In-Vivo Detection of the Facial Nerve From Adjacent Tissues Using Microelectrodes With Selective Passivation During Parotidectomy

Iatrogenic facial nerve injury often occurs during parotidectomy owing to the difficulty associated with accurately locating the facial nerve from adjacent tissues (parotid gland and muscle). This injury causes postoperative facial nerve dysfunction, leading to functional and/or cosmetic problems. In this study, we propose an in-vivo detection method to distinguish the facial nerve from the adjacent tissues using electrochemical impedance spectroscopy (EIS). The electrical impedance of the facial nerve, parotid gland, and muscle via in-vivo experiments using guinea pigs (n = 3) was measured using microelectrodes on polyimide film (MoP), consisting of detection and connection parts. The connection part was selectively coated with a photoresist that exhibits high resistivity to attenuate a distortion of the sensor output. Statistically significant differences in impedance of the real and imaginary parts were observed between the facial nerve and the adjacent tissues in the frequency range of 0.99 kHz to 1 MHz (p-value < 0.05, t-test). Optimal frequency, where the difference between adjacent tissues and facial nerve had the most distinction, were 13.64 kHz in the imaginary part of impedance. Additionally, the estimated electrical properties (conductivity and permittivity) of the facial nerve and adjacent tissues were statistically distinguishable (p-value < 0.05, t-test). These findings indicate that MoP with EIS could enable surgeons to easily locate the facial nerve during parotidectomy.