Surgical Anatomy of the Cervical Part of the Hypoglossal Nerve

Abstract

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) mm and 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.

Iatrogenic hypoglossal nerve palsy, a rare complication post suspension laryngoscopy

“…The hypoglossal nerve is a paired cranial nerve, arising from its nuclei in the medulla, which exits the skull base via the hypoglossal canal and passes deep into the internal jugular vein and superficial to the carotid arteries, mainly crossing superior to the carotid bifurcation. 5 The nerve then passes above the hyoid bone, goes in between the mylohyoid and hyoglossus muscles, and finally supplies all the tongue muscles except the palatoglossus. 6…”

Topography of the Anatomical Landmarks of Carotid Bifurcation and Clinical Significance

“…There were studies evaluating the level of CB according to the mastoid process, gonion, hyoid bone, and thyroid cartilage [ 1 , 4 , 5 , 9 , 16 , 17 , 24 - 27 ]. Some of them evaluated this relationship as a relative position [ 5 , 9 , 17 , 24 ], some by specifying distance [ 25 , 27 ], and some as a combined [ 1 , 4 , 16 , 26 ]. Two of these studies were CTA [ 4 , 16 ], and the others were cadaveric studies.…”

“…The difference between our study and that of Klosek et al was that they did not identify a difference between the sexes. The position of the CB relative to the thyroid cartilage was evaluated as "above" by 70% or more in some studies [ 1 , 4 , 16 , 24 , 26 ]. In one study, this rate was at 55%, while it was reported to be at the same level as 39% [ 5 ].…”

Hypoglossal Nerve Neuropathies—Analysis of Causes and Anatomical Background

“…The relations between the HN and the ECA can be classified into three types [32,33]. Type I-the HN crossing the ECA inferior to the origin of the OA.…”