MSC Neuro 2025 P1

SignsofPupillaryReflexFailure

Nolightreflex→Parasympatheticpathwaydamage(Edinger-Westphal nucleus/oculomotornerve).

Noconsensualreflex→ Longitudinalbundledamage.

Noresponsetoaccommodation(nearreflex)→Perlia’snucleus/parasympathetic pathwaydamage.

Nodilationtopain(ciliospinalreflex)→Sympatheticdamage.

Anisocoria(Unequalpupils)

Causes&Features:

SpecificSyndromes

1.ArgyllRobertsonSyndrome

Cause:Neurosyphilis(alsodiabetes,MS).

Pupils:Small,irregular, reacttoaccommodationbutnotlight.

2.Adie’sSyndrome(Adie’stonicpupil)

Cause:Idiopathicorpost-viraldegeneration ofciliaryganglion.

Pupil: Dilated,poor/absentlightreaction,slowconstrictionwithneare ort, slowre-dilation.

KeytoRemember:

Lightreflexabsent, accommodationpresent→ ArgyllRobertson.

Slowtonicconstrictionwithnearreflex>lightreflex→ Adie’spupil.

Miosis+ptosis+anhidrosis→ Horner’ssyndrome.

17.Oculomotor,trochlear,abducensandoculomotorsystem;symptomsofdamage OculomotorNerve(CN III)

Motor:

Extraocular muscles– superiorrectus,medialrectus,inferiorrectus,inferior oblique.

Levatorpalpebraesuperioris→raiseseyelid.

Parasympatheticfibers:sphincterpupillae(pupilconstriction),ciliarymuscle (accommodation).

Lesionsymptoms(completeIIInervepalsy):

Ptosis→paralysisoflevatorpalpebrae.

"Down&out"eyeposition→onlylateralrectus(VI)andsuperioroblique(IV)act unopposed.

Diplopia→worsensonnearvision(medialrectuslost).

Mydriasis(dilatedpupil)→sphincterpupillae paralysis.

Lossoflightreflex& accommodation→parasympatheticdamage.

Lossofconvergence→medialrectus+accommodation pathwaylost.

Restrictedmovements→noup,down,inwardgaze.

Sometimesmildexophthalmosduetolossofmuscletone.

TrochlearNerve(CNIV)

SmallestCN,onlynervethatdecussates(crosses).

Innervates: Superiorobliquemuscle→depresses&intortseye (mainly downandin). Lesion:

Diplopiawhenlookingdown&in (e.g.,reading, descendingstairs).

Patienttiltsheadtooppositesidetocompensate.

Eye movementrestrictionwhenlookingdownwards.

Easytoremember:“Di icultygoingdownstairs”= trochlearpalsy.

AbducensNerve(CNVI)

Nucleusinpons.

Innervates: Lateralrectus(abductseye). Lesion:

Lossofabduction→eye pulledmedially =convergentstrabismus.

Diplopia,especially lookingtowardslesionside.

Gazepalsyifnuclearlesion(sinceVInucleusalsohasinternuclearconnectionsto contralateralmedialrectusvia MLF).

QuickClinicalDi erentiation

CNIIIpalsy:Ptosis+eye“down&out”+dilatedpupil+diplopia.

CNIV palsy:Verticaldiplopia(esp.downgaze),di icultydescendingstairs,headtilt tooppositeside.

CNVIpalsy:Medialstrabismus,failuretoabducteye,horizontaldiplopia.

KeyMCQ/Exampoint:

Light-neardissociation (pupilreactstoaccommodationbutnotlight)→ Argyll Robertsonpupil(syphilis).

Completeophthalmoplegiawithbigfixedpupil→ CNIIIlesionduetoaneurysm (PComartery).

18.Mediallongitudinal fasciculus.Regulationofgaze,corticalandbrainstemgazeparesis; Parinaud'ssyndrome,internuclearophthalmoplegia.

MedialLongitudinalFasciculus(MLF)

Anatomy:

A pairedcomplexfiberbundleinthebrainstemnearmidline,ventraltothe periaqueductalgray,extendingfromthemidbrain(nucleusofDarkshevich andintermediatenucleusofCajalatmetathalamuslevel)throughthepons andmedulla, continuingintocervicalspinalcordanteriorhorns.

Connectsmotornucleiofocularnerves:CNIII(oculomotor),IV(trochlear), VI(abducens),andvestibularnuclei.

Function:

Coordinatesconjugate(friendly)eye movements,especiallyhorizontalgaze byconnectingtheabducensnucleus(lateralrectus)on onesidewiththe contralateraloculomotornucleus(medialrectus).

Integrates headmovementviavestibulo-ocularreflexpathwaystostabilize gazeduringheadmotion.

GazeRegulation

Cortical center:Frontaleyefields(middlefrontalgyrus)initiatevoluntaryconjugate gaze.

Fibersdescendviainternalcapsuletocontralateralpontine gaze center (abducensnucleus/PPRF).

Brainstemcenters:

Pontinegazecentercontrolshorizontalgaze.

Midbraintegmentumandposteriorcommissureinvolvedinverticalgaze control(lesionherecauses verticalgazeparesis,e.g.,Parinaud’ssyndrome).

Lesione ects:

Pontinelesion→horizontalgazeparesistowardsideoflesion(patient looks towardlesion).

Midbrainlesion→verticalgaze paresis(impairedup/downgaze).

InternuclearOphthalmoplegia(INO)

Cause:UnilaterallesionoftheMLFbetweenabducensnucleus andoculomotor nucleus.

Clinicalfeatures:

Ipsilateraleyehasimpairedadduction(medial rectusweakness),slowedor absentmedialmovementpastmidline.

Contralateraleyeshowsabductingnystagmuswithattemptedlateralgaze.

Convergencepreserved(di erentpathway).

Possibleverticalmisalignment:a ectedeyemaysithigher(HertwigMagendie sign).

BilateralINO:Bothsides involved,withbilateraladductionweaknessandimpaired verticalconjugategaze.

Causes:Multiple sclerosis(youngadults),brainstemstroke(elderly),trauma, metabolicorparaneoplasticsyndromes.

Parinaud’sSyndrome(DorsalMidbrainSyndrome)

Clinicalsyndromeduetolesionnearposteriorcommissure/midbrainroof.

Featuresverticalgazepalsy(impairedupgaze>down gaze).

Oftenassociatedwithhydrocephalus,pinealtumors.

OculocephalicReflex(Vestibulo-ocularReflex)

Reflexallowingeyestomoveoppositetheheadtomaintainsteadygaze.

Pathway:Vestibularapparatus→vestibularnuclei→MLF→ocularmotornuclei.

Testedincomatosepatients;absentreflexsuggestsbrainstemdysfunction.

19.Trigeminalnerve,syndromology.

TrigeminalNerve(CNV)Overview

Type:Mixed(sensory+motor)cranialnerve.

Origin:Emergesfromthelateralsurfaceoftheponsnearthe middlecerebellar peduncle.

Components:

Sensoryroot:Larger,containscellbodies inthe trigeminal(Gasserian) ganglionlocatedinMeckel’scave.

Motorroot:Smaller,passesalongsidesensoryroot,entersmandibular division.

Branches:

1.Ophthalmic(V1-sensoryonly):

Sensoryinnervationtoscalp,forehead, uppereyelid,cornea,nose dorsum,andmucosaofnoseandsinuses.

Exitsskullviasuperiororbitalfissure.

2.Maxillary(V2-sensoryonly):

Sensorytolowereyelid,cheek,upperlip,upperteeth,palate,nasal cavity.

Passesthroughforamenrotundum.

3.Mandibular(V3-sensory+motor):

Sensorytolowerlip,lowerteeth,chin,jaw,partsofexternalear, anteriortwo-thirdsoftongue(generalsensation,nottaste).

Motortomusclesofmastication(masseter,temporalis,pterygoids), mylohyoid,tensortympani,tensorvelipalatini.

Exitsviaforamen ovale.

TrigeminalNeuralgia(TicDouloureux)

Presentation:

Sudden,severe,stabbingpainlastingseconds to2minutesovertrigeminal distribution.

Usuallya ectsV2and/orV3branches,rarelyV1(~5%).

Painisunilateral,doesnotcrossmidline.

Attackstriggeredbytalking,chewing,touchingface,washing,shaving.

Patientsmayexhibitpainfulfacialspasms(tic).

Nopainbetweenattacks.

Triggerzonesofteninnasolabialregion.

Etiology:

Oftencausedbyvascularcompression ofthetrigeminalnerve root.

20.Mimicparesisofthe centraland peripheraltype.VariAntsoffacialnervedamage.

FacialNerve(CN VII)Paresis:CentralvsPeripheral

PeripheralFacialNervePalsy(LowerMotorNeuronLesion)

Cause:Damage tothefacialnervenucleusorthenerveafteritleavesthebrainstem (nuclearorinfranuclear).

Features:

Paralysisofallipsilateralfacialmusclesincludingupperandlower face.

Symptoms:

Lagophthalmos(inabilitytofullycloseeyelid).

LossofBell’sphenomenon(upwardeyemovementwhentryingto closelids).

Flattenednasolabialfold.

Weaknessoforbicularisoris(mouthmuscles)→inabilitytowhistle, showteethproperly,cornerofmouthdroops.

Lossorweakeningofcornealreflex(supraorbitalreflex).

Possibleassociatedfindingsiflesionisproximalinthefacialcanal:

Disturbedtasteonanterior2/3oftongue(chordatympani involvement).

Decreasedlacrimationandsalivation(parasympatheticfibersvia intermediatenerve).

Hyperacusis(stapediusparalysis).

Deafnessifauditorycanalinvolved.

Examples:Bell’spalsy,trauma, infections(RamsayHuntsyndrome).

CentralFacial NervePalsy(UpperMotorNeuronLesion)

Cause:Lesionofcorticobulbarfibersabovethefacialnervenucleus(incortexor corticobulbartract).

Features:

Paralysisofonlythecontralaterallowerfacial muscles(lowerhalfofface).

Foreheadmusclessparedduetobilateralcorticalinnervation(both hemispheresinnervateupperface).

Nolagophthalmosortotaleyelidclosure loss.

AssociatedwithotherCNSsignslikehemiparesis,dysarthria,dependingon lesionsite.

Examples: Stroke,tumors,demyelinationa ectingcorticobulbartracts.

VariantsofFacialNerveDamage

Nucleardamage: Rare;a ectsallfacialmusclesipsilaterally.

Peripheralnervedamage: Usuallya ectsallmusclessuppliedbythe nerve onthe sameside.

Intermediatenerve(Wrisberg'snerve)involvement:

Containssensoryandparasympatheticfibers.

Damageheremaycause:

Lossoftasteonanterior2/3oftongue.

Decreasedsalivationandlacrimation.

Dryeyes(iflacrimal fibersinvolved).

Hyperacusis.