Anatomic variations of the marginal mandibular nerve.

Marginal Mandibular Nerve (MMN) is a branch of the facial nerve. Muscles supplied by this nerve are responsible for facial symmetry, facial expressions and phonation. Aim was to study the branching pattern and variations in the position of marginal mandibular nerve. 202 patients who underwent neck dissection from June 2005 to October 2006 at Regional Cancer Centre, Trivandrum, India were included in the study. During the course of neck dissection, the marginal mandibular nerve was first identified around the point where the facial artery crossed the lower border of the mandible. Once the nerve was identified, it was traced both backwards and forward till the whole nerve was exposed. Position of the nerve and its relation to lower border of mandible at the point where the facial artery crossed the lower border of the mandible was noted and number and position of each branches were recorded. In 161of the 202 patients (79.7%) the MMN had a single division. Two branches were noted in 26 patients (12.9%). Three branches for MMN are not uncommon, it was noted in 14 patients (6.9%) and in one patient there were four branches. Every effort should be made to preserve all the branches of MMN to ensure cosmesis and decrease morbidity. The mean distance from the lower border of the mandible to the point where the marginal mandibular nerve crossed the facial artery for all the branches taken together was 1.73 mm below the mandible. In 49 patients there was communication between MMN and the cervical branch of facial nerve. The point where the facial artery crosses the lower border of the mandible is a reliable landmark to locate the MMN. Variation in the branching pattern of marginal mandibular nerve is very common.