Is Characteristic Frequency Limiting Real-Time Electrocochleography During Cochlear Implantation?

Area of Science:

• Audiology
• Neurosurgery
• Biomedical Engineering

Background:

• Electrocochleography (ECochG) aids in assessing hearing preservation during cochlear implantation.
• Estimating the impact on residual hearing is crucial for successful cochlear implant outcomes.

Purpose of the Study:

• To compare the efficacy of 250-Hz versus 500-Hz stimuli in detecting residual hearing decrement during cochlear implantation.
• To investigate if crossing the 500-Hz tonotopic place contributes to issues observed with 500-Hz stimuli.

Main Methods:

• Multifrequency ECochG using interleaved 250-Hz and 500-Hz stimuli to elicit cochlear microphonics (CMs) during insertion.
• Identifying significant ECochG drops (≥30% CM reduction) and correlating them with low-frequency pure tone average (LFPTA) shifts post-activation.
• Utilizing postoperative CT scans to assess cochlear dimensions and insertion depth.

Main Results:

• A stronger correlation (r=0.58) was found between 250-Hz ECochG drops and LFPTA shift in perimodiolar insertions compared to 500-Hz (r=0.31).
• Insertion tracings showed distinct tonotopic peaks for 250-Hz and 500-Hz stimuli, with the 500-Hz peak typically occurring more apically.
• In cases with smaller cochlear diameters and deeper insertions, the 500-Hz response maximum was often observed at non-apical electrodes.

Conclusions:

• The 250-Hz stimulus provides more reliable ECochG feedback for hearing preservation during cochlear implantation than the 500-Hz stimulus.
• Misinterpretation of the 500-Hz stimulus as intracochlear trauma can occur when the electrode advances beyond the 500-Hz characteristic frequency place.
• Multifrequency ECochG effectively distinguishes between cochlear trauma and electrode advancement beyond the characteristic frequency.