Imaging cochlear implantation with round window insertion in human temporal bones and cochlear morphological variation using high-resolution cone beam CT

Conclusions: The present experimental set-up of high spatial resolution cone-beam computed tomography (CBCT) showed advantages of demonstrating the critical landmarks of the cochlea in identifying the position of intracochlear electrode contacts and has the potential for clinical application in cochlear implant (CI) surgery. Objective: To evaluate a newly developed CBCT system in defining CI electrode array in human temporal bone and cochlear morphological variation. Methods: Standard electrode, flexible tip electrode (Flex28), and an experimental electrode array with 36 contacts from MED-EL were implanted into the cochleae of six human temporal bones through an atraumatic round window membrane insertion. The cochleae were imaged with 900 frames using an experimental set-up based on a CBCT scanner installed with Superior SXR 130-15-0.5 X-ray tube in combination with filtration of copper and aluminum. Results: In all temporal bones, the landmarks of the cochlea, modiolus, osseous spiral lamina, round window niche, and stapes were demonstrated at an average level of 3.4–4.5. The contacts of electrode arrays were clearly shown to locate in the scala tympani. There was a linear correlation between the ‘A’ value and cochlea height, and between the A value and actual electrode insertion length for the first 360° insertion depth.     

Evaluating cochlear implant trauma to the scala vestibuli

Objectives: Placement of cochlear implant electrodes into the scala vestibuli may be intentional, e.g. in case of blocked scala tympani or unintentional as a result of trauma to the basilar membrane or erroneous location of the cochieostomy. The aim of this study was to evaluate the morphological consequences and cochlear trauma after implantation of different cochlear implant electrode arrays in the scala vestibuli. Design: Human temporal bone study with histological and radiological evaluation. Setting: Twelve human cadaver temporal bones were implanted with different cochlear implant electrodes. Implanted bones were processed using a special method to section undecalcified bone. Main outcome measures: Cochlear trauma and intracochlear positions. Results: All implanted electrodes were implanted into the scala vestibuli using a special approach that allows direct scala vestibuli insertions. Fractures of the osseous spiral lamina were evaluated in some bones in the basal cochlear regions. In most electrodes, delicate structures of the organ of Corti were left intact, however, Reissner's membrane was destroyed in all specimens and the electrode lay upon the tectorial membrane. In some bones the organ of Corti was destroyed. Conclusions: Scala vestibuli insertions did not cause severe trauma to osseous or neural structures, thus preserving the basis for electrostimulation of the cochlea. However, destruction of Reissner's membrane and impact on the Organ of Corti can be assumed to destroy residual hearing.     

Symposium: Cochlear implant, 1978—fact or supposition. Traumatic intracochlear electrode implantation

The success of intracochlear electrode implantation hinges on the ability of peripheral auditory neurons to survive long-term interface with an electrode array and prolonged electrical stimulation. Histopathological studies have been conducted on a series of neomycin sulphate otointoxicated cats to assess the long-term effects of electrode implantation on an impaired cochlea (analogous to potential human sensory deaf implant candidates). The results of these studies may be summarized as follows: 1. Long-term electrode implantation can be achieved without significant loss of primary auditory neurons using an electrode array embedded in Silastic which is molded to conform to the basal scala tympani if surgical implantation has not disrupted the basilar membrane or osseous spiral lamina. 2. A fibrous tissue matrix forms around the Silastic, displacing perilymph and effectively sealing the electrode at the round window preventing perilymph fistula. 3. While osteoneogenesis will occur whenever the periosteum of the bony labyrinth is disrupted, the molded Silastic sheathing prevents electrode displacement by small areas of new bone formations. 4. Traumatic electrode insertion, with fracture of the osseous spiral lamina or rupture of the basilar membrane, produces severe loss of neural elements in the region of injury and extensive new bone formation preventing satisfactory electrical stimulation. The findings suggest that long-term cochlear implantation is feasible in sensory deafened animals using Silastic sheathed electrode arrays which have been molded to conform to the basal scala tympani provided the integrity of the scala tympani, osseous spiral lamina and basilar membrane is maintained.     

A true minimally invasive approach for cochlear implantation: high accuracy in cranial base navigation through flat-panel-based volume computed tomography.

OBJECTIVE: High-precision intraoperative navigation using high-resolution flat-panel volume computed tomography makes feasible the possibility of minimally invasive cochlear implant surgery, including cochleostomy. Conventional cochlear implant surgery is typically performed via mastoidectomy with facial recess to identify and avoid damage to vital anatomic landmarks. To accomplish this procedure via a minimally invasive approach--without performing mastoidectomy--in a precise fashion, image-guided technology is necessary. With such an approach, surgical time and expertise may be reduced, and hearing preservation may be improved. INTERVENTIONS: Flat-panel volume computed tomography was used to scan 4 human temporal bones. A drilling channel was planned preoperatively from the mastoid surface to the round window niche, providing a margin of safety to all functional important structures (e.g., facial nerve, chorda tympani, incus). MAIN OUTCOME MEASURES: Postoperatively, computed tomographic imaging and conventional surgical exploration of the drilled route to the cochlea were performed. RESULTS: All 4 specimens showed a cochleostomy located at the scala tympani anterior inferior to the round window. The chorda tympani was damaged in 1 specimen--this was preoperatively planned as a narrow facial recess was encountered. CONCLUSION: Using flat-panel volume computed tomography for image-guided surgical navigation, we were able to perform minimally invasive cochlear implant surgery defined as a narrow, single-channel mastoidotomy with cochleostomy. Although this finding is preliminary, it is technologically achievable.     

Scalar localization of the electrode array after cochlear implantation: clinical experience using 64-slice multidetector computed tomography.

OBJECTIVE: To use the improved resolution available with 64-slice multidetector computed tomography (MDCT) in vivo to localize the cochlear implant electrode array within the basal turn. STUDY DESIGN: Sixty-four-slice MDCT examinations of the temporal bones were retrospectively reviewed in 17 patients. Twenty-three implants were evaluated. SETTING: Tertiary referral facility. PATIENTS: All patients with previous cochlear implantation evaluated at our center between January 2004 and March 2006 were offered a computed tomographic examination as part of the study. In addition, preoperative computed tomographic examinations in patients being evaluated for a second bilateral device were included. INTERVENTION: Sixty-four-slice MDCT examination of the temporal bones. MAIN OUTCOME MEASURE: Localization of the electrode array within the basal turn from multiplanar reconstructions of the cochlea. RESULTS: Twenty-three implants were imaged in 17 patients. We were able to localize the electrode array within the scala tympani within the basal turn in 10 implants. In 3 implants, the electrode array was localized to the scala vestibuli. Migration of the electrode array from scala tympani to scala vestibuli was observed in three implants. Of the 7 implants in which localization of the electrode array was indeterminate, all had disease entities that obscured the definition of the normal cochlear anatomy. CONCLUSIONS: Sixty-four-slice MDCT with multiplanar reconstructions of the postoperative cochlea after cochlear implantation allows for accurate localization of the electrode array within the basal turn where normal cochlear anatomy is not obscured by the underlying disease process. Correlating the position of the electrode in the basal turn with surgical technique and implant design could be helpful in improving outcomes.     

Quality control after cochlear implant surgery by means of rotational tomography.

OBJECTIVE: To investigate the intracochlear electrode position in using rotational tomography in adult cochlear implant patients. STUDY DESIGN: Retrospective. SETTING: Tertiary referral center. PATIENTS: Eighteen adult patients being implanted either with a Nucleus straight electrode array or a Contour electrode with a total of 22 implanted ears. Preoperative computed tomography had been without evidence for obliteration, ossification, or malformation of the cochlea. INTERVENTION: Rotational tomography. MAIN OUTCOME MEASURES: The intracochlear electrode position was evaluated with regard to scala tympani, scala vestibuli, and a dislocation from one scala to the other. The intraoperative procedure was compared with the electrode position by analyzing the operating reports. RESULTS: Preliminary results indicate, respectively, that there is a higher incidence of intracochlear trauma in using the Contour electrode array than expected with a more frequent dislocation of electrode arrays from scala tympani to scala vestibuli and that there is a higher rate of scala vestibuli insertions. CONCLUSIONS: The impact of these findings may influence further developments of electrode arrays as well as surgical techniques for implantation.     

Imaging procedures in cochlear implant patients--evaluation of different radiological techniques

The purpose of this study was to evaluate the feasibility and usability of different radiologic methods (single-slice computed tomography (CT), multi-slice CT and rotational tomography (RT)) for assessment of the position of cochlear implant electrodes. Cochlear implants in an isolated human temporal bone and in a complete formalin-fixed cadaver head were examined and the electrode position was determined. Subsequently, the labyrinth bone was isolated out of the cadaver head and histologically examined to compare the results of histology with imaging. Single-slice CT reliably identifies the electrode inside the human cochlea; however, due to the technically based large electrode artifact its position inside the cochlear spaces (e.g. electrode position in scala tympani or scala vestibuli) cannot be detected. Multi-slice CT of the cadaver head also showed artifacts that complicate the assessment of electrode position. Using RT the electrode artifact is small and therefore the electrode position within the cochlear spaces, scala tympani versus scala vestibuli, can be assessed. This technique was also applicable in a complete cadaver head, which is in contrast with former studies. In conclusion, CT allows the identification of electrode arrays inside the human cochlea. Multi-slice CT permits a much more precise depiction of the electrode inside the cochlea. RT alone has minimized electrode artifacts to a high extent and permits the assessment of the electrode position within the scala tympani or scala vestibuli. As RT was performed successfully in a complete cadaver head, further studies for evaluation of the intracochlear electrode position can now be performed in patients.     

Evaluation of the HiFocus electrode array with positioner in human temporal bones

The aim of the study presented was to assess the insertion mode and possible intracochlear trauma after implantation of the HiFocus electrode with positioner in human temporal bones. The study was performed in five freshly frozen temporal bones. The position of electrodes was evaluated using conventional X-ray analysis, rotational tomography and histomorphological analysis. Insertion of the HiFocus electrode with positioner resulted in considerable trauma to fine cochlear structures including fracture of the osseous spiral lamina, dislocation of the electrode array from the scala tympani into the scala vestibuli and fracture of the modiolus close to the cochleostomy. The implication of the results regarding clinical outcome will be discussed.     

Scalar localization of the electrode array after cochlear implantation: a cadaveric validation study comparing 64-slice multidetector computed tomography with microcomputed tomography.

HYPOTHESIS: Improved resolution available with 64-slice multidetector computed tomography (MDCT) could potentially be used clinically to localize the cochlear implant (CI) electrode array within the basal turn. BACKGROUND: In CI surgery, the electrode array should be inserted into and remain within the scala tympani to avoid injury to Reissner's membrane and the scala media. Correlating the position of the electrode in the basal turn with surgical technique and implant design could be helpful in improving outcomes. METHODS: After a standard left mastoid exposure of the round window niche through the facial recess performed on a cadaver head, an electrode array from a Nucleus Softip Contour CI was fully inserted through a cochleostomy. The head was then scanned axially on a 64-slice MDCT with 0.4-mm slice thickness and reconstructed into the oblique axial, oblique coronal, and oblique sagittal planes of the cochlea. The temporal bone was then harvested and imaged on a microcomputed tomographic scanner using 20-microm slice thickness. Identical reconstructions were made and compared with the 64-slice images to confirm exact location of the electrode array. RESULTS: The 64-slice MDCT accurately localized the electrode array to the scala tympani. This was best demonstrated in the oblique sagittal plane, identifying the electrode array in the posterior inferior portion of the basal turn, posterior to the spiral lamina. CONCLUSION: This ex vivo validation study suggests that 64-slice MDCT has the potential to allow accurate localization of the CI electrode array within the basal turn of the cochlea.     

Intracochlear assessment of electrode position after cochlear implant surgery by means of multislice computer tomography

The development of electrode arrays, the past years, has focused on modiolus-hugging cochlear implant electrodes. Besides, atraumatic implantation of electrodes is of importance for the use in hearing preservation, in cases of combined electric and acoustic stimulation. Intracochlear positioning of the individual electrodes by means of multislice computer tomography (CT) has not yet been shown. In this study we formulated and tested a CT imaging protocol for postoperative scanning of the temporal bone in cochlear implant subjects. Both a fresh human temporal bone and a fresh human cadaver head were implanted with a cochlear implant. Multislice CT was performed for adequate depiction of the cochlear implant. All scans were analyzed on a viewing workstation. After mid-modiolar reconstruction we were able to identify the intracochlear electrode position relative to the scala tympani and scala vestibuli. This was possible in both the implanted isolated temporal bone and the fresh human cadaver head. The feasibility of imaging the electrode position of the cochlear implant within the intracochlear spaces is shown with multislice CT. An imaging protocol is suggested.     

Anatomy of the middle-turn cochleostomy

Objective: Middle‐turn cochleostomies are occasionally used for cochlear implant electrode placement in patients with labyrinthitis ossificans. This study evaluates the anatomic characteristics of the middle‐turn cochleostomy and its suitability for placement of implant electrodes. Methods: Ten cadaveric human temporal bones were dissected using a facial recess approach. A middle‐turn cochleostomy was drilled 2 mm anterior to the oval window and just inferior to the cochleariform process. The preparations were then stained with osmium tetroxide and microdissections were performed. The location of the cochleostomy on the cochlear spiral and its path through the various cochlear compartments were evaluated in all 10 specimens. A Cochlear Corporation depth gauge was inserted in five of the specimens and insertion trauma, number of contact rings, and depth of insertion were recorded. Results: Eight of the 10 cochleostomies were placed at approximately 360° on the cochlear spiral, near the transition between the basal and middle turns. In one case, the cochleostomy was found to enter the cochlear apex and in another it entered scala vestibuli of the proximal basal turn. The cochleostomy entered scala media in six bones and scala vestibuli in four specimens. A depth gauge was inserted in five specimens. The number of contacts placed within the cochlear lumen ranged from four to nine. There was evidence of insertional trauma to the lateral wall of the cochlear duct, basilar membrane, and Reissner's membrane, but no evidence of fractures to the osseous spiral lamina or modiolus. Conclusion: This study demonstrates that electrodes inserted via a middle‐turn cochleostomy are likely to enter scala vestibuli and have access to the middle‐ and apical‐cochlear turns. It is also possible that the electrode could be directed into the descending portion of the basal turn depending on cochleostomy orientation. Middle‐turn cochleostomy seems to be a viable alternative for electrode placement when preservation of residual hearing is not a concern.     

Cochlear patency problems in cochlear implantation

Sensory deafness may be associated with partial or total obliteration of the cochlear scalae. Before undertaking cochlear implant surgery, a preoperative assessment of cochlear patency with high-resolution computed tomography (CT) is indicated. To determine the accuracy of pre-implant CT, a review of the radiographic and surgical findings in 36 implanted ears was performed. An abnormal CT scan was found to be a reliable predictor of compromised cochlear patency at operation. These findings help the surgeon to select the side most favorable for implantation and to anticipate problems that may be encountered during device insertion. A normal pre-implant CT scan, however, does not exclude the possibility of compromised cochlear patency. A 46% false negative rate was encountered, presumably because subtle degrees of osseous or fibrous obliteration of the cochlea are beyond the resolution by current generation CT scanners. In our opinion, the radiographic finding of cochlear ossification is not a contraindication to an attempt at cochlear implantation. The only assured way of determining the extent of cochlear patency is by performing an ‘exploratory cochleostomy’ with fenestration of the basal cochlear turn. Drilling anteriorly through an ossified basal scala tympani will often expose an adequate lumen and permit insertion of even a long multichannel electrode into a partially ossified cochlea. Nevertheless, it is essential that the implant team be prepared with devices appropriate for whatever existing or surgically created lumen may be available.     

Surface microstructure of the perilymphatic space: implications for cochlear implants and cell- or drug-based therapies

OBJECTIVE: To study the surface microstructure of the scala tympani and scala vestibuli in humans and cats using scanning electron microscopy. DESIGN: Cochleas from 8 humans and 4 cats were harvested and the otic capsule and soft tissue removed before the cochleas were prepared for scanning electron microscopy. Micrographs were taken of the bony surface of both the scala tympani and scala vestibuli in each cochlear turn. The diameter and density of the micropores (canaliculi perforantes) and the thickness of the osseous spiral lamina (OSL) adjacent to Rosenthal's canal was measured. RESULTS: The human cochlea exhibits numerous canaliculi on the surface of the scala tympani, particularly associated with the OSL. There was a large range of diameters in the modiolar region of the OSL (0.2-23.0 micro m). The OSL was also very thin, with a mean thickness of 26.8 micro m in the base, tapering to 8.4 micro m in the apical turn. Far fewer canaliculi were evident in the scala vestibuli. Examination of the cat cochleas showed a similar distribution of canaliculi to that seen in the human; however, they were smaller in diameter and the OSL was thicker than in the human cochleas. CONCLUSIONS: The OSL is a thin and highly porous bony lamina that would appear to provide an open and extensive fluid communication channel between the scala tympani and Rosenthal's canal. These findings have important implications for the design and application of perimodiolar cochlear implant electrode arrays and may provide a potential route for drug- and cell-based cochlear therapies delivered via the scala tympani.     

Anatomy of the round window and hook region of the cochlea with implications for cochlear implantation and other endocochlear surgical procedures.

HYPOTHESIS: The goal of this study was to create a three-dimensional model of the anatomy of the hook region to identify the optimal site for cochleostomy in cochlear implant surgery. BACKGROUND: The anatomy of the hook region is complex, and spatial relationships can be difficult to evaluate using two-dimensional histological slides or cadaveric temporal bones. METHODS: The right temporal bone of a 14-year-old adolescent boy was used to create a three-dimensional model. Sections containing the round window membrane (RWM) and surrounding cochlear structures were stained, digitized, and imported into a general purpose three-dimensional rendering and analysis software program (Amira, version 4.1). Three-dimensional models of the RWM, basilar membrane, osseous spiral lamina, spiral ligament, cochlear aqueduct, inferior cochlea vein, scala media, ductus reuniens, scala vestibuli, scala tympani, and surrounding bone were generated. The relationship between these structures and the RWM and adjacent otic capsule was evaluated. Histological sections from a different temporal bone were also analyzed. This temporal bone was sectioned in a plane perpendicular to the axis corresponding to the surgical view of the RWM, seen through the facial recess. RESULTS: The anteroinferior margin of the RWM or adjacent otic capsule was identified as the site for a cochleostomy that will avoid damage to critical cochlear structures and allow implantation directly into the scala tympani. The model can be downloaded from: https://research.meei.harvard.edu/otopathology/3dmodels. CONCLUSION: This three-dimensional model has implications for surgical procedures to the inner ear that aim to minimize insertional trauma.     

Evaluation of the insertion-trauma of the Nucleus Contour Advance electrode-array in a human temporal bone model

BACKGROUND: The development of intracochlear electrode arrays is aiming at a placement close to the modiolus with an insertion as atraumatic as possible. A new perimodiolar electrode model the Nucleus Contour Advance was to be evaluated regarding the possible intracochlear trauma. METHODS: The implantation of the Contour Advance electrode was performed in 11 frozen native temporal bones. Beneath a regular insertion in 5 temporal bones in 6 cases the insertion was carried out using the "advance-off-stylett" technique with a fixed stylett. The temporal bones were embedded in metacrylate based resin for histomorphological evaluation. The evaluation was performed regarding to the intracochlear placement close to the modiolus and the damage to intracochlear fine structures (basilar membrane, osseus spiral lamina). RESULTS: In 2 out of 11 cases we found a perforation from the scala tympani to the scala vestibuli independent of the insertion-technique. A severe intracochlear trauma was observed in one case with fracture of osseus spiral lamina using the AOS-technique. A close position to the modiolus could be achieved by insertion the scala tympani without perforation of the basilar membrane. CONCLUSIONS: The Nucleus Contour Advance electrode array showed minimal trauma in human temporal bones by using a standard insertion technique. By using the freehand AOS-technique a severe cochlear trauma is possible. Therefore further development in electrode design and the use of an insertion-tool is recommended.     

Kochleaimplantate im Felsenbeinpräparat

Background

For the functional outcome after cochlear implant surgery, the electrode position is of essential importance. Therefore, radiological techniques to localize the electrode within the cochlea are becoming increasingly important. In our study, we used multi-slice computed tomography (CT) to find radiological criteria to allocate the electrode within the cochlea.

Methods

Ten Nucleus 24 RCA electrodes were implanted into isolated human temporal bones using an extended cochleostomy and the Advance Off-Stylet technique. Five electrodes were implanted into the scala tympani and five into the scala vestibuli. After implantation, the temporal bones were blinded to the radiologist, and 64-slice CT scans were performed and analysed.

Results and conclusions

In all 10 cases, the surgical positioning of the electrode was equal to the radiological analysis of the CT scans. Radiological criteria were found that permit correct identification of the electrode within the cochlea. We think that this technique is sufficient for most questions concerning quality control and is widely available.     

人工耳蜗植入术后植入电极的影像学检查

目的 探讨建立螺旋CT扫描及三维重建技术观察人工耳蜗植入电极方法，并比较X线摄片方法与螺旋CT扫描三维重建方法的耳蜗内电极的影像学特征及其临床应用价值。方法 18例人工耳蜗植入患者全部作术后X线摄片检查。其中9例用经眼眶前后位摄片，9例采用侧斜位60。摄片。3例患者施行术后螺旋CT扫描及内耳三维重建方法。结果 2种投射头位的X线摄片均可显示电极形态及单个电极对，可间接判断电极在耳蜗内的植入深度。螺旋CT扫描三维重建图可直观地显示耳蜗形态、电极形态及其在耳蜗内植入的深度，可清晰识别单个电极对。结论 螺旋CT扫描三维重建方法可直观观察植入电极的形态及位置，可准确判断电极在耳蜗内植入的深度，有其独特的临床应用价值。     

The consequences of neural degeneration regarding optimal cochlear implant position in scala tympani: a model approach

Cochlear implant research endeavors to optimize the spatial selectivity, threshold and dynamic range with the objective of improving the speech perception performance of the implant user. One of the ways to achieve some of these goals is by electrode design. New cochlear implant electrode designs strive to bring the electrode contacts into close proximity to the nerve fibers in the modiolus: this is done by placing the contacts on the medial side of the array and positioning the implant against the medial wall of scala tympani. The question remains whether this is the optimal position for a cochlea with intact neural fibers and, if so, whether it is also true for a cochlea with degenerated neural fibers. In this study a computational model of the implanted human cochlea is used to investigate the optimal position of the array with respect to threshold, dynamic range and spatial selectivity for a cochlea with intact nerve fibers and for degenerated nerve fibers. In addition, the model is used to evaluate the predictive value of eCAP measurements for obtaining peri-operative information on the neural status. The model predicts improved threshold, dynamic range and spatial selectivity for the peri-modiolar position at the basal end of the cochlea, with minimal influence of neural degeneration. At the apical end of the array (1.5 cochlear turns), the dynamic range and the spatial selectivity are limited due to the occurrence of cross-turn stimulation, with the exception of the condition without neural degeneration and with the electrode array along the lateral wall of scala tympani. The eCAP simulations indicate that a large P(0) peak occurs before the N(1)P(1) complex when the fibers are not degenerated. The absence of this peak might be used as an indicator for neural degeneration.     

Reliability of cone beam computed tomography in scalar localization of the electrode array: a radio histological study

Postoperative imaging plays a growing role in clinical studies concerning prognostic factors in cochlear implantation. Indeed, intracochlear position of the cochlear implant has recently been identified as a contributor in functional outcomes and radiological tools must be accurate enough to determine the final placement of the electrode array. The aim of our study was to validate cone beam computed tomography as a reliable technique for scalar localization of the electrode array. We performed therefore a temporal bone study on ten specimens that were implanted with a perimodiolar implant prototype. Cone beam reconstructions were performed and images were analyzed by two physicians both experienced in cochlear implant imaging, who determined the scalar localization of the implant. Temporal bones then underwent histological control to document this scalar localization and hypothetical intracochlear lesions. In four cases, a dislocation from scala tympani to scala vestibuli was suspected on cone beam reconstructions of the ascending part of the basal turn. In three of these four specimens, dislocation in pars ascendens was confirmed histologically. In the remaining temporal bone, histological analysis revealed an elevation with rupture of the basilar membrane. Histological assessment revealed spiral ligament tearing in another bone. We conclude that cone beam is a reliable tool to assess scalar localization of the selectrode array and may be used in future clinical studies.     

Effects of inner ear trauma on the risk of pneumococcal meningitis

OBJECTIVE: To examine the risk of pneumococcal meningitis in healthy rats that received a severe surgical trauma to the modiolus and osseous spiral lamina or the standard insertion technique for acute cochlear implantation. DESIGN: Interventional animal studies. SUBJECTS: Fifty-four otologically normal adult Hooded-Wistar rats. INTERVENTIONS: Fifty-four rats (18 of which received a cochleostomy alone; 18, a cochleostomy and acute cochlear implantation using standard surgical techniques; and 18, a cochleostomy followed by severe inner ear trauma) were infected 4 weeks after surgery with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges in cochlear implant recipients with meningitis. RESULTS: Severe trauma to the osseous spiral lamina and modiolus increased the risk of pneumococcal meningitis when the bacteria were given via the middle or inner ear (Fisher exact test, P<.05). However, the risk of meningitis did not change when the bacteria were given via the hematogenous route. Acute electrode insertion did not alter the risk of subsequent pneumococcal meningitis for any route of infection. CONCLUSIONS: Severe inner ear surgical trauma to the osseous spiral lamina and modiolus can increase the risk of pneumococcal meningitis. Therefore, every effort should be made to ensure that cochlear implant design and insertion technique cause minimal trauma to the bony structures of the inner ear to reduce the risk of pneumococcal meningitis.