Hypoglossal nerve

A Short presentation of Hypoglossal Nerve

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

5. INTRODUCTION ORIGIN COURSE & RELATIONS ACTIONS EXAMINATION LOCALISATION

6. 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

7. 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

8. INTRODUCTION ORIGIN COURSE & RELATIONS ACTIONS EXAMINATION LOCALISATION

9. 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

10. Relations at the brain stem

11. 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

12. 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.

13. Hypoglossal canal

14. 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

15. 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.

16. branches The branches of the hypoglossal nerve MENINGEAL, DESCENDING, THYROHYOID, MUSCULAR,

17. Meningeal branch The meningeal branches send filaments derived from communicating branches with C1 and C2 to the dura of the posterior fossa

18. 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.

19. 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

20. 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.

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22. 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.

23. INTRODUCTION ORIGIN COURSE & RELATIONS ACTIONS EXAMINATION LOCALISATION

24. 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.

25. 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.

26. 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.

27. 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.

28. Clinical finding Atrophy Fasciculations and tremors Ankyloglossia Macroglossia Atrophic Glossitis Burning tongue Ulcerations.

29. INTRODUCTION ORIGIN COURSE & RELATIONS ACTIONS EXAMINATION LOCALISATION

30. localisation Supranuclear lesions Nuclear Lesions and Intramedullary Cranial Nerve XII Lesions Peripheral Lesions of Cranial Nerve XII.

31. 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

32. 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

33. 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 .

34. 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.

35. 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)

36. Medial medullary syndrome

37. 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

38. 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.

39. 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.

40. . 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.

41. 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

42. 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.

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