Introduction
In surgery for benign parotid tumors, the tumor must be completely removed while ensuring that the facial nerve is preserved. To achieve this, it is important to understand the positional relationship of the tumor and the facial nerve before surgery. Delineating the facial nerve using MRI or ultrasound is generally difficult, but in recent years, intraoperative facial nerve monitoring (FNM) has been used as an assistive method 1). Using FNM in parotid surgery provides a more reliable confirmation of the course of the facial nerve and has led to reports of reduced frequency of postoperative facial nerve palsy 2, 3) and a shorter operative time 4). However, some authors have reported that the use of FNM does not change the rate of postoperative facial nerve palsy 5, 6). Postoperative facial nerve palsy is the most important complication in parotid surgery, and even if the facial nerve can be reliably preserved during surgery, some paralysis is likely to occur. Even if it is transient, facial nerve palsy can decrease patients’ quality of life until recovery.
Whether the use of FNM during surgery can predict postoperative facial nerve palsy is also an interesting question. Maier et al. 7) analyzed the electromyography recordings of 37 patients who underwent parotid surgery with intraoperative FNM and reported that it was difficult to predict postoperative facial nerve palsy despite this assistance. Meanwhile, Mamelle et al. 8) measured the amplitude of response to stimulation at the facial nerve trunk before and after tumor resection in 50 patients who underwent parotid surgery, and reported that it was significantly lower after resection in patients who developed paralysis than in those who did not.
Here, we examined a new method for predicting facial nerve palsy after parotid surgery by using intraoperative FNM.