The hypoglossal nerve originates in the hypoglossal nucleus of the medulla and innervates the muscles of the tongue. It exits the skull through the hypoglossal canal and descends through the neck. Lesions can occur at the supranuclear, nuclear, or peripheral levels. Supranuclear lesions of the corticobulbar tract cause contralateral tongue weakness without atrophy. Nuclear lesions in the medulla result in ipsilateral tongue paresis, atrophy and fasciculations. Peripheral lesions of the hypoglossal nerve cause ipsilateral tongue paresis through the hypoglossal canal.

1. HYPOGLOSSAL NERVE
DR ADARSH I NATH
SENIOR RESIDENT
DEPT OF NEUROSURGERY
GOVT MEDICAL COLLEGE, KOZHIKODE

2. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

3. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

4. INTRODUCTION
• The hypoglossal nerve (CN XII) is a purely motor nerve, supplying the tongue.
• Its cells of origin are in the hypoglossal nuclei, which are upward extensions of
the anterior gray columns of the spinal cord; they consist of large, multipolar cells,
similar to the anterior horn motoneurons.
• The column of cells extends from the caudal-most medulla oblongata to the
medullary-pontine junction and contains the somatic efferent fibres

6. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

7. ORIGIN
• Its fiber arise from the hypoglossal nucleus, a longitudinal cell column in the
paramedian medulla that lies beneath the hypoglossal trigone of the floor of the
fourth ventricle.
• The column of cells extends from the caudal-most medulla oblongata to the
medullary-pontine junction.
• The nucleus is somatotopically organized, with different cell groups innervating
different tongue muscles.
• From rostral to caudal, the innervation is intrinsic tongue muscles, then
genioglossus, hyoglossus and styloglossus

12. SUPRANUCLEAR CONTROL
• Supranuclear control lies in the lower portion of the precentral gyrus near and
within the sylvian fissure.
• The supranuclear fibers run in the corticobulbar tract through the genu of the
internal capsule and through the cerebral peduncle.
• Some corticolingual fibers shift to the medial lemniscus in the pons
• Other fibers leave the main ventral pyramidal tract and cross the midline at the
pontomedullary junction to enter the hypoglossal nucleus from the lateral aspect

13. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

14. COURSE
• From the hypoglossal nucleus, the nerve fibers travel in a ventrolateral direction
through the medullary reticular formation and medial portion of the inferior olive,
coursing immediately lateral to the medial longitudinal fasciculus, medial
lemniscus, and pyramid.
• Exit the medulla a series of 10 to 15 rootlets on each side, anterior to the rootlets
of CNs IX, X, and XI

18. RELATIONS AT THE BRAIN STEM

21. COURSE
• The hypoglossal fibers gather into two bundles, which perforate the dura mater
separately, pass through the hypoglossal canal, and then unite.
• After bundles unite they descend vertically through the neck to the angle of the
mandible

22. HYPOGLOSSAL CANAL
• The hypoglossal canal is located between the occipital condyle and jugular
tubercle and runs obliquely forwards (posteromedial to anterolateral).
• Its proximal portion is often divided by a fibrous (sometimes ossified) septum,
which separates the two roots of the hypoglossal nerve (these have formed by
the convergence of numerous rootlets).
• These roots merge within the canal and a single nerve emerges.

23. HYPOGLOSSAL CANAL

25. COURSE
• In the upper portion of its course, the nerve lies beneath the internal carotid
artery and internal jugular vein, and near the vagus nerve.
• It passes between the artery and vein, runs forward above the hyoid bone,
between the mylohyoid and hyoglossus muscles, and breaks up into a number of
fibers to supply the various tongue muscles.
• The nerve sends communicating branches to the inferior vagal ganglion and to
the pharyngeal plexus

26. COURSE
• The ansa hypoglossi is formed by the descending hypoglossal ramus (CN XII and
C1 cervical root) and the descending cervical ramus(C2 and C3 cervical roots).
• The descending hypoglossal ramus, which courses downward to form the ansa
hypoglossi, is given off from the hypoglossal nerve proper in the neck.

29. BRANCHES
• The branches of the hypoglossal nerve
• MENINGEAL,
• DESCENDING,
• THYROHYOID,
• MUSCULAR,

30. MENINGEAL BRANCH
• The meningeal branches send filaments derived from communicating branches
with C1 and C2 to the dura of the posterior fossa

31. DESCENDING BRANCH
• The descending ramus join with fibers from C1, sends a branch to the omohyoid,
and then joins a descending communicating branch from C2 and C3 to form the
ansahypoglossi
• Which supplies the omohyoid, sternohyoid, and sternothyroid muscles.

32. THYROHYOID BRANCH
• The thyrohyoid branch supplies the thyrohyoid muscle.
• The descending and thyrohyoid branches carry hypoglossal fibers but are derived
mainly from the cervical plexus

33. MUSCULAR BRANCHES
• The muscular, or lingual, branches constitute the real distribution of the
hypoglossal nerve.
• CN XII supplies the intrinsic muscles, and all of the extrinsic muscles of the tongue
except the palatoglossus, and possibly the geniohyoid muscle.

35. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

37. ACTIONS
• The suprahyoid muscles also influence tongue movement by changing the
position of the hyoid bone.
• The geniohyoid is supplied by C1 fibers traveling in the hypoglossal nerve.

38. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

39. EXAMINATION
• The clinical examination of hypoglossal nerve function consists of evaluating the
strength, bulk, and dexterity of the tongue—looking especially for weakness,
atrophy, abnormal movements.
• Note the position and appearance of the tongue at rest in the mouth.
• Then the patient is asked to protrude it, move it in and out, from side to side, and
upward and downward, both slowly and rapidly.

40. EXAMINATION
• Motor power can be tested by having the patient press the tip against each cheek
as the examiner tries to dislodge it with finger pressure.
• The normal tongue is powerful and cannot be moved.
• For more precise testing, press firmly with a tongue blade against the side of the
protruded tongue, comparing the strength on the two sides.

41. CLINICAL FINDINGS
• When unilateral weakness is present, the tongue deviates toward the weak side on
protrusion because of the action of the normal genioglossus, which protrudes the
tip of the tongue by drawing the root forward.
• The patient cannot push the tongue against the cheek on the normal side but is
able to push it against the cheek on the side toward which it deviates.
• Also at rest, it may deviate or curl slightly toward the healthy side because of
unopposed action of the styloglossus, which draws the tongue upward and
backward.

43. CLINICAL FINDINGS
• Lateral movements of the tip of the non protruded tongue, controlled by the
intrinsic tongue muscles, may be preserved.
• Facial muscle weakness or jaw deviation makes it difficult to evaluate deviation of
the tongue. Patients with significant lower facial weakness often have distortion
of the normal facial appearance that can produce the appearance of tongue
deviation when none is present.

44. CLINICAL FINDING
• Atrophy
• Fasciculations and tremors
• Ankyloglossia
• Macroglossia
• Atrophic Glossitis
• Burning tongue
• Ulcerations.

46. • INTRODUCTION
• ORIGIN
• COURSE & RELATIONS
• ACTIONS
• EXAMINATION
• LOCALISATION

47. LOCALISATION
• Supranuclear lesions
• Nuclear Lesions and Intramedullary Cranial Nerve XII Lesions
• Peripheral Lesions of Cranial Nerve XII.

48. SUPRANUCLEAR LESION
• Lesions of the corticobulbar tract anywhere in its course from the lower precentral
gyrus to the hypoglossal nuclei may result in tongue paralysis.
• The cortical area for controlling tongue movement may be the most lateral part
of the precentral gyrus lateral to the precentral knob.
• A lesion of the precentral and postcentral gyri may thus cause a contralateral
supranuclear hypoglossal palsy (“pseudoperipheral tongue weakness”) with
deviation of the tongue away from the lesion.
• A supranuclear lesion is not accompanied by atrophy or fibrillations of the tongue

49. SUPRANUCLEAR LESIONS
• Interruption of the corticolingual pathway to the tongue is crucial in the
pathogenesis of dysarthria following strokes affecting the internal capsule, basis
pontis, or corona radiata
• Damage to those uncrossed fibers may cause ipsilateral supranuclear lingual
paresis
• Bilateral upper motor neuron affection of the corticobulbar fibers to the
hypoglossal nuclei results in a paretic tongue with no atrophy or signs of
denervation

50. LEVEL OF DECUSSATION
• Pontine lesions at the ventral paramedian base close to the midline affect the
contralateral corticohypoglossal projections, whereas lateral lesions at the pontine
base affect ipsilateral projections.
• Lesions of the dorsolateral and mediolateral medulla impair only ipsilateral
corticohypoglossal projections.
• This suggests that the main decussation of supranuclear projections to the
hypoglossal nucleus in the brainstem is located close to the pontomedullary junction.
• Corticohypoglossal projections usually cross at the pontomedullary junction whereas
the uncrossed projections pass laterally in the basis pontis.

51. NUCLEAR LESIONS AND INTRAMEDULLARY CRANIAL
NERVE XII LESIONS
• Unilateral lesions of the HYPOGLOSSAL NUCLEUS or nerve result in paresis,
atrophy, furrowing, fibrillations, and fasciculations that affect the corresponding
half of the tongue.
• Because of close proximity- dorsal medullary lesions (e.g., multiple sclerosis,
syringobulbia) often result in bilateral lower motor neuron lesions of the tongue.
• ALS, Poliomyelitis, Infectious Mononucleosis.

52. INTRAMEDULLARY CRANIAL NERVE LESIONS
• Intramedullary hypoglossal involvement is suggested by the associated affection
of the medial lemniscus, pyramid, or other neighboring intramedullary structures.
• Causes-tumor, demyelinating disease, syringobulbia, vascular insult ( a rare
syndrome, Medial Medullary syndrome)

53. MEDIAL MEDULLARY SYNDROME

54. PERIPHERAL LESIONS OF CRANIAL NERVE XII
• The Cranial nerve XII leaves the skull through Hypoglossal canal.
• A basilar skull lesion (e.g., tumor, trauma, vascular lesion, or synovial cyst of the
occipito-cervical junction)may involve the twelfth cranial nerve alone, producing
an isolated cranial nerve XII lower motor neuron lesion.
• Frequently the other lower cranial nerves (IX, X, and XI) are variably involved as
well, due to the close proximity

57. PERIPHERAL LESIONS OF CRANIAL NERVE XII
• Isolated hypoglossal nerve palsy due to compression by a kinked vertebral artery
(hypoglossal vertebral entrapment syndrome) has been described.
• Combined abducens nerve and hypoglossal nerve palsies are rare. This is often an
ominous combination as may be seen with nasopharyngeal carcinoma
(Godtfredsen syndrome) and with other clival lesions, especially tumors (three-
fourths of which are malignant.

58. PERIPHERAL LESIONS OF CRANIAL NERVE XII
• Lesions, usually tumors or chronic inflammatory lesions, of the occipital condyle
may cause occipital pain associated with an ipsilateral hypoglossal nerve injury
(occipital condyle syndrome).
• The hypoglossal nerve may be injured in isolation in the neck or in its more distal
course near the tongue.

59. . The causes are
• Carotid aneurysms, aneurysms of a persistent hypoglossal artery, vascular
entrapment, spontaneous dissection of the extracranial internal carotid artery,
local infections, tuberculosis of the atlantoaxial joint, rheumatoid arthritis,
osteophytic projection from the atlanto-occipital joint,
• Surgical (e.g., carotid endarterectomy) or accidental trauma (e.g., occipital
condyle fracture), birth injuries, neck radiation,
• Epidural abscess of the nasopharyngeal/oropharyngeal carotid space, synovial
cysts, and tumors of the retroparotid or retropharyngeal spaces, neck, salivary
glands, and base of the tongue
• Tumors are the most important cause followed by trauma.

61. ABNORMAL TONGUE MOVEMENTS.
• Choreiform movements of the tongue may result in bizarre lingual movements
and an inability to keep the tongue protruded on command (trombone tongue)
• Galloping tongue refers to an episodic, rhythmic involuntary movement of the
tongue that has been described after head and neck trauma, consisting of three
waves per second that began as posterior midline focal tongue contractions.
• Continuous lingual myoclonus has been described after head injury (EEG normal)
and is thought to be a form of branchial myoclonus without palatal myoclonus

62. DYSARTHRIA
• Dysarthria refers to impaired speech due to abnormal neuromuscular control and
is manifested by abnormalities of articulation, respiration, prosody, resonance of
voice, and phonation..
• The evaluation of motor speech requires the assessment of three speech
activities, they include-A sample of contextual speech, Vowel prolongation,
alternate motion rate of the lips, tongue, and mandible.

64. • THANK YOU