Hypoglossal nerve palsy

Last revised by Patrick O'Shea on 30 Mar 2022

Hypoglossal nerve palsies, or twelfth nerve palsies, result in weakness of the muscles supplied by the hypoglossal nerve, namely the intrinsic and extrinsic tongue muscles, except for palatoglossus.

The hypoglossal nucleus receives a major component of contralateral cortical supply 1. As a result, supranuclear (i.e. upper motor neuron) lesions of the hypoglossal nerve often present with 2:

  • on tongue protrusion: deviation towards the contralateral side
  • contralateral tongue weakness or paralysis
    • commonly mild and readily compensated for by the unaffected side

When the lesion is nuclear or infranuclear, clinical findings of hypoglossal nerve palsy present in the tongue due to denervation of the ipsilateral tongue musculature. Findings seen are those common to lower motor neuron lesions in general, including 3:

  • on tongue protrusion: deviation towards the ipsilateral side
    • due to ipsilateral genioglossus muscle weakness
  • ipsilateral tongue weakness
  • denervation hypersensitivity (fasciculation)
  • ipsilateral tongue atrophy
    • significant atrophy suggests a chronic palsy

Compared to the other cranial nerves, lesions of the hypoglossal nerve are rare and often present alongside other nerve palsies 2. The numerous possible etiologies may be divided based on the anatomical course of the nerve 2,4:

  • intraparenchymal portion
    • infarct
    • glioma
    • demyelinating diseases
  • cisternal portion
    • neurovascular disease
      • posterior inferior cerebellar artery
      • vertebral artery
    • aneurysm
    • vascular ectasia
    • meningioma
    • rheumatoid arthritis
  • skull base portion
    • skull base metastasis
    • nasopharyngeal carcinoma
    • nerve sheath tumor
    • glomus tumor
  • extracranial portion: carotid space
    • carotid artery dissection or aneurysm
    • squamous cell carcinoma
    • lymphadenopathy
    • post-carotid surgery 5
  • extracranial portion: anterior segment
    • sublingual space infection
    • squamous cell carcinoma
    • post-surgical intervention

The first radiological sign that draws attention to a possible hypoglossal nerve palsy is often unilateral tongue atrophy 2. It is important to be alert to the various radiologic appearances of tongue denervation, as the imaging findings depend heavily on the chronicity of the nerve insult. 

MRI is most useful to characterize these tongue changes, which include 2:

  • subacute phase
    • increased interstitial water content causes the tongue to appear hypointense on T1 and hyperintense on T2
    • the area may also show increased uptake of intravenous contrast, due to the increased capillary density in the atrophying muscle and easy accumulation of contrast in the expanded interstitium
  • chronic phase
    • progressive fatty infiltration causes the affected tongue volume to decrease and the base of the tongue to protrude posteriorly
    • on MRI the affected tongue will appear hyperintense on both T1 and T2-weighted imaging
      • regions of T1 hyperintensity appear approximately five months from the causative insult 2

CT findings of the tongue in the subacute phase are nonspecific. In the chronic phase, fat density will be present within the tongue.

Unilateral palsies are readily compensated for by the remaining hypoglossal nerve. Patients may not report significant weakness or discomfort. In contrast, bilateral palsies can lead to severe difficulty speaking and swallowing 3.

  • a useful memory device for recalling the direction of tongue deviation in supranuclear versus nuclear/infranuclear hypoglossal nerve palsy is: "up, up, and away" 
  • disorder of the infrahyoid (strap) muscles localizes the lesion to the portion of the hypoglossal nerve distal to the point where it is joined by a branch of the cervical plexus (i.e. just after the nerve exits the skull base) 2
  • deviation of the uvula when the patient says "ahh" suggests vagus nerve involvement rather than hypoglossal, as the palatoglossus muscle responsible for this movement is innervated by the vagus nerve

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Cases and figures

  • Isolated hypoglossal nerve paralysis
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  • Skull base metastasis - tongue swelling
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