What is the anatomical landmark for the marginal mandibular nerve?

Anatomical Landmark for the Marginal Mandibular Nerve

The marginal mandibular branch of the facial nerve is typically located 2 cm below the inferior border of the mandible, making this the critical anatomical landmark for avoiding nerve injury during surgical procedures in the submandibular region. 1

Anatomical Course and Variations

The marginal mandibular nerve demonstrates significant anatomical variability in its course relative to the mandible:

• Number of branches: The nerve may present as:

  • Single branch (32-43%)
  • Two branches (40-63.6%)
  • Three branches (13-28%) 2, 3

• Relationship to mandibular border: The nerve's position varies:

  • Above the mandibular border (28%)
  • Below the mandibular border (44%)
  • Both above and below (28%) 2

• Specific measurements relative to mandibular landmarks:

  • At the gonion (mandibular angle): 0.75 mm below
  • At the antegonial notch: 0.08 mm superior to posterior border
  • Where facial artery crosses mandible: 3.6 mm superior
  • At vertical line from lip commissure: 10.9 mm superior to mandibular border 4

Clinical Implications for Surgery

When performing surgical procedures in the submandibular region:

• Safe incision placement: Maintain incisions at least 2 cm from the inferior border of the mandible to avoid nerve damage 1

• High-risk zones:

  • Maximum distance between nerve and mandible can reach up to 40.08 mm (average 21.91 mm) 5
  • The nerve crosses facial vessels approximately 24 mm posteroinferior to the mandibular angle 3

• Relationship to facial vessels:

  • In 97.7% of cases, the nerve runs lateral to the facial artery
  • Rarely (2.3%), branches may run between facial artery and vein 5

Surgical Technique Considerations

To minimize risk of nerve injury:

• Flap elevation technique:

  • Above mandibular border: subplatysmal flap is adequate
  • Below mandibular border: subfascial flap is safer 2

• Nerve identification:

  • Routine identification of facial nerve branches in the operative field is strongly recommended 1
  • Careful dissection following fascial planes helps avoid damage 1

• Special considerations for floor-of-mouth tumors:

  • Initial dissection below the marginal mandibular nerve level
  • Transect tissues to mylohyoid muscle level
  • Mobilize lymph nodes away from oral cavity 6

By understanding these anatomical relationships and following proper surgical techniques, the risk of iatrogenic injury to the marginal mandibular nerve can be significantly reduced, preventing cosmetic and functional deformities that may result from nerve damage.