Anatomical variations of the marginal mandibular nerve

Introduction: The Marginal Mandibular Nerve (MMN), despite being didactically described as being a unique branch of the other branches of the Facial Nerve, has in practice an abundant anatomical variation. Both in relation to its ramifications and the positioning of these in relation to the lower edge of the mandible, as well as its anastomoses along its path, play a fundamental role in the surgical strategy during the approach of this cervicofacial site, and can generate, as underestimated its characteristics, inadvertent injuries and motor consequences to the patient. Objective: To analyze the types of anatomical variations of the MMN in relation to its position, ramification, and distance from reference points, as well as its incidence that could imply technical difficulties in surgery. Methods: A systematic review was conducted in the literature in search of anatomical studies, in vivo or in cadavers, between 1981 and 2024, which described the quantification of the MMN branches, their positioning and peculiarities in relation to anastomoses with other peripheral nerves. Results: 511 hemifaces were studied, with the identification of 290 cases of single nerve, 160 cases of double branch, 54 cases of triple branch, and 7 cases of quadruple branch. Of the 456 nerves that were possible to study, the average distance when superior to the lower limit of the mandible was 1.61 cm, while its lower analysis was 2.53 cm. The branches presented different proportions of presentation in relation to this reference point depending on how many branches it had, being more common to remain below it. Anastomoses were identified between the MMN and the buccal and cervical branch of the Facial Nerve, as well as with the Trigeminal Nerve. Conclusion: The varied presentations of the MMN, both in its anatomical positioning and in the number of branches leads us to question whether the surgical thinking when performing an exploration in this site may not be the reason whythe authors verify several motor complaints superior to described injuries.