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

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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.


Tertiary referral center.


The study included 73 patients with IP-II that underwent cochlear implant surgery between 2002 and 2017.


Analysis of preoperative temporal bone computed tomography (CT) scans and surgical records.

Main Outcome Measures:

Preoperative CT modiolar anomalies and intraoperative CSF leakage status.


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.


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.

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