Hypoglossal Nerve: Anatomy, Anatomical Variations Comorbidities and Clinical Significance

We review the anatomical variations of the hypoglossal nerve and their surgical and clinical significance, and we report multiple diseases that affect function of the nerve leading to paresis, either unilateral or bilateral. The hypoglossal nerve is the 12th cranial nerve, and knowledge of the detailed anatomy and relationship with critical structures is of paramount importance in neurosurgery, head and neck surgery, and vascular surgery. Numerous studies have depicted conventional landmarks in the cervical part of the hypoglossal nerve, but their findings have not been consistent reliable. We analyze and review these critical landmarks used to identify and preserve the hypoglossal nerve during surgery and to minimize iatrogenic complications in head and neck, neurosurgical, and vascular procedures. We performed an online database search during January and February 2019 to pinpoint the diseases that affect function of the nerve. According to this literature review, apart from iatrogenic injury during surgery, the most frequently observed cause of paresis is pressure due to the presence of tumours and head injury. Furthermore, motor neuron degenerative conditions, such as amyotrophic lateral sclerosis, multiple sclerosis or tooth infection and presence of an aberrant vessel in the hypoglossal canal can affect the function of the nerve.