Surgical Anatomy of the Cervical Part of the Hypoglossal Nerve

Iatrogenic injuries to cranial nerves, half of which affect the hypoglossal nerve, occur in up to 20% of surgical procedures involving the neck. The risk of injury could be minimized by in-depth knowledge of its positional and relational anatomy. Forty-one hypoglossal nerves were dissected from cadaveric specimens and positions described in relation to the internal carotid artery (ICA), external carotid artery (ECA), carotid bifurcation, mandible, hyoid bone, mastoid process, and the digastric tendon. The distance of the nerve from where it crossed the ICA and ECA to the carotid bifurcation was 29.93 (+/- 5.99) mmand 15.19 (+/- 6.68) mm, respectively. The point where it crossed the ICA was 12.24 (+/- 3.71) mm superior to the greater horn of hyoid, 17.16 (+/- 4.40) mm inferior to the angle of the mandible, and 39.08 (+/- 5.69) mm from tip of the mastoid. The hypoglossal nerve loop was inferior to the digastric tendon in 73% of the cases. The hypoglossal nerves formed high loops in this study population. Caution should be exercised during surgical procedures in the neck. The study also revealed that the mastoid process is a reliable fixed landmark to locate the hypoglossal nerve.