TrigeminalNerveInjuryandManagement

KristopherLeeBScDDS,MD,FRCD(c),DipABOMS

StaffSurgeon,OralandMaxillofacialSurgeryMountSinaiHospital

Outline

•  Reviewofanatomy•  Mechanismsofinjury•  InjuryclassificaLon•  Diagnosis,neurosensorytesLng•  Management•  Outcome

Anatomy

•  669LNsfrom430cadavers•  14%LNabovelingualcrest•  AtitstypicallocaLon,

meandistanceisV=3mm,H=2mm

•  22%LNindirectcontactwithlingualplate

Microanatomy

•  4connecLveLssuesheaths– Mesoneurium– Epineurium– Perineurium– Endoneurium

•  Vasonervorum•  LymphaLc•  Nervefiber

NeuralFascicularPaZerns

IANandlingualnervesarepolyfascicularmoreresistanttoneedleinjuryalmostimpossibletoalignfascicle

FibertypesA-alpha-  Largestmyelinatedfibers-  6-8umdiameter-  ConducLonvelociLesof70-120m/s-  Associatedwithmusclespindles,tendonafferents,andskeletalmuscleefferentfibers

A-beta-  Myelinatedneuron-  6-8nmdiameter-  ConducLonvelociLesof30-70m/s-  Sensibilityoftouch

FiberTypesA-delta-  Smallestmyelinatedneurons-  2.5-4um-  ConducLonvelociLesof12-30m/s-  SenseoftemperatureandfastpainC-fibers-unmyelinated-  1umdiameter-  Transmitat0.5-2m/s-  TransmitsLmuliencodedforsloworsecondpain,temperature,andefferentsympatheLcfibers

Terminology

•  Anesthesia–absenceofanyresponse•  Paresthesia–abnormalsensaLon,spontaneousorevoked,notunpleasant

•  Dysesthesia–unpleasant,abnormalsensaLon•  Hyperaesthesia–increasedsensiLvitytoeitherofpainfulornonpainfulsLmulaLon– Allodynia-painfromanordinarilynon-painfulsLmulus

– hyperalgesia

•  Neuralgia–paininthedistribuLonofanerveornerves

•  Neuropathy–adisturbanceoffuncLonorpathologicchangeoffuncLonofanerve,excludingdescripLonofinjury

Mechanismofinjury-  Compression-  Stretch-  LaceraLon-  Compartmentsyndrome-  Chemicalinjury

MechanismofInjury-  TraumaLc

-  Jawfracture

-  Iatrogenic-  Localanesthesia-  OralSurgery:ExtracLons,Implants,bonegraeing,orthognathicsurgery,ablaLvesurgery

-  Periodontalsurgery-  EndodonLcs-  Chemical:endodonLcmaterials,hemostaLcagents

3rdMolarextracLon

•  Rangesfrom0.4%to22%,mosttypicallyreportedas5%

•  Spontaneousrecoverywilloccurinasmanyas75%ofthesein6monthsto1year

•  Resultsina0.5%to2%permanentparesthesiarateforIANandLN

RiskFactorsforIAN/LNinjurywith3rdmolars

•  Age>35•  DepthofimpacLon•  Generalanesthesia?•  AngulaLon•  Lingualordistoangular•  Integrityofthelingualcortex•  NeedfortoothsecLoning•  Surgeonexperience•  OperaLveLme•  IntraoperaLveexposureofthenerve•  Rood’spanoramicindicators

Rood’sfeaturesofmandibular3rdmolarandIANanatomy

•  LossofcorLcaLonofthecanal•  ConstricLonofthecanal•  DeflecLonofcanal•  Shadowingofroots•  Narrowingofroot•  Darkening/bifidrootapex

•  Incidenceofnerveinjurycanbe20-36%

NerveinjurywithlocalanesthesiainjecLon

•  PogrelesLmatedincidenceat1:26,000to1:160,000

Overallincidence:1inmanymillionsPrilocaine4%:1in2millionsArLcaine4%:1in4millions

•  PotenLalmechanisms:-ChemicalinjurypossiblyrelatedtoanestheLcconcentraLon(4%)-  Directneuraltrauma,laceraLonfromabarbedneedle-  Intraneuralhematoma

InjecLoninjuries•  Difficulttopredictorprevent•  ElectricshocksensaLonuncommoninthosewhosustain

injury•  Non-anatomicdistribuLonofsymptomspossible•  Morecommoninfemales•  Lingualnervemorecommonlyaffected(greaterstretch

withmouthopening??)•  Majorityofcasesresolvein8weeks•  IflasLngmorethen8weeksthenonly1/3resolve

spontaneously•  Dysesthesiamorecommonwiththistypeofinjury•  SurgeryisapooropLon

InjuryfromendodonLctreatment

•  OverinstrumentaLon•  ExtrusionofendodonLcmaterial•  ManagementinvolvespromptsurgicalexploraLon,washout,externalneurolysisornervegraeasneeded

InjuryfromdentalImplants

•  Mostcommonwithposteriormandibularimplants

•  Injuryhappensmostlikelyfromtwistdrillsratherthandirectcompressionoffixure

•  Hematomacausingcompartmentsyndrome•  Managementinvolvesremovalofimplantoncerecognizedinthepostopperiod

•  Dysesthesiaareverycommonwiththeseinjuries

Strategiestoavoidinjury

•  PreoperaLveCBCT•  Drillstops•  Shortimplants

HemostaLcagents

•  SurgicelhasimmediatedamagingeffectsonnervefuncLon

•  Itappearsthatbonewax,bovinecollagenfibrils(Avitene),gelfoamarebenigntonervefuncLon

ClassificaLonofNerveInjuries

•  SeddonClassificaLon•  Sunderland•  DellonandMackinnonmodificaLonofSunderland

Seddon

•  Neuropraxia•  Axonotmesis•  Neurotmesis

Neuropraxia

•  AconducLonblockduetoanoxiafrominterrupLonofepineurialorendoneurialbloodsupply–includesinterfascicularedema

•  NoaxonaldegradaLonordemyelinaLon•  Completerecoverywithin24hrsto2months•  Aphysiologicnotanatomicinjury•  Ifischemiaisprolonged,ahighergradeinjurywillresultfrominfarcLonandsubsequentfibrosis

•  (Sunderlandfirstdegreeinjury)

Axonotmesis

•  AxonalinjurywithsubsequentdegeneraLonandregeneraLon

•  OccurswithoutdisrupLonofendo/peri/epineurium

•  IniLalanesthesiawithTinel’ssign•  Completerecoverywithin12months,onsetofsensoryreturnwithin2-4months

(Sunderland2nddegreeinjury)

Neurotmesis

•  SeveredisrupLonoftheconnecLveLssuecomponentsofthenervetruckwithcompromisedsensoryandfuncLonalrecovery

•  Sunderland3rd,4th,5thdegreeinjurydependingonwhichofthethreelayersaredisrupted

•  Immediateanesthesiawithpossibledevelopmentofparesthesiaorneuropathia

Sunderland

SunderlandGrade6injury

•  DescribedbyDellonandMcKinnonin1988•  RecognizestheheterogeneityofpresentaLonanddiagnosLcambiguitytypicalofperipheralnerveinjurieswhereinfeaturesofallclassesmaybepresent

Consequencesofinjury•  Complexstructural,metabolicandphysiologicchanges

•  Changesoccurthelengthofnerve,notjustatsiteofinjury

•  “injurycurrent”generatedwithinfluxofNa+,andCa++ionstriggeringpleiotropicenzymaLcandtranscripLonalacLvity.

IneffecLveHealing-neuromas

•  Disorganizedmassofcollagenfibersandrandomlyorientedsmallnervefascicles

•  Classifiedaccordingtotheirgrossmorphology

Management

PaLentEvaluaLon

•  History•  SubjecLvesensaLon,0-100%•  ObjecLveneurosensorytesLng•  Clinicalexam

ClinicalExam

•  Ideally1sttestconductedwithin2weeksfollowinginjurytoestablishpostopbaseline– Thenfollowonceamonth

ClinicalExam•  Neurosensorytest– Mappingofinvolveddermatome–  StaLclighttouch–  BrushdirecLonaldiscriminaLon–  TwopointdiscriminaLon–  Pinprick/nocicepLon–  ThermaldiscriminaLon

•  Determinepresenceofsensorydeficit,typeandmagnitudeofdeficit

•  DocumentobjecLvelythelevelofsensaLonforfuturecomparison

Mappingoftheinvolvedarea

SLmuluslocalizaLon

•  EsLmatetheamountofsynesthesia•  WithwoodenendofcoZonswab•  Shouldlocalizewithin1-2mmofsLmulus

TwopointdiscriminaLon

•  AssessthedensityandquanLtyoffuncLonalsensoryreceptorsandafferentfibers

•  A-delta,C-fibers•  Boleygauge/Caliperat1mmincrements

TwopointdiscriminaLon

BrushdirecLonaldiscriminaLon

•  A-alpha,A-beta,lanceolateendings,PaccinianandMessinercorpuscles

•  PropriocepLon•  SeriesofrandomdirecLons,usingcoZonswap

StaLclighttouch•  Merkelcell,Ruffiniending,andA-betaintegrityrequired

•  Weinstein-semmesfilament/vonfreyfilaments

NocicepLon

•  Assessfreenerveendings–CandA-deltafibers

•  Use27gaugeneedle•  PresswithoutindentaLonàpaLentabletofeel=normalresponse

•  PresswithindentaLonàabnormalresponse

ThermaldiscriminaLon

•  AdjuncLve,andnotveryuseful•  Integrityofsmalldiametermyelinatedandunmyelinatedfibers

•  WarmthaZributedtoA-deltafibersandcoldtoC-fibers

DiagnosLcnerveblocks

•  Aidtolocalizesiteofinjury•  Usefulinneuropathicpain•  Helpsdeterminewhetherpainiscentrallyorperipherallymediatedorwhatdegreeofeach

ClinicalExam

•  EvaluaLonofwound•  PalpaLonforTinel’ssign(lingualnerve)•  PalpaLonforneuroma(lingualnerve)•  Panorex:ruleoutforeignbodies/rootLpscompressingnerve

Medicalmanagement

•  Mostlylimitedtodysesthesia/neuropathicpain

Surgicalmanagement

•  Dilemma:allowingenoughLmeforspontaneousrecoverybutnotsomuchtoimpairsurgicaloutcome

•  WhyisLmethoughttobecriLcal?– DistalnervedegeneraLon– Ganglioncelldeath– CentralcorLcalchanges

SurgicalManagement

•  Decidewhetherornottorepairorobserve•  Takeintoaccountthetype,mechanism,severity,andlocaLonofnerveinjury,paLent’sdesireswithrespecttotreatment.

SurgicalmanagementIndicaLons:•  Evidenceofnervecompression–immediateremovalof

theobject(rootLp,bonefragment,implant)•  EndodonLcmaterial–mayrequireimmediatewashout,

decompression•  WitnessedtransecLon–mayrequireimmediaterepair•  Closedinjury:followmonthly.Repairifnoimprovement

at1-3monthsforLN,3-6monthsforIAN•  Orpainat4months

Outcomes

Outcome

Postopcourse

•  Variableperiodofcompleteanesthesia,typically3month

•  Regrowthoccursat1mm/dtherefore3cmpermonth

•  Occursmoreslowlywithnervegrae•  Dysesthesiaisalwayspossibleaeeranynervesurgery

Keypoints•  SpontaneousrecoveryhappensinsomebutnotallpaLents.Difficulttopredictwhowillfallintowhichcategory(letusmakethatdecision)– witnessedtransecLonmayrequireimmediaterepair– OtherwisewefollowwithrepeatneurosensorytesLng,andrepairwhenindicated:•  forLNat1-3months,IANat3-6months,ifparesthesiaissignificantandnoimprovement

•  Painat4months•  Ifparesthesiaisimproving,conLnuetofollow

•  IANrecoversmoreoeenthanlingualnervebecauseofbonyconduit

Keypoints•  InjecLoninjuriesarepoorsurgicalcandidates– Mostresolvesaeer8weeks,ifnot,only1/3willimprove

•  Dysesthesiaisverydifficulttomanage.Responsetosurgeryishighlyunpredictable.MostpaLentsneedlongtermmanagementwithmedicaLons

ThankYou

kristopher.lee@gmail.com