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The Facial Nerve

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The Facial Nerve TheThe FacialFacial NerveNerve Dr K Lehmann Department of Otorhinolaringology University of Stellenbosch and Tygerberg Hospital IntroductionIntroduction •• TheThe facialfacial nervenerve hashas aa complexcomplex coursecourse throughthrough temporaltemporal bonebone andand parotidparotid glandgland •• Components:Components: – Motor – Sensory (N. Intermedius) – Secretomotor (parasympathetic) •• FacialFacial nervenerve nucleusnucleus situatedsituated inin ponspons •• NerveNerve fibresfibres turnturn aroundaround thethe nucleusnucleus ofof thethe 6th6th nervenerve inin thethe brainstembrainstem AnatomyAnatomy •• FibresFibres fromfrom contralateralcontralateral hemispherehemisphere supplysupply thethe nucleusnucleus inin thethe ponspons •• MotorMotor fibresfibres runrun fromfrom thethe ipsilateralipsilateral hemispherehemisphere andand suppliessupplies thethe portionportion ofof nucleusnucleus thatthat suppliessupplies thethe foreheadforehead –– UpperUpper motormotor neuronneuron innervationinnervation ofof thethe foreheadforehead isis bilateralbilateral AnatomyAnatomy (continued) •• EmergeEmerge fromfrom brainstembrainstem atat lowerlower borderborder ofof ponspons betweenbetween oliveolive andand inferiorinferior cerebellarcerebellar pendunclependuncle •• CrossesCrosses cerebellopontinecerebellopontine angleangle andand entersenters temporaltemporal bonebone throughthrough thethe internalinternal auditoryauditory canalcanal AnatomyAnatomy (continued) •• StructuresStructures foundfound inin internalinternal auditoryauditory canal:canal: –– FacialFacial nervenerve –– VestibuloVestibulo cochlearcochlear nervenerve –– NervusNervus intermediusintermedius –– InternalInternal auditoryauditory arteryartery andand veinvein •• RunsRuns throughthrough fallopianfallopian canalcanal inin aa laterallateral direction,direction, betweenbetween cochleacochlea andand vestibulevestibule AnatomyAnatomy (continued) •• SeparatedSeparated fromfrom middlemiddle cranialcranial fossafossa byby thinthin layerlayer ofof bonebone •• ReachesReaches medialmedial wallwall ofof epitympanicepitympanic recess,recess, turnsturns sharplysharply backwardsbackwards atat thethe firstfirst genu:genu: geniculategeniculate ganglionganglion •• Branch:Branch: greatergreater superficialsuperficial petrosalpetrosal nervenerve •• CourseCourse throughthrough temporaltemporal bone:bone: LabyrinthineLabyrinthine portionportion AnatomyAnatomy (continued) •• FromFrom geniculategeniculate ganglionganglion thethe nervenerve tunstuns posteriorlyposteriorly andand slightlyslightly inferiorlyinferiorly •• BonyBony fallopianfallopian canalcanal formsforms aa cylindricalcylindrical ridge,ridge, inferiorinferior toto thethe laterallateral semisemi--circularcircular canalcanal andand superiorsuperior toto thethe ovaloval windowwindow (with(with stapes)stapes) andand promontory:promontory: TympanicTympanic portionportion •• AnteriorAnterior limitlimit ofof nerve:nerve: processusprocessus cochleariformiscochleariformis withwith tensortensor tympanitympani tendontendon AnatomyAnatomy (continued) •• InIn bonybony floorfloor ofof additusadditus thethe nervenerve makesmakes aa gradualgradual turnturn (second(second genu)genu) andand turnsturns inferiorlyinferiorly toto commencecommence thethe verticalvertical segment:segment: MastoidMastoid postionpostion •• BranchesBranches inin middlemiddle ear:ear: chordachorda tympani;tympani; stapediusstapedius •• RunsRuns inferiorlyinferiorly toto stylomastoidstylomastoid foramenforamen surroundedsurrounded byby mastoidmastoid airair cellscells AnatomyAnatomy (continued) •• EmergesEmerges fromfrom stylomastoidstylomastoid foramenforamen •• RunsRuns forwardforward betweenbetween deepdeep andand superficialsuperficial lobelobe ofof parotidparotid salivarysalivary glandgland •• DevidesDevides intointo fivefive branches:branches: –– TemporalTemporal –– ZygomaticZygomatic –– BuccalBuccal –– MandibularMandibular –– CervicalCervical GeneralGeneral •• DamageDamage toto facialfacial nervenerve resultsresults inin facialfacial weaknessweakness andand cosmeticcosmetic deformitydeformity •• LevelLevel ofof damagedamage determinesdetermines clinicalclinical picturepicture •• UpperUpper motormotor neuronneuron vsvs lowerlower motormotor neuronneuron •• ForeheadForehead oftenoften sparedspared inin upperupper motormotor neuronneuron lesionslesions GeneralGeneral (continued)(continued) •• DegreeDegree ofof recoveryrecovery dependentdependent onon extentextent ofof nervenerve damagedamage •• InternationalInternational systemsystem forfor degreedegree ofof facialfacial nervenerve weaknessweakness •• HouseHouse--brackmannbrackmann gradinggrading system:system: –– SixSix grades:grades: II –– VIVI –– GradeGrade I:I: normalnormal functionfunction –– GradeGrade VI:VI: nono movementmovement TestingTesting ofof facialfacial nervenerve functionfunction •• ToTo determinedetermine sitesite ofof facialfacial nervenerve injuryinjury •• ReliesRelies onon knowledgeknowledge ofof facialfacial nervenerve branchesbranches TestingTesting ofof facialfacial nervenerve functionfunction (continued) Branches:Branches: •• GreaterGreater superficialsuperficial petrosalpetrosal nervenerve:: – Lachrymation Test: Schirmer test •• NerveNerve toto stapediusstapedius:: – Stapedius reflex Test: Audiometrical evaluation •• ChordaChorda tympanitympani nervenerve:: – Taste Test: Testing taste ElectrodiagnosisElectrodiagnosis •• ToTo decidedecide ifif lesionlesion willwill recoverrecover isis paramountparamount •• ElectricalElectrical testingtesting helpfulhelpful toto determinedetermine statusstatus ofof nervenerve andand toto predictpredict potentialpotential forfor recoveryrecovery •• TestsTests ofof nervenerve conductivityconductivity andand cancan showshow degenerationdegeneration asas earlyearly asas threethree daysdays afterafter injuryinjury •• NerveNerve stimulatedstimulated throughthrough skinskin withwith anan electrodeelectrode ElectrodiagnosisElectrodiagnosis (continued) •• MinimalMinimal excitabilityexcitability testtest •• MaximalMaximal stimulationstimulation testtest (MST)(MST) •• ElectroneuronographyElectroneuronography (ENoG)(ENoG) •• StrengthStrength--durationduration curvescurves (SD(SD curves)curves) •• ElectromyographyElectromyography •• CompoundCompound actionaction potentialpotential afterafter stimulationstimulation ElectrodiagnosisElectrodiagnosis (continued) •• StimulatingStimulating electrodeelectrode overover stylomastoidstylomastoid foramen;foramen; recordingrecording electrodeelectrode inin regionregion ofof nasolabialnasolabial foldfold •• NormalNormal sideside comparedcompared toto abnormalabnormal •• DifferenceDifference inin amplitudeamplitude isis directlydirectly proportionalproportional toto degreedegree ofof degenerationdegeneration eg.eg. 2525 reductionreduction == 75%75% degenerationdegeneration •• NotNot usefuluseful forfor 7272 hourshours afterafter injuryinjury ElectrodiagnosisElectrodiagnosis (continued) Electromyography:Electromyography: •• MeasurementMeasurement ofof electricalelectrical activityactivity inin musclemuscle usefuluseful toto demonstratedemonstrate survivalsurvival ofof motormotor unitsunits •• ImpliesImplies preservationpreservation ofof somesome intactintact fibresfibres •• ShowsShows presencepresence ofof fibrillationfibrillation potentials,potentials, indicatingindicating denervationdenervation:: indicationindication ofof recoveryrecovery beforebefore itit isis clinicallyclinically apparentapparent •• NotNot helpfulhelpful forfor recentrecent onsetonset ElectrodiagnosisElectrodiagnosis (continued) •• Thus:Thus: allall electricalelectrical testingtesting limitedlimited byby factfact thatthat itit cannotcannot provideprovide anan indicationindication ofof statusstatus ofof facialfacial nervenerve inin immediateimmediate postpost injuryinjury statestate DiagnosisDiagnosis ofof facialfacial paralysisparalysis •• MostMost causescauses idiopathicidiopathic •• PotentiallyPotentially treatabletreatable causescauses mustmust bebe excludedexcluded •• GoalGoal ofof diagnosisdiagnosis toto arrivearrive atat prognosisprognosis andand treatmenttreatment ManagementManagement •• TimeTime ofof onset:onset: RecentRecent onsetonset afterafter trauma:trauma: –– SurgicallySurgically exploreexplore andand repairrepair withinwithin 33 -- 66 weeksweeks LateLate onsetonset afterafter trauma:trauma: –– ConservativeConservative -- steroidssteroids CausesCauses ofof facialfacial nervenerve •• UpperUpper motormotor vsvs lowerlower motormotor Rules:Rules: •• CongenitalCongenital vsvs acquiredacquired •• ImmediateImmediate vsvs delayeddelayed Site Aetiology Intracranial Acoustic neuroma CVA* Brain stem tumour* Intratemporal Bell’s palsy Herpes zoster oticus Middle ear infection Trauma – surgical – temporal bone fracture Extratemporal Parotid tumours Miscellaneous Sarcoidosis, polyneuritis CongenitalCongenital •• MayMay bebe traumatictraumatic oror inherited/inherited/ developmentaldevelopmental TraumaticTraumatic:: – Difficult delivery – Forceps – Large infant TreatmentTreatment:: – Usually resolves – EMG will differentiate between traumatic and inherited/developmental InheritedInherited •• MyotonicMyotonic dystrophydystrophy:: – Autosomal dominant – Progressive muscle wasting – Mental impairment – Facial nerve paralysis early sign •• AlbersAlbers--SchoenbergSchoenberg:: diseasedisease – Autosomal recessive pattern – Disorder of bone metabolism • Bone density increases • Primary bone resorption decreases – Osteopetrosis of bony canals with cranial nerve compression
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