Mapping the Masseteric Nerve for Facial Reanimation: An Anatomical Study of Two Dissection Strategies

<i>Background and Objectives:</i> The masseteric nerve (Mn) is increasingly used for facial reanimation because of its reliable location, high axon count, low donor morbidity, and favorable clinical outcomes. Precise topographic knowledge of the Mn relative to reproducible intraoperative landmarks is essential for safe dissection. This study investigated the intramuscular position of the Mn relative to two defined reference lines. <i>Materials and Methods:</i> Seventy-two hemicrania from 36 individuals (aged 54-99 years) embalmed postmortem using the Thiel method were examined. Measurements were referenced to two defined anatomical lines: the angle-canthus line (ACL), extending from the mandibular angle to the lateral canthus of the eye, and the articular eminence line (AEL), extending from the articular eminence to the base of the zygomatic temporal process. <i>Results:</i> The Mn crossed the ACL at an average distance of 39.9 ± 5.9 mm from the mandibular angle with up to four branches. The first intramuscular branch arose 15.6 ± 4.7 mm superior to the ACL. The Mn was located 4.9 ± 1.9 mm anterior to the articular eminence and 4.7 ± 1.5 mm inferior to the AEL, coursing at an average angle of 68.5 ± 11.6° to the AEL. The AEL and ACL provide reliable and clearly defined reference lines for locating the Mn and improve intraoperative reproducibility. The Mn followed a predictable oblique course and was consistently identified in the masseter muscle (Mm) beneath an intramuscular aponeurosis. Nerve diameter varied by site, underscoring the need for standardized measurement locations. Distal localization along the ACL may enable preservation of early intramuscular branches and reduce donor morbidity. Further studies should evaluate axon counts at defined points and clarify the relationship of the Mn to the masseteric artery for better intramuscular orientation during dissection. <i>Conclusions:</i> The Mn can be located within a 63 mm² area beneath the AEL at the masseter entry and more distally on the ACL. ACL-based access may protect the first intramuscular branch of the Mn and the temporal branch of the facial nerve (TBFN), and it represents a potential alternative for smile reconstruction for patients with preserved eye closure.