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

Several surface anatomy landmarks have been described to aid in the surgical dissection of facial nerve donor branches for neurotization purposes yet are 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.

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.

In the cadaveric series, branch-by-branch analysis demonstrated a sensitivity of 92.9% (95% confidence interval [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.

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.