Localization of the Vertical Part of the Facial Nerve in the High-Resolution Computed Tomography During Pediatric Cochlear Implantation.

BACKGROUND: This study proposed a classification of the vertical portion of the facial nerve (VPFN) location, incorporating the previous classifications regarding the posterior-to-anterior and medial-to-lateral dimensions. We also evaluated the implication of this proposed classification on the round window visibility during pediatric cochlear implantation (CI). METHODS: It was a retrospective multicenter observational cohort study. This study included 334 cases that underwent CI between 2015 and 2022 at multiple referral institutes. Two physicians evaluated the preoperative computed tomography images of 334 patients and determined the radiological type of the VPFN. These types were matched with intraoperative round window accessibility. RESULTS: The Spearman's correlation coefficient showed a strong correlation between the proposed VPFN type and the intraoperative round window visibility, as the P-value was <.001. CONCLUSION: This classification could provide the surgeon preoperatively with the precise location of the VPFN in the lateral-to-medial and posterior-to-anterior dimensions. Furthermore, this location classification of the VPFN was significantly correlated with intraoperative round window accessibility, with an accuracy of 90.42%. Therefore, types C and D were expected to have difficult accessibility into the round window, and more surgical interventions were needed to modify the posterior tympanotomy or use other approaches.

Round Window Niche Veil is Visible on High-Resolution Computed Tomography and a Predictor of Local Drug Efficacy to Inner Ear.

OBJECTIVES: To determine the morphologies and effect of the round window niche veil (RWNV) on local drug delivery efficacy and develop diagnostic criteria on high-resolution computed tomography (HRCT). METHODS: Patients diagnosed with otosclerosis, bilateral profound sensorineural hearing loss or vestibular schwannoma were enrolled from 2019 to 2022, receiving temporal bone HRCT scanning, and anatomic variations of RWMV were summarized intraoperative. For patients with vestibular schwannoma, 1 mL of dexamethasone solution (4 mg/mL) was administered via facial recess during operation, and samples of perilymph were collected to analyze. The diagnostic criteria of RWNV on HRCT were developed and verified. RESULTS: A total of 85 patients were enrolled. RWNV was observed in 54 cases intraoperatively with an incidence of 63.5% (95% CI, 52.9%-73.0%). The median perilymph concentrations were 4.86-fold higher in the group without RWNV than with RWNV (p < 0.0001). RWNV could be visualized on HRCT with a window width of 3500-4500 HU and a window level of 300-500 HU. The characteristic features were as follows: (1) a thin soft tissue shadow could be seen at the entrance of the round window niche (RWN); (2) it was visible in at least 2 consecutive layers along the upper margin of RWN from top to bottom; (3) it was discontinuous with the adjacent bone margin. The sensitivity and specificity of the diagnostic criteria were 77.8% and 93.6%, respectively. CONCLUSION: RWNV could reduce local dexamethasone diffusion efficacy to the inner ear, which could be diagnosed on HRCT and used as a predictor of local drug delivery efficacy to the inner ear. LEVEL OF EVIDENCE: 3 Laryngoscope, 134:1396-1402, 2024.

Assessment of jugular bulb variability based on 3D surface models: quantitative measurements and surgical implications.

PURPOSE: High-riding jugular bulbs (JBs) among other anatomical variations can limit surgical access during lateral skull base surgery or middle ear surgery and must be carefully assessed preoperatively. We reconstruct 3D surface models to evaluate recent JB classification systems and assess the variability in the JB and surrounding structures. METHODS: 3D surface models were reconstructed from 46 temporal bones from computed tomography scans. Two independent raters visually assessed the height of the JB in the 3D models. Distances between the round window and the JB dome were measured to evaluate the spacing of this area. Additional distances between landmarks on surrounding structures were measured and statistically analyzed to describe the anatomical variability between and within subjects. RESULTS: The visual classification revealed that 30% of the specimens had no JB, 63% a low JB, and 7% a high-riding JB. The measured mean distance from the round window to the jugular bulb ranges between 3.22 ± 0.97 mm and 10.34 ± 1.41 mm. The distance measurement (error rate 5%) was more accurate than the visual classification (error rate 15%). The variability of the JB was higher than for the surrounding structures. No systematic laterality was found for any structure. CONCLUSION: Qualitative analysis in 3D models can contribute to a better spatial orientation in the lateral skull base and, thereby, have important implications during planning of middle ear and lateral skull base surgery.

Validation of the radiological detection of the chorda-facial angle: impact on the round window accessibility during pediatric cochlear implantation.

OBJECTIVES: The facial recess, an essential landmark for the posterior tympanotomy approach, is limited by the facial nerve and the chorda tympani, with a complicated relationship. This study tried to find the most appropriate radiological method to evaluate the chorda-facial angle (CFA). We also checked the effect of this angle on the round window accessibility during cochlear implantation. METHODS: It was a retrospective study that included cochlear implant surgeries of 237 pediatric patients, from September 2016 to April 2021. Two physicians evaluated the CFA in the para-sagittal cut of the preoperative HRCT. The round window accessibility was assessed in the unedited surgery videos. RESULTS: The CFA ranged from 21° to 35° with a mean of 27.14 ± 3.5°. It was detected in all cases with a high agreement between the two CT reviewers' measurements. The CFA differed significantly between the accessible group and the group with difficult accessibility (p value < 0.001). Spearman's correlation coefficient revealed a strong correlation between the CFA and the intraoperative round accessibility. 25.5° was the best cutoff point; below this angle, difficult accessibility into the RW was expected, with high sensitivity, specificity, and accuracy CONCLUSIONS: Our study on a relatively large number of cases provided a precise, valid, reliable, and applicable method to evaluate the CFA in the HRCT scan. We found a significant-close relation between the CFA and the round window accessibility; the difficulty increased with a need for posterior tympanotomy modification when the angle decreased. KEY POINTS: • Radiological detection of the chorda-facial angle was always problematic, without a previous straightforward method in the literature. • We used the para-sagittal cut of the high-resolution CT scans to evaluate the CFA. This cut was beneficial to seeing the chorda tympani nerve in every examined case. There was a high agreement between the two CT reviewers' measurements. • Preoperative evaluation of the CFA in the HRCT accurately predicted the round window accessibility. Patients with CFA less than 25.5° were expected to have difficult accessibility into the round window during cochlear implantation.

Radiological and surgical aspects of round window visibility during cochlear implantation: a retrospective analysis.

PURPOSE: The round window approach has become the most preferred option for cochlear implant (CI) insertion, however, sometimes it may not be possible due to the (in)visibility of the round window membrane (RWM). We addressed the prevalence, consequences and indicators of difficult detection of the RWM in cochlear implant surgery. METHODS: This study retrospectively analysed the operative reports and preoperative high resolution axial-computed tomography (CT) scans of a consecutive cohort of patients who underwent a CI insertion. The main outcomes were surgical outcomes of the RW approach, and assessment of radiological markers. RESULTS: The operative reports showed that RWM insertion was feasible in 151 out of 153 patients. In 18% of the patients the RWM was difficult to visualize. All these patients had at least one intraoperative event. The chorda tympani nerve (CTN) or posterior canal wall was affected in 8% of the 153 patients and the fallopian canal in 6%. These patients had a facial-chorda tympani nerve distance on the CT scan that was considerably smaller than normal patients (1.5 mm vs 2.3 mm). In addition, a prediction line towards the anterolateral side of the RWM was found to be more prevalent in these patients' CT scans (sensitivity 81%, specificity 63%). CONCLUSION: The RW approach is feasible in almost all patients undergoing CI surgery. Difficult visualisation of the RWM seems to lead to at least one intraoperative event. Radiological measures showed that these patients had a smaller facial recess and a more anteriorly placed facial nerve, which can be used to better plan a safe insertion approach.

Effect of ossicular chain deformity on reverse stimulation considering the overflow characteristics of third windows.

Stimulating the round window membrane via an active actuator of the middle ear implant, named the reverse stimulation, has become an option to help patients with ossicular chain deformity (OCD) to restore hearing. However, there is still no concise description of how OCD affects reverse stimulation considering the overflow characteristics of third windows. In the present study, an impedance model considering the vestibular and cochlear aqueducts was used to investigate the dynamic response of the cochlea to reverse stimulation under OCD. First, a finite-element (FE) model of the middle ear and the ear canal was used to estimate the changes in reverse middle-ear impedance caused by ossicular chain fixation and ossicular chain interruption. Then, the impedance model was used to predict the reverse transfer function, which characterizes the effect of OCD on the dynamic response of the cochlea. The results show that ossicular chain fixation reduces the reverse stimulation's performance. Moreover, the existence of the third windows complicates the effect of ossicular chain fixation on the reverse stimulation and boosts obviously the reverse stimulation's performance at low frequencies. In contrast, regardless of the existence of third windows, ossicular chain interruption enhances the effect of reverse stimulation.

[A case of obliteration of a round window in otosclerosis]. / Sluchai obliteratsii kruglogo okna pri otoskleroze.

The article presents a brief review of the literature on the anatomy and physiology of the round window (RW) niche, the causes of occlusion, the diagnosis of this pathology, the features of auditory disorders and tactics when it is detected in patients with otosclerosis (OS). A clinical case of diagnosis and effective surgical treatment for obliteration of RW in a patient with advanced OS, which occurred in 2019 in 0.7% of cases, is described. Removal of RW niche obliteration was carried out with a curette and microcresis by smoothing the canopy over RW until partial visualization of the secondary membrane. It was this stage of the operation that made it possible to restore the normal hydrodynamics of the inner ear fluids and contributed to a functional result. Thus, the diagnosis of RW obliteration in patients with OS is difficult, but possible when using computed tomography of the temporal bones and assessing the mobility of the RW membrane or analyzing changes in hearing at the end of the operation, if it is performed under local anesthesia. The simultaneous performance of stapedoplasty and the removal of bone obliteration of RW makes it possible to safely achieve functional rehabilitation in patients with OS.

Round window anatomy predicts ease of cochlear implantation in children.

OBJECTIVES: We aim to evaluate the utility of the Round Window Angle (RWA) as a predictor of difficulty and operative time in cochlear implantation. METHODS: A retrospective study of pediatric patients that underwent cochlear implantation and CT temporal bone imaging from January 2008 to November 2019. Correlation, univariate, and multivariate analysis were conducted. RESULTS: 347 implantations met inclusion criteria. We found a difference in RWA for difficult (median: 101°, n = 5) and non-difficult (median: 74, n = 317) implantations (p < 0.0001). There was also a difference in RWA in patients with round windows visualized intra-operatively (p < 0.0197). When controlling for age and intraoperative round window visualization, logistic regression showed RWA was significantly associated with difficult insertion (OR: 1.687; p = 0.0246). Further, there was positive correlation between RWA and operative time (r = 0.1779, p = 0.0013) with patients with acute RWAs having shorter operative times (mean 115.7 ± 32.1 min) than those with obtuse RWA (mean 183.5 ± 97.0 min) (p = 0.0035). When accounting for surgeon and patient age, multivariate linear regression showed round window visualization (ß = 3.456, p = 0.0006) and obtuse RWA (ß = 6.172, p < 0.0001) was associated with an increase in operative time. CONCLUSION: Further research is needed to identify difficult cochlear implantations to increase the success and reduce risks associated with the surgery. Our study reports the possibility that an obtuse RWA both significantly increases difficulty and time of operation due to decreased round window visualization.

Subcochlear canaliculus patterns in the pediatric and adult population: radiological findings and surgical implications.

INTRODUCTION: The pneumatization of the different regions of the temporal bone is strictly related to the age and the degree of development of the mastoid and the middle ear. Petrous apex pneumatization is the last step of the development of the petrous bone system. The subcochlear canaliculus is an anatomical cavity, originating in the space between the fustis and the finiculus, and connecting the round window area to the petrous apex. The aim of the present article is analyzing the trend of development of the subcochlear canaliculus pneumatization, classified through CT scan examination, in different age subgroups. MATERIALS AND METHODS: We conducted a retrospective review of patients who underwent temporal bone CT scans between 2014 and 2019. Pediatric and adult patients were included and divided into different age subgroups. The subcochlear canaliculus was examined through coronal view scans at the level of the round window niche and classified into 3 different groups (A, B and C) according to the degree of pneumatization. RESULTS: A total of 270 Petrous bone CT scans was analyzed. The percentage of type A subcochlear canaliculus was significantly higher in the pediatric population if compared to the adult population (p = 0.001326). As far as type B subcochlear canaliculus is concerned, the difference between children and adults was not statistically significant (p = 0.2378). On the other hand, type C subcochlear canaliculus was predominant in the adult population (p = 0.000256). CONCLUSIONS: There is a constant increase in pneumatization of the subcochlear canaliculus from 0 to 19 years and then a progressive decrease. This discovery has relevant surgical implications and has to be borne in mind in particular for cholesteatoma surgery and cochlear implantation surgery in the age groups in which the subcochlear canaliculus is highly pneumatized.

[Laser Doppler vibrometric measurements on human temporal bones]. / Laser-Doppler-vibrometrische Messungen an humanen Felsenbeinen.

Laser Doppler vibrometric (LDV) measurements on human temporal bones represent the standard method for predicting the performance of active middle ear implants (AMEI) and are used as preclinical tests in the development, approval process, and indication expansion of AMEI. The quality of the coupling of the floating mass transducer to the mobile structures of the middle ear is decisive for the performance of the implant and patients' hearing perception. The cochlea can be stimulated via the oval window (forward stimulation) or the round window (reverse stimulation). For forward stimulation, the ASTM standard F2504-05 defines a method to ensure physiologically normal properties of the temporal bones used in the experiments. For reverse stimulation, which depends even more critically on the quality of the temporal bone, a comparable standard method is lacking. Appropriate preparation and storage of the human petrous bone as well as suitable LDV test setups with respect to calibration and reproducibility of measuring positions and angles provide results that allow a comparison of different types of coupling and also correlate well with clinical data.

Atlas-based segmentation of cochlear microstructures in cone beam CT.

PURPOSE: To develop an automated segmentation approach for cochlear microstructures [scala tympani (ST), scala vestibuli (SV), modiolus (Mod), mid-modiolus (Mid-Mod), and round window membrane (RW)] in clinical cone beam computed tomography (CBCT) images of the temporal bone for use in surgical simulation software and for preoperative surgical evaluation. METHODS: This approach was developed using the publicly available OpenEar (OE) Library that includes temporal bone specimens with spatially registered CBCT and 3D micro-slicing images. Five of these datasets were spatially aligned to our internal OSU atlas. An atlas of cochlear microstructures was created from one of the OE datasets. An affine registration of this atlas to the remaining OE CBCT images was used for automatically segmenting the cochlear microstructures. Quantitative metrics and visual review were used for validating the automatic segmentations. RESULTS: The average DICE metrics were 0.77 and 0.74 for the ST and SV, respectively. The average Hausdorff distance (AVG HD) was 0.11 mm and 0.12 mm for both scalae. The mean distance between the centroids for the round window was 0.32 mm, and the mean AVG HD was 0.09 mm. The mean distance and angular rotation between the mid-modiolar axes were 0.11 mm and 9.8 degrees, respectively. Visually, the segmented structures were accurate and similar to that manually traced by an expert observer. CONCLUSIONS: An atlas-based approach using 3D micro-slicing data and affine spatial registration in the cochlear region was successful in segmenting cochlear microstructures of temporal bone anatomy for use in simulation software and potentially for pre-surgical planning and rehearsal.

Combined preoperative HRCT parameters for prediction of round window visibility in pediatric cochlear implant patient.

OBJECTIVE: To evaluate the add value of combined analysis of high resolution computed tomography (HRCT) temporal bone parameters in accurate prediction of round window (RW) visibility through posterior tympanotomy. PATIENTS AND METHODS: a retrospective observational study was held in a tertiary center, conducted on 45 cochlear implant pediatric candidates between January 2017 and September 2019. Candidates were referred for CT temporal bone. They were classified into fully visible RW cases and partially or non-visible RW cases. Radiological measurements were compared between the two groups for prediction of RW visibility separate and in combination. RESULTS: 45 patients were included in the study (26 males (57.8%) and 19 females (42.2%)). Their median age was 4 years (2-12 years). There were 38 (84.4%) fully visible and 7 (15.6%) partially or non-visible RW cases. Kashio posterior line (n:32/3), fascial recess width (FRW) (mean: 4.9 (3.5-7.5)/4.2 (4-4.7) mm) and round window location (RWL) (3 (1-4)/2.8 (1-3)mm) measurements significantly differentiated between the two groups; (P value 0.034, 0.012 & 0.025 respectively). Posterior kashio line and cut off values of ≥4.75 mm of FRW & 2.95 mm of RWL were showed sensitivity 84.2%, 63.2% & 65.8%, and accuracy 80%, 68.9% &68.9% in prediction of RW visibility respectively. Combination of Kashio prediction line with cut off value ≥ 7.45 mm (sum of FRW & RWL) showed P value 0.003 with further improve in the sensitivity and overall accuracy in prediction of RW visibility from 84.2% to 80% up to 91.4% and 88.6% respectively. CONCLUSION: combined parameters using Kashio line with FRW and RWL increases sensitivity and overall accuracy in prediction of RW visibility rather than single parameter.

Radiologic Evaluation of the Round Window Niche Configuration: A One-Stop Approach.

BACKGROUND: Preoperative radiological prediction of the round window niche configuration. METHODS: Fifty patients were evaluated. A single-axial high-resolution computed tomography image at the level of the cochlear aqueduct was compared to the intraoperative surgical images. Radiological configuration was classified as open, hooded, or covered depending on the extent of bony overhang. Surgical images were processed using Image J software to determine the amount of drilling required before the round window membrane is exposed. These images were classified according to the St. Thomas classification into 3 grades. RESULTS: In all patients, the axial cut showing the cochlear aqueduct was obtained. There were 12 cases in the open category, 17 in the hooded category, and 21 in the covered one. Intraoperatively, the actual findings were type I 12, type II 18, and type III 20. The correspondence between the expected and actual classification was correct in 8, 12, and 18 cases, respectively. Comparing the intraoperative findings with the expected radiological configuration, there was a good concordance with a statistically non-significant difference ( χ2=0.2613; P=.87751). CONCLUSION: It is possible to predict the configuration of the round window niche on a single-axial computed tomography cut and plan the most suitable axis of approach and predict the amount of drilling expected to expose the round window membrane.

The role of high-resolution Computer Tomography in prediction of the round window membrane visibility and the feasibility of the round window electrode insertion.

OBJECTIVE: The aim of this work is to assess the role of pre-operative high-resolution computerized tomography (HRCT) in prediction of the round window membrane (RWM) visibility and the feasibility of round window electrode insertion. MATERIALS AND METHODS: Retrospective study on a series of 97 cases of cochlear implant (CI) who were implanted in tertiary referral centers. We reviewed HRCT of all cases, and we implicated two radiological measurements on HRCT which are membrano-facial angle (MFA) and length of the bony overhang of the round window niche (RWN). We reviewed the intra-operative surgical video recordings of all cases for detection of the type of RWM visibility, according to The St Thomas' Hospital classification. RESULTS: The MFA was 21.9 ± 14.5. The length of the bony overhang of the RWN was 2.4 ± 0.33 mm. About 37% of the studied patients needed cochleostomy. The best cut-off of MFA in the prediction of the RW (type 2B and 3) was ≥ 15.1o with sensitivity 100%, and specificity 82%. CONCLUSION: HRCT offers highly reliable and reproducible measurements for the prediction of RWM visibility and, therefore, prediction of the utility of the RW approach for electrode insertion. Membrano-facial angle (MFA) is a new measurement that can be used for this purpose.

A Micro-Computed Tomography Study of Round Window Anatomy and Implications for Atraumatic Cochlear Implant Insertion.

HYPOTHESIS: The goal of this study was to interrogate high-resolution three-dimensional reconstructions of round window anatomy to illustrate and characterize structural variability with implications for atraumatic cochlear implant insertion. BACKGROUND: Cochlear implants are increasingly used to improve sound detection in patients with substantial residual hearing. However, traumatic cochlear implant insertion through the round window involving upward deviation of the electrode into the spiral ligament, basilar membrane, and osseous spiral lamina, medial impaction on the modiolus, or interscalar excursion into the scala vestibuli are associated with lower rates of hearing preservation and poorer speech perception.Successful atraumatic insertion is dependent on an anatomical understanding of the middle and inner ear. The round window bony niche lacks distinct demonstrable anatomical landmarks for the position of the round window membrane, and there is limited guidance on the amount of bony overhang that can be safely drilled away. A greater understanding of the anatomical variation around the round window could enhance treatment efficacy. METHODS: Fourteen human cadaver temporal bones were imaged using microcomputed tomography. Resulting scans were digitally reconstructed, segmented, and measured. RESULTS: Round window niche walls vary substantially in size and projection. Round window average short diameter measured 1.30 mm (range 1.07-1.44), and is limited by the crista fenestrae at the inferoanterior margin of the round window. Crista fenestrae size and morphology varied considerably. Reconstructions with solid and translucent panels are presented. CONCLUSION: Anatomical heterogeneity should be considered in cochlear implant selection, drilling, and choice of insertion vector.

Effect of stimulation sites on the performance of electromagnetic middle ear implant: A finite element analysis.

Electromagnetic middle ear implants (MEIs), which use the mechanical vibration of their implanted transducers to treat hearing loss, have emerged to overcome the limitations of conventional hearing aids. Several reports have indicated that the electromagnetic MEI's performance changed with different stimulation sites of the transducer. The aim of this study was to analyze the influence of the transducers' stimulation sites on the electromagnetic MEIs' performance. To aid this investigation, a human ear finite-element model was developed from micro-CT images of an adult's right ear. The validity of the model was confirmed by comparing the model-derived results with experimental data. Then, stimulation forces, which simulate ideal electromagnetic transducers, were respectively applied at five typical coupling sites: the umbo, incus body, incus long process, the round window, and the stapes. The stimulation sites' influence on the electromagnetic MEI's performance was studied by analyzing their corresponding basilar membrane displacements. The results show that stimulation of the round window with a force produces more cochlear stimulation than equal force stimulation of the umbo, incus body, incus long process and the stapes, though the superiority of the round window depends on its smaller area compared to the stapes footplate. Among the forward stimulation, the stapes is the optimal stimulation site for the electromagnetic transducer regarding its hearing compensation's efficiency. The performance of the umbo stimulation is comparable to that of the incus-long-process stimulation. Driving the incus body is less efficient than stimulating the other forward driving sites. Additional, using the stapes response to evaluate the forward stimulation gives results similar to those deduced by the basilar membrane response; in contrast, for the round-window stimulation, the evaluation result based on the stapes response is prominently less than the one calculated by the basilar membrane response, especially in the mid-high frequency range.

Exploratory tympanotomy in sudden sensorineural hearing loss for the identification of a perilymphatic fistula - retrospective analysis and review of the literature.

OBJECTIVE: The diagnostic value of exploratory tympanotomy in sudden sensorineural hearing loss remains controversial. This study and review were performed to identify the incidence of perilymphatic fistula in patients with sudden sensorineural hearing loss. The effectiveness of tympanotomy for sealing of the cochlear windows in cases with perilymphatic fistula was evaluated. METHODS: A search in common databases was performed. Overall, 5034 studies were retrieved. Further, a retrospective analysis on 90 patients was performed. RESULTS: Eight publications dealing with tympanotomy in patients with sudden sensorineural hearing loss were identified. In 90 patients diagnosed with sudden sensorineural hearing loss and undergoing exploratory tympanotomy, 10 patients (11 per cent) were identified with a perilymphatic fistula, and this corresponds to the results obtained from our review (13.6 per cent). CONCLUSION: There was no significant improvement after exploratory tympanotomy and sealing of the membranes for patients with a definite perilymphatic fistula.

Predicting round window visibility by HRCT during cochlear implantation in children.

Objective: The present study aimed to radiologically evaluate the visibility of round window during cochlear implantation by high-resolution computed tomography (HRCT) imaging of temporal bone. Study design: This was a cross-sectional descriptive analytic study. Methods: Two new radiologic measurements were evaluated on the presurgical HRCT of temporal bone, including (1) the angle between the line parallel to coronal axis that passes through the middle of the round window niche (RWN) and the line that connects the anterior portion of facial nerve (FN) to the middle of the RWN (RWN angle) and (2) the vertical distance between this coronal plane and the anterior portion of the FN, modified facial recess distance (MFRD). The measurements were then compared with the visibility of the round window (RW) during operation, as reported by the surgeon. Result: The present study compared the abovementioned CT scan findings of cochlear implanted children in visible (n = 21) and nearly invisible (n = 21) RW during surgery, as reported by the surgeon. The analysis revealed that both MFRD (P < 0.01) and RWN angle (P < 0.04) were significantly different between the two groups. Conclusion: the RWN angle and MFRD are fairly reliable predictors of round window visibility during cochlear implantation.

Anatomical landmarks for cochlear implantation in ossified cochleas.

PURPOSE: In this study, we aimed to introduce the facial nerve as a new anatomical landmark which can be used in ossified cochleas during cochlear implantation. We also set out to define a safe line to preserve the internal auditory canal (IAC) while drilling the basal turn of the cochlea. METHODS: Thirty patients who had temporal computed tomography (CT) were studied. The distances from the facial nerve and the round window to the IAC, carotid artery, and jugular bulb were measured in the reformatted CT images. We have created a line in the direction of the stapedial tendon from the round window to the IAC and called it ROWIAC (Round window-IAC) line. We have investigated whether this line intersects the IAC and measured the distances from this line to the IAC. RESULTS: Fifty-four temporal CT scans were included to the study. The mean distances from the facial nerve to the IAC, carotid artery, and jugular bulb were 8.8 ± 0.9, 15.0 ± 2.0, and 12.2 ± 2.9 mm, respectively. The mean distances from the round window to these structures were 3.8 ± 0.7, 9.4 ± 2.2, and 8.3 ± 2.9 mm, respectively. ROWIAC line did not intersect the IAC in any of the patients. The mean distance between this line and the IAC was 0.8 ± 0.4 mm. CONCLUSION: We propose that facial nerve and ROWIAC line can be used as potential landmarks during cochlear implantation in ossified cochleas to protect the adjacent neurovascular structures.