The Association Between Modiolar Base Anomalies and Intraoperative Cerebrospinal Fluid Leakage in Patients With Incomplete Partition Type-II Anomaly: A Classification System and Presentation of 73 Cases

Objective:Modiolus and modiolar base abnormalities in patients with incomplete partition-II anomaly (IP-II) increase the risk of intraoperative cerebrospinal fluid (CSF) leakage. This study aimed to classify modiolar abnormalities and define objective radiological measures for preoperatively evaluating intraoperative CSF leakage risk.Study Design:Retrospective case series.Setting:Tertiary referral center.Patients:The study included 73 patients with IP-II that underwent cochlear implant surgery between 2002 and 2017.Intervention:Analysis of preoperative temporal bone computed tomography (CT) scans and surgical records.Main Outcome Measures:Preoperative CT modiolar anomalies and intraoperative CSF leakage status.Results:Among the 73 patients (41 men and 32 women), mean age at cochlear implant surgery was 11.4 (range, 0-42) years. Preoperative CT-based modiolar base anomaly classification was as follows: grade 1 (complete modiolus, n=1), grade 2 (thin plate of bone in the modiolar base+partial modiolus, n=14); grade 3 (thin plate of bone in the modiolar base, n=53); grade 4 (total modiolar base defect, n=5). The gusher rate was 8%. All patients with grade 4 anomaly had an intraoperative gusher. Patients with grade 3 anomaly accounted for 86% of oozing cases. Oozing, pulsation, and no CSF leakage rates were similar in those with grade 2 anomaly.Conclusions:The modiolus and modiolar base must be carefully evaluated in patients with IP-II. Gushers primarily occur in IP-II patients with grade 4 anomaly. A thin plate of bone in the modiolar base most commonly prevents gushers.