Monitoring residual hearing during cochlear implantation by intra-operative brainstem audiometry

Intra-operative hearing monitoring methods in middle ear surgeries

Hearing loss is a condition affecting millions of people worldwide. Conductive hearing loss (CHL) is mainly caused by middle ear diseases. The low frequency area is the pivotal part of speech frequencies and most frequently impaired in patients with CHL. Among various treatments of CHL, middle ear surgery is efficient to improve hearing. However, variable success rates and possible needs for prolonged revision surgery still frustrate both surgeons and patients. Nowadays, increasing numbers of researchers explore various methods to monitor the efficacy of ossicular reconstruction intraoperatively, including electrocochleography (ECochG), auditory brainstem response (ABR), auditory steady state response (ASSR), distortion product otoacoustic emissions (DPOAE), subjective whisper test, and optical coherence tomography (OCT). Here, we illustrate several methods used clinically by reviewing the literature.

Using the Implant Electrode Array to Conduct Real-time Intraoperative Hearing Monitoring During Pediatric Cochlear Implantation: Preliminary Experiences

OBJECTIVES

To present the preliminary experiences and findings from a pilot study evaluating a novel technique for monitoring cochlear electrophysiological function during electrode insertion in cochlear implantation surgery.

STUDY DESIGN

Prospective pilot cohort study.

SETTING

Tertiary academic neuro-otology center.

PATIENTS

Pediatric patients with residual hearing undergoing hearing preservation cochlear implant surgery.

INTERVENTION

Monitoring of intraoperative cochlear microphonics during cochlear implant surgery.

MAIN OUTCOME MEASURE

Intraoperative intracochlear microphonic measurement, preservation of these responses postoperatively and preservation of hearing as measured by audiometry.

RESULTS

Intracochlear microphonics could be identified in both patients presented and were preserved during the surgical procedure and postoperatively. The preservation of intracochlear microphonics correlates with preservation of hearing.

CONCLUSION

The novel approach using the electrode array to detect and measure intracochlear microphonics during cochlear implantation surgery shows promise as an instrument to alert the operating surgeon to hair cell damage during electrode insertion. Further refinement of the technique is required to better understand the measurements and correlate these with pre- and postoperative hearing and risk of hearing loss from surgery. Improvements in the software algorithm will reduce the time required for each measurement, leading to the development a more real-time monitoring technique.

[Surgical technique in cochlear implantation]

The cochlear implant (CI) has become a standard option for treating prelingually deaf children. But postlingual late deafness in adults is becoming increasingly common. In addition, hybrid implantation with a CI and a hearing aid in the same ear has come into focus, which demands a soft insertion technique that spares the apical parts of the cochlea. Also, the chorda tympani should be saved, especially in bilateral implantations, which are gaining importance because improved speech discrimination in noisy conditions is seen as proven today. Control of the electrode position intraoperatively with intraoperative computed tomography can further increase the safety and reliability of the position. The position and length of the skin incision is a more aesthetic issue. Future developments will include fully implantable CIs and navigation-assisted, minimally invasive drilling of a hole from the surface of the skull into the cochlea. Bioactive, neurotrophic-drug-releasing electrode designs for improved and sustainable connectivity to the neurons may become applicable.