High-Frequency Ultrasound Mapping of Facial Nerve Branches: Validation of a Systematic Technique and Clinical Application

BACKGROUND: several surface anatomy landmarks have been described to aid in the surgical dissection of facial nerve donor branches for neurotization purposes yet limited by considerable anatomical variability. High-frequency ultrasound has shown promise for facial nerve imaging and could be a more precise complementary tool to intraoperative neurostimulation. We aimed to validate a systematic ultrasound examination technique to determine the exact location for each main extratemporal branch and to assess its preliminary clinical feasibility and safety profile for preoperative mapping. METHODS: ten cadaveric hemifaces with a total of 56 facial nerve extratemporal branches were examined to validate a branch-by-branch ultrasound-based mapping technique. The accuracy of skin markings and ultrasound-guided methylene blue injections for each branch was confirmed by subsequent dissection. Additionally, a retrospective clinical series, comprising five cross-face nerve grafts and one facial nerve-to-muscle neurotization, was analyzed to assess reproducibility in the clinical setting. RESULTS: in the cadaveric series, branch-by-branch analysis demonstrated a sensitivity of 92.9% (95% CI: 84.2–97.7), a positive predictive value of 92.9% (95% CI: 84.2–97.7), and an overall agreement between ultrasound findings and dissection of 86.7% (95% CI: 75.4–93.3). In the clinical series, the targeted facial nerve branches were successfully identified without complications. CONCLUSION: the proposed systematic ultrasound-based mapping technique, readily performed by surgeons trained in ultrasonography, shows promising accuracy in the identification of facial nerve arborization and a good preliminary feasibility and safety profile in the clinical setting.