Facial nerve stimulation in the narrow bony cochlear nerve canal after cochlear implantation

Objectives/Hypothesis To evaluate the correlation between a narrow bony cochlear nerve canal (BCNC) and facial nerve stimulation (FNS) after cochlear implantation (CI) and their underlying mechanisms and to predict the risk of FNS preoperatively. Study Design Retrospective cohort study. Methods A total of 64 pediatric cases that underwent CI were included. Among them, 32 cases experienced FNS after CI, and another 32 cases were selected from 817 pediatric implantees by stratified random sampling. The width of the BCNC, the status of the cochlear nerve (CN) and the internal auditory canal (IAC), T level, and C level were compared and analyzed. Strategies for eliminating FNS were also analyzed. Results The FNS group showed a narrower BCNC (1.09 ± 0.52 mm) than the control group (1.99 ± 0.61 mm; P <.01), a lower CN/facial nerve ratio (0.32 ± 0.36) than the control group (1.34 ± 0.76; P <.01), and narrower IAC diameter (4.06 ± 1.71 mm) than the control group (5.66 ± 1.36 mm; P <.01). The FNS group also showed higher T level (165.7 ± 28.3 μA) than the control group (142.2 ± 21.2 μA; P <.01). Adjustment of the C levels and/or pulse width and switching off offending electrodes were attempted to eliminate FNS, with a 75.0% success rate. The FNS group still showed low Categories of Auditory Performance scores (3.00 ± 1.90) compared with the control group (5.94 ± 1.41, P <.01) after adjustment. Conclusions A narrow BCNC could be a cause of FNS after CI. Therefore, careful selection of the side for CI and programming strategies are required to reduce FNS.