Cranial nerve XII: The hypoglossal nerve

Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
Seminars in Neurology (Impact Factor: 1.79). 03/2009; 29(1):45-52. DOI: 10.1055/s-0028-1124022
Source: PubMed


The hypoglossal nerve provides motor innervation to the tongue, and may be affected by pathology at multiple locations along its pathway. Knowledge of its anatomy and careful examination of the tongue are important in the diagnosis of lesions and determination of appropriate testing. The hypoglossal nerve anatomy and physiology, clinical disorders, and the evaluation of the hypoglossal nerve are reviewed.

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    • "It exits the cranium through the hypoglossal foramen, travels next to the internal carotid artery and vagus nerve, descends toward the carotid bulb and internal jugular vein, and lies next to the posterior belly of the digastric muscle, beneath the submandibular gland to innervate the extrinsic (genioglossus, hyoglossus and styloglossus) and intrinsic muscles of the tongue. Therefore, lesions to the nerve not only affect the initial process of swallowing, but also speech, coordinated chewing and breathing [11,12]. IONM of the hypoglossal nerve has been reported on proximal lesions located near its exits from the cranium into the neck, such as lesions comprising the cerebellopontine angle or lesions at the skull base [8-10]. "
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    ABSTRACT: Intraoperative nerve monitoring (IONM) has many applications in different surgical fields. In head and neck surgery, IONM has been used to perform surgery of the parotid, thyroid and parathyroid glands, preserving the facial and recurrent nerves. However, hypoglossal nerve neuromonitoring has not been addressed with such relevance. A retrospective review of surgeries performed on patients with special tongue and floor of mouth conditions was undertaken to examine the indications that prompted its use. Particular attention was given to the pathology, intraoperative findings and the final outcome of each patient. Four patients, aged between 6 years and 68 years, with complex oral tongue and floor of mouth lesions were reviewed. Three patients were male, aged 22 years and younger, and two of these patients had oral tongue cancers with previous surgery. Oral tongue and neck conditions are challenging since the functions of the hypoglossal nerve are put at risk. The use of IONM technology allowed us to preserve nerve functions, speech and swallowing. Although IONM of the hypoglossal nerve is not a common indication in tongue and floor of mouth lesions, under special conditions its application can be extrapolated to challenging surgical cases, like the ones described.
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    ABSTRACT: The XIIth cranial nerve plays a role in chewing, respiration, suckling, swallowing, and speech [Lowe, A.A., 1981. The neural regulation of tongue movements. Prog. Neurobiol. 15, 295-344.]. The muscles innervated by this nerve are functionally subdivided into three categories: those causing protrusion, retrusion, and changing the shape of the tongue. Myosin heavy chain (MHC) II isoform makes up the majority of the MHC phenotype with some variability among mammalian species and some evidence suggests between genders. In addition, there are regional differences in fiber type within some of these muscles that suggest functional compartmentalization. The transition from developmental MHC isoforms to their adult phenotype appears to vary not only from muscle to muscle but also from species to species. Motor units within this hypoglossal motor system can be categorized as predominantly fast fatigue resistant. Based on twitch contraction time and fatigue index, it appears that hypoglossal innervated muscles are more similar to fast-twitch muscles innervated by spinal nerves than, for example, extraocular muscles.
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