Conjoined Twins

Juan A. Tovar

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Etiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Clinical Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Preoperative Ethical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Preoperative Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Wall Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Early and Long Term Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Conclusion and Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

AbstractMonozygotic, monochorionic, and isosexualtwins united by a part of their anatomy areknown as Conjoined Twins. This is a rare andfascinating malformation that represents one ofthe more complex challenges of pediatric

surgery. The twins are classified into twomain groups: asymmetric and symmetric.Asymmetric ones are acardius acephalus,fetus-in-fetu, or heteropagus twins. In allthese, only one component, the autositus sup-plying circulation, is viable. Symmetric twinsare designated craniopagus, thoracopagus,omphalopagus, rachiopagus, ischiopagus,pygopagus, or parapagus according to thelocation of the joining bridge. This can belarge and often contains shared organs. Thecardiovascular systems of both components

J. A. Tovar (*)Department of Pediatric Surgery, Hospital Universitario LaPaz, Universidad Autonoma de Madrid, Madrid, Spaine-mail: juan.tovar@salud.madrid.org;jatovar44@telefonica.net

# Springer-Verlag GmbH Germany, part of Springer Nature 2019P. Puri (ed.), Pediatric Surgery,https://doi.org/10.1007/978-3-642-38482-0_86-2

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of the set are communicated and the internalenvironment is also shared to a variable extent.

Mortality is high before and after birthbecause of frequent and severe associatedmalformations. Viability of separation is diffi-cult to determine and requires sophisticatedimaging studies. Separation not only involveslengthy and complex operations but alsodifficult ethical decisions with familial, medi-cal, and even court participation.

Separation, when possible, requires variousgroups of specialists under a strong leadership.Bony parts, nervous system, hearts, great ves-sels, digestive and genitourinary organs, aswell as the skin and musculoskeletal tissueshave to be divided and reconstructed to achieveseparation with preservation for eachcomponent of as much function as possible.Survival is nearly impossible when the heartsare united, but it is possible for one or bothtwins in all the other forms. Complications arefrequent and long-term quality of life is oftenburdened by fecal and urinary incontinence orby abnormal limbs and genitalia that are theprice to pay for separation.

The quality of a pediatric surgical group isheavily put to test by these cases that can onlybe managed when outstanding expertise isavailable in the various specialties involved.

KeywordsConjoined · Twin · Acardius · Acephalus ·Heteropagus · Parasitic · Craniopagus ·Thoracopagus · Omphalopagus · Ischiopagus ·Pygopagus · Parapagus · Separation · Ethics

Introduction

Conjoined twins are physically fused at birth.They share a single chorion, placenta, and amni-otic sac (Arnold et al. 2018). Genetically identicalindividuals joined by a part of their anatomy andoften sharing one or more organs are known as“conjoined twins.” This event occurs in 1:50,000to 1:100,000 live births (Mutchinick et al. 2011),and it involves complex anomalies and technical

and ethical issues that represent one of the hardestchallenges of pediatric surgery.

This obvious condition that may involve dra-matic obstetric issues was known from ancienttimes. Probably two-faced deities like Jano ormultiple-headed creatures like Hydra were intro-duced into mythology after observation of suchtwins. There are pictures and carvings depictingconjoined twins in cultures from variouscontinents. Conjoined twinning raised moraldilemmas and risky definitions (for instance,how many souls they have?). One of the firstdescriptions of esophageal atresia was based onthe autopsy of a set of conjoined twins but theyonly became popular after certain sets wereexhibited as freaks or circus attractions. This wasthe case of Chang and Eng Bunker, the originalSiamese twins, who were taken for this purposefrom Siam to the USA, where they eventuallysettled and lived for more than 50 years. Manyexamples have been publicized ever since andthey are often addressed in the media.

Due to the complexity of the technical prob-lems involved, it is understandable for the firstseparations to be relatively recent (17th century)(van der Weiden 2004). However, many unsuc-cessful separations were never reported and thehigh mortality of this condition is still largelyhidden.

Etiology

The current etiology of conjoined twins is still notfully understood. There are two theories for thepathogenesis of conjoined twins. The first oneasserts that incomplete fission of the early embryoproduces identical twins that shared anatomicstructures (Spitz and Kiely 2003; Arnold et al.2018). Monozygostic twins occur when anembryo divides before day 13. An embryo thatdivides on or after day 13 will not dividecompletely and will remain with fused organs ofvarious degrees, producing conjoined twins. Theextent of division and subsequent developmentwill determine the degree of shared anatomybetween the twins. The second theory states thatconjoined twins are the result of secondary fusion

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of embryos from a completely separated fertilizedegg (Arnold et al. 2018; Kobylarz 2014; Spencer1996). The twins are always joined by centralparts of their anatomies and they are alwayshomologous in the sense that they never havethe head or the lower limbs on opposite sides.This is consistent with the previously mentionedinterpretation of the embryonic mechanism.

Some experiments in amphibians and a fewmodern molecular genetic observations suggestthat fusion of two originally separated embryosmay be the explanation for some rare cases inwhich there is sex discordance (Logrono et al.1997; Martinez-Frias 2009).

Classification

The location, extent, and nature of the bridge thatjoins both twins vary widely and this complicatesdescription of the anatomy of each individualset (Pierro et al. 2015). Several classificationsattempted at simplifying description. Conjoinedtwins were divided into ventrally and dorsallyjoined and subdivided according to the level offusion (Spencer 2003). It is probably simpler todivide them according to their asymmetric orsymmetric nature and to the level of the fusionthat is followed by the suffix pagus.

Asymmetric twins include “fetus in fetu,”acardius acephalus, and heteropagus parasitictwins. The adscription of the first variety oforganoid teratomata to the family of conjoinedtwins is only acceptable when they are “organoid”and contain a more or less rudimentary spine(Spencer 2001). Acardius acephalus is a varietyof parasitic twin devoid of heart and head that isconnected by marginal placental vessels with thehealthy twin (the autositus) that accounts forcirculation and nutrition of both. Heteropagustwins are usually attached to the abdominal wallof an anatomically normal autositus twin, withoutor with exomphalos, and appear as organoidparasitic masses containing various organs andlimbs unable to sustain independent circulationby themselves (Bhansali et al. 2005; Abubakaret al. 2011).

Symmetric conjoined twins are classifiedaccording to the body parts that are fused:cephalopagus (11%, head to umbilicus),thoracopagus (19%, thorax to umbilicus),omphalopagus (18%, umbilicus), ishiopagus (11%,lower abdomen and pelvis), paragagus (28%, lowerabdomen and pelvis), craniopagus (5%, cranium,but not foramen magnum/skull based), rachipagus(2%, vertebral column), and pygopagus (6%,sacrum and perineum) (Arnold et al. 2018; Bakenet al. 2013).

Clinical Presentation

Nowadays, most conjoined twins are prenatallydiagnosed by ultrasound and this allows preven-tion of potentially serious problems during vagi-nal delivery. Except in the thoracopagus twinswith common heart and in the asymmetric twins,both fetal heart tones can be heard like in regulartwins. The heads and the limbs of conjoined twinsare on the same side (this is why they are termed“homologous”) in contrast with regular twins thatare usually arranged in opposite directions. Thisallows fetal ultrasonographic (US) diagnosis thatleads to more sophisticated US and/or magneticresonance imaging (MRI) studies aimed at definingthe anatomy of the fusion and the chances of sep-aration (Andrews et al. 2006; Lopes et al. 2013).Associated anomalies that can be diagnosed readilyin expert hands (Brizot et al. 2011) are more fre-quent in regular twins than in singletons and this ismore so in conjoined ones. Since they may condi-tion viability of the twins, their detection some-times prompts termination of pregnancy.

Most sets of conjoined twins are delivered bycesarean section and can be taken care of bymultidisciplinary teams from the beginning. Incases delivered vaginally, it is frequent for lesionsdue to obstetric trauma to be present at birth:intracranial hemorrhage, long bone fractures, rup-ture of exomphalos, evisceration, etc. The anat-omy varies widely according to the modality ofjoining. Thoracopagi with common hearts almostconstantly have severe cardiovascular and arterialanomalies that produce early symptoms and maybe rapidly lethal (Marin-Padilla et al. 1981;

Conjoined Twins 3

McMahon and Spencer 2006). The most frequentforms, omphalopagi and thoracopagi, have oftenan omphalocele as a part of the joining bridge.Abdominal viscera, like the liver or different partsof the intestine, are contained in the gelatinousmembrane that is in continuity with the umbilicalcord (Figs. 1 and 2). The livers are often fused andthey show amazingly complex biliary and vascularcommunications. A common arrangement consistsof a more or less thick arterial trunk that communi-cates both aortas trough the abdominal cavity. Theintestines are usually connected or shared. Themore common arrangement is a fusion of bothsmall bowels at jejunal level and an ileal divergenceclose to the ileo-cecal valves. Sometimes this fusionconsists of a cystic dilatation of the bowel andoccasionally there are intestinal atresias of varioustypes in either one of the small bowels. The bladdermay be common and sometimes opens at the lowerpart of the bridge as an exstrophy (Fig. 3). In casesjoined by the rump (Figs. 4 and 5), the anatomicalvarieties in terms of gastrointestinal and urogenitalopenings are multiple but sometimes the urinary,genital, and digestive tracts end in a single cloacalorifice shared by both twins.

Serious malformations or trauma suffered byonly one of the twins may create difficult clinicalsituations because crossed circulation creates asingle internal environment which is hard tomanipulate: the healthier twin can compensate in

part for the problems of the diseased one, but thelatter may expose the former to disbalances,toxins, or medications (Lai et al. 1997).

Diagnosis

The diagnosis remains easy, even if some of theassociated congenital abnormalities cannot beseen at the early gestational stage. A comprehen-sive understanding of the anatomy of the organsand the distribution of their functions is necessaryfor planning viable separation strategies. PlainX-rays, gastrointestinal (g.i.), or urogenital (g.u.)tract contrast studies may depict the points ofjunction and other features of the correspondingorgans but, due to the atypical anatomy (Kingstonet al. 2001), incomplete understanding leads tounexpected surprises. Ultrasonographic(US) study helps at every diagnostic step(Andrews et al. 2006). Ultrasound enables anearly and accurate diagnosis of conjoined twins.The first trimester ultrasound is the best methodfor diagnosing conjoined twins in early pregnancy(Mathew et al. 2017; Melo et al. 2018). Angiog-raphy, widely used in the past for imaging thenature of the blood supply in the shared organs,is currently replaced by computerized tomogra-phy (CT) or magnetic resonance angiography(angio-MRI) (McHugh et al. 2006). CT

Fig. 1 (a) Set ofomphalopagus twins.Severe brain hemorrhage intwin on the right aftervaginal delivery promptedneonatal separation. Onlythe twin on the leftsurvived. Fourteen yearslater (b), she is a bright,normal girl whose onlyconcern is breastasymmetry (Tovar 2011)

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angiography is the best way for depicting thevascular arrangement (Ohashi et al. 2012; Tannuriet al. 2013). MRI is an excellent imaging modalityfor tissue characterization and better depicts thefused neural and meningeal tissues incraniopagus, rachiopagus, ischiopagus,pygopagus, or parapagus. Both CT and MRI arecrucial for imaging the anatomy of conjoinedhearts. Helical CT reconstruction of the bonyjunctions may help in preparing strategies ofskeletal separation (Martinez et al. 2003) (Figs. 4and 5). Nuclear imaging may help to define thefunctional anatomy of the liver, kidney, or otherorgans (Rubini et al. 1995; Chen et al. 2011).However, unexpected anatomical surprises thatmay change the order or the nature of the

participation of the different specialists involvedare frequent. In most cases, the expected anatomydoes not fully fit the surgical findings and someingenuity is required for improvising solutions.

Hematologic and biochemical studies are oftenmisleading due to the situation of crossed circula-tion. When the vascular channels are large, para-biosis is complete, but when only minor territoriesare in connection, both twins maintain some inter-nal environmental differences that can be relevantin cases in which blood tests are necessary fordiagnosis. Other tests, like ECG, are challengingwhen the hearts are connected (Carton et al.2011). Metabolic rate may show considerable dif-ferences between twins upon calorimetry (Powiset al. 1999).

Fig. 2 Four sets ofthoracopagus twins withcommon heart. Separationwas undertaken only in setA because they were joinedonly by a narrow atrialbridge. Unfortunately, thetwins did not survive (Tovar2011)

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Treatment

Preoperative Ethical Issues

The principles that regulate the practice of medi-cal profession are particularly difficult to respectin conjoined twins and serious ethical dilemmasare to be expected (Atkinson 2004; Lee et al.2011; Spitz 2015):

The principle of autonomy (the decisionstaken by the patient after honest and completeinformation should be respected) cannot be fullyapplied in children for obvious reasons and has tobe exerted by proxy by the parents. This may be asource of conflicts among them (for instance, onemay want a separation to be attempted and the

other one may refuse it) or with doctors or thecourts. Any effort to reach unanimous decisionsagreed upon after informed consent should bemade (Boudreaux and Tilden 2002).

The principle of justice (similar chances forboth patients) is obviously at risk when it comesto separation that may involve mutilation or shar-ing of organs. Choices should be made taking intoaccount that distribution of organs and tissues hasto be fair for both members of the set. All possibleactions should attempt at complying with thisprinciple although the limitations are obvious.

The principles of beneficiency and non-maleficiency (the benefit of the patients shouldbe sought and no harm should be inflicted tothem), that are considered as the ethical back-bone of medical decision-making process,

Fig. 3 Omphalopagustwins with incompletecloacal exstrophy. Thesingle bladder opened underthe exomphalos (a). Asingle colonic opening wasvisible in the middle of thebladder plate (b). Both hadanorectal agenesis with onesingle urogenital canal anddouble uterus and vaginas(c). Separation involveddivision of the colon withcolostomies and bladderclosure (d). Later on,saggital anorectoplasty withcolonic and vaginal pull-through were performed(Modified from Tovar 2011)

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are also difficult to apply if separation is nec-essary for the survival of only one twin, ifdistribution of organs is uneven, and if separa-tion involves, as it is usually the case, loss ofsome functions that might be preserved with-out separation.

When separation of conjoined twins is consid-ered, the patients are usually too young for decid-ing by themselves, the parents are heavilyinfluenced by information delivered by doctors,and the team involved is usually so large and oftenethically discordant that keeping a unified line ofdecision becomes difficult. Acknowledgement ofa strong moral leadership after open discussion ofevery issue is required before providing informa-tion about the chances and the consequences ofseparation to the caretakers. In case of seriousdiscrepancies among all participants in the

process of decision, the courts might be involved(Gillon 2001).

Furthermore, the media (whose interference isdifficult to avoid due to the large amount of peopleinvolved) almost constantly creates new difficul-ties. The twins and their family have to be pro-tected from these agents and, if possible, the entireprocess of decision-making and even the separa-tion should be kept in the shade. Unfortunately,this is difficult to put into effect. Too many peopleare involved in the treatment of conjoined twinswhile being mesmerized by them. Corruption bythe media can easily put unauthorized pictures andfilms in circulation and sometimes, the familiesthemselves cast information in exchange ofeconomic support. All these actions may be dam-aging for the twins and should be prevented when-ever possible.

Fig. 4 (a) Ischiopagustetrapus (four legs) twins.(b) The spines and thespinal cords were joined atthe caudal end as shown byhelicoidal CTreconstruction. Duringseparation, the spines weredivided, the meningeal sacswere reconstructed, aquadruple iliac osteotomywas performed for joiningboth pubic bones in eachtwin, the urogenital systemwas reconstructed, andcolostomies werefashioned. (c) Patients at theage of 12. They deambulatenormally and enjoyrelatively normal lives withpermanent colostomies andintermittent bladdercatheterization. (d) and (e):CT reconstruction of thebony pelvis of both twins atthe age of 11 (Modifiedfrom Tovar 2011)

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Preoperative Meetings

When separation has been decided, one or moremeetings with scrub nurses, nurses, anesthesiolo-gists, and surgeons of the specialties involved(general pediatric, orthopedic, plastic, urologic,neurologic and cardiovascular surgery) shouldbe scheduled (Al Rabeeah 2006). Technicalaspects should be discussed, and the operationitself should be rehearsed because installation ofthe set of twins on the table, skin prep and draping,as well as transport of one twin with thecorresponding anesthetic equipment to anothertable for reconstruction after separation shouldbe carried out according to a previouslyestablished plan (Kiely and Spitz 2015). Theexpected order and extent of the participation ofeach specialist team in the separation should bescheduled as well. The surgeon in charge of the

direction of the operation acts as an orchestralconductor and his/her coordinating activityextends well beyond the end of the separationitself.

Recent advances, such as 3D printing, may aidin surgical pre-planning, thereby enabling suc-cessful surgical separation of conjoined twins(Mathew et al. 2017).

Separation

Anesthesia is a serious challenge not only becauseof the obvious anatomical difficulties for intuba-tion, insertion of lines, and invasive monitoringbut mainly because of the previously mentionedsituation of parabiosis in which one single inter-nal environment is shared to variable extents bythe twins. The drugs administered to one pass on

Fig. 5 (a) Caudalparapagus twins with anextra thoracic limb irrigatedfrom the abdominal aorta oftwin on the left. (b) Therewas a single pelvis with twolower limbs and two spineswith communicating spinalcanals and joined cords.Separation involved twosurgical steps. First, thespinal cords and meningealsacs were separated andsubcutaneous expanderswere inserted. (c) Secondly,the sacrum, the g.i., andg.u. tracts were divided andthe parietal defects wereclosed. In twin on the left,the skin and muscle of theadditional limb were usedas a vascularized flap. Intwin B, a synthetic meshwas used for this purpose.Colostomies werefashioned. Both twins areable to deambulate withbraces (d) (Tovar 2009)

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into the other one and biochemical and gas mon-itoring may be confusing (Thomas and Lopez2004; Szmuk et al. 2006). In difficult cases, itmay be worth to proceed with preanestheticmanipulations and line insertions one day beforethe operation itself in order to leave time enoughfor this.

Asymmetric conjoined twins represent ingeneral surgical challenges that are not unlikeother ones met in this specialty. The Acardiusacephalus parasitic twin is inviable and diesupon clamping the umbilical cord of the host(autositus). Intrauterine occlusion of the umbilicalcord of the parasitus allows termination in casesin which cardiac failure of the autositus threatenssurvival. It should be pointed out that a consider-able proportion of host fetuses have severe cardiacproblems at birth as a result to adaptation of thenew hemodynamic situation after separation. TheFetus in fetu is treated as a tumor. In fact, it is ateratoma with organoid tissues and a more or lessrudimentary spine. Depending on size and loca-tion, the operation may be variably hazardous.Most cases are central or paraspinal and theymay have close relationship with large vessels.Heteropagus asymmetric parasitic twins areremoved with attention at preserving as muchtissue of the host as possible in order to respectthe organs and allow for wall reconstruction. Sur-vival of the parasitus devoid of heart and brain isimpossible and this allows for a large use of itstissues. After excision of the membrane of theexomphalos, the abdominal wall can bereconstructed with aponeurotic and/or muscleflaps using skin of the parasitus for coverage.Sometimes, bony parts of this have to be removed.In cases in which wall closure is impossible withautologous tissues, synthetic grafts can be used asin symmetric forms of conjoined twinning.

Separation of Craniopagus may be extremelydifficult or even impossible given the complexityof the neural, arterial, and venous connectionsinvolved. Modern imaging and sophisticated neu-rophysiologic monitoring are particularly usefulin these cases. The final amount and nature of thebrain tissue and the vascular network shared bythe twins set the limits for separation that mayinvolve several stages (Browd et al. 2008;

Staffenberg and Goodrich 2012). Serious difficul-ties are to be expected for separation, particularlyvenous and neurologic deficits, determined by thelocation and size of the brain junction, are verylikely even after successful operations.

Separation of Omphalopagus twins involvesvariable difficulties depending on the extent oforgan sharing. These twins have more oftenfused livers and g.i. tracts. It is customary to startseparation by the liver, where more difficulties areto be expected. A small liver bridge without majorvascular connections is relatively easy to takedown but a large mass of anatomically atypicalliver with wide arterial, venous, and biliary con-nections (Meyers and Matlak 2002) may be aformidable undertaking. Perioperative ultraso-nography and parenchyma dividing devices usedfor liver resection (ultrasonic or water jet knives)are very useful for this purpose. The surgeonsshould ensure that adequate arterial and portalinflows, hepatic veins outflow, and patent biliarytracts are preserved in each half of the liver mass.Anatomic orientation may be difficult and all pre-cautions are justified. In a number of cases, a largearterial trunk joins the abdominal aortas of bothtwins and temporary clamping is advisable beforedivision. The raw liver surface is treated like inany other major liver resection. Careful ligation ofthe vascular and biliary radicals and coveragewith fibrin adhesive in some cases will limit com-plications. As far as the gastrointestinal tract isconcerned, the most common form of connectioninvolves fusion of the small bowel from the upperjejunum down and divergence near the distalileum. Separation consists in most cases of allo-cating half the available gut to each twin. Addi-tional problems may be met when atresia of one ofthe tracts or a common cystic dilatation of the midbowel are present. Regular techniques used indigestive neonatal surgery are also indicated inthese cases (Cywes et al. 1997; el-Gohary 1998;Spitz and Kiely 2003; Rode et al. 2006).

Thoracopagus twins without connected heartsare separable in contrast with those with commonmyocardium (Thomas Collins et al. 2012). Only afew of them are amenable to surgery under car-diopulmonary bypass. Except in very rare cases inwhich narrow atrial or ventricular bridges exist,

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the only chance of separation involves using thebulk of myocardial material for one of the twins.Even if separation is attempted, the conductionsystem is heterotopic, and severe arrhythmiascan intervene during surgery. In addition, thesetwins often have cardiovascular defects that mayfurther complicate or preclude separation (Lopeset al. 2013). The aorta and the pulmonary arteriesmay be hypoplastic and, as described above, theremay be communications between the infra-diaphragmatic aortas. In the very few cases suc-cessfully separated, only one twin survives andthe tissues of the other one, including the sternumand/or ribs, can be used for bridging the largedefect created in the thoracic wall during separa-tion. Of those twins that cannot be separated, mostdie of the associated heart defects in the firstmonths or years of life.

Rachiopagus, Ischiopagus, Pygopagus, andParapagus twins share to different extent parts ofthe spine, central nervous system, gastrointestinal,and genitourinary tracts and they may representformidable challenges. The separation of the bonyparts requires highly skilled orthopedic surgeons.Careful design of the operation is necessarybecause osteotomies or synthesis of osseous tissueshould aim at reconstructing the pelvis or thelimbs, and this may require planned coveragewith the available tissue. In some cases, the recon-struction of the pelvic rim requires bilateral iliacosteotomies and pubic fixation (Fig. 4). In othercases, even refashioning a bony pelvis is impos-sible and the subsequent prosthetic treatment isdifficult (Kim et al. 2002; Fieggen et al. 2004)(Fig. 5). When the twins are united side by side,splitting the sacrum is necessary. Sometimes, thisis better performed in two operative steps: one atthe time of insertion of skin expanders and theother one during separation itself. The spine hasoften malformations at other levels, includingasymmetric vertebra, anomalies in number, ormalposition, and scoliosis has to be taken intoaccount during follow-up.

Neurosurgical separation may involve dividinga common brain tissue or a spinal cord. In bothcases reconstruction of the dura or dural sacs oneach side directly or using biological prostheses isnecessary (Fieggen et al. 2004). The motor and

sensitive effects of separation of nervous tissueare variable depending on the location and extentof the fused tissue. Fused spinal cords (end-to-endin pygopagus and side-to-side in parapagus) areusually quite distal and separations have limitedneurological effects. The neurosurgical part ofsome separations is particularly delicate becauseof the contaminated environment that is unavoid-able when the gastrointestinal or genitourinarytracts have to be divided and particularly whenenterostomies are established and when prosthesisare used for bridging dural defects.

Sharing the common lower g.i. tract betweenboth twins entails the loss of continence for one orboth of them. In twins joined by the lower abdomenor pelvis, there is often a single colon. The func-tional reconstruction of the colorectal area is there-fore rarely possible. Rectal function can be seldompreserved in one twin but more often this is impos-sible in both and enterostomies have to be fashionedat some stage. Even if reconstruction of the anusand rectum are feasible, patients will only have halfthe colon or less and achieving reasonable conti-nence is often impossible. All refinements ofadvanced bowel management (diet, enemas, ante-grade wash-outs through a continent apendicealstoma or a cecal button) are necessary to obtainsubsequent adaptation of these patients to a moreor less normal social life (Kim et al. 2002).

The same can be said about distributing theurogenital tract structures between the twins.Keeping a bladder and urethra for one of them israrely possible in most frontally united sets.Again, all refinements of reconstructive urology,bladder augmentation, clean intermittent catheter-ization, and continent urinary diversion may helpto readapt these patients (Holcomb et al. 1989;McLorie et al. 1997; Lazarus et al. 2011). Thenative genital tract can be reconstructed if dupli-cated but sometimes vaginal replacement is nec-essary (Kim et al. 2002).

Wall Reconstruction

One of the major technical problems posed byseparation of conjoined twins is the coverage ofthe huge parietal defects left. When only one

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survives, part of the wall of the other one can beused to bridge the defects but in other cases,additional procedures are necessary. Severaltypes of muscle and/or fascial flaps have to befashioned, and in a number of cases, only the useof biologic or synthetic prostheses allows closingthe gaps. When planning the separation, the avail-ability of skin and subcutaneous tissue necessaryfor the type of closure elected should be estimated.Skin expansion with subcutaneous inflatable sili-cone expanders is often useful prior to separation.However, the same limitations mentioned for neu-rosurgical or bone procedures apply for expanderssince the risk of bacterial colonization and infec-tion with loss of the expansion is considerablewhen the operative field is contaminated byopening the gastrointestinal tract or simply byenterostomies.

Complications

The nature of these risky operations involves alarge number and variety of possible complica-tions. Intraoperative hemorrhage and damage tovital structures is always possible due to theatypical anatomy. Bone division or meningealmembrane opening simultaneous to gastrointesti-nal or the genitourinary procedures increase therisk of serious infection. Wound closure avoidingcompartment syndrome may necessitate syntheticmaterials that are also exposed to contamination.Wound disruption and infection are therefore notrare. Finally, a wide range of complications notunlikely those seen after other major operationsmay occur: internal hemorrhage, abscesses, vas-cular thromboses, or postoperative intussuscep-tions, among others, are possible.

Early and Long Term Results

Overall mortality in conjoined twinning is high.When diagnosis is made during early pregnancy,interruption of gestation is common practice indeveloped countries particularly for the formswith poor prognosis (Martinez-Frias et al. 2009;Brizot et al. 2011). Fetal mortality or stillbirths

are also frequent. Obstetric mortality or severebirth trauma remain a real risk when prenataldiagnosis was missed, and this happens moreoften in undeveloped countries in which preg-nancies are not monitored. A considerable pro-portion of twins have multiple malformationsthat cause demise in the first hours or days oflife (Kaufman 2004). When separation is deemedpossible, it must be reminded that neonatal sep-arations involve higher mortality mainly becausethey are only indicated for life-threatening rea-sons (for instance, one twin may be very ill ordevelop intestinal obstruction) but also becausethese complex operations are better performedwhen most anatomical and functional featuresof the set have been ascertained.

Thoracopagus twins with a common heartrarely survive because most have severemalformations. Of those sets in which separationis attempted, only a few individual twins survive(Chiu et al. 1994; Fishman et al. 2002). However,thoracopagus without shared heart can be success-fully separated.

Most omphalopagus twins can be separatedand survive if no obstetric trauma or severe asso-ciated malformation are present (Fig. 1). In allother forms of conjoined twinning a high propor-tion of the twins can be separated and survivealthough with more or less extensive deficits thatrequire follow-up for life and often additionaloperations.

In the long term, separation of conjoined twinsrarely produces independent individuals withoutsequelae. Some cases of asymmetrical twins andomphalopagi may survive separation and face anormal life. Most other cases keep orthopedic orneurologic sequelae or have fecal and urinarycontinence problems that become predominantwith the passage of time. Orthopedic and motordeficits may require prolonged rehabilitationand/or prosthetic appliances. Permanent enteros-tomies are not rare and the most sophisticatedprocedures for obtaining urinary continence ordryness are necessary (Votteler and Lipsky 2005).

It is particularly discouraging that these preg-nancies are often terminated in advanced medicaland social environments able to provide lifelongassistance for rehabilitation and social integration

Conjoined Twins 11

whereas twins from less privileged countries thatare diagnosed at term and eventually separatedlack all the necessary facilities, all along theirlives.

Conclusion and Future Directions

The intrinsic difficulties of separation of con-joined twins and the predictable deficits that willimpair the quality of lives of survivors makestermination of pregnancy a widespread decisionafter prenatal diagnosis. Interestingly, this hap-pens in developed countries where the healthcare systems and the social assistance institutionswould allow the best integration of survivors. Themajority of conjoined twins are born in less devel-oped countries where often the expertise for sep-aration and the framework of social assistance arelacking. These patients are often sent to the moreexperienced institutions, but it is difficult to offerthem the life-long care that they require.

By any respect, conjoined twinning representsa major test for the quality of pediatric surgicalcare. Only institutions offering highly sophisti-cated pediatric surgical specialties can undertakethese operations with a reasonable chance of suc-cess. It is therefore desirable to concentrate con-joined twins in only a few of them.

Cross-References

▶Anorectal Anomalies▶Cardiovascular Physiology▶Colonic and Rectal Atresias▶Conjoined Twins▶Disorders of Anus and Rectum▶Duplications of the Alimentary Tract▶Embryology of Congenital Malformations▶Ethical considerations in Pediatric Surgery▶Long-Term Outcomes in Newborn Surgery▶Omphalocele

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