Another evidence for pressure transfer mechanism in incomplete partition two anomaly via enlarged vestibular aqueduct.

A female patient with unilateral enlarged vestibular aqueduct (EVA) demonstrated scala vestibuli dilatation on that side while on the contralateral side both vestibular aqueduct and scala vestibuli were normal. This important radiological finding demonstrates that modiolar defects (hence 'cystic apex') observed in Incomplete partition-II is due to pressure transfer via EVA during embryological development. Therefore, it supports the previous histopathological ideas radiologically. Depending on the patency of EVA, variety of modiolar defects may arise.

Cone-beam computed tomography in children with cochlear implants: The effect of electrode array position on ECAP.

OBJECTIVES: To assess the feasibility of using cone-beam computed tomography (CBCT) in young children with cochlear implants (CIs) and study the effect of intracochlear position on electrophysiological and behavioral measurements. METHODS: A total of 40 children with either unilateral or bilateral cochlear implants were prospectively included in the study. Electrode placement and insertion angles were studied in 55 Cochlear® implants (16 straight arrays and 39 perimodiolar arrays), using either CBCT or X-ray imaging. CBCT or X-ray imaging were scheduled when the children were leaving the recovery room. We recorded intraoperative and postoperative neural response telemetry threshold (T-NRT) values, intraoperative and postoperative electrode impedance values, as well as behavioral T (threshold) and C (comfort) levels on electrodes 1, 5, 10, 15 and 20. RESULTS: CBCT imaging was feasible without any sedation in 24 children (60%). Accidental scala vestibuli insertion was observed in 3 out of 24 implants as assessed by CBCT. The mean insertion angle was 339.7°±35.8°. The use of a perimodiolar array led to higher angles of insertion, lower postoperative T-NRT, as well as decreased behavioral T and C levels. We found no significant effect of either electrode array position or angle of insertion on electrophysiological data. CONCLUSION: CBCT appears to be a reliable tool for anatomical assessment of young children with CIs. Intracochlear position had no significant effect on the electrically evoked compound action potential (ECAP) threshold. Our CBCT protocol must be improved to increase the rate of successful investigations.

Micro-optical coherence tomography of the mammalian cochlea.

The mammalian cochlea has historically resisted attempts at high-resolution, non-invasive imaging due to its small size, complex three-dimensional structure, and embedded location within the temporal bone. As a result, little is known about the relationship between an individual's cochlear pathology and hearing function, and otologists must rely on physiological testing and imaging methods that offer limited resolution to obtain information about the inner ear prior to performing surgery. Micro-optical coherence tomography (µOCT) is a non-invasive, low-coherence interferometric imaging technique capable of resolving cellular-level anatomic structures. To determine whether µOCT is capable of resolving mammalian intracochlear anatomy, fixed guinea pig inner ears were imaged as whole temporal bones with cochlea in situ. Anatomical structures such as the tunnel of Corti, space of Nuel, modiolus, scalae, and cell groupings were visualized, in addition to individual cell types such as neuronal fibers, hair cells, and supporting cells. Visualization of these structures, via volumetrically-reconstructed image stacks and endoscopic perspective videos, represents an improvement over previous efforts using conventional OCT. These are the first µOCT images of mammalian cochlear anatomy, and they demonstrate µOCT's potential utility as an imaging tool in otology research.

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.

Intraoperative Electrophysiologic Variations Caused by the Scalar Position of Cochlear Implant Electrodes.

OBJECTIVE: The position of cochlear implant (CI) electrodes in the cochlea is fundamental for the interaction between the implant and the neurons of the spiral ganglion. The scalar position of the electrode in the cochlea is assumed to be an important parameter for the clinical outcome. In our study, the intraoperative electrophysiologic characteristics in dependence of the position of CI electrodes in the scala tympani or in the scala vestibuli after scalar change should be determined. MATERIALS AND METHODS: The intraoperative impedances and neural response telemetry (NRT) data of 23 patients implanted with a Nucleus Advance Contour (Cochlear Pty, Sydney, Australia) electrode were recorded. One CI surgeon and two radiologists evaluated the electrode array's position independently radiologically by flat-panel tomography. Results from 17 patients with the electrode positioned in the scala tympani and six patients with the electrode changing intraoperatively from the tympanic into the vestibular scala were retrospectively analyzed. RESULTS: We found a statistically significant difference with an NRT threshold-based ratio for the groups. An estimation of the (radiologically confirmed) scalar position based on the NRT ratio was possible retrospectively. CONCLUSION: The evaluation of specific intraoperative electrophysiologic data allowed separating between a regular and an irregular (i.e., scalar changing) position of CI electrodes. This noninvasive methodology can support the postoperative radiologic evaluation of the CI electrode array position.

Scalar localization by cone-beam computed tomography of cochlear implant carriers: a comparative study between straight and periomodiolar precurved electrode arrays.

OBJECTIVE: To compare the incidence of dislocation of precurved versus straight flexible cochlear implant electrode arrays using cone-beam computed tomography (CBCT) image analyses. STUDY DESIGN: Consecutive nonrandomized case-comparison study. SETTINGS: Tertiary referral center. PATIENTS: Analyses of patients' CBCT images after cochlear implant surgery. INTERVENTION(S): Precurved and straight flexible electrode arrays from two different manufacturers were implanted. A round window insertion was performed in most cases. Two cases necessitated a cochleostomy. The patients' CBCT images were reconstructed in the coronal oblique, sagittal oblique, and axial oblique section. MAIN OUTCOME MEASURES: The insertion depth angle and the incidence of dislocation from the scala tympani to the scala vestibuli were determined. RESULTS: The CBCT images and the incidence of dislocation were analyzed in 54 patients (61 electrode arrays). Thirty-one patients were implanted with a precurved perimodiolar electrode array and 30 patients with a straight flexible electrode array. A total of nine (15%) scalar dislocations were observed in both groups. Eight (26%) scalar dislocations were observed in the precurved array group and one (3%) in the straight array group. Dislocation occurred at an insertion depth angle between 170 and 190 degrees in the precurved array group and at approximately 370 degrees in the straight array group. CONCLUSION: With precurved arrays, dislocation usually occurs in the ascending part of the basal turn of the cochlea. With straight flexible electrode arrays, the incidence of dislocation was lower, and it seems that straight flexible arrays have a higher chance of a confined position within the scala tympani than perimodiolar precurved arrays.

Radiologic and functional evaluation of electrode dislocation from the scala tympani to the scala vestibuli in patients with cochlear implants.

BACKGROUND AND PURPOSE: Localization of the electrode after cochlear implantation seems to have an impact on auditory outcome, and conebeam CT has emerged as a reliable method for visualizing the electrode array position within the cochlea. The aim of this retrospective study was to evaluate the frequency and clinical impact of scalar dislocation of various electrodes and surgical approaches and to evaluate its influence on auditory outcome. MATERIALS AND METHODS: This retrospective single-center study analyzed a consecutive series of 63 cochlear implantations with various straight electrodes. The placement of the electrode array was evaluated by using multiplanar reconstructed conebeam CT images. For the auditory outcome, we compared the aided hearing thresholds and the charge units of maximum comfortable loudness level at weeks 6, 12, and 24 after implantation. RESULTS: In 7.9% of the cases, the electrode array showed scalar dislocation. In all cases, the electrode array penetrated the basal membrane within 45° of the electrode insertion. All 3 cases of cochleostomy were dislocated in the first 45° segment. No hearing differences were noted, but the charge units of maximum comfortable loudness level seemed to increase with time in patients with dislocations. CONCLUSIONS: The intracochlear dislocation rate of various straight electrodes detected by conebeam CT images is relatively low. Scalar dislocation may not negatively influence the hearing threshold but may require an increase of the necessary stimulus charge and should be reported by the radiologist.

Scalar position in cochlear implant surgery and outcome in residual hearing and the vestibular system.

OBJECTIVE: To evaluate the effect of the intracochlear electrode position on the residual hearing and VNG- and cVEMP responses. DESIGN: Prospective pilot study. STUDY SAMPLE: Thirteen adult patients who underwent unilateral cochlear implant surgery were examined with high-resolution rotational tomography after cochlear implantation. All subjects were also tested with VNG, and 12 of the subjects were tested with cVEMP and audiometry before and after surgery. RESULTS: We found that although the electrode was originally planned to be positioned inside the scala tympani, only 8 of 13 had full insertion into the scala tympani. Loss of cVEMP response occurred to the same extent in the group with full scala tympani positioning and the group with scala vestibuli involvement. There was a non-significant difference in the loss of caloric response and residual hearing between the two groups. Interscalar dislocation of the electrode inside the cochlea was observed in two patients. A higher loss of residual hearing could be seen in the group with electrode dislocation between the scalae. CONCLUSIONS: Our findings indicate that intracochlear electrode dislocation is a possible cause to loss of residual hearing during cochlear implantation but cannot be the sole cause of postoperative vestibular loss.

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.

Automatic segmentation of intracochlear anatomy in conventional CT.

Cochlear implant surgery is a procedure performed to treat profound hearing loss. Clinical results suggest that implanting the electrode in the scala tympani, one of the two principal cavities inside the cochlea, may result in better hearing restoration. Segmentation of intracochlear cavities could thus aid the surgeon to choose the point of entry and angle of approach that maximize the likelihood of successful implant insertion, which may lead to more substantial hearing restoration. However, because the membrane that separates the intracochlear cavities is too thin to be seen in conventional in vivo imaging, traditional segmentation techniques are inadequate. In this paper, we circumvent this problem by creating an active shape model with micro CT (µCT) scans of the cochlea acquired ex vivo. We then use this model to segment conventional CT scans. The model is fitted to the partial information available in the conventional scans and used to estimate the position of structures not visible in these images. Quantitative evaluation of our method, made possible by the set of µCTs, results in Dice similarity coefficients averaging 0.75. Mean and maximum surface errors average 0.21 and 0.80 mm.