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1、ThyroidAnatomy,13#,ThyroidAnatomy13/13,ThyroidAnatomy12/13,Mostoftheanterolateralsurfaceoftheneckiscoveredbythethinplatysmamuscles,remnantsofthepanniculuscarnosusofmammals(watchadogshakeitscoat).Thismuscleisatthelevelofthesuperficialfasciaanditsundersideprovidesanexcellentplaneofdissectionexposingth
2、edeepfasciaoftheneck.BecauseoftheinvertedV-shapedgapinthislayeranteriorly,dissectionofflapsinacollarincisionshouldbeginlaterally.,ThyroidAnatomy11/13,Thesternocleidomastoidmusclesflankthestrapsandcovertheinternaljugularsandcarotidsheaths.Theyareenclosedinanencirclinggirdleofdeepcervicalfasciacalledt
3、heinvestinglayer.Thislayercontinuesposteriorlytoenclosethetrapeziusmuscles(seeneckclinicalfolio).Theexternaljugularveinsdescendacrosstheposteriorportionsofthesternocleidomastoidsandanteriorjugularveinsdescendalongthestrapsanteriorly.,ThyroidAnatomy10/13,Thethyroidiscoveredbythesternohyoidandsternoth
4、yroid(strap)muscles.Theseareenclosedinanintermediatelayerofdeepcervicalfascia(seeThryoidAnatomy:1)withthesternohyoidsbeingapposedinthemidlineandtheunderlyingsternothyroidsbeingslightlymorelateral.Whenmobilizingthestrapsitisimportanttostayintheplanedeeptobothmuscles.Theomohyoidmusclesascenddiagonally
5、acrosstheupperpartofthestrapsandareautomaticallymobilizedwiththosemuscles.,ThyroidAnatomy9/13,Venousdrainageofthethyroidrunswiththesuperiorlaryngealarteriesabove,passeslaterally(middlethyroidveins)directlyintotheinternaljugularveins,anddrainsinferiorlyintothebrachiocephalicveins.Thedominantlymphatic
6、drainageaccompaniesthevesselswithinthelooseareolarcarotidsheaths.Theveinsformaplexusonthesurfaceoftheglandwithintheareolarthyroid(visceral)fascia.Remainingexternaltothiscapsuleprovidesarelativelybloodlessdissection.Entryintothecapsuleisabloodymess.,ThyroidAnatomy4/13,Twocommonvariantsarethepresenceo
7、fapyramidallobeextendingupwardfromtheisthmusandathyroidimaarteryascendingfrombelow.Thepyramidallobeisaremnantofthetrackthethyroidfollowedinembryologiclifefromtheforamencecumatthebaseofthetongue,throughthesiteofthefuturehyoidbonetoitsfinallocation.Incompletedescentofthethyroidcanbemistakenforatumor.I
8、nthefaceofahighmidlineneckmass,itisimperativetodocumentthyroidtissueinthenormallocationbyscanbeforeexcision.Thethyroidimaarteryarisesfromanyofthegreatvesselsofthechestandneck.,ThyroidAnatomy2/13,Thearterialsupplytothethyroidcomesprincipallyfromthesuperiorandinferiorthyroidarteries.Theformerarisefrom
9、theexternalcarotidandthelatterareusuallyabranchofthethyrocervicaltrunkoffthesubclavianarteries.Theinferiorthyroidarteriespassbehindthecommoncarotidstoreachthelowerthirdofthethyroidglandoneachside.Notethepositionsofthevagusandrecurrentlaryngealnerves(detailsinsubsequentimages,ThyroidAnatomy3/13,Theth
10、yroidglandisthmussaddlesoneortwooftheuppermosttrachealringsandusuallyblocksthesiteofanoptimaltracheostomy.Itisroutinelydividedinsuchcases.Thelobesoftheglandwrapposteriorlytoembracetheuppertracheaandlowerlarynx.Theposteriorfaceofeachlobeliesonthecarotidsheath(seealsoneckanatomy).,ThyroidAnatomy1/13,T
11、hethyroidglandisenclosedinathinlayerofpretrachealorvisceralfasciawhichalsoincludesthetracheaandesophagus.Thevisceralcompartmentoftheneckisdeeptotheintermediatefasciasurroundingthestrapmusclesandtheinvestingfasciaenclosingthesternocleidomastoidandtrapeziusmuscles(seeneckanatomyimages).Behindtheviscer
12、alcompartmentistheprevertebralfasciaoverlyingthecervicalvertebrae(seebrachialplexusanatomy).Thespacebetweentheesophagusandprevertebralfasciaextendsdownintothemediastinum.Therecurrentlaryngealnerveisinthetracheoesophagealgrooveoranteriortoitinthemajorityofindividuals(detailsinsubsequentimages).,Thyro
13、idAnatomy5/13,Thelarynxisinnervatedbybranchesofthevagusnerve(cranialnerveX).Allthemusclesofthelarynxexceptthecricothyroid(seelarynx)aresuppliedbytherecurrentlaryngealnerves.Theterminalportionofthisnervepassesbeneaththeinferiorpharyngealconstrictortoenterthelarynxbehindthearticulationoftheinferiorcor
14、nuofthethyroidcartilagewiththecricoidcartilage.Recurrentlaryngealnerveinjuryresultsinparalysisofthevocalcordinarelativelyadductedposition.Bilateralrecurrentnerveinjuryduringtotalthyroidectomymayresultinacutepostoperativeairwayobstruction.Itisimportanttodopre-andpostoperativelaryngoscopytodocumentvoc
15、alcordfunction.Thesuperiorlaryngealnervearisesfromthenodoseganglionofthevagusjustoutsidethejugularforamenatthebaseoftheskullandpassesdiagonallydownwardclosetothesidesofthelarynx.Itsendsasensorybranchthroughthethyrohyoidmembraneandcontinuesasamotorbranchtothecricothyroidmuscleandinferiorconstrictor.T
16、hecricothyroidmusclemaintainstensiononthevocalcords.Injurytothesuperiorlaryngealnerveresultsinlossoftimbre,enduranceandhighrangesingingcapability.,ThyroidAnatomy6/13,Therecurrentlaryngealnerveontherightarisesfromthevagusatthelevelofthesubclavianartery,passesbeneaththearteryandascendsnearthetrachea-e
17、sophagealgroove(seebelow).TheleftrecurrentlaryngealarisesattheleveloftheaorticarchandpassesbeneaththeaortajustdistaltotheligamentumarteriosumandalsoascendsneartheleftT-Egroove,ThyroidAnatomy7/13,Rarely,oneofthelaryngealnervesisnotrecurrentbuttakesastraightcoursetothelarynxfromabove.Thishappenswhenan
18、aorticarchdevelopmentalanomalyresultsinaberranttakeoffofasubclavianarteryfromthedistalarch.Theconditionisrareandusuallyinvolvesanaberrantrightsubclavianartery(lessthan1%ofthepopulation)passingposteriortotheesophagus.Inthatcasetherightnerveisnon-recurrent.Compressionoftheesophagusiscalleddysphagialusoria.Veryrarely(1in2000),thereisarightsidedaorticarchwithamirrorimageanomalyresultinginanon-re
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