How Deleterious Is Facial Nerve Dissection for the Facial Nerve in Parotid Surgery: An Electrophysiological Evaluation.

Objective: This study was conducted to investigate subclinical electrophysiological deleterious effect due to microtrauma to the nerve in response to the dissection of a tumor and parotid tissue from the facial nerve and its branches and surgical traction experienced during the operation.
Methods: The study included 34 adult patients who underwent parotidectomy operations under intraoperative facial nerve monitoring. Three measurements were taken from each patient to evaluate facial nerve functions, with 3 stimuli of different intensities applied with different timing. An initial stimulus of 1 mA was applied to confirm the identification of the main trunk of the facial nerve (Group 1: Initial-Normal). Then, a threshold value was found by stimulating the main trunk until muscle fasciculations were observed on facial muscles (Group 2: Basal-Minimal). The same procedure was repeated after the tumor was resected (Group 3: Final-Minimal).
Results: There was no significant difference between the stimulus thresholds of Group 2 (0.31 mA) and Group 3 (0.30 mA). The highest amplitude in all 3 groups was observed at the mental branch, and the lowest at the frontal. The highest latency value was measured at the frontal branch and the lowest at the mental branch. Five (14.7%) of the patients developed postoperative pareses that was completely resolved by the seventh postoperative day visit in these patients.
Conclusion: This study demonstrated that the surgical trauma of a meticulously conducted dissection and surgical traction did not cause any deleterious electrophysiological alteration on the facial nerve.