Drilling accuracy evaluation of a mouldable surgical targeting system for minimally invasive access to anatomic targets in the temporal bone.

PURPOSE: Minimally invasive cochlear implant surgery using a micro-stereotactic surgical targeting system with on-site moulding of the template aims for a reliable, less experience-dependent access to the inner ear under maximal reduction of trauma to anatomic structures. We present an accuracy evaluation of our system in ex-vivo testing. METHODS: Eleven drilling experiments were performed on four cadaveric temporal bone specimens. The process involved preoperative imaging after affixing the reference frame to the skull, planning of a safe trajectory preserving relevant anatomical structures, customization of the surgical template, execution of the guided drilling and postoperative imaging for determination of the drilling accuracy. Deviation between the drilled and desired trajectories was measured at different depths. RESULTS: All drilling experiments were successfully performed. Other than purposely sacrificing the chorda tympani in one experiment, no other relevant anatomy, such as facial nerve, chorda tympani, ossicles or external auditory canal were harmed. Deviation between the desired and achieved path was found to be 0.25 ± 0.16 mm at skulls' surface and 0.51 ± 0.35 mm at the target level. The closest distance of the drilled trajectories' outer circumference to the facial nerve was 0.44 mm. CONCLUSIONS: We demonstrated the usability for drilling to the middle ear on human cadaveric specimen in a pre-clinical setting. Accuracy proved to be suitable for many applications such as procedures within the field of image-guided neurosurgery. Promising approaches to reach sufficient submillimetre accuracy for CI surgery have been outlined.

Ex Vivo Evaluation of a Minimally Invasive Approach for Cochlear Implant Surgery.

OBJECTIVES: Drilling a minimally invasive access to the inner ear is a demanding task in which a computer-assisted surgical system can support the surgeon. Herein, we describe the design of a new micro-stereotactic targeting system dedicated to cochlear implant (CI) surgery and its experimental evaluation in an ex vivo study. METHODS: The proposed system consists of a reusable, bone-anchored reference frame, and a patient-specific drilling jig on top of it. Individualization of the jig is simplified to a single counterbored hole drilled out of a blank. For accurate counterboring, the setup includes a manufacturing device for individual positioning of the blank. The system was tested in a preclinical setting using twelve human cadaver donors. Cone beam computed tomograph (CBCT) scans were obtained and a drilling trajectory was planned pointing towards the basal part of the cochlea. The surgical drill was moved forward manually and slowly while the jig constrained the drill along the predetermined path. RESULTS: Drilling could be performed with preservation of facial nerve in all specimens. The mean error caused by the system at the target point in front of the cochlea was 0.30 mm ± 0.11 mm including an inaccuracy of 0.09 mm ± 0.03 mm for counterboring the guiding aperture into the jig. CONCLUSION: Feasibility of the proposed system to perform a minimally invasive posterior tympanotomy approach was shown successfully in all specimens. SIGNIFICANCE: First evaluation of the new system in a comprehensive ex vivo study demonstrating sufficient accuracy and the feasibility of the whole concept.

Toward a cochlear implant electrode array with shape memory effect for post-insertion perimodiolar positioning.

For cochlear implants (CI) a final position of the electrode array (EA) along the inner wall of the spirally shaped cochlea is considered to be beneficial because it results in a closer proximity to the auditory nerve fibers. A shape memory effect (SME) could facilitate such shift of the EA toward the cochlear inner wall, but its implementation remains to be solved. The current study presents an EA prototype featuring the SME with minute adjustments of the material properties of Nitinol, a shape memory alloy, in combination with a suitable cooling strategy to prevent premature curling. Ten samples were successfully inserted by a CI surgeon into an artificial cochlear model submerged into a temperature-controllable water bath to simulate temporary hypothermia of the inner ear (31°C). Gentle insertions were possible, with an average insertion speed of 0.81 ± 0.14 mm/s. After recovery of body temperature, the desired position shift toward the modiolus was observed in all trials. Angular insertion depth increased by approximately 81.8° ± 23.4°. We demonstrate for the first time that using the body temperature responsive SME for perimodiolar EA positioning is feasible and does not impede a gentle surgical insertion.

Concept description and accuracy evaluation of a moldable surgical targeting system.

Purpose: We explain our concept for customization of a guidance instrument, present a prototype, and describe a set of experiments to evaluate its positioning and drilling accuracy. Methods: Our concept is characterized by the use of bone cement, which enables fixation of a specific configuration for each individual surgical template. This well-established medical product was selected to ensure future intraoperative fabrication of the template under sterile conditions. For customization, a manually operated alignment device is proposed that temporary defines the planned trajectory until the bone cement is hardened. Experiments ( n = 10 ) with half-skull phantoms were performed. Analysis of accuracy comprises targeting validations and experiments including drilling in bone substitutes. Results: The resulting mean positioning error was found to be 0.41 ± 0.30 mm at the level of the target point whereas drilling was possible with a mean accuracy of 0.35 ± 0.30 mm . Conclusion: We proposed a cost-effective, easy-to-use approach for accurate instrument guidance that enables template fabrication under sterile conditions. The utilization of bone cement was proven to fulfill the demands of an easy, quick, and prospectively intraoperatively doable customization. We could demonstrate sufficient accuracy for many surgical applications, e.g., in neurosurgery. The system in this early development stage already outperforms conventional stereotactic frames and image-guided surgery systems in terms of targeting accuracy.

The Use of Clinically Measurable Cochlear Parameters in Cochlear Implant Surgery as Indicators for Size, Shape, and Orientation of the Scala Tympani.

OBJECTIVES: (1) To assess variations of the human intracochlear anatomy and quantify factors which might be relevant for cochlear implantation (CI) regarding surgical technique and electrode design. (2) Search for correlations of these factors with clinically assessable measurements. DESIGN: Human temporal bone study with micro computed tomography (µCT) data and analysis of intracochlear geometrical variations: µCT data of 15 fresh human temporal bones was generated, and the intracochlear lumina scala tympani (ST) and scala vestibuli were manually segmented using custom software specifically designed for accurate cochlear segmentation. The corresponding datasets were processed yielding 15 detailed, three-dimensional cochlear models which were investigated in terms of the scalae height, cross-sectional size, and rotation as well as the interrelation of these factors and correlations to others. RESULTS: The greatest anatomical variability was observed within the round window region of the cochlea (basal 45°), especially regarding the cross-sectional size of the ST and its orientation relative to the scala vestibuli, which were found to be correlated (p < 0.001). The cross-sectional height of the ST changes substantially for both increasing cochlear angles and lateral wall distances. Even small cochleae were found to contain enough space for all commercially available CI arrays. Significant correlations of individual intracochlear parameters to clinically assessable ones were found despite the small sample size. CONCLUSION: While there is generally enough space within the ST for CI, strong intracochlear anatomical variations could be observed highlighting the relevance of both soft surgical technique as well as a highly flexible and self-adapting cochlear implant electrode array design. Cochlear dimensions (especially at the round window) could potentially be used to indicate surgically challenging anatomies.

Common Audiological Functional Parameters (CAFPAs) for single patient cases: deriving statistical models from an expert-labelled data set.

Objective: Statistical knowledge about many patients could be exploited using machine learning to provide supporting information to otolaryngologists and other hearing health care professionals, but needs to be made accessible. The Common Audiological Functional Parameters (CAFPAs) were recently introduced for the purpose of integrating data from different databases by providing an abstract representation of audiological measurements. This paper aims at collecting expert labels for a sample database and to determine statistical models from the labelled data set.Design: By an expert survey, CAFPAs as well as labels for audiological findings and treatment recommendations were collected for patients from the database of Hörzentrum Oldenburg.Study sample: A total of 287 single patient cases were assessed by twelve highly experienced audiological experts.Results: The labelled data set was used to derive probability density functions for categories given by the expert labels. The collected data set is suitable for estimating training distributions due to realistic variability contained in data for different, distinct categories. Suitable distribution functions were determined. The derived training distributions were compared regarding different audiological questions.Conclusions: The method-expert survey, sorting data into categories, and determining training distributions - could be extended to other data sets, which could then be integrated via the CAFPAs and used in a classification task.

Dimensions of artefacts caused by cochlear and auditory brainstem implants in magnetic resonance imaging.

Background: The aim of the study was to investigate the extent of MRI artefacts due to the magnet of selected auditory implants.Study design: Artefacts of the Synchrony cochlear implant at 1.5 T as well as at 3 T MRI devices were examined in cadavers and compared to the artefacts in MRI scans at 1.5 T of 17 patients implanted with CI (n = 12) and auditory brainstem implants (ABI) (n = 5).Results: None of the scanned implants showed any failure after MRI. After removal of the magnet, only a portion of the images in the direct neighbourhood of the implant, especially in the temporal and parietal lobe, contained artefacts. More anatomical substructures were visible without artefacts using the MedEl Synchrony device.Conclusion: Artefacts can be markedly reduced by rotating, self-aligning magnet. Removal of the magnet also results in reduction of artefacts.

Relations Between Scalar Shift and Insertion Depth in Human Cochlear Implantation.

OBJECTIVE: The intracochlear position of an electrode array may influence the outcome after cochlear implantation. The design of the electrode array can increase the risk of trauma causing penetration of the basilar membrane or shift of the electrode array into the scala vestibuli. The aim of the present study was to identify a scalar shift after implantation of two different electrode arrays developed by one manufacturer. STUDY DESIGN: Retrospective analysis. SETTING: Tertiary referral center. PATIENTS AND INTERVENTION: Cochlear implant recipients implanted between 2010 and 2014 and receiving either a mid-scala (n = 30) or a perimodiolar (n = 30) electrode array. MAIN OUTCOME MEASURE: Occurrence of scalar shift in association with the electrode type. RESULTS: Scalar shift occurred in 26.7% (8 of 30) of the patients implanted with a perimodiolar electrode array and in 6.7% (2 of 30) of the patients implanted with the mid-scala electrode array. The mean insertion depth in the patients experiencing scalar shift after implantation of the mid-scala electrode was much deeper (21.59 ±â€Š0.34 mm) when compared with the mean insertion depth of the patients with scalar shift after implantation with a perimodiolar electrode array (17.85 ±â€Š2.19 mm). There tends to be a correlation between the cochlear length and the occurrence of a scalar shift. However, the number of patients with scalar shift in the mid-scala group is rather small. CONCLUSION: Based on the presented data, more patients implanted with a perimodiolar electrode array have a scalar shift when compared with the midscalar electrode array.

Characterizing the size of the target region for atraumatic opening of the cochlea through the facial recess.

Surgical treatment with a cochlear implant (CI) for hearing rehabilitation requires a highly accurate and personalized opening of the inner ear (cochlea) to protect the delicate intra-cochlear fine structures, whose functional integrity needs to be maintained to preserve residual hearing. Spatial orientation within the complex anatomy of the lateral skull base during the procedure is a highly demanding task for the surgeon. In order to reduce risk of facial nerve palsy and loss of residual hearing as well as to establish minimally invasive CI surgery (minCIS), image-guided procedures incorporating surgical assistance systems are under development. However, there is a lack of an accuracy threshold value or range that such a system needs to fulfill to be considered sufficiently accurate for atraumatic opening of the inner ear. In this study, high resolution three-dimensional (3D) morphological images of eight human temporal bone specimens were manually segmented to build anatomical models of the human inner ear including all surgically relevant intra-cochlear structures as well as the facial recess. These 3D models were used to plan the surgical access path to the basal turn of the cochlea using the mastoidectomy posterior tympanotomy approach (MPTA). Therefore, custom-made image-processing software was developed to perform both path planning and identification of the valid target region- i.e., the largest possible region for atraumatic opening of the scala tympani. The developed 3D models provide visualization of the complex and variable anatomy of the basal portion of the human cochlear duct (also known as cochlear "hook region") as well as its spatial relationship to the facial recess. Their spatial arrangement directly impacts the accessibility of the hook region and limits the entry direction into scala tympani. The average diameter of the target region was found to be 1.56 mm ±â€¯0.10 mm (range: 1.43 to 1.72 mm). The anatomic variability and the need for a high safety level of at least 95% for hearing preservation CI surgery lead to a remaining safety margin of approximately 0.3 mm. In the future, this accuracy threshold value can serve as benchmark during the pre-clinical evaluation of image-guidance technologies to allow for highly accurate CI surgery.

Workflow assessment as a preclinical development tool : Surgical process models of three techniques for minimally invasive cochlear implantation.

PURPOSE: Minimally invasive cochlear implant surgery is a challenging procedure due to high demands on accuracy. For clinical success, an according assistance system has to compete against the traditional approach in terms of risk, operating time and cost. It has not yet been determined what kind of system is the most suited. The purpose of this study is a proof of concept of surgical process modeling as a preclinical development tool and the comparison of workflow concepts for this new approach. METHODS: Three preclinical systems (two stereotactic and one robotic) for minimally invasive cochlear implant surgery are compared using the method of surgical process modeling. All three systems were successfully tested with ex vivo human specimen to create minimally invasive surgical access to the cochlea. Those systems where chosen for comparison, because they represent three diverse approaches with different corresponding workflows for the same intervention. The experiments were used to create a process model for each system by recording the interventions. RESULTS: All three conceptual systems developed by our group have shown their eligibility. The recorded process models provide a convenient method for direct comparison. Reduction in the surgical time has a higher impact on the process, than time that is needed for setting up a system beforehand. The stereotactic approaches have little preparation effort and are low cost in terms of hardware compared to the robotic approach, which in return is beneficial in terms of workload reduction for the surgeon. CONCLUSION: Surgical process modeling is suitable for comparison of different assistant systems for minimally invasive cochlear implantation. The benefit of reduced trauma, compared to the traditional mastoidectomy, can now be assessed with consideration of the workflow of each technique. The process models enable an assessment in the regard of surgical time and workload.

Common Audiological Functional Parameters (CAFPAs): statistical and compact representation of rehabilitative audiological classification based on expert knowledge.

OBJECTIVE: As a step towards objectifying audiological rehabilitation and providing comparability between different test batteries and clinics, the Common Audiological Functional Parameters (CAFPAs) were introduced as a common and abstract representation of audiological knowledge obtained from diagnostic tests. DESIGN: Relationships between CAFPAs as an intermediate representation between diagnostic tests and audiological findings, diagnoses and treatment recommendations (summarised as "diagnostic cases") were established by means of an expert survey. Expert knowledge was collected for 14 given categories covering different diagnostic cases. For each case, the experts were asked to indicate expected ranges of diagnostic test outcomes, as well as traffic light-encoded CAFPAs. STUDY SAMPLE: Eleven German experts in the field of audiological rehabilitation from Hanover and Oldenburg participated in the survey. RESULTS: Audiological findings or treatment recommendations could be distinguished by a statistical model derived from the experts' answers for CAFPAs as well as audiological tests. CONCLUSIONS: The CAFPAs serve as an abstract, comprehensive representation of audiological knowledge. If more detailed information on certain functional aspects of the auditory system is required, the CAFPAs indicate which information is missing. The statistical graphical representations for CAFPAs and audiological tests are suitable for audiological teaching material; they are universally applicable for real clinical databases.

Feasibility Assessment of Optical Coherence Tomography-Guided Laser Labeling in Middle Cranial Fossa Approach.

INTRODUCTION: Different approaches have been developed to find the position of the internal auditory canal (IAC) in middle cranial fossa approach. A feasibility study was performed to investigate the combination of cone beam computed tomography (CBCT), optical coherence tomography (OCT), and laser ablation to assist a surgeon in a middle cranial fossa approach by outlining the internal auditory canal (IAC). MATERIALS AND METHODS: A combined OCT laser setup was used to outline the position of IAC on the surface of the petrous bone in cadaveric semi-heads. The position of the hidden structures, such as IAC, was determined in MATLAB software using an intraoperative CBCT scan. Four titanium spheres attached to the edge of the craniotomy served as reference markers visible in both CBCT and OCT images in order to transfer the plan to the patient. The integrated erbium-doped yttrium aluminum garnet laser was used to mark the surface of the bone by shallow ablation under OCT-based navigation before the surgeon continued the operation. RESULT: The technical setup was feasible, and the laser marking of the border of the IAC was performed with an overall accuracy of 300 µm. The depth of each ablation phase was 300 µm. The marks indicating a safe path supported the surgeon in the surgery. CONCLUSION: The technique investigated in the present study could decrease the surgical risks for the mentioned structures and improve the pace and precision of operation.

Patient specific selection of lateral wall cochlear implant electrodes based on anatomical indication ranges.

OBJECTIVES: The aim of this study was to identify anatomical indication ranges for different lateral wall cochlear implant electrodes to support surgeons in the preoperative preparation. METHODS: 272 patients who were implanted with a FLEX20, FLEX24, FLEX28, or a custom-made device (CMD) were included in this study. The cochlear duct length (CDL) and basal cochlear diameter (length A) were measured within preoperative imaging data. The parameter A was then employed to additionally compute CDL estimates using literature approaches. Moreover, the inserted electrode length (IEL) and insertion angle (IA) were measured in postoperative CT data. By combining the preoperative measurements with the IA data, the covered cochlea length (CCL) and relative cochlear coverage (CC) were determined for each cochlea. RESULTS: The measurements of the CDL show comparable results to previous studies. While CDL measurements and estimations cover similar ranges overall, severe deviations occur in individual cases. The electrode specific IEL and CCL are fairly consistent and increase with longer electrodes, but relatively wide ranges of electrode specific CC values were found due to the additional dependence on the respective CDL. Using the correlation of IEL and CCL across electrode arrays, CDL ranges for selected arrays were developed (FLEX24: 31.3-34.4, FLEX28: 36.2-40.1, FLEXSoft: 40.6-44.9). CONCLUSIONS: Our analysis shows that electrode specific CC varies due to the CDL variation. Preoperative measurement of the CDL allows for an individualized implant length selection yielding optimized stimulation and a reduced risk of intraoperative trauma. The CDL, as derived from preoperative CT imaging studies, can help the implant surgeon select the appropriate electrode array to maximize the patient's outcomes.

Investigation of ultra-low insertion speeds in an inelastic artificial cochlear model using custom-made cochlear implant electrodes.

PURPOSE: Latest research on cochlear implantations focuses on hearing preservation during insertion of the implant's electrode array by reducing insertion trauma. One parameter which may influence trauma is insertion speed. The objective of this study was to extend the range of examined insertion speeds to include ultra-low velocities, being lower than manually feasible, and investigate whether these reduce insertion forces. METHODS: 24 custom-made cochlear implant test samples were fabricated and inserted into an artificial scala tympani model using 12 different insertion speeds while measuring the resulting insertion forces. Three commercially available slim straight electrode carriers were inserted using the same setup to analyze whether the results are comparable. RESULTS: Insertions of the test samples using high insertion speeds (2.0/2.8 mm/s) showed significantly higher insertion forces than insertions done with low insertion speeds (0.2 mm/s) or ultra-low insertion speeds (< 0.1 mm/s). The insertions with commercial slim straight electrode arrays showed significantly reduced insertion forces when using a low insertion speed as well. CONCLUSIONS: Slow insertions showed significantly reduced insertion forces. Insertion speeds which are lower than manually feasible showed even lower insertion forces.

Cochlear helix and duct length identification - Evaluation of different curve fitting techniques.

OBJECTIVE: Within the field of cochlear implantation (CIs), the role of utilizing patient-specific cochlear anatomy for choosing the optimal implant electrode is becoming increasingly important. Unfortunately, performing detailed anatomical measurements of a cochlea using clinical imaging data is rather time consuming and hence difficult to implement into the clinical routine. In order to accelerate clinical cochlear anatomy evaluations, previously developed mathematical models can be adjusted to the patient-specific anatomy by measuring just a few overall cochlear dimensions. However, the accuracy of model-based cochlear anatomy estimations is unclear, and incorrect evaluations may lead to false conclusions regarding the suitability of specific implant electrodes. METHODS: Based on 10 cochleae, an error evaluation of various commonly used curve fitting approaches for cochlear shape and duct length approximation was conducted. Spline tracings of the cochlear contours were used as reference values for the various approximations. RESULTS: Parameterized average cochlear helix models and two of five analytical approaches were found to be suitable for reconstructing the cochlear helical shape and estimating its length. DISCUSSION: Spline curve reconstructions are the most accurate and reliable method for assessing patient-specific cochlear geometry, especially in the case of anatomical irregularities. The most accurate results within the group of model-based evaluations still resulted in mean overall cochlear length deviations of approximately 5%. CONCLUSION: Spline curve reconstructions appear to be the best option for anatomical diagnostics in clinical practice. Retrospective studies can be performed to further evaluate model-based evaluations.

On the accuracy of cochlear duct length measurement in computed tomographic images.

PURPOSE: Patient specific selection of cochlear implants would benefit from pre-operative knowledge of cochlear length. Several methods for its measurement or estimation have been described in literature. This study focused on the achievable accuracy in clinically available imaging. METHODS: Five simplified cochlea models milled into porcine bone were scanned in water using clinical cone beam computed tomography. Due to their well-known dimensions these phantoms served as gold standard for the length measurements. Each phantom was measured ten times using the custom software Comet. In addition, cochleae in ten image datasets taken indiscriminately from clinical routine were measured ten times each to test the precision under realistic conditions. The results were also compared to estimations based on the diameter of the basal turn (A value) as described in literature. RESULTS: Measurement accuracy of the phantoms' lengths was high (average error: - 0.2 mm; standard deviation: 0.3 mm). The pooled standard deviation for the measurements in clinical datasets was 0.6 mm. Errors resulted mainly from problems locating the helicotrema. The estimations differed on average - 1.7 to + 0.4 mm from the manual measurements and had standard deviations between 0.5 and 0.6 mm depending on the algorithm. CONCLUSIONS: The program Comet was successfully used to accurately measure the length of the cochlea models in clinically available imaging. The lower image quality of patient scans reduced the precision of the measurement. Estimations using the A value are a quicker alternative for averagely sized cochleae in cases where the lack of accuracy is tolerable.

Numerical analysis of intracochlear mechanical auditory stimulation using piezoelectric bending actuators.

Cochlear implantation can restore a certain degree of auditory impression of patients suffering from profound hearing loss or deafness. Furthermore, studies have shown that in case of residual hearing, patients benefit from the use of a hearing aid in addition to the cochlear implant. The presented studies aim at the improvement of this electromechanical stimulation (EMS) approach by substituting the external hearing aid by an internal stimulus provided by miniaturized piezoelectric actuators. Finite element analyses are performed in order to derive fundamental guidelines for the actuator layout aiming at maximal mechanical stimuli. Further analyses aim at investigating how the actuator position inside the cochlea influences the basilar membrane oscillation profile. While actuator layout guidelines leading to maximized acoustic stimuli could be derived, some of these guidelines are of complementary nature suggesting that further studies under realistic boundary conditions must be performed. Actuator positioning inside the cochlea is shown to have a significant influence on the resulting auditory impression of the patient. Based on the results, the main differences of external and internal stimulation of the cochlea mechanism are identified. It is shown that if the cochlea tonotopy is considered, the frequency selectivity resulting from the mechanical cochlea stimulus may be improved.

Three-dimensional hard and soft tissue imaging of the human cochlea by scanning laser optical tomography (SLOT).

The present study focuses on the application of scanning laser optical tomography (SLOT) for visualization of anatomical structures inside the human cochlea ex vivo. SLOT is a laser-based highly efficient microscopy technique which allows for tomographic imaging of the internal structure of transparent specimens. Thus, in the field of otology this technique is best convenient for an ex vivo study of the inner ear anatomy. For this purpose, the preparation before imaging comprises decalcification, dehydration as well as optical clearing of the cochlea samples in toto. Here, we demonstrate results of SLOT imaging visualizing hard and soft tissue structures with an optical resolution of down to 15 µm using extinction and autofluorescence as contrast mechanisms. Furthermore, the internal structure can be analyzed nondestructively and quantitatively in detail by sectioning of the three-dimensional datasets. The method of X-ray Micro Computed Tomography (µCT) has been previously applied to explanted cochlea and is solely based on absorption contrast. An advantage of SLOT is that it uses visible light for image formation and thus provides a variety of contrast mechanisms known from other light microscopy techniques, such as fluorescence or scattering. We show that SLOT data is consistent with µCT anatomical data and provides additional information by using fluorescence. We demonstrate that SLOT is applicable for cochlea with metallic cochlear implants (CI) that would lead to significant artifacts in µCT imaging. In conclusion, the present study demonstrates the capability of SLOT for resolution visualization of cleared human cochleae ex vivo using multiple contrast mechanisms and lays the foundation for a broad variety of additional studies.

Impact of the round window membrane accessibility on hearing preservation in adult cochlear implantation.

This study was conducted to evaluate the effect of the round window membrane accessibility on the residual hearing after cochlear implantation surgery in adults. Moreover, the effects of the other demographics and intra-operative factors on the residual hearing loss have been evaluated. The hearing preservation cochlear implantation surgery was performed on 64 adults with residual hearing thresholds ≤80 dB at 250 and 500 Hz, who had referred to our tertiary academic center. All the patients underwent a standardized surgical approach with the same straight electrode inserted through the round window membrane. The hearing thresholds at 250, 500, and 1000 Hz were compared in pre-operative and 1 month postoperative pure-tone audiograms. The average hearing threshold shifts at these frequencies was used to evaluate the hearing preservation. The effects of the round window accessibility and other factors (including gender, age, side of the surgery, necessity of anterior-inferior drilling of the round window margin and average insertion speed) on hearing threshold shifts were analyzed. The mean low-frequency hearing threshold shift was found to be 17.5 dB for all the patients. The hearing preservation goal (threshold shifts ≤30 dB) was achieved in 58 patients. Among the evaluated parameters, only accessibility of the round window membrane could change the hearing threshold shifts significantly (p = 0.026), and was a predictor for the hearing loss (B coefficient = 7.5, p = 0.006). Incomplete accessibility of the round window membrane may be a predictor for increased hearing threshold shifts in short-term evaluations after cochlear implantation.

Investigation of the effect of cochlear implant electrode length on speech comprehension in quiet and noise compared with the results with users of electro-acoustic-stimulation, a retrospective analysis.

OBJECTIVES: This investigation evaluated the effect of cochlear implant (CI) electrode length on speech comprehension in quiet and noise and compare the results with those of EAS users. METHODES: 91 adults with some degree of residual hearing were implanted with a FLEX20, FLEX24, or FLEX28 electrode. Some subjects were postoperative electric-acoustic-stimulation (EAS) users; the other subjects were in the groups of electric stimulation-only (ES-only). Speech perception was tested in quiet and noise at 3 and 6 months of ES or EAS use. Speech comprehension results were analyzed and correlated to electrode length. RESULTS: While the FLEX20 ES and FLEX24 ES groups were still in their learning phase between the 3 to 6 months interval, the FLEX28 ES group was already reaching a performance plateau at the three months appointment yielding remarkably high test scores. EAS subjects using FLEX20 or FLEX24 electrodes outscored ES-only subjects with the same short electrodes on all 3 tests at each interval, reaching significance with FLEX20 ES and FLEX24 ES subjects on all 3 tests at the 3-months interval and on 2 tests at the 6- months interval. Amongst ES-only subjects at the 3- months interval, FLEX28 ES subjects significantly outscored FLEX20 ES subjects on all 3 tests and the FLEX24 ES subjects on 2 tests. At the-6 months interval, FLEX28 ES subjects still exceeded the other ES-only subjects although the difference did not reach significance. CONCLUSIONS: Among ES-only users, the FLEX28 ES users had the best speech comprehension scores, at the 3- months appointment and tendentially at the 6 months appointment. EAS users showed significantly better speech comprehension results compared to ES-only users with the same short electrodes.