vertigo in Menière's disease (MD) because of hearing preservation and a minimally invasive posterior fossa retrosigmoid approach. The present study aimed to assess the quality of life and the long-term vestibular function in patients submitted to yearly follow-up after VN because of intractable MD. METHODS: Retrospective series of 15 MD patients undergoing retrosigmoid VN for recurrent vertigo. Outcome measures included cVEMPs and oVEMPs (cervical and ocular vestibular evoked myogenic potentials), VHIT (Video Head Impulse Test) and caloric test, besides to DHI (Dizziness Handicap Inventory) and PTA (Pure Tone Audiometry). RESULTS: Mean DHI score resulted within normal values in 74% of patients, significantly correlated to the duration of the follow-up. In the operated side, cVEMPs and oVEMPs have not been elicited respectively in 11 patients (73%) and 13 patients (87%), whereas it was not possible to evoke any response at bithermal caloric test in 4 cases. The gain of VOR from VHIT resulted always below normal values after VN except in one patient, who has also undergone an episode of posterior BBPV. The difference between average PTA threshold before and after VN resulted not significant. CONCLUSION: The vestibular outcomes prove VN to be an effective and safe surgery in MD; furthermore, the unexpected occurrence of BPPV after VN can justify the presence of neural anastomosis between the inferior vestibular nerve and the cochlear nerve, allowing to still perceive vestibular symptomatology despite of a proper neurectomy.

Evidence of surgical treatments for intractable Meniere's disease.

Meniere's disease is an inner ear disease, characterized by recurrent rotatory vertigo, sensorineural hearing loss and tinnitus. There are some with frequent vertigo attacks, progressive hearing loss and persistent annoying tinnitus even through the continuous standard medical treatments. These cases are thought to account for 10%-20% of all cases of Meniere's disease. In this review article, we would like to demonstrate the evidences for surgical treatments according to the previous papers, and consider the next therapeutic strategies including surgical options according to the international guidelines.

Delayed Effect of Active Pressure Treatment on Endolymphatic Hydrops.

OBJECTIVE: To identify eventual correlations between the effect of low-pressure treatment and endolymphatic hydrops in Ménière patients. MATERIAL AND METHODS: The study group consisted of subjects affected by definite Ménière disease (2015) and a severe degree of disability, who received a ventilation tube with or without a low-pressure treatment before undergoing a surgical procedure (vestibular neurectomy). After the placement of the ventilation tube, the subjects were either left alone with the tube or received 1 month of self-administered low-pressure therapy with a portable device. In all subjects, an electrocochleography (ECochG) was performed and specific questionnaires - Dizziness Handicap Inventory (DHI) and Functional Scale Level (FSL) - were completed before starting either arm of treatment, at the end of treatment, and then 3 and 6 months later. RESULTS: All selected subjects presented with an ECochG pattern that was indicative of endolymphatic hydrops before starting either treatment. At the end of pressure treatment, 80% showed symptomatic improvement while maintaining the hydropic ECochG pattern. At the 3-month control stage, the hydropic pattern resulted normalized (<0.5) in all the improved subjects. CONCLUSIONS: Although 1 month of low-pressure treatment provided a positive symptomatological outcome, normalization of the hydropic ECochG parameters occurred only at a later time. Therefore, it is possible to assume that endolymphatic hydrops could be concurrent with a non-symptomatic stage of Ménière disease, and that the anti-hydropic effect of the low-pressure treatment, if any, would present with a certain delay after its completion.