Implications of Phase Changes in Extracochlear Electrocochleographic Recordings During Cochlear Implantation

Area of Science:

• Otoacoustic Emissions and Auditory Evoked Potentials
• Neurosurgery and Otolaryngology

Background:

• Cochlear implantation (CI) is a common treatment for severe to profound hearing loss.
• Extracochlear electrocochleography (ECochG) is used to assess cochlear function.
• Understanding changes in ECochG during CI surgery is crucial for predicting hearing outcomes.

Purpose of the Study:

• To determine the frequency of phase changes in extracochlear ECochG during cochlear implantation.
• To investigate the relationship between these phase changes and post-operative hearing loss.

Main Methods:

• Extracochlear ECochG recordings were obtained before and after CI electrode insertion in 69 ears.
• Acoustic stimuli included tone bursts at 250, 500, 750, and 1000 Hz.
• Pure tone average (PTA) was measured pre- and post-surgery.

Main Results:

• Phase changes (≥45°) were observed in 23% of ECochG recordings.
• A phase change of ≥90° was associated with significantly greater post-operative hearing loss (26 dB vs. 17 dB).
• Ears with both amplitude drop and phase change showed near-complete loss of cochlear function.

Conclusions:

• Phase changes are a frequent occurrence during extracochlear ECochG in cochlear implantation.
• Significant phase changes (≥90°) may serve as an independent indicator of cochlear trauma or altered inner ear mechanics.
• These findings highlight the potential of ECochG phase changes to predict post-operative hearing outcomes.