Association Between Cochlear Nerve Deficiency Grade and Cerebrospinal Fluid Gusher in Incomplete Partition Type I Ears

OBJECTIVE: To investigate whether the severity of cochlear nerve deficiency (CND) on preoperative MRI predicts the risk of cerebrospinal fluid (CSF) gusher during cochlear implantation (CI) in incomplete partition type I (IP-I) malformation. PATIENTS: Between 2020 and 2025, 12 ears with IP-1 from 10 patients underwent CI at a single tertiary referral hospital. INTERVENTION: CND was graded on internal auditory meatus MRI images (IAM grade 2 to 3 = severe CND; grade 4 = mild/normal). CSF gusher was recorded intraoperatively. Associations were analyzed using Fisher exact test and Firth bias-reduced logistic regression. MAIN OUTCOME MEASURES: CSF gusher was recorded intraoperatively. Associations were analyzed using Fisher exact test and Firth's bias-reduced logistic regression. RESULTS: CSF gusher occurred in 7 of 13 ears (58.3%). All ears with severe CND (IAM Gr 2 to 3) exhibited gusher (5/5, 100%), whereas most ears with mild/normal CND (IAM Gr 4) did not (5/6, 83.3%). Fisher exact test showed a significant association between CND grade and CSF gusher ( P = 0.015). Firth logistic regression yielded an odds ratio of 40.3 (95% CI: 0.97-1669.4), indicating higher odds of CSF gusher in ears with severe CND. CONCLUSIONS: Greater CND severity on MRI correlates with increased likelihood of CSF gusher in IP-I malformation. CND grading may serve as a useful imaging marker for preoperative risk assessment and surgical planning in CI for IP-I ears.