Facial Nerve Anatomy, Diseases And its Management

The facial nerve (cranial nerve VII) controls facial expressions, taste, and some gland functions. Key branches include the temporal, zygomatic, buccal, mandibular, and cervical branches. Diseases include Bell’s palsy, trauma, tumors, and infections. Management ranges from medications (steroids, antivirals), physiotherapy, and, in severe cases, surgery.

1. ANATOMY, DISEASES OF FACIAL NERVE AND MANAGEMENT - DR FARHAT KHAN, ASST. PROFESSOR, DEPARTMENT OF ENT

2. INDEX: Nerve fibre components Course and branches Functional components Classification of nerve injury Evaluation of facial nerve paralysis Investigations Facial nerve disorders

3. NERVE FIBER COMPONENTS: Axon Myelin sheath Endoneurium Perineurium Epineurium ( It has no perineurium from brainstem to IAC )

4. VII cranial nerve Nerve of second branchial arch Mixed nerve – sensory & motor

5. COURSE OF FACIAL NERVE IS DIVIDED INTO: Intra-cranial part – pons to internal acoustic meatus ( 15-17 mm ) Intra-temporal part – internal acoustic meatus (IAM) to stylo -mastoid foramen Meatal segment (8-10 mm) : within IAM Labrynthine segment (4 mm) : from IAM to geniculate ganglion – nerve takes a turn posteriorly forming a genu {bend} Narrowest diameter ( 0.61-0.68 mm ) Tympanic/Horizontal segment (11 mm) : geniculate ganglion to just above the pyramidal eminence. Lies above oval window and below lateral semi circular canal Mastoid/Vertical segment (13 mm) : pyramid to stylomastoid foramen Between the tympanic and the mastoid segment is the second genu of the nerve 3. Extra-cranial part – stylomastoid foramen to termination into peripheral branches

6. Motor fibres originate from the nucleaus of the VII nerve, hook around the nucleus of VI th nerve and are joined by the sensory root (nerve of Wrisberg ) Facial nerve leaves the brain stem at ponto -medullary junction, travels through posterior cranial fossa and enters the internal acoustic meatus At the fundus of meatus (lateral most part) the nerve enters the bony facial canal, tranverses the temporal bone and comes out of the stylo -mastoid foramen. Crosses the styloid process and divides into terminal branches

7. BRANCHES: GREATER SUPERFICIAL PETROSAL NERVE Origin – geniculate ganglion Carries secreatomotor fibres to lacrimal gland and glands of nasal mucosa NERVE OF STAPEDIUS Origin- 2 nd genu Supplies stapedius muscle CHORDA TYMPANI Origin- middle of vertical segment Passes between incus and neck of malleus and leaves the tympanic cavity through petro tympanic fissure Carries fibres to sublingual and submandibular gland Brings taste from ant. 2/3 rd of tongue

8. COMMUNICATING BRANCH Joins the auricular branch of vagus nerve supplies the choncha , retro auricular groove, post meatus and outer surface of tympanic membrane POST AURICULAR NERVE Supplies muscles of pinna , occipital belly of occipito frontalis and communicates with auricular branch of vagus

9. MUSCULAR BRANCHES To stylohyoid and post belly of digastric PERIPHERAL BRANCHES 1)Temporal 2) Zygomatic 3) Buccal 4)Mandibular 5)Cervical Supplies all the muscles of facial expression

10. FUNCTIONAL COMPONENTS: Special visceral or branchial efferent to muscles responsible for facial expression and for elevation of the hyoid bone. General visceral efferent or parasympathetic these fibers are secretomotor to the submandibular and sublingual salivary gland, lacrimal gland, and glands of the nose, the palate and the pharynx. General visceral afferent component carries afferent impulses from the previously mentioned glands.

11. Special visceral afferent fibers carry taste sensations from the anterior two-thirds of the tongue except from valate papillae and from palate. General somatic afferent general sensation from concha, postero -superior part of EAC and the TM.

12. CLASSIFICATION OF NERVE INJURY: SEDDON CLASSIFICATION SUNDERLAND CLASSIFICATION HOUSE BRACKMANN CLASSIFICATION

13. SEDDON CLASSIFICATION (1943): Neuropraxia Low severity injury Leads to complete recovery Structure of the nerve remains intact but electrical conduction down the axon is interrupted, Typically by ischemia or compression injury Secondary injuries can be caused by vascular damage leading to intra-fascicular edema. Complete recovery of function with no distal Wallerian degeneration

14. Axonotmesis Disruption of the neuronal axon. Myelin sheath is intact. Endoneural tubules are preserved but Wallerian degeneration occurs. Crush based injury. Depending on the severity of the injury, regeneration may occur over the timescale of weeks to years. Neurotmesis Complete nerve transection occurs Commonly a neuroma forms over the proximal stump of the nerve, preventing normal continued regeneration to occur.

15. Not a perfect Grading system because of – 1. The problems of inter & intra-observer variations 2. Applicable only to disorders of nerve proximal to pes anserinus 3. Not appropriate for single branch injuries

16. LOCALISATION OF FACIAL NERVE INJURY: Central facial paralysis Caused by cerebrovascular accidents (hemorrhage, thrombosis, embolism), tumor or an abscess. It causes paralysis of only the lower half of face on the contralateral side. Forehead movements are retained due to bilateral innervation of Frontalis muscle. Involuntary emotional movements and the tone of facial muscles are also retained.

17. Peripheral Facial Paralysis All the muscles of the face on the involved side are paralysed . Patient is unable to frown, close the eye, purse the lips or whistle A lesion at the level of nucleus -identified by associated paralysis of VIth nerve. A lesion at cerebellopontine angle -identified by the presence of vestibular and auditory defects and involvement of other cranial nerves such as Vth , IXth , Xth and XIth . A lesion in the bony canal, from internal acoustic meatus to stylomastoid foramen, can be localised by topodiagnostic tests. A lesion outside the temporal bone, in the parotid area, affects only the motor functions of nerve. It may sometimes be incomplete as some branches of the nerve may not be involved in tumour or trauma

18. CAUSES OF FACIAL PARALYSIS: Central Intra-cranial part Intra-temporal part Extra-cranial part Systemic

19. CENTRAL Brain abscess Pontine glioma Poliomyelitis Multiple sclerosis

20. INTACRANIAL PART Acoustic neuroma Meningioma Congenital cholesteatoma Metastatic CA Meningitis

21. INTRATEMPORAL PART Idiopathic : Bell’s palsy Melkersson’s syndrome Infections : ASOM CSOM Herpes Zoster Oticus Trauma : Surgical: Mastoidectomy, Stapedectomy Accidental: # temporal bone Neoplasms : Glomus jugulare tumour Facial nerve neuroma Metastatic CA

22. EXTRACRANIAL PART Malignancy of parotid Surgery of parotid Accidental injury in parotid region Neonatal facial injury(forceps delivery)

23. SYSTEMIC DISEASES Diabetes Uraemia Hypothyroidism Leprosy, sarcoidosis Demyelinating disease

24. BELL’S PALSY Most common world wide Idiopathic, peripheral facial paralysis or paresis of acute onset First described by Sir Charles Bell

25. DEMOGRAPHICS: Race : slightly higher in persons of Japanese descent. Sex : No difference exists Age : highest in persons aged 15-45 years. Bell palsy is less common in those younger than 15 years and in those older than 60 years. Recurrence rate 4-15% Familial incidence 6-8% Less common in pregnancy but prognosis is significantly worse in pregnant women

26. PATHOPHYSIOLOGY: Latent herpes viruses (herpes simplex virus type 1 and herpes zoster virus), which are reactivated from cranial nerve ganglia Herpes zoster virus shows more aggressive biological behaviour than herpes simplex virus type 1 PCR techniques have isolated herpes virus DNA from the facial nerve during acute palsy. Inflammation of the nerve initially results in a reversible neurapraxia .

27. PHYSICAL EXAMINATION: Bell's palsy causes a peripheral LMN palsy Sudden onset Unable to close eyes Bell’s phenomenon (eyeball turns up and out on attempting to close the eye) Dribbling of saliva Asymmetrical face Epiphora Pain in ear precede or accompany nerve paralysis Noise intolerance and loss of taste

28. MANAGEMENT: STEROID : Usual regimen is 1mg/kg/day for 1 week. To be tapered in the 2nd week. ANTI-VIRALS : Acyclovir, Famciclovir, Valacyclovir

29. DECOMPRESSION: If the patient either progresses to complete paralysis or present with complete paralysis, an ENOG is obtained 3 days after occurrence of complete paralysis If degeneration <90% -conservative Repeat ENOG every 1-3 day If degeneration >90% -surgical decompression is an option However, if >90% degeneration occur after the 2week, surgical decompression does not alter outcome

30. OUTCOMES: It has a fair prognosis without treatment, with almost 3/4 of patients recovering normal mimetical function and just over a tenth having minor sequelae . A sixth of patients are left with either moderate to severe weakness, contracture, hemifacial spasm, or synkinesis . In patients who recover without treatment, major improvement occurs within three weeks in most. If recovery does not occur within this time, then it is unlikely to be seen until four to six months, when nerve regrowth and re-innervation have occurred. Patients with a partial palsy fair better, with 94% making a full recovery. The outcome is worse when herpes zoster virus infection is involved

31. BAD PROGNOSTIC FACTOR: Complete facial palsy No recovery by three weeks Age over 60 years Severe pain Ramsay Hunt syndrome (herpes zoster virus) Associated conditions—hypertension, diabetes, pregnancy

32. RAMSAY HUNT SYNDROME Caused by reactivation varicella zoster virus (herpes virus type 3) Facial paralysis + hearing loss +/- vertigo Herpes zoster oticus Two-thirds of patients have rash around ear Other cranial nerves, particularly trigeminal nerves (5th CN) often involved Worse prognosis than Bell’s (complete recovery: 50%) Important cause of facial paralysis in children 6-15 years old

33. MELKERSSON-ROSENTHAL SYNDROME Acute episodes of facial paralysis Facial swelling Fissured tongue Very rare Familial but sporadic Usually begins in adolescence Leads to facial disfigurement No definite therapy

34. LYME DISEASE Lyme disease ( borreliosis ) Endemic areas (Northeast USA, central Europe, Scandinavia, Canada) Consider in children w/atypical facial palsy Imaging: small white matter lesions similar to multiple sclerosis, enhancement of facial & other cranial nerves Bilateral facial paralysis: 25% Important to make diagnosis early because it is curable early w/antibiotics

35. OTHER INFECTIOUS CAUSES Acute facial paralysis may result from bacterial or tuberculous infection of middle ear, mastoid & necrotizing otitis externa Incidence of facial paralysis with otitis media: 0.16% ◦ Infection extends via bone dehiscence to nerve in fallopian canal leading to swelling, compression & eventually vascular compromise & ischemia Immune compromised patients are at risk for pseudomonal infection Poor prognosis (complete recovery is < 50%)

36. NEOPLASMS 27% of patients with tumors involving the facial nerve develop acute facial paralysis Most common causes: schwannomas , hemangiomas (usually near geniculate ganglion) & perineural spread such as with head and neck carcinoma, lymphoma & leukemia Other neoplasms can also involve the facial nerve ◦ Adults: metastatic disease, glomus tumors , vestibular schwannomas & meningiomas ◦ Children: eosinophilic granuloma & sarcomas

37. RECURRENT FACIAL PALSY Seen in Bell’s Palsy Melkersson’s Syndrome Diabetes Sarcoidosis Tumuors

38. Simultaneous bilateral facial paralysis Seen in GBS Sarcoidosis Sickle Cell Anaemia Acute Leukemia Bulbar Palsy Leprosy

39. TRAUMATIC CAUSE 1. TEMPORAL BONE FRACTURE 5% of trauma patients sustain a temporal bone fracture – 3 types » Longitudinal » Transverse » Mixed Facial palsy is seen more often in transverse fractures (50%). Paralysis is due to intraneural hematoma or by compression Delayed onset paralysis is treated conservatively like Bell's palsy Immediate onset paralysis may require surgery (decompression, re-anastomosis of cut ends or cable nerve graft)

40. 2. EAR OR MASTOID SURGERY Facial nerve is injured during stapedectomy , tympanoplasty or mastoid surgery. Paralysis may be immediate or delayed and treatment is the same as in temporal bone trauma. Sometimes, nerve is paralysed due to pressure of packing on the exposed nerve and this should be relieved first.

41. 3. PAROTID SURGERY AND TRAUMA TO FACE Facial nerve may be injured in surgery of parotid tumors or deliberately excised in malignant tumors. Accidental injuries in the parotid region can also cause facial paralysis.  Application of obstetrical forceps may also result in facial paralysis in the neonate due to pressure on the extra-temporal part of nerve.

42. ELECTRO-DIAGNOSTIC TESTING When a conduction block exists, the patient is unable to move his face voluntarily, but a facial twitch can still be elicited by percutaneous electrical stimulation of the nerve distal to the lesion. The electrical response of the facial muscles to voluntary, mechanical, or electrical activation of the nerve is recorded. Tests is based on these two principles – electrical stimulation recording of the electromyographic (EMG) response Useful to differentiate between neuropraxia and degeneration of the nerve. Helps to indicate time for surgical decompression of the nerve.  EVALUATION OF FACIAL PARALYSIS:

43. ELECTRO-DIAGNOSTIC TESTS Nerve excitability test (NET) Maximal stimulation test (MST) Electromyography (EMG) Electroneuronography (evoked electromyography) ( ENoG )

44. MINIMAL NERVE EXCITIBILITY TEST The nerve is stimulated at steadily increasing intensity till facial twitch is just noticeable. This is compared with the normal side. There is no difference between the normal and paralyzed side in conduction block. In other injuries, where degeneration sets in, nerve excitability is gradually lost. When the difference between two sides exceed 3.5 milli-amperes, the test is positive for degeneration. Degeneration of fibers cannot be detected earlier than 48-72 hours of its commencement

45.   MAXIMAL STIMULATION TEST (MST) This test is similar to the minimal nerve excitability test but instead of measuring the threshold of stimulation, the current level which gives maximum facial movement is determined and compared with the normal side. Response is visually graded as equal, decreased or absent. Reduced or absent response with maximal stimulation indicates degeneration and is followed by incomplete recovery

46. ELECTRONEURONOGRAPHY ( ENoG )  Sort of evoked electromyography. The facial nerve is stimulated at the stylo -mastoid foramen and the compound muscle action potentials are picked up by the surface electrodes. Supramaximal stimulation is used to obtain maximal action potentials. The response of action potentials of the paralyzed side are compared with that of the normal side on similar stimulation and thus percentage of degenerating fibers is calculated. Studies reveal that degeneration of 90% occurring in the first 14 days indicates poor recovery of function. Faster rate of degeneration occurring in less than 14 days has a still poorer prognosis. ENoG is most useful between 4 and 21 days of the onset of complete paralysis

47. ELECTROMYOGRAPHY (EMG) This tests the motor activity of facial muscles by direct insertion of needle electrodes usually in orbicular oculi and orbicularis oris muscles and the recordings are made during rest and voluntary contraction of muscle. In a normal resting muscle, biphasic or triphasic potentials are seen every 30-50 milliseconds. In a denervated muscle spontaneous involuntary action potentials called fibrillation potentials are seen. They appear 14-21 days after denervation. With regeneration of the nerve after injury, polyphasic reinnervation potentials replace fibrillation potentials. They appear 6-12 weeks prior to clinical evidence of facial function and thus provide the earliest evidence of recovery.

48. Electromyography is useful in planning reanimation procedures. Presence of normal or polyphasic potentials after 1 year of injury indicates that reinnervation is taking place and there is no need for reanimation procedure. If fibrillation potentials are seen, it indicates intact motor end plates but no evidence of reinnervation and need for nerve substitution. Electrical silence indicates atrophy of motor end plates and need for muscle transfer procedures rather than nerve substitution. Voluntary contraction causes motor discharge. Diminished or no response to voluntary contraction is seen after nerve injury

49. LIMITATION OF ELECTRO DIAGNOSTIC TESTING Electric impulse can stimulate only normal/ neuropraxic fibres and can’t distinguish b/w axonotemesis or neurotemesis Provides no useful information in cases of incomplete facial paralysis It fails to provide information on the immediate post paralysis period (first 72 hours)

50. TOPOGNOSTIC TESTING Schirmer test for lacrimation (Geniculate ganglion) Stapedial reflex test (stapedial branch) Taste testing (chorda tympani nerve) Salivary flow rates and pH (chorda tympani)

51. SCHIRMER TEST Greater superficial petrosal nerve, Geniculate ganglion Filter paper strip is placed in the lower conjunctival fornix bilaterally Rate of tear production of the two side is compared after ~5 minutes Normally the portion of the filter paper in contact with the conjunctiva acts as an irritant, stimulating an increased flow of tears, which are then wicked along the filter paper strip by capillary action Schirmer's test is usually considered positive if : The affected side shows less than half the amount of lacrimation seen on the normal side.

52. STAPEDIAL REFLEX Stapedius branch of the facial nerve A loud (supra threshold) tone is presented to either the ipsilateral or contralateral ear Evokes a reflex movement of the stapedius muscle Changes the tension on the tympanic membrane (which must be intact for a valid test) resulting in a change in the impedance of the ossicular chain. An absent reflex or a reflex that is less than half the amplitude of the contralateral side is considered abnormal

53. TASTE TESTING (ELECTROGUSTOMETRY) Psychophysical assessment can be performed with natural stimuli, such as aqueous solutions of salt, sugar, citrate, and quinine, or with electrical stimulation of the tongue. Electirical stimulation ( electrogustometry ), has the advantages of speed and ease of quantification The tongue is stimulated electrically to produce a metallic taste & Threshold of the test is compared between two sides  Impairment of taste indicates lesion above the chorda tympani. Disadvantage : False + ve in acute phase of Bell’s palsy

54. SALIVARY FLOW TESTING Chorda tympani Cannulation of Wharton's ducts bilaterally Gustatory stimulus – 6% citric acid on anterior Part of tongue Output is measured after 5 minutes. Significant if 25% reduction in flow of the involved side as compared to the normal side Salivary pH, Flow Rate, Submandibular salivary pH of 6.1 or less predicts incomplete recovery in cases of Bell's palsy (Saito et al, 1977)

55. COMPLICATIONS OF FACIAL NERVE PARALYSIS Incomplete recovery Facial asymmetry persists Eye cannot be closed resulting in epiphora Weak oral sphincter results in drooling and difficulty in taking food Exposure keratitis Dryness, exposure keratitis and corneal ulcer occurs (eye cannot be closed and tear film from cornea evaporates) Worse when tear production is also affected

56. Synkinesis (mass movement) When the patient wishes to close the eye, corner of the mouth also twitches or vice versa. It is due to cross innervation of fibers. There is no treatment. Tics and spasms Result of faulty regeneration of fibers. Involuntary movements are seen on the affected side of the face. Contractures   Results from fibrosis of atrophied muscles or fixed contraction of a group of muscles. Affect movements of face but facial symmetry at rest is good.

57.   Crocodile tears (gustatory lacrimation)   Unilateral lacrimation with mastication. Due to faulty regeneration of parasympathetic fibers which now supply lacrimal gland instead of the salivary glands. It can be treated by section of greater superficial petrosal nerve or tympanic neurectomy.   Frey’s syndrome (gustatory sweating) There is sweating and flushing of skin over the parotid area during mastication

58.   Psychological and social problems Drooling during eating and drinking and impairment of speech causes social problems.

59. HYPERKINETIC DISORDERS OF FACIAL NERVE They are characterized by involuntary twitching of facial muscles on one or both sides Hemifacial Spasm Characterized by repeated, uncontrollable twitching of facial muscles on one side. 2 types: a) essential/ idiopathic- cause is unknown b) Secondary – cause is acoustic neuroma , congenital cholesteatoma or glomus tumor. Many cases of facial spasm are due to irritation of nerve because of vascular loop at the cerebellopontine angle. Microvascular decompression through posterior fossa craniotomy has met with high success rate

60. Idiopathic type has been treated by selective section of the branches of facial nerve in the parotid or by puncturing the facial nerve with a needle in its tympanic segment Botulinum toxin has been used in the affected muscle. It blocks the neuromuscular junction by preventing release of acetylcholine.

61. Blepharospasm Twitching and spasms are limited to the orbicularis oculi muscles on both sides. Eyes are closed due to muscle spasms causing functional blindness. Cause is uncertain but probably lies in the basal ganglia. It is treated by selective section of nerves supplying muscles around the eye on both side Botulinum - A toxin injected into the periorbital muscles gives relief for 3-6 months. Injection can be repeated if necessary.

62. Decompression End To End Anastomosis Nerve Graft (Cable Graft) Hypoglossal – Facial Anastomosis Plastic Procedures SURGERY OF FACIAL NERVE

63. TREATMENT PROTOCOL Upto 3 weeks : nerve decompression or nerve repair 3 weeks- 2 years : nerve repair or nerve transposition >2yrs with fibrillation in EMG nerve repair or nerve transposition >2yrs with electrical silence in EMG muscle transposition/ eyelid implant/ facial sling

64. DECOMPRESSION Nerve may be compressed by edema, hematoma or a fractured bone in its intratemporal part. The bony canal is exposed and uncapped. The sheath of nerve is also slit to relieve pressure due to edema or intraneural hematoma

65. END TO END ANASTOMOSIS This done when the gap between severed ends of the nerves is only a few millimeters. Its is a suitable procedure for extratemporal part of the nerve. There should not be any tension in the approximated ends.

66. NERVE GRAFT (CABLE GRAFT) When the gap between the severed ends cannot be closed by end to end anastomosis, a nerve graft is more suitable than extensive re-routing or mobilisation of nerve. Nerve graft is taken from greater auricular, lateral cutaneous nerve of thigh or the Sural nerve. In the bony canal, the graft may not require any suturing

67. HYPOGLOSSAL – FACIAL ANASTOMOSIS Hypoglossal nerve is anastomosed to the severed peripheral end of the facial nerve. It improves the muscle tone and permits some movements of facial muscles, but at the expense of atrophy of tongue on that side. However, disability of tongue due to atrophy is not so severe and patient adjusts to the difficulty in chewing and articulation after a few weeks.

68. PLASTIC PROCEDURES They are used to improve cosmetic appearance when nerve grafting is not feasible or has failed. The procedures include facial slings, face lift operation or slings of masseter and temporalis muscle. The latter also gives some movement to face in addition to symmetry.

69. Thank you