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BackgroundConjoined twinning is one of the most fascinating human malformations and has also been reported in other animalsmammals, fishes, birds, reptiles, and amphibians.[1, 2, 3]Treating conjoined twins can be a daunting challenge for the surgeon. Furthermore, these cases often raise religious,moral, ethical,and legal[6, 7]issues.Approximately 75% of conjoined twins are female, and 70% are fused at the thorax (thoracopagus) or abdomen (omphalopagus). The union can be in the frontal, transverse, or sagittal plane. The following two photographs show union in a transverse plane in the lower body area, so that the twins face each other.Union in a transverse plane in the lower body area, so that the twins face each other.Union in a transverse plane in the lower body area, so that the twins face each other.The two main categories of conjoined twinning are as follows: Symmetrical or equal conjoined twins (ie, two well-developed babies) Asymmetrical or unequal conjoined twins (ie, a small part of the body is duplicated, or an incomplete twin is attached to a fully developed twin)In broad terms, conjoined twins may be regarded as a doubling anomaly. The later the incomplete embryologic separation occurs, the higher the likelihood of a complicated fusion.History of the ProcedureThe term Siamese twins comes from Eng and Chang Bunker (1811-1874), the famous conjoined twins from Thailand (Siam). They settled in the United States, married healthy women (who were sisters), had children, and lived to age 63 years. P.T. Barnum, with whom they were affiliated at one time, was responsible for introducing the term Siamese twin; however, this term has fallen out of favor because it seems to convey that conjoined twins are circus freaks or monsters.One of the earliest documented cases was that of Mary and Eliza Chulkhurst, who were born in 1100 in England. They have been described as being joined at the shoulders and hips, which is, in fact, unlikely based on the known types of conjoined twinning. Also known as the Biddenden Maids, the sisters lived for 34 years in Biddenden, County of Kent, England. The major types of conjoined twins were described in 1573 by the French renaissance surgeon Ambroise Pare.Successful separation of a set of omphalopagus twins was first reported in 1689 in Basel, Switzerland.While series of experience with conjoined twins have been reported in literature,successful separation of large numbers of conjoined twins is limited to a few centers in the world (13 sets described by O'Neill et al from the Children's Hospital of Philadelphia in 1988,14 sets reported by Mackenzie et al from the same hospital in 2002,17 sets reported by Spitz and Kiely in the same year from the Great Ormond Street Hospital, London,and 46 sets reported by Rode et al from Red Cross Children's Hospital, Cape Town, South Africa.Surgical experience with conjoined twins has also been reported in other parts of the world, such as China, Saudi Arabia, and New Zealand.[14, 15, 16]In England, the separation of a pair of conjoined twins from Malta, Jodie and Mary, born August 8, 2000, raised considerable ethical and legal issues.The parents refused to grant permission for the surgery, and the matter was referred to court. The judges concluded that separation was in the best interests of both children, even though it meant the death of the weaker twin, Mary. In the United States, the decision of the parents might have been final.In Singapore in 2003, skull and brain separation of 29-year-old craniopagus Iranian twins, Ladan and Laleh Bijani, was unsuccessful, and the sisters died of exsanguination on the operating table.Craniopagus conjoined twins Mohamed and Ahmed Ibrahim were separated at the Children's Medical Center in Dallas, Texas. They were born in Egypt on June 2, 2001, and were separated on October 12, 2003, during a 34-hour operation. The operation involved skin grafting and separation of the venous sinuses. Later, they underwent skull reconstructive surgery, received rehabilitation therapy, and, finally, left for Egypt on November 19, 2005. A successfully staged separation of craniopagus twins (Carl and Clarence Aguirre) took place from 2003-2004 at Montefiore Medical Center in New York.A support group for conjoined twins, Conjoined Twins International, was founded in 1996 in Prescott, Arizona, by the grandparents of a set of conjoined twins. Facebook also has a support circle of friends of conjoined twins. In addition, blog sites have been set up for certain sets of twins.ProblemThe term conjoined twinning refers to an incomplete splitting of monozygotic twins after 12 days of embryogenesis. See the diagram below.The term conjoined twinning refers to an incomplete splitting of monozygotic twins after 12 days of embryogenesis. Image created by Samantha Cloutier and Aaron Cloutier.The delivered fetuses are physically joined at some point as a result. The point of union is used to classify twins; the label used is the Greek wordpagos,which means "that which is fixed." An even more rare condition occurs when one incompletely formed (ie, parasitic) twin is dependent on the well-formed one. This is known as heteropagus twinning. See the images below.This is a much more rare occurrence termed heteropagus twinning. One twin is not fully formed (parasitic twin) and is dependent on the well-formed one. A malformed head, upper limb, and large ears are present in the parasitic twin. Three legs (tripus) are present.Ethical issues arose in this set. The parents refused separation on the basis that the nonviable twin was still breathing. The wishes of the parents were respected. This set of twins was lost to follow-up.Another example of parasitic twin, in which the head is not visible, and the ethical decision is easier to make, is shown below.An example of parasitic twin, in which the head is not visible.A nonoperated case of parasitic twins, presenting late, is shown below.A nonoperated case of parasitic twins, presenting late.The parasitic twin (sacrificed) after separation is shown below.The parasitic twin (sacrificed) after separation.Multiple limbs attached to the thorax is shown below.Multiple limbs attached to the thorax.EpidemiologyFrequencyTwinning occurs in approximately 1 of every 87 live births. Monozygotic twins account for one third of twin births. Conjoined twins account for 1% of monozygotic twins. In the United States, the incidence is 1 per 33,000-165,000 births and 1 per 200,000 live births.The stillbirth rate is 40%-60%. More cases are being reported now because of the routine use of fetal ultrasonography.The condition is probably more common in Indian and African populations than in whites. Exact epidemiology across different races and nations is not known because of underreporting and lack of facilities for prenatal diagnosis.When born live, females are affected more often than males, with a female-to-male ratio of 3:1 or greater. Stillborn conjoined twins are predominantly male.Conjoined twins show characteristic points of attachment. They are classified according to the site of union, with the following frequency: Thoracoomphalopagus (ie, joined at the chest, abdomen, or both) - 74% Thoracopagus or xiphopagus (ie, joined at the chest) - 40% Omphalopagus (ie, joined at the abdomen) - 34% Pygopagus (ie, joined at the buttocks) - 18% Ischiopagus (ie, joined at the ischium) - 6% Craniopagus (ie, joined at the head) - 2%See omphalopagus in the photos below.Omphalopagus twins.Omphalopagus twins.See an example of craniopagus twins in the image below.Craniopagus twins.A radiograph of the skull, showing the conjoined heads in the case above is shown below.A radiograph of the skull, showing the conjoined heads in the case in previous two images.An MRI or CT may show the brain structure, while a magnetic resonance angiography can show the extent of vascular connections. See the image below.An MRI or CT may show the brain structure, while a magnetic resonance angiography can show the extent of vascular connections.EtiologyThe incomplete anatomic separation between monozygotic twins occurs sporadically, with no increased risk in future pregnancies.Seven cases (2 published) have been reported in which conjoined twinning occurred with the use of clomiphene for induction of ovulation. Two cases of thoracopagus have been reported in which conjoined twinning occurred with periconceptional maternal griseofulvin intake.Spina bifidais associated with conjoined twinning, and one case of conjoined twinning after maternal exposure to valproic acid has been reported.No gene mapping or linkage analysis currently exists for the malformation. Some investigators implicate abnormal X inactivation. The latter may be related to the increased incidence in female twins. Other studies refute abnormal X-chromosome inactivation.PathophysiologyThe morula becomes a blastocyst on day 6 after the ovum is fertilized. An inner cell mass develops at one end within this vesicle. The inner cell mass can form a whole fetus. Conjoined twins are produced when this inner cell mass, derived from a single zygote, incompletely splits late, after the 12th day of gestational life.PresentationCephalothoracopagus twinning is characterized by the anterior union of the upper half of the body, with two faces angulated variably on a conjoined head. The anomaly is occasionally known as janiceps, named after the 2-faced Roman god Janus. The prognosis is extremely poor because surgical separation is not an option, as a single brain and heart are present and the GI tracts are fused. This malformation is extremely rare (see the image below).Cephalothoracopagus twins.Craniopagus occurs in 2% of conjoined twins. In this variety, the twins have cranial fusion (see the images below). Stone and Goodrich have recently subclassified craniopagus into 4 varieties, depending on whether a significantly shared dural venous sinus system (total vs partial) is present, and whether the inter-twin longitudinal angulation is below 140 degrees.Craniopagus twins.Craniopagus twins.Bicephalus or dicephalus means that 2 heads are present on a single trunk (see the images below).This set of conjoined twins was a stillbirth. Prenatal ultrasonography failed to reveal the second head. An emergent cesarean section was performed after failure to progress.This is an example of double-headed (bicephalus) conjoined twins, a rare occurrence.In omphalopagus, the anterior abdomens are united (see the image below). Omphalopagus (34%) is considered a subset of thoracoomphalopagus. Its incidence is usually combined with that of thoracopagus (40%) to provide an incidence of thoracoomphalopagus (74%). Pure omphalopagus twins have no cardiac union.Thoracoomphalopagus twins.A case of thoracoomphalopagus twins, after separation, is shown below.A case of thoracoomphalopagus twins, after separation.In the condition parapagus, (see the image below) or diprosopus,twins have lateral union of their trunks so that both faces are forward looking in the same plane.Parapagus twins.Pygopagus (see the image below) is the term used when the twins face in opposite directions. The sacra are fused, and the twins may share a portion of the spinal cord. In addition, the rectum and perineal structures are usually fused.Pygopagus twins.In rachipagus (see the image below), the twins are joined back-to-back at any point, usually above the lumbar spine. They may have extensive vertebral fusion in the dorsal midline and may have meningocele, neural connection, or both. One of the embryos generally fails to survive, leaving some body part attached to the other twin's dorsal column. In these cases, rachipagus must be differentiated from fetus in feto (within a body cavity) and teratoma (no mature organ).Rachipagus twins.Thoracopagus is the most common variety, occurring in 40% of conjoined twins. The chests are joined, and the hearts are almost always fused in some way (see the images below). As noted above, thoracopagus is often combined with omphalopagus.Conjoined twins unified at the thorax and abdomen.Another view of the same set of twins as shown in the previous image.A superior radiographic view of the same set of twins as shown in the previous 2 images. The twins have 2 hearts that are not conjoined, making this a possible operation.Esophagram showing union at the level of stomach.Thoracoomphalopagus twins.Thoracoomphalopagus twins.In ischiopagus twins (see the image below), the lower abdomen and the pelves are fused.[22, 23]The twins may have 3 legs (ie, tripus) or 4 legs (ie, tetrapus). The genitourinary system and the rectum are shared; the liver may also be fused.Ischiopagus tetrapus twins.IndicationsOf all types of conjoined twins, omphalopagus twins are the most favorable candidates for elective surgery because of good survival rates.Historically, conjoined twins in general have been placed into 3 groups: Group 1 - Those who do not survive delivery plus those who die shortly after birth Group 2 - Those who survive to undergo an elective procedure Group 3 - Those in whom an emergent procedure is requiredEmergent conditions may arise at any time and include intestinal obstruction, rupture of an omphalocele, congestive cardiac failure, severe degree of respiratory compromise, and terminal illness in one of the twins.Harper and Kenigsberg suggest that the abdominal cavities grow as the twins age, whereas the bridge connecting the omphalopagus twins does not grow in diameter.Hence, abdominal wall closure can be performed more easily at approximately age 1 year.The moral and ethical aspects of separation must be considered, especially in the following circumstances: A choice must be made concerning single organ systems. The twin who receives the organ system will live and thrive, whereas the other twin will suffer or die. A similar problem arises when unequal limbs are present. The twins have conjoined hearts. Surgical separation of the cardiac complex has been mostly unsuccessful. In some cases, one twin is allowed to live with the entire cardiac complex. The availability of 2 heart transplants at the same time may improve the options. The twins are craniopagus and have complete brain junction. These twins are usually inseparable.Relevant AnatomyThe larger the connecting bridge, the more complex its contents.ContraindicationsEthical questions may arise in conjoined twins. For example, will the surgery be successful? Is sacrificing one twin to save the other justified? A conjoined heart is a contraindication because the heart complex is usually inseparable. Postoperatively, the divided heart often goes into congestive cardiac failure. Cephalopagus twins with extensive brain union cannot be separated. Furthermore, in the United States, parental refusal is a contraindication to surgery.
Medical TherapyNutritional support is very important in survival of the separated twins, as delayed healing and infections may occur. Parenteral or enteral feedings must be carefully planned.Surgical TherapyOnce the diagnosis has been confirmed, the parents should be counseled on the possible outcomes. The team that will attempt the possible separation should provide this advice. The delivery should take place close to the surgical unit where the separation will be performed. With prenatal diagnosis, the delivery should always be by caesarean section. An elective cesarean delivery should be performed near term after confirmation of fetal lung maturity. Twin delivery may otherwise lead to overdistension and uterine atony.The following are indications for emergent separation: One or both twins are in a life-threatening situation. A correctable, life-threatening associated congenital anomaly (eg, intestinal atresia, malrotation with midgut volvulus, ruptured exomphalos, anorectal agenesis) is present.If the condition of the twins is stable and early separation is not indicated, the surgery is usually delayed until age 6-12 months. At that age, the twins are larger and better able to tolerate surgery. Rapid expansion of the body wall can occur to close substantial defects. The anatomy of the junction and the shared organs and structures dictate the technical details of the procedure.Preoperative DetailsA systematic approach to the workup is necessary in conjoined twins. The type of conjoined twinning present determines the specific studies needed; the possible areas of fusion are predictable in each type. Three-dimensional modelsshould be built to depict the shared anatomy. The shared structures must be divided, if possible, so as to maintain functional integrity for each twin. Some shared organs (eg, a single rectum) may not be divisible. Cardiovascular system: Prenatal and postnatal echocardiography must be performed to accurately define the extracardiac and intracardiac anomalies. Catheterization should be performed in complex cardiac anomalies. Obtaining an ECG and radionucleotide angiogram may be helpful in deciding whether a separation operation can be carried out. A single QRS complex is an ominous sign. Hepatobiliary tree: The number of gallbladders, livers, and pancreata should be known. The conjoined liver may be oriented in an oblique plane to the axis of the twins. Hepatic venous drainage for each twin must be ascertained. A portoenterostomy or even a cutaneous biliary fistula in one of the separated twins may be required if only a single extrahepatic biliary tree exists. GI system: This should be evaluated from top to bottom because fusion may occur at any point. An imperforate anus may be present. Laparascopy may be used to determine bowel distribution between the twins. Urinary tract: Imaging studies are performed to assess the status (eg, number, reflux, anatomy) of the kidneys, ureters, urinary bladders, and urethras. Genital system: In pygopagus and ischiopagus twins, the number, duplicity of vaginas, presence of a cervix, and urogenital sinus must be noted. In males, penile and scrotal status must be established. CNS: The nature and extent of nervous system junction needs to be established in pygopagus twins, who may also have associated hemivertebrae. Skin: Vascular territories of the skin must be mapped by intravenous fluorescein dye. The amount of skin needed to close the wound after separation must be evaluated. Skin and tissue expanders may be required to allow subsequent wound closure. Muscle and bone: All postoperative defects of the muscle and bone need to be covered.Preoperative team conferences should be held, reviewing all the details and models. Moral, ethical, and legal issues need to be fully addressed before surgery.Intraoperative DetailsTwo complete anesthesia teams are required. Two surgical teams are necessary after the twins are apart. Full monitoring is necessary. All administered drugs and IV fluids are calculated on a total-weight basis, with half being delivered to each twin. The IV drugs administered may have an unpredictable effect because of the cross-circulation. Thus, particular care is needed when drugs are administered.During the surgery, abnormal vascular communications and previously unidentified anomalies (eg, intestinal and genitourinary malformations) may be encountered. Unexpected findings are common even after an extensive preoperative evaluation. The surgical team should be aware of this and should be prepared to vary the operative procedure accordingly.Where primary skin closure of the defect would otherwise be impossible, silastic skin expanders have been used to subsequently achieve tension-free closure. A tight thoracic wall closure can lead to cardiac tamponade. Absorbable synthetic mesh has been used with success to close thoracic and abdominal gaps. A porous polyethylene implant and a monofilament polypropylene patch have been suggested to reconstruct the sternum and abdominal wall, respectively.A skin graft from a nonviable twin may be used in certain cases. Since skin grafts need intact body wall for a bed, they are not a very useful primary form of skin coverage.Postoperative DetailsMonitoring must be continued postoperatively in the ICU. Because surgery is prolonged, infants are mechanically ventilated for a variable period. Fluid and electrolyte balance should be closely monitored. Sepsis is a major cause of morbidity and mortality, and precautions must be exercised, particularly when large skin defects are present.Follow-upReconstructive surgery is important in ischiopagus twins, who require GI, genitourinary, reproductive, or skeletal reconstruction. One twin keeps the shared anus and rectal canal, and the other receives reconstructed ones. Reconstruction is easier in twins with tetrapus than in twins with tripus.ComplicationsComplications are common and may include the following: Congestive cardiac failure: This is observed when a conjoined heart is divided. Inadequate or incomplete organ systems: This complication occurs when the twins have unequal distribution of their organs (eg, one shared biliary tract). Adequate preplanning in these cases is essential. Enormous skin defect: This may result following separation of a large bridge and can often be avoided by delaying the surgery until age 1 year. Preseparation tissue expanders may be useful to avoid this problem. The expanders are essentially pouches, which are gradually filled with saline solution. This stretches the skin, allowing the surgeons to close the wounds after separation surgery. Infection: Strict infectious precautions are required for 2 days following the surgical procedure, and patients are kept in the ICU. If they do well, routine precautions are adequate for follow-up care. Hemorrhage: Life-threatening exsanguination can result, especially in craniopagus twins who have a large communicating venous sinus.Outcome and PrognosisSeveral factors may predict or influence outcome, including the following: Prenatal MRI and ECG: These techniques can be performed to accurately define the conjoined anatomy, and an outcome can be predicted. However, the echocardiogram can underestimate the complexity of the cardiac anatomy. Currently, 9 weeks is the earliest gestational age at which conjoined twins have been detected. However, false-positive cases are common before 10-11 weeks, as the fetal movements are limited. Monoamniotic twins may appear conjoined. Postnatal surgery: Generally, the twins are separated at age 6-12 months. The prognosis improves with elective surgery and meticulous preoperative planning. Cardiac anatomy occasionally necessitates urgent separation at birth. However, urgent operations carry a high (40-80%) mortality rate. Skin closure material: Use of skin expanders and prosthetic mesh has improved outcome through providing better wound closure. However, prosthetic mesh used for abdominal closure often results in fistula formation. Thoracopagus with cardiac conjunction: The prognosis for separating twins with conjoined ventricles remains poor, unless two cadaveric cardiac transplants were made available. Only one case of successful separation of conjoined atria has been reported. Craniopagus: Usually, the twins have 2 largely separate brains; however, the venous sinus may be shared. Division of this sinus carries a high risk for life-threatening exsanguination.Future and ControversiesSeparating twins with a conjoined heart remains a challenge. In certain circumstances, separating conjoined twins presents ethical, legal,and religious issues. A choice sometimes has to be made to sacrifice one twin to give the other one a chance of survival. In these instances, consultation with the hospital ethics committee prior to going to the courts has helped. In these cases, a legal ruling must be made before proceeding with surgery.http://emedicine.medscape.com/article/934680-treatment#showallhttp://emedicine.medscape.com/article/934680-overview#showallLaboratory StudiesSee the list below: Chromosomal studies are inconclusive. An abnormal X-chromosome inactivation has been proposed, but this has not been proven. Amniocentesis with an estimation of the lecithin-sphingomyelin ratio is performed to assess fetal lung maturity and to determine the optimal time for a cesarean delivery.Imaging StudiesSee the list below: Prenatal ultrasonography can reveal conjoined twinning as early as 8 weeks' gestation. Conversely, twins with extreme fusion may be mistaken for a singleton. The twin fetuses do not move apart with fetal movement.Polyhydramniosis frequent (75%). A monoamniotic cavity is present, and more than 3 umbilical vessels may be observed. Fusion sites include the thorax (thoracopagus), abdomen (omphalopagus), pelvis (ischiopagus), sacrum (pygopagus), or skull (craniopagus). Extensive zones of fusion may be named by the prefix di- (meaning 2), followed by the portion of the twins that is unfused. Examples include dicephalus (2 heads on one body), and dipygus (double buttocks; single head and torso with separate pelves and 4 legs). Serial scans may be required to monitor for hydrops. Prenatal echocardiography has better yield than postnatal echocardiography in thoracopagus twins, because surface scanning may be difficult. MRI of the brain is performed along with magnetic resonance angiography and magnetic resonance venography to delineate structures and blood supply in the craniopagus variety. Radionuclide angiography is performed to calculate the extent of cross-circulation. Selective angiography is usually not necessary in twins with a shared liver. Sonography allows for a complete anatomic examination and search for associated lethal malformations. A detailed ultrasound examination to exclude the possibility of conjoined twins is mandatory in all multiple pregnancies. Two-dimensional ultrasonography is instrumental in prenatally diagnosing conjoined twins, but precise classification is difficult because of 3-dimensional structures. Three-dimensional ultrasound has shown promise in improving the visualization of complex anatomic spatial relationships. Abdominal ultrasonography is performed to determine how many gallbladders are present (1 or 2) and to determine the polarity of the liver and pancreas if these organs are also conjoined. Often, however, this determination may not be precise. Advantages of sonography include the following: Images other structures (eg, aorta, pancreas, liver) Identifies complications (eg, stenosis, obstruction) Can be rapidly performed at the bedside Does not involve radiation (important in pregnancy) Disadvantages of sonography include the following: Dependent on the type and extent of fusion, as well as the operator's abilities Inability to image the ductal system proximal to the common bile duct Decreased sensitivity for the site and extent of duplication or fusion compared with CT scanning or MRI. Fetal MRI can identify shared anatomy of twins with precise detail. However, this test is not 100% accurate. CT scanning has been used in some studies.However, the yield for complex anatomy is lower than that obtained from MRI. CT scanning may be helpful in shared bony pelvis and shared pelvic perineal muscles. Contrast studies are performed to evaluate the extent of GI (see the image below), genitourinary, and reproductive system fusions.Esophagram showing union at the level of stomach. Diisopropyl iminodiacetic acid (DISIDA) scanning is a nuclear medicine study performed to visualize the biliary tract. Technetium-labeled analogue of DISIDA is administered intravenously (IV) and is secreted by hepatocytes into bile, enabling visualization of the gall bladder and biliary tree in 30 minutes.Other TestsSee the list below: On ECG, a single QRS indicates that cardiac separation is not possible. However, the presence of 2 separate patterns does not guarantee a successful separation. EEG may be performed to evaluate baseline brain activity in craniopagus twins.Diagnostic ProceduresSee the list below: Cardiac catheterization is performed to determine the nature of complex cardiac anomalies. An accurate estimation of all major inflow and outflow vessels should be made.http://emedicine.medscape.com/article/934680-workup#showall