Extraosseous mental nerve anatomy in fresh-frozen Vietnamese cadavers: anatomical considerations for vestibular incisions and trocar placement in transoral endoscopic thyroidectomy via the vestibular approach.

BACKGROUND: Transoral endoscopic thyroidectomy via the vestibular approach (TOETVA) provides excellent cosmetic outcomes but introduces specific anatomical challenges related to the mental nerve. Although the location of the mental foramen has been extensively studied, detailed information regarding the extraosseous course, branching pattern, and layer-based relationships of the mental nerve remains limited. This study aimed to characterize the extraosseous anatomy of the mental nerve in fresh-frozen Vietnamese cadavers and provide anatomical information relevant to vestibular incision planning and trocar placement in TOETVA. METHODS: A descriptive anatomical study was performed on 15 fresh-frozen Vietnamese adult cadavers, providing 30 mental nerves for analysis. The mental foramen and extraosseous mental nerve branches were dissected systematically. Morphometric parameters, branching patterns, and relationships between nerve branches and surrounding soft tissue layers were recorded. RESULTS: The mental foramen was most commonly located in line with the second premolar (50.0%). The mental nerve divided early after exiting the foramen, with a mean distance to the first branching point of 3.17 ± 2.55 mm. Branching patterns showed considerable variability, with all five Hu classification types observed and side-to-side asymmetry present in 46.7% of cadavers. After exiting the foramen, the mental nerve was consistently superficial to the periosteum. The angular and lateral inferior labial branches coursed deep to the orbicularis oris muscle in all specimens, while the mental branch most commonly followed a superficial course relative to the mentalis muscle. CONCLUSION: The mental nerve demonstrates early extraosseous branching and consistent layer-based anatomical relationships after exiting the mental foramen. These findings provide important anatomical information relevant to vestibular incision planning and trocar placement in TOETVA.