FACIAL NERVE PALSY

DR PRIYANKA SHASTRI FACIAL NERVE PALSY

ORIGIN AND COURSE OF FACIAL NERVE

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Histology of facial nerve

Each nerve fibre : nerve cell body, axon : surrounded by myelin secreted by schwann cellsEndoneurium : to form tubuleMultiple tubules : perineuriumEpineurium : nerve sheath

The facial nerve gets its 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

Posterior auricular artery supplies the facial nerve at & distal to stylomastoid foramen

Venous drainage parallels the arterial blood supply

Degrees of nerve injuryNeuropraxia : no wallerian degenrationAxonotmesis : distal wallerian degenration occurs, intact perineurium, total paralysisNeurotmesis : wallerian degenration occurs

Sunderland classification

1: Partial block: Neuropraxia2: Loss of axons, endoneurial tubes remain intact: axonotmesis3: Injury to the endoneurium: neurotemesis4: Injury to the perineurium in addition to above: partial transection5: Injury to the epineurium in addition to above: complete transectionThe first three degrees are seen in viral and inflammatory disorders while 4th and 5th are seen in surgical or accidental trauma

CAUSES OF FACIAL PARALYSIS

Altered function of facial nerve following injurySYNKINESIS- Abnormal synchronization movement occuring with voluntary and reflex activity of muscle which normally do not contract together.CROCODILE TEARS- Increased unilateral lacrimation on involved side associated with eating.STAPEDIUS TENDON CONTRACTION Hyperkinetic syndrome with faulty facial regeneration causes fullness and roaring in ear.FACIAL MYOKYNIA Continuous fine fibrillary movement of facial muscles giving bag of worms facial appearance.

APPROACH

FACIAL NERVE PALSY

TOPOGNOSTIC TESTING

SCHIRMER TEST- decrease in lacrimation of 75% or more as compared to normal side. Or < 10mm for both sides at 5 min.STAPEDIAL REFLEX TESTING - if absent , site of lesion between geniculate ganglion and stapedius muscle. If present then site of lesion is distal to stapedius muscle.TASTE TESTING conc. Sweet, salt, sour and bitter solution tested along lateral margin of anterior 2/3 of tongue towards tip / electrogustometry ( EGM )SUBMANDIBULAR GLAND FLOW- compared by sialometry using 6% citric acid.TESTING FACIAL MOVEMENT

ELECTRICAL TESTING

Nerve Excitability Test - minimal current necessary to stimulate muscle movement when applied to a branch of facial nerve. A difference of 3.5mA or greater between two sides is thought to be significant.Maximum Stimulation Test strength and duration of stimulation is gradually increased from 1mA to 5mA. Useless 90% degeneration.No use < 72 hrs.

NERVE EXCITABILITY TEST (NET)Compares transcutaneous current threshold required to elicit minimal muscle contraction between two sides A difference of 3.5 milliamperes (mA) or more in thresholds between the two sides a reliable indicator of progressive degeneration :indicator for surgical decompression

If the paralysis becomes total, the test can determine whether a pure conduction block exists or whether degeneration is occurring, as indicated by progressive loss of excitability.

MAXIMAL STIMULATION TEST (MST)Instead of measuring threshold, however, maximal stimuli (current levels at which the greatest amplitude of facial movement is seen) is employed.degree of facial contraction is subjectively assessed as either equal, mildly decreased, markedly decreased, or without response compared with that on the normal side.

Movements on the paralyzed side are subjectively expressed as a percentage (0%, 25%, 50%, 75%, 100%) of the movement on the normal side.Symmetric response within first ten days complete recovery in > 90%No response within first ten days incomplete recovery with significant sequelae

ELECTROMYOGRAPHYThe recording of spontaneous and voluntary muscle potentials by needles introduced into the muscle is called electromyography (EMG).Records motor unit potentials of the orbicularis oculi & orbicularis oris muscle during rest & voluntary contractionIn a normal resting muscle biphasic / triphasic potentials are seen every 30-50msec.

EMG can be used to determine:-1.If a nerve in question is in fact in continuity(volitional activity recorded)2.Evidence of degenration ( fibrillation after 10-14 days)3.If there are early sign of reinnervation (polyphasic innervation potentials after 4-6 weeks)

Fibrillation potentials typically arises 2-3 weeks following injuryWith regeneration of nerve after injury, polyphasic reinnervation potential replaces fibrillation potentialReinnervation potentials may precede clinical signs of recovery by 6-12 weeks

Polyphasic potential indicate regenrative process & surgical intervention is therefore not indicatedFibrillation indicate lower motor neuron denervation but viable motor end plates, so surgical intervention needed(to achieve nerve continuity)Electrical silence indicates atrophy of motor end plates & need for muscle transfer procedure

EVOKED ELECTROMYOGRAPHY (EEMG) OR EVOKED ELECTRONEURONOGRAPHY (EnoG)Records compound muscle action potential (CMAP) with surface electrodes placed transcutaneously in the nasolabial fold (response) and stylomastoid foramen (stimulus)

EVOKED ELECTROMYOGRAPHY (EEMG) OR EVOKED ELECTRONEURONOGRAPHY (EnoG)Waveform responses are analyzed to compare peak-to-peak amplitudes between normal and uninvolved sides where the peak amplitude is proportional to the number of intact axons.Most valuable prognostic indicator---Its main indicaion acute onset complete facial paralysisThis method offers the potential advantage of an objective registration of electrically evoked responses, and the amplitude of response of the paralyzed side (in mV) can be expressed as a precise percentage of the normal side's response.

ELECTRONEURONOGRAPHY (EnoG))Response 90% of normal within 3 weeks of onset- 80-100% probability of recoveryTesting every other day Not useful until 4th day of paralysis as it takes about 3 days for degeneration to reach completionAlso of less value after three weeks bcoz of nerve fibre desynchronizationAdvantages: ReliableDisadvantages: UncomfortableCostTest-retest variability due to position of electrodes

Limitation of electophysiological testingElectric impulse can stimulate only normal/ neuropraxic fibres and cant distinguish b/w axonotemesis or neurotemesisProvides no useful information in cases of incomplete facial paralysisIt fails to provide information on the immediate post paralysis period( first 72 hours)

ImagingMagnetic resonance imaging (MRI) with intravenous gadolinium contrast has revolutionized tumor detection in the cerebellopontine angle and temporal bone and is currently the study of choice when a facial nerve tumor is suspected (e.g., in a case of slowly progressive or longstanding weakness) However, enhancement also occurs in most cases of Bells palsy and herpes zoster opticus, usually in the perigeniculate portions of the nerve. This enhancement may persist for more than 1 year after clinical recovery; can be distinguished from neoplasm by its linear, unenlarged appearance; and has no apparent prognostic significance.

Computed tomography (CT) is valuable for surgical planning in cholesteatomas and temporal bone trauma involving facial nerve paralysis but probably is less useful than MRI in the investigation of atypical idiopathic paralysis. Unfortunately, even MRI fails to detect a substantial number of malignant parotid tumors.MRI shows the greatest utility in predicting location and depth of parotid gland tumors, but even in this capacity it is no better than simple manual palpation alone.

SIGN DIFFERENTIATING SUPRANUCLEAR FROM INFRANUCLEAR LESIONSSUPRANUCLEARINFRANUCLEARForehead intact bilaterallyFND, Hemiplegia on side of facial palsyAtaxiaReflexes intactTone maintainedDrooping corner of mouthSlight flattening of nasolabial fold.No muscle atrophy/ fasciculationTotal facial palsyNo FNDNo hemiplegiaNo ataxiaNo reflexesFlaccidNot an isolated findingNot an isolated findingMuscle atrophy / fasciculations present.

BELLS PALSYFirst described more than a century ago by Sir Charles Bell

Bell palsy is certainly the most common cause of facial paralysis worldwide

U/l spontaneous idiopathic lower motor neuron facial palsyIncidence of Bells palsy is 20 to 30 patients per 100,000 populationThe incidence is greater in patientsolder than 65 years and lower in children younger than age 13. The male-to-female ratio for Bells palsy is approximately equal,except for a predominance in women younger than 20 years of age and a slight predominance in men older than 40 The left and right sides of the face are equally involved

Diagnosis by exclusion

Criteria

Paralysis or paresis of all muscle groups of one side of the face

Sudden onset

Absence of signs of CNS disease

Absence of signs of Ear disease

30% of patients will have incomplete paralysis on presentation70% will have a complete paralysis. Bilateral paralysis occurs in 0.3%Have a history of previous paralysis. A family history of Bells palsy can be elicited in 8% of patients

PathophysiologyMain cause of Bell's palsy is latent herpes viruses (herpes simplex virus type 1 and herpes zoster virus), which are reactivated from cranial nerve gangliaEdema of nerve within inelastic fallopian canal

Recovery begins by 3 weeks, full recovery by 6months70 % : 15 % : 15%

most important prognostic factor is whether the paralysis is incomplete or complete. The prognosis for affected persons in whom complete facial paralysis never develops is excellent: 95% to 100%factors associated with poor outcome include hyperacusis; decreased hearing; age older than 60 years; diabetes mellitus; hypertension;and severe aural, anterior facial, or radicular pain

Ramsay Hunt SyndromeCaused by reactivation varicella zoster virus (herpes virus type 3)Facial paralysis + hearing loss +/- vertigoHerpes zoster oticusTwo-thirds of patients have rash around earOther cranial nerves, particularly trigeminal nerves (5th CN) often involvedWorse prognosis than Bells (complete recovery: 50%)Important cause of facial paralysis in children 6-15 years old

The timing of the appearance of the vestibular eruption may have prognostic significance. In most cases, eruption and paralysis occur simultaneously. In approximately 25% of cases, the eruption precedes the paralysis; these patients have a higher likelihood of recovery.Patients with Ramsay Hunt syndrome also are more likely than patients with Bells palsy to have associated cranial nerve symptoms, including hyperacusis, hearing loss, and pain. In approximately 10% of patients, the vesicular rash appears well after the initial facial paralysis, many patients demonstrate a rise in antibody to VZV without ever exhibiting cutaneous or mucous membrane vesiclesso-called Ramsay Hunt sine herpete.

Severe ocular complications can occur with herpes zoster ophthalmicus.These complications include uveitis, keratoconjunctivitis, optic neuritis, and glaucoma and are almost always associated with involvement of the ophthalmic division of the trigeminal nerve

Management of patients with herpes zoster, including cephalic zoster, consists of systemic corticosteroids. A specific benefit of corticosteroid therapy is a reduction in postherpetic neuralgia. The usefulness of corticosteroids in fostering recovery from the facial paralysis is controversial; however, early institution of corticosteroids seems torelieve acute pain, reduce vertigo, and decrease the incidence of postherpetic neuralgiaThe antiviral agent acyclovir also is recommended to treat herpes zoster facial

Congenital Facial Paralysis

The incidence of facial paralysis in newborns has been estimated at 0.23% of live births. Birth trauma usually causes isolated facial paralysis and other signs of injury, including facial swelling, ecchymosis, and hemotympanum. Abnormalities of other cranial nerves or abnormalities on brainstem audiometry (prolongation of the I to III or I to V interval) suggest that the facial paralysis is congenital and not traumatic.Of facial paralysis cases in infants, 78% are related to birth trauma.These cases are equally divided between forceps deliveries and vaginal deliveries plus cesarean sections, suggesting that intrauterine facial nerve injury can occur from pressure on the infants face by the sacral prominence during birth

Mbius syndrome represents a broad spectrum of clinical and pathologic findings ranging from isolated unilateral facial paralysis (usually associated with sixth cranial nerve paralysis) to bilateral absence of facial and abducens nerve function. Multiple other cranial nerves,including the glossopharyngeal, vagus, hypoglossal, and other extraocular motor nerves, also may be affected

Infectious causesAcute facial paralysis may result from bacterial or tuberculous infection of middle ear, mastoid & necrotizing otitis externaIncidence of facial paralysis with otitis media: 0.16%Infection extends via bone dehiscences to nerve in fallopian canal leading to swelling, compression & eventually vascular compromise & ischemiaImmune compromised patients are at risk for pseudomona infectionPoor prognosis (complete recovery is < 50%)

Neoplasms27% of patients with tumors involving the facial nerve develop acute facial paralysisMost common causes: schwannomas, hemangiomas (usually near geniculate ganglion) & perineural spread such as with head and neck carcinoma, lymphoma & leukemia, congenital cholesteatomaOther neoplasms can also involve the facial nerveAdults: metatstatic disease, glomus tumors, vestibular schwannomas & meningiomasChildren: eosinophilic granuloma & sarcomas

Slowly progressive facial paralysisEarly diagnosis : high degree of suspicionh/o recurrent palsy, involvement of other cranial nerves.CT and MRITumout resection with grafting

Recurrent facial palsy: seen in Bells palsy, Melkerssons syndrome, diabetes, sarcoidosis tumuors

Melkersson-Rosenthal Syndrome Acute episodes of facial paralysisFacial swellingFissured tongueVery rareFamilial but sporadicUsually begins in adolescenceLeads to facial disfigurementNo definite therapy

Bilateral simultaneous facial palsyMoebius syndromeGB SyndromeSarcoidosisMyotonic dystrophySkull traumaInfectious mononucleosisCMVAcute porphyriaBotulismLyme diseaseBells herpes simplex

Traumatic facial nerve palsySecond most common cause of FN paralysis- Represents 15% of all cases of FN paralysis- Most common cause of traumatic facial nerve injury is temporal bone fracture

Temporal bone fracturesLongitudinalTransverse70-90%Parietal , temporal traumaHemotymoanum, ossicular chain disruptionFacial nerve paralysis : 10-20 %: horizontal segment

10-30%OccipitalSnhl, vestibular dysfnFacial nerve palsy : 50%: labyrinthine segmentCan be from iac to horizontal segment

IatrogenicSurgicalMost common overall surgery with FN injury is parotidectomyMost common otologic procedures with FN paralysisMastoidectomy 55% of surgical related FN paralysisTympanoplasty 14%Mechanism - direct mechanical injury or heat generated from drillingMost common area of injury distal tympanic segment including the 2nd genu, followed by mastoid segmentUnrecognized injury during surgery in nearly 80% of cases

SURGICAL LANDMARKS OF FACIAL NERVEFOR MIDDLE EAR AND MASTOID SURGERYProcessus cochleariformis Oval window and horizontal canalShort process of incusPyramidTympanomastoid sutureDigastric ridge

For parotid surgeryCartilaginous pointer of conleyTympanomastoid suturePosterior belly of digastricStyloid process

Surgical management Facial nerve decompressionNeurorrhaphy(nerve repair) 1.direct end to end anastomosis 2. interposition cable graftingNerve transposition: hypoglossal-facialMuscle transposition: temporalis, masseterMicro-neuro-vascular muscle flapStatic procedure: eyelid implant, facial sling

Intratemporal Approaches to DecompressionNerve may be injured along multiple segmentslocalize injured site pre-operativelyFull exposure of the nerve from IAC to the stylomastoid foramen if cant localizeApproach to full exposure is based on patients auditory and vestibular statusIntact - Transmastoid/Middle cranial fossa approachAbsent Transmastoid/Translabyrinthine approach

General principlesMonitoring of facial nerveInstrumentationSharp dissection

Retrolabyrinthine and retrosigmoid approachAdvantagesComplicationsAccess to FN in CP angle without sacrificing the inner ear functionNo cerebellar compressionAICA and other vessels easily manipulated

Visualization of nerve hampered by location of 8th nerveIncreased risk of hearing loss during separation from 8th nerveCsf leakVascular complications

Middle cranial fossa approach

AdvantagesComplications the only method that exposes the entire internal auditory canal and labyrinthine segment with preservation of hearingmost commonly used for decompression of the facial nerve in Bells palsy and with longitudinal temporal bone fractures.Dural elevation can be difficultPersistent CSF leakageConductive and sensorineural hearing losses can result

Transmastoid approachAdvantagesComplicationsexcellent exposure of the mastoid and tympanic segments of the facial nerveused in conjunction with middle fossa and retrolabyrinthine approaches if total facial nerve exposure is required and inner ear function is to be preservedlimited access to the geniculate ganglion and the inability to reach the labyrinthine segment.Conductive or sensorineural hearing loss also can be a complication if the incus is removed or touched by a rotating burr during the procedure.

Translabyrinthine approachAdvantagesComplicationsThe translabyrinthine exposure of the facial nerve is used primarily when the cochlear and vestibular functions have been lost preoperatively.The greatest advantage with this technique of facial nerve exposure is the ability to access the entire nerve using one approachHearing and balance function must be sacrificed for total exposure of the nerveCSF leakage and infection are the greatest risks

Facial ReanimationFacial reanimation is a family of different surgical techniques to make one's paralyzed face move more normally.

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Assessment and PlanningCause of facial paralysisFunctional deficit/extent of paralysisTime course/duration of paralysisLikelihood of recoveryOther cranial nerve deficitsPatients life expectancyPatients needs/expectations

Primary Nerve RepairEnd-to-end anastomosis preferredCan be performed with defect < 17 mmExtratemporal repair performed < 72 hrs of injuryMost common methodsGroup fascicular repairEpineural repair

Group fascicular repair

Primary Nerve RepairSevered ends of nerve exposedDevitalized tissue/debris removed with fine scalpelSmall bites of epineuriumEpineural sheath approximated with 9-0 nonabsorbable sutureEpineural repair recommended for injury proximal to pes anserinus and intratemporalHorizontal segment rarely accessible to suture repair

Epineural repair technique

Nerve Repair Recovery of function begins around 4-6 months and can last up to 2 years following repairNerve regrowth occurs at 1mm/dayGoal is tension free, healthy anastomosisRule is to repair earlier than later - After 12-18 months, muscle reinnervation becomes less efficient even with good neural anastomosis Some authors have reported improvement with repairs as far out as 18-36 months

2 weeks following injury -> collagen and scar tissue replace axons and myelinNerve endings must be excised prior to anastomosis for this reason if this far out

The clinical uses of interposition grafts (1) radical parotidectomy with nerve sacrifice; (2) temporal bone resection; (3) traumatic avulsions; (4) cerebellopontine angle tumor resection; (5) any other clinical situation in which viable proximal nerve can be sutured and distal elements of facial nerve can be identified

Interposition GraftingCable graftsUsed when defect > 17mm; nerve cannot be reapproximated w/o tensionMost commonGreater Auricular NerveSensory nerves from superficial cervical plexusSural nerveMedial antebrachial cutaneous nerve

Useful featuresProximity to facial nerveCross-sectional area (~equal)Limited morbidity LimitationsReconstruction of long defects and/or branching nerve gapsmaximum of 10 cm

Pros:Length (70cm)AccessibilityLow morbidity associated with sacrificeTwo team approachReduced surgical timeCons:Variable caliberOften too largeDifficult to make graft approximationUnsightly scar

MBCN

Important landmarks:Medial epicondyle of humerusBiceps tendonBasilic and medial cubital veinsFascial plane separating bicep from tricep

Upper extremity can be prepped from axilla to wrist or continuous with the head/neck.

Nerve diameter and branching pattern aresimilar to those of the facial nerve, and donor site morbidity is minimalwith nerve harvest

Surgical Technique

For the surgical technique of neurorrhaphy, interrupted sutures using9-0 or 10-0 monofilament nylon are preferred. Both ends of the nerve graft and the proximal and distal stumps should be transected cleanly with a fresh sterile blade.Epineural suturesApproximation of the nerve ends using an acrylic glue has beendescribed : Histacryl or cyano-butyl-acrylateThe nerve graft should lie in the healthiest possible bed of supporting tissue Suction drainage systems should be placed away from any portions of the nerve graft.

Grafting and Nerve Transfer - OverviewApproach is based on availability of proximal nerve endingPerformed for defects > 17mmResults in partial or complete loss of donor nerve functionBest functional results are obtained with cable grafting when a segment of the facial n. is disruptedAlso recommended if there is tension at the anastomotic site of a primary nerve repairGraft should be aprox. 25% longer than needed to allow for a tension free anastomosis

Facial nerve transposition

Reinnervation by connecting an intact proximal facial nerve to the distal ipsilateral facial nerve

Hypoglossal-Facial Technique modification aka partial XII-VII transferDonor nerve harvestedOne end of donor nerve is sutured to severed main trunk of CN VII; other end hooked up to proximal segment of partially severed CN XIIThe procedure has been modified by only partially sectioning the hypoglossal nerve and interposing, by end to-side anastomoses,by a greater auricular nerve graft between the hypoglossal and facial nerves. Since the hypoglossal nerve is transected only halfway, tongue function can be preserved.Limits tongue dysfunction and atrophy

Cross-facial Nerve GraftingContralateral CN VII used to reinnervate paralyzed side using a nerve graftSural nerve often employed~25-30cm of graft neededRestitution of smile and eye blinking when successfulDisadvantage2nd surgical siteViolation of the normal facial nerve

Cross-facial Nerve Grafting4 techniquesSural nerve graft routed from buccal branch of normal CN VII to stump of paralyzed CN VIIZygomaticus and buccal branch of normal CN VII used to reinnervate zygomatic and marginal mandibular portions respectively4 separate grafts from temporal, zygomatic, buccal and marginal mandibular divisions of normal CN VII to corresponding divisions on paralyzed side.Entire lower division of normal side grafted to main trunk on paralyzed side.

Muscle Transposition (aka Dynamic Sling)When to use:Facial neuromuscular system absentNeural techniques unsuitablei.e. congenital facial paralysisFacial nerve interruption of at least 3 years Loss of motor endplatesCrossover techniques not possible due to donor nerve sacrifice

Muscle transposition most commonly employs the temporalis muscle because of its good location, length,contractility, and vector of pull.good for reanimation of the mouth in patients with long-standing (at least 1 year in length) paralysis.Allows patients to have a voluntary smile.Temporalis

TemporalisOvercorrection at oral commissure is critical2nd or 3rd molar of upper dental arch should be exposed when procedure is finishedHarvest and placement of temporoparietal facial flap recommended to fill donor siteOral support possible within 6 weeksMovement achieved by clenching the jawsUnnatural contraction requiring rehabilitation/Physiotherapy

MasseterUsed when temporalis muscle is not availableMay be preferred due to avoidance of large facial incisionDisadvantage:Less available muscle compared to temporalisVector of pull on oral commisure is more horizontal than superior/oblique like temporalis

Facial Paralysis(Acute < 3 wks)Intermediate(3 wks-2 years)Chronic (>2 years)CN VII decompressionNerve repairPrimaryCable graft -G. auricular -Sural -MACNNerve transfer -hypoglossal -masseteric -spinal acc.Cross-facialGraft

RegionalMuscleTransfer -Temporalis -Masseter -DigastricFree MuscleTransfer -Gracilis -serratus -L. dorsi -Pec minor+/-Static Techniques: Slings, Gold weight/Lid procedures, etcReanimation

Summary

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