Stimulation Crosstalk Between Cochlear And Vestibular Spaces During Cochlear Electrical Stimulation

OBJECTIVES

Possible beneficial "crosstalk" during cochlear implant stimulation on otolith end organs has been hypothesized. The aim of this case-control study is to analyze the effect of electrical cochlear stimulation on the vestibule (otolith end-organ), when using a cochleo-vestibular implant, comparing vestibular stimulation (VI) and cochlear stimulation (CI).

METHODS

Four patients with bilateral vestibulopathy were included. A double electrode array research implant was implanted in all cases. Dynamic Gait Index (DGI), VOR gain measured by using vestibular head impulse test (vHIT), acoustic cervical myogenic responses (cVEMP) recordings, and electrical cVEMP were used in all cases. Trans-impedance Matrix (TIM) analysis was used to evaluate the current flow from the cochlea to the vestibule.

RESULTS

While patients did not have any clinical vestibular improvement with the CI stimulation alone, gait metrics of the patients revealed improvement when the vestibular electrode was stimulated. The average improvement in the DGI was 38% when the vestibular implant was activated, returning to the normal range in all cases. Our findings suggest that any current flow from the cochlear space to the otolith organs was insufficient for effective cross-stimulation. The functional results correlated with the data obtained in TIM analysis, confirming that there is no current flow from the cochlea to the vestibule.

CONCLUSION

The only way to produce effective electrical otolith end-organ stimulation, demonstrated with this research implant, is by direct electrical stimulation of the otolith end organs. No effective cross-stimulation was found from cochlear electrode stimulation.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:2349-2355, 2024.

[Increased report completeness and satisfaction with structured neurotological reporting in the interdisciplinary assessment of vertigo]

BACKGROUND

Results of neurotological function diagnostics in the context of interdisciplinary vertigo assessment are usually formulated as free-text reports (FTR). These are often subject to high variability, which may lead to loss of information. The aim of the present study was to evaluate the completeness of structured reports (SR) and referrer satisfaction in the neurotological assessment of vertigo.

MATERIALS AND METHODS

Neurotological function diagnostics performed as referrals (n = 88) were evaluated retrospectively. On the basis of the available raw data, SRs corresponding to FTRs from clinical routine were created by means of a specific SR template for neurotological function diagnostics. FTRs and SRs were evaluated for completeness and referring physician satisfaction (n = 8) using a visual analog scale (VAS) questionnaire.

RESULTS

Compared to FTRs, SRs showed significantly increased overall completeness (73.7% vs. 51.7%, p < 0.001), especially in terms of patient history (92.5% vs. 66.7%, p < 0.001), description of previous findings (87.5% vs. 38%, p < 0.001), and neurotological (33.5% vs. 26.7%, p < 0.001) and audiometric function diagnostics (58% vs. 32.3%, p < 0.001). In addition, SR showed significantly increased referring physician satisfaction (VAS 8.8 vs. 4.9, p < 0.001).

CONCLUSION

Neurotological SRs enable a significantly increased report completeness with higher referrer satisfaction in the context of interdisciplinary assessment of vertigo. Furthermore, SRs are particularly suitable for scientific data analysis, especially in the context of big data analyses.

Subjective visual vertical and postural control in patients following cochlear implantation

BACKGROUND

Cochlear implantation (CI) is associated with changes in the histopathology of the inner ear and impairment of vestibular function.

OBJECTIVE

The objectives of our study were to evaluate patients for clinical manifestations of space perception and balance changes before surgery, compare them with asymptomatic subjects (controls), and report changes in posturography and subjective visual vertical (SVV) during the acute post-surgery period in patients.

METHODS

Examination was performed using static posturography and the SVV measurement. We examined 46 control subjects and 39 CI patients. Patients were examined pre-surgery (Pre), 2nd day (D2) and then 14th day (D14) after implantation.

RESULTS

Baseline SVV was not different between patients and control group. There was a statistically significant difference (p < 0.001) in SVV between subgroups of right- and left-implanted patients at D2 (-1.36±3.02° and 2.71±2.36°, right and left side implanted respectively) but not Pre (0.76±1.07° and 0.31±1.82°) or D14 (0.72±1.83° and 1.29±1.60°). Baseline posturography parameters between patients and control group were statistically significantly different during stance on foam with eyes closed (p < 0.05). There was no statistically significant difference in posturography among Pre, D2 and D14.

CONCLUSIONS

CI candidates have impaired postural control before surgery. CI surgery influences perception of subjective visual vertical in acute post-surgery period with SVV deviation contralateral to side of cochlear implantation, but not after two weeks.

Lateral Semicircular Canal Pressures During Cochlear Implant Electrode Insertion: a Possible Mechanism for Postoperative Vestibular Loss

HYPOTHESIS

Insertion of cochlear implant electrodes generates transient pressure spikes within the vestibular labyrinth equivalent to high-intensity acoustic stimuli.

BACKGROUND

Though cochlear implant (CI) surgery is regarded as having low risk of impacting the vestibular system, several studies have documented changes in vestibular function after implantation. The mechanism of these changes is not understood. We have previously established that large, potentially damaging pressure transients can be generated in the cochlea during electrode insertion, but whether pressure transients occur within the vestibular labyrinth has yet to be determined. Here, we quantify the exposure of the vestibular system to potentially damaging pressure transients during CI surgery.

METHODS

Five human cadaveric heads were prepared with an extended facial recess and implanted sequentially with eight different CI electrode styles via a round window approach. Fiber-optic sensors measured intralabyrinthine pressures in scala vestibuli, scala tympani, and the lateral semicircular canal during insertions.

RESULTS

Electrode insertion produced a range of high-intensity pressure spikes simultaneously in the cochlea and lateral semicircular canal with all electrodes tested. Pressure transients recorded were found to be significantly higher in the vestibular labyrinth than the cochlea and occurred at peak levels known to cause acoustic trauma.

CONCLUSION

Insertion of CI electrodes can produce transients in intralabyrinthine fluid pressure levels equivalent to high-intensity, impulsive acoustic stimuli. Results from this investigation affirm the importance of atraumatic surgical techniques and suggest that in addition to the cochlea, the vestibular system is potentially exposed to damaging fluid pressure waves during cochlear implantation.

Cochlear Implant Surgery and the Risk of Falls in an Adult Population

OBJECTIVE

To determine the effect of cochlear implant surgery on the balance and risk of falls in an adult patient population using a mobile posturograph.

DESIGN

Prospective clinical pilot study.

SETTING

Cochlear implant center at a tertiary referral hospital.

SUBJECTS AND METHODS

Twenty adult patients undergoing cochlear implant surgery were tested using a mobile posturograph (VertiGuard). The standard balancing deficit test, or the geriatric standard balancing deficit test protocol (for patients older than 60 yr), was performed both 1 day before and 3 to 5 days after surgery.

OUTCOME MEASURES

The risk of falls (%) was calculated from the body sway both forward-to-backward and side-to-side in degrees per second.

RESULTS

The mean preoperative risk of falls in the whole study population was 51% (24-max. 86%) and was thus already higher than that in a normal healthy population (norm 0-40%). Comparison of the postoperative risk of falls to the preoperative risk for all 20 patients revealed a mean increased risk of falls of 1.25% after CI surgery. This is not a statistically significant increase. There was also no statistically significant increase when comparing the fall risk calculated using either the standard balancing deficit test protocol or the geriatric standard balancing deficit test protocol alone.

CONCLUSION

Postural control in cochlear implant candidates is already decreased before surgery compared with a healthy population. However Comparison of pre- and postoperative body sway measurements did not reveal a significant increase in fall risk as a result of cochlea implant surgery. Therefore in this study population, cochlear implant surgery did not influence balance and risk of falls. Further testing with a larger study population would be necessary to determine the development of falls risk over time after cochlear implant surgery.

Balance, gait and dizziness in adult cochlear implant users: A cross sectional study

Objective: Cochlear implantation is associated with vestibular impairment due to the close proximity of the structures. The aim of the study was to quantify dizziness/vertigo, gaze instability, balance and gait problems in a sample of adult cochlear implant (CI) users.Methods: An observational, cross sectional study evaluated subjective dizziness (Vestibular Rehabilitation Benefit Questionnaire (VRBQ)), balance confidence (Activities Specific Balance Questionnaire (ABC)), gait (Functional Gait Assessment (FGA) and 10m walk test), balance (Equitest Sensory Organisation Test (SOT)), and computerised dynamic visual acuity (DVA). The Dix Hallpike test was performed to test for benign paroxysmal positional vertigo (BPPV).Results: Twenty participants (n=10F), 2.8(±2.7) years post implantation, with mean age 59.3(±15.8) years were assessed. Subjective dizziness (VRBQ) was low (15.0% (±15.5)) and balance confidence was high (ABC: 82.1%±14.9). FGA scores (25.1 ± 4.4) and gait speed (1.8 (±0.3) m/sec) were below normal. Dx Hallpike was positive in 3. Gaze instability was found in 50% (DVA loss, 0.29 (± 0.16) LogMAR), while 79% demonstrated balance impairment (mean SOT score, 57.8%±14.5), with 42% falling on SOT condition 5.Discussion: Evidence of vestibular dysfunction was identified in these adult CI users.Conclusion: Access to vestibular function assessment and rehabilitation is required in adult CI users.

Impaired fixation suppression is a risk factor for vertigo after cochlear implantation

Objectives:

To analyse the correlation between visual fixation suppression test results and the occurrence of post-operative vertigo in patients receiving a cochlear implant, and to compare this with other possible risk factors.

Methods:

In a prospective study setting, caloric vestibular responses, visual fixation suppression and subjective vertigo symptoms were assessed in 59 adult patients undergoing cochlear implantation. These parameters were compared in patients with post-operative vertigo versus vertigo-free patients.

Results:

Vertigo symptoms were reported by 49 per cent of patients. Thirty-nine per cent of the patients had a decrease in caloric response on the implanted side. There was no statistically significant difference between the two patient groups regarding canal paresis, age, sex, implanted electrode type, implant side, surgeon, cause of deafness, petrous bone computed tomography findings and incidence of pre-operative vertigo. Patients with post-operative vertigo had a significantly greater prevalence of insufficient visual fixation suppression. All patients who suffered long-term post-operative vertigo had insufficient visual fixation suppression.

Conclusions:

Pre-operative impaired visual fixation suppression is a major risk factor for the occurrence of vertigo after cochlear implantation.

Pre- and post-operative dizziness, tinnitus, and taste disturbances among cochlear implant recipients

Objective:

To determine the pre- and post-operative prevalence of dizziness, tinnitus and taste disturbances in adult cochlear implant recipients.

Methods:

A questionnaire regarding pre- and post-operative dizziness, tinnitus and taste disturbances was sent to 170 cochlear implant recipients implanted between January 2003 and March 2009. Seventy-seven patients (41 per cent) responded.

Results:

Pre-operatively, 20 per cent of the participants experienced dizziness, 52 per cent experienced tinnitus and 3 per cent experienced taste disturbances. Post-operative dizziness developed in 46 per cent of patients and resolved in the majority of these; however, 15 per cent reported dizziness more than six months after implantation. Tinnitus worsened in 25 per cent of patients, whereas 73 per cent reported attenuation or termination of tinnitus. Post-operatively, tinnitus developed in 12 per cent and taste disturbances developed in 17 per cent of the patients.

Conclusion:

The high prevalence of dizziness, tinnitus and taste disturbances reported by cochlear implant recipients necessitates that assessment of symptoms related to inner ear and chorda tympani damage are included when evaluating operative results.

Value of pre-operative caloric test in predicting speech perception after cochlear implantation in adults with post-lingual hearing loss

CONCLUSION

This study shows that, in cochlear implantation (CI) surgery, pre-operative caloric test results are not correlated with post-operative outcomes of dizziness or speech perception.

OBJECTIVES

To determine the role of pre-operative caloric tests in CI.

METHODS

The records of 95 patients who underwent unilateral CI were reviewed retrospectively. Patients were divided into four groups according to caloric response. Forty-six patients with normal caloric responses were classified as Group A, 19 patients who underwent CI in the ear with worse caloric responses as Group B, 18 patients with bilateral loss of caloric responses as Group C, and 12 patients who underwent CI in the ear with better caloric responses as Group D. Speech performance and post-operative dizziness were compared between the four groups. Speech perception was determined by evaluating consonant-vowel phoneme detection, closed-set word and open-set mono-syllabic and bi-syllabic word identification, and sentence comprehension test scores.

RESULTS

The speech perception and aided pure-tone average (PTA) test results at 3 and 6 months and at 1, 2, and 3 years after implantation were not significantly different between Groups A, B, C, and D (p > 0.05). Eight patients (8.4%) reported post-operative dizziness, but there was no significant difference between the four groups (p = 0.627).

What vestibular tests to choose in symptomatic patients after a cochlear implant? A systematic review and meta-analysis

Vestibular function after cochlear implantation is difficult to understand, as subjective vestibular symptoms seem uncorrelated with the results of objective tests. Consequently, clinicians may struggle to decide what assessments to perform for a symptomatic patient. We used a systematic review and meta-analysis approach to enlighten this point. After a study inclusion process, results were classified into four different groups for each test in each study: (1) 'true positive' if the test showed impairment from pre-operative to post-operative in symptomatic patients; (2) 'false positive' if the test showed impairment from pre-operative to post-operative in asymptomatic patients; (3) 'true negative' if the test showed no impairment in asymptomatic patients; and (4) 'false negative' if the test showed no impairment in symptomatic patients. From these groups, sensitivities and specificities of each test were calculated in a meta-analysis. After reviewing more than 3000 references, 16 studies were included, representing 957 patients. The meta-analysis revealed a sensitivity of 0.21 (CI 95 % 0.08-0.40) for the caloric tests, of 0.32 (CI 95 % 0.15-0.54) for the cervical vestibular evoked myogenic potentials (c-VEMP), and of 0.5 (CI 95 % 0.07-0.93) for the head impulse tests. The analysis of prevalence revealed that c-VEMPs were the most often impaired, and the HIT the most often conserved. Our review and meta-analysis revealed that no vestibular test is sensitive enough to be recommended as a single test. Ideally, all the five vestibular sensors should be tested. In clinical practice, we suggest a case-to-case strategy according to patient's symptoms and their suspected origin.

Effects of Unilateral Cochlear Implantation on Balance Control and Sensory Organization in Adult Patients with Profound Hearing Loss

Many studies were interested in the consequence of vestibular dysfunction related to cochlear implantation on balance control. This pilot study aimed to assess the effects of unilateral cochlear implantation on the modalities of balance control and sensorimotor strategies. Posturographic and vestibular evaluations were performed in 10 patients (55 ± 20 years) with profound hearing loss who were candidates to undergo unilateral multichannel cochlear implantation. The evaluation was carried out shortly before and one year after surgery. Posturographic tests were also performed in 10 age-matched healthy participants (63 ± 16 years). Vestibular compensation was observed within one year. In addition, postural performances of the patients increased within one year after cochlear implantation, especially in the more complex situations, in which sensory information is either unavailable or conflicting. Before surgery, postural performances were higher in the control group compared to the patients' group. One year after cochlear implantation, postural control was close to normalize. The improvement of postural performance could be explained by a mechanism of vestibular compensation. In addition, the recovery of auditory information which is the consequence of cochlear implantation could lead to an extended exploration of the environment possibly favoring the development of new balance strategies.

Vestibular function and cochlear implant

Vestibular lesions are found after cochlear implantation in 23-100 % of cases. The objectives of this study were to evaluate the vestibular function before and after implantation while focusing its feasibility. This prospective study included 35 patients, mean age 49 years. Each patient enjoyed a vestibular balance before and after implantation in a median period of 5 months compared to surgery. Vestibular evaluations were performed using vestibular-evoked myogenic potentials (VEMP) and videonystagmography. Before implantation, the VEMPs were bilateral in 73 % of cases. They are modified after implantation for 13 patients, including 12 missing or reduced potentials on implanted side (p = 0.0015). Caloric tests found themselves a significant decrease in the reflectivity of the ear implanted (p < 0.0001). Vestibular symptoms were independent of changes on vestibular tests. No relation was found between the occurrence of post-operative vestibular symptoms and the results of the vestibular investigations. However, the achievement of these exams is not easy especially for children and only part of the vestibule is tested. In conclusion, the vestibular assessments help to choose the side of implantation, assess the pre-operative vestibular condition and assess and locate vestibular lesions induced. Further tests should enable a complete vestibular assessment.

The Role of Vestibular Caloric Tests in Cochlear Implantation

Objective

Vestibular function tests are often undertaken before cochlear implantation, in part to help select the side of surgery. The authors aim to determine whether implantation on the side of better vestibular function leads to greater perception of dizziness by patients than implantation on the side of worse or similar function.

Study Design

Historical cohort study.

Setting

Tertiary cochlear implantation center.

Subjects and Methods

The records of 177 adult recipients of a unilateral cochlear implant were reviewed retrospectively in 2 groups. Group A included patients with an implant in the ear with worse or similar caloric responses. Group B included patients with an implant in the ear with the stronger caloric response. All patients underwent preoperative bithermal caloric testing: a clinically significant difference was defined by a 20% lateral canal paresis. They were assessed postoperatively by the Dizziness Handicap Inventory and supplementary questions.

Results

Fifty-seven percent of both groups reported dizziness in the first 7 days postoperatively. At 2 months, 20% of group A and 34% of group B experienced some dizziness. Fourteen percent of group A and 10% of group B felt that cochlear implantation had resulted in impaired balance. The Dizziness Handicap Inventory scores of 86% of group A (median score 0) and 76% of group B (median score 10) corresponded with low handicap. None of these results differed significantly between groups A and B.

Conclusion

Although cochlear implantation may result in dizziness, it is almost always short-lived and mild, even when the ear with the stronger caloric response is implanted.

Influence of cochlear implantation on peripheral vestibular receptor function

Objective: The objectives of this study were 1) to assess the influence of a cochlear implantation on peripheral vestibular receptor function in the inner ear in the implant and in the nonimplant side, and 2) to analyze a possible correlation with resulting vertigo symptoms.

Study Design: Prospective clinical study.

Setting: Cochlear implant center at tertiary referral hospital.

Subjects and Methods: A total of 32 patients, aged 15 to 83 years, undergoing cochlear implantation were assessed pre- and postoperatively for caloric horizontal semicircular canal response and vestibular-evoked myogenic potentials of the sacculus, and postoperatively for subjective vertigo symptoms. Patients with vertigo were compared with patients without symptoms with regard to the findings of the vestibular function tests.

Results: Cochlear implantation represents a significant risk factor for horizontal semicircular canal impairment ( P < 0.001) and sacculus impairment ( P = 0.047) in the implanted ear. In eight of 16 patients with preoperatively preserved caloric response, this response was decreased postoperatively. Before surgery, 14 of 30 patients had regular vestibular-evoked myogenic responses. Two months after implantation, six patients had a new loss and another six showed depression of sacculus function on vestibular-evoked myogenic potentials testing. The impaired vestibular function did not correlate with vertigo symptoms. Function on the contralateral side remains unaffected ( P > 0.05).

Conclusion: Cochlear implantation is a relevant risk factor for damage of peripheral vestibular receptor function. Therefore, preservation not only of residual hearing function but also of vestibular function should be aimed for, by using minimally invasive surgical techniques.

Influence of Cochlear Implantation on Sacculus Function

OBJECTIVES: To examine the influence of cochlear implantation (CI) on the sacculus function and to analyze a possible correlation with resulting vertigo symptoms.

METHODS: In a prospective study including 25 patients undergoing CI, preoperative and postoperative assessment of vestibular evoked myogenic potentials (VEMP), caloric horizontal semicircular canal (hSCC) response, and subjective vertigo symptoms were assessed. The patients with postoperative vertigo were compared to the patients without postoperative vertigo with regard to the findings of VEMP responses and caloric testing.

RESULTS: Nine patients reported postoperative vertigo. Before surgery, eight of 23 patients (35%) had regular VEMP responses. Two months after CI, four patients had a new loss of sacculus function on VEMP testing. The CI represents a significant risk factor for sacculus impairment. In seven of 12 patients with preoperatively preserved caloric response, this decreased after the operation. The impaired vestibular function did not correlate with vertigo symptoms. When comparing the patient group with vertigo and the group without vertigo after CI, there is a significant difference in the patients' age.

CONCLUSIONS: Although CI can cause damage to sacculus and hSCC function, this is probably not the only cause for postoperative vertigo. Advanced age is a significant risk factor for vertigo after CI.