MESIALTEMPORALSCLEROSIS

DrVijayKAggarwalConsultantRadiologist-MRISpecialistNorvic Hospital

ClinicalFellowshipNeuroradiology,USAClinicalFellowshipBodyMRI,USA

Learningobjectives

1.ToreviewtheMRanatomyofthetemporallobe,especiallymedialregion.

2.TodiscussoptimalMRItemporallobeprotocol.

3.TodescribeprimaryaswellassecondarymagneticresonancefeaturesofMTS.

4.TodiscusstheroleofMRspectroscopyandfunctionalimagingmethodsinthepre-surgicalworkupoftemporallobeepilepsy(TLE).

Temporallobeepilepsy

Causes:• Mesialtemporalsclerosis (MTS):~70%• Temporallobetumours:~10%MCGanglioglioma.• Corticaldysplasia:5-10%• Vascularmalformations:~5%• Trauma• Infection• Congenital• Temporalpoleencephalocele - Rare

CASE

• 25-year-male

• Hadexperiencedcomplexpartialseizuressincechildhood.

• Seizures,whichfeaturedautomatismsanddystonicposturing,hadstartedfollowingafebrileillnesswithaprolongedseizurewhenhewasfouryearsofage.

• Unsuccessfulcontrolofseizuresusingmultipleantiepilepticdrugsresultedinweeklyseizures,renderinghimunabletodrive.

Anatomy

• HippocampusisaprominentC-shapedstructurebulginginthefloorofthetemporalhornofthelateralventricle.

• Consistsofcornuammonis(CA1-CA4).

• Otherregionsthattogethercomprisethehippocampalformation consistofthedentategyrus,thesubicularcomplex,andtheentorhinalcortex.

• Basedonitsextrinsicconnectivity,thehippocampalformationreceivesavastamountofhighlyprocessedmultimodalsensoryinformationthatisfunneledintothehippocampalformationmainlybytheentorhinalcortex.

Anatomy

MRImaginganatomyoftemporallobe

CoronalT2-weighted(A)andsagittalT13-dimensionalinversionrecovery(B)images,showingmesialtemporallobestructures:sylvianfissure(1);superior(2),medial(3),inferior(4)temporalgyri;parahippocampalgyrus(5);collateralwhitematter(6);uncus(U);amygdala(A);andhead(H),body(B),andtail(T)ofthehippocampus.

MTS

• Characterizedbypatternofneuronallosswithinthehippocampusaffectingprincipallythepyramidalcelllayersofthecornuammonis(CA)andthegranulelayerofthedentategyrus.

• Changesinclude:Ø SelectivelossofinhibitoryinterneuronsØ AbnormalspoutingofaxonsØ ReorganizationofneuraltransmitterreceptorsØ AlterationsinsecondmessengersystemsØ Hyperexcitabilityofthegranulecells.

FigA:Normalhippocampushistopath.FigB:SurgicalspecimenshowalmostcompletelossofneuronsfromtheCA1sectorofthehippocampalcortexaswellasfromCA3andCA4.ThereisrelativepreservationofneuronalnumbersinCA2.Thereisalsodepletionofneuronsfromthedentate.Theneuronaldepletionisaccompaniedbymoderateastrocyticgliosis.Thefeaturesareofhippocampalsclerosis.

• Hippocampalformationisnotuniformlyaffected,withthedentategyrus,andtheCA1,CA4andtoalesserdegreeCA3sectionsofthehippocampusbeingprimarilyinvolved.

• Histologicallythereisneuronalcellloss,gliosisandsclerosis.

Pathophysiology

• Notcompletelyunderstood.

• Itispostulatedthataninsulttothedevelopingbrainduringchildhood, suchasacomplicatedfebrileseizureorencephalitis,damagesthedentateinterneuronsystem.

• Thedamageddentategyrusbecomesreorganized,leadingtoanaberranthyperexcitablesynapticsystem.

• Thisisclinicallymanifestedasrecurrentseizures,orepilepsy

Lateraldiagramofthecircuitryassociatedwiththehippocampus.

Clinical Investigations

• MRIisthemodalityofchoicetoevaluatethehippocampus,howeverdedicatedTLEprotocolneedstobeperformedifgoodsensitivityandspecificityistobeachieved.

• Thinsectionobliquecoronalsequencesatrightanglestothelongitudinalaxisofthehippocampusarerequired,tominimizevolumeaveraging.

EpilepsyProtocolMRI

RoutineMRimagingincludes:

• T1W,T2W,FLAIR,DiffusionweightedandSWIsequences inaxialplanewith5mmslicethickness.

• T1Inversion recovery(IR),FLAIRandT2Woblique coronal imagescoveringwholebrainareacquired.

• Obliquecoronalplane isperpendicular tothelongaxisofhippocampus ortheparahippocampal convolution.

• Forhippocampal volumetry, aObliquecoronal threedimensionalgradientechosequenceslicethickness0.85mm, interslicegap1.3mm)isobtained perpendicular tolongaxisofhippocampus ortheparahippocampalconvolution(onlyinselected cases).

MR features of hippocampal sclerosis

Primarysigns:1.Smallatrophicunilateralhippocampus.2.HyperintensityonT2W/FLAIRimages.3.Lossofthehippocampalinternalarchitectureandthatof

normaldigitationsofthehead.

Ø Oftenmentioned,butprobablyoneoftheleastspecificfindings,isenlargementofthetemporalhornofthelateralventricle.Ifanything,caremustbetakennottoallowanasymmetricenlargedhorntotrickyouintothinkingthehippocampusisreducedinsize.

DiagramofacoronalT1-weightedMRimageshowingclassicfindingsassociatedwithmesial temporalsclerosis.

MR features of hippocampal sclerosis. Primary signs: 1.Small left atrophic unilateral hippocampus. 2. Hyperintensity on T2W images. 3. Loss of the hippocampal internal architecture and that of normal digitations of the head.

RightmesialtemporalsclerosisoncoronalobliqueT2W

BilateralmesialtemporalsclerosiscoronalobliqueT2W

Whensevereandlongstanding,additionalassociatedfindingsinclude:

Ø Atrophyoftheipsilateralfornixandmamillarybody.

Ø Increasedsignalandoratrophyoftheanteriorthalamicnucleus

Ø Atrophyofthecingulategyrus

Ø Increasedsignaland/orreductioninthevolumeoftheamygdala.

Ø Dilatationoftemporalhornandtemporallobeatrophy

SecondarySigns

SecondarySignsØ Collateralwhitematterandentorhinalcortexatrophy

Ø Thalamicandcaudateatrophy

Ø Ipsilateralcerebralhypertrophy

Ø Contralateralcerebellarhemiatrophy

Ø Reducedwhitemattervolumeintheparahippocampalgyrus.

Ø Reductioninthevolumeofthesubiculum

Secondarysigns:1. Atrophyofcaudate2. Atrophyofthalamus3. Atrophyoffornix4. UnilateralatrophyofRtemporallobe5. AtrophyofRmamillary body6. Dilatedtemporalhorn

CoronalobliqueT2-Wshowingsecondarysignsofmesialtemporalsclerosis

T1IR-atrophywithhypointensityoftheleftHippocampus(arrow).

AxialT2-weightedFLAIRimageshowshyperintensityoftherighthippocampuswithvolumeloss(whitearrows),characteristicofrightmesialtemporalsclerosis.

Mesialtemporalsclerosisinepilepsy:VincentR.Spano,BMSc(H)andDavidJ.Mikulis,MD

CoronalobliqueFLAIRofptwithpersistentrefractoryseizures,after rightselectivetranscorticalamygdalohippocampectomy(*).Noterighthippocampus(arrow)isatrophicandshowshyperintensesignalcompatiblewithsclerosis,atrophyoftherightfornix.

3yearsmalewithleftMTSandleftMBatrophy

13yearsfemalewithrightMTSatrophyofrightMB

18yearsmalewithleftMTS

51yearsfemalewithleftMTSandleftMBatrophy

MRSpectroscopy

• N-acetylaspartate(NAA)occursinneuronsbutnotinmatureglialcells.

• Thus,itisconsideredamarkerofneuronalabundanceorfunction.

• Incomparison,creatineactivityandcholineactivityareassociatedmorewithglialcellsthanwithneurons.

MR Spectroscopy

• Findingstypicallyrepresentneuronaldysfunction:

Ø DecreasedNAAØ DecreasedNAA/ChoandNAA/CrratiosØ Increasedlipidandlactatesoonafterasseizure

Ø ThecorrespondencebetweenthedecreasedNAA:creatineratioandthesideofMTSorEEG-detectedseizureonset(EEGseizureonset)isashighas90%intemporallobeepilepsy.

MRPerfusion

• DemonstratessimilarchangestoSPECTwithbloodperfusiondependingonwhenthescanisobtained.

Ø Ictalscan:Hyperperfusion.Ø Interictalscan:Hypoperfusion.

SPECTscaninapatientpresentingwithepilepsyshowinghypoperfusion inrighttemporalregioninbothinterictalandictalphases.

BloodoxygenationleveldependentBOLDfunctionalMRI

• ClinicalfMRIisbasedonbloodoxygenationlevel-dependent(BOLD)contrast.

• BOLDsignalresponsearisesfromlocalizedhemodynamicchangesinducedbyregionallyincreasedneuronalactivityassociatedwithprocessingastimulusorperformingacognitivetaskdefinedbytheparadigm.

• BOLDfMRIisahighspatialresolutiontechniquewithoutionizingradiationthatmapsphysiologicandmetabolicconsequencesofalteredelectricalactivityinthebrain.

• fMRIhasthepotentialtopredictthepossibledeficitsinlanguage,andinvisual,motor,andsensoryfunctionsthatwouldarisefromthesurgicalintervention.

A16-year-oldwithcorticaldysplasia(thickarrow)involvingprecentralgyrus ontheleftside.

Real-timefMRIobtainedafterrightfingertappingvsrestshowsactivationofprimaryhandmotorarea(thinarrow)placedclosetothelesion.

Ifresectionextendstoprimaryhandmotorarea,thepatientislikelytodeveloppostprocedureneurologicdeficit.

Conclusion1.MRI formsthemainstayforstructuralandfunctional

neuroimaginginpatientswithepilepsy.

2.TheMRIdemonstrationofalesionverymuchhelpsinfurtherpresurgicalevaluation.InpatientswithnegativeMRI,PETandSPECTmaybeusedascomplimentarytoolsinthepresurgicalworkup.

3.Neuroimaginghashelpedtounderstandthepathophysiologyofepilepsybetterandalsotoprognosticatetheoutcomeofmedicalandsurgicaltreatments.

4.Advancementsinneuroimaginghavealsoprovidednoninvasivetoolstodetecttheepileptogenicfocus.

References

• Mesialtemporalsclerosisinepilepsy:VincentR.Spano,BMSc(H)andDavidJ.Mikulis,MD

• MagneticResonanceImagingofMesialTemporalSclerosis(MTS):Whatradiologistsoughttoknow? P.Singh1,G.Mittal2,R.Kaur2,K.Saggar1;

• Anatomyofthehippocampalformation.SchultzC1,EngelhardtM

• MRofMesialTemporalSclerosis:HowMuchIsEnough?RichardBronen,YaleUniversitySchoolofMedicine,NewHaven,Conn

THANKYOU