Morphometric Study of the Hypoglossal Nerve and the Hypoglossal Canal for the Surgery of the Upper Cervical Spine

Abstract

Objective The upper cervical pathology is not an uncommon disease in the congenital anomaly, elderly population, and patients with rheumatoid. Newly developed operative techniques in high cervical region could be related to neurovascular injury. The objective of this study was to determine the anatomic relationship of the hypoglossal nerve (HN), internal carotid artery (ICA), bony structures, and hypoglossal canal and demonstrate the vulnerability of the neurovascular structures. Methods Eleven fresh cadavers (5 male and 6 female) were dissected bilaterally to expose neurovascular structures of the high anterior cervical region and hypoglossal canal. The anatomical relationship was evaluated between C1 bony structures (midline, lateral mass, and C1 transverse process) and the ICA and HN. The angle of the hypoglossal canal was also evaluated. Results The HN consistently traveled toward the midline at C2–3 and was safe caudal to C3–4. The HN is usually located lateral to the ICA. Relative anatomical relationship between the HN and surrounding bony structures at the level of C1 are as given below. The mean diameter of the HN was 2.4 mm (2–3.5 mm). The mean distance between the midline and the HN was 30.15 mm (24–35 mm). The mean distance between the margin of the C1 lateral mass (LM) and the HN was 4 mm (−3–11 mm). The mean distance between the C1 transverse process and the HN was 9.3 mm (3–16 mm). The transverse angle of the hypoglossal canal was between 31.6 and 55.5 degrees. The mean distance between the midline and the ICA was 26.06 mm (18–32 mm). In the cases of the medially displaced ICA, the HN is located more on the medial side relative to the LM. There was no reversed anatomical location of the HN and the ICA in the studied specimen. Conclusion On the basis of this study, spine surgeons can have enhanced knowledge of upper cervical anatomy. Although it has been rarely reported in the literature, the hypoglossal nerve and the ICA may be damaged during upper cervical spine surgery, especially in the cases with the ICA displaced medially.