Computed tomography evaluation of the morphometry and variations of the infraorbital canal relating to endoscopic surgery

www.bjorl.org

Brazilian

Journal

of

OTORHINOLARYNGOLOGY

ORIGINAL

ARTICLE

Computed

tomography

evaluation

of

the

morphometry

and

variations

of

the

infraorbital

canal

relating

to

endoscopic

surgery

夽

Gülay

Ac

¸ar

_,

_Kemal

_Emre

_Özen

_{, ˙Ibrahim}

_Güler

_,

_Mustafa

_Büyükmumcu

a_{NecmettinErbakanUniversity,MeramFacultyofMedicine,DepartmentofAnatomy,Konya,Turkey} b_{˙IzmirKâtipC¸elebiUniversity,FacultyofMedicine,DepartmentofAnatomy, ˙Izmir,Turkey}

c_{SelcukUniversity,FacultyofMedicine,DepartmentofRadiology,Konya,Turkey}

Received24July2017;accepted18August2017 Availableonline8September2017

KEYWORDS Endoscopicsinus surgery; Infraorbitalcanal; Infraorbitalcanal corpustypes; Infraorbitalforamen; Multidetector computed tomography Abstract

Introduction:Thecourseoftheinfraorbitalcanalmayleavetheinfraorbitalnervesusceptible toinjuryduringreconstructiveandendoscopicsurgery,particularlywhensurgically manipulat-ingtheroofofthemaxillarysinus.

Objective: Weinvestigatedboththemorphometryandvariationsoftheinfraorbitalcanalwith theaimtoshowtherelationshipbetweenthemrelativetoendoscopicapproaches.

Methods:Thisretrospectivestudywasperformedonparanasalmultidetectorcomputed tomo-graphyimagesof200patients.

Results:TheinfraorbitalcanalcorpustypeswerecategorizedasType1:withinthemaxillary bonyroof(55.3%),Type2:partiallyprotrudingintomaxillarysinus(26.7%),Type3:withinthe maxillarysinus(9.5%),Type4:locatedanatomicallyattheouterlimitofthezygomaticrecessof themaxillarybone(8.5%).Theinternalangulationandthelengthoftheinfraorbitalcanal,the infraorbitalforamenentryanglesandthedistancesrelatedtotheinfraorbitalforamen localiza-tionweremeasuredandtheirrelationshipswiththeinfraorbitalcanalvariationswereanalyzed. Wereportedthattheinternalangulationsinbothsagittalandaxialsectionsweremostlyfound ininfraorbitalcanalType1and4(69.2%,64.7%)but,therewerecommonlynoangulationin Type 3 (68.4%)(p<0.001). The lengthofthe infraorbitalcanal and thedistances fromthe infraorbitalforamentotheinfraorbitalrimandpiriformaperturewasmeasuredasthelongest

夽 _{Pleasecitethisarticleas:Ac¸arG,ÖzenKE,Güler ˙I,BüyükmumcuM.Computedtomographyevaluationofthemorphometryandvariations}

oftheinfraorbitalcanalrelatingtoendoscopicsurgery.BrazJOtorhinolaryngol.2018;84:713---21.

∗_{Correspondingauthor.}

E-mail:gulayzeynep73@gmail.com(G.Ac¸ar).

PeerReviewundertheresponsibilityofAssociac¸ãoBrasileiradeOtorrinolaringologiaeCirurgiaCérvico-Facial.

https://doi.org/10.1016/j.bjorl.2017.08.009

1808-8694/©2017Associac¸˜aoBrasileiradeOtorrinolaringologiaeCirurgiaC´ervico-Facial.PublishedbyElsevierEditoraLtda.Thisisanopen accessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).

PALAVRAS-CHAVE Cirurgiaendoscópica sinusal; Canalinfraorbitário; Tiposdecorpodo canalinfraorbitário; Forame infraorbitário; Tomografia computadorizada multidetectores

Avaliac¸ãotomográficadamorfometriaevariac¸õesdocanalinfraorbitáriorelativosà cirurgiaendoscópica

Resumo

Introduc¸ão: Otrajeto docanal infraorbitário podepredisporonervoinfraorbitário alesões durantecirurgiasreconstrutoraseendoscópicascommanipulac¸ãodotetodoseiomaxilar.

Objetivo:Investigamos a morfometriae asvariac¸ões docanal infraorbitário eobjetivamos demonstrararelac¸ãoentreelas,visandoasabordagensendoscópicas.

Método: Esteestudoretrospectivofoirealizado emimagensdetomografiacomputadorizada multidetectoradeseiosparanasaisde200pacientes.

Resultados: OstiposdecorposdocanalinfraorbitárioforamcategorizadoscomoTipo1; inseri-dosnotetoósseomaxilar(55,3%),Tipo2;projetando-separcialmentedentrodoseiomaxilar (26,7%),Tipo3; dentrodoseiomaxilar(9,5%),Tipo 4;localizadoanatomicamentenolimite externodorecessozigomáticodoossomaxilar(8,5%).A angulac¸ãointernaeocomprimento docanal infraorbitário,osângulosdeentradadoforameinfraorbitário easdistâncias rela-cionadasàlocalizac¸ãodoforameforammedidos esuasrelac¸õescomasvariac¸ões docanal infraorbitárioforamanalisadas.Observamosqueasangulac¸õesinternasem ambososcortes sagitaleaxialforamencontradasemsuamaioriaemcanaisinfraorbitáriosTipo1e4(69,2%, 64,7%)e,nogeral,nãohouveangulac¸ãonocanalTipo3(68,4%)(p<0,001).Ocomprimentodo canalinfraorbitárioeasdistânciasdesdeoforameinfraorbitárioatéorebordoinfraorbitário eaaberturapiriformeforammedidoseosmaislongosforamidentificadasnoTipo3eosmais curtosnoTipo1(p<0,001).Osângulosdeentradadoforameinfraorbitárioemprojec¸ãosagital foramsignificativamentemenoresnoTipo3emaioresnoTipo1,emrelac¸ãoaosoutrostipos (p=0,003).SeptosnosseiosmaxilareseascélulasdeHallerforamobservadosem28%e16% dasimagens,respectivamente.

Conclusão:Oconhecimentoprecisodostiposdecorpodocanalinfraorbitárioearelac¸ãocoma morfometriapermitemqueocirurgiãoescolhaumaabordagemcirúrgicaapropriadaparaevitar lesõesiatrogênicasdonervoinfraorbitário.

© 2017 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Publicado por Elsevier Editora Ltda. Este ´e um artigo Open Access sob uma licenc¸a CC BY (http:// creativecommons.org/licenses/by/4.0/).

Introduction

The maxillary nerve that leaves the skull base through foramen rotundum gives off an infraorbital nerve (ION) in the pterygopalatine fossa. The ION is responsible for sensory innervation to the skin of the face from lower eyelidtoupper lip enters throughtheinferior orbital fis-sureandcoursesanteriorlyintheinfraorbitalgroove(IOG) overtheorbitalfloorandentersintotheinfraorbitalcanal (IOC) which is opened by the infraorbital foramen (IOF) under the infraorbital rim (IOR).1 _{The IOC, which is}

cov-eredwiththeextremely thinbone,is oneof theweakest points of the orbital floor and thus provides the least support to orbital bony strength. So, orbital floor frac-tures and surgeries like endoscopic approaches, orbital decompression and reconstruction can cause ION injury,

which can result in massive hemorrhage, complete anes-thesia or progressive infraorbital hypoesthesia from ION entrapment.2

TheIOCcommonly coursesupwardandlaterallywithin themaxillarysinusroofbutitcanprotrudefromthe maxil-larycorpusintothesinusasseeninsagittalsectionsofthe computedtomography(CT)scans.Theincreasingdegreeof the protrusionof the IOC cancause iatrogenicION injury during surgical operations manipulating or reconstructing the orbital floor.1 _{Therefore, having a precise knowledge}

of the anatomic variations and the morphometry of the IOCiscriticalforsurgeons.Inaddition,preoperative radio-logical evaluationoftheIOCcorpus typesis necessaryfor surgicalmanagementofreconstructionoftheorbitalfloor, regionalIONblockandradiofrequencyablationneurotomy inV2trigeminalneuralgia.3

Figure1 (A)AxialparanasalsinusCTimageshowing right-sidedinfraorbitalcanalType 1withinthemaxillarybonyroof and left-sidedinfraorbitalcanal Type2partiallyprotrudinginto maxillarysinus(thickarrows).(B)Rightparasagittalimageshowing infraorbitalcanalType1(arrowhead).

Figure2 (A)AxialparanasalsinusCTimageshowingbilateralinfraorbitalcanalType2partiallyprotrudingintothemaxillary sinus(arrowheads).(B)RightparasagittalimageshowinginfraorbitalcanalType2(arrowhead).

Intheliterature,therearemanystudiesconcerningthe variations or morphometry of the IOC, IOG and IOF. But, thereisnoclinicalstudyinvestigatingwhetherthese mor-phometricparametersarealteredbytheIOCcorpustypes. Therefore,itwasofgreatinteresttoustostudythistopic.In thisstudy,weespeciallyfocusedontheinternalangulation oftheIOCandaimedtofindoutwhethertherearefactors thatareofvalueinevaluatingtheIONinjury.Weanalyzed therelationship betweenthe morphometryand the varia-tions of theIOC corpus types by usingCT scansof actual patientsandtriedtoshowitspotentialutility asan endo-scopicsurgicallandmark.Also,weevaluatedthe surround-ingstructuressuchasmaxillarysinusseptaandHallercell.

Methods

This retrospective study wasapprovedby ourlocal ethics committee with a number2016/522 and performed using paranasalMultidetectorComputedTomography(SyngoVia) imagesof 200 patients whopresented tothe Department of Radiology for clinical purposes between January 2015 and December2015. AxialCT images wereobtained with a section thickening of 0.625mm, and these source data wereusedtoobtainassociatedcoronalandsagittalimages of 1mm slice thickness. No patient underwent a new CT

examination for this study. Patients with paranasal sinus anomalies,orbitalfracturesandpatientswhohadprevious sinussurgerywereexcludedfromthestudy.

We categorized the IOC corpus types according tothe relationshipwiththemaxillarysinusintofourtypesas fol-lows,whicharebasedontheFerenceetal.2_{classificationof}

theIONandRusuetal.4_{definitionofthelateroantraltype.}

IOCType1,withinthemaxillarybonyroof(Fig.1AandB). IOC Type 2, partiallyprotruding into the maxillary sinus (Fig.2AandB).

IOCType3,totallyprotrudingintothemaxillarysinuswith astalk(Fig.3AandB).

IOC Type 4, located anatomically at the outer limit of thezygomaticrecessofthemaxillarybone(lateroantral) (Fig.4AandB).

The morphometric measurements that were shown in

Table1wereperformedbetweensixreferencepointswhich aremodifiedfromtheHwangetal.5_{andPrzygockaetal.}6

study.Thosereferencepoints: C,theanteriormarginoftheIOG.

S,theposteriormarginoftheIOG(inferiororbitalfissure). A,theinternalangulationpointoftheIOC.

Figure3 (A)AxialparanasalsinusCTimageshowingbilateralinfraorbitalcanalType3totallyprotrudingintothemaxillarysinus withastalk(arrowheads).(B)RightparasagittalimageshowinginfraorbitalcanalType3(arrowhead).

IOR,theinferiormarginoftheorbitalrim.

PA,themostlateraledgeofthepiriformaperture(PA).

WedefinedtheIOCasthecanalwhichiscoveredbybone andendingattheanteriormarginof theIOGwhichisnot coveredbythebone.The internalangulation pointofthe IOC wasidentified as the change in direction of the axis oftheinitial IOC.Afterthemeasurementsinsagittal sec-tionswerefinishedthehorizontalplanewasrotatedtoan obliquepositionthatpassedalongtheIOC.All morphomet-ricmeasurements wereperformed in the axialsection of thisposition.We usedthe piriform aperture (PA)and IOR asa reference points to identify the location of the IOF andmeasuredthedistancefromIOFtoPA(Fig.4A)andIOR (Fig.5AandB).Weevaluatedcomprehensivelytheinternal angulationoftheIOCandwhetheritwasabsentorpresent (Fig.5AandB).InIOCswithaninternalangulationthelength oftheIOCwasdividedintoIOC1(initialsegment)andIOC2 andweremeasuredseparatelyinsagittalandaxialsections (Fig.5A).ThelengthoftheIOGwasmeasuredonlyinsagittal

sections.Also,wemeasuredthelengthoftheIOCandthe IOGinIOCswithoutinternalangulation(Fig.5B).

To identify the direction of the injecting needle we measuredtheangleoftheaxisoftheIOCrelativetothe ver-ticalplanewhichwasparalleltosagittalplane,andpassed throughthecenteroftheIOFinaxialsectionsandidentified itastheaxialIOFentryangle(Fig.6A).Also,theangle of theaxisoftheIOCrelativetothehorizontalplane (Frank-forthorizontalplane)whichwasparalleltothenasalfloor andpassedthroughtheIOFinsagittalsectionswasmeasured anddescribedasthesagittalIOFentryangle (Fig.6B).On theotherhand,weanalyzedthepresenceoftheHallercell andthemaxillarysinus septain400IOC’s CTscans.Then, wedemonstratedtherelationshipbetweentheIOCcorpus typesandthemorphometricmeasurements.

StatisticalsoftwareSPSS22wasusedforstatistical analy-sis.Themean,standarddeviation,minimum,andmaximum for eachof measurementswerecalculated.Forstatistical comparisonsunpairedt-test,Chi-squareanalysesandANOVA were used and p<0.05 was considered to be statistically significant.

Figure4 (A)CoronalparanasalsinusCTimageshowingbilateralinfraorbitalcanalType4whichislocatedattheouterlimitofthe zygomaticrecessandthehorizontaldistance(whitedashedline)fromthecenteroftheIOF(arrows)totheplanepassingthrough thepriformaperture(arrowheads).(B)Anoblique/axialimageshowingbilaterallateroantralcanals(arrows)whichareidentified coursinglaterallytothemaxillarysinuses(asterisks)andopenedbyinfraorbitalforamina(curvedarrows).

Table1 Definitionsofmeasurementsoftheinfraorbitalcanal.

Measurements Definitions

IOC1length (A---IOF) Thedistancefromtheinternalangulationpointoftheinfraorbitalcanaltothe infraorbitalforamen

IOC2length (A---C) Thedistancefromtheinternalangulationpointoftheinfraorbitalcanaltothe anteriorborderoftheinfraorbitalgroove

TotalIOClength (C---IOF) Thedistancefromtheanteriorborderoftheinfraorbitalgroovetothe infraorbitalforamen

IOGlength (C---S) Thedistancebetweentheanteriorandtheposteriorborderoftheinfraorbital groove

IOFlocation Superior(IOR---IOF) Thedistancefromtheinferiororbitalrimtotheinfraorbitalforamen Medial(PA---IOF) Thedistancefromthepiriformaperturetotheinfraorbitalforamen

IOCinternalangulation Sagittal Theinternalangulationoftheaxisoftheinfraorbitalcanalinsagittalsection Axial Theinternalangulationoftheaxisoftheinfraorbitalcanalinaxialsection IOFentryangle Sagittal Theanglebetweentheaxisoftheinfraorbitalcanalandthehorizontalplane

(Frankfortplane)thatwasparalleltothenasalfloor

Axial Theanglebetweentheaxisoftheinfraorbitalcanalandtheverticalplane thatwasparalleltothesagittalplane

Figure5 Measurementsregardingtoinfraorbitalcanal,foramenandgroove.A,Rightparasagittalimageshowingtheinfraorbital canalwithaninternalangulation.ThelengthoftheIOC1(a)wasthedistancefromthecenteroftheinfraorbitalforamen(IOF) totheinternalangulationpoint(A). ThelengthoftheIOC2(b) wasthedistancefromtheinternalangulationpoint(A)tothe anteriormarginoftheinfraorbitalgroove(C).ThelengthoftheIOGwasthedistancefromtheanterior(C)toposteriormarginof theinfraorbitalgroove(S).ThemeasurementsoftheinternalangulationoftheIOC(z)andthedistance(c)fromtheinfraorbital rim(IOR)tothecenteroftheinfraorbitalforamen(IOF).B,Rightparasagittalimageshowinginfraorbitalcanalwithoutinternal angulation.Themeasurementsofthelengthoftheinfraorbitalcanal(a+b)andthedistance(c)fromtheinfraorbitalrim(IOR)to thecenteroftheinfraorbitalforamen(IOF).Theanterior(C)andposteriormarginoftheinfraorbitalgroove(S)wereidentified.

Table2 Theinternalangulationoftheinfraorbitalcanalinrelationtoinfraorbitalcanalcorpustypes. Degreeoftheinternal

angulationoftheIOC

Section IOCtype p-Valuea

Type1 No.(%) Type2 No.(%) Type3 No.(%) Type4 No.(%)

IOCwithoutangulation Sagittal 68(30.8%) 45(42.1%) 26(68.4%) 12(35.3%) <0.01 IOCwithangulation 153(69.2%) 62(57.9%) 12(31.6%) 22(64.7%)

IOCwithoutangulation Axial 98(44.3%) 45(42.1%) 24(63.2%) 7(20.6%) 0.04 IOCwithangulation 123(55.7%) 62(57.9%) 14(36.8%) 27(79.4%)

IOC,infraorbitalcanal;Type1,withinmaxillarybonyroof;Type2,partiallyprotrudingintomaxillarysinus;Type3,totallyprotruding intomaxillarysinuswithastalk;Type4,locatedexternaltothezygomaticrecessofthemaxillarybone(lateroantral).

Figure6 Angularmeasurementsoftheentryintoinfraorbitalforameninaxialandsagittalsections.(A)Theangle(x)wasthe angleoftheaxisoftheinfraorbitalcanalrelativetotheverticalplanethatpassedthroughthecenteroftheinfraorbitalforamen. (B)Theangle(y)wastheangleoftheaxisoftheIOCrelativetohorizontalplanethatpassedthroughthecenteroftheIOF.

Results

TheCTscansofpatientsconsistedof88females(44%)and 112males(56%)withamedian ageof44.15±17.46 years forfemalesand38.89±17.33yearsformales.

IOCvariations

Fourvariationsof400IOCcorpusanatomyaccordingto rela-tionwithmaxillarysinuswerefoundasfollows;Type1which was locatedwithin maxillary bonyroof (55.3%, 221/400),

Table3 Thedistributionofthecomparisoninmorphometricmeasurementsbetweenfemalesandmales.

Measurements Total Female Male p-Valuea

Mean±SD Mean±SD Mean±SD

SagittalIOC1length(mm) 7.0±2.7 6.7±2.7 7.3±2.7 0.019 SagittalIOC2length(mm) 3.4±2.2 3.3±2.1 3.5±2.4 0.571 SagittalIOGlength(mm) 18.9±4.2 18.1±3.8 19.5±4.4 <0.001 SagittalIOFentryangle(◦) 36.57±8.21 34.69±7.98 38.06±8.51 0.014 AxialIOC1length(mm) 8.0±2.7 7.6±2.6 8.4±2.7 0.004 AxialIOC2length(mm) 2.7±2.8 2.4±2.8 2.9±2.9 0.125 AxialIOFentryangle(◦) 56.80_±13.60 56.51_±13.54 56.90_±13.66 0.642 IOF-IORdistance(mm) 8.2±1.7 7.8±1.6 8.5±1.7 <0.001 IOF-PAdistance(mm) 13.8_±2.6 13.3_±2.6 14.1_±2.5 0.002

IOC,infraorbitalcanal;IOG,infraorbitalgroove;IOF,infraorbitalforamen;IOR,infraorbitalrim;PA,piriformaperture.

a_{Unpairedt-test.Total(n=400);female(n=88);male(n=112).}

Table4 Therelationshipbetweenthemorphometricmeasurementsandtheinfraorbitalcanalcorpustypes.

Measurements IOCtype p-Valuea

Type1 Type2 Type3 Type4 Mean±SD Mean±SD Mean±SD Mean±SD

(S)TotalIOClength(mm) 9.6_±2.1 10.8_±2.2 14.9_±3.4 10.8_±2.3 <0.001 (S)IOGlength(mm) 19.4±3.8 18.9±3.9 14.7±5.1 18.5±4.3 <0.001 (S)IOFentryangle(◦) 38.13_±11.67 36.84_±8.02 30.67_±7.47 32.22_±7.95 0.003 (A)TotalIOClength(mm) 9.8±2.0 11.0±2.0 15.0±2.5 11.4±2.3 <0.001 (A)IOFentryangle(◦) 57.66_±13.64 55.36_±13.46 54.20_±12.17 57.81_±13.85 0.018 IOF---IORdistance(mm) 7.7±1.3 8.3±1.7 10.5±1.7 7.3±1.5 <0.001 IOF---PAdistance(mm) 13.7±2.6 13.7±2.6 13.9±2.1 14.0±2.7 0.925

S,sagittal; A, axial;IOC,infraorbital canal;IOG,infraorbital groove;IOF, infraorbitalforamen; IOR,infraorbitalrim; PA,piriform aperture;Type1,withinmaxillarybonyroof;Type2,partiallyprotrudingintomaxillarysinus;Type3,totallyprotrudingintomaxillary sinuswithastalk;Type4,locatedexternaltothezygomaticrecessofthemaxillarybone(lateroantral).

Table5 Thesurroundinganatomicalstructuresinmaxillarysinusinrelationtotheinfraorbitalcanalcorpustypes.

Surroundingstructures IOCtype p-Valuea

Type1 Type2 Type3 Type4

Nomaxillarysepta 176(79.7%) 65(60.8%) 25(65.8%) 22(64.8%) 0.060 >0maxillarysepta 45(20.3%) 42(39.2%) 13(34.2%) 12(35.2%)

NoHallercell 193(87.4%) 8(79.7%) 28(73.7%) 29(85.3%) 0.145 >0Hallercell 28(12.6%) 21(19.6%) 10(26.3%) 5(14.7%)

IOC,infraorbitalcanal;Type1,withinmaxillarycorpus;Type2,partiallyprotrudingintomaxillarysinus;Type3,totallyprotrudinginto

maxillarysinus;Type4,locatedexternaltothezygomaticrecessesofthemaxillarybone(lateroantral).

a_{Chi-squaretest.}

Type 2which was partiallyprotruded into maxillarysinus (26.7%,107/400),Type3whichwastotallyprotrudedinto maxillarysinus witha stalk(9.5%, 38/400), Type 4which waslocatedattheouterlimitofthezygomaticrecess(8.5%, 34/400).

IOCinternalangulationmeasurements

WedeterminedthattheaxisoftheIOCshowedamean inter-nalangulation(min.5.92◦andmax.53.71◦)as28.18◦±9.2◦ insagittalsections(62.3%)andas28.4◦±10.0◦(60%)inaxial sections,respectively.Also,theprevalenceoftheIOCs with-out an internal angulation was found as37.7% in sagittal sectionsand40%inaxialsections,respectively.InTable2, wedemonstratedthattheIOCType3mostlyhadnoan inter-nalangulationinbothofsagittal(68.4%)andaxial(63.2%) sections.Conversely,IOCType4showedthehighest preva-lenceoftheinternal angulationinbothofsagittal(64.7%) andaxial(79.4%)sections(p<0.01,p=0.04).

IOCandIOGlengths

In IOCs with an internal angulation the mean length of the IOC1 (initial IOC) was measured as 7.0±2.7mm and 8.0±2.7mm in sagittal and axial sections, respectively. Also,we measured the meanlength of the total IOC and theIOGas10.4±2.5mmand18.9±4.2mminsagittal sec-tions, respectively as seen in Table 3. We compared the morphometric measurements with respect to gender and sides. InTable 3,we demonstratedthatallmorphometric measurementswerehigherinmalesthanfemalesandshow statisticallysignificantdifferenceexceptforthemeanaxial IOFentryangleandIOC2length(p<0.05).Also,therewas nostatisticallysignificantdifferencebetweensides.Onthe otherhand,wereportedthatthemeanlengthofthetotal IOCandtheIOGwas10.6±2.8mmand18.8±4.1mminall IOCsandthelengthofthetotalIOCwasfoundasthelongest inIOCType3andthesmallestinType1:however,the oppo-sitewastrueforthelengthoftheIOGasshowninTable4

(p<0.001).

IOF

location

and

entry

angles

ThemeandistancesbetweentheIOF-PAandIOF-IOR were foundas13.8±2.6mmand8.2±1.7mm,respectively.The distance from the IOF to IOR in IOC Type 3 was quite

longerthanthatinothertypes,buttheopposite wastrue for the IOCType 1 and4 asshown in Table4 (p<0.001). Conversely, the IOF-PA distance did not show a statisti-callysignificant differencewithrespecttothe IOCcorpus types (p=0.925). We measured the mean sagittal IOF entryangle as36.57◦±8.21◦ and axialIOFentry angle as 56.80◦±13.60◦,respectively.Wereportedthatsagittaland axialIOFentryanglevaluesweresmallerinIOCType3and largerinType1thanthatinothertypesinTable4(p=0.003,

p=0.018).InTable5,theprevalenceofthepresenceofthe Hallercellandthemaxillarysinusseptawereindicatedand thecorrelationofthemwithspecificIOCtypeswasnotfound statisticallysignificant(p=0.06,p=0.145).

Discussion

TraumaticIONinjuryespeciallyinzygomaticomaxillary com-plexfractures, often results in numbness of the midface and ipsilateral paresthesia. The occurrence ratio of the paresthesiaandpermanentsensorydisturbancein innerva-tionareaoftheIONwas30---80%inpatientswithmaxillary fractures.7,8_{The IONiswellprotectedbythebonyroofof}

the maxillary sinus, but increasing degree of the protru-sionofthe IOCintothe maxillarysinus canbeassociated withcanal dehiscence and thinner bony sheet. So, iatro-genic ION injury has been reported during interventional procedureslike periorbitalendoscopicapproaches,orbital reconstructive surgery, Caldwell-Luc operation, regional blockanesthesiaandradiofrequencyneurotomyof trigemi-nalganglion.1,2,9_{Theincidenceoftheiatrogenictemporary}

IONhypoesthesiawasreportedas0.5%duringmidfaciallift surgery. As a result,postoperative trigeminal neuropathy, corneal anesthesia with keratitis, retrobulbar hematoma andneurovascularinjuryoftheIOCcanocur.3_Theanatomic

knowledge of the location of the IOC with its surround-ing structures and preoperative CT imaging of the IOC corpus types is important and guides the surgeon to the mostappropriateapproachwhichwillavoidiatrogenicION injury.10,11

Yenigunetal.classifiedtheconfigurationoftheIOCinto threetypesandreportedthatthemostcommontypewas Type 2 (51.2%).11 _{Ference et al. indicated that the IONs}

werecategorizedasType 1(60.5%), Type2 (27.0%),Type 3 (12.5%).2 _{Lantos et al. evaluated retrospective 500 CT}

scansand reportedthat protrusionof the IOCinto maxil-larysinuswasidentifiedin10.8%ofpatients(5.6%bilateral, 5.2% unilateral).1 _{In our study, we consider lateroantral}

lateroantraltypethatcandeterminemodificationsof com-monproceduresshouldbekeptinmindbydentalsurgeons preoperatively.4

Previousanatomicalstudiesdealingwiththe morphom-etryoftheIOC,IOFandIOGhavebeenperformedbyusing CTscans,skulls, cadaversand photogrammetry.1,5,6,10,12---14

Especially,thecadaveric-driedskullsweremostlyusedand showedlimitationsrelated toconvenience inliving actual patientsandimaginarysections.Thecraniofacialbonescan beevaluatedfromvariousanglesbyusingCT.5 _{Asa result}

of the proper application of the multiple planar recons-tructionstechniquethe length,angulation of theIOCand the locationof the IOF can be determined accurately.In literature,thecompactstudywhich investigatingwhether IOCmorphometricparametersarealteredbytheIOC cor-pustypes notfound. Inthisrespect,this studyhasa new methodologyanalysing the relationship between them. In thisstudy,wecarriedoutanindepthstudyaboutthe inter-nalangulationoftheIOC.Asaresult,wereportedthatthere wereaninternalangulationoftheIOCinsagittalandaxial sectionsasamean28.18◦±9.2◦ and28.4◦±10.0◦, respec-tively.Also,theprevalenceoftheinternalangulationofthe IOCwasfoundinaveryhighratioinbothsagittalandaxial sections(62.3%and 60%).Our studyalso found an associ-ationbetweenthe internalangulation andthe IOCcorpus types.AsseeninTable2,IOCType4mostlyshowsan inter-nalangulationinbothofsagittal(64.7%)andaxial(79.4%) sections.Conversely,therewascommonlynointernal angu-lationintheIOCType3inbothofsagittal(68.4%)andaxial (63.2%)sections (p<0.01, p=0.04) andalso thelength of theIOCvariedfrom8to20mm.

InIOCswithaninternalangulationtoindicatethedepth ofthe puncturewe measuredthe meanlengthof the ini-tialIOC(IOC1)as7.0±2.7mminsagittaland8.0±2.7mm in axial sections and demonstrated the length of the IOC1>IOC2inbothofsagittalandaxialsectionsinTable3. Theinternalangulationdecreasesthedepthofthepuncture bydecreasingthelengthofinitialIOCandcomplicatesthe IONblockandradiofrequencyneurotomy.Intheliterature, themeasuredsofttissuethicknessovertheIOFrangedfrom 12to19mm.So,thedepthofthepuncturecanberanged between 17and 25mm during radiofrequency neurotomy, withtheneedlebeinginsertednotmorethan5mmintothe IOCtoavoidorbitalinjuryandskinulceration.5,15

Inpreviousstudiesusingdriedskulls,themeasuredmean lengths of the IOC ranged from 12.75 to 23mm and IOG length values ranged as 6---16mm.3,6,15,16 _{Using CT scans}

Hwang et al. reported that the mean length of the IOC, IOGandtotalIOC/IOGcomplexweremeasuredas11.7mm,

respectively.Thesemeasurementsshowedconsistencybut, stilllargerthanthatinotherstudiesduetodifferent defi-nitionsofangles.AccordingtoTable4thesagittalandaxial IOFentryanglevaluesweresignificantlysmallerinIOCType 3but,largerinIOCType1thanthatinothertypes(p=0.003,

p=0.018).Asaresult,theIOCType3withnointernal angu-lation, the longer length of the IOC and the smaller IOF entryanglecanfacilitatetheIONblockandradiofrequency neurotomybutcomplicatesurgicaloperations.

Most studies using dried skulls reported that the IOF-IOR and the IOF-PA distances ranged as 5---10.9mm and 14---18mm,respectively.3,6,12,13,16---18 _{Also,thestudies using}

CT scanning reported that the measured mean distances betweenIORandIOFranged between9.04and10mm.5,14

WemeasuredthemeandistancesfromIOFtoIORandPAas 8.2±1.7mmand13.8±2.6mmsimilartothem.Notably,we analyzedthattheIOF-IORdistancewassignificantlylonger inIOCType3 thanthatinother types(p<0.001) but,the IOF-PAdistancehadnostatisticallysignificantrelationship withtheIOCtypes(p=0.925)asshown inTable4.So,the IOF-IORdistanceincreasedparalleltothedegreeofthe pro-trusionoftheIOCwhichmaycausetheiatrogenicIONinjury duringsurgicalinterventions.

Cakuretal.andYenigunetal.andKoymenetal.reported thattheprevalenceofthemaxillarysinusseptawas35.3% and16.5%,respectively.11,19,20_{Inourstudy,wedetermined}

theprevalenceofthepresenceofthemaxillarysinussepta as28%(40.2% withType1; 37.5%withType2;11.6%with Type3;10.7%withType4)inTable5.But,astatistically sig-nificantcorrelationwiththeIOCcorpustypeswasnotfound (p=0.06).TheprevalenceofthepresenceoftheHallercell was16%and therewasnoastatistically significant corre-lation between thepresence of Haller celland IOC types (p=0.145).

Conclusion

These resultsagain emphasizedthe value ofpreoperative CTimaging,whichcanofferaccurateunderstandingofthe regional anatomy of and around the IOC. We take into accountthattherewerepersonalvariationsintheIOC cor-pus typeswhichaffectthe localizationoftheIOFandthe morphometricparameters.Therefore,radiologic identifica-tionofthespecificlocalizationforeachcorpustypewillplay akeyrolewhenchoosinganappropriatesurgicalapproach toavoidiatrogenicIONinjuryandhelptosurgeonwhen per-forminganestheticinterventions. Also,thesuccessrateof

themaxillofacialsurgeryandregionalblockanesthesiacan beincreased.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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