Facial Nerve BY DR SOMYA CHOUBEYMS ENT.pptx

FACIAL NERVE PRESENTATION
BY DR SOMYA CHOUBEY
MS ENT

1. FACIAL NERVE ANATOMY AND PATHOLOGY DR SOMYA CHOUBEY DEPARTMENT OF ENT

2. INTRODUCTION The nerves intermedius emerges between the pons and inferior cerebellar peduncle. Facial nerve is seventh cranial nerve The VII cranial nerve emerges from the brainstem, between the pons and olive. Joining the main facial nerve in its cisternal segment, it traverses the cerebellopontine angle to enter the porous of the IAM, together with the VIII cranial nerve

3. Lying anterosuperior in the IAM, it is above the cochlear nerve, the  superior and inferior vestibular nerves being posteriorly located. At the lateral extent of the IAM, the facial nerve passes through its narrowest portion via the labyrinthine segment, between the cochlea and vestibule INTRODUCTION

4. INTRODUCTION From the first genu, VII runs in its horizontal tympanic segment in the medial wall of the middle ear, passing above the promontory. It curves over the oval window niche before reaching the second genu, just inferior to the lateral semicircular canal, at which point it curves downwards into its vertical mastoid segment behind the external auditory canal.

5. INTRODUCTION The nerve to Stapedius branches off here, reaching the muscle via a tiny canaliculus. Just before it exits the skull base, VII gives off the fibers of the  nervus intermedius as the chorda tympani, there after passing through the stylomastoid foramen as a purely as motor nerve

6. EMBRYONIC DEVELOPMENT OF FACIAL NERVE Facial nerve course, branching pattern, and anatomical relationships are established during the first 3 months of prenatal life. The nerve is not fully developed until about 4 years of age the first identifiable facial nerve tissue is seen at the third week of gestation-faciao acoustic primordium or crest

7. EMBRYONIC DEVELOPMENT OF FACIAL NERVE Weeks Features 0-4 Appearance of facio-acoustic primordium/crest Splitting of facial nerve Presence of chorda tympani 5-6 Separation of facial and acoustic nerves Appearance of geniculate ganglion Formation of GPN 7 Formation of peripheral branches 8 Formation of fallopian canal 10-15 More extensive branching

8. NUCLEI OF ORIGIN Motor nucleus Motor nucleus or brachiomotor Upper face receives bilateral innervation. lower face receives unilateral innervation. Muscles of facial expression. posterior belly of digastric. stylohyoid muscle. stapedius. Lacrimatory and Superior salivatory nucleus Submandibular & sublingual salivary glands lacrimal gland Nucleus of solitary tract ( gustatory nucleus) Mediates taste

9. FUNCTIONAL COMPONENT

10. COURSE OF NERVE INTRACRANIAL Intra pontine course Attachment to the brain stem Course through posterior cranial fossa Intrapetrous MEATAL SEGMENT I NTERNAL ACOUSTIC CANAL Facial Canal Part TYMPANIC SEGMENT (10-12MM) LABYRINTHINE SEGMENT (3-5MM) Mastoid segment EXTRATEMPORAL Exit from the cranium

11. INTRACRANIAL COURSE The Fibers From The Motor Nucleus Course Through The Pons Taking A Sharp Bend Around The Abducent Nucleus Producing Internal Genu Of The Facial Nerve And They Leave The Pons Between The Nucleus Of Spinal Tract Of Trigeminal And The Other Facial Nucleus. INTRAPONTINE COURSE :

12. INTRACRANIAL COURSE The sensory and motor roots are attached to the lateral aspects of the pontomedullary junction. ATTACHMENT TO THE BRAIN STEM:

13. INTRACRANIAL COURSE From the superficial attachment to the brainstem to the opening of the internal acoustic meatus the two roots of the facial nerve pass laterally and forward in the cerebellopontine angle along with vestibulochoclear nerve and labyrinthine artery. These structures together enter the internal acoustic meatus Course Through Posterior Cranial Fossa

14. INTRAPETROUS COURSE FrIt is in the internal acoustic meatus where the motor root is lodged in a groove on the antero-inferior surface of the vestibulochoclear nerve but the sensory root separates them. At the bottom of the internal acoustic meatus , the two roots unite to form the trunk of the facial nerve and then it enters the facial canal. Meatal segment :

15. INTRAPETROUS COURSE Labyrinthine segment : passes laterally above the vestibule of the inner ear to reach the anterior end of the medial wall of the middle ear. Here it bends backwards at a sharp turn called the external genu of the facial nerve which has the geniculate ganglion on it Facial canal Part: is divided into 3 segments:

16. INTRAPETROUS COURSE It passes backwards in the medial wall of the middle ear till it reaches the posterior end of this wall. It is also known as the horizontal part Tympanic segment

17. INTRAPETROUS COURSE It begins at the posterior end of the medial wall and passes downwards in relation to the posterior wall of the middle ear to reach the stylomastoid foramen. Mastoid segment or vertical segment

18. EXIT FROM THE CRANIUM The facial nerve leaves the cranium through stylomastoid foramen

19. EXTRACRANIAL COURSE The facial nerve crosses the lateral side of the base of the styloid process. It enters the posteromedial surface of the parotid gland

20. EXTRACRANIAL COURSE Within the gland it runs forward for a short distance superficially to the retromandibular vein and external carotid artery and then divides into a)Temprofacial and b)Cervicofacial trunks.

21. EXTRACRANIAL COURSE Temporofacial and Cervicofacial

22. EXTRACRANIAL COURSE The terminal branches radiate like a goose’s foot from the anterior border of the parotid gland – “Pes anserinus”

23. Branches of Distribution Facial canal Nerve to stapedius Greater petrosal nerve Chorda tympani Stylomastoid foramen Posterior auricular Nerve to digastric (posterior belly). Nerve to stylohyoid In face Temporal,Cervical ,Marginal mandibular,Buccal,Zygomatic

24. COURSE & RELATIONSHIPS PF LEFT FACIAL NERVE

25. FACIAL CANAL 1- Greater superficial petrosal nerve (GSPN) : carries preganglionic parasympathetic fibers These fibers are conveyed by the NI to geniculate ganglion. Pass through the ganglion without synapsing into the greater petrosal nerve, which goes forward through the hiatus of the facial canal to join deep petrosal nerve from the carotid sympathetic plexus to form the vidian nerve, or the nerve of the pterygoid canal, which runs to the sphenopalatine ganglion, from where postganglionic fibers proceed to the lacrimal gland. 2-Nerve to stapedius: supplies the stapedius muscle.

26. Chorda tympani nerve: It arises from the facial nerve 6 mm above the stylomastoid foramen and runs upwards to perforate the posterior bony wall of the tympanic cavity. It carries taste and general visceral afferent (GVA) fibers as well as preganglionic parasympathetics.

27. General Somatic afferents (GSA)/Sensory Fibers carrying somatosensory afferents in chorda tympani have their cell bodies in the geniculate ganglion. Peripheral processes innervate part of the external auditory canal, tympanic membrane, lateral surface of the pinna, and small area behind the ear and over the mastoid process. Their central processes terminate in the spinal tract and nucleus of the trigeminal

28. Special Visceral Afferent/Taste Taste sensation from the anterior two-thirds of tongue is carried through lingual nerve to the chorda tympani, then to geniculate ganglion. Also carry taste sensation from the mucosa of soft palate through the sphenopalatine ganglion. Central processes carrying taste and GVA sensation terminate in the nucleus of the solitary tract.

29. General Visceral Efferent/Parasympathetic Chorda tympani also carries Preganglionic parasympathetic fibers to the submandibular ganglion. Postganglionic fibers convey secretory and vasodilator impulses to the submandibular and sublingual salivary glands and mucous membranes of mouth and tongue. These glands also receive sympathetic innervation through superior cervical ganglion and the carotid plexus. Parasympathetic fibers cause vasodilation and a copious, thin, watery secretion high in enzymes; Sympathetic fibers cause vasoconstriction and a scant, thick, mucoid secretion low in enzyme content

30. II- At exit from the stylomastoid foramen 1- Posterior auricular nerve: Supplies the occipitalis , posterior auricular, and transverse and oblique auricular muscles. 2- Digastric branch: Posterior belly of digastric muscle 3- Stylohyoid branch: Stylohyoid muscle

31. SURGICAL LANDMARKS OF THE FACIAL NERVE Landmarks for Extratemporal Part : Tragal pointer (of Conley): The nerve is located medial and about 1 cm antero-inferior to the tragal cartilage Tympanomastoid suture (TMS): This is located at the apex of the vagino-mastoid angle or valley of the nerve. It is the angle where the vaginal process of the tympanic portion of the temporal bone meets the mastoid process. The facial nerve runs just deep (6-8mm) to this suture.

32. SURGICAL LANDMARKS OF THE FACIAL NERVE Landmarks for Extratemporal Part : 3.Styloid process: The nerve passes lateral to the styloid process at the skull base 4Tendon of the posterior belly of digastric muscle

33. SURGICAL LANDMARKS OF THE FACIAL NERVE Landmarks for Extratemporal Part : 5. By tracing the terminal branches of the facial nerve backwards: The ramus frontalis is located by a line from the tragus to lateral canthus The ramus buccalis- a line from the tragus towards the alae of the nose parallel to the zygoma but 1 cm below Ramus mandibularis- near the angle of the mandible; a point 4–4.5 cm from the attachment of the lobule of the pinna. 6.During submandibular gland excision, to save the marginal mandibular branch, dissection should be carried out in the plane deep to the fascia overlying the submandibular gland .

34. Landmarks in the Mastoid and the Middle Ear: The cog, which is a bony ridge, hangs from the tegmen, anterior to the head of the malleus, is useful in identifying the first genu Cochleariform process is immediately inferior to the anterior portion of the tympanic segment of the facial nerve. The oval window is a useful guide to the posterior portion of the horizontal segment of the nerve. The nerve lies above the oval window The lateral semicircular canal lies postero-superior to the second genu. This is a very constant landmark

35. Landmarks in the Mastoid and the Middle Ear: The nerve is located medial to the inferior portion of the tympanic annulus-, the minimal distance from the annulus tympanicus to the facial nerve is about 1 mm at 9 o’clock position Pyramidal ridge- The upper portion of the vertical segment lies in the base of this bony ridge that separates the sinus tympani from the facial recess. The processus pyramidalis attaches to the superior aspect of this ridge

36. Landmarks in the Mastoid and the Middle Ear: Short process of incus- The facial nerve lies medial to the short process of incus at the level of the aditus Digastric ridge points to the lateral and inferior aspect of the vertical segment of the facial nerve ie; the nerve leaves the mastoid at the anterior end of the ridge

37. Landmarks in the Mastoid and the Middle Ear: Retrofacial cells: These cells extend from the central mastoid tract always medial to the facial nerve draining into the hypotympanic space. The facial nerve was posterosuperior to promontory and oval window and the nerve passed below lateral semi-circular canal

38. Landmarks in the Middle Cranial Fossa : Greater superficial petrosal nerve Internal auditory canal Arcuate eminence

39. VARIATONS AND ANOMALIES OF FACIAL NERVE Congenital Bony Dehiscence More commonly seen in the tympanic portion Most frequent site is above and posterior to the oval window

40. VARIATIONS AND ANOMALIES OF FACIAL NERVE Ear: PROLAPSE OF NERVE The dehiscent nerve may prolapse over the stapes and make stapes surgery or ossicular reconstruction difficult. HUMP The nerve may make a hump posteriorly near the horizontal canal making it vulnerable to injury while exposing the antrum during mastoid surgery

41. VARIATIONS AND ANOMALIES OF FACIAL NERVE Ear: BIFERCATION AND TRIFERCTION . The vertical part of facial nerve divides into two or three branches , each occupying a separate canal and exiting through individual foramen 5)BIFERCATION AND ENCLOSING STAPES The nerve divides proximal to oval window –one part passing above and other below reuniting BETWEEN THE OVAL AND ROUND WINDOW Just before oval window the nerve crosses the middle ear passing between oval and round windows

42. ANASTOMOTIC PATTERNS OF TERMINAL BRANCHES Classified by Davis et al (1956) Type I : No anastamosis between branches of Facial Nerve Type II: Presence of an anastamotic connection between branches of temporofacial division. Type III: A single anastamosis between temporofacial and cervicofacial division. Type IV : A combination of Type II and III Type V: Two anastamotic ramii passed from cervicofacial division to interwine with branches of temporofacial division. Type VI : Plexiform arrangement, the mandibular branch sends twing to join any members of temporofacial division.

43. Terminal branches within the parotid gland

44. Communicating branches

45. Terminal branches within the parotid gland

46. Ganglia Associated With Facial Nerve GENICULATE GANGLION : is located on the first bend of the facial nerve, in relation to the medial wall of the middle ear. it is a sensory ganglion the taste fibers present in the nerve are present in the genigulate ganglion

47. SUBMANDIBULAR GANGLION : is a parasympathetic ganglion for relay of secretomotor fibers to the submandibular and sublingual salivary glands. .

48. SUBMANDIBULAR GANGLION : The motor or parasympathetic fibers pass from the lingual nerve to the ganglion through the posterior root. These are preganglionic fibers that arise in the superior salivatory nucleus and pass through the facial nerve- the chorda tympani and the lingual nerve to reach the ganglion.

49. PTERYGOPLATINE GANGLION (SPHENOPALATINE GANGLION):

50. PTERYGOPLATINE GANGLION (SPHENOPALATINE GANGLION): Is the largest parasympathetic peripheral ganglion. It serves as a relay station for secretomotor fibers to the lacrimal gland and to the mucous glands of the nose,paranasal sinuses,palate and the pharynx. It is also called hay fever ganglion.

51. BLOOD SUPPLY The facial nerve gets it’s blood supply from 4 vessels : . Anterior inferior cerebellar artery At the cerebellopontine angle Labyrinthine artery (branch of anterior inferior cerebellar artery) – within internal acoustic meatus Superficial petrosal artery (branch of middle meningeal artery) – geniculate ganglion and nearby parts Stylomastoid artery (branch of posterior auricular artery) – mastoid segment

52. BLOOD SUPPLY The arteries form external plexus lying within the epineurium and an internal plexus which is intraneural Venous drainage is into the venae commutants of the superficial petrosal and stylomastoid viens

53. SURGICAL ANATOMY OF FACIAL NERVE Variations of facial nerve branching patterns Flower (1961) reviewed seven variations including changes in angulation. Curtis and May (1986) reported a case of progressive facial nerve canal along the internal auditory canal, creating a double internal auditory canal. Caprosa and Klassen (1966) observed bifurcation of facial nerve just distal to the geniculate ganglion. Duncan, Shea and Sleeck x (1967) found bifurcation of branches of the chorda tympani.

54. CLINICAL RELEVANCE-DAMAGE TO THE FACIAL NERVE

55. Three Degrees of Facial Nerve Fiber Injury

56. Three Degrees of Facial Nerve Fiber Injury

57. Level Of Nerve Injury And Symptoms The facial nerve has a wide range of functions. Thus, damage to the nerve can produce a varied set of symptoms, depending on the site of the lesion.

58. FACIAL PARALYSIS Paresis : weakness of facial muscles to perform motor functions is called paresis ( partial dysfunction) Paralysis : Total flaccidity of facial muscles to perform motor function is called facial paralysis

59. SUPRANUCLEAR FACIAL PARALYSIS It is usually hemiplegia- it is the lower part of the face that is chiefly affected, while the upper part remains unaffected,i.e.,the frontalis and orbicularis oculi muscles escape. This is because there is bilateral control

60. INFRANUCLEAR FACIAL PARALYSIS The lower motor neuron lesion of facial nerve cause paralysis of all facial muscles on the same side

61. BELL’S PALSY It is defined as an idiopathic paresis or paralysis of the facial nerve of sudden onset. The name was ascribed to SIR CHARLES BELL , who in 1821 demonstrated the separation of motor and sensory innervation of face.

62. BELL’S PALSY Inability to smile, close eye and raise eyebrow. Whistling is impossible Drooping of corners of the mouth. Slurred speech Inability to close eyelid (Bell’s sign) Loss of blinking reflex Inability to wrinkle forehead Mask like appearance of the face. Loss or alteration of taste

63. BELL’S PALSY COURSE AND PROGNOSIS Partial paralysis always resolves completely within a few weeks. Recovery from complete paralysis takes longer (months) and is complete in only about 60-70% of cases. Approximately 15% of patients are left with troublesome residual palsy .

64. RAMSAY HUNT SYNDROME A special form of herpes zoster infection of the geniculate ganglion with the involvement of the external ear and the oral mucosa

65. MELKERSSON ROSENTHAL SYNDROME Recurrent attacks of facial paralysis Associated with multiple episodes of non-pitting, non-inflammatory painless edema of the face Chelitis granulomatosa Fissured tongue

66. MOBIUS SYNDROME Results from the underdevelopment of cranial nerve VI and VII The VI cranial nerve controls lateral eye movement, and the VII cranial nerve controls facial expression and is manifested in infancy

67. MOBIUS SYNDROME Because of partial or complete facial paralysis, the infant exhibits : ➢No change in facial expression (mask like appearance) ➢Failure to close eyes during sleep. ➢Mouth may remain partially open

68. CROCODILE TEARS SYNDROME Due to injury to facial nerve proximal to the geniculate ganglion, there may be a misdirection of nerve fibres to lacrimal gland instead of going to submandibular gland, through the greater petrosal nerve. As a result patient lacrimates is termed as ‘ crocodile tear syndrome ’ and can be treated by dividing greater petrosal nerve.

69. Evaluation of Nerve function HISTORY is of vital importance to establish the onset characteristics, duration and degree of recovery. Previous trauma, surgery or infection may help in arriving at a diagnosis Examination of the face at rest and movement. Radiologic evaluations : CT, MRI Nerve function tests : topognostic testing, ear pain, taste, tearing, salivation, stapeus reflex/auditory testing, vestibular testing, electronystagmography, Electrophysiologic testing: Evoked electromyography.

70. CONCLUSION The most important thing about the intracranial course of Facial Nerve is its relationship to the middle ear. The most important thing about the extracranial course is its relationship to the parotid gland. Hence a complete understanding of its anatomy is essential and care should be taken during surgical procedures

71. THANKYOU