Cochlear implant surgery and perioperative dizziness is associated with utricular hyperfunction.

BACKGROUND: Dizziness is a common perioperative complication after cochlear implantation (CI). To date, the exact cause behind this phenomenon remains unclear. There is recent evidence to suggest that otolith function, specifically utricular, may be affected shortly after CI surgery, however whether these changes are related to patient symptoms has not yet been investigated. OBJECTIVE: To determine whether CI surgery and perioperative dizziness is associated with changes in utricular function. METHODS: We performed an observational study on patients undergoing routine CI surgery. Utricular function was assessed using the Subjective Visual Vertical (SVV), and perioperative dizziness was determined using a questionnaire. The study followed patients before surgery and then again 1-day, 1-week and 6-weeks after implantation. RESULTS: Forty-one adult CI recipients participated in the study. The SVV deviated away from the operated ear by an average of 2.17° a day after implantation, 0.889° 1 week and -0.25° 6 weeks after surgery. Dizziness contributed to a tilt of 0.5° away from the implanted ear. These deviations were statistically significant. CONCLUSIONS: CI surgery causes utricular hyperfunction in the operated ear that resolves over 6 weeks. SVV tilts were greater in participants experiencing dizziness, suggesting that utricular hyperfunction may contribute to the dizziness.

Spironolactone Ameliorates Cochlear Implant Induced Endolymphatic Hydrops.

BACKGROUND: Endolymphatic hydrops (EH) has been observed in both animal and human cochleae following cochlear implant (CI) surgery. We tested whether EH could be eliminated by administration of mineralocorticoid steroid antagonist spironolactone and explored the electrophysiological consequences of this. METHODS: Sixty-four adult guinea pigs underwent cochlear implantation with a dummy electrode. Animals then survived either 2, 7, or 28 days. Auditory function was monitored by recording electrocochleography from the round window membrane preimplantation, and on the last day of the experiment. Spironolactone or control solution was added to animals' feed for 7 days (if they survived that long) beginning immediately prior to surgery. The presence of EH was determined using thin-sheet laser imaging microscopy. RESULTS: Treatment with spironolactone resulted in significant reduction in EH in the second cochlear turn 7 days postimplantation. In all animals, the compound action potential (CAP) threshold was elevated 2 days postimplantation, but for most frequencies had recovered substantially by 28 days. There was no treatment effect on CAP thresholds. SP/AP ratios were elevated at day 2. The amplitude growth of the CAP did not differ between test and control groups at any time after implantation. CONCLUSIONS: EH can be suppressed by antagonism of mineralocorticoid receptors in the week after cochlear implantation. Reduction in EH did not lead to any change in hearing, and there was no indication of synaptopathy signalled by reduced CAP amplitude at high sound intensities. We found no electrophysiological evidence that EH early after implantation impacts negatively upon preservation of residual hearing.

Intraoperative Observational Real-time Electrocochleography as a Predictor of Hearing Loss After Cochlear Implantation: 3 and 12 Month Outcomes.

OBJECTIVE: A decrease in intracochlear electrocochleographic (ECochG) amplitude during cochlear implantation has been associated with poorer postoperative hearing preservation in several short-term studies. Here, we relate the stability of ECochG during surgery to hearing preservation at 3- and 12-months. METHODS: Patients with hearing ≤80-dB HL at 500 Hz were implanted with a slim-straight electrode array. ECochG responses to short, high-intensity, 500-Hz pure tones of alternating polarity were recorded continuously from the apical-most electrode during implantation. No feedback was provided to the surgeon. ECochG amplitude was derived from the difference response, and implantations classified by the presence ("ECochG drop") or absence ("no drop") of a ≥30% reduction in ECochG amplitude during insertion. Residual hearing (relative and absolute) was reported against the ECochG class. RESULTS: ECochG was recorded from 109 patients. Of these, interpretable ECochG signals were recorded from 95. Sixty-six of 95 patients had an ECochG drop during implantation. Patients with an ECochG drop had poorer preoperative hearing above 1000 Hz. Hearing preservation (in decibels, relative to preoperative levels and functionally) was significantly poorer at 250-, 500-, and 1000-Hz at 3 months in patients exhibiting an ECochG drop. Twelve-month outcomes were available from 85 patients, with significantly poorer functional hearing, and greater relative and absolute hearing loss from 250 to 1000 Hz, when an ECochG drop had been encountered. CONCLUSION: Patients exhibiting ECochG drops during implantation had significantly poorer hearing preservation 12 months later. These observational outcomes support the future development of surgical interventions responsive to real-time intracochlear ECochG. Early intervention to an ECochG drop could potentially lead to prolonged improvements in hearing preservation.

Intraoperative Intracochlear Electrocochleography and Residual Hearing Preservation Outcomes When Using Two Types of Slim Electrode Arrays in Cochlear Implantation.

OBJECTIVES: To report residual hearing preservation outcomes in patients with low frequency hearing, after cochlear implant (CI) electrode insertion with two types of electrode arrays: one straight and other perimodiolar, when using intraoperative intracochlear electrocochleography (ECochG) during (CI) electrode insertion. STUDY DESIGN: Prospective, randomized study. SETTING: Tertiary referral otology center. PATIENTS: Fifteen patients ranging from 33 to 54 years old (mean 51.19). They had been diagnosed with a bilateral, profound sensorineural hearing loss and treated with a unilateral cochlear implant: eight of them with the CI532 and seven of them with the CI522 (Cochlear Ltd, Sydney, Australia). INTERVENTION: Pure-tone audiometry was performed preoperatively and at 1 and 6 months postoperatively. Interoperatively, intracochlear ECochG was performed using the apical-most electrode. The amplitude of the first harmonic was plotted and monitored in real time by the audiologist-surgeon team during their CI electrode insertion. The different ECoch patterns of the insertion track were recorded and analyzed. RESULTS: In 12 cases ECochG responses were successfully recorded. In three cases no ECochG responses could be recorded with no residual hearing observed postoperatively in two of them. With respect to the first harmonic amplitude changes, we found: four cases with an overall increase in amplitude measured from the beginning of insertion until completion, all of them showed residual hearing (<15 dB HL) at 6 months postoperation. Three cases with an increasing amplitude at the beginning of insertion, with a decrease in amplitude as insertion progressed to completion, in two cases dropping of residual hearing (15-30 dB HL) were observed after 6 months postoperation and, in one case, complete residual hearing was observed at 6 months postoperatively. And finally five cases presented amplitudes at the start of insertion with modifications of amplitude during the insertion dynamic, with increasing and descending in amplitude range during the whole insertion, two of them showed residual hearing at 6 months postoperation and three cases a drop of residual hearing (15-30 dB HL) was observed after 6 months postoperation. No statistical differences between CI532 and CI522 electrodes were found. Data of the ECochG responses are also presented (p value ≥ 0.05). CONCLUSION: ECochG is a useful tool to evaluate the residual hearing in CI patients with straight and perimodiolar cochlear implant. More studies are needed to fully understand the relationship between ECochG and the presence of residual hearing, cochlear trauma, and functional outcomes.

Electrode Impedance Fluctuations as a Biomarker for Inner Ear Pathology After Cochlear Implantation.

OBJECTIVES/HYPOTHESIS: Cochlear implant surgery now aims to preserve residual low frequency hearing. The current research explores whether fluctuations in the electrical impedance of cochlear implant electrodes may act as a biomarker for pathological changes that lead to the delayed loss of residual hearing. STUDY DESIGN: Secondary analysis of a double-blinded randomized trial, where methylprednisolone was administered intravenously before cochlear implantation with a view to preserving residual hearing. METHODS: Seventy-four patients with residual hearing after cochlear implant surgery were investigated for an impedance "spike," defined as a median rise of ≥4 kΩ across all electrodes from the baseline measurements. Spikes were related to objective and subjective hearing loss, dizziness, and tinnitus. RESULTS: An impedance spike occurred in 14% (10/74) of enrolled patients. Three months after surgery, five patients exhibited spikes and three of these patients had a total loss of their residual hearing. 4.3% of the 69 patients without spikes lost residual hearing. At 1 year, 9 of 10 patients who exhibited spikes had lost all their residual hearing. 8.1% of the 37 patients who did not experience a spike lost their residual hearing. Seventy percent of patients exhibiting a spike also experienced vertigo. The administration of steroids at the time of surgery did not influence the occurrence of spikes. CONCLUSION: Our results suggest that there is a relationship between a spike and the loss of residual hearing. It seems that rises in impedance can reflect pathology within the inner ear and predict the future loss of residual hearing.