A State-of-the-Art Method for Preserving Residual Hearing During Cochlear Implant Surgery

Summary

The preservation of cochlear structures and possible residual hearing is one important factor to consider during cochlear implant surgery. Here, we present a state-of-the-art method for preserving residual hearing during cochlear implant surgery under local anesthesia.

Abstract

The developments in surgical techniques and cochlear implant (CI) electrode design have expanded the indications for CI treatment. Currently, patients with high-frequency hearing loss may benefit from CIs when low-frequency residual hearing can be preserved, as this enables combined electric-acoustic stimulation (EAS). The possible benefits of EAS include, for example, improved sound quality, music perception, and speech intelligibility in noise.

The risks of inner ear trauma and a deterioration or even complete loss of residual hearing vary according to the surgical technique and the type of electrode array used. Short, lateral-wall electrodes with shallower angular insertion depths have demonstrated higher rates of hearing preservation than longer electrodes. The very slow insertion of the electrode array through the round window of the cochlea contributes to insertion atraumaticity and, thus, may lead to favorable hearing preservation results. However, residual hearing can be lost even after an atraumatic insertion.

Electrocochleography (ECochG) can be used to monitor inner ear hair cell function during the insertion of the electrode. Several investigators have demonstrated that the ECochG responses during surgery may predict postoperative hearing preservation results.

In a recent study, we correlated the patients' subjective hearing perception with simultaneously recorded intracochlear ECochG responses during the insertion. This is the first report evaluating the association between intraoperative ECochG responses and hearing perception in a subject undergoing cochlear implantation under local anesthesia without sedation. The combination of intraoperative ECochG responses with the patient's real-time feedback to sound stimuli has excellent sensitivity for the intraoperative monitoring of cochlear function. This paper presents a state-of-the-art method for the preservation of residual hearing during CI surgery. We describe this treatment procedure with the special consideration of performing the surgery under local anesthesia, which makes it feasible for monitoring the patient's hearing during the insertion of the electrode array.

Introduction

Cochlear implantation is the only treatment in clinical use that restores the function of a sensory organ. Currently, cochlear implantation is applied to treat severe-to-profound sensorineural hearing loss in children and adults. The cochlear implant (CI) system consists of an implantable internal device that is combined with an external sound processor. The internal device is inserted during surgery through the mastoid cavity. The facial recess is opened to gain access to the middle ear and cochlea. The electrode array is inserted into the cochlea through the posterior tympanotomy and round window of the cochlea. The electrode array provides the electric stimulation ....

Protocol

The protocol was approved by the Institutional Review Board (5551877) and the Research Ethics Committee of the Northern Savo Hospital District (1690/2019) and was carried out according to the guidelines of the Declaration of Helsinki. Informed consent was taken from all of the patients who volunteered for the study.

1. Preoperative considerations

1. Assessment of the residual hearing threshold
   1. Ensure that the preoperative pure-tone threshold averages (PTA).......

Discussion

The optimal utilization of cochlear implantation is important for the effective management of hearing loss. The expansion of the indications for CI rehabilitation has created a grey zone where individualized decisions must be made regarding the rehabilitation modalities used. Nowadays, for patients with high-frequency hearing loss, there is a trend toward the provision of CIs. However, residual hearing in the low frequencies cannot be preserved in every patient. Cochlear monitoring via ECochG has been proposed a.......

Materials

Name	Company	Catalog Number	Comments
EarPhone and sound tube	AB/Cochlear/Medel		Usually provided by the company in sterile packages, can be inserted in ear without sterility issues
Ecocgh program	AB/Cochlear/Medel		AB and Medel provides software for clinical use. Also Cochlear has software for ECochG, atleas for research purposes.
Equipments for Cochlear implantation			Basic setup and instrumentation for Cochlear implantation, not spesific to the ECoGh or Subjective hearing monitoring
Laptop/tablet	AB/Cochlear/Medel		AB has tablet consept as "AIM" for intraoperative ECochG measuring. It is provided by the company. Cochlear and Medelare operated with laptop
Sound Processor	AB/Cochlear/Medel		Also company-specific, need for the connection to the electrode and measuring during the insertion