5.12. Cranial Nerve XII
Anatomy
- Nucleus extends from the caudal medulla to the pontomedullary junction
- Two discrete nerve bundles intracranially; unite after emergence through the hypoglossal canal
- Passes over the internal and external carotid artery; lies beneath the digastric, stylohyoid and mylohyoid muscles
- Muscular or lingual branches supply the intrinsic tongue muscles and the hypoglossus, styloglossus, genioglossus, geniohyoid (extrinsic muscles)
- Descending hypoglossal ramus: forms the ansa hypoglossi in the neck:
- Fibers from C1–C3 cervical roots (associated)
- Innervate infrahyoid muscles: sternohyoid, omohyoid, sternothyroid, thyrohyoid and geniohyoid
- Corticobulbar fiber controlling the genioglossus are crossed; other tongue muscle bilateral supranuclear control
- Lateral movements of non-protruded tongue are performed by intrinsic muscles therefore patient cannot turn tip of the tongue to affected side.
Vascular Disease Affecting XII
- Medial medullary syndrome (Dejerine's):
- Infarction of the vertebral or anterior spinal artery
- Ipsilateral XII paresis (atrophy and fasciculations)
- Contralateral hemiplegia
- Contralateral loss of lemniscal sensation (proprioception and vibration)
- May occur bilaterally (quadriplegia with facial sparing), bilateral lower motor neuron tongue paralysis, loss of lemniscal sensation of all extremities
- Tongue may occasionally be spared in anterior spinal artery syndrome
- Rare XII nerve involvement with ectasia from hypertension, AVM, cavernous hemangioma or telangiectasia
- Carotid artery dissection with pseudoaneurysm and compression
- Dolichoectasia of the vertebral artery in the medulla
Trauma
- Fracture through the hypoglossal canal or foramen magnum
- Head injury (blunt)
- Penetrating head and neck wounds (knife, bullet, ensuing carotid fistula and pseudoaneurysm with nerve involvement)
- Dental operative procedures; extractions
- Subluxation of odontoid process (rheumatoid arthritis, connective tissue disease, tear of the alar and cruciate ligaments)
- Surgical trauma (particularly carotid endarterectomy)
- Numb tongue-neck syndrome (cervical plexus; intrinsic proprioceptive fibers in the nerve)
Tumors Involving the XII Nerve
- Retroparotid tumors
- Retropharyngeal tumors
- Salivary gland (adenocarcinoma; mixed)
- Squamous cell (base of the tongue)
- Metastatic (bronchial, thyroid, esophageal)
- Lymphoma (Hodgkin/non-Hodgkin)
- Leukemia
- Schwannoma
- Meningioma (foramen magnum)
- Occipital condylar syndrome:
- Metastasis to posterior occipital condyle
- Ipsilateral XIIth nerve involvement
- Mediastinal tumor
Anterior Horn Cell/NMJ/Nerve Involving the XII Nerve
- MND
- MG
- Eaton–Lambert
- Diphtheria
- AIDP
- CIDP
- EBV (infectious, mononucleosis)
- X-RT
- Machado–Joseph Disease (SCA); facial lingual fasciculations
Intraparenchymal Lesions Involving the XII Nerve
- Syrinx (syringobulbia)
- Tumor
- Demyelinating disease (rare)
Abnormal Tongue Movements
- Oral buccal lingual dyskinesia
- Athetosis
- Palatal myoclonus
- Trombone tongue (choreiform movements; syphilis)
- Galloping tongue:
- Episodic
- Rhythmic
- Involuntary
- May spread to head and neck
- Three per second waves
- Starts posteriorly in the midline
- Focal tongue contraction
- Putative pontine lesion
- Continuous lingual myoclonus after head injury
Glossodynia
- Burning pain of tongue and oral mucosa
- Middle aged and elderly patients
- B vitamin deficiency (putative)
Macroglossia
- Cerebral gigantism
- Syndromic
- Primary amyloidosis
- Acromegaly
- Hypothyroidism
- Mucopolysaccharidosis
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