ContentslistsavailableatScienceDirect
European
Journal
of
Radiology
Open
j o ur na l h o me pa g e :w w w . e l s e v i e r . c o m / l o c a t e / e j r o
Staging
of
pelvic
lymph
nodes
in
patients
with
prostate
cancer:
Usefulness
of
multiple
b
value
SE-EPI
diffusion-weighted
imaging
on
a
3.0
T
MR
system
Valentina
Vallini
a,
Simona
Ortori
a,
Piero
Boraschi
a,
Francesca
Manassero
b,
Michela
Gabelloni
a,
Lorenzo
Faggioni
a,∗,
Cesare
Selli
b,
Carlo
Bartolozzi
aaDepartmentofDiagnosticandInterventionalRadiology,UniversityofPisa,ViaParadisa2,56124Pisa,Italy bDepartmentofUrology,UniversityofPisa,ViaParadisa2,56124Pisa,Italy
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:Received22November2015 Accepted24November2015 Availableonline11December2015 Keywords: Diffusion-weightedMRimaging 3Tsystem Lymphnodes Prostatecancer
a
b
s
t
r
a
c
t
Purpose:Toevaluatetheusefulnessofdiffusion-weightedimaging(DWI)withamultiplebvalue
SE-EPIsequenceona3.0TMRscannerforstagingofpelviclymphnodesinpatientswithprostatecancer candidatetoradicalprostatectomyandextendedpelviclymphnodedissection(PLND).
Materialsandmethods:Institutionalreviewboardapprovalwasobtainedandwritteninformedconsent
wastakenfromallenrolledsubjects.Aseriesof26patientswithpathologicallyprovenprostatecancer (highorintermediateriskaccordingtoD’Amicoriskgroups)scheduledforradicalprostatectomyand PLNDunderwent3TMRIbeforesurgery.DWIwasperformedusinganaxialrespiratory-triggered spin-echoecho-planarsequencewithmultiplebvalues(500,800,1000,1500s/mm2)inalldiffusiondirections.
ADCvalueswerecalculatedbymeansofdedicatedsoftwarefittingthecurveobtainedfromthe corre-spondingADCforeachbvalue.FittedADCmeasurementswereperformedatthelevelofproximaland distalexternaliliac,internaliliac,andobturatornodalstationsbilaterally.Lymphnodeappearancewas alsoassessedintermsofshortaxis,long-to-shortaxisratio,nodecontourandintranodalheterogeneity ofsignalintensity.
Results:A totalof173lymphnodesand104nodalstationswereevaluatedonDWIand
pathologi-callyanalysed.MeanfittedADCvalueswere0.79±0.14×10−3mm2/sformetastaticlymphnodesand
1.13±0.29×10−3mm2/sinnon-metastaticones(P<0.0001).Thecut-offforfittedADCobtained by
ROCcurveanalysiswas0.91×10–3mm2/s.Atwo-point-levelscorewasassignedforeachqualitative
parameter,andthemeangradingscorewas6.09±0.61formetastasticlymphnodesand5.42±0.79for non-metastaticones,respectively(P=0.001).Usingascorethresholdof4formorphological,structural, anddimensionalMRIanalysisandacut--offvalueof0.91×10–3mm2/sforfittedADCmeasurements
ofpelviclymphnodes,per--stationsensitivity,specificity,PPV,NPVanddiagnosticaccuracywere100%, 7.9%,15.6%,100%and21.3%,and84.6%,89.5%,57.9%,97.1%and88.8%,respectively.
Conclusions:3.0TDWIwithamultiplebvalueSE-EPIsequencemayhelpdistinguishbenignfrom
malig-nantpelviclymphnodesinpatientswithprostatecancer.
©2015TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Thepresenceofpelviclymphnodemetastasesinpatientswith prostatecancerisofmajorrelevancesinceitiscrucialfor treat-mentplanning.Currently, pelvic lymphnodedissection(PLND) representsthemostaccurateand reliablestagingprocedurefor thedetectionoflymphnodeinvasioninprostatecancer,butnotall
∗Correspondingauthor.
E-mailaddress:[email protected](L.Faggioni).
patientsareatthesameriskofharboringpelviclymphnode metas-tases[1].RadicalprostatectomywithPLNDisatime-consuming andrelativelyexpensiveprocedurethatrequiresinpatient hospi-talizationandisassociatedwithpotentiallyearlypost-operative complications(suchasbleeding,infections,lymphocele)andlate post-operativecomplications(e.g.,urinaryincontinence,erectile dysfunction,anastomoticstenosis).Forthisreason,non-invasive imagingisimportanttostreamlinethesurgicalresectionprotocol andhasapotentialroleinselectingpatientswhoaresuitablefor PLND[2,3].
http://dx.doi.org/10.1016/j.ejro.2015.11.004
2352-0477/©2015TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4. 0/).
Table1
D’Amicoriskgroups.
Highrisk PSA*>20orGleason≥8orareinclinicalstageT2c-3a IntermediateriskGleasonscoreof7orPSAof10–20orareinclinicalstageT2b Lowrisk PSA≤10ng/mlandGleasonscore≤6orareinclinicalstageT1-2a PSA∗=prostate-specificantigen,expressedinng/ml.
Nodalstagingisroutinelyperformedbycross-sectionalimaging
suchascomputedtomography(CT)andisbasedonthe
morpho-logicalanddimensionalfeaturesoflymphnodes,includingtheir
size(withathresholdof10mminshortaxisdiameterorclusters
of smallerregionallymph nodes),long-to-shortaxisratio,
bor-ders(lobulatedorspiculated),extra-capsularspread,andabnormal internalarchitecture(suchascentralnecrosis)[4,5].
MRdiffusion-weightedimaging(DWI)isanon-invasive imag-ingtechniqueyieldinguniqueinformationonmoleculardiffusion propertiesoftissues.DWIallowstoevaluatetherandomthermal motionofwatermolecules(Brownianmotion),whichisgenerally limitedincancertissuesbecauseoftheirrelativelyhighcell den-sityandabundanceofcellularmembranesascomparedtonormal tissues.Themobilityofwatermoleculesisquantifiedbythe appar-entdiffusioncoefficient(ADC)[4].Conventionally,restrictedwater diffusioninareasofhighcellulardensity(e.g.,tumors)resultsin lowADCvaluescomparedwithareaswithlowercellulardensity, whichtypicallyshowhigherADCvalues.
Astothedifferentialdiagnosisbetweenbenignandmalignant lymphnodeswithDWI,thehighsignalintensityoflymphnodes inhighbvalueimagesmustnotbemisinterpreted,becausealso reactivenodalhyperplasiacanresultinincreasedcellularityand thushighsignalintensityonDWIimages[4].Inclinicalpractice, DWIoflymphnodesisperformedusinghighbvaluestoincrease theconspicuityof highcellularitylymphnodes [6],and in this settingatleasttwoormorebvaluesareusedforDWIanalysis. Inlightoftheaboveassumptions,quantitativeevaluationofADC mapsmightprovideusefulinformationforpresurgicalassessment ofpelviclymphnodes,whichhoweverneedstobeinterpretedwith caution[4].
ThepurposeofourstudywastoevaluatetheusefulnessofDWI withamultiplebvaluespin-echoecho-planar(SE-EPI)sequenceon a3.0TMRscannerforstagingofpelviclymphnodesinpatientswith prostatecancercandidatetoradicalprostatectomyandextended PLND.
2. Materialsandmethods 2.1. Patientspopulation
BetweenJune2011andNovember2013,aseriesof26patients (medianage66.3±6.7years,range49–76years)with pathologi-callyprovenprostatecancer(highorintermediateriskaccording toD’Amicoriskgroups;Table1)scheduledforradical prostatec-tomyandPLNDunderwentMRIbeforesurgery.Exclusioncriteria werethefollowing:knownbonemetastases,previoustreatment forprostate cancer,previous/concomitant malignancy,and con-traindicationstoMRI.
Allpatientswereexaminedona3.0TMRIscanner(Discovery MR750;GEHealthcare,Milwaukee,WI) usinga phasedarray 8-channelsurface coil(gradientfield strength50mT/m, slewrate 200T/m/s).Institutionalreviewboardapprovalwasobtained,and awritteninformedconsentwasobtainedfromallenrolledpatients afterthenatureoftheprocedurehadbeenfullyexplained.
Allpatientsunderwent radicalprostatectomywithin15days ofMRI.Lymphnodesweresurgicallymappedandclassifiedinto tendifferentanatomicregions(proximalanddistalexternaliliac,
Table2
Demographicandbiometricinformation(patientsn=26).
Patients,N 26
Age,mean(range) 66.3(49–76)
PreoperativePSA,mean(range) 14.8(3–40.6) BiopsyGleasongrade
6(3+3) 2 7(3+4) 7 7(4+3) 6 8(4+4) 5 9(4+5) 4 9(5+4) 2
Dissectedlymphnodes,n 442
Lymphnodecount,mean(range) 17(7–32) Dissectednodalstations,n 212 Metastaticnodalstations,n/N(%) 21/212(9.9) Non-metastaticnodalstations,n/N(%) 191/212(90.1)
proximalanddistalinternaliliac,andobturator,eachonboththe rightandleftsides).
In 6 out of 26 patients (23%), extended lymphadenectomy
includingthetenabove-mentionednodalstationswasperformed,
while inthe remaining20 patients(77%)all tennodalstations
werenotcompletelyremovedat thesurgeon’s discretion,since
lymphadenectomy was not extended to stations where lymph
nodes wereneitherevidentonMRI norintraoperativelyvisible
orpalpable.Atotal of212nodalstations,correspondingto442
lymphnodes(median17lymphnodesperpatient,range7–32per
patient),weresurgicallyremovedandpathologicallyanalysed.A
pathologistwithmorethan15yearsofexperienceinurogenital
pathologywasresponsibleforassessingallpathologicalspecimens,
andreceivedananatomicaltemplatemarkingthedissectednodal
stations.However,ifnonodeswerefound,theentiretissue under-wentpathologicalanalysis.
Demographicandbiometricdataofthestudygroupare
sum-marisedinTable2.
2.2. MRimageacquisitionprotocolandanalysis
Theentirepelvisspanningfromtheaorticbifurcationtothe pubicsymphysiswasimagedbyperforming,asafirststep,afast spinecho(FSE)T1-weightedsequence(TR600–800ms,TE6–7ms; slicesection4mm,spacing0.4mm,matrix320×320,3Nex)and subsequently,aFSET2-weightedsequence(TR5000–8000ms,TE 80–85ms,slicesection4mm;spacing0.4mm,matrix384×352,4 Nex)acquiredinthetransverseandcoronalplanes.
DWIwasperformedusinganaxialrespiratory-triggeredSE-EPI sequencewithmultiplebvalues(500,800,1000,1500s/mm2)in
alldiffusiondirections.Imagingparameterswerethefollowing:TR (repetitiontimeautomaticallyadaptedtothepatient’sbreathing pattern)3500–9200ms,TE65–69ms,slicesection4mm,spacing 0.4mm,matrix96×224,4Nex.Theacquisitiontimeforthewhole MRIexaminationrangedfrom25to30min.Themultiplebvalue DWIacquisitionlastednomorethan6minoverall.
MRimageswereanalysedinconsensusbytworadiologistswith morethan15yearsofexperienceinurogenitalimagingandMRI, whowereblindedtopatient-relatedinformationsuchaspatient identificationdata,historyorfinaldiagnosis.Lymphnodeswere identifiedonT2-weightedFSEimagesandclassifiedintoten differ-entstations,asdescribedinSection2.1.
ThefeaturesofpelviclymphnodesontheFSEMRimageswere assessedintermsoftheirshortaxis,long-to-shortaxisratio,node contour,andheterogeneityofintranodalsignalintensity.To quan-tifyeachoftheseparameters,agradingscore(Table3)wasassigned basedonatwo-point-levelsystem,andtheglobalgradingofeach nodalstationwasobtainedbysummingthepoint-levelobtained foreachofthefollowingfourparameters:
Table3
Gradingscoresystem.
1point 2points Intranodalsignalintensity Homogeneous Inhomogeneous
Shortaxis ≤10mm >10mm
Nodalcontour Regular Irregular
Long-to-shortaxisratio ≥2 <2
1.Shortaxis≤10mm(1point)or>10mm(2points) 2.Long-to-shortaxisratio≥2(1point)or<2(2points) 3.Regular(1point)orirregularnodecontour(2points)
4.Homogeneous (1 point) or inhomogeneous intranodalsignal
intensity(2points).
Consequently,theglobalGradingScorerangedbetween4 (indi-catorofabenignnature)and8,i.e.,theworstscoreindicatorofa malignantnature.
TheADCvaluesof pelviclymph nodeswerecalculated ona
dedicatedworkstation(Advantage Windows4.5,GEHealthcare,
Milwaukee,WI).AllADCmeasurementswereobtainedfromthe
multiplebvalueSE-EPIDWIsequencebymeansofdedicated
soft-warefittingthecurveobtainedfromthecorrespondingADCfor
eachbvalue. TocalculatefittedADCvalues, regionsof interest
(ROIs)wereplaced inlymphnodes byanotherradiologistwith
5years ofexperienceinabdominal imagingand MRI,whowas
blindedtopatientinformationincludingclinicalhistory,previous radiologicalfindings,andfinaldiagnosis.TomeasurefittedADC val-ues,carewastakentoplacethreeROIsassimilaraspossibleinside eachlymphnode.Inordertomaximizethereproducibilityof mea-surements,circularROIswerechosentosamplethelargestpossible areawithinpelviclymphnodes.Toavoiderrorsduetopartial
vol-umeaveraging,ROIsnotsmallerthan30mm2 weretraced,and
nodessmallerthan5mmintheirlargestdiameterwereexcluded
fromquantitativeanalysis.
ForeachfittedADCvalue,weobtainedthreeADCmeasurements
andconsideredtheiraveragevalue.Likewise,innodalstations
com-prisingmultiplelymphnodeswemeasuredthefittedADCvalueof
everylymphnodeandconsideredtheiraveragevalue.
2.3. Statisticalanalysis
Statisticalanalysiswascarriedoutusingcommerciallyavailable statisticalsoftware(MedCalcversion12.6.1.0,www.medcalc.org). Thedistributionofqualitativevariableswasexpressedasthe relative frequency of thevarious modalities underobservation, whilethedistributionofquantitativevariableswasexpressedas mean,standarddeviation,minimum,maximum,andnumber of observations.
Thetwo-tailedStudent’sttestwasusedtocomparethefitted ADCvaluesmeasuredatnodalstationsinthemetastaticand non-metastaticlymphnodegroups.TheglobalGradingScoresinthe twogroupswerecomparedusingthetwo-tailedMann–Whitney test.APvaluelessthan0.05wassetasthresholdforstatistical significance.
ToevaluatethediagnosticperformanceofthefittedADCin dif-ferentiatingmetastaticfromnon-metastaticlymphnodes,receiver operatingcharacteristic (ROC) curveanalysis wasperformedto extracttheoptimalthresholdyieldingthebestseparationbetween them.Sensitivity,specificity,positivepredictivevalue(PPV), nega-tivepredictivevalue(NPV)anddiagnosticaccuracywerecalculated bothforthefittedADCvaluesandtheglobalgradingscore.
Table4
Locationofpelvicnodalstationsandnumberoflymphnodesperstationanalysed. Pelvicnodalstations No. No.oflymphnodes Rightproximalexternaliliac 16 34
Leftproximalexternaliliac 7 12 Rightdistalexternaliliac 16 29 Leftdistalexternaliliac 13 26 Rightproximalinternaliliac 8 10 Leftproximalinternaliliac 1 1 Rightdistalinternaliliac 4 4 Leftdistalinternaliliac 5 7
Rightobturator 14 17
Leftobturator 19 32
Rightcommoniliac 1 1
Leftcommoniliac 0 0
Total 104 173
3. Results
AllpatientstoleratedtheMRexaminationwellandwereable
tocompletetheMRprotocol.
Imaginganalysiswaslimitedto104nodalstationsforatotal
of173lymphnodes,sinceonlynodeswithamaximumdiameter
notsmallerthan5mmandavailablepathologicaldiagnosiswere
included.Allremaininglymphnodesinthevariouspelvicnodal
stationswerenotconsideredandthereforeexcludedfrom
analy-sis.Locationofthepelvicnodalstationsandthenumberoflymph nodesperstationanalysedarereportedinTable4.
The mean global grading score was6.09±0.61 (range 5–7) inthemetastaticnodegroupand 5.42±0.79 (range4–7)inthe non-metastaticnodegroup(P=0.001).AGradingScoreequalto4 (highlyindicativeofabenignnature)wasfoundin6/85nodal sta-tionsonlyofthenon-metastaticnodegroup,whiletheremaining 79nodalstationsshowedagradingscoregreaterthan4(atotal gradingscore>4wasconsideredsuspiciousformalignancy).Inthe metastaticnodegroup,allnodalstationsshowedagradingscore greaterorequalthan5.Alllymphnodesinthemetastaticnode groupdetectedonFSEimagesweresmallerthan10mmintheir shortaxis,andonepatienthadabenignlymphnodelargerthan 10mm(13.5mm)initsshortaxis.
Withascorethresholdof4,per-stationsensitivity,specificity, PPV,NPVanddiagnosticaccuracyforFSE-MRIanalysiswere100%, 7.9%,15.6%,100%and21.3%,respectively.
ThemeanfittedADCvaluewas0.79±0.14×10−3mm2/sinthe
metastaticnodegroupand1.13±0.29×10−3mm2/sinthe
non-metastaticnodegroup(P<0.0001).
MeantotalGradingScoresandmeanfittedADCvaluesinthe twodifferentlymphnodegroupsarereportedinTable5. Exam-plesoffindingsrelatedtobenignandmalignantlymphnodesare illustratedinFigs.1–3.
TheareaundertheROCcurverelated totheADCdifference betweenthemetastaticandnon-metastaticnodegroupswas0.89 (Fig. 4). The ADC threshold value yielding the best separation betweenmetastatic and non-metastatic lymph nodes as deter-minedbyROCcurveanalysiswas0.91×10−3mm2/s.Accordingly,
Table5
MeantotalgradingscoreandmeanfittedADCvaluesinthetwodifferentgroupsof pelviclymphnodes.
Pathologicallymetastatic Pathologicallybenign Pvalue No.ofnodalstations 19 85
ADCvalue* 0.79±0.14 1.13±0.29 <0.0001
(Mean±SD,range) 0.63–1.12 0.10–2.20
Globalgradingscore 6.09±0.61 5.42±0.79 0.001
(Mean±SD,range) 5–7 4–7
Fig.1.Anexampleofbenignlymphnode.(a)T2wimage.(b)DWimage.(c)ADCmap.(d)Gradingscore=6.
Fig.3.Anotherexampleofmetastaticlymphnode.(a)T2wimage.(b)DWimage.(c)ADCmap.(d)Gradingscore=7.
Fig.4.Thereceiveroperatingcurve(ROC)analysisshowedanareaunderthecurve (AUC)of0.89.
afitted ADCvalue equaltoor lessthan 0.91×10−3mm2/swas
consideredtobeassociatedwithlymphnodemetastasis(Table6). Finally,per-stationsensitivity,specificity,PPV,NPVvaluesand diagnosticaccuracy for DWI analysiswere 84.6%, 89.5%, 57.9%, 97.1%and88.8%,respectively.
4. Discussion
Preoperativedetectionoflymphnodemetastasesinpatients withprostate cancer is crucial for selection of the appropriate treatmentstrategyand isthereforerelevantforpatient progno-sis.SomeauthorsfavorperformingPLNDinallpatientswhoare candidatesforradicalprostatectomy,regardlessofbaselinetumor characteristics[7].Nevertheless,thestagingbenefitisbalancedby
Table6
MRIfindingsaccordingtotheapparentdiffusioncoefficient(ADC)mappernodal station(n=104).
ADCvalue Positivepathologicalspecimen ≤0.91×10−3mm2/s 15
>0.91×10−3mm2/s 4
theriskofexposingacertainnumberofpatientstosignificantand
potentiallyunnecessaryPLND-relatedcomplications.Conventional
cross-sectionalimagingtechniquessuchasCTcannotaccurately
differentiatebetweenbenignandmalignantlymphnodes,
espe-cially in the case of smaller nodes (<10mm), so that smaller
metastasesoftengoundetected.Similarly,standardMRI,dynamic
contrast-enhancedMRI,andevenMRspectroscopicimaginghave
shown no advantage over CT in predicting metastatic
involve-mentoflymphnodes[8,9].Indeed,recentstudieshaveshownthat meticulouslymphnodedissectioninpatientswithprostate can-cerdisclosesarateofmetastasesashighas25%inpatientswith preoperativelynegativestandardimagingstudies[10].Theuseof lymphotropicultrasmallsuperparamagneticparticlesofironoxide (USPIO)asMRIcontrastagentshasbeenevaluatedaswell.Ina studyincluding80menwithclinicallylocalizedprostatecancer, thistechniquehasshowntoincreasethesensitivityfordetectionof lymphnodemetastasesfrom35%whenusingMRIaloneto90%[11]. However,imageinterpretationistime-consuming,sincea node-by-nodecomparisonmustbemadebetweenpre-andpost-contrast MRIimages,andrequiresspecialexpertise.Moreover,this tech-niquecannotovercometheproblemoffalse-negativenormal-sized lymphnodesharboringmicrometastases,andUSPIOagentsarenot availableinthedailyclinicalpractice[11].However,the combina-tionofDWIandUSPIOhasyieldedinterestingresults[12].Infact, innormallymphnodes,theuptakeofironoxideparticlesbythe reticuloendothelialsystemproducesasignaldecreaseonT2/T2*
-weightedimages,whilemalignantlymphnodesshowhighsignal intensityduetothecombinationofthetwoeffects(i.e.,reduced
dif-fusiontogetherwithrelativelyunchangedT2/T2*followingUSPIO
administration),resultinginbetterseparationfromnormallymph nodes,whicharesupposedtobecomeinvisibleduetothereduced T2/T2*.
LymphnodeassessmentwithDWIiscurrentlyoneofthemost interestingfieldsofresearchinoncologicalimaging,andADCis aquantitativeparameterthatreflectsthediffusionofwaterand tissue perfusion. In particular, DWI has beeninvestigated as a potentialtooltodifferentiatebenignfrommalignantlymphnodes inheadandneckcancer[13].AlargespectrumofADCvaluesamong metastaticlymphnodeswasfoundandcanbeexplainedby differ-encesinthecellularcompositionoftumors.WhencomparingADC valuesforanyorganandlesionreportedintheliterature,attention hasalsotobepaidtothechoiceoftheunderlyingbvalue,onwhich ADCisstronglydependent[14].
Basedonourpreliminaryfindings,DWImayhelpdistinguish benign from malignant lymph nodes in patients with prostate cancer,sincefittedADCvalueofmetastaticlymphnodeswere sig-nificantlylowerthanthoseofnon-metastaticlymphnodeswitha NPVashighas97.1%.
Astothemorphological,structural,anddimensionalMRI analy-sisofpelviclymphnodes,wefoundasignificantdifferencebetween thetotalGradingScoreinthemetastaticandnon-metastaticnode groups,yetverylowspecificity,PPVanddiagnosticaccuracywere observed.Wealsofoundthatthemeandiameter(shortaxis)of metastaticlymphnodeswassmallerthan10mm(5.77±1.81mm, range3.7–9mm),whichisthestandardcut-offreportedinthe lit-eratureforpelviclymphnodes[15,16].
Tothebestofourknowledge,nootherstudyhassofar specifi-callytackledtheissueofnodalstaginginprostatecancerbymeans ofDWIusing fittedADCmeasurementsobtainedfroma multi-plebvalueDWIsequence.Thiskindofevaluationovercomesthe problemof choosing a specificb valuefor ADCmeasurements, becausefittedADCarecalculatedonthebasisofalogarithmiccurve obtainedwithmultiplebvalues.Moreover,theusageofahigher magneticfieldstrength(3.0Tversus1.5T)shouldbeadvantageous asitcanprovidehigherspatialresolutionandsignal-to-noiseratio. However,tomaximizeaccuracyinMRI-basedlymphnode stag-ing,itisimportanttobeawareofthefollowingpotentialpitfallsof DWI:
1.Smallnodes(<4mminlongaxisdiameter)maybedisplayed andanatomicallylocalisedusingDWI,butthepresenceof malig-nantdiseasecannotalwaysbeestablishedbasedonthesoleDWI findings;
2.ADC measurements in normal-sized lymph nodes may be degradedbypartialvolumeeffects;
3.Necrosis inside metastatic nodes may lead to false-negative resultsduetotheresultantADCincrease,andtherefore macro-scopicareasofintranodalnecrosismustbecarefullydiscarded; 4.AnyreactivechangesinlymphnodesmayresultinlowerADC
values;
5.Technicalfactorssuchasimagenoiseandmotionartefactscan leadtosystematicorrandomerrorsinADCquantification; 6.Micrometastasesinsmallerlymphnodeswithinsufficient
intra-nodaltumorburdenmaynotimpedewaterdiffusionandcan thereforeleadtofalse-negativeresults[4].
Besides,ourstudyhasseverallimitations.First,thenumberof patients(andinparticular,ofthosewithmalignantlymphnodes) wasrelativelylow.Second,weexcludedfromimageanalysisall lymph nodes smaller than 5mm in their maximum diameter, whichstillcouldbemalignantinnature.Third,astation-by-station insteadofanode-by-nodeanalysiswasperformed.Nevertheless, surgicalspecimensoftenincludedmultiplelymphnodes,soitwas
notpossibletohavea100%pathologicalcorrelationateachsingle lymphnodelevel,especiallyinthecaseofmultiplelymphnodesat asinglenodalstation.
Inconclusion,ourpreliminaryexperiencesuggeststhat3.0T SE-EPIdiffusion-weightedMRimaging withmultiplebvalues may help distinguish benign frommalignant pelvic lymph nodes in patientswithprostatecancer.Inparticular,fittedADC measure-mentscouldrepresentausefulmethodinthisdifferentialdiagnosis when using a threshold value of 0.91×10–3mm2/s. Since DWI
requiresonlyaveryshortprolongationofthestandardMRI exam-inationprotocol,thistechniquecouldberecommendedaspartof aroutineMRIstudyofthepelvisasanadditionaltoolfor charac-terisationofpelviclymphnodes.However,furtherstudieswitha largerpatientsamplearenecessarytoconfirmourfindings.
Conflictofinterest
None.
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