Scala Tympani Volume Influences Initial 6-Month Hearing Preservation With Lateral Wall Electrode Arrays.

Objectives: To examine the effects of scala tympani (ST) volume, cochlear duct length (CDL), and angular insertion depth (AID) on low-frequency hearing preservation for cochlear implant (CI) recipients of lateral wall electrode arrays.

Methods: A retrospective review identified 45 adult CI recipients of 24-, 28-, or 31.5-mm lateral wall electrode arrays with preoperative unaided hearing thresholds ≤45 decibel hearing level (dB HL) at 250 Hz. All patients underwent preoperative and postoperative computed tomography to evaluate cochlear morphology and electrode array position. A linear mixed effects model evaluated effects of ST volume, CDL, AID, preoperative low-frequency pure-tone average (LFPTA; 125, 250, and 500 Hz), age at surgery, and biological sex on the postoperative change in LFPTA at activation and 6 months post-activation.

Results: There were significant main effects of ST volume (p = 0.044), age (p = 0.028), and biological sex (p = 0.003), indicating better low-frequency hearing preservation for CI recipients with larger ST volumes, younger age at surgery, and female biological sex. Although CDL positively correlated with ST volume (r = 0.74, p < 0.001), there was no significant main effect of CDL (p = 0.367). A broad range in AID of the most apical electrode contact was observed (301.4°-681.8°); however, there was no significant main effect of AID on low-frequency hearing preservation (p = 0.700).

Conclusions: During the initial 6 months following implantation, intrinsic factors such as cochlear morphology may have a greater impact on low-frequency hearing preservation than apical positioning of a flexible lateral wall electrode array when using soft surgical techniques.

Level of evidence: 3 Laryngoscope, 2024.