7TH CRANIAL NERVE ANATOMY COURSE AND FUNCTIONS

7TH CRANIAL NERVE ANATOMY COURSE AND FUNCTIONS

1. Facial nerve Presenter : Dr. Ritesh Karwaria MCh Resident, 1 ST YEAR Department of Neurosurgery SPMC & Associated PBM Hospital

2. CONTENTS ANATOMY INTRODUCTION COURSE OF FACIAL NERVE BRANCHES CAUSES OF FACIAL NERVE PARALYSIS AND THEIR MANAGEMENT

3. INTRODUCTION VII Cr Nv ; Mixed Nerve 10,000 fibers- Motor , Sensory , Parasympathetic fibers Motor root – 7000, S pecial V isceral E fferent Fibers Sensory & Parasympathetic – 3000 carried by “ NERVUS INTERMEDIUS ” (Nv of Wrisberg) NI consists of – G eneral V isceral E fferent – S pecial V isceral A fferent – S omatic A fferent

4. FACIAL NERVE NUCLEI 3 nuclei Motor nucleus – lower Pons below 4 th ventricle Superior salivatory nucleus – dorsal to motor Nucleus Nucleus of tractus solitarius – medulla oblongata

5. COURSE

6. INTRA CRANIAL PORTION From brainstem to fundus of IAM Length 24mm FN crosses CP angle with 8 th CN & NI Devoid of epineurium Thin layer of pia mater Surg imp : Iatrogenic trauma in CP angle tumour surgery Difficult to identify in schwannoma (no connective tissue)

7. INTRA TEMPORAL PORTION From fundus to Stylomastoid foramen Length – 28 to 30 mm “Fallopian canal” Longest bony canal

8. MEATAL SEGMENT Enters in ant sup segment of IAC Length 5 – 12 mm Crista falciformis Bills bar No separate sheath Shares with NI & 8 th CN

9. LABYRINTHINE SEGMENT Narrowest (0.68) & Shortest (3-5mm) No anastomosing arteries Periostium is thicker Postero-Superior to cochlea Antero-Medial to SSCC Distal end – Geniculate ganglion;1 st genu

10. Surgical importance: Anatomical bottle neck – ischemia in oedema Part most vulnerable for ischemia (no arterial anastomosis ) Temporal bone # - MC injured Geniculate ganglion : Bipolar gang cells Afferent input – somatic & special visceral afferents Secretomotor Fibers to lacrimal gland (without synapse)

11. TYMPANIC SEGMENT Horizontal segment From GG to 2 nd genu Length – 8 to 11mm Lies beneath LSCC & above OW above & medial to “ Processus cochleariformis ”

12. Nerve lies lateral & posterior to Pyramidal process Creats 2 recesses Facial recess (lat) Sinus tympani(med) 2 nd genu

13. Surgical importance: Processus cochleariformis ( consistant landmark) Imp landmark for 2 nd genu – -LSCC -Pyramidal eminence -B/w short process of incus(L) & LSCC(M)

14. MASTOID SEGMENT Vertical Segment From 2 nd Genu To SMF Longest (13mm) segment Landmark – “ Digastric Ridge”

15. EXTRA TEMPORAL REGION From SMF to terminal branches Runs in substance of parotid Main trunk divides - upper temperofacial - lower cervicofacial “Pes anserinus” Superficial to Retromandibular Vein

16. BRANCHES Intra temporal region : GSPN Nerve to stapedius Chorda tympani Sensory auricular branch

17. GSPN From GG 2 types of fibers Pregang para symp – Pterygopalatine gang. Post gang – lacrimal G Sensory fibers to nasal & palatine glands Joins deep petrosal N – N to pterygoid canal

18. NERVE TO STAPEDIUS Arises 6mm above SMF Supply stapedius muscle SENSORY AURICULAR BRANCH Joins auricular branch of vagus Supply retro auricular groove & concha.

19. CHORDA TYMPANI 4mm above SMF Lateral & anterior to Facial Nerve Lateral to Long Process of incus & medial to malleus 2 types of fibers Pre Ganglionic Parasympathetic – submandibular gland Post Ganglionic – submandibular & subligual Glands Special sensory – anterior 2/3 rd of tongue

20. Extra temporal region Posterior auricular Nerve ( occipito frontalis & muscles of pinna) Muscular Branches ( posterior belly of digastric & stylohyoid )

21. TERMINAL BRANCHES

22. CAUSES OF FACIAL NERVE PARALYSIS BIRTH Moulding Forceps delivery Dystrophia myotonia Moebius syndrome {facial diplegia a/w other cranial NV defects} TRAUMA Basal skull fracture Facial injuries Barotruma {scuba diving , altitude paralysis}

23. NEUROLOGICAL Opercular syndrome (cortical lesion in facial motor area) Millard – Gublar syndrome ( abducens palsy with contralateral hemiplegia d/t lesion in base of pons ) INFECTION Otitis externa Otitis media , cholesteatoma Mastoiditis Herpes zoster cephalicus (Ramsay Hunt Syndrome) Encephalitis Others

24. METABOLIC Diabetes mellitus Hyperthyroidism Pregnancy Hypertension Acute porphyria NEOPLASTIC Facial Nerve neuroma Cholesteatoma Glomus jugular tumor Primary Temporal Bone tumors Meningiomas Hemangioblastoma Hemangioma Pontine glioma Parotid tumor

25. TOXIC Thalidomide Carbon monoxide Tetanus Diphtheria IATROGENIC Mandibular block anesthesia Dental procedures Parotid surgery Mastoid surgery

26. IDIOPATHIC Bell’s palsy Melkersson – Rosenthal syndrome (recurrent alternating facial palsy , furrowed tongue , faciolabial oedema ) Hereditary hypertrophic neuropathy ( charcot marie tooth disease ) Temporal arteritis Thrombotic thrombocytopenic purpura Myasthenia gravis Sarcoidosis ( Heerfordt Syndrome- uveoparotid fever)

27. Facial Nerve Lesions Supra nuclear type: Features : Paralysis of lower part of face (opposite side) Partial paralysis of upper part of face Normal taste and saliva secretion Stapedius not paralysed

28. 2. Nuclear type : Features : Paralysis of facial muscle (same side) Paralysis of lateral rectus Internal strabismus

29. 3. Peripheral lesion At internal acoustic meatus Features : Paralysis of secretomotor fibers Hyper acusis Loss of corneal reflex Taste fibers unaffected Facial expression and movements paralysed

30. Lesion at int acoustic meatus

31. Injury distal to geniculate ganglion Features : Complete motor paralysis (same side) No hyper acusis Loss of corneal reflex Taste fibers affected Facial expression and movements paralysed Pronounced reaction of degeneration

32. Lesion distal to g e n ic u la t e ganglion

33. c) Injury at stylomastoid foramen Condition known as Bell’s Palsy

34. Central facial paralysis Upper motor neuron lesion Movements of the frontal and upper orbicularis oculi tend to be spared Because of uncrossed contributions from ipsilateral supranuclear areas Involvement of tongue Involvement of lacrimation and salivation

35. Peripheral paralysis Lower motor neuron lesion At rest : less prominent wrinkles on forehead of affected side, eyebrow drop, flattened nasolabial fold, corner of mouth turned down Unable to : wrinkle forehead, raise eyebrow, wrinkle nasolabial fold, purse lips, show teeth, or completely close eye

36. House-Brackmann grading system Grade I - Normal Grade II - Mild dysfunction, slight weakness on close inspection, normal symmetry at rest Grade III - Moderate dysfunction, obvious but not disfiguring difference between sides, eye can be completely closed with effort Grade IV - Moderately severe, normal tone at rest, obvious weakness or asymmetry with movement, incomplete closure of eye Grade V - Severe dysfunction, only barely perceptible motion, asymmetry at rest Grade VI - No movement

37. Testing of Facial Nerve Branches Testing the temporal branches of the facial nerve To test the function of the temporal branches of the facial nerve, a patient is asked to frown and wrinkle his or her forehead. Testing the Zygomatic branches of the facial nerve The patient is asked to close their eyes tightly.

38. Testing the buccal branches of the facial nerve Puff up cheeks (buccinator) Smile and show teeth (orbicularis oris) Tap with finger over each cheek to detect ease of air expulsion on the affected side

39. SPECIAL INVESTIGATIONS There are three imp. issues when confronted with facial nerve paralysis: The cause The site of lesion The prognosis TOPODIAGNOSTIC TESTING ELECTROPHYSIOLOGY

40. TOPODIAGNOSTIC TESTING TEST NERVE BRANCH ASSESSED 1. SCHIRMER TEST Greater superficial petrosal nerve 2. STAPEDIAL REFLEX Nerve to stapedius muscle 3. ELECTROGUSTROMETRY Chorda tympani 4. SALIVARY FLOW TESTING Chorda tympani

41. ELECTROPHYSIOLOGY MINIMAL NERVE EXCITABILITY TEST MAXIMAL STIMULATION TEST (MST) ELECTRONEURONOGRAPHY (ENoG) ELECTROMYOGRAPHY (EMG)

42. Topographic Diagnosis To determine the anatomical level of a peripheral lesion Lacrimation Geniculate ganglion Stapedius reflex motor nerve of stapedius muscle T aste chorda tympani

43. Schirmer's Test Geniculate ganglion & petrosal nerve function test Schirmer’s test +ve when Affected side shows less than half the amount of lacrimation seen on the normal side Sum of the lengths of wetted filter paper for both eyes less than 25 mm Lesion at or proximal to the geniculate ganglion

44. Schirmer's Test

45. Stapedius reflex Nerve to stapedius muscle test Impedence audiometry can record the presence or absence of stapedius muscle contraction to sound stimuli 70 to 100 db above hearing threshold An absence reflex or a reflex less than half the amplitude is due to a lesion proximal to stapedius nerve

46. Taste ( Electrogustometry) Chorda tympani nerve test Solution of salt, sugar, citrate, quinine or Electrical stimulation Compares amount of current require for a response each side of tongue Normal : difference < 20 uAmp (thresholds differening by more than 25%= abnormal) Total lack of Chorda tympani : No response at 300 uAmp Disadvantage : False +ve in acute phase of Bell’s palsy

47. Maximum stimulation Test: MST : Indication: complete paralysis<3wks Interpretation: Marked weakness or no muscle contraction: advanced degeneration with guarded prognosis

48. Electroneurography: ENoG Indication: complete paralysis<3wks Interpretation : < 90% degeneration: prognosis is good; > or = 90%: prognosis is a question Limitation : False-positive results in deblocking phase .

49. Electromyography: EMG Indication: Acute paralysis less than 1 week or chronic paralysis longer than 2 weeks Interpretation: Active mu: intact motor axons Mu + fibrillation potentials: partial degeneration Polyphasic mu: regenerating nerve Limitation: cannot assess degree of degeneration or prognosis for recovery

50. IDIOPATHIC BELL’S PALSY Diagnostic criteria- Paralysis or paresis of all muscle groups on one side of the face; Sudden onset; Absence of signs of central nervous system disease; Absence of signs of ear or CPA disease. Aetiology – Microcirculatory failure of vassa nervosum Ischaemic neuropathy Infectious ( HSV-1 ,HSV-2,VZV,EBV,Influenza B) Genetic Immunologic

51. TREATMENT STEROIDS Prednisolone -1mg/kg for 5 days f/b a ten day taper. ANTIVIRAL DRUGS Oral Acyclovir – (200-400 mg five times a day) for ten days.

52. Surgical treatment Facial nerve decompression Indication: Completely paralysis ENoG less than 10% in 2 weeks Appropriate time for surgery is 2-3 weeks after paralysis

53. Unilateral involvement Inability to smile, close eye or raise eyebrow Whistling impossible Drooping of corner of the mouth Inability to close eyelid (Bell’s sign) Inability to wrinkle forehead Loss of blinking reflex Slurred speech Mask like appearance of face Loss/ alteration of taste Features of Bell’s Palsy

54. Fore head

55. RAMSAY HUNT SYNDROME ( Varicella Zoster Virus Infection ) Definition – peripheral facial nerve palsy accompanied by an erythematous vesicular rash on the ear ( zoster oticus ) or in the mouth. Mechanism - reactivation of the latent VZV in the geniculate ganglion Persistent excruciating Pain and SNHL

56. TREATMENT - If started within three days of onset = significant improvement Prednisolone - 1mg/kg for 5 days f/b a ten day taper Intravenous acyclovir (250 mg three times daily) or ora l acyclovir (800 mg five times daily)

57. FRACTURES OF TEMPORAL BONE LONGITUDINAL FRACTURE More common (80%) Parietal blow Conductive hearing loss CSF otorrhoea Facial paralysis less (20%). Delayed onset TRANSVERSE FRACTURE Less common (20%) Occipital blow SNHL Facial paralysis more common (50%). Immediate onset MIXED

58. TREATMENT Surgical exploration - goals: To decompress the nerve To remove bony fragments that impinge on nerve. To re establish continuity in case of transaction Early post injury stage – Acute onset incomplete palsy without progression – Medical Treatment Acute complete paralysis / incomplete paralysis that progresses to complete paralysis – Surgical Exploration ( ENoG shows>90%denervation within 6 days of onset )

59. 2. Late post injury stage – Late Exploration- End to end anastomosis Interposition grafting (cable grafts- ipsilateral great auricular nv , sural nv , medial antebrachial cutaneous nvs ) Rerouteing Reinnervation – hypoglossal facial anastomosis , cross facial nerve grafting ( using a sural nv graft ) Static or Dynamic Facial Reanimation Procedures ( if EMG findings suggest long term denervation ) Temporalis muscle transfer Masseter muscle transfer

60. THANK YOU