Comparison of Temporal Bone Parameters before Cochlear Implantation in Patients with and without Facial Nerve Stimulation

Background and Objectives: Facial nerve stimulation (FNS) is a complication of cochlear implantation (CI). This study compared the thickness and density of the bone separating the upper basal turn of the cochlea (UBTC) and the labyrinthine segment of the facial nerve (LSFN) on preoperative computed tomography (CT) in patients with and without FNS after CI. Subjects and Methods: Adult patients who underwent CI from January 2011 to February 2017 with preoperative CT at a tertiary referral hospital were considered for this retrospective case-control study. Patients were divided into two groups: with FNS (n=4) and without FNS (n=53). The density and thickness of the bone between the LSFN and UBTC were measured on preoperative CT. Charts were reviewed for other parameters. Results: A statistically significant difference was seen in the thickness (p=0.007) but not in the density (p=0.125) of the bone between the UBTC and LSFN. Four patients had FNS at the mid-range electrode arrays, and one of them additionally had FNS at the basal arrays. Conclusions: Decreased thickness of the bone between the UBTC and LSFN can explain postoperative FNS, confirming the histologic and radiologic findings in previous studies, which indicated that the thickness of the temporal bone between the LSFN and UBTC is less in patients who experience FNS. While the density in this region was also less, it was not statistically significant.