Novel method for the detection of the facial nerve using electrical impedance spectroscopy during otologic surgery

Abstract

Iatrogenic facial nerve injuries, which may occur during otologic surgery, can cause facial paralysis that eventually leads to devastating complications such as cosmetic problems, limitation to eye lubrication, and problems with eating, drinking, and speaking. We aimed to prevent iatrogenic nerve injury using an electrical impedance spectroscopy (EIS) technique and developed a facial nerve detector (FND) with coplanar bipolar electrodes on a flexible polyethylene terephthalate film using micro electro-mechanical systems technology. The discrimination capability of the FND was preliminarily evaluated by analyzing electrical impedances of solutions of various concentrations of phosphate-buffered saline and by extracting sample resistance using curve fitting with an electrical equivalent circuit. The impedances of bone, facial nerve covered by thin bone, and facial nerve of a cadaver were investigated using the optimal frequency range obtained based on the proposed discrimination index. To generalize the sensor output without regard to the shapes and dimensions of the EIS sensors, electrical conductivities of the samples were estimated by matching the extracted sample resistances with resistances obtained in the finite element method (FEM) simulation. Finally, in order to determine the location of the facial nerve before the facial nerve is exposed, resistance and conductivity changes were investigated using an FEM simulation based on the thickness of the bone covering the facial nerve. Thus, physicians can obtain information regarding the thickness of the bone covering the facial nerve while grinding the bone in otologic surgery. This will enable physicians to easily avoid iatrogenic facial nerve injury during otologic surgery.