HYPOGLOSSAL NERVE.pptx

Nerve system

1. HYPOGLOSSAL NERVE Dr Irin Binoy JR1

2. INTRODUCTION The HYPOGLOSSAL nerve is the twelfth cranial nerve and the purely motor nerve of the tongue. It’s fibres arise from the HYPOGLOSSAL NUCLEUS, a longitudinal column of cells in the paramedian medulla that lies underneath the HYPOGLOSSAL TRIGONE of the floor of the fourth ventricle. The column of cells extend from the caudal most medulla to the medullary pontine junction and it contains general somatic efferent fibres. The nucleus is somatotropically organised with different cell groups innervating different tongue muscles, from rostral to caudal, intrinsic muscles, genioglossus , hyoglossus and styloglossus

3. COURSE AND RELATIONS From the HYPOGLOSSAL nucleus, the nerve fibres travel in a ventrolateral direction through the medullary reticular formation and medial portion of the olive, coursing lateral to the MLS, Medial lemniscus and pyramid The fibres emerge from the medulla in the preolivary sulcus between the inferior Olivary complex and pyramid as 10-12 rootlets medial to cranial nerves IX X XI These rootlets unite into two bundles that pass separately through the dura and HYPOGLOSSAL canal of the skull

4. After leaving the skull, the two nerve bundles unite and descend vertically through the neck to the angle of mandible.The nerve lies beneath the ICA and IJV and near the vagus nerve. It passes between the artery and vein and runs forward above the hyoid bone between the mylohyoid and hyoglossus muscles and breaks up into a number of different fibres to supply the tongue muscles. ( MUSCULAR OR LINGUAL BRANCHES) The DESCENDING HYPOGLOSSAL RAMUS which courses downwards to form the ANSA HYPOGLOSSI is given off in the neck. It is formed by descending hypoglossal ramus ( XII and C1 cervical root) and descending cervical ramus ( C2 and C3 cervical roots)

5. BRANCHES OF HYPOGLOSSAL NERVE MENINGEAL BRANCHES send filaments derived from the communicating branches with C1 and C2 to the dura of posterior cranial fossa. DESCENDING RAMUS joins with fibres from C1, sends a branch to omohyoid and then joins the descending communicating branches of C2C3 to form ansa cervicalis which supplies omohyoid , sternohyoid and sternothyroid muscles. The THYROHYOID BRANCH also supplies corresponding muscles MUSCULAR OR LINGUAL BRANCHES constitute the real distribution of hypoglossal nerve. Supplies all the intrinsic and extrinsic muscles of tongue except palatoglossus muscle and possibly the geniohyoid

6. The paired extrinsic muscles ( genioglossus , styloglossus , hyoglossus , chondroglossus ) pass from the skull or hyoid bone to the tongue. The genioglossus is the largest and most important of the extrinsic muscles The extrinsic muscles protrude and retract the tongue and move the root up and down. The intrinsic muscles change the length width and the curvature of the dorsal surface and turn the nonprotruded tip from side to side The suprahyoid muscles also influence tongue movement by changing the position of the hyoid bone.

7. SUPRANUCLEAR CONTROL SUPRANUCLEAR control of the tongue is mediated by corticobulbar fibres that originate mainly within the lower portion of the precental gyrus ( persylvian area). The cortical tongue area may be the most lateral part of the precentral gyrus Corticobulbar fibres controlling the genioglossus muscles are crossed and other muscles have bilateral supranuclear control Corticohypoglossal fibres branch off from the main ventral pyramidal tract and cross the midline in the pontomedullary junction and enter the HYPOGLOSSAL nucleus from the lateral aspect

8. EXAMINATION Clinical examination of the hypoglossal nerve function consists of evaluating the strength, bulk and dexterity of the tongue- looking esp for weakness, atrophy and abnormal movements. Note the position and appearance of the tongue at rest in the mouth. Ask the patient to protrude it, move it in and out, side to side, upward and downward both slowly and rapidly. Tongue dexterity can be tested by having repeat lingual sounds like la-la or use words with a t or d phoneme.

9. Motor power can be tested by having the patient press tip against each cheek as the examiner tries to dislodge it with finger pressure. For more precise testing, press firmly with a tongue blade against the side of the protruded tongue and compare strength on two sides.

10. CLINICAL FINDINGS When unilateral weakness is present, tongue deviates towards the weak side on protrusion because of the action of the normal genioglossus muscle which protrudes the tongue by drawing the root forward. There is impairment of ability to deviate the protruded tongue towards the opposite side. The patient cannot push the tongue against the cheek on the normal side but is able to do it on the side which it deviates. At rest, it may deviate or curl slightly towards the healthy side because of unopposed action of styloglossus which draws the tongue upward and backward.

11. Lateral movements of the tip of the unprotruded tongue are controlled by the intrinsic muscles and may be preserved. Facial muscle weakness or jaw deviation makes it difficult to evaluate deviation of tongue. Protruding tongue may cause an appearance of deviation towards the side of facial weakness. But manually pulling up the weak side of the face eliminates deviation. Tongue position can also be gauged in relation to tip of nose or notch between upper incisors.

12. In rare cases of Hypoglossal nerve damage, motor denervation induces denervation pseudohypertrophy . This features extensive fatty replacement in contrast to true hypertrophy Bilateral LMN lesions result in atrophy, weakness and fibrillations of the tongue. Dysphagia is prominent and breathing difficulties may occur when flaccid tongue falls backwards to obstruct the pharynx. When atrophy supervenes, the loss of bulk is first apparent along the borders or at the tip, and tongue may take on a scalloped appearance. As paralysed side becomes wasted, the protruded tongue may curve strikingly towards strophic side assuming a sickle shape.

13. LOCALIZATION SUPRANUCLEAR LESIONS NUCLEAR LESIONS AND INTRAMEDULLARY LESIONS PERIPHERAL LESIONS

14. SUPRANUCLEAR LESIONS Lesions in the corticobulbar tract anywhere in its course from the lower precentral gyrus to the HYPOGLOSSAL nuclei may result in tongue paralysis. Since supranuclear control of genioglossus originates mainly from the contra lateral cortex, a lesion of corticobulbar fibres above decussation results in weakness of contra lateral half of tongue. HENCE TONGUE DEVIATES TO THE SIDE OPPOSITE TO LESION Therefore, in a internal capsule lesion, tongue may deviate towards side of hemiplegia. Interruption of the corticolingual pathway is crucial in Patho genesis of dysarthria following strokes of IC, CR or basis Pontis .

15. Sudden isolated dysarthria can occur in lacunar infarcts affecting corona radiata or internal capsule which interrupts in isolation the corticolingual pathways to the tongue called CENTRAL MONOPARESIS OF TONGUE Main decussation of supranuclear projections is located close to the pontomedullary junction. Hence, pontine lesions at ventral paramedian base close to midline affect contra lateral hypoglossal projections whereas lateral lesions affect ipsilatetal projections Bilateral UMN affection of corticobulbar fibres results in a paretic tongue with no atrophy or signs of denervation called SPASTIC TONGUE

16. NUCLEAR LESIONS Unilateral lesions of the hypoglossal nucleus or nerve results in paresis, atrophy, furrowing, fibrillation and fasciculations that affect the corresponding half of tongue. Due to close proximity of the two nuclei, dorsal medullary lesions like MS, Syringobulbia often result in bilateral LMN lesions of tongue. Isolated CN XII palsy has been reported in association with IMN INTRAMEDULLARY hypoglossal involvement is suggested by associated affection of the medial lemniscus , pyramid or other neighbouring structures. This can be a tumour, demyelination, syringobulbia or vascular insult

17. MEDIAL MEDULLARY SYNDROME DEJERINE’S ANTERIOR BULBAR SYNDROME This syndrome results from the occlusion of the ASA or it’s parent vertebral artery. The anterior spinal artery supplies the ipsilateral pyramid, medial lemniscus , HYPOGLOSSAL nerve IPSILATERAL PARESIS, ATROPHY AND FIBRILLATIONS OF THE TONGUE. THE TONGUE DEVIATES TOWARDS LESION AND AWAY FROM HEMIPLEGIA CONTRALATERAL HEMIPLEGIA CONTRALATERAL LOSS OF POSITION AND VIBRATION SENSE

18. PERIPHERAL LESIONS Cranial nerve XII has a close spatial relationship with cranial nerves IX X XI in the posterior cranial fossa as it leaves in the hypoglossal canal. A basilar skull lesion involving the twelfth cranial nerve in isolation can also frequently involve other lower cranial nerves. When all four are damaged, eg by a base of skull fracture or tumour COLLET- SICARD SYNDROME PARALYSIS OF TRAPEZIUS AND SCM PARALYSIS OF VOCAL CORD AND PHARYNX HEMIPARALYSIS OF TONGUE WITH LOSS OF TASTE POSTERIOR 1/3 HEMIANESTHESIA OF PALATE PHARYNX AND LARYNX

19. Other multiple cranial nerve palsy syndromes may occur with lesions in posterior cranial fossa, skull, retropharyngeal and retrostyloid spaces or in the neck. With neck lesions, cervical sympathetic chain may be involved resulting in ipsilateral Horner’s syndrome.

20. HYPOGLOSSAL VERTEBRAL ENTRAPMENT SYNDROME Isolated HYPOGLOSSAL nerve palsy due to compression by a kinked vertebral artery

21. OCCIPITAL CONDYLE SYNDROME Lesions, usually tumours or chronic inflammation of the occipital condyle may cause occipital pain associated with ipsilateral HYPOGLOSSAL nerve injury. These patients complain of severe localised unilateral occipital pain made worse by neck flexion and associated with neck stiffness. Rotating head towards side of the pain often offers relief . There is accompanying dysarthria, dysphagia specifically related to to difficulty in movement of tongue Ipsilateral tongue is weak and atrophic with fasciculations.

22. JUGULAR FORAMEN SYNDROME OF VERNET It is characterised by paresis of IX X XI nerves with or without XII N due to lesion at the jugular foramen usually a glomus tumour, meningioma, schwannoma or other mets It causes dysphonia, palatal palsy, dysphagia, loss of sensation of tongue posterior 1/3 and weakness of trapezius and SCM

23. GODTFREDSEN SYNDROME Combined ABDUCENS and HYPOGLOSSAL nerve palsies are rare but is often an ominous combination seen usually in nasopharyngeal carcinoma due to involvement of the clivus

24. Other causes of HYPOGLOSSAL nerve lesions include carotid aneurysm, aneurysm of persistent hypoglossal artery, vascular entrapment, spontaneous dissection of the extracranial ICA, local infections, tuberculosis of the atlantoaxial joint, rheumatoid arthritis and osteophytic projections Surgical trauma eg in carotid endarterectomy, birth injuries and neck radiation Epidural abscess of the nasopharyngeal or oropharyngeal carotid space, synovial cysts and tumours of the retroparotid or retropharyngeal spaces.

25. ABNORMAL TONGUE MOVEMENTS Various movement disorders may affect the tongue, including drug induced oral-buccal-lingual dyskinesia, athetosis, palatal myoclonus and tremors Choreiform movements of the tongue may result in bizarre lingual movements and an inability to keep tongue protruded on command TROMBONE TONGUE GALLOPING TONGUE refers to episodic rhythmic involuntary movements of tongue described after head and neck trauma CONTINUOUS LINGUAL MYOCLONUS has been described after head injuries

26. Tongue may also be involved in myotonic disorders. This can be tested by placing the edge of a tongue blade across the tongue and then percuss it sharply. Myotonia may cause a temporary focal contraction along the line of percussion causing the tongue to narrow sharply at that point, called NAPKIN RING SIGN. Coarse tremors of the tongue can occur in Parkinsonism, alcoholism, general paresis Fine tremors can occur in thyrotoxicosis BONBON sign is a dystonic or dyskinesia movement of the tongue characterized by protrusion or lateral tongue movements within the mouth producing a bulge in cheek as if pt were storing a piece of candy, seen in tardive dyskinesia

27. SYSTEMIC DISEASES AND TONGUE Progressive bulbar palsy and advanced ALS may cause atrophy so severe tongue cannot be protruded and lies inert on the floor of mouth called GLOSSOPLEGIA . In myasthenia graves, tongue atrophy may develop and lead to a triple furrowed appearance with grooves paralellling the median sulcus on each side called TRIDENT TONGUE Profuse fasciculations in LMN lesions may cause the tongue to have a BAG OF WORM APPEARANCE MACROGLOSSIA of tongue is seen in hypothyroidism, Down’s syndrome, amyloidosis, acromegaly, sarcoidosis etc

28. ATROPHIC GLOSSITIS refers to atrophy of epithelium and papillae causing a smooth glistening often reddened tongue seen in vit B12, folate and iron deficiency Scarlet red and swollen tongue seen in pellagra Magenta tongue seen in riboflavin deficiency Fusion and atrophy of the papillae and fissuring may cause a geographic or scrotal tongue seen in Melkersson-Rosenthal syndrome.

29. Thank you