Anatomic Variations From 120 Mental Nerve Dissections: Lessons for Transoral Thyroidectomy

Area of Science:

• Anatomy
• Surgical Techniques
• Head and Neck Surgery

Background:

• Transoral endoscopic thyroidectomy vestibular approach (TOETVA) offers scarless thyroidectomy but carries a risk of mental nerve injury.
• Understanding mental nerve anatomy variations is crucial for improving TOETVA safety.
• Injury to mental nerves can occur during the placement of endoscopic ports in TOETVA.

Purpose of the Study:

• To investigate the anatomical variations of mental nerve branches exiting the mental foramen.
• To identify safe surgical zones for port placement during TOETVA to minimize mental nerve injury.
• To compare observed branching patterns with existing classifications and describe novel patterns.

Main Methods:

• Dissection of mental nerve branches from the mental foramen in 60 human cadavers (120 sides).
• Measurement of distances from the mental foramen to the midline and evaluation of nerve branching patterns.
• Classification of branching patterns and comparison with established systems.

Main Results:

• Significant variability in the midline-to-mental foramen distance (mean 29.2 mm, range 18.8-36.8 mm).
• Differences observed in this distance between left and right sides (P=0.03).
• Eight distinct branching patterns identified, including three novel types; one pattern showed dense medial branching in 9.2% of cases.

Conclusions:

• Mental foramen location and mental nerve branching patterns exhibit considerable variability.
• A safe zone for lateral port placement in TOETVA is identified lateral to the mental foramen plane.
• Caution is advised for middle port placement due to frequent clustering of mental nerve branches.