Sonographic Anatomy and Imaging of the Extracranial Component of the Hypoglossal Nerve (CNXII).

The hypoglossal nerve (HN) provides motor innervation to tongue muscles responsible for tongue movement, speech, mastication, swallowing, respiratory functions and management of oral secretions. Injury, compression, entrapment or lesions of the HN at any point along its path can result in HN palsy and subsequent dysphagia, dysarthria and tongue muscular atrophy. A combined imaging approach is required to investigate the HN and causes of HN palsy. Magnetic resonance imaging (MRI) and computed tomography (CT) imaging are used to investigate the intracranial HN and where it emerges in the upper neck. The extracranial HN can be assessed by sonographic imaging along with the muscles directly and indirectly innervated by the HN. Ultrasound imaging can be challenging without an appropriate understanding of the detailed relative anatomy of the HN and the muscles it innervates, the associated sonographic technique and sonographic appearances, all of which are outlined in this paper.