Persistent fontanelles in Chihuahuas and inter- and intra-rater reliability of fontanelle area measurement in computed tomography images

Abstract

Background: The Chihuahua dog breed is known for frequent occurrence of a bregmatic fontanelle on the dorsal skull. A common conception is that this skull defect is clinically irrelevant in Chihuahuas. No studies, however, describe the prevalence of this malformation, whether it is accompanied by fontanelles at other locations on the skull or how to assess the severity of these lesions. Our primary aim was, by using computed tomography imaging, to describe the presence, number, and location of persistent fontanelles (PF) at cranial sutures on dorsal, lateral and caudal cranial surfaces in Chihuahuas. The secondary aim was to develop a method to measure the fontanelle area in computed tomography images by using the closed polygon tool of Osirix Medical Imaging Software.
Results: Of the 50 dogs evaluated, 46 (92%) had either one or several PFs. The mean ± SD number of affected cranial sutures per dog was 2.4 ± 2.3 (range 0-10), and mean ± SD number of PFs was 2.8 ± 3.0 (range 0-13). Of the 46 dogs with affected sutures, 7 (15%) had no PF at a location typical for a bregmatic fontanelle. The inter-rater reliability of the fontanelle area measurement was almost “perfect”, and intra-rater reliability reached “excellent” agreement.
Conclusions: PFs are almost ubiquitous in the examined group of Chihuahuas. They are located at dorsal, lateral, and caudal surfaces of the cranium, and hence are not all recognized reliably by palpation in adult dogs. Though the pathogenesis of the PFs described here is unknown, bone-deficient lesions may occur due to congenital defects in cranial bone ossification, delayed closure of cranial sutures, or bone resorption, as is observable in children with craniosynostosis (premature cranial suture closure). Because the imaging findings described in the Chihuahuas of this study are similar to findings among children with craniosynostosis/premature cranial base synchondrosis closure, this growth disorder may be a predisposing factor for the PFs described here. Further studies are necessary to evaluate the pathogenesis and clinical relevance of these lesions. Due to high inter- and intra-rater reliability of the method of fontanelle area measurement it may be useful in future studies.

Full text

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Preprint:Pleasenotethatthisarticlehasnotcompletedpeerreview.
PersistentfontanellesinChihuahuasandinter-and
intra-raterreliabilityoffontanelleareameasurement
incomputedtomographyimages
CURRENTSTATUS:UND ERREVIEW
Anna-MariamKiviranta
HelsinginYliopisto
anna-mariam.kiviranta@helsinki.fiCorrespondingAuthor
ORCiD:https://orcid.org/0000-0002-9542-7247
ClareRusbridge
UniversityofSurrey
AnuK.Lappalainen
HelsinginYliopisto
JouniJ.T.Junnila
4PharmaLtd.
TarjaS.Jokinen
HelsinginYliopisto
DOI:
10.21203/rs.2.22165/v1
SUBJECTAREAS
SmallAnimalMedicine
KEYWORDS
brachycephaly,Chihuahua,craniosynostosis,fontanelle,ossification,syringomyelia

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Abstract
Background:TheChihuahuadogbreedisknownforfrequentoccurrenceofabregmaticfontanelleon
thedorsalskull.AcommonconceptionisthatthisskulldefectisclinicallyirrelevantinChihuahuas.No
studies,however,describetheprevalenceofthismalformation,whetheritisaccompaniedby
fontanellesatotherlocationsontheskullorhowtoassesstheseverityoftheselesions.Ourprimary
aimwas,byusingcomputedtomographyimaging,todescribethepresence,number,andlocationof
persistentfontanelles(PF)atcranialsuturesondorsal,lateralandcaudalcranialsurfacesin
Chihuahuas.Thesecondaryaimwastodevelopamethodtomeasurethefontanelleareaincomputed
tomographyimagesbyusingtheclosedpolygontoolofOsirixMedicalImagingSoftware.
Results:Ofthe50dogsevaluated,46(92%)hadeitheroneorseveralPFs.Themean±SDnumberof
affectedcranialsuturesperdogwas2.4±2.3(range0-10),andmean±SDnumberofPFswas2.8±
3.0(range0-13).Ofthe46dogswithaffectedsutures,7(15%)hadnoPFatalocationtypicalfora
bregmaticfontanelle.Theinter-raterreliabilityofthefontanelleareameasurementwasalmost
“perfect”,andintra-raterreliabilityreached“excellent”agreement.
Conclusions:PFsarealmostubiquitousintheexaminedgroupofChihuahuas.Theyarelocatedat
dorsal,lateral,andcaudalsurfacesofthecranium,andhencearenotallrecognizedreliablyby
palpationinadultdogs.ThoughthepathogenesisofthePFsdescribedhereisunknown,bone-
deficientlesionsmayoccurduetocongenitaldefectsincranialboneossification,delayedclosureof
cranialsutures,orboneresorption,asisobservableinchildrenwithcraniosynostosis(premature
cranialsutureclosure).BecausetheimagingfindingsdescribedintheChihuahuasofthisstudyare
similartofindingsamongchildrenwithcraniosynostosis/prematurecranialbasesynchondrosis
closure,thisgrowthdisordermaybeapredisposingfactorforthePFsdescribedhere.Furtherstudies
arenecessarytoevaluatethepathogenesisandclinicalrelevanceoftheselesions.Duetohighinter-
andintra-raterreliabilityofthemethodoffontanelleareameasurementitmaybeusefulinfuture
studies.
Background
TheChihuahuaisadogbreedknownforitsverysmallsize,roundhead,andfrequentoccurrenceofa

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bregmaticfontanelle(ormolera)onthetopoftheskull,betweenthepairedfrontalandparietal
bones.Itisacommonconceptionthatthebregmaticfontanelleisclinicallyirrelevantinsmall-breed
dogs,especiallyinChihuahuas[1].Nostudies,however,describetheprevalenceofthismalformation
orstatewhetheritisaccompaniedbyfontanellesatotherlocationsontheskull.
Theskullconsistsoftheviscerocraniumformingtheskeletonofthefaceandtheneurocranium
formingthecranialbaseandthecranialvault[2].Theneurocraniumdevelopsfrommesodermaland
neuralcrestcellsduringembryonicdevelopment[3].Theskullbase(occipital,sphenoid,andethmoid
bones)developsthroughendochondralossification,whereasthecranialroof(frontal,parietal,
squamouspartofthetemporalbone,andinterparietalpartoftheoccipitalbone)developsthrough
membranousossification[2,4–6].
Fontanellesarefibrous,membrane-coveredgapsthatliebetweenthecranialbonesformedby
intramembranousossificationandattheintersectionofthecranialsutures.Thecranialsuturesare
thejunctionsbetweenmembranousbones,andbetweenmembranousandendochondralbones.They
arethemajorsitesofboneexpansion—duringpost-natalcranialgrowth—ofthecranialvaultthatwill
accommodatetheenlargingbrain.Thisexpansionoccursinresponsetosignalsfromtheexpanding
neurocranium.Bycontrast,theendochondralbones,(i.e.cranialbasebones),areconnectedby
cartilaginoussynchondrosesandexpandthroughchondrocytehypertrophy[7].
Atmaturation,whichdisablesfurthergrowthofthecranium,thecranialsuturesclose.Information
concerningcaninecranialsutureclosuretimesisscarce,butonesuggestionisthattheinterparietal,
i.e.sagittal,sutureclosesattheageof2to3yearsandtheinterfrontal,i.e.metopicsutureatthe
ageof3to4years[8].Inhumans,cranialsuturescloseduringthethirddecadeoflife[7].
Childrenarebornwithsixfontanelles:twoalongthemidline,theanterior(alsocalledasthe
bregmaticfontanelle)andtheposteriorfontanelle,andtwooneachsideoftheskull,theleftandright
sphenoid,andleftandrightmastoidfontanelles[9].Thelargestfontanelleinchildren,theanterior
fontanelle,islocatedatthejunctionofthetwofrontalandparietalbonesandclosesbetween3to27
months,withthemedianageofclosurerangingfrom9to14months[10,11].Theposterior
fontanelleislocatedbetweentheoccipitalandtwoparietalbones,isopeninonly1.5%ofnewborn

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children,andclosesinthosechildrenby2monthsofage[12].Furthermore,thepairedsphenoid
fontanellesoccurattheintersectionofthefrontal,parietal,sphenoid,andtemporalbonesandclose
ataround3monthsofage.Caudaltothesphenoidfontanelles,andbetweentheparietal,temporal
andoccipitalbones,arethemastoidfontanellesthatcloseduringthesecondyearoflife[13].
Indogs,fewstudiesdescribethefontanelle-closuretimes,andthosethatdo,onlydescribethe
bregmaticandoccipitalfontanelleclosuretimes:Bregmaticfontanelleclosureisassumedtooccurat
birthorwithinamonthafterwards[5,14].Thefontanelleresemblingtheposteriorfontanellein
children,herewecalltheoccipitalfontanelle,closesataround45daysofgestationwhenthe
unpairedinterparietalbonefuseswiththeparietalandsupraoccipitalbones.Insomedogs,the
interparietalbonedoesnotfusewiththesupraoccipitalbone,andremainsasaseparatebone[5].
InChihuahuabreedstandardsofdifferentkennelclubstheoccurrenceofamolera,apersistent
fontanel(PF)attheintersectionofthepairedfrontalandparietalbones,variesfrombeingan
acceptedtraittobeingadisqualifyingfault[15–18].TheexistenceofthisPFiscommonlytestedby
palpatingthehead,whichonlyenablestherecognitionofPFinareasoftheskulllackingathick
musclelayersuchasthemid-dorsalregion(thelocationofthebregmaticfontanelle).Cranial
computedtomography(CT)imagingprovidesmorecompleteassessmentpermittingdeterminationof
howcommonPFsareinChihuahuasandalsoiftheseskulldefectsoccuroncranialsurfacesnot
detectedbypalpation.Developinganobjectivemethodtoevaluatetheseverityoftheselesions
wouldinthefutureallowassessmentoftheclinicalrelevanceandpathogenesisofthesefindingsin
Chihuahuas.Inchildren,suturaldiastasis(delayedclosureofacranialsuture)anddisordersofcranial
ossificationareassociatedwithdevelopmentaldisordersofcranialgrowthduetoprematurecranial
sutureclosure[19].Reliablediagnosticmethodswouldallowcomparisonbetweenthepathogenesis
ofPFsinChihuahuasandbonedeficientskulllesionsinchildren.
Theprimaryobjectiveofourprospectivestudywastodescribethepresence,number,andlocationof
PFsinChihuahuas.Thesecondaryobjectivewastoevaluatetheinter-andintra-raterreliabilityofthe
fontanelleareameasurementmethodinCTimages.OurprimaryhypothesiswasthatPFsare
commoninChihuahuasandoccurnotonlyattheintersectionofthefrontoparietal,sagittal,and

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interfrontalsutures—henceatthelocationofthebregmaticfontanelle—butatotherlocations,aswell.
Oursecondaryhypothesiswasthatthefontanelle-areameasurementmethodisrepeatablebothby
differentevaluatorsandbetweenseparatemeasurementtimes(inter-andintra-raterreliabilities).
Results
Thestudygroupof50Chihuahuascomprised26(52%)smooth-haired,23(46%)long-haired
Chihuahuas,and1(2%)Chihuahuamix.Thesecomprised27(54%)femalesand23(46%)males
(includingonecastratedmale).Themean±SDageofthese50dogswas58±28months(range7-
139months),andtheirmean±SDweightwas2.8±0.6kg(range,1.4–4.3kg).Ofthe50included
dogs21werenotclinicallyaffectedand29hadclinicalsignsrelatedtoChiari-likemalformationor
syringomyelia(CM/SM).Ofthose29clinicallyaffecteddogs,7dogshadconcurrentdiseasespossibly
causingsimilarclinicalsignsthanCM/SM.

Presence,number,andlocationofpersistentfontanelles
Ofthe50dogsevaluated,46(92%)hadeitheroneorseveralPF.Themean±SDnumberofaffected
suturesperdogwas2.4±2.3(range0-10),andmean±SDnumberofPFswas2.8±3.0(range0-
13).DuetoonedogthathadmissingCTimagesoftheveryrostralskull,thecohortforevaluationof
distributionofaffectedsuturesandPFscomprised49dogs.Atotalof34dogs(69%)had1to3
affectedsutures,7dogs(14%)had4to6suchsutures,and4dogs(8%)had7to10.Similarly,
groupingdogsbytheirnumberofPFsshowedthatof49dogs,32(65%)had1to3PFs,7(14%)had4
to6PFs,and6(12%)had7to13.(Tables1and2).
Atotalof118affectedsuturesoccurredinthese49dogs:57(48%)occurreddorsally,44(37%)
caudally,and17(14%)laterally(7ontheleftside,10ontherightside).Furthermore,ofthetotal138
PFs,72(52%)appeareddorsally,49(36%)caudally,and17(12%)laterally(7ontheleftside,10on
therightside)(Table3).
Ofthe46dogswithaffectedsutures,7(15%)hadnoPFatalocationtypicalofabregmatic
fontanelle.Ofthosedogs,eachdoghad1to7affectedsuturesoneitherdorsal,lateral,orcaudal
surfacesofthecranium.Furthermore,44(32%)ofthe138fontanellesoccurredinotherlocations

6
thanthoseinchildren(theanterior,posterior,sphenoid,ormastoidfontanelles).
ThenumberofthePFsvariedfromsingle(Figure1)tomultiplelesions(Figure2)atonesuture,and
theshapefromsharplyedged(Figure3)tolesionswithnon-distinctmargins(Figure4).Occasionally,
thelesionsappearedtobeconnectedtoradiolucentlinesresemblingvenousstructures(Figure5).

Inter-andintra-raterreliabilityofpersistentfontanelleareameasurementincomputed
tomographyimages
Theinter-raterrepeatabilityofthetotalfontanelleareameasurementsbetweentheassessorswas
99.8%.Whenassessingconsistencybetweenthetwoassessments,Krippendorff’salphaforthetotal
fontanelleareawas0.999(95%CIs0.997-1.000)(Table4).
Theintra-raterrepeatabilityofthetotalfontanelleareameasurementswere99.6%foroneand
99.8%fortheotherassessor.Furthermore,theintra-classcorrelationcoefficient(ICC)forreliability
withinassessorofthetotalfontanellearearangedfrom0.997to0.999,(95%confidenceintervals(CI)
0.994-0.999)(Table5).
Discussion
Ourstudyshowsthataccordingtoourprimaryhypothesiscranialbonelesions,calledherePFs,area
commonfindinginadultChihuahuas.Inadditiontotheirwell-knownlocationonthedorsalsurfaceof
thecranium(i.e.thebregmaticfontanelleattheintersectionofthefrontoparietal,sagittal,and
interfrontalsutures),PFsarecommononothersutureslocatedonthelateralandcaudalsurfacesof
theskullaswell.Similarly,accordingtothesecondaryhypothesis,themethodusedinthecurrent
studyforPFareameasurementwasreliableasitshowedalmost“perfect”inter-raterand“excellent”
intra-raterreliabilityandcanthusbeutilizedinfurtherstudies.
Persistentfontanelles
TheChihuahuasofthisstudyalmostallhadeitheroneorseveralPFs.ThePFoccurredonallcranial
surfaces,withapproximatelyhalfofallPFsoccurringonthedorsalsurfaceandslightlyoverone-third
occurringonthecaudalsurfaceofthecranium(Fig.6).Clinicallythisissignificantas,indogs,other
locationsthanthesiteofthebregmaticfontanelle(mid-sagittal,dorsalsurfaceofthecranium)are

7
coveredwithmusclesthickenoughtopreventreliablerecognitionbypalpation.
Thefrontoparietalsuture,thelocationofthebregmaticfontanelle,wasthesuturemostcommonly
affected.Thebregmaticfontanelle,however,wasnotalwayspresentalthoughthedoghadother
affectedsutures.Thispreventstheuseofthebregmaticfontanelleasamarkerofthesebonylesions
elsewhereonthecranialsurface.Furthermore,becausemagneticresonanceimagingislesssensitive
thanCTindetectingopensutures,thecommonuseofmagneticresonanceimagestoruleout
structuralbraindiseasescouldpredisposesmallPFstobeingoverlooked[20].
Onlythebregmaticandcaudallylocatedfontanelle,resemblingthehumanposteriorfontanelle,and
herecalledtheoccipitalfontanelle,aredescribedindogs,withtheliteraturelackingthedescriptions
ofthesphenoidandmastoidfontanelles.Furthermore,althoughthelesionsareherecalledPFs,one-
thirdofthePFsoccurredatlocationsotherthanthelocationssimilartothoseofthefontanelles
describedinchildren.Hence,additionaletiologiesmayexistthanjustdelayedfontanelleclosure.
Areasdeficientinbonecanoccur,forexampleduetodisordersofossificationofthedevelopingbone,
atrophyofmaturebone,orsuturaldiastasis(delayedclosure).Basedonthecurrentstudydesign,
andwithallbuttwoChihuahuasofthisstudyhavingbeenagedover12months,itisnotpossibleto
evaluatewhetherthePFsdescribedherearecongenitaldefectsofboneformationoracquiredbone
remodelingorboneatrophy.Itisgenerallythoughtthatthebregmaticfontanelleisacommonfinding
inimmatureChihuahuas,onesuggestiveof,butnotconclusivelyconsideredtobeacongenitallesion.
AsthePFsontheremainderoftheskullsurfacearenotrecognizablebypalpation,thenatureofthose
lesionsremainsparticularlyinconclusive.Bothformsofacquiredbonedefects,i.e.,boneremodeling
andboneatrophy,occurindogs:IncavalierKingCharlesspaniels,similarlyaffectedwithCMasare
Chihuahuas,foramenmagnumheightincreasesovertime,suggestingactivesupraoccipitalbone
remodelingduetocerebellarpulsation[21–23].Furthermore,suggestiveofboneatrophy,skullbone
defectscanoccurasaresultofmultiplechoroidplexuscarcinomasleadingtonon-communicating
hydrocephalusandincreasedintracranialpressure[24].
Tobetterevaluateallpossiblecausesbehindthebone-deficientlesionsheredescribed,
understandingskulldevelopment,ossification,andcranialgrowthispivotal:intramembranous

8
ossificationofthebonesofthecranialvaultisinitiatedbycondensationofmesenchymalcells
betweenthedermalepitheliumandtheformingmeninges[2].Themesenchymalcellsdifferentiateto
becomefirstosteoblastsandlaterosteocytesthatproducebone-formingmatrix.Intheendochondral
ossification,themesenchymalcellsdifferentiateintohypertrophicchondrocytesthatforman
avascularanlagen,acartilaginoustemplatethatislaterreplacedbybone[25].
Cranialgrowthoccursatthesynchondrosesandatthecranialsutures:Thesynchondrosesallow
rostrocaudalexpansionofthecranialbase,andthecranialvaultgrowthoccursperpendiculartothe
cranialsutures.Thepaceofthemesenchymalcellsdifferentiatingintoosteoblasts,regulatedbythe
growingbrainviaduramater,affectsbonegrowthatcranialsuturegrowthsites.Inadditiontosutural
bonegrowth,constantmodelingandremodelingofbothattheinner-andoutersurfacesofthebone
occurstofitthesurroundingtissues,suchasthecontoursofthebrain[2,25].Cranialsuturalgrowth
normallycontinuesuntilthebrainhasmatured,andthecranialbasesynchondrosescontinueto
lengthen.Toenablemembranousbonegrowth,thecranialsuturesneedtoremaininanun-ossified
state[7].Abnormalosteoblastapoptosisatthecranialsuturescausesprematurecranialsuture
closure,craniosynostosis[26].Thispreventsfutureboneformation,andhenceexpansionofthe
neurocraniumatthesiteoftheclosedcranialsuture,andleadstoabnormalcompensatorycranial
growth[7].
Inchildren,prematurecranialsutureclosure,craniosynostosis,isararegrowthdisorder,occurringin
approximately3to7ofevery10000livebirthsanddisablingnormalexpansionoftheskull[27–28].
Itpreventsnormalbonegrowthperpendiculartotheaffectedsutureandresultsinacharacteristic
head-shapetypicalofthattypeofcraniosynostosis.Forexample,abilateralcoronalsuturesynostosis
(betweenthefrontalandparietalbones)causesshorteningoftheskullandresultsinbrachycephaly
[29].Ascraniosynostosiscausescertainsuturestocloseprematurely,ascompensation,itmaydelay
orpreventothersfromclosing(suturaldiastasis).Asaresult,childrenwithcraniosynostosisaremore
likelytohavesuturaldiastasis[19].Additionally,inchildren,craniosynostosiscanoccur
simultaneouslywithprematurecranialbasesynchondrosisclosure[30].
Inbrachycephalicdogs,andespeciallyincavalierKingCharlesspaniels,thecranialbasespheno-

9
occipitalsynchondrosisclosesprematurely,restrictingrostocaudalskullexpansion[31].Asasignof
compensatorycranialgrowthduetoprematurecranialsutureandsynchondrosisclosurein
brachycephalicdogs,ahigherproportionofclosedorclosingrostralcranialsuturesorcranialbase
synchondroseswasassociatedwithdorsaldeviationoftheprebasialangle,alsocalledairorynchy
[32].Furthermore,inChihuahuas,ashortskullbaseatthecaudalcranialfossacausesovercrowding
ofthecraniocervicaljunction.SuchovercrowdingpredisposestobothSMandCM/SM-relatedclinical
signs[23,33].Furthermore,incavalierKingCharlesspaniels,brachycephaly,i.e.ashortskullbase
withcompensatorydomingoftheskull,isassociatedwithCM-associatedpain[34].
Differencesinsynchondrosisandincranialsuture-closuretimes,describedinearlymorphometric
studies,couldexplainthelargevarianceinskulldimensionsofdifferentdogbreeds[35].Tosupport
thattheory,arecentstudydescribedtheprematureclosureofthesagittalsutureaspossibly
explainingthetypicallyhighhead-shapeoftheboxers[20].Furthermore,alaterstudy,evaluating
head-shapeinheritance,showedthat,forfacial-lengthvariationbetweendogbreeds,aSMOC2locus
explained36%.Itsuggeststhatthecranialsutureclosuretimesappeargeneticallyregulated[36].
ManyofthePFsintheChihuahuasofthisstudyoccurredatotherthantheexpectedfontanelle
locations.Inchildren,non-fontanellecranialbonedefectsoccur,onessuchaslacunarskulland
diffusecopper-beatenappearance:lacunarskull,alsocalled“Lückenshädelskull”(Germanforholes
intheskull),isadevelopmental,congenitaldefectofboneossification,whereasthecopper-beaten
appearanceisanacquiredremodelingofbone[37].Bothoftheselesionsaffecttheinnertableofthe
cranialvault,causingeitherthinningorlossofbone,withthecopper-beatenpatternappearingwith
indistinctmargins,varieddepth,andfollowingthegyralmargins.Ontheotherhand,lacunarskull
defectshavesharplydemarcatedmarginsandareseparatedbybranchesofbone[19,38–40].A
lacunarskull,whenoccurringwithfull-thicknessdefects,isalsocalledcraniofenestra[41].Boththe
copper-beatenappearanceandlacunarskullareassociatedwithcraniosynostosis,butcanalsooccur
asincidentalfindings[19].
InourChihuahuas,theshapeofPFsvaried;somecomprisedsharplydemarcated,full-thickness
lesionsshowingsimilaritieswithlacunarskulldefects(includingcraniofenestra).Ontheotherhand,

10
sometimesthePFshadindistinctmarginsandweresurroundedbyareasofthinbone,suggestinga
moreactiveboneremodeling,thoughlackingthegyralpatternanddiffusedistributionofthecopper-
beatenappearance.Copper-beatenappearanceispreviouslydescribedinaGriffonBruxelloiswith
clinicallyrelevantCMandSM[42].
SomeofthePFsappearedtooccurincloseproximitytoradiolucentareasresemblingvenous
structures.Thiscouldbeaconsequenceofactiveboneremodelingduetoincreasedvenouspressure.
IncavalierKingCharlesspaniels,cranial-baseshorteningduetoprematuresynchondrosisclosureis
suspectedtocausevenousoutflowobstructionresultingfromnarrowedjugularforamina[43].
Supportingatheoryofdecreasedvenousoutflowthroughthejugularforamina,anotherstudy
describeddecreasedvolumesofcaudalcranialfossavenoussinusesinsyringomyelia-affected
cavalierKingCharlesspaniels[44].Jugularforamenobstructionoccursalsoinachondroplastic
childrenwithprematuresynchondrosisclosure.Inthosechildren,ashortenedskullbaseleadsto
jugularforamenstenosisand,duetoincreasedvenouspressure,maycausecommunicating
hydrocephalus[45].Furthermore,inchildren,craniosynostosismayoccuralongsideenlarged
emissaryveins[46].
Inter-raterandintra-raterreliabilitiesoffontanelleareameasurement
Repeatabilityoftotal,dorsal,leftandrightlateral,andcaudalfontanelle-areameasurementsbetween
theassessors,theinter-raterreliability,wasalmostperfectwhenassessingboththepercentage
agreementandKrippendorff’salpha.Similarly,repeatabilityofthetotal,dorsal,leftandrightlateral,
andcaudalfontanelleareawithinthesameassessor,theintra-raterreliability,reachedexcellent
reliabilitywhenassessingbothpercentageagreementandICC.Hence,theexcellentinter-andintra-
raterreliabilitiesreportedinthisstudysuggestthatthefontanelleareameasurementismethodis
suitableforfurtheruse.
Ourexcellentresultscanbethusexplained:weobtainedallCTimageswiththesamescanner,weset
clearguidelinesforthemeasurementmethodwhileevaluatingthepilotdogs(notincludedinthefinal
analysis),andeachevaluatorusedthesamecomputerscreenwhileanalyzingalltheCTimages
(intra-raterreliability).Furthermore,thoughneitheroftheevaluatorshadpreviousexperiencewith

11
thecurrentmethod,bothwereexperiencedinanalyzingcranialCTimages.Ontheotherhand,
differencesinindex-linepositioningandplacementoftheareabordersoftheclosedpolygontool
explainwhytheevaluatorsdidnotreachaperfectconsensus.
Thoughdescriptionsofsimilarfontanelleareameasurementarelacking,earlierstudiesdescribe
measurementofthecaninecranialcavity,caudalcranialfossa,orforamenmagnumareasusing
eitherCTormagneticresonanceimaging[47–50].Furthermore,severalstudiesdescribevolumetric
measurementsofthecaninecranialcavity[44,51–54].Noneofthesestudiesdescribesintra-orinter-
raterreliabilities,possiblyduetothelaboriousnessofthearea-andvolume-measurementmethods.
Inchildren,onestudydescribesitsanteriorfontanelleareameasurementinCTimages:calculationof
thesurfaceareainvolvedmultiplyingthewidthofthefontanellebyitsanterioposteriorlength,and
dividingitbytwo[55].Duetotheirregularshapeofthefontanellesindogs,wedidnotadoptthat
sameformula.
Limitationsofthisstudywererelatedtoitsimageanalysisandcohortcollection:Evaluationofthe
presenceofPFswasoccasionallydifficultduetoverythinbone,andthelowspatialresolution
providedbytheimagingequipment(2-sliceCT),makingitsometimesdifficulttodifferentiate
betweenthinningofbonefromatrue,full-thicknesslesion.Furthermore,asthecranialsutureswere
difficulttodefine,itwasoccasionallychallengingtodeterminetheexactlocationofthelesion.
However,consensusbetweenourevaluatorsimprovedtheaccuracyoftheclassificationofthe
lesions,bothastotheirpresenceandlocation.Astheaimofthestudywastodescribethe
occurrenceofthesebonylesions,wedidnotattempttogroupthembasedontheirpossibleetiology
(suchascongenitaldefectofossificationorasactiveboneremodeling/atrophy).Furthermore,as
mostofthedogswerealiveattheendofthestudy,theydidnotundergoanautopsytocomparethe
CT-areameasurementfindingswiththeactualPFareasincadavericskulls.Finally,themajorityofthe
Chihuahuaswerefromthesamecountry,makingmulticenterstudiesevaluatinginternationalcohorts
essential.
Conclusions
Inconclusion,thelesionsdescribed,herecalledPFs,are,inthisgroupofChihuahuas,verycommon

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andalmostubiquitous.ThenumberofPFsvaried,perdog,fromsingletomultiple.Theywerelocated
ondorsal,lateral,andcaudalsurfacesofthecranium,andhencewerenotallreliablyrecognizableby
palpation.ThePFareameasurementmethoddescribedhereappearsreliablebothbetweendifferent
assessorsandatdifferentmeasurementtimes.ThePFsdescribedinthisgroupofChihuahuasshow
somesimilaritieswiththeimagingfindingsofbone-deficientlesionsincraniosynostoticchildren.
ThoughadditionalstudiesarenecessarytoevaluatethepathogenesisofthePFsinChihuahuas,
notablesimilaritieswiththeimagingfindingssuggestthatprematuresynchondrosisclosureor
craniosynostosisorbothmayprovetobepredisposingfactorsalsoinChihuahuas.Understandingthe
mechanismsresponsibleforthePFsinChihuahuasmaythereforeinthefutureprovideadditional
informationforthemechanismsofcraniosynostosisinchildren.
MaterialsAndMethods
Caseselectionandassessmentofclinicalsigns
Ourprospectivedataincluded50Chihuahuas,membersofthesamecohort(comprising53
Chihuahuas)participatinginanother,concurrentstudypublishedearlier:Thestudyincludedclient-
ownedChihuahuaswithorwithoutCM/SM-relatedclinicalsigns.Thedogswererecruitedfromthe
case-loadoftheVeterinaryTeachingHospitaloftheUniversityofHelsinkibetween2012–2015.
Imagingoftheclinicallyaffecteddogswasadiagnosticprocedureandthenon-affecteddogswere
imagedforbreedingselectiontodetectCM,SM,andcraniocervicaljunctionovercrowding[23].Non-
affecteddogshadtobeatleastthreeyearsold,butnoagelimitwassetforclinicallyaffecteddogs.
Allthedogswithapriorhistoryofacentralnervoussystemdisease(otherthanCM,SMor
craniocervicaljunctionovercrowding)orasevereorthopedicproblemwereexcluded.Thestudywas
approvedbytheFinnishNationalAnimalExperimentBoard,participationwasvoluntary,andalldog
ownersprovidedawrittenconsent.Thecurrentstudyincludedallthedogsfromtheearlierstudythat
underwentCTtoevaluatethecraniocervicaljunction.Alltheprocedureswereundertakenduringone
visitattheVeterinaryTeachingHospital.
Twooftheclinicallyaffecteddogswithprevioushistoryofepilepticseizureswereeuthanizeddueto
statusepilepticusduringanesthesiarecoveryandrecurrentepilepticseizuresfor> 48hours.Epileptic

13
seizuresrecurredthoughthedogsweremedicatedfirstwithloadingdosesofphenobarbital
(24mg/kgiv),levetiracetam(60mg/kgiv),andpotassiumbromide(400–600mg/kgp.r.),andthen
withmaintenancedosesofthesamemedications(phenobarbital3mg/kgevery12hoursi.v.,
levetiracetam20mg/kgevery8hoursi.v.,potassiumbromide10mg/kgevery12hoursp.r.)and
continuousrateinfusionsofeitherpropofolordexmedetomidineandmidazolam.Bothdogswere
euthanizedduetohumanereasonsandbyownerrequest.OneofthedogswaseuthanizedatThe
VeterinaryTeachingHospital:aftersedationwithintravenousadministrationofdexmedetomidinand
butorphanol,bolusesofintravenouspropofolandpentobarbitonewereadministereduntilcardiac
arrestoccurred.Theotherdogwaseuthanizedattheirlocalveterinarianafterbeingdischargedat
owner’srequestfromtheintensivecareunitofTheVeterinaryTeachingHospital.Alltheotherdogs
remainedaliveattheendofthestudy.Asthedogswereclient-owned,noneofthedogswere
releasedandtheyreturnedtoliveinhome-environmentwiththeirowners.Theclinicallyaffected
dogscontinuedtohavecontrolvisitsatTheVeterinaryTeachingHospital,atthereferring/local
veterinarianorwerelostfromfollow-up.Nofurthervisitsoccurredintheclinicallynon-affecteddogs,
buttheownerscouldcontactthefirstauthorincasequestionsemerged.
Diagnosticimagingprocedures
AlldogsunderwentCTundergeneralanesthesia.Ananesthesiologistplannedtheanesthesia
individuallyforeachpatient.Duringanesthesia,heartandrespiratoryrate,bloodpressure,andend-
tidalcarbondioxidepartialpressureweremonitored.Toobtainheadandcervicalspine(tothelevel
ofthecaudalC3vertebra)CTimages,weusedahelicaldual-sliceCTscanner(SomatomEmotion
Duo,SiemensAG,Forcheim,Germany),withabonealgorithmandaslicethicknessof1.0mm
(feed/rotation2mm,reconstructionincrement0.5mm).Thedogswerepositionedsothatthebaseof
theskullwasalignedperpendiculartotheventralvertebralcanalinthecranialcervicalspine.Our
previousstudyprovidesfullCTimagingdetails[23].
Imageanalysis
OsiriXMedicalImagingSoftware(PixmeoSARL,Bernex,Switzerland)servedforanalysisoftheCT
imagesofallincludeddogsforpresence,number,andlocationofthePFs,andthefontanelleareasat

14
dorsal,lateral,andcaudalcranialsutures.Additionally,thetotalfontanelleareawascalculatedusing
theclosedpolygontoolofthesoftware.
Presenceofpersistentfontanelles
Apersistentfontanellewasdefinedasfull-thicknesslossofboneatacranialsuture.Itspresencewas
assessedatthecranialsutures,i.e.thejunctionsbetweenthemembrane-derivedbones(nasal,
lacrimal,frontal,parietal,interparietal,squamouspartofthetemporal)andbetweenthemembrane-
andcartilage-derivedbones(maxillary,palatine,sphenoid,temporal,occipital)whichformthedorsal,
lateral,andcaudalsurfacesofthebraincase.Thecranialbase,formedofcartilage-derivedbones
connectedwithsynchondroses,andnaturallyoccurringwithmultipleforamina,wasnotevaluated
(seeTable3,Figs.7–9).Toimprovethemethod’sreliabilityandtoexcludenon-fused,normalcranial
sutures,thefontanelleareahadtobelargeenough,bysubjectiveassessment,tobemeasurable
usingtheclosedpolygontool.ThesmallestPFsmeasuredwereapproximately1mmindiameter.
Asthedistinctionbetweensomedorsalandlateralboneswasdifficult,duetotheirsmallsizeand
irregularshape,wemadenoattempttodistinguishbetweenthem,andthesutureswereclassifiedas
one(Table3,Fig.7,No.1;Fig.8,No.7).Furthermore,asaPFwasoccasionallylocatedbetweenthe
supraoccipitalandinterparietalbones,thoughnotatatruesuture,andasthesetwobones,inadult
dogs,aresuggestedtobefused,thejunctionbetweenthemwasconsideredanadditionallocation
(Table3,Fig.9,No.16)[5].Additionally,theintersectionsofthelateralsutures,onesresembling
sphenoid(Table3,Fig.8,N:o8)andmastoidfontanellesinchildren(Table3,Fig.9,No12and13),
wereclassifiedasadditionallocations[13].
Twoboard-certifiedneurologists(A-M.K.andT.S.J.)evaluatedindependentlytheanonymizedCT
imagesandwerehenceunawareofthedogs’clinicalstatus.Theevaluatorsfirstassessedeach
cranialsuturein3-dimensionalskullmodelsusingvolume-renderingtechniqueimagestorecordthe
presenceandnumberofallpossiblePFs(Fig.1),andthenconfirmedtheirfindingsinthemultiplanar
images(Figs.10a-c).Ifaftertheindividualassessment,theevaluatorsdidnotagreeaboutthe
presenceornumberofPFs,orastothesuturesaffected,theevaluatorsre-assessedtheCTimages
togethertoreachaconsensus.TheevaluatorsagreedthatalltheassessedPFswerelocatedat

15
cranialsutures.
Totalfontanellearea
Aftertheconsensus,theevaluatorsindependentlymeasuredtheareaofeachfontanellefromthe
anonymizedCT-imagesusingtheclosedpolygontool(Fig.11).Becauseindogsnostudiesdescribe
thePFareameasurementmethod,wefirsttesteditbyassessingCTimagesof10pilotdogs,onesnot
includedinthestudy.Thefollowingguidelineswereset:Thefontanelleareameasurementwas
carriedoutbymeansofmultiplanarCTimages(WL500HU,WW3500HU)withoneofthetwoindex
linespositionedtangentialtotheouterskullsurface,andinthemid-thicknessofthebone
surroundingit.Then,theotherindexlinewaspositionedperpendiculartothepreviousindexlineand
inthecenterofthePF(Figs.10a-c).AstheareaofthePFwasoccasionallylargeandextendedover
convexsurfaces,makingitimpossibletomeasureitreliablyinoneplane,weusedamaximum-
intensity–projection-techniqueimage,withslicethicknessof14to16.Thisslicethicknesswas
selectedbyvisuallyoptimizingtheabilitytomeasurealsoconvexsurfacesandwithouttheareatobe
measuredbeingaffected.Whilemeasuringthepilotdogs’fontanelleareas,theevaluatorshadthe
possibilitytodiscussthemeasurementtechniquetooptimizeitsreliabilityandreproducibility.When
measuringtheactualstudydogs,thetwoevaluatorsmeasuredtheareasindependently.
StatisticalAnalysis
First,toevaluatethereliabilityofthemethodforfontanelleareameasurements,theinter-,andintra-
raterreliabilitiesneededevaluation.Weassessedthesumofdorsal,lateral,andcaudalfontanelle
areasbothseparatelyandasthetotalsumofallfontanelles.Weevaluatedtherandomvariation
causedbyassessors(inter-raterreliability)intwodifferentways:First,wecalculatedarepeatability
statisticbetweentheassessorsfromaone-wayanalysisofvariancemodel,wheretheeffectofthe
dogservedasthesolefixedeffect,andthevalueswereconsideredasapercentageofperfect
agreement.Inthesemodels,thewithin-groupvariationdescribesthevariationbetweenthe
assessors.
Second,todetermineinter-raterreliabilityestimatebetweenthetwoassessors,wecalculated
Krippendorff’salphawith95%confidenceintervals(CI)toassessconsistencybetweenthetwo

16
assessmentsofthefontanelleareas[56].Analpha-valueof1describesperfectagreement,avalueof
0.8describessimilarinterpretation,andavalue ≥ 0.67isinterpretedasthelowestconceivablelimit
[57].
Next,weevaluatedtheintra-raterreliability:Thetwoevaluatorsindependentlyre-measured,aftera
fewmonths’interval,arandomlyselected25dogsamong50dogs’fontanelleareas.Duetothe
laboriousnessofthemethod25/50(50%)ofthedogs’CTimageswerere-evaluated.Theintra-rater
reliabilityassessmenttookplacebytwodifferentmethods:first,wecalculatedarepeatabilitystatistic
similartothatforinter-raterreliabilitybetweenthetworepeats(totalfontanellearea)byeach
evaluator.Second,todeterminetheintra-raterreliabilityestimatebetweentherepeats,we
calculatedtheICCwith95%CIstoassessconsistencybetweentherepeats.AnICCof< 0.5indicates
poorreliability,0.5–0.75moderatereliability,0.75–0.9goodreliability,and> 0.9indicatesexcellent
reliability[58].AllstatisticalanalysesusedtheSAS®SystemforWindows,version9.4(SASInstitute
Inc.,Cary,NC,USA).
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syringomyelia.BMCV e t  R e s . 2 0 12;doi:10.1186/17 4 6 - 6 1 4 8 -8-158
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21
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imagingformorpho m e t r i c  a n a lysisofthecaudalcran i a l  f o s s a  i n C avalierKing
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Morphologyoftheca u d a l  f o s s a inCavalierKingCharles  S p a n i e l s .  VetRadiol
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cranialcavitiesinCavalie r  K i n g  C h a rlesSpanielswithChiari- lik e  m a l f o r mationand
otherbrachycephalic d o g s  a s  m easuredviacompu t e d  t o m o g raphy.AmJVetRes
2009;70(4):508-512.
52.  D r i v e rCJ,RusbridgeC,McG o n n e l l  I M ,  V olkHA.Morphometric  a s s e s s m entofcranial
volumesinage-matc h e d  C a v a li e rKingCharlesspaniels w i t h  a n d  w ithout
syringomyelia.VetRe c  2 0 1 0 ; 1 67(25):978-979.
53.  S c h m idtMJ,AmortKH,Failin g  K ,  K l i n g l e r M,KramerM,Ondr e k a  N .  C o mparisonofthe

22
endocranial-andbrain  v o l u m e s inbrachycephalicdog s ,  m e s a t i c ephalicdogsand
CavalierKingCharless p a n i e l s  i n  r e lationtotheirbodyweig h t .  A c t a  V e tScand
2014;56:30.
54.  S o k o ło wskiW,CzubajN,Sk i b n i e w s k i  M ,BarszczK,Kupczyńs k a  M ,  K i n d aW,etal.
Rostralcranialfossaa s  a  s i t e  f o r cerebrospinalfluiddra i n a g e  -  v o l u metricstudiesin
dogbreedsofdiffere n t  s i z e  a n d morphotype.BMCV e t  R e s  2 0 18;
doi:10.1186/s12917-018-1483-3
55.  P i n d r i k J,YeX,JiBG,Pendleton  C ,  A h n  E S .Anteriorfontanelleclos u r e  a n d  s i z einfull-
termchildrenbasedo n  h e a d  c omputedtomograph y .  C l i n  P e d i a tr(Phila)
2014;53(12):1149-1157.
56.  H a y e sAF,KrippendorffK. A n s w e r i n g theCallforaStandard  R e l i a b i l i t y  M easurefor
CodingData.Comm u n i c a t i o n  M ethodsandMeasure s  2 0 0 7 ; 1 (1):77-89.
57.  K r i p p endorffK.ReliabilityinCo n t e n t  A n a l y sis:SomeCommon M i s c o n c e p tionsand
Recommendations. H u m a n  C ommunicationResea r c h  2 0 0 4 ;30(3):411-433.
58.  K o o  T K,LiMY.AGuidelineofS e l e c t i n g  a n dReportingIntraclass C o r r e l a t i o n
CoefficientsforReliability  R e s e a r c h .JChiroprMed2016 ; 1 5 : 1 5 5 - 163.
Abbreviations
CI:confidenceinterval
CM:Chiari-likemalformation
CT:computedtomography
ICC:intraclasscorrelationcoefficient
PF:persistentfontanelle
SM:syringomyelia
Declarations
Ethicsapprovalandconsenttoparticipate:Nohumansubjects,humanmaterial,orhumandatawere
involvedinthisresearch.

23
Consentforpublication:Notapplicable.
Availabilityofdataandmaterials:Dataandmaterialsareavailablefromthecorrespondingauthoron
reasonablerequest.
Competinginterests:A-M.K.andT.S.J.arepartoftheFinnishKennelClubNeurologyadvisorygroup.
Funding:TheFinnishVeterinaryFoundationandAgria/SvenskaKennelklubbenForskningsfond(grant
numberN2018-0024)supportedthestudywithgrants.
Authors'contributions:Allauthorscontributedtothestudydesign.A-M.K.examinedallthepatients.
A-M.K.,andT.S.J.analyzedtheCTimages.J.T.J.performedthestatisticalanalysis.A-M.K.draftedthe
manuscriptwiththehelpofalltheco-authors.Allauthorsread,commentedon,andapprovedthe
finalversionofthemanuscript.
Acknowledgements:WewouldliketothanktheFinnishChihuahuaClubandChihuahuaownersfor
theirparticipationinthestudyandTheFinnishVeterinaryFoundation,Agria/SvenskaKennelklubben
Forskningsfond,andTheVeterinaryTeachingHospitalofHelsinkiUniversityforfinancialsupportof
thestudy.Furthermore,wewanttothankalltheVeterinaryTeachingHospital’sradiologytechnicians
fortheirexpertiseinprovidingtheCTimages.
Tables
Table1:suturesaffectedperdog.
Numberofaffectedsutures Numberofdogs Percentagefromalldogs(%)
0 4 8.2
1 21 42.9
2 9 18.4
3 4 8.2
4 3 6.1
5 1 2.0
6 3 6.1
7 2 4.1
8 1 2.0
9 0 0
10 1 2.0
Total 49 100.0


Table2:Fontanellesaffectedperdog


24
Numberoffontanelles Numberofdogs Percentagefromallfontanelles
(%)
0 4 8.2
1 19 38.8
2 11 22.4
3 2 4.1
4 3 6.1
5 2 4.1
6 2 4.1
7 1 2.0
8 2 4.1
9 0 0
10 1 2.0
11 1 2.0
12 0 0
13 1 2.0
Total 49 100.0



25

Table3:Cranialsuturesandfontanellesevaluated
Location Bone Connecting
bone
Suture/intersect
ion
Figure/No: Human/canine
fontanelle
equivalent
Dorsalsutures Frontal Nasal,maxillar,
lacrimal
Frontonasal,
frontomaxillar,
frontolacrimal
Fig7,No.1 NA
Frontal Interfrontal Fig7,No.2 NA
Parietal Frontoparietal Fig.7,No.3 Bregmatic
Parietal Parietal Sagittal Fig.7,No.4 NA
Leftinterparietal Left
parietointerpariet
al
Fig.7,No.5 NA
Rightinterparietal Right
parietointerpariet
al
Fig.7,No.6 NA
Lateralsutures Frontal Palatinal,
sphenoid
Left
frontopalatine,
sphenofrontal,
Fig.8,No.7 NA
Right
frontopalatine,
sphenofrontal
NA NA
Sphenoid,
parietal
Leftintersection Fig.8,No.8 Leftsphenoid
Rightintersection NA Rightsphenoid
Parietal Sphenoid,
temporal
Left
sphenoparietal,
squamous
Fig.8,No.9 NA
Right
sphenoparietal,
squamous
NA NA
Caudalsutures Occipital Parietal Left
occipitoparietal
Fig.9,No.10 NA
Right
occipitoparietal
Fig.9,No.11 NA
Parietal,temporal Leftintersection Fig.9,No.12 Leftmastoid
Rightintersection Fig.9,No.13 Rightmastoid
Temporal Left
occipitosquamous
Fig.9,No.14 NA
Right
occipitosquamous
Fig.9,No.15 NA
Interparietal Notatruesuture Fig.9,No.16 Posterior
Thesuturesaregroupedbydorsal,lateralandcaudalsurfaces,andthebonesthatthesuturesare
connectingarenominated.Incasethesuturalintersectionsformafontanelle,theveterinaryora
humanequivalenttermisgiven.Additionally,thefigureinwhichthesutureisvisualizedandthe
numbermarkingitisprovided.
NA:notapplicable,Fig.:figure,No.:number



26
Table4.
Inter-raterreliability:RepeatabilityandKrippendorff'salphareliabilityestimatesbetween
assessors
Areameasured Repeatability(%) alpha 95%CI numberofpairs
Totalfontanellearea 99.8 0.999 0.997-
1.000
50
Dorsalfontanellearea 99.6 0.997

0.995-
0.999
50
Leftlateralfontanellearea 99.7 0.998

0.995-
1.000
6
Rightlateralfontanellearea 99.5 0.996

0.989-
1.000
9
Caudalfontanellearea 99.6 0.997

0.994-
0.999
50
Inter-raterreliability:RepeatabilityandKrippendorff'salphareliabilityestimatesoftotal,dorsal,left
andrightlateral,andcaudalfontanelleareameasurementsbetweenthetwoassessors.CI:
confidenceinterval.


Table5.
Intra-raterreliability:fontanelleareaintra-classcorrelationcoefficient
 Assessor1 Assessor2 Combined
Areameasured ICC 95%CI ICC 95%CI ICC
Totalfontanellearea 0.999 0.997-
0.999
0.997 0.994-
0.999
0.998
Dorsalfontanellearea 0.999 0.998-
1.000
0.998 0.995-
0.999
0.999
Leftlateralfontanellearea 0.996 0.970-
1.000
0.999 0.988-
1.000
0.997
Rightlateralfontanellearea 0.999 0.989-
1.000
1.000 0.996-
1.000
0.999
Caudalfontanellearea 0.993 0.984-
0.997
0.992 0.981-
0.996
0.992
Intra-raterreliability:Fontanelleareaintra-classcorrelationcoefficienttoassesstherepeatabilityof
themeasurementofthetotal,dorsal,leftandrightlateral,andcaudalfontanelleareameasurements.
ICC:intraclasscoefficient,ICC:intraclasscorrelationcoefficient,CI:confidenceinterval.
Figures

27
Figure1

28
Bregmaticfontanelle.Avolume-renderingtechniquecomputedtomographyimageofa
Chihuahuaskullindorsalviewshowingasingle,sharplydemarcatedpersistentbregmatic
fontanelleattheintersectionofthepairedfrontalandparietalcranialbones(the
frontoparietalsuture).

29
Figure2
Multiplebregmaticfontanelles.Avolume-renderingtechniquecomputedtomographyimage
ofaChihuahuaskullindorsalviewshowingmultiple,sharplydemarcatedpersistent
bregmaticfontanellesattheintersectionofthepairedfrontalandparietalcranialbones(the
frontoparietalsuture).
Figure3
Sphenoidalfontanelle.Avolume-renderingtechniquecomputedtomographyimageofa
Chihuahuaskullinrightlateralviewshowingasingle,sharplydemarcatedpersistent
fontanelleattheintersectionofthefrontal,sphenoidal,andparietalbones,resemblingthe
locationoftherightsphenoidalfontanelleinchildren.

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Figure4
Bregmaticfontanellewithindistinctmargins.Adorsalmaximum-intensityprojection
computedtomographyimage(windowlevel500,windowwidth3500,slicethickness15mm)
ofaChihuahuaskullwithabregmaticfontanellewithindistinctmarginsbetweenthepaired
frontalandparietalbones.

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Figure5
PersistentfontanelleconnectedtoaradiolucentlineresemblingavenousstructureCaudal
maximum-intensityprojectioncomputedtomographyimage(windowlevel500,window
width3500,slicethickness15mm)ofaChihuahuaskullwithmultiplepersistentfontanelles.
Apersistentfontanelle,locatedbetweentherightinterparietalandparietalbones,is
connectedtoaradiolucentlineresemblingavenousstructure(arrow).Theradiolucentline

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appearstobeconnectedtoapersistentfontanelleatthelocationoftherightmastoid
fontanelle(star)betweentherightparietal,occipital,andtemporalbones.
Figure6

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Multiplepersistentfontanellesonacaudalcranialsurface.Volume-renderingtechnique
computedtomographyimageofaChihuahuaskullincaudalviewshowingmultiple,sharply
demarcatedpersistentfontanellesandanenlargedforamenmagnum.Thepersistent
fontanelles(redstar)wereconfirmedinmultiplanarimagestopenetratethroughthebone.
Therestofthelesionsappearingaspersistentfontanelles(withoutaredstar)areareasof
thinbone.

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Figure7
DorsalcranialsuturesDorsalmaximum-intensityprojectioncomputedtomographyimage
(windowlevel500,windowwidth3500,slicethickness25mm)ofamixed-breeddog’s
(weight5.1kg)skull:Numbers1-6markdorsalcranialsuturesevaluatedinthestudy.(See
Table3forsuturesandconnectingbones.)Tobeabletoshowthedorsalcranialsuturesin
oneplane,weselectedamixed-breeddogwithlessdomingoftheheadthaninChihuahuas.

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Figure8
LateralcranialsuturesAleftlateralmaximum-intensityprojectioncomputedtomography
image(windowlevel500,windowwidth3500,slicethickness25mm)ofamixed-breed
dog’s(weight,5.1kg)skull:Numbers3and7-9markdorsalandlateralcranialsutures
evaluatedinthestudy.(SeeTable3fordetailsofsuturesandconnectingbones.)Tobeable
toshowthelateralcranialsuturesinoneplane,weselectedamixed-breeddogwithless
domingoftheheadthaninChihuahuas.

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Figure9
CaudalcranialsuturesCaudalmaximum-intensityprojectioncomputedtomographyimage
(windowlevel500,windowwidth3500,slicethickness25mm)ofamixed-breeddog’s
(weight,5.1kg)skull:Numbers5-6and9-16markdorsal,lateralandcaudalcranialsutures
evaluatedinthestudy.(SeeTable3fordetailsofsuturesandconnectingbones.)Tobeable
toshowthelateralcranialsuturesinoneplane,weselectedamixed-breeddogwithless
domingoftheheadthaninChihuahuas.

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Figure10
PositioningoftheindexlinesTransverse(a),sagittal(b)anddorsal(c)multiplanar
computedtomographyimages,(windowlevel500,windowwidth3500,slicethickness1
mm)showingthepositionofindexlinespositionedsothatthefirstindexlinewastangential
totheouterskullsurfaceandinthemid-thicknessofthebonesurroundingit(blueindex
line).Thesecondindexlinewaspositionedperpendiculartothepreviousindexlineandin
thecenterofthepersistentfontanelle(yellowindexlineinFig10a,purpleindexlineinFig
10b).Inthedorsalview(Fig10c),theintersectionoftheindexlineswaspositionedatthe
centerofthepersistentfontanelle.

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Figure11
FontanelleareameasurementDorsalmaximum-intensityprojectioncomputedtomography
image(windowlevel500,windowwidth3500,slicethickness15mm)ofaChihuahuaskull
withabregmaticfontanellebetweenthepairedfrontalandparietalbones.Theareaofthe
bregmaticfontanelle,82.4mm2,ismeasuredbyOsiriXMedicalImagingSoftware’sclosed
polygontool.
SupplementaryFiles

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Thisisalistofsupplementaryfilesassociatedwiththispreprint.Clicktodownload.
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