Closed loop obstruction: Pictorial essay

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional

ICONOGRAPHIC REVIEW / Gastrointestinal imaging

Closed loop obstruction: Pictorial essay

A. Mbengue

, A. Ndiaye

, T.O. Soko

, M. Sahnoun

, A. Fall

, C.T. Diouf

, D. Régent

, I.C. Diakhaté

aDépartementd’imageriemédicale,hôpitalPrincipal,1,avenueNelson-Mandela,BP3006, Dakar,Senegal

bServicederadiologie,CHRUdeNancy-Brabois,rueduMorvan,54511Vandœuvre-lès-Nancy, France

KEYWORDS Closedloop obstruction;

Incarceration;

Volvulus

Abstract Closedloopobstructionoccurswhenasegmentofbowelisincarceratedattwocon- tiguouspoints.Thediagnosisisbasedonmultipletransitionalzones.Theincarceratedloops appearinUorCformorpresentaradiallayoutaroundthelocationoftheobstruction.It’svery importanttospecifythetypeofobstructionbecause,inpatientswithsimplebowelobstruc- tion,aconservativeapproachisoftenadvised.Ontheotherhand,aclosedloopobstruction immediatelyrequiresasurgicalapproachbecauseofitshighmorbidityandtheriskofdeathin caseofalatediagnosis.

©2013Éditionsfranc¸aisesderadiologie.PublishedbyElsevierMassonSAS.Allrightsreserved.

An obstruction is said tobe closed loop or incarceration when a bowel segment of variablelengthis obstructedat twocontiguouspoints.The incarceratedanddistended looprisks,iflongenough,pivotingonitsaxisandresultinginavolvulus[1].

Whyshouldaclosedloopobstructionberecognized?

In thesmallintestine,mechanical obstruction caused byadhesionspresentsalower risk of complications and therefore, a more conservative approach by suction and hydroelectrolytic restorationmay beconsidered.However,closedloopobstructions are characterizedbytheir completenatureandhigh morbidityandrisk ofdeathincase of delayedsurgery[2].

Inthecolon,ischemiccomplicationsonlyoccuronvolvulus.Themostimportantfactor intheprognosisisthetimebeforecare.Simplemechanicalcolonobstructionsmoreoften presentariskofdiastaticperforation.

∗Correspondingauthor.

E-mailaddress:mbenguerx@yahoo.fr(A.Mbengue).

2211-5684/$—seefrontmatter©2013Éditionsfranc¸aisesderadiologie.PublishedbyElsevierMassonSAS.Allrightsreserved.

http://dx.doi.org/10.1016/j.diii.2013.10.011

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional The consequences of intestinaltractobstruction differ

according to whether it involves a simple obstruction or incarceration.

In simple mechanical obstruction

The supralesional effect is fast and first involves hyper- peristaltism. The accumulation of gas upstream fromthe obstacleis theinitial causeof intestinaldistensionwithin three to six hours. This gas distension is then increased byretention offluids after12hours,resultingfrominthe absorptionandexaggeratedintestinalsecretion.

In close loop obstruction

Twoobstructivefeaturescombineandareresponsible.

Closedloopsyndrome

Theincarceratedloop(closedloop)continuessecretingand will very quickly distend, inducing parietal vascular con- straints.Itdoesnotcontaingas,orcontainsverylittlegas, exceptwhenitinvolvesthecolon(fermentationgases).

Thevenousstasisinducestheextravasationofbloodand plasmabothintheexcludedloopandintheadjacentmesen- tery,increasingtheintestinaldistension.

Asupralesionalsyndrome

Thesegmentofintestineupstreamfromtheproximalpoint ofobstruction progressivelydistendstothestomach. This distensionisslowerthanincaseofaincarceratedsegment.

Twosituationsarepossible:

• theupstreamsegmentdistendsprovokingtympanitesand vomiting;

• insomecases,theevolution issofastthatthesuprale- sionalsegmentdoesn’thaveenoughtimetodilate.Only theincarceratedloopisdistended.Theseso-called‘‘flat belly’’obstructionsevolveontheischemicside,quickly

Figure1. Illustrationofasimpleobstruction(a),aclosedloopobstruction(b)andaclosedloopobstructionwithvolvulus(c).

• thedistensionoftheobstructedclosedloop;

• the torsion of the intestinal loop upstream, its feeder vesselsanditsmesenteryincaseofassociatedvolvulus.

When installed, the arterial ischemia quickly leads to gangrene and then perforation with generalized peritoni- tis. In experimental animal models, a complete vascular obstructionleadstoalossofvilliwithin1hourandparietal infarctionafter8hours[5].

CAT-scan diagnosis

Closedloopobstructions without volvulusof the incarcer- ated loop where the signs of lesion are mainly on the lattershouldbedistinguishedfromobstructionswithvolvu- lus where the signs of volvulus are in the forefront and possiblyassociatedwithsignsofincarceration.

TheCAT-scanis currentlythebestimagingtoolfor the pre-surgical assessmentofhigh grademechanicalobstruc- tionswithasensitivityof90to96%,aspecificityof96%and a diagnosticprecision of 95%[6]. Withitsperformance in thedetectionofstrangulation,itisthebestwaytoselect patientswhomaybenefitfromprimarymedicalcare.

Semiological basis of closed loop obstruction

Incasesofsimpleobstruction,thesignsincludeasinglezone oftransitionseparatingadistendedproximalsegmentfrom aflatdownstreamsegment.

The semiologydiffersin closed loopobstruction and is relatedtothe presence of2 zonesof proximaland distal obstruction.Thesiteofobstructionpresentsintheformof severalcontiguouszonesoftransition,oftenwitha‘‘beak- like’’appearance.Thenumberoftransitionpoints(2or3) dependsonpresenceor notofdistensionoftheupstream segment(Fig.2).Theproximallevelofobstructionischar- acterizedbyadoubledilationonbothsidesandthezoneof

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure2. Illustrationofthenumberoftransitionalzonesaccordingtothetypeofobstruction;a:simpleobstruction:1beak-shapedzone oftransition;b:incarcerationwithoutdistensionupstream(flatbellyobstruction):2zonesoftransition;c:incarcerationwithdistension upstream:3zonesoftransition.

transition.Itisthereforenecessarytocarefullylookforthe distal place of obstruction that complies withthe classic semiologyof distendedloop—transitional zone—flatdown- streamloop(Fig.3)[3].Thepresenceofseveral‘‘contiguous beaks’’isveryspecificforincarceration.

Theincarceratedintestinalsegmentpresentsliquiddis- tension with a configuration depending on the degree of distension,the length andorientation of the loops in the abdomen:

• a‘‘U’’or‘‘C’’shapedlayout,iftheincarceratedsegment isalmostentirelyvisibleinthesameplane.Usingmulti- planereformationsisveryhelpfulindetectingthislayout oftheloops(Fig.4);

• aradiallayoutoftheloopsandmesentericvesselscon- vergingtowardstheplaceoftorsioniftheincarcerated segmentisverylong.(Figs.5and6)[1,2].

Specific case of ‘‘flat belly’’ obstructions

In‘‘flatbelly’’obstruction,theCTdetectsaliquiddisten- sionofagroupofloopscorrespondingtotheincarcerated segment. The proximal loops and the stomach are flat.

Foranuninformedobserver,thelackofsupralesionaldila- tion(proximal loops) may leadto a diagnosticerror. It is

necessarytocarefullyanalyzethewallofthedistendedloop segmentsthatareveryoftentheseatofsuffering(Fig.7).

Close loop obstruction with volvulus.

Volvulusmaycomplicateaclosedloopobstructionwhenthe incarceratedsegment is long enough. It may also be the primarymechanismwhenalooptopplesoverfromanadhe- sioninserted at itstop, in volvulus of the smallintestine onincompletejointmesenteryorvolvulusofthesigmoid.It formsthemostseriousvascularobstruction.

Inthesmallintestine,itmostoftencomplicatesincarcer- ationonadhesions.IntheCT,signsofclosedloopobstruction areassociatedwith a‘‘whirl sign’’ [2]. The ‘‘whirl sign’’

correspondstothe windingof the mesentericvesselsand mesosthat convergetowardsthemesenteric pointoftor- sion.The association ofmultiple transitionzones(specific withincarceration) andwhirl signis highlyindicative ofa volvulus witha100% specificity reportedin theliterature [7].Itisnecessarytorememberthata‘‘whirlsign’’maybe foundinnormalsubjectsandthereforeisonlysignificantin acontextofmechanicalobstruction[8].

In the colon, the volvulus is generally spontaneous by rotationofa long sigmoidloop.On both types ofsigmoid

Figure3. Closedloopobstructionofthesmallintestine:3‘‘beaksign’’;a:proximalpointofobstruction:doubledilationonbothsides ofthetransitionalzone(arrow);b:distalpointofobstruction:smallintestinedilatedupstream—zoneoftransition(arrow)—smallintestine flatupstream(star).

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure4. FrontalCTimageof2differentpatients.ObstructionbyincarcerationwithlayoutinC(a)andU(b)oftheincarceratedloop.

volvulusdescribed,onlyoneofthemformsaclosedloop[9]

(Fig.8):

• the organo-axial volvulus (recently individualized) does notcorrespondtoaclosedloopbecausethetorsionarises followingtothelongitudinalaxisononlyonesiteofthe sigmoid.IntheCT,thereisdistensionofadolicho-sigmoid without pelvic convergence of the distended segments (Fig.9);

• the mesenterico-axial volvulus forms a closed loop obstruction by rotation of the sigmoid loop around its

mesowithconvergenceof2descenderstowardsthetor- sionpoint(Fig.10).

Strangulation — ischemia

Theclinicaldiagnosisofstrangulationremainsdifficultand theCTisthebestimagingexaminationtoconfirm,witha sensitivityof80to100%andaspecificityrangingfrom61to 93%[10,11].

Figure5. Obstructionbyincarcerationcomplicatedbyintestinalnecrosisina65-year-olddiabetic.Coronal(a)andaxialview(b)after injection:radiallayoutofthedilatedloopsconvergingtowardstheplaceofobstructionassociatedwithparietalpneumatosis.Transmural necrosisconfirmedbysurgery(c).

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure6. FrontalCTimageofamechanicalclosedloopobstructionofthesmallintestine.Contiguouszonesoftransition(rightarrow)with doubledilationonbothsidesoftheplaceofproximalobstruction(a).Radiallayoutofincarceratedloopstowardstheplaceofobstruction (asterix)(b).

Usually, the CT signs of the severity of a mechanical obstructionofthesmallintestinearethesameasinclose loopobstructioninadditionwithspecificsignofstrangula- tion.

Twostagesofstrangulationmaybedifferentiated[12]:

• low grade,often reversiblestrangulationresultingfrom essentially venous vascular compression. It appears as in parietal thickening with target enhancement (attesting to a sub-mucous oedema), mesenteric

venous engorgementandsometimes peritoneal effusion (Fig.11);

• ischemiawithtransmuralinfarction,resultingfromtight arterialconstriction(Fig.12).Itcombinesvariably,spon- taneoushyperdensityoftheintestinallining,infiltration of the meso, a lack of enhancement after injection (Figs. 7 and 13), sero-haematic inter-loop effusion and an ultimate stage of parietal pneumatosis (Fig.5) with portalandmesentericvenousgas[10,11].

Figure7. Flatbellyobstruction:coronal(a)andaxial CTimage(b).IncarceratedloopdistendedinC(curvedarrow).Nodistension upstream;flatjejunalloops(stars)(a).Lackofenhancementoftheincarceratedloopandascitesattestingtointestinalnecrosis(a,b).

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure8. Illustrationof2formsofvolvulusofthesigmoid;a:organo-axialvolvulus;b:mesenterico-axialvovulvus.

Figure9. Organo-axialvolvulusofthesigmoid.Colicgasdistensionwithout‘‘coffeebeanimage’’ontheabdominalpainfilm(a).Coronal CTimage(b):torsionofthesigmoidarounditslongitudinalaxis.

Figure10. Mesenterico-axialvolvulusofthesigmoid.‘‘Coffeebean’’imageabdominalpainfilm(a).Coronal(b)andaxialCTimage(c, d):convergenceof2sigmoiddescenders(asterix)towardstheplaceoftorsion.

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure11. Front(a)and axial (band c)CT imagesafterinjectionof anobstructionbyincarceration.Notethe mesentericvenous engorgementnearthezoneofobstructionassociatedwithpelvicperitonealeffusion.Nosignofintestinaldistressduringsurgery.

Figure12. Closedloopobstructionwithintestinalischemia.Lackofenhancementoftheincarceratedloop(curvedarrow)with‘‘feces sign’’.

Pleasecitethisarticleinpressas:MbengueA,etal.Closedloopobstruction:Pictorialessay.DiagnosticandInterventional Figure13. CoronalCT imagewithout(a) andwithinjection(b) ofaclosedloop obstructiononadhesionswithintestinal ischemia.

Spontaneoushyperdensity ofthewalls oftheincarcerated loops(arrow in a)and lackofenhancementafter injection(b).Note the hyperdensesero-haematiccontentsoftheischemicloop(a).

Conclusion

Closed loop obstructions or obstructions by incarceration should immediately be considered as serious mechanical obstructions. Their diagnosis by CT-scan is based on the detection of multiple adjacent zones of transition with either a radial layoutor a layoutin C or U of the incar- ceratedloops towardstheplaceofobstruction. Anydelay inthediagnosisisharmfulduetothehighriskofintestinal necrosis.Itisimperativetodifferentiatethemfromasimple obstructionthatmaybenefitfromconservativeapproach.

Disclosure of interest

Theauthorsdeclarethattheyhavenoconflictsofinterest concerningthisarticle.

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