Auditory outcomes after scala vestibuli array insertion are similar to those after scala tympani insertion 1 year after cochlear implantation.

PURPOSE: In cochlear implantation, a scala vestibuli (SV) insertion of an electrode array is a rare occurrence and is reported to be linked to poor hearing outcomes. Using the same electrode array, the auditory performance of patients with a complete SV location was compared with that of patients having a complete scala tympani (ST) location 1 year after implantation. METHODS: Thirty-three patients were included in this retrospective case-control study (SV, n = 12; ST, n = 21). The matching criteria were electrode array type, age at implantation, and duration of severe or profound deafness. The array location was analyzed using 3D reconstruction of postoperative CT scans. Postoperative audiological evaluation of the implanted ear was performed using pure-tone audiometry, speech recognition of monosyllabic words in quiet, and words and sentences in noise. RESULTS: On the preoperative CT scan, six patients in the SV group presented with both round window (RW) and ST ossification, three with RW ossification alone, and three with no RW ossification. Auditory performance did not differ between SV and ST groups 1 year after cochlear implantation. Speech recognition of words was 49 ± 7.6% and 56 ± 5.0% in quiet and 75 ± 9.5% and 66 ± 6.0% in noise in SV and ST groups, respectively. CONCLUSION: ST insertion is the gold standard that allows the three cochlear scalae to preserve scalar cochlear integrity. However, 1 year after implantation, a planned or unexpected SV insertion is not detrimental to hearing outcomes, providing similar auditory performance in quiet and noise to ST insertion.

Prolonged Insertion Time Reduces Translocation Rate of a Precurved Electrode Array in Cochlear Implantation.

HYPOTHESIS: Insertion speed during cochlear implantation determines the risk of cochlear trauma. By slowing down insertion speed tactile feedback is improved. This is highly conducive to control the course of the electrode array along the cochlear contour and prevent translocation from the scala tympani to the scala vestibuli. BACKGROUND: Limiting insertion trauma is a dedicated goal in cochlear implantation to maintain the most favorable situation for electrical stimulation of the remaining stimulable neural components of the cochlea. Surgical technique is one of the potential influencers on translocation behavior of the electrode array. METHODS: The intrascalar position of 226 patients, all implanted with a precurved electrode array, aiming a mid-scalar position, was evaluated. One group (n = 113) represented implantation with an insertion time less than 25 seconds (fast insertion) and the other group (n = 113) was implanted in 25 or more seconds (slow insertion). A logistic regression analysis studied the effect of insertion speed on insertion trauma, controlled for surgical approach, cochlear size, and angular insertion depth. Furthermore, the effect of translocation on speech performance was evaluated using a linear mixed model. RESULTS: The translocation rate within the fast and slow insertion groups were respectively 27 and 10%. A logistic regression analysis showed that the odds of dislocation increases by 2.527 times with a fast insertion, controlled for surgical approach, cochlear size, and angular insertion depth (95% CI = 1.135, 5.625). We failed to find a difference in speech recognition between patients with and without translocated electrode arrays. CONCLUSION: Slowing down insertion speed till 25 seconds or longer reduces the incidence of translocation.

Scala vestibuli cochlear implant supported by 3D modeling of the inner ear.

Patients with scala tympani (ST) ossification present a distinct surgical challenge. Three-dimensional (3D) segmentation of the inner ear offers accurate identification of ossification and surgical planning of the cochleostomy to access the scala vestibuli. The scala vestibuli placement of cochlear implantation electrode is an alternate solution in these patients and is well supported by the literature.The present report describes a case of cochlear implantation in the scala vestibuli assisted by 3D segmentation of the cochlea for a patient with ossification in the ST and reviews the relevant literature. Clinical presentation of a 45-year-old Austrian female who was referred with a history of sudden sensorineural hearing loss 2 years ago in the right ear, confirmed by pure tone audiometry (PTA) and acoustically evoked auditory brainstem response (ABR). 3D segmentation of the inner ear identified the extent of ossification in the ST and assisted in the surgical planning of cochleostomy drilling anterior-superior to the round window to access the scala vestibuli for the electrode placement. Postoperative computed tomography (CT) to confirm the electrode placement in the scala vestibuli and PTA was performed to assess the hearing threshold following the cochlear implantation. Postoperative CT confirmed the full insertion of a flexible electrode. The hearing threshold measured by PTA was ≤ 40 dB across all frequencies tested. Review of the literature identified a total of 13 published reports on cochlear implantation electrode placement in scala vestibuli in cases with ossification in the ST.

Comparative Impacts of Scala Vestibuli Versus Scala Tympani Cochlear Implantation on Auditory Performances and Programming Parameters in Partially Ossified Cochleae.

OBJECTIVE: To compare scala vestibuli versus scala tympani cochlear implantation in terms of postoperative auditory performances and programming parameters in patients with severe scala tympani ossification. STUDY DESIGN: Retrospective case-control study. SETTING: Tertiary referral center. PATIENTS: One hundred three pediatric and adult patients who underwent cochlear implant surgery between 2000 and 2016. Three groups were formed: a scala vestibuli group, a scala tympani with ossification group, and a scala tympani without ossification group. Patients were matched based on their age, sex, duration of deafness, and side of implantation (ratio of 1:2:2). INTERVENTIONS: Postoperative evaluation of auditory performances and programming parameters following intensive functional rehabilitation program completion. MAIN OUTCOME MEASURES: Multimedia adaptive test (MAT), hearing in noise test (HINT SNR +10 dB, HINT SNR +5 dB, and HINT SNR +0 dB), impedances, neural response telemetry thresholds (NRT), neural response imaging thresholds (NRI), comfortable levels (C-levels), and threshold levels (T-levels) were compared between groups. RESULTS: Twenty-one patients underwent scala vestibuli cochlear implantation: 19 adults and two children. Auditory performances were similar between groups, although sentence recognition in a noisy environment was slightly higher in the scala vestibuli group. Impedance values were also higher in the scala vestibuli group, but all other programming parameters were similar between groups. CONCLUSIONS: We present the largest series of patients with scala vestibuli cochlear implantation. This approach provides at least comparable auditory performances without having any deleterious effects on programming parameters. This viable and useful insertion route might be the primary surgical alternative when facing partial cochlear ossification.

Cochlear Implantation in Otosclerosis: Surgical and Auditory Outcomes With a Brief on Facial Nerve Stimulation.

OBJECTIVES: 1) To review the surgical and auditory outcomes in patients of cochlear implantation in otosclerosis. 2) To review complications and postimplantation facial nerve stimulation (FNS). 3) To compare the auditory outcomes between patients displaying cochlear ossification to the nonossified ones. STUDY DESIGN: Retrospective study. SETTING: Quaternary Otology and Skull base surgery center. SUBJECTS AND METHODS: Charts of 36 patients (38 ears) with otosclerosis undergoing cochlear implantation were reviewed from the cochlear implant database. Demographic features, operative findings, auditory outcomes, and postimplantation FNS were analyzed. Operative findings included extent of cochlear ossification, approach (posterior tympantomy/subtotal petrosectomy), electrode insertion (partial/complete, scala tympani/vestibuli), and complications. All the patients underwent implantation using straight electrodes. Auditory outcomes were assessed over a 4-year follow-up period using vowel, word, sentence, and comprehension scores. Patients were divided into two groups (with and without cochlear ossification) for comparison of auditory outcomes. RESULTS: The mean age and duration of deafness of patients was 59.72 and 28.9 years respectively. Twenty-three of 38 ears had cochlear ossification, with exclusive round window involvement in 60% of the patients, with the rest having partial or complete basal turn ossification. 36.8% ears underwent subtotal petrosectomy for cochlear ossification. One patient underwent scala vestibuli insertion and two had incomplete electrode insertion. Patients with no ossification had no intra or postoperative complications. One patient had bilateral FNS managed by alterations in programming strategy. Auditory outcomes in patients without any ossification were better than in patients with ossification, though statistically insignificant in most parameters. CONCLUSION: Cochlear implantation in otosclerosis provides good auditory outcomes, despite high incidence of cochlear ossification. Patients of FNS can be managed by alterations in programming strategy, without affecting auditory outcomes.

Development of Insertion Models Predicting Cochlear Implant Electrode Position.

OBJECTIVES: To assess the possibility to define a preferable range for electrode array insertion depth and surgical insertion distance for which frequency mismatch is minimalized. To develop a surgical insertion guidance tool by which a preferred target angle can be attained using preoperative available anatomical data and surgically controllable insertion distance. DESIGN: Multiplanar reconstructions of pre- and post-operative CT scans were evaluated in a population of 336 patients implanted with the CII HiFocus1 or HiFocus1J implant (26 bilaterally implantees included). Cochlear radial distances were measured on four measurement axes on the preoperative CT scan. Electrode contact positions were obtained in angular depth, distance from the round window and to the modiolus center. Frequency mismatch was calculated based on the yielded frequency as a function of the angular position per contact. Cochlear diameters were clustered into three cochlear size groups with K-sample clustering. Using spiral fitting and general linear regression modeling, the feasibility of different insertion models with cochlear size measures and surgical insertion as input parameters was analyzed. The final developed model was internally validated with bootstrapping to calculate the optimism-corrected R. RESULTS: Frequency mismatch was minimalized for surgical insertion of 6.7 mm and insertion depth of 484°. Cochlear size clusters were derived consisting of a "small" (N = 117), "medium" (N = 171), and "large" (N = 74) cluster with mean insertion depths of 506°, 480°, and 441°, respectively. The relation between surgical insertion (LE16) and insertion depth (θE1) differed significantly between the three clusters (p < 0.01). The insertion models based on spiral fitting showed an R of 62% with mean of the residuals of -0.5 mm (SD = 1.2 mm) between the measured and predicted LE16 and a mean of 15° (SD = 83°) for θE1. Using general linear regression modeling resulted in a residual mean of -0.2 µm (SD = 0.9 mm) for measured and predicted LE16 and 0.01° (SD = 33°) for θE1. The model derived from general linear regression modeling resulted in an R of 78.7% and was validated with bootstrapping. An optimism of 0.6% was calculated using this analysis. The optimism-corrected R of 78.1% defined the estimated performance of the final insertion model in future populations. CONCLUSIONS: A minimal frequency mismatch for an electrode array design can be calculated to define preferable electrode array position within the cochlea. In general, to achieve a minimal frequency mismatch, the surgeon should attempt to insert the HiFocus 1 or 1J array around 6, 7, or 8 mm in case of a "small," "medium," or "large" cochlea, respectively. Development of different insertion models showed the feasibility of obtaining a surgical guidance tool to lead the surgeon during cochlear implantation depending on individual cochlear size and controllable surgical distance. The developed final insertion model predicted 78.1% of the variation in final HiFocus1 or HiFocus1J implant position.

Characterization of intracochlear rupture forces in fresh human cadaveric cochleae.

HYPOTHESIS: To develop a method to measure the forces required for a probe to translocate from the scala tympani (ST) to the scala vestibuli (SV) in fresh human cochleae. BACKGROUND: Translocation of cochlear implant electrodes from the ST to the SV may lead to suboptimal audiologic outcomes. Prior work investigating the rupture forces of human intracochlear membranes comes from a single study conducted on isolated ex vivo cadaveric specimens. METHODS: Fresh (postmortem <120 h), nonfixed, never-frozen human temporal bones underwent preparation consisting of surgical isolation of the cochleae and exposure of the osseous spiral lamina, basilar membrane, and Reissner's membrane complex by removing bone covering the ST and the SV. Each isolated cochlea was mounted to a force sensor using an adjustable mounting platform. A 300-µm-diameter ball-tipped probe was attached to a piezoelectric linear motor and advanced at 1 mm/s from the ST to the SV while recording force from the load cell concurrent with video. RESULTS: Ten specimens were successfully exposed and analyzed. The range of rupture forces was 42 to 122 mN, with a mean of 88 mN. Nine of the 10 specimens failed via simple puncture, whereas one failed by being avulsed from its medial attachment. CONCLUSION: Using a novel technique, we report the forces required to translocate a model of an electrode from the ST to the SV. Correlation to human perceptual ability is necessary to determine if a surgeon can detect such translocation during cochlear implant surgery.

Scalar localization by computed tomography of cochlear implant electrode carriers designed for deep insertion.

OBJECTIVES: This study aimed to evaluate the possibility of predicting radiologically the scalar localization of a 31.5-mm-long, free-fitting electrode carrier for cochlear implantation, using conventional planar computed tomography. STUDY DESIGN: A cross-sectional human temporal bone study was conducted. SETTING: Twenty human temporal bones were acquired postmortem and implanted with 31.5-mm-long electrode carriers. Ten of these were implanted into the scala tympani using the round window approach, whereas the other 10 electrodes were inserted into the scala vestibuli by cochleostomy. Computed tomography was then performed, and 2 experienced blinded radiologists evaluated the intracochlear position of the array. MAIN OUTCOME MEASURE: The estimated position of the electrode carrier was described using a 5-point scale. After sectioning and histologic investigation, the results of the radiologic and histologic investigations were compared. RESULTS: In 17 of 20 cases, it was possible to estimate the correct position of the electrode carrier within the basal turn of the cochlea by means of computed tomography. As the insertion angles widened beyond 360 degrees, it became increasing difficult for the radiologists to correctly determine the position of the electrode carrier. CONCLUSION: The comparison of our temporal bone experiment results with the computed tomography results revealed the difficulty of assessing the correct position of intracochlear electrodes. Scalar localization of deeply inserted electrode carriers cannot be precisely determined by means of computed tomography.

Midmodiolar reconstruction as a valuable tool to determine the exact position of the cochlear implant electrode array.

HYPOTHESIS: A midmodiolar reconstruction with multislice computed tomography could potentially be used clinically to determine the cochlear implant electrode array position if the technique was validated with a cadaveric temporal bone study. BACKGROUND: Several radiologic studies using sophisticated techniques have been described. This study was designed to validate a standard multislice computed tomography scan technique to determine the electrode array position. METHODS: This ex vivo study was conducted on 18 cadaveric temporal bones without malformation. Cochlear electrode dummies were implanted by a single experimented surgeon with the Advance Off-Stylet technique. After randomization, the placement was processed through an anteroinferior or superior cochleostomy for respective scala tympani or vestibuli positioning with direct location of the basilar membrane. Cadaveric temporal bones were then scanned (Philips Brilliance 40 computed tomographic scan) and reconstructed into the midmodiolar computed tomography scan plane (± 45 degrees, z-axis in the cochlear coordinate system). Two independent neuroradiologists, who were unaware of the implanted scala, evaluated the electrode array position on a computed tomographic scan through the midmodiolar reconstruction. In the end, the microanatomic study was the criterion standard to determine the exact scala localization of the electrode array. RESULTS: Nine electrodes were inserted into the scala tympani, and 9 were inserted into the scala vestibuli. According to our anatomic criterion standard, the midmodiolar reconstruction sensitivity and the specificity for the scala tympani position were 0.875 (range, 0.722-1.0) and 1.0, respectively; the sensitivity and specificity for dislocation and the scala vestibuli position were both 1.0. The radioanatomic concordance was 0.94 (range, 0.89-0.98) for determining the electrode array position into scalae with midmodiolar reconstruction. CONCLUSION: Our cadaveric study validates midmodiolar reconstruction as a valuable tool to routinely determine the precise position of the cochlear implant electrode array. This study opens the field for further clinical studies.

Preservation of vestibular function after scala vestibuli cochlear implantation.

A 58-year-old man, in whom the cochlear implant (CI) had been inserted into the left ear, had right middle-ear cancer. The CI was removed immediately before receiving subtotal removal of right temporal bone. Four months later, the CI was again inserted in his left cochlea. Because of obliterated scala tympani, the 22 active electrodes of the CI were placed into the scala vestibuli. After the surgery, the patient complained that he experienced rotary vertigo and "jumbling of vertical direction" of objects on walking. Using rotation test, we evaluated vestibular function of remaining left ear. Numerous horizontal nystagmus beats were induced during earth-vertical axis rotation, whereas vertical downbeat nystagmus was scarcely induced during off-vertical axis rotation. The horizontal vestibulo-ocular reflex (VOR) was almost normally induced by sinusoidal stimulation at 0.8Hz. These data suggest that the scala vestibuli insertion of CI would be not so invasive against the lateral semicircular canal.

Clinical outcomes of scala vestibuli cochlear implantation in children with partial labyrinthine ossification.

CONCLUSION: Cochlear implantation via the scala vestibuli is a viable approach in those with ossification in the scala tympani. With extended cochlear implant experience, there is no significant difference in the mapping parameters and auditory performance between those implanted via scala vestibuli and via scala tympani. OBJECTIVES: To assess the clinical outcomes of cochlear implantation via scala vestibuli. PATIENTS AND METHODS: In a cohort follow-up study, 11 prelingually deafened children who received cochlear implantation between age 3 and 10 years through the scala vestibuli served as participants. The mapping parameters (i.e. comfortable level (C), threshold level (T), dynamic range) and auditory performance of each participant were evaluated following initial cochlear implant stimulation, then at 3 month intervals for 2 years, then semi-annually. The follow-up period lasted for 9 years 9 months on average, with a minimum of 8 years 3 months. RESULTS: The clinical results of the mapping parameters and auditory performance of children implanted via the scala vestibuli were comparative to those who were implanted via the scala tympani. No balance problem was reported by any of these patients. One child exhibited residual low frequency hearing after implantation.