Evaluation of Cochlear Implant Receiver Position and Its Temporal Changes

Customized Cochlear Implant Positioning in a Patient With a Low- Grade Glioma: Towards the Best MRI Artifact Management

OBJECTIVE

To report the personalized decision-making pro- cess adopted for a cochlear implant (CI) candidate requiring magnetic resonance imaging (MRI) brain surveillance.

STUDY DESIGN

Clinical capsule report.

SETTING

Tertiary academic referral center.

PATIENT

A 23-year-old man affected by posttraumatic bilat- eral profound hearing loss, already in radiological follow-up for a suspected small left cuneal low-grade glioma.

INTERVENTIONS

A multidisciplinary approach involving preoperative MRI simulations and 3D printed (3DP) models aiming to adapt the CI position to facilitate MRI brain lesion visibility.

MAIN OUTCOME MEASURES

MRI visibility and surgical approach.

RESULTS

Preoperative MRI scans with the placement of an Ultra 3D CI were performed simulating different implant location to assess the brain lesion visibility in MRI. CI was positioned 9 cm away from the external auditory canal with an angle of 90 degrees. To assess the technical feasibility of the surgical procedure, a patient-specific 3DP head model was produced preoperatively. The postoperative course was uneventful, the patient showed a significant benefit from CI, and the brain lesion was highly visible at the MRI follow-up.

CONCLUSIONS

The employment of strategies aimed at improving the MRI quality in CI recipients still represents a topic requiring attention. Thanks to multidisciplinary team collaboration, in our case, the CI position was successfully determined to allow unhindered MRI visibility of a specific intracranial structure.

Clinical Translation of an Insertion Tool for Minimally Invasive Cochlear Implant Surgery

The objective of this paper is to describe the development of a minimally invasive cochlear implant surgery (MICIS) electrode array insertion tool concept to enable clinical translation. First, analysis of the geometric parameters of potential MICIS patients (N = 97) was performed to inform tool design, inform MICIS phantom model design, and provide further insight into MICIS candidacy. Design changes were made to the insertion tool based on clinical requirements and parameter analysis results. A MICIS phantom testing model was built to evaluate insertion force profiles in a clinically realistic manner, and the new tool design was evaluated in the model and in cadavers to test clinical viability. Finally, after regulatory approval, the tool was used for the first time in a clinical case. Results of this work included first, in the parameter analysis, approximately 20% of the population was not considered viable MICIS candidates. Additionally, one 3D printed tool could accommodate all viable candidates with polyimide sheath length adjustments accounting for interpatient variation. The insertion tool design was miniaturized out of clinical necessity and a disassembly method, necessary for removal around the cochlear implant, was developed and tested. Phantom model testing revealed that the force profile of the insertion tool was similar to that of traditional forceps insertion. Cadaver testing demonstrated that all clinical requirements (including complete disassembly) were achieved with the tool, and the new tool enabled 15% deeper insertions compared to the forceps approach. Finally, and most importantly, the tool helped achieve a full insertion in its first MICIS clinical case. In conclusion, the new insertion tool provides a clinically viable solution to one of the most difficult aspects of MICIS.

Effect of head position on cochlear implant MRI artifact

PURPOSE

A new generation of cochlear implant (CI) magnets and specific surgical techniques (e.g., implant positioning) has changed the relationship between a CI and magnet resonance imaging (MRI). MRI allows a pain free in vivo evaluation of the inner ear fluid state and internal auditory canal after the insertion of an electrode. The aim of this study is to evaluate how the patient's head position in the MRI scanner influences the CI magnet-related artefact.

METHODS

We performed in vivo measurement of MRI artefacts at 3 T with a CI system containing a bipolar diametrical magnet. The implant magnet was positioned with a head bandage at different positions from the nasion and external auditory canal in three volunteers. We used a turbo spin echo (TSE) T2w sequence on the axial and coronal planes and observed three positions: (1) regular position, (2) chin to chest (anteflexion), and (3) hyperextension (retroflexion).

RESULTS

By comparing the positions, anteflexion of the cervical spine in a chin-to-chest position allowed us to place the artefact in a more apical position from the IAC in the coronal plane. The hyperextension of the cervical spine position shifts the artefact father towards the cochlea's direction.

CONCLUSION

The head's position can influence the location of MRI artefacts. In cases where the artefact diminished the IAC or cochlea, anteflexion of the cervical spine in the chin-to-chest position of the head in the MRI scanner should be attempted to allow a visualization of the IAC.

Cochlear Implant Receiver Location and Migration: Experimental Validation Pilot Study of a Clinically Applicable Screening Method

Objectives: Postoperative follow-up after cochlear implantation lacks a reliable screening method to detect cochlear implant receiver device migration. This study aims to validate a clinically applicable method to assess the position and migration of the cochlear implant receiver device.

Study design: Validation study.

Setting: Tertiary university medical center.

Participants and method: To assess the cochlear implant receiver device location, round markers representing the external magnet were placed on both sides of the head of volunteers. Four independent clinicians took measurements of the distances between reference points on the head and the center of the marker. The reference points were: the lateral canthus (LC), tragus tip (TT), the mastoid angle (MA), and the mandibular angle (AM).

Main outcome measures: The inter-clinician reliability was determined by calculating the intraclass correlation coefficient (ICC) and confidence interval (CI) with a two-way mixed model and both consistency and absolute agreement types for each distance.

Results: Eight volunteers were included resulting in 16 individual cases. The consistency type ICC's for each reference point were: LC 0.90 (CI = 0.80, 0.96), TT 0.83 (CI = 0.69, 0.93), MA 0.75 (CI = 0.56, 0.89), and AM 0.29 (CI = 0.05, 0.59). The absolute agreement ICC's were: LC 0.87 (CI = 0.73, 0.95), TT 0.83 (CI = 0.68, 0.93), MA 0.68 (CI = 0.42, 0.86), and AM 0.18 (CI = 0.01, 0.46). The inter-clinician reliability was good to excellent for the lateral canthus and tragus tip reference points.

Conclusions: The cochlear receiver device location can be assessed reliably by measuring the distance between the LC, TT, and the external magnet. This method can be used to registrate implant receiver location after implantation and detect implant migration postoperatively.

[Postoperative imaging of the internal auditory canal : Visualization of active auditory implants. German version]

BACKGROUND

Assessment of the internal auditory canal (IAC) and the cochlea is of central importance in neurotology. The artefacts and visibility of the different types of active auditory implants in MRI vary, due to their specific ferromagnetic components. Knowledge of the size of MRI artefacts and the options for handling these is important for the auditory rehabilitation of specific diseases (e. g., vestibular schwannoma).

METHODS

The current paper is a literature review RESULTS: MRI assessment of the IAC and cochlea after surgical placement of an active auditory implant is feasible only with a percutaneous bone-anchored hearing aid (BAHA, Ponto). When specific factors (implant position and MRI sequence) are taken into consideration, these structures can be visualized even after cochlear implantation. Complications such as magnet dislocation and pain may occur.

CONCLUSION

The possibility of assessing the IAC and cochlea by MRI is an important aspect that needs to be taken into consideration when planning the auditory rehabilitation of patients after acoustic neuroma surgery.

Postoperative imaging of the internal auditory canal : Visualization of active auditory implants

BACKGROUND

Assessment of the internal auditory canal (IAC) and cochlea is of central importance in neurotology. The artefacts and visibility of active auditory implants on magnetic resonance imaging (MRI) vary because of their specific magnetic components. Knowledge of the size of MRI artefacts and the options for handling them is important for the auditory rehabilitation of specific diseases (e. g., vestibular schwannoma).

METHODS

The current article is a literature review.

RESULTS

MRI assessment of the IAC and cochlea after surgical placement of an active auditory implant is feasible only with a percutaneous bone-anchored hearing aid (BAHA, Ponto). When specific factors (implant position and MRI sequence) are taken into consideration, these structures can be visualized even after cochlear implantation. Complications such as magnet dislocation and pain may occur.

CONCLUSION

The possibility of assessing the IAC and cochlea by MRI is an important aspect that needs to be taken into consideration when planning the auditory rehabilitation of patients after acoustic neuroma surgery.