ANATOMY OF FACIAL NERVE PGIMERCHD PPT.pptx

ANATOMY OF FACIAL NERVE.

1. ANATOMY OF FACIAL NERVE - HARINI CHAKRIKA.M MODERATOR – DR. APOORVA

2. CONTENTS INTRODUCTION EMBRYOLOGY FUNCTIONAL COMPONENTS BRANCHES AND FUNCTIONS COURSE BLOOD SUPPLY AND LYMPHATICS SURGICAL CONSIDERATIONS PREVENTION OF FACIAL NERVE INJURY DISORDERS OF FACIAL NERVE FACIAL NERVE TESTING CONCLUSION

3. INTRODUCTION Seventh cranial nerve Comprised of motor efferent and sensory afferent fibres Courses tortuously from its intracranial origins through temporal bone to its extratemporal terminations An understanding of the anatomy and function of the facial nerve is necessary to localize pathology, prevent surgical injury, and treat facial nerve disorders.

4. EMBRYOLOGY Derived from second branchial arch

5. EMBRYOLOGY

6. FUNCTIONAL COMPONENTS

7. FUNCTIONAL COMPONENTS

8. FUNCTIONAL COMPONENTS

9. BRANCHES AND FUNCTIONS

10. BRANCHES AND FUNCTIONS Within the facial canal: Greater petrosal nerve - carries taste afferents from the soft palate and sensory afferents from the dura mater, internal carotid artery, and the pterygopalatine ganglion to the geniculate ganglion; increases secretomotor function of nasal-palatal glands and mucosa and mediates reflexive tearing at the lacrimal glands . Nerve to the stapedius - innervates the stapedius muscle in the middle ear  stabilizes and protecting the inner ear by dampening sound. Chorda tympani - conveys taste sensation from the ipsilateral anterior two-thirds of the tongue + parasympathetic innervation of the submandibular gland.

11. BRANCHES AND FUNCTIONS As it exits from the stylomastoid foramen: Posterior auricular - sensory fibers to the external auricle and ear canal + motor fibers to the inferior auricular and occipitalis muscles Digastric - motor fibers to the posterior belly of the digastric Stylohyoid - motor fibers to the stylohyoid muscle

12. BRANCHES AND FUNCTIONS Terminal branches within the parotid gland: Temporal Zygomatic Buccal Marginal mandibular Cervical

13. BRANCHES AND FUNCTIONS

14. COURSE Discussed as following segments

15. FACIAL NERVE NUCLEI Three main nuclei within brainstem Motor nucleus of facial nerve – Located in ventrolateral pontine tegmentum Receives input from the central motor nucleus in the pre-central gyrus via descending corticobulbar tracts from both cerebral hemispheres D ivided into an upper part - conveys contralateral + ipsilateral output fibers to the upper face ; lower part - conveys contralateral fibers to lower face

16. FACIAL NERVE NUCLEI Efferent fibers loop dorsally around CN VI nucleus in floor of 4th ventricle forming facial colliculus Fibers then course anterolaterally to exit lateral brainstem at pontomedullary junction

17. FACIAL NUCLEI Superior salivatory nucleus – autonomic parasympathetic R eceives involuntary hypothalamic input Sends parasympathetic motor supply for the submandibular, sublingual and lacrimal glands. Solitary nucleus – sensory and taste components C ontains gustatory nucleus - receives sensory input via the geniculate ganglion G eniculate ganglion transmits general sensory information from the auricle and taste via the chorda tympani and lingual branch of the trigeminal nerve.

18. CISTERNAL Short segment coursing from the brainstem to the internal acoustic meatus (IAM) V entrolateral pontomedullary junction  courses laterally as - motor root and sensory root - nervus intermedius (intermediate nerve)  courses parallel and anterior to CN VIII. M otor root – conveys SVE fibers from the facial nuclei to muscles of the second branchial arch. N ervus intermedius - contains all autonomic and sensory nerves Nerve roots are invested only in pia mater and lack perineurium Sensory root is more vulnerable to injury in this segment

19. INTRATEMPORAL COURSE

20. MEATAL L ies in anterosuperior portion of the internal auditory meatus, with the motor root anterior to sensory root. F alciform crest - divides the IAM into superior and inferior halves - separates facial nerve from the cochlear nerve inferiorly. Bill’s bar - separates the facial nerve from the vestibular nerve posteriorly. Within the IAM, the facial nerve are sheathed in arachnoid matter, but lacks an epineurium and perineurium. C ourses with the vestibulocochlear nerve for 7-10 mm  branches off the IAM  Fallopian canal or facial canal.

21. LABRYNTHINE E xtends from IAM to the geniculate ganglion within petrous temporal bone N arrowest segment of the intratemporal facial nerve - 3-5 mm long C ourses superiorly and laterally towards cochlea  turns sharply forward  reaches geniculate ganglion  acute turn to run posteriorly  transitions into tympanic segment. Just distal to geniculate ganglion  GPSN At the end of the labyrinthine segment - first genu

22. TYMPANIC H orizontal s egment - travels horizontally for about 8-12 mm through temporal bone. P roximal portion - extends from geniculate ganglion to the cochleariform process, where it lies superomedial to this process. T ravels distally to the level of the pyramidal eminence running anteriorly and immediately inferiorly to the semicircular canals.

23. TYMPANIC P rominence is seen as it courses along the medial wall of the middle ear cavity superior to the oval window, or fenestra vestibuli. E nd of tympanic segment  second genu above the pyramidal eminence  courses vertically and inferiorly as mastoid segment.

24. MASTOID V ertical segment - longest and widest segment of the fallopian canal - presents the greatest anatomic variability Extends 8-15mm  exits temporal bone at stylomastoid foramen  extratemporal facial nerve segment emerges with epineurium and thick connective tissue. Gives rise to three branches - nerve to stapedius, general sensory branch of the facial nerve, and chorda tympani. C horda tympani - arises in the inferior one-third of this segment - 5 mm above the stylomastoid foramen  courses between the malleus and incus  exits at petrotympanic fissure  joins lingual nerve

25. GANGLIA ASSOCIATED WITH FACIAL NERVE Geniculate  Sits between the cochlea and the tympanic cavity. Taste fibers present in nerve as peripheral processes of pseudounipolar neurons present in geniculate ganglion Sensory innervation of other sites, such as the palate, the pinna of the ear and ear canal

26. GANGLIA ASSOCIATED WITH FACIAL NERVE Pterygopalatine S ensory root - sphenopalatine  branches P arasympathetic root -   nervus intermedius  through the  greater petrosal nerve . S ympathetic efferent (postganglionic) -fibers from the  superior cervical ganglion through deep petrosal nerve Supplies the  lacrimal gland ,  paranasal sinuses , glands of the mucosa of the  nasal cavity  and  pharynx ,  hard palate and gin giva

27. GANGLIA ASSOCIATED WITH FACIAL NERVE Submandibular S ituated above the deep portion of submandibular gland , on the  hyoglossus muscle , near posterior border of the  mylohyoid muscle . Topographically - related to lingual nerve but functionally related to chorda tympani Sympathetic fibers - from the  external carotid plexus Preganglionic  parasympathetic fibers - from the  superior salivatory nucleus  via the  chorda tympani  and  lingual nerve Postganglionic  parasympathetic fibers - to the  oral mucosa  and the  submandibular  and  sublingual  salivary glands. 

28. EXTRATEMPORAL B egins at the stylomastoid foramen  divides with complex branching pattern. Before entering the parotid gland  gives rise to 3 branches - the posterior auricular, digastric, and stylohyoid branches E nters parotid gland  separates the gland into superficial and deep lobes and travels at the level of the retromandibular vein. Within the gland  divides at the pes anserinus into 2 superior temporo-facial and inferior cervico -facial branches at an obtuse angle  s ubdivides into terminal branches  interlaces and forms parotid plexus.

29. EXTRATEMPORAL C lassically 5 main subdivisions within the parotid gland Temporofacial division - includes temporal, zygomatic, and buccal branches C ervicofacial division - includes marginal mandibular and cervical branches. Exits the parotid gland  deep to parotido -masseteric fascia  pierces this layer near the anterior border of the masseter muscle  proceeds deep to superficial musculoaponeurotic system  innervates facial muscles. While most facial muscles are innervated on their deep surface, the mentalis, buccinator, and levator anguli oris are innervated on their superficial surface.

30. BRANCHING PATTERNS

31. Davis et al. classified these patterns into six types Most common type – Type III Type I – no anastomosis between temporofacial and cervicofacial division Type II – Anastomosis only between the branches of temporo-facial division Type III – Single anastomosis between the branches of temporofacial and cervicofacial divisions Type IV - Combination of Types II and III Type V – Double anastomosis between the branches of temporofacial and cervicofacial divisions Type VI – Complex numerous anastomosis between two divisions, where the buccal branch receives many fibres from mandibular branch and cervicofacial division. BRANCHING PATTERNS

32. TEMPORAL BRANCH F rontal division C onsists of 3-4 nerves - travels between temporo-parietal fascia and superficial layer of the deep temporal fascia Penetrate the frontalis muscle at the same level at which superficial temporal artery gives descendant branch to muscle

33. TEMPORAL BRANCH Pitanguy’s line - commonly used approximation for the path of the temporal branch - drawn from 0.5 cm inferior to the tragus extending to a point 1 cm above the lateral eyebrow or 1.5 cm lateral to the lateral canthus. C rosses zygomatic arch 4 cm behind the lateral canthus and between 10 mm anterior to the EAC and 19 mm posterior to the lateral orbital rim – Gosain et al

34. ZYGOMATIC BRANCH 2 to 6 branches Upper zygomatic branches  enters the superolateral aspect of the orbicularis oculi muscle above the lateral canthal area. L ower zygomatic branches enters the lateral third of the inferior part of the orbicularis oculi muscle Main zygomatic branches coursed under the zygomaticus major muscle and supplied the upper lip levator muscles. Several communicating branches between the zygomatic and buccal branches  I njury to single branch of zygomatico -buccal nerve goes unnoticed

35. ZYGOMATIC BRANCH L ocation of the zygomatico -buccal branch - estimated within 2.3 mm from Zuker’s point S urface landmark defined as the midpoint on a line which extends from the root of the helix to the oral commissure.

36. BUCCAL BRANCH 2 to 5 branches O riginates from the superior division and, in 70 percent, from the cervicofacial division I nterconnections with the lower zygomatic or marginal mandibular branches E ventually courses within the buccal fat pad pg parotid gland, pd parotid duct, zm zygomaticus major, m masseter, oo orbicularis oculi, asterisks zygomatic branches, white arrow exit point of buccal branches in the anterior border of the parotid gland, black arrows buccal branches (right side).

37. BUCCAL BRANCH 75% - buccal branch leaves parotid gland inferior to the duct; 10% - branch is superior to the duct; 15% - both superior and inferior branches were present Buccal branch usually maintained a parallel course to duct; 25% - nerve crossed the duct at a mean distance of 2.3mm from edge of parotid gland Once parotid duct is identified  buccal branch is most likely inferior and within 5.43 +/- 3.65mm vertically.

38. MARGINAL MANDIBULAR BRANCH Varies between a single branch and up to 3-4 branches. E xits parotid gland  travels in variable relation to mandibular border T ravels midway between angle and mental protuberance  innervates muscles of lower lip.

39. MARGINAL MANDIBULAR BRANCH The position of this branch is variable when posterior to the facial artery – A bove the inferior border of the mandible in 81% Below the inferior border of the mandible in 19% of the cases Anterior to facial artery – 100% of branches are above the inferior border of mandible

40. MARGINAL MANDIBULAR BRANCH In 98% of the specimens, mandibular branch crossed on superficial surface of posterior facial vein  superficial surface of anterior facial vein and artery Branching pattern of marginal mandibular nerve is also variable

41. MARGINAL MANDIBULAR BRANCH Lowermost branch of nerve lies 0.6cm above inferior border to 1.2cm below inferior border. 47% of the mandibular branches were above the inferior border for their whole course and 53 % below the mandible until they reached the facial vessels. Of the latter, 6 % of the nerves continued below the mandible for a distance ranging between 0.8 to 1.5 cm Branching pattern was also variable

42. CERVICAL BRANCH 1 to 3 branches E xits parotid gland  travels 1-15 mm behind the angle of the mandible  runs along the superficial part of posterior edge of the submandibular gland  meets the greater cornu of the hyoid bone  divides into sub-branches penetrating the platysma muscle Communicates with cervical plexus and marginal mandibular nerve. Found roughly half the distance from the mentum to the mastoid and approximately 1cm below this line about the position of the angle of the mandible

43. BLOOD SUPPLY AND LYMPHATICS Facial nerve gets its blood supply from 4 vessels Anterior inferior cerebellar artery – at cerebellopontine junction Labyrinthine artery – Internal acoustic meatus Superficial Petrosal Artery (branch of middle meningeal artery) -geniculate ganglion and nearby parts Stylomastoid artery (branch of posterior auricular artery) - mastoid region

44. SURGICAL CONSIDERATIONS

45. FASCIA RELATIONS Downward extension of galea aponeurotica above zygomatic arch – superficial temporal fascia or temporo-parietal fascia Superficial temporal fascia is distinct from deep temporal fascia – separated by avascular plane of loose areolar tissue Inominate fascia – highly vascular plane superficial to deep temporal fascia Deep temporal fascia – splits at the temporal line of fusion just below the level of superior orbital margin

46. FASCIA RELATIONS Deep temporal fascia splits into into superficial lamella attached to superficial edge of arch and deep lamella attached to deep edge of arch Encased between lamellae – superficial temporal fat pad Parotido -masseteric fascia –deep cervical fascia – deep to SMAS and superficial to masseter

47. FASCIA RELATIONS Infero -lateral wall of the submandibular space. From outward to inward, the wall comprises  S kin Su bcutaneous tissue – comprises external fat layer, SMAS containing platysma, internal fatty layer S uperficial layer of deep cervical  fascia , which is attached superiorly to the  mandible , inferiorly to the  hyoid bone  and posteriorly to the stylohyoid ligament.

48. DANGER ZONES Frontal Branch The frontal branch becomes more superficial as it courses cephalically in the temple. Nerve branches are always located anterior and inferior to the frontal branch of the superficial temporal artery E xits parotid gland within the parotid-masseteric fascia  continues within innominate fascia across the zygomatic arch

49. DANGER ZONES F ascial transition zone - point 1.5cm above the superior border of the arch F rontal branches transition from innominate fascia to run on the undersurface of the superficial temporal fascia  enters frontalis or orbicularis oculi muscle.

50. DANGER ZONES SECKEL’S DANGER ZONE 2 – Outlined by drawing a line 0.5 cm below the tragus to a point 2 cm above the lateral eyebrow, drawing a second line to the zygoma to the lateral orbital rim and connecting these two lines by a third line

51. DANGER ZONES Zygomatic Branch Crosses over the superficial layer of masseter and deep to SMAS Most vulnerable to injury in the region just lateral and inferior to the zygomatic eminence. This area of facial soft tissue tends to be fibrous to dissect as the zygomatic and upper masseteric ligaments merge.

52. SECKEL’S FACIAL DANGER ZONE 4 - This zone contains the zygomatic and buccal branches of the facial nerve that are superficial to and rest on the Buccal Pad of Fat. Outline by placing a point on the highest point of the malar eminence, another point on the mandibular angle and a third point on the oral commissure. These three points are connected to form a triangle DANGER ZONES

53. DANGER ZONES Cervical and Marginal Branch Marginal mandibular branch exits the anterior caudal margin of the parotid  remains deep to the parotido -masseteric fascia and investing layer of deep cervical fascia. C ervical branch is typically situated in the plane between superficial and deep fascia and innervates the platysma along its deep surface. Cervical branch is more prone to injury due to its superficial location

54. SECKEL’S FACIAL DANGER ZONE 3 – This zone contains the marginal mandibular branch of the facial nerve at a point in its course where it is most vulnerable as the platysma- SMAS layer thins below and the nerve courses superiorly to innervate the depressor anguli oris muscle. Described by drawing a point on the middle of the mandibular body 2 cm posterior to the oral commissure and drawing a circle with radius 2 cm around this point. DANGER ZONES

55. DANGER ZONE FOR MARGINAL MANDIBULAR AND CERVICAL BRANCHES Posteriorly – 2cm behind gonion and posterior border of ascending ramus Inferiorly – 2cm below gonion extending back to posterior landmark and extending forward 2cm below inferior border as far forward as 2 nd premolar tooth. Anteriorly – Line drawn through long axis of lower 2 nd premolar to 2cm below inferior border of body of mandible

56. INJURY TO FACIAL NERVE IN PAROTID AND ITS REPAIR Injury to the main trunk or temporo-zygomatic or cervicofacial divisions is always repaired Clear lacerations with immediate onset of facial palsy  repair is undertaken in the first 3 days or if not possible, three weeks later Gross contamination  proximal and distal segments should be identified and tagged

57. INJURY TO FACIAL NERVE IN PAROTID AND ITS REPAIR Primary end to end anastomosis results in greater functional return than interposition grafting with multiple anastomosis In parotid surgery, when facial nerve is to be preserved  stimulate near stylomastoid foramen before wound closure If there is no movement then careful inspection under microscope is carried out for evidence of injury like accidental ligature on nerve crush injury When facial nerve injury occurs posterior to the anterior margin of masseter, concomitant injury to the parotid duct is looked for.

58. PREVENTION OF FACIAL NERVE INJURY

59. IDENTIFYING FACIAL NERVE AFTER OBTAINING WIDE EXPOSURE EMPLOYING THE FOLLOWING LANDMARKS : Tympano -mastoid suture by palpation – most consistent – approximately 2-6mm inferior to suture Digastric muscle – nerve is 1cm superior and parallel to upper border Tragal pointer – Facial nerve trunk found 1cm inferior and deep Parotido -masseteric fascia – incised as final step before identifying nerve trunk

60. SAFE AREAS OF DISSECTION Temporal region – 1cm above perpendicular line drawn at superior aspect of zygomatic arch and to within 2cm above perpendicular line drawn at lateral aspect of eyebrow Subaponeurotic plane of dissection remaining below the areolar tissue Repeat dissection – loose areolar tissue is obliterated by scar tissue  superior to zygomatic arch take plane of dissection between superficial and deep lamellae of deep temporal fascia Zygomatic arch - subperiosteal dissection

61. ALKAYAT AND BRAMLEY INCISION Question mark-shaped incision Begins about a pinna's length away from the ear, antero-superiorly just within the hair line  curves backwards and downwards well posterior of the main branches of the temporal vessels  meets the upper attachment of the ear. Pre auricular incision is placed always with 0.8 cm from the anterior border of external auditory canal to prevent injury to the temporal nerve

62. ALKAYAT AND BRAMLEY INCISION Point C – Most anterior concavity of EAC Point Z – Midway pt on lateral surface of zygomatic arch where most posterior twig of temporal ramus of CN VII crosses Point B – Lowest concavity of bony EAC Point F – Pt of bifurcation of facial nerve PG – Lowest point of post-glenoid tubercle

63. ALKAYAT AND BRAMLEY INCISION Facial nerve division (Pt F) from Pt B – 1.5 – 2.8 cm Facial nerve division (Pt F) from Pt PG – 2.4 – 3.5 cm Distance of temporal branch of facial nerve (Pt Z) to Pt C – 2 cm ranging between 0.8 to 3.5 cm

64. Incision is carried through the skin and superficial fascia to the level of the temporal fascia. Blunt dissection in this plane is carried downwards to a point about 2 cm above the malar arch where the temporal fascia splits. Beyond this point there should be no attempt at further dissection of the superficial fascia from the temporal fascia. The bifurcation of the facial nerve is not nearer than 2.4 cm in an infero -posterior direction from the post-glenoid tubercle.

65. SUBMANDIBULAR INCISION For marginal Mandibular branch Incision is placed 1.5-2 cm below the lower border of mandible. Dissecting above the superfcial musculoaponeurotic system (SMAS) and platysma Nerve is located close by / within / just deep to the superficial layer of deep cervical fascia  identify nerve with electric nerve stimulator and retract superiorly

66. SUBMANDIBULAR INCISION For Cervical branch I ncisions laterally along the platysma at least 15 mm posterior and 30 mm inferior to gonion Subplatysmal dissection closer to the mandibular angle and/or mandibular body should be performed under direct vision

67. SUBMANDIBULAR INCISION Hayes-Martin maneuver F acial vein is identified and ligated over the surface of the submandibular gland at two fingerbreadths below the mandible L igated vein is flipped superiorly by retracting investing cervical fascia, as in the majority of cases, the nerve courses over the facial vein

68. RETROMANDIBULAR APPROACH Anteparotid transmasseteric – The buccal branch is at most risk for injury Parotid is bluntly pushed upwards while looking on the surface of the masseter muscle for branches of the facial nerve The surgical field near the anterior-inferior edge of the parotid gland is usually free of branches of the facial nerve - occasionally the buccal branch is encountered

69. RETROMANDIBULAR APPROACH Transparotid – Marginal mandibular branch is at most risk for injury Blunt dissection within the parotid parallel to the expected course of the facial nerve branches and towards the periosteum of the posterior border of the mandible is performed. The marginal mandibular branch and/ or the retromandibular vein maybe encountered during dissection and should be protected

70. DISORDERS OF FACIAL NERVE

71. FACIAL NERVE PALSY I ncludes paralysis + weakness of the seventh cranial nerve K ey element in the initial assessment of a patient presenting with facial weakness is distinguishing between a lower motor neuron (LMN) versus an upper motor neuron (UMN) palsy Bilateral facial Palsy in diabetic patient with associated herpes Labialis

72. ETIOLOGY

73. HOUSE BRACKMANN GRADING Used to quantify and describe facial paralysis

74. SUPRANUCLEAR VS INFRANUCLEAR LESION Paralysis of only the lower half of face on contralateral side Forehead movements retained due to bilateral innervation of frontalis muscle Ipsilateral paralysis of both upper and lower half of the face All the muscles of the face on the involved side are paralyzed

75. BELL’S PALSY Incidence - 11.5 to 53.3 per 100,000 - m ost frequent type of facial nerve palsy Defined as “ acute idiopathic lower motor neuron palsy of the facial nerve that is unilateral, self limiting, non progressive, non life threatening and spontaneously remitting after 4-6 months and mostly after 1 year. Mostly diagnosed by exclusion - theoretically considered to be accurate only when there is no evidence of other cause of facial palsy.

76. BELL’S PALSY ETIOLOGY: Anatomical variation of the fallopian canal Cold / viral prodrome- due to HSV or a rising titre to Herpes zoster Primary ischemia - Vasospasm  edema and congestion of facial nerve - Reversible with medical treatment Secondary ischemia- Pressure from the fallopian canal – managed by decompression Tertiary ischemia - thickening of the nerve sheath with formation of fibrous band or band  leads to residual palsy. Facial nerve decompression required.

77. CLINICAL FEATURES Pain in the post auricular region - begins as deep seated ache and progresses to severe catch in the upper part of the neck in the ipsilateral side Soap getting into the ipsilateral eye and inability to gargle while washing face and deviation of face to the opposite side. Palsy is acute in onset and unilateral with associated numbness and stretching of the side of the face involved. Can have a history of viral prodrome or history of familial palsy

78. CLINICAL FEATURES Epiphora, deviation of face, dribbling of saliva, collection of food in the cheek. 90% of cases show absent stapedial reflex and chorda tympanic nerve appear red on otoscopic examination Bells phenomenon- Upward movement of eyeball in attempting to close one eye.

79. MANAGEMENT OF FACIAL NERVE PALSY Management can be divided into Medical management Surgical management 1/3 rd of the patients with incomplete palsy  evidence of recovery with medical management within 3 weeks and eventually progress to complete recovery. Start with medical line of managements as soon as possible, and monitor the progress using serial EMG and Nerve Excitability Test repeated every week. Acoustic reflex monitoring is to be performed weekly, since it is the first sign of return of nerve function.

80. MEDICAL MANAGEMENT High dose of steroids - starting with Presdnisolone - 1mg/kg/day or 60 mg given orally in tapering doses over a period of 3 weeks Antivirals – Vancyclovir - 3000 mg/day Combination of corticosteroid and antiviral therapy - prednisolone (60 mg/day) for 10 days + Vancyclovir (3000 mg/ day) for 7 days Vasodilators like Xanitol , nicotinate

81. MEDICAL MANAGEMENT Ascorbic acid Multi vitamins- Vit B1, B6 and B12 Eye taping Passive physiotherapy If there is no improvement with 3 weeks of medical management, advocate surgical therapy.

82. SURGICAL MANAGEMENT Marsh and Coker Criteria (1991) state the following indications for the surgical treatment of Facial nerve Palsy Complete denervation Paralysis of more than 4-6 weeks Incomplete return of function in 60 days Recurrent facial palsy Nerve excitability test shows a difference of 3.5 mA on both the sides

83. SURGICAL MANAGEMENT DECOMPRESSION : Decompression of the facial nerve by Middle cranial fossa approach Trans-labyrinthine approach Trans-mastoid extra labyrinthine approach Total decompression by combination approaches

84. SURGICAL MANAGEMENT NERVE EXPLORATION FOLLOWING TRAUMATIC INJURY : The process of nerve exploration is to be done within 72 hours or Wallerian degeneration sets in. Firstly, the hematoma is to be evacuated from the mastoid antrum. Then the facial nerve is visualized the facial nerve is decompressed all along the length. If required, the facial nerve can be lifted out of the canal followed by widening of the canal can be done.

85. SURGICAL MANAGEMENT IF TRANSECTED DURING SURGERY : Explore 5-10mm of the involved segment  Stimulate both proximally and distally Response with 0.05mA = good prognosis; further exploration not required If only responds distally = poor prognosis, and further exposure is warranted If loss of function is noted following surgery, wait 2 -3 hr and then re-evaluate the patient.

86. SURGICAL MANAGEMENT Unsure of nerve integrity – re-explore as soon as possible Integrity of nerve known to be intact High dose steroids – prednisone at 1mg/kg/day x 10 days then taper. 72 hours : ENoG to assess degree of degeneration >90% degeneration – re-explore <90% degeneration – monitor If worsening paralysis occurs re-explore If no regeneration, but no worsening, timing of exploration or whether not to is controversial

87. SURGICAL MANAGEMENT FACIAL REANIMATION : Reconstruction can be - dynamic or static . Aims of the treatment are to: Protect the eye Full function of the face at rest and during expression, but this is rarely achieved. Symmetry of oral fissure. Control of oral and ocular sphincter function Spontaneous and natural expression of emotions.

88. Dynamic Reconstruction Neural Repair 1 Direct nerve repair and grafting 2. Cross-face nerve grafting 3. Nerve crossover Muscle Repair 1. Muscle transfers: Gracilis muscle transposition, Temporalis muscle transposition 2. Free muscle graft 3. Free microneurovascular muscle transfer

89. Static Methods of Reconstruction Suspension-fascia lata , tendon or alloplastic materials Mechanical devices: Various mechanical devices like gold weights , springs , and magnets are used for eyelid closure Selective neurectomy Selective myectomy Botulinum toxin Thread lift technique has been described as another method to achieve static suspension.

90. SYNDROMES ASSOCIATED WITH FACIAL NERVE PALSY

91. MELKERSSON-ROSENTHAL SYNDROME Rare neuro- myocutaneous disorder Triad of recurrent facial paralysis, recurrent facial and labial edema (cheilitis granulomatosa ) and fissured tongue (lingua plicata). Etiology - infection, allergy and hereditary along with familial causes

92. RAMSAY-HUNT SYNDROME Herpes zoster oticus or herpes zoster cephalicus Herpes zoster virus affects geniculate ganglion  ganglionitis and herpetic eruption of the “geniculate zone”. This “zone” is supplied by the sensory portion of the CN VII and is situated within the auricle and the external auditory canal

93. RAMSAY-HUNT SYNDROME CLINICAL FEATURES : Severe pain in and around the ear Vesicles involving the pinna, tongue and buccal mucosa Lower motor neuron facial palsy Sensorineural hearing loss Disturbance of vestibular function Involvement of several cranial nerves - trigeminal, vestibulocochlear, vagus and glossopharyngeal nerves

94. RAMSAY-HUNT SYNDROME CLASSIFICATION (Hunt, 1907) - Depending on the clinical presentation Herpes auricularis (without neurological signs) Herpes auricularis with facial palsy Herpes auricularis with facial palsy and auditory symptoms. MANAGEMENT Antiviral agents (Acyclovir) Analgesics Local application of soothing anesthetic ointment Eye care Active and passive physiotherapy. Facial nerve decompression - to prevent residual facial palsy and for a speedier recovery

95. MOEBIUS SYNDROME Rare congenital disorder CLINICAL FEATURES : Bilateral facial palsy Unilateral or bilateral Abducens palsy Anomalies of the extremities Involvement of the other cranial nerves especially the hypoglossal nerve Absence of various muscle groups particularly the pectoral group of muscles.

96. MOEBIUS SYNDROME ETIOLOGY : Hypoplasia or absence of central brain nuclei Destructive degeneration of central brain nuclei Peripheral nerve involvement Myopathies. MANGEMENT : Reconstructive surgery such as orthognathic and static sling surgery.

97. HEERFORDT SYNDROME It is a peculiar symptom complex commonly seen in sarcoidosis Characterized by acute onset uveitis, iritis, parotid enlargement and fever Symptom complex is also associated with Bell's palsy and Sjögren's syndrome. The disease is usually benign and resolves without any specific treatment.

98. FACIAL NERVE TESTING Topognostic tests Prognostic tests Intraoperative monitoring Imaging Lacrimation test Stapedial reflex Salivary flow test Test for taste on anterior two- thirds of tongue Clinical evaluation of terminal facial nerve branch functions Electromyography Nerve excitability test Nerve conduction time Maximal stimulation test Electroneurography Electrically evoked potential Mechanically evoked potential Computerised tomography Magnetic resonance imaging

99. TOPOGNOSTIC TEST Helps determine the site of nerve injury.

100. SCHIRMER’S TEST A strip of filter paper 5cm x 5 cm is placed on lower conjunctival fornix of each eye for 5 min Soakage of both sides are compared with inhalation of ammonia to enhance lacrimation. Reduction of lacrimation by 30% as compared to the normal side or bilateral reduction to less than 4 mm is considered significant

101. STAPEDIAL REFLEX Dynamic changes which result from contraction of  stapedius  in response to stimuli of 500, 1000, 2000, and 4000 Hz, at intensities of 70–115 dB sound pressure level, are measured and thresholds for activation documented Restoration of stapedial reflex within three weeks after onset of facial palsy indicates a functional recovery.

102. TASTE TEST It can be measured by a drop of salt or sugar solution placed on one side of the protruded tongue Can be measured by electrogustometry Impairment of taste indicates lesion above the chorda tympani

103. SALIVARY FLOW TEST A polyethylene catheter is introduced into both the Warton’s papillae for 3 mm. The amount of saliva collected is noted over 5 min. A 25% reduction between the sides is considered significant.

104. CLINICAL EVALUATION OF TERMINAL FACIAL NERVE BRANCHES MOVEMENT MUSCLE NERVE Frown and wrinkle forehead Frontalis Temporal Close eyes tightly Orbicularis oculi Zygomatic Puff up cheeks, pucker lips Buccinator, orbicularis oris Buccal Move lower lips downward and laterally and evert vermilion border Depressor anguli oris , depressor labii inferioris , mentalis Marginal mandibular Clench teeth Platysma Cervical

105. PROGNOSTIC TESTS

106. ELECTRONEUROGRAPHY Electrical stimulation of the facial nerve at stylomastoid foramen and the subsequent measurement of the motoric response at the naso -labial fold Most accurate method of diagnosing facial palsy Testing done 72 hours post-onset of paralysis upto 21 days

107. ELECTRONEUROGRAPHY > 90% DEGENERATION = Surgical decompression to be done < 90% DEGENERATION = (within 3 weeks) predicts 89-100% spontaneous recovery Amplitude of the waveform indicates the integrity and the latency or velocity indicates the myelination .

108. ELECTROMYOGRAPHY Records electrical potential generated by muscle cells when these cells are electrically or neurologically activated Five criteria of measurement - insertional activity, spontaneous activity, motor unit action potential, recruitment pattern and interference pattern. M onitors spontaneous facial nerve regeneration or regeneration after facial nerve repair. P redict future recovery, as reinnervation can be detected about 2–3 months before clinical movements.

109. PROGNOSTIC TESTS NERVE CONDUCTION VELOCITY (LATENCY) EMG equipment is used to stimulate the nerve at the stylomastoid foramen  Electrodes are placed along nerve to measure the velocity Least reliable prognostic test. NERVE EXCITABILITY TEST (NET) Easy to perform, easily available and inexpensive Lowest electric current (threshold) to elicit a facial twitch on the paralyzed side of the face is compared with the threshold value of the normal side. A difference of 3.5 milliampere (mA) between sides suggests a poor prognosis

110. PROGNOSTIC TESTS MAXIMAL STIMULATION TEST (MST) Modified NET Maximal rather than minimal stimulation is given to peripheral branches of the facial nerve. MAGNETIC STIMULATION TEST Stimulation of the motor cortex by time varying magnetic fields to induce electrical depolarization Depolarization of the facial nerve at the root entry zone (REZ) by a transcranial penetration

111. INTRA OPERATIVE MONITORING Intra operative monitoring of the facial nerve is done using Intraoperative EMG Recording of compound nerve action potential (CNAP) Facial muscle F wave recording Video monitoring. Blockade of the neuromuscular junction interferes with meaningful monitoring of EMG activity  recommended not to use any paralytic agent during FN monitoring.

112. IMAGING OF FACIAL NERVE MRI with contrast – study of choice for facial nerve tumor + enhancement seen in case of Bell’s palsy and herpes zoster oticus Distinguishing feature from neoplasm – linear, unenlarged appearance CT – HRCT of temporal bone for trauma involving facial nerve paralysis. T1- weighted contrast-enhanced MR images demonstrate abnormal enhancement of the distal left cisternal (arrow, (a) labyrinthine (arrow, (b)), first genu (arrowhead, (b))

113. CONCLUSION The anatomical course and physiology of the facial nerve illustrate the intricacies of operating in the head and neck region. The proper knowledge of anatomy, use of modern technologies and modified incisions can be useful in preventing the nerve damage. Successful treatment of facial paralysis necessitates understanding each component of the facial nerve as it courses intracranially, intratemporally and extratemporally in addition to its innervation of facial muscles and glands. Proper diagnosis and evaluation of the patient are the most important factors governing the outcome of treatment of nerve damage