The Role of Cochlear Anatomy in Hearing Preservation After Cochlear Implantation in Adults: A Systematic Review.

OBJECTIVE

To evaluate the association between cochlear anatomical parameters and postoperative hearing preservation (HP) following cochlear implantation in adults with preoperative residual hearing (RH).

METHODS

This systematic review followed PRISMA guidelines (PROSPERO: CRD420250630915). Embase, MEDLINE, PubMed, Scopus, and Web of Science were searched for studies published between 2010 and 2026. Eligible studies included adults (≥ 18 years) with preoperative RH undergoing cochlear implantation, assessed cochlear anatomy using computed tomography or magnetic resonance imaging, reported HP within 6 months postoperatively, and examined the relationship between cochlear anatomy parameter(s) and HP. Risk of bias was evaluated using the QUIPS tool. Data were synthesized narratively; where possible, a meta-analysis using a random-effects model was performed. Certainty of evidence was assessed using GRADE.

RESULTS

Ten studies (487 implants) were included. Risk of bias was highest for study participation and confounding. Longer cochlear duct length and larger cochlear volume were suggested to be associated with better HP, though findings were inconsistent. Six studies examined angular insertion depth; four were pooled. Meta-analysis indicated a small positive correlation (pooled r = 0.23; p = 0.004; 95% confidence interval: -0.14 to 0.54), suggesting poorer HP with deeper insertion, with moderate heterogeneity (I 2 = 48.5%). Certainty of evidence for all outcomes was rated very low.

CONCLUSION

Cochlear anatomy may influence hearing preservation following cochlear implantation, with longer cochlear duct length and larger cochlear volume showing the most consistent associations with favorable outcomes. However, the certainty of evidence was very low, precluding firm conclusions regarding the predictive value of anatomical factors.

LEVEL OF EVIDENCE: 3.