Course Patterns of the Marginal Mandibular Branch of the Facial Nerve over the Facial Vessels in Relation to the Inferior Mandibular Border.

The marginal mandibular branch of the facial nerve (MMB) is a surgically relevant extracranial branch of cranial nerve VII, vulnerable during submandibular, parotid, and cervicofacial procedures. Its relationship to the facial vessels and the inferior border of the mandible (IBM) is variable and has been studied for more than six decades. This review analyses the course of the MMB as it crosses the facial artery and vein, focusing on its vertical position relative to the IBM, together with branching patterns, fascial relationships, anastomoses, landmarks, injury, and recovery. The MMB usually crosses the facial vessels superficially, but deep passage and looping have been reported. Its vertical position is segment-dependent: posterior to the facial artery, one or more branches may descend below the IBM in approximately 19-39% of cases, whereas anterior to the artery the nerve is almost always above it. A meta-analysis of 1861 hemifaces reported a pooled prevalence of 39% for at least one branch below the IBM. Reported iatrogenic injury rates range from 16% to 47% (largely transient), and recovery is variable, reflecting a richer communicating network than once assumed. The facial artery crossing at the IBM is a practical landmark for locating the MMB. The traditional 2 cm rule does not reliably protect the nerve, which may descend below this level, especially posterior to the vessels and during neck extension. Safer access depends on combined bony and vascular landmarks, subplatysmal dissection, and assessment of branching variability.