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

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.