Quantifying Residual Hearing Loss from Electrode Insertion Trauma in Cochlear Implant Surgery: A Prospective Double-Blind Study

BACKGROUND: The aim is to quantify the electrode insertion trauma-induced hearing loss (EITHL), its risk factors, and its impact on speech outcomes in prelingually deafened children undergoing cochlear implantation. METHODS: This was a prospective, observational study conducted at a single center between 2021 and 2024. Forty children aged 1-5 years with severe-to-profound sensorineural hearing loss underwent cochlear implantation using either the cochleostomy or round-window (RW) techniques. Auditory steady-state response (ASSR) thresholds were utilized to assess hearing preservation levels. Speech outcomes were evaluated by measuring word recognition scores (WRS) at 6, 12, and 24 months. The correlation between electrode insertion depth, hearing preservation, and speech outcomes was analyzed. RESULTS: All participants achieved Grade 1 hearing preservation (>75%). The mean hearing preservation rates at 3, 6, 9, and 12 months were 93.2%, 92.3%, 92.9%, and 92.1%, respectively. Although the RWT demonstrated better hearing preservation than the CS technique, the difference was not statistically significant. A significant increase in low-frequency hearing thresholds was observed over time, with 12-month values of 84.9 ± 3.5 dB (250 Hz), 90.2 ± 3.7 dB (500 Hz), and 92.4 ± 4.0 dB (1000 Hz). A negative correlation was found between the depth of electrode insertion and hearing preservation (r=-0.45, P=.03). Word recognition scores improved over time, with bilateral implant recipients showing significantly higher scores (P < .00). CONCLUSION: Cochlear implantation via both CS and RW approaches preserves residual hearing in prelingually deafened children, with RW insertion demonstrating superior preservation. Deeper electrode insertion is associated with poorer hearing preservation, while better hearing preservation correlates with improved speech outcomes.