Objective: To review the surgical anatomy of the hypoglossal nerve in the neck, analyse its relationship to surrounding structures and offer landmarks to identify the nerve during carotid endarterectomy.
Method: The carotid bifurcation, external carotid artery, internal carotid artery, extracranial part of the hypoglossal nerve, occipital artery, sternocleidomastoid artery and surrounding neurovascular structures were dissected and studied on 15 formalin-fixed adult cadaver heads (30 sides and 15 pairs) via a surgical microscope. Landmarks for the hypoglossal nerve and measurements of its distance from the carotid bifurcation are described. The relationship between the sternocleidomastoid artery and the occipital artery is also described.
Results: The distance from the carotid bifurcation to the point at which the hypoglossal nerve crosses over the internal carotid artery was variable, ranging from 3.89 to 37.03 mm (mean, 20.95 +/- 7.78 mm). The distance from the bifurcation to the point at which the hypoglossal nerve crosses over the external carotid artery ranged from 2.63 to 29.43 mm (mean, 15.33 +/- 7.86 mm; Table 1). The sternocleidomastoid artery had a very characteristic course and close relationship with the hypoglossal nerve. Ascending for a short distance in a cranial direction, it crossed over the hypoglossal nerve and then descended toward the sternocleidomastoid muscle. The sternocleidomastoid artery originated from the occipital artery (33.4%), the external carotid artery-internal carotid artery junction (30%), the external carotid artery itself (30%) or even the lingual artery (6.6%).
Conclusion: The relationship between the hypoglossal nerve and the carotid bifurcation is quite variable, and this explains the vulnerability of the nerve during carotid endarterectomy. The sternocleidomastoid artery is a good landmark for identifying the hypoglossal nerve. If there is exact anatomical knowledge about the relationship between the sternocleidomastoid artery and the hypoglossal nerve, the incidence of nerve injuries during carotid endarterectomy can be minimized.