Intraoperative facial nerve monitoring during cochlear implant surgery: an observational study

Iatrogenic facial nerve injury is one of the most severe complications of cochlear implantation (CI) surgery. Intraoperative facial nerve monitoring (IFNM) is used as an adjunctive modality in a variety of neurotologic surgeries. The purpose of this retrospective study was to assess whether the use of IFNM is associated with postoperative facial nerve injury during CI surgery. The medical charts of 645 patients who underwent CI from 1999 to 2014 were reviewed to identify postoperative facial nerve palsy between those who did and did not receive IFNM. Four patients (3 children and 1 adult) were found to have delayed onset facial nerve weakness. IFNM was used in 273 patients, of whom 2 had postoperative facial nerve weakness (incidence of 0.73%). The incidence of facial nerve weakness was 0.54% (2/372) in the patients who did not receive IFNM. IFNM had no significant effect on postoperative delayed facial palsy (P = 1.000). All patients completely recovered within 3 months after surgery. Interestingly, all 4 cases of facial palsy received right CI, which may be because all of the surgeons in this study used their right hand to hold the drill. When right CI surgery is performed by a right-handed surgeon, the shaft of the drill is closer to the inferior angle of the facial recess, and it is easier to place the drilling shaft against the medial boundary (facial nerve) when the facial recess is small. The facial nerve sheaths of another 3 patients were unexpectedly dissected by a diamond burr during the surgery, and the monitor sounded an alarm. None of these 3 patients developed facial palsy postoperatively. This suggests that IFNM could be used as an alarm system for mechanical compression even without current stimulation. Although there appeared to be no relationship between the use of monitoring and delayed facial nerve palsy, IFNM is of great value in the early identification of a dehiscent facial nerve and assisting in the maintenance of its integrity. IFNM can still be used as an additional technique to optimize surgical success.