Scala vestibuli cochlear implant supported by 3D modeling of the inner ear

SummaryPatients with scala tympani (ST) ossification present a distinct surgical challenge. Three-dimensional (3D) segmentation of the inner ear offers accurate identification of ossification and surgical planning of the cochleostomy to access the scala vestibuli. The scala vestibuli placement of cochlear implantation electrode is an alternate solution in these patients and is well supported by the literature.The present report describes a case of cochlear implantation in the scala vestibuli assisted by 3D segmentation of the cochlea for a patient with ossification in the ST and reviews the relevant literature. Clinical presentation of a 45-year-old Austrian female who was referred with a history of sudden sensorineural hearing loss 2 years ago in the right ear, confirmed by pure tone audiometry (PTA) and acoustically evoked auditory brainstem response (ABR). 3D segmentation of the inner ear identified the extent of ossification in the ST and assisted in the surgical planning of cochleostomy drilling anterior-superior to the round window to access the scala vestibuli for the electrode placement. Postoperative computed tomography (CT) to confirm the electrode placement in the scala vestibuli and PTA was performed to assess the hearing threshold following the cochlear implantation. Postoperative CT confirmed the full insertion of a flexible electrode. The hearing threshold measured by PTA was ≤ 40 dB across all frequencies tested. Review of the literature identified a total of 13 published reports on cochlear implantation electrode placement in scala vestibuli in cases with ossification in the ST.

Scalar localisation of peri-modiolar electrodes and speech perception outcomes

ObjectiveTo identify the intracochlear electrode position in cochlear implant recipients and determine the correlation to speech perception for two peri-modiolar electrode arrays.MethodsPost-operative cone-beam computed tomography images of 92 adult recipients of the ‘CI512’ electrode and 18 adult recipients of the ‘CI532’ electrode were analysed. Phonemes scores were recorded pre-implantation, and at 3 and 12 months post-implantation.ResultsAll CI532 electrodes were wholly within scala tympani. Of the 79 CI512 electrodes intended to be in scala tympani, 58 (73 per cent) were in scala tympani, 14 (17 per cent) were translocated and 7 (9 per cent) were wholly in scala vestibuli. Thirteen CI512 electrodes were deliberately inserted into scala vestibuli. Speech perception scores for post-lingual recipients were higher in the scala tympani group (69.1 per cent) compared with the scala vestibuli (54.2 per cent) and translocation (50 per cent) groups (p < 0.05). Electrode location outside of scala tympani independently resulted in a 10.5 per cent decrease in phoneme scores.ConclusionCone-beam computed tomography was valuable for demonstrating electrode position. The rate of scala tympani insertion was higher in CI532 than in CI512 electrodes. Scala vestibuli insertion and translocation were associated with poorer speech perception outcomes.

Evaluation of the Relationship between the NRT-Ratio, Cochlear Anatomy, and Insertions Depth of Perimodiolar Cochlear Implant Electrodes

The position of the cochlear implant electrode array within the scala tympani is essential for an optimal postoperative hearing benefit. If the electrode array changes in between the scalae intracochlearly (i.e., from scala tympani to scala vestibuli), a reduced auditory performance can be assumed. We established a neural response telemetry-ratio (NRT-ratio) which corresponds with the scalar position of the electrodes but shows within its limits a variability. The aim of this study was to determine if insertion depth angle or cochlea size influences the NRT-ratio. The intraoperative electrophysiological NRT data of 26 patients were evaluated. Using a flat panel tomography system, the position of the electrode array was evaluated radiologically. The insertion depth angle of the electrode, the cochlea size, and the NRT-ratio were calculated postoperatively. The radiological results were compared with the intraoperatively obtained electrophysiological data (NRT-ratio) and statistically evaluated. In all patients the NRT-ratio, the insertion depth angle, and the cochlea size could be determined. A significant correlation between insertional depth, cochlear size, and the NRT-ratio was not found. The NRT-ratio is a reliable electrophysiological tool to determine the scalar position of a perimodiolar electrode array. The NRT-ratio can be applied independent from insertion depth and cochlear size.

Semiautomatic Cochleostomy Target and Insertion Trajectory Planning for Minimally Invasive Cochlear Implantation

A major component of minimally invasive cochlear implantation is atraumatic scala tympani (ST) placement of the electrode array. This work reports on a semiautomatic planning paradigm that uses anatomical landmarks and cochlear surface models for cochleostomy target and insertion trajectory computation. The method was validated in a human whole head cadaver model (n=10ears). Cochleostomy targets were generated from an automated script and used for consecutive planning of a direct cochlear access (DCA) drill trajectory from the mastoid surface to the inner ear. An image-guided robotic system was used to perform both, DCA and cochleostomy drilling. Nine of 10 implanted specimens showed complete ST placement. One case of scala vestibuli insertion occurred due to a registration/drilling error of 0.79 mm. The presented approach indicates that a safe cochleostomy target and insertion trajectory can be planned using conventional clinical imaging modalities, which lack sufficient resolution to identify the basilar membrane.