Retrosigmoid Craniotomy for Auditory Brainstem Implantation in Adult Patients with Neurofibromatosis Type 2

Ten-year follow-up of auditory brainstem implants: From intra-operative electrical auditory brainstem responses to perceptual results

The auditory brainstem implant (ABI) can provide hearing sensation to individuals where the auditory nerve is damaged. However, patient outcomes with the ABI are typically much poorer than those for cochlear implant recipients. A major limitation to ABI outcomes is the number of implanted electrodes that can produce auditory responses to electric stimulation. One of the greatest challenges in ABI surgery is the intraoperative positioning of the electrode paddle, which must fit snugly within the cochlear nucleus complex. While there presently is no optimal procedure for intraoperative electrode positioning, intraoperative assessments may provide useful information regarding viable electrodes that may be included in patients' clinical speech processors. Currently, there is limited knowledge regarding the relationship between intraoperative data and post-operative outcomes. Furthermore, the relationship between initial ABI stimulation with and long-term perceptual outcomes is unknown. In this retrospective study, we reviewed intraoperative electrophysiological data from 24 ABI patients (16 adults and 8 children) obtained with two stimulation approaches that differed in terms of neural recruitment. The interoperative electrophysiological recordings were used to estimate the number of viable electrodes and were compared to the number of activated electrodes at initial clinical fitting. Regardless of the stimulation approach, the intraoperative estimate of viable electrodes greatly overestimated the number of active electrodes in the clinical map. The number of active electrodes was associated with long-term perceptual outcomes. Among patients with 10-year follow-up, at least 11/21 active electrodes were needed to support good word detection and closed-set recognition and 14/21 electrodes to support good open-set word and sentence recognition. Perceptual outcomes were better for children than for adults, despite a lower number of active electrodes.

Detailed insight in intraoperative eABR measurements to assist auditory brainstem implantation in a patient with neurofibromatosis type 2

Auditory brainstem implant (ABI) is used to provide auditory sensations in patients with neurofibromatosis type 2 who lost their hearing due to a surgical removal of the tumor. ABI surgery, implant activation and follow-up sessions present unique challenges including the exact placement of the electrode pad in the lateral recess of the IVth ventricle, identification of electrodes that trigger non-auditory sensation and their deactivation which lowers the number of electrodes responsible for hearing, changes of T- and C-levels across follow-up sessions. We present a complete procedure using an example case starting from the surgical part with the detailed description of intraoperative eABR measurement as a guidance for pad placement to the ABI activation and first fitting sessions with auditory sensation assessment. Since the first ABI electrode pad position presented non-satisfactory intraoperative eABR results it was decided to move the pad slightly which resulted in better eABR (more electrodes with auditory responses). The discussed patient demonstrated great auditory and speech perception results after the first ABI fitting (which included three sessions over 2 consecutive days). Repositioning of the ABI electrode pad during the surgery was carried out taking into account the intraoperative eABR results and this led to an overall positive outcome for the patient. The placement of ABI electrode pad is crucial for later auditory results. This study provides detailed insight in this very specialized procedure that is not performed in every clinic and adds to the knowledge of intraoperative navigation using eABR measurements during ABI surgery.

Effect of anesthesia on evoked auditory responses in pediatric auditory brainstem implant surgery

OBJECTIVE

Electrically evoked auditory brainstem responses (EABR) guide placement of the multichannel auditory brainstem implant (ABI) array during surgery. EABRs are also recorded under anesthesia in nontumor pediatric ABI recipients prior to device activation to confirm placement and guide device programming. We examine the influence of anesthesia on evoked response morphology in pediatric ABI users by comparing intraoperative with postoperative EABR recordings.

STUDY DESIGN

Retrospective review.

METHODS

Seven children underwent ABI surgery by way of retrosigmoid craniotomy. General anesthesia included inhaled sevoflurane induction and propofol maintenance during which EABRs were recorded to confirm accurate positioning of the ABI. A mean of 7.7 ± 2.8 weeks following surgery, the ABI was activated under general anesthesia or sedation (dexmedetomidine) and EABR recordings were made. A qualitative analysis of intraoperative and postoperative waveform morphology was performed.

RESULTS

Seven subjects (mean age 20.6 months) underwent nine ABI surgeries (seven primary, two revisions) and nine activations. EABRs were observed in eight of nine postoperative recordings. In three cases, intraoperative EABRs during general anesthesia were similar to postoperative EABRs with sedation. In one case, sevoflurane and propofol were used for intra- and postoperative recordings, and waveforms were also similar. In four cases, amplitude and latency changes were observed for intraoperative versus postoperative EABRs.

CONCLUSION

Similarity of EABR morphology in the anesthetized versus sedated condition suggests that anesthesia does not have a large effect on far-field evoked potentials. Changes in EABR waveform morphology observed postoperatively may be influenced by other factors such as movements of the surface array.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:507-513, 2020.

Auditory Brainstem Implants: Recent Progress and Future Perspectives

The auditory brainstem implant (ABI) was first developed nearly 40 years ago and provides auditory rehabilitation to patients who are deaf and ineligible for cochlear implant surgery due to abnormalities of the cochlea and cochlear nerve. The aims of the following review are to describe the history of the ABI and innovations leading up to the modern ABI system, as well as highlight areas of future development in implant design.

Pediatric Auditory Brainstem Implant Surgery

Auditory brainstem implants (ABIs) provide auditory perception in patients with profound hearing loss who are not candidates for the cochlear implant (CI) because of anatomic constraints or failed CI surgery. Herein, the authors discuss (1) preoperative evaluation of pediatric ABI candidates, (2) surgical approaches, and (3) contemporary ABI devices and their use in the pediatric population. The authors also review the surgical and audiologic outcomes following pediatric ABI surgery. The authors' institutional experience and the nearly 200 cases performed in Europe and the United States indicate that ABI surgery in children can be safe and effective.