Iatrogenic facial nerve exposure in cochlear implant surgery: incidence and clinical significance in the absence of intra-operative nerve monitoring

Objectives: Iatrogenic facial nerve injury is one of the most feared complications of cochlear implantation. Intraoperative facial nerve monitoring is used as an adjunctive modality in a variety of neurotologic surgeries including cochlear implantation. With the lack of nerve monitoring, there is a theoretically higher risk of iatrogenic fallopian canal dehiscence with facial nerve exposure, particularly the mastoid portion, during cochlear implant surgery. The purpose of this study is to determine the incidence of iatrogenic exposure of the facial nerve and its relation to the incidence of post-operative facial paralysis in the absence of facial nerve monitoring. Methods: This was a retrospective study. Medical charts of 307 patients who underwent cochlear implantation without facial nerve monitoring, from 2012 to 2017 were reviewed to identify cases with a reported iatrogenic defect over the mastoid facial nerve. The incidence of post-operative facial palsy was determined and compared to the incidence with the use of intra-operative monitoring which has been reported in the literature. Results: The incidence of iatrogenic dehiscence with facial nerve exposure was 46.58%. However, the incidence of post-operative facial palsy was only 2.1% which decreased to 0.72% in cases without injury of the facial neural sheath. This was not significantly different from the 0.73% rate reported in the literature with the use of intra-operative facial monitoring (P = 0.99). Conclusion: The incidence of iatrogenic facial nerve exposure during cochlear implantation may be relatively high. However, no additional risk of post-operative facial nerve paralysis was found, provided that the integrity of the neural sheath was preserved, even with the lack of intra-operative monitoring.