Round Window Research Articles

Developing a Virtual Model of the Rhesus Macaque Inner Ear

A virtual model of the rhesus macaque inner ear was created in the present study. Rhesus macaques have been valuable in cochlear research; however, their high cost prompts a need for alternative methods. Finite Element (FE) analysis offers a promising solution by enabling detailed simulations of the inner ear. This study employs FE analysis to create a virtual model of the rhesus macaque’s inner ear, reconstructed from MRI scans, to explore how cochlear implants (CIs) impact residual hearing loss. Harmonic-acoustic simulations of sound wave transmission indicate that CIs have minor effects on the displacement of the basilar membrane and thus minimally impact residual hearing loss post-implantation, but stiffening of the round window membrane worsens this effect. While the rhesus macaque FE model presented in this study shows some promise, its potential applications will require further validation through additional simulations and experimental studies.

Round Window Membrane Visibility and its Implications in Cochlear Implant Surgery

Round Window Membrane Visibility and its Implications in Cochlear Implant Surgery

Intratympanic injections made from eutectic liquid (camphor and menthol)-based oil-less emulsions containing morin hydrate-lipoid E80 complex: An approach to augment drug permeation into inner ear region in a healthy rabbit model

Morin hydrate (MH, flavonols of plants, family-Moraceae) promotes inner ear stem cell survival and differentiation process to preserve the healthy hearing function. However, round window membrane (RWM) of inner ear provides a barrier for MH to reach an adequate amount at inner ear region. Since MH possesses a low aqueous solubility (28.72 ± 0.97 μg/ml), intratympanic (IT) injections of camphor-menthol eutectic liquid-based oil-less emulsions containing MH-Lipoid E80 complex was developed to promote MH ferrying action across RWM. At 360 min post-dissolution time point, the MH solution displayed 92.88 ± 6.26 % drug release, but the drug-Lipoid E80 complex-loaded oil-less emulsions showed 58.05 ± 11.62 % only. The MTT assay results indicate the possible non-toxicity of oil-less emulsions to L-929 cells up to 100 μg/ml concentration. Significant differences were seen between the Cmax and AUC0-t values observed at 90 min in the perilymph after the IT injections of MH solution (14.13 ± 0.33 × 103 ng/ml & 429.55 ± 9.20 × 103 ng min/ml) and MH-Lipoid E80 complex-loaded oil-less emulsions (117.93 ± 4.24 × 103 ng/ml & 5529.46 ± 37.65 × 103 ng min/ml) into the healthy albino rabbits. Hence the IT injections of eutectic liquid-based oil-less emulsions could facilitate the drugs crossing over of RWM in the inner ear regions.

A novel therapeutic pathway to the human cochlear nerve.

Traditional approaches to the human cochlear nerve have been impeded by its bony encasement deep inside the skull base. We present an innovative, minimally invasive, therapeutic pathway for direct access to the nerve to deliver novel regenerative therapies. Neuroanatomical studies on 10 cadaveric human temporal bones were undertaken to identify a potentially safe therapeutic pathway to the cochlear nerve. Simulations based on three-dimensional delineation of anatomical structures obtained from synchrotron phase-contrast imaging were analyzed. This enabled the identification of an approach to the nerve in the fundus of the internal auditory meatus by trephining the medial modiolar wall of the cochlea via the round window for a median depth of 1.48mm (range 1.21-1.91mm). The anatomical access was validated on 9 additional human temporal bones using radio-opaque markers and contrast injection with micro-computed tomography surveillance. We thus created an effective conduit for the delivery of therapeutic agents to the cochlear nerve.

Impact of cochlear detailed morphology on insertion results and intracochlear trauma of a slim pre-curved electrode array: a micro-CT study.

This study aimed to evaluate the impact of detailed cochlear dimensions, assessed using micro-CT (µCT) imaging, on insertion outcomes and associated trauma with a new slim, precurved electrode array. Eleven temporal bone specimens underwent implantation of a 22-electrode slim precurved array via the round window. High-resolution µCT scans post-implantation enabled visualization of cochlear structures and electrode positioning. Combination with subsequent scans taken after electrodes removal, we analyzed angular insertion depth (AID), insertion length, number of electrodes inserted, cochlear dimensions (specifically cochlear duct length (CDL), basal turn diameter, scala tympani dimension), and intracochlear trauma of fine structures. Statistical analyses were performed to correlate cochlear detailed dimensions and morphology with insertion outcomes and trauma. The mean AID was 351.82°, and the mean insertion length was 21.07mm. CDL showed positive correlations with AID and insertion length. Basal turn diameter (value B) positively correlated with AID and insertion length, unlike value A. Middle-basal turn (M/B) relationships (angle and height) significantly influenced insertion depth. The cochleae with smaller M/B heights and specific angles were more susceptible to insertion trauma. Larger basal turn diameters correlated with increased trauma and electrode translocation into the scala vestibuli. This study highlights the importance of precise cochlear measurements in predicting and optimizing cochlear implant outcomes. Specific cochlear dimensions and anatomical shapes were identified as critical factors affecting insertion depth, trauma risk, and electrode positioning. Utilizing micro-CT provided detailed insights into cochlear anatomy and insertion outcomes, offering valuable data for advancing cochlear implant technology and surgical practices.

Are tinnitus burden and tinnitus exacerbation after cochlear implantation influenced by insertion technique, array dislocation, and intracochlear trauma?

Although numerous studies suggest that cochlear implantation (CI) generally alleviates the overall burden of tinnitus, certain patients experience tinnitus exacerbation following CI. The exact cause of this exacerbation is still uncertain. This prospective study aimed to investigate whether cochlear trauma, resulting from scalar dislocation of the electrode array, affected postoperative tinnitus intensity, tinnitus burden, and speech perception. Additionally, the influence of CI insertion technique, insertion depth, insertion angle, and cochlear morphology on postoperative tinnitus was assessed. We evaluated 66 CI recipients preoperatively at 2 days, 4 weeks, and 12- and 24-months following surgery. Digital volume tomography was employed to document scalar position, insertion depth, and cochlear morphology postoperatively. Speech perception was analyzed using Freiburg monosyllables. The tinnitus burden was evaluated using the tinnitus questionnaire, while the tinnitus intensity was quantified using a visual analog scale. Study results pertaining to tinnitus intensity and burden did not reveal a significant difference in elevation regarding scalar position and dislocation after CI surgery compared to preoperative tinnitus levels. However, dislocation was only identified in four patients, and scala vestibuli insertions were observed in two patients. Comparing preoperative and 1-year postoperative outcomes, CI was noted to substantially reduce the tinnitus burden. When the speech processor was worn, the tinnitus intensity was significantly diminished. In comparison to round window (RW) insertion, the insertion technique cochleostomy (CS) did not exhibit a significant difference or a trend toward increased tinnitus intensity. This study demonstrates that CI significantly decreases the tinnitus burden. The observation implies that the electrical stimulation of the auditory pathway, facilitated by wearing the speech processor, significantly reduced the tinnitus intensity. The incidence of dislocations and scala vestibuli insertions has declined to the extent that it is no longer feasible to formulate statistically significant conclusions.

Crista Fenestra Heights Measured by HRCT Predicts the Necessity for Extended Round Window Approach for Slim Modiolar Electrode.

To evaluate the morphology of the crista fenestra (CF) using three-dimensional reconstruction based on high-resolution computed tomography (HRCT) and to examine the influence of CF height on the insertion approach used for CI632/532 implants. Retrospective study. Tertiary referral center. Forty-five ears of 37 patients who received CI632/532 implants were included. HRCT images were reconstructed into three-dimensional images, and CF structures were identified. The patients were divided into two group based on the insertion approach: round window approach (RW; n = 27) and extended round window approach (eRW; n = 18). To evaluate CF interference, 10 cases in the eRW group in which the sheath or electrode did not pass through the RW before widening the RW niche (nRW group) were specifically included in the analysis. The identified CF cross-sections were confirmed by HRCT axial sectioning, and CF heights were measured. The mean CF height was significantly greater in the nRW group than in the RW group (0.97 vs. 0.78 mm). CF was identified using three-dimensional computer graphics (3DCG) and the CF height on the HRCT axial sections. Thus, measuring the CF height using 3DCG reconstruction can facilitate the preoperative selection of the electrode insertion approach.

Comparison of long term speech and impedance outcome of cochlear implantation in prelingual deaf pediatric patients between cochleostomy and round window insertion.

Comparison of long term speech and impedance outcome of cochlear implantation in prelingual deaf pediatric patients between cochleostomy and round window insertion.

Proposal of a Theoretically Feasible Method to Perform Perilymph Sampling in Clinical Settings

The ability to analyze perilymph could allow inner ear pathologies to be studied. However, today, perilymph sampling is only performed for research purposes because of the risk of negative outcomes such as hearing loss or balance disorders. This paper aims to analyze the current literature on perilymph sampling and propose a method to collect perilymph in clinical settings. The published literature on perilymph sampling and its analyses was screened, and the results were analyzed and discussed in this mini review. Also, articles that discussed microneedle technology were reviewed and included in the analysis of the data. Based on the results of this review, we would like to propose a feasible technique to perform perilymph sampling in clinical settings. A total of eight studies analyzing perilymph were identified; data on proteomic, metabolomic and miRNA features present within human perilymph were collected and described. Two articles describing the use and auditory outcomes post microneedle drug injection into the inner ear were identified. Based on the methods for perilymph sampling described in humans and the recent innovations introduced by the use of microneedles, we suggested a feasible method to collect perilymph in the outpatient setting. The analysis of perilymph undoubtedly represents a valid instrument to fully understand inner ear diseases. A combination of traditional and innovative techniques, such as gaining access to the round window through the transcanalar approach using micro-endoscopes and microneedles to perform sampling, might simplify the sampling procedure and make it practicable in a clinical setting.

Tinnitus Suppression with Electrical Stimulation at the Most Basal Contact of the Cochlear Implant Electrode as a Model for Round Window Stimulation.

The objective of this research was to test whether efficient tinnitus suppression could be achieved by electrical stimulation of the single most basal electrode contact of a cochlear implant. This approach simulates the effects of electrical stimulation using a round-window electrode. The study was performed in 10 adult cochlear implant patients showing complete or almost complete tinnitus suppression during electrical stimulation with their standard fitting-MAP. In all patients, tinnitus appeared again when the implant was switched off. Five Nucleus implant (1 CI532, 4 CI24RE CA) users and 5 Mi12xx series with FLEX28 electrodes with at least 6 months of CI experience were included. Two types of stimulation were presented at the most basal CI contact: a constant pulse train and a modulated pulse train. The variation in pulse rates was low rate (100-300 pps) and high (≥900 pps), and the current level ranged from the C-level to less than the T-level for both stimulation types. The effect of acute electrical stimulation at the most basal electrode contact was compared to the effect obtained with multichannel stimulation with the patient's current fitting MAP. Electrical stimulation was paused between tests with different stimulation types until tinnitus returned to baseline intensity. Patients reported Visual Analog Scale (VAS) scores for tinnitus loudness and intrusiveness during normal CI use and for each single contact stimulation type. Eight participants perceived complete suppression with one or more stimulation patterns. In 2 patients, suppression was less efficient than full-band CI stimulation. Louder stimuli are generally perceived as annoying and less effective in reducing tinnitus. In FLEX28 patients, it was also possible to obtain full tinnitus suppression with current amplitudes under the thresholds for auditory perception (this was not tested in patients with the Nucleus device). In 8 of the 10 included patients, we were able to obtain complete or almost complete tinnitus suppression with electrical stimulation at only 1 most basal electrode contact. Therefore, round-window stimulation with a single electrode may be a potential treatment for tinnitus in patients with significant residual hearing. The long-term effects of this therapy should be confirmed in future studies.

Outer hair cells stir cochlear fluids.

We hypothesized that active outer hair cells drive cochlear fluid circulation. The hypothesis was tested by delivering the neurotoxin, kainic acid, to the intact round window of young gerbil cochleae while monitoring auditory responses in the cochlear nucleus. Sounds presented at a modest level significantly expedited kainic acid delivery. When outer-hair-cell motility was suppressed by salicylate, the facilitation effect was compromised. A low-frequency tone was more effective than broadband noise, especially for drug delivery to apical locations. Computational model simulations provided the physical basis for our observation, which incorporated solute diffusion, fluid advection, fluid-structure interaction, and outer-hair-cell motility. Active outer hair cells deformed the organ of Corti like a peristaltic tube to generate apically streaming flows along the tunnel of Corti and basally streaming flows along the scala tympani. Our measurements and simulations coherently indicate that the outer-hair-cell action in the tail region of cochlear traveling waves is for cochlear fluid circulation.

Microneedle-Mediated Delivery of siRNA via Liposomal-Based Transfection for Inner Ear Gene Therapy.

Microneedle-mediated intracochlear injection of siRNA-Lipofectamine through the round window membrane (RWM) can be used to transfect cells within the cochlea. Our laboratory has developed 100-μm diameter hollow microneedles for intracochlear injection through the guinea pig RWM. In this study, we test the feasibility of microneedle-mediated injection of siRNA and Lipofectamine, a commonly used reagent with known cellular toxicity, through the RWM for cochlear transfection. Fluorescently labeled scramble siRNA was diluted into Lipofectamine RNAiMax and OptiMEM. One microliter of 5 μM siRNA was injected through the RWM of Hartley guinea pigs at a rate of 1 μl/min (n = 22). In a control group, 1.0 μl of Lipofectamine, with no siRNA, was diluted into OptiMEM and injected in a similar fashion (n = 5). Hearing tests were performed before and either at 24 hours, 48 hours, or 5 days after injection. Afterward, animals were euthanized, and cochleae were harvested for imaging. Control cochleae were processed in parallel to untreated guinea pigs. Fluorescence, indicating successful transfection, was observed within the basal and middle turns of the cochlea with limited distribution in the apex at 24 and 48 hours. Signal was most intense in the organ of Corti, spiral ligament, and spiral ganglion. Little to no fluorescence was observed at 5 days post-injection. No significant changes in auditory brainstem response (ABR) were noted post-perforation at 5 days, suggesting that siRNA-Lipofectamine at low doses does not cause cochlear toxicity. Small volumes of siRNA and Lipofectamine can be effectively delivered to cochlear structures using microneedles, paving the way for atraumatic cochlear gene therapy.

Cochlear implantation in otosclerosis: surgical and audiological outcomes between ossified and non-ossified cochlea.

To evaluate (1) Audiological and surgical outcomes in patients with otosclerosis following cochlear implantation. (2) surgical difficulties and outcomes between both groups. (3) Audiological outcomes between both groups. Retrospective study conducted at Otology and Skull Base Surgery Center. Data were analyzed from 111 patients with otosclerosis (114 ears) who underwent cochlear implant surgery using the cochlear implant database. Demographic characteristics (age, sex, and operated ear), auditory outcomes, and operative details (extent of cochlear ossification, surgical approach [posterior tympanotomy or subtotal petrosectomy], electrode insertion [partial/complete, scala tympani or vestibuli], and complications) were analyzed Auditory outcomes were assessed over at least one year follow-up period using pure tone audiometry and speech discrimination scores. Patients were divided into two groups (with and without cochlear ossification) to compare auditory outcomes and surgical outcomes. The mean age of patients with ossified and non-ossified cochlea was 60.04 and 62.22years respectively. Sixty-five of 114 ears had cochlear ossification, with complete round window involvement in 75.4% of these patients, while the rest had partial or complete basal turn ossification. Subtotal petrosectomy was performed in 63.1% and 28.6% of ossified and non-ossified cochlea respectively while the rest underwent cochlear implantation through posterior tympanotomy. Only one case had scala vestibuli insertion and four had incomplete electrode insertion. Six patients underwent re-implantation due to infection, device failure, and erosion of the posterior canal wall. Auditory outcomes among patients with ossified otosclerosis were slightly better than those without ossification but this difference was not statistically significant. Cochlear implantation for otosclerosis yields excellent auditory outcomes with a low rate of surgical complications, despite the high incidence of cochlear ossification.

Cochlear Implantation in a Patient with Intractable Tinnitus: A Case Report of an Endoscope-Assisted Approach.

Preservation of residual hearing and vestibular function is a crucial factor in cochlear implantation (CI), especially in patients with residual low-frequency hearing thresholds. We report a case of a patient who underwent unilateral endoscope-assisted CI with a challenging surgical view following rigorous posterior tympanotomy. A 53-year-old male presented with left-sided intractable tinnitus due to sudden sensorineural hearing loss that had occurred 10 years prior. Due to the abnormal location of the round window (RW), which was far more posterior and inferior than usual and impeded insertion of the electrode using the conventional RW approach, endoscope-assisted CI was performed. Pure-tone audiometry at 3 months after CI revealed satisfactory hearing thresholds. Furthermore, there was alleviation of the left-sided tinnitus, which was indicated by a marked decrease in both the subjective visual analog scale loudness and Tinnitus Handicap Inventory scores. With proper indications, we strongly recommend applying the RW approach with endoscopic assistance over conventional bony cochleostomy for the preservation of low-frequency hearing thresholds in cases where RW visualization is insufficient following posterior tympanotomy.

Molded Round Window Niche Implant as a Dexamethasone Delivery System in a Cochlear Implant-Trauma Animal Model.

Preserving residual hearing after cochlear implant (CI) surgery remains a crucial challenge. The application of dexamethasone (DEX) has been proven to positively affect residual hearing. To deliver DEX in a localized and controlled way, a round window niche implant (RNI), allowing drug diffusion via the round window membrane into the cochlea, may be used. To prove this concept, an RNI for guinea pigs as a CI-trauma model was manufactured by molding and tested for its drug release in vitro and biological effects in vivo. The RNIs were molded using silicone containing 10% DEX. Release was analyzed over time using high-performance liquid chromatography (HPLC). Fourteen adult guinea pigs were randomly assigned to two groups (CI or CI + RNI group). All animals received a unilateral CI electrode insertion trauma followed by CI insertion. The CI + RNI group was additionally implanted with an RNI containing 10% DEX. Animals were followed up for 4 weeks. Acoustically evoked auditory brainstem response and impedance measurement, micro-computed tomography (µCT) imaging, and histology were performed for evaluation. DEX was released for more than 250 days in vitro, with an initial burst followed by a slower release over time. Comparing the hearing threshold shift (from day 0 to day 28) of the CI and CI + RNI groups, significant differences were observed at 32 and 40 kHz. The impedance shift at basal contacts was lower in the CI + RNI group than in the CI group. Moreover, the fibrosis in the lower basal turn was reduced in the CI + RNI group in contrast to the CI group. The RNI containing 10% DEX has anti-inflammatory potential concerning fibrosis inhibition and has beneficial effects on hearing preservation at high frequencies.

An acoustic bellows-type round window transducer for middle-ear implants

BackgroundThis study describes the development of output devices for round window middle-ear. To overcome the problems of output devices that apply sound pressure directly to the round window, an acoustic bellows-type round window transducer was implemented by combining a small bellows, acoustic tube, and balanced armature driver. MethodsThe output characteristics of the proposed acoustic bellows-type round window transducer were confirmed through bench tests and distortion measurements. To compare the vibration transmission characteristics of the proposed transducer with those of sound pressure stimulation devices, an experiment was performed using four human temporal bones. FindingsThe average output magnitude of the acoustic bellows-type round window transducer was equivalent to sound pressure levels of 92, 96, and 108 dB for frequency ranges of <1, 1–2, and > 2 kHz, respectively. The results showed that the proposed transducer delivered vibration consistently without reducing the sound pressure level due to leakage, unlike the sound pressure stimulation device. InterpretationTherefore, the acoustic bellows-type round window transducer is a more stable and suitable output device for round window middle-ear implants than a sound pressure stimulation device. It is expected to overcome the limitations of sound pressure stimulation devices and to contribute to new technical solutions in the field of round window middle-ear implants development.

Development of Magnetic Nanosystems with Potential for the Treatment of Inner Ear Pathologies.

Hearing loss (HL) affects more than 5% of the global population, with projections indicating an impact of up to 50% on young individuals in the next years. HL treatments remain limited due to the inner ear's hermeticism. HL often involves inflammatory processes, underscoring the need for enhanced delivery of antiinflammatory agents to the inner ear. Our research focuses on the development of a directed therapy based on magnetic nanoparticles (MNPs). We previously synthesized biocompatible folic acid-coated iron oxide-core nanoparticles (MNPs@FA) as potential carriers for the anti-inflammatory Diclofenac (Dfc). This study aims to incorporate Dfc onto MNPs@FA to facilitate targeted drug delivery to the inner ear. Through optimizing the loading procedure, we achieved optimal loading capacity. Dfc release was studied in the simulated target fluid and the administration vehicle. Complete characterization is also shown. In vitro biocompatibility testing ensured the biosafety of the resulting formulation. Subsequent ex vivo targeting assays on murine cochleae validated the nanosystems' ability to penetrate the round window membrane, one of the main HL therapy barriers. These findings serve as validation before continuing to more complex in vivo studies. Together, the data here presented represent an advancement in addressing unmet medical needs in HL therapy.

Prediction of difficult round window visibility during cochlear implantation via a reformatted CT facial recess view: A retrospective study with surgical correlation.

Cochlear implant surgery is performed commonly through the facial recess via the round window (RW) approach. This study aims to evaluate the utility of reformatting the pre-operative CT temporal bone scan into a CT facial recess view in alerting surgeons to a potentially difficult surgery with poorly visualized round window. This is a retrospective study of 41 patients (43 ears), who had undergone cochlear implant surgery. Intraoperative findings of round window position relative to 2nd genu-mastoid portion of facial nerve, and round window membrane orientation were recorded by the surgeons. Pre-operative CTs were analyzed by two radiologists in axial and a reformatted facial recess plane that simulates the surgeon's view via the facial recess. Radiological assessment markers include the facial nerve-chorda tympani nerve width (FN-CTN) measured 1.2mm inferior to the exit point of the chorda tympani nerve into the tympanic cavity, round window position relative to 2nd genu-mastoid segment of the facial nerve and RW membrane's angle from the vertical axis. The best predictor for difficult round window intraoperative visibility is the RW position relative to the 2nd genu-mastoid segment of the facial nerve lying lateral to it on CT facial recess reformatted images. A RW that lies partially to completely posterior to the posterior border of the 2nd genu-mastoid segment of the facial nerve had up to 55.6% risk of encountering difficult access, while those positioned anterior to or partially anterior to the anterior edge of the 2nd genu-mastoid segment of the facial nerve had 0% risk of difficult access (p<0.05). There are substantial agreements in the intra-rater (Kappa=0.751, p<0.001) and inter-rater reliability (Kappa= 0.698, p<0.001). There is no significant association between surgical difficulty and facial nerve-chorda tympani distance or RW angle (p>0.05). Identification of round window positions in the reformatted CT facial recess view is a useful tool in predicting potentially difficult round window access in cochlear implant surgery. RW= Round window, FN-CTN= facial nerve to chorda tympani nerve width.

Comparative Histopathologic Analysis of Inner Ear Damage in Meningitis: Otogenic Versus Meningogenic Routes.

To distinguish the patterns of inner ear changes between meningogenic and otogenic routes in meningitis cases. Our hypothesis is that pinpointing distinct patterns linked to each route could aid in the development of diagnostic strategies and targeted therapies. Temporal bones (TBs) from patients with a history of meningitis and histopathological evidence of labyrinthitis were divided into two groups (otogenic and meningogenic). Inner ear histopathological examination was performed to identify qualitative and semi-quantitative changes. This assessment encompassed inflammation patterns, indications of early ossification, hair cell loss, and alterations in the lateral wall, round window membrane, cochlear aqueduct and vestibular aqueduct. Thirty-six TBs were included in the study (otogenic, 21; meningogenic, 15). Generalized labyrinthitis was more common in otogenic cases (100% vs. 53%, p < 0.001). Early signs of cochlear ossification were exclusively observed in otogenic cases (9 TBs). The spiral ligament of otogenic cases has shown a uniform loss of fibrocytes across all cochlear turns, while meningogenic cases showed more severe loss in the apical turn. Otogenic cases exhibited a higher prevalence of severe inflammation of the cochlear aqueduct and endolymphatic sac. Meningogenic cases showed more severe loss of vestibular hair cells in the otolithic organs. Otogenic cases displayed a higher prevalence of changes in the spiral ligament and signs of early ossification, whereas meningogenic cases were associated with a higher degree of vestibular damage. Our findings emphasize the importance of considering the infection route and its implications for timely diagnosis and development of pathology-oriented treatment strategies. NA Laryngoscope, 2024.

Cochlear Apex Triangulation Utilizing Ct Measures And Middle Ear Landmarks.

To better characterize the cochlear apex in relation to surgically relevant landmarks to guide surgeons and improve procedural success of apical electrode placement. Retrospective image analysis. Tertiary referral center. Cochlear implant recipients with available preoperative computed tomography (CT) imaging. None. Cochlear dimensions and cochlear apex distance measures to surgically relevant middle ear landmarks and critical structures. Eighty-two temporal bone CT scans were analyzed utilizing multiplanar reformats. The average lateral width of promontory bone over the cochlear apex was 1.2 mm (standard deviation [SD], 0.3). The anteroposterior distance from the round window (avg, 4.2 mm; SD, 0.5), oval window (avg, 3.3 mm; SD, 0.3), cochleariform process (avg, 2.3; SD, 0.5), and superior-inferior distance from the cochleariform process (avg, -0.9; SD, 0.8) to the cochlear apex were measured. The relationship of the cochlear apex to critical structures was highly variable.A newly developed stapes vector was created and found to mark the posterior/superior boundary of the apex in 94% of patients. When a vector parallel to the stapes vector was drawn through the round window, it marked the anterior/inferior boundary of the cochlear apex in 89% of patients. This study assists in characterizing cochlear apex anatomy and its relation to surrounding structures as a means of improving procedural accuracy and reducing trauma during apical cochleostomy. Understanding both distance relationships and expected boundaries of the apex could help to inform future surgical approaches.