We outline the method and demonstrate the efficacy of superficial facial nerve mapping, a novel technique to help guide complex craniofacial surgeries.

Facial nerve mapping has been long utilized during procedures involving the mastoid, parotid gland, or neck. The technique involves stimulating the approximate course of CN7 in the surgical field intraoperatively based on visual evaluation while monitoring for EMG responses. However, for procedures in patients with variant anatomy or scarring from previous procedures in the area, the course of the facial nerve may be difficult to visualize. In these cases, intraoperative surface mapping of the course of the facial nerve prior to initial incision can be valuable.

We review cases from 2022-2023 at a single academic center utilizing superficial facial nerve mapping. The parameters and methods of recording are evaluated along with the clinical context.

Four reviewed cases involved bipolar surface stimulation of the facial nerve prior to incision. Triggered EMG responses were recorded through intramuscular needle electrodes in the orbicularis oculi, nasalis, orbicularis oris, and mentalis muscles. EMG-guided stimulation was carried out at various skin sites using handheld bipolar instruments. At each site, thresholds were determined creating a surface map of the nerve path. Thresholds for response ranged from 4.5mA to 12mA, with pulse widths from 100 to 200µs. Mandibular branch segments were marked when EMG responses were elicited in mentalis and orbicularis oris. Buccal branch segments were marked when EMG responses were elicited in nasalis. All patients exhibited facial symmetry prior to procedure and one of the four was noted to have mild asymmetry postoperatively.

Surface mapping of the facial nerve can be a crucial tool in complex craniofacial surgeries to avoid post-operative weakness. In cases of aberrant or complex anatomy, we recommend consideration of immediate preoperative electrophysiologic testing to delineate the course of the facial nerve.