MESH Twins; conjoint BDE 0202 MIM 27641 ICD9 759.4 CDC 759.430

Address correspondence to Cheryl Norris, BS, Vanderbilt University Medical Center, Department of Radiology, 21^st and Garland Avenue, Nashville, TN 37232-2675. Ph: 615-322-0888, Fax 615-343-4890. ¶Phoenix Perinatal Associates, Phoenix, AZ. §Arizona Pediatric Heart Specialists, #Pathology Consultants, Wichita, KS, ¤Womens Health, Wichita, KS.

Introduction

Conjoined twinning is a rare anomaly, occurring in 0.2:10,000 births^3,21, with 75% occurring in females¹. Thoraco-omphalopagus occurs most frequently, and the prognosis is generally poor¹⁸. Conjoined twins are derived from a single ovum and therefore have the same genetic and chromosomal constitution. We present a second trimester ultrasound diagnosis of thoraco-omphalopagus twins.

Case report

A 22-year-old woman G₂P₀₀₁₀ was referred for ultrasound evaluation at 22 weeks gestation for suspected conjoined twins. The patient was not exposed to any medications or any possible teratogenic exposures, and her personal and family history were unremarkable. The ultrasound revealed a live, thoraco-omphalopagus twin gestation with moderate polyhydramnios without fetal gastrointestinal obstruction. Both twins were in breech presentation. Heads, spines, and extremities appeared normal on both twins. The abdominal walls were fused but otherwise normal, and the external genitalia were female. The liver was shared but the stomachs (fig. 1) and bladders separated. The abnormal heart was shared, and the patient was referred for a fetal cardiac evaluation (fig 2-4). A single umbilical cord contained one vein and three arteries (fig. 5).

Figure 1: Section at the level of the stomachs demonstrating correct position.

Figure 2: Ultrasound image of conjoined thorax.

Figure 3: View of the conjoined heart. The hypoplastic right heart of the left twin is seen (HRV), as well as the intercardiac communication (arrow), the left ventricles (LV) and the dextropositioned apex of the heart of the right fetus (A).

Figure 4: View of the common atrium (CA) and ascending aorta of the left fetus.

Figure 5: Four-vessel cord containing one vein and three arteries.

The echocardiogram demonstrated extensive cardiac fusion at both the atrial and ventricular levels. The right-sided twin had the morphology of tricuspid atresia and the left-sided twin had a morphology of a double outlet single ventricle. There were large communications between the atria and ventricles of the two twins, and the ventricular mass was a single muscular mass. The single cardiac rhythm was shared between the two hearts. All the inferior vena cava and hepatic venous return came to the right-sided twin"s heart.

The patient was counseled about therapeutic options, including expectant management and surgical or medical abortion. Since the ventricles were shared, the twins were considered unseparable^21,22. The patient opted for termination of the pregnancy.

Premature delivery of a stillborn was the method of termination of pregnancy selected by the patient. The outpatient procedure included mechanical dilatation of the cervix, repeated insertion of osmotic dilators, and the application of intrafetal digoxin. Twilight anesthesia was employed for the delivery, and a quadruple footling breech technique was used after one and a half hours of labor. No maternal lacerations or complications were experienced.

Autopsy

The autopsy revealed the bodies of female twins facing each other, weighing a total of 939g and joined at the thorax and upper abdomen (fig. 6-7).

Figure 6: The X-ray of the twins

Figure 7: The conjoined twins at delivery.

There was a common umbilical cord, with two umbilical arteries from fetus #1, and right umbilical artery from fetus #2, and a single umbilical vein. There were conjoined livers, with both hepatic veins joining inferior vena cava of fetus #1. There were common thoracic, pericardial and abdominal cavities. The heads appeared normal as well as ears, noses, lips and palates. The mouths and tongues were of normal size, and the chins and necks appeared normal as well. The following organs and systems were separate: neck organs, respiratory tracts and lungs, thymus, gastrointestinal tracts, pancreas, spleens, adrenal glands, kidneys and urinary tracts, and internal genitalia. The gastrointestinal tract was dextrorotated and of normal caliber. The backs were both mildly scoliotic but had no visible or palpable defects.

The complex malformation of conjoined cardiovascular system is reported in Table 1 and figure 8.

Figure 8: Schematic drawing of the flow and anatomy of the conjoined heart.

Table 1: Heart and great vessel findings at autopsy:

Right-sided fetus (#1)	Left-sided fetus (#2)
1 left superior vena cava	1 entrance of inferior vena cava into right atrium of fetus #1 after coursing through diaphragm adjacent to aorta and across thoracic cavity
1 entrance of inferior venae cavae of both fetuses into right atrium	1 small smooth-walled right atrium with absent appendage, receiving only superior vena cava
1 long, predominantly smooth-walled right atrium with absent appendage	1 tricuspid valve atresia
1 right atrial communication with right atrium of fetus #2	1 absence of interatrial foramen
1 tricuspid valve atresia	1 right atrial communication with right atrium of fetus #1
1 absence of atrial septum	1 rudimentary right ventricle
1 ventricular septal defect, membranous	1 truncus arteriosus Type I
1 hypoplastic right ventricle	1 pulmonary artery stenosis
1 pulmonary stenosis	1 left ventricular communication with left ventricle of fetus #1
1 left ventricular communication with left ventricle of fetus #2	1 ductus arteriosus not identified
1 small ductus arteriosus
1 relative hypoplasia of lungs of fetus #1: combined weight 9.35g, compared to 12.15g for lungs of fetus #2

Discussion

History

The earliest record of conjoined twins is that of the Biddenden maids born in 1100 CE, in England, who were united from the hips to the shoulders with only one pair of shared upper and lower extremities and lived to the age of 34³¹. The most famous ones are the "siamese twins" Chang and Eng Bunker, who were xiphopagus twins exhibited worldwide and died at the age of 63¹³. They were born in 1811 in Siam (now Thailand). The twins married sisters and fathered 21 children¹². The first report of successful antenatal diagnosis by ultrasonography was reported in 1977²⁶. The earliest reported diagnosis of the presence of thoracopagus twins has been possible at the 13^th week of gestation⁵. The history of surgical separation dates to the 15^th century, and the first successful separation of conjoined twins, with both twins surviving, was recorded in 1689. The first successful operation for thoraco-omphalopagus, with at least one twin surviving, was done in 1900⁴.

Ultrasound diagnosis

Until the 1950s, the diagnosis of conjoined twins was only made at delivery, generally because of dystocia¹⁸. In 1950, Gray et al. ²⁹ described four signs seen on plain radiographs that suggested the presence of thoraco-omphalopagus:

• both heads at the same level and in the same plane,

• two hyperextended spines,

• both heads and spines abnormally close to each other, and

• constant relationship regardless of active movements and external attempts at moving the twins.

In the past, conjoined twins were only occasionally suspected prenatally by means of radiographic studies, whereas at present, the diagnosis is usually made by ultrasound¹³ by visualizing regions of anatomic fusion between the twins. In the absence of clearcut signs of fusion, additional sonographic findings summarized by Koontz et al include²⁴:

• the lack of a separating membrane,

• inability to separate the fetal bodies,

• detection of other anomalies in a twin gestation,

• more than three vessels present in the umbilical cord,

• both fetal heads persistently at the same level,

• backward flexion of the cervical and upper thoracic spine, and

• no change in the relative positions of the fetuses despite attempts at manual manipulation of the twins²⁴.

The bifid appearance of the first-trimester fetal pole should be added to the list of sonographic features of conjoined twins. The diagnosis of conjoined twins is usually clear, but several pitfalls should be avoided. Inseparable skin contact sites must be persistent, and at symmetric body zones, to avoid a false-positive diagnosis. A relatively small zone of fusion may be pliable and permit the twins to rotate as much as 180° , so that a vertex-breech presentation does not necessarily exclude conjoined twinning. With a vertex-vertex presentation, engagement of one head within the pelvis may alter the apparent symmetry, thwarting diagnosis. With extreme degrees of fusion, the twins may be mistaken for a singleton³³. Sonography allows a complete anatomical examination and search for associated lethal malformations. A detailed ultrasound examination to exclude the possibility of conjoined twins is mandatory in all multiple pregnancies.

Embryology

Conjoined twins are monozygotic, monochorionic twins. It is believed that the malformation occurs soon after the blastula stage (fig. 7594-7-8, p7594-7). At this stage of development, between the 13^th and 15^th days after fertilization, the inner cell mass is split into equal halves, each capable of forming a normal individual. In conjoined twins, complete separation of the inner cell mass within the chorionic mass does not occur, and nonseparated parts of the otherwise normal twins remain fused throughout development⁴. When the failed separation occurs later (heteropagus twin), one of the twins is incomplete and attached to the more normal twin (autosite). If the separation is further delayed, then an infant with only duplication of one region is formed: a duplicata incompleta.

Pathogenesis

Conjoined twinning is classified by the most prominent site of connection, plus the Greek root pagoz: ice, and, by extension "frozen in place". Such sites include the thorax (thoracopagus), abdomen (omphalopagus), pelvis (ischiopagus), sacrum (pyopagus) or skull (craniopagus). Very extensive zones of fusion may be named by the prefix di- (meaning two), followed by the portion of the twins that is unfused. Examples include dicephalus (two heads on one body), and dipygus (single head and torso with separated pelves and four legs). Asymmetric forms, termed heteropagus, are exceedingly rare and have a parasitic attachment of a variably sized portion of anatomy appended to or even within any region of the body³³. The types and frequency of conjoined twins, as well as the organs shared, are illustrated in Table 2³⁰. Thoracopagus is the most common, accounting for 40%³⁰. Some authors group thoracopagus and omphalopagus as thoraco-omphalopagus, therefor accounting for 74%.

Table 2: Type and frequency of anomalies

Type	Incidence	Organs shared
Thoracopagus	40%	Heart, liver, GI
Omphalopagus	34%	Liver, GI
Pygopagus	18%	Spine, GU, lower GI
Ischiopagus	6%	Pelvis, GU, GI, liver
Craniopagus	2%	Brain

Associated anomalies

Conjoined twins, in most cases, have more malformations than separate monozygotic twins. The malformations occurring in conjoined twins are often more severe and major. Some of the malformations are related to the junction regions, but others are distant from the junctional sites and not related to the twinning process itself². Neural tube defects, orofacial clefts, imperforate anus, and diaphragmatic hernia are the most common defects not associated with fusion¹. Congenital heart disease is found in 75% of patients. In 90%, there is some degree of fusion of the pericardial sac. The most frequent abnormality is a conjoined heart, with two ventricles and a varying number of atria (1 to 4). Ventricular septal defects are found in virtually all patients with other ventricular deformities¹.

Nichols et al. ⁴² presented a comprehensive review on the findings in 45 sets of thoraco-omphalopagus twins. The cardiovascular findings were as follows: in 75% of thoraco-omphalopagus twins the hearts are conjoined, and in 90% the pericardium is common. In all except one case, the ventricles intercommunicated. The ventricular structure of the 45 sets of thoraco-omphalopagus twins is described in figure 9²⁹.

It was common, as in our case, that specific cardiac malformations were present in each twin. These anomalies included failure of the pulmonary artery to form or failure of development of the ventricular septum.

Nichols et al. report that a conjoined liver was present in each, a conjoined biliary tract in 22%, and conjoined gastrointestinal tract in 46%. A single umbilicus, as in our case, is usual, as is fusion of the sternum.

Figure 9: Cardiac ventricular structure in a series of 45 thoracopagus twins. The four possibilities are: one ventricle shared by both twins, two ventricles (a single ventricle for each twin), three ventricles (one for one twin and two for the other), and four ventricles (two for each twin).

Prognosis

Thirty-nine percent of conjoined twins are stillborn, and 34% die within the first day of life¹. Survival depends upon the type of conjunction and the presence of associated anomalies. In thoraco-omphalopagus, the degree of fusion of the heart determines the prognosis. When a common heart is present, the chances for a successful surgical separation are negligible (see Treatment).

Management

After the diagnosis of conjoined twins, timing and mode of delivery should be planned on the basis of possibility of survival, size, nature of the fusion, and parental wishes²⁷. Early diagnosis by ultrasound allows elective pregnancy termination. After viability, serial examinations are indicated to monitor fetal growth and the development of hydrops, and to detect fetal demise. Scheduled delivery in a tertiary care center is ideal so that procedures required to evaluate the twins can be carried out shortly after birth. The method of delivery depends upon the prenatal assessment of the likelihood of survival. Cesarean section is recommended in most third-trimester deliveries because of the high incidence of dystocia and resultant fetal damage¹². Vaginal delivery should be reserved for stillbirths and for forms of conjoined twins that are incompatible with life. There may also be a risk of birth canal trauma with large conjoined twins and destructive fetal procedures may be performed to deliver vaginally. After birth, evaluation of both twins should be conducted to assess the extent of organ system sharing.

Treatment

Options for the treatment of thoraco-omphalopagus conjoined twins are largely dependent on the anatomy of the cardiovascular system. Separation of the liver and gastrointestinal tracts can be managed readily in most cases. The number and nature of the hearts, and the presence of any vasculature intercommunications, are of particular importance if surgical separation is to be considered in conjoined twins¹⁹. Seo et al. has introduced a new classification of the cardiovascular system in conjoined twins¹⁵. The classification has 5 types and is based on the degree of fusion and the symmetry of the hearts and great vessels (see table 2). Types I and II are easily separable. Separation of hearts with interatrial fusion (Type IIIa and IIIb) may be possible, and the analysis of the conduction system of the cases is important. The heart with atrioventricular fusion (Type IV) and the single hearts (Type V) are inoperable¹⁵.

Hershlag et al. separated the cardiac findings into a simpler three category system: 1) pericardial union only; 2) atrial connection; and 3) ventricular connection, usually associated with multiple cardiac defects. Separation of twins with pericardial and atria union is feasible, while cases with ventricular communication are inoperable¹⁰ (Table 3).

Table 3: The Seo (top) and Herslag (bottom) classifications of conjoined hearts and their surgical separability

Type	Degree of fusion	Separability
I	No significant fusion	Easy
II	Fusion of the great vessels	Easy
III IIIa IIIb	Atrial fusion Mirror image right atrial fusion Other type of atrial fusion	Possible Possible Possible
IV	Atrioventricular fusion	Not possible
V	Single heart in one of the twins	Not possible

 

Type	Degree of fusion	Separability
I	Pericardial union only	Easy
II	Atrial connection	Possible
III	Ventricular connection	Not possible

Before 1975, the perioperative mortality rate for thoraco-omphalopagus twins was 55.6%. Between 1975 and 1979, the perioperative mortality rate was essentially unchanged at 58.3%; however, from 1980 to 1987, it decreased to 26%, a 32% decrease⁴. The current outcomes, even in difficult cases of conjoined twinning, suggest that separation should be considered. Delay of surgical separation is preferred to allow time for adequate diagnostic studies of the major organ systems and maturation of lungs, liver, and soft tissues. Separation is best delayed until infants are relatively mature (6-12 months of age). Operative survival was 50% in those operated on in the neonatal period, but 90% in those over 4 months of age⁹. Earlier surgical intervention may, however, be necessitated by ruptured omphalocele, intestinal obstruction, or deterioration of one or both twins.

References

1. Romero R, Pilu G, Jeanty P, et al.: Prenatal diagnosis of congenital anomalies. CT, Appleton & Lange, 403-408, Norwalk, 1988.

2. Jaffe R, Porterfield C, Gould N: Conjoined twins, structural anomalies. The Fetus 2:7594-5, 1992.

3. McCurdy C, Magann E, Nolan T: Twins, conjoined, omphalopagus. The Fetus 2:7954-1, 1992.

4. Hoyle RM: Surgical separation of conjoined twins. Surg Obstet Gynecol 170:549, 1990.

5. Maggio M, Callan NA, Hamod KA, et al.: The first-trimester ultrasonic diagnosis of conjoined twins. Am J Obstet Gynecol 152:833, 1985.

6. Turner RJ, Hankins GD, Weinreb JC, et al.: Magnetic resonance imaging and ultrasonography in the antenatal evaluation of conjoined twins. Am J Obstet Gynecol 155:645-9, 1986.

7. Hoshina H, Tanaka O, Obara H, et al.: Thoraco-omphalopagus conjoined twins: Management of anesthetic induction and postoperative chest wall defect. Anesthesiology 66:424-6, 1987.

8. Zubowiez VN, Ricketts R: Use of skin expansion in separation of conjoined twins. Annal Plast Surg 20:272-6, 1988.

9. ONeill JA Jr., Holcomb EW III. Schnaufer L, et al.: Surgical experience with thirteen conjoined twins. Annal Surg 208:299-312, 1988.

10. Hershlag A, Vinograd I, Nissan S, et al.: Cardiac assessment by first-pass angioscintigraphy in conjoined thoraco-omphalopagus twins. Eur J Nucl Med 10:84-5, 1985.

11. Grutter F, Marguerat P, Maillard-Brignon C, et al.: Thoraco-omphalopagus fetus. Ultrasonic diagnosis at 16 weeks. Journal de Gynecologie, Obstetrique et Biologie de la Reproduction 18:355-9, 1989.

12. Kalchbrenner M, Weiner S, Templeton J, et al.: Prenatal ultrasound diagnosis of thoraco-omphalopagus conjoined twins. JCU 15:59-63, 1987.

13. Quiroz VH, Sepulveda WH, Mercado M, et al.: Prenatal ultrasonographic diagnosis of thoraco-omphalopagus conjoined twins. J Perinatal Med 17: 297-303, 1989.

14. Rosa FW, Hernandez C, Carlo WA: Griseofulvin teratology, including two thoraco-omphalopagus conjoined twins. Lancet 1(8525):171, 1987.

15. Seo JW, Shin SS, Chi JG: Cardiovascular system in conjoined twins: An analysis of 14 Korean cases. Teratoloty 32:151-61, 1985.

16. Munayer Calderon JE, Acosta Valdez JL, Salgado Escobar JL, et al.: Hemodynamic and angiocardiographic assessment of thoraco-omphalopagus twins for surgical separation purposes. Archivos del Instituto de cardiologic de Mexico 61:257-9, 1991.

17. Karsdorp VH, van der Linden JC, Sobotka-Plojhar MA, et al.: Ultrasonographic prenatal diagnosis of conjoined thoraco-omphalopagus twins: A case report. Eur J Obstet Gynecol Reprod Biol 39:157-61, 1991.

18. Plattner V, Heloury Y, Cohen JY, Nomballais MF, et al.: Anatomical study of five prenataly diagnosed sternopagus twins. Surg Radiol Anat 15:35-9, 1993.

19. Gerlis LM, Seo JW, Ho SY, et al.: Morphology of the cardiovascular system in conjoined twins: Spatial and sequential segmental arrangements in 36 cases. Teratology 47:91-108, 1993.

20. Berman W Jr., Joehl R, Whitman V, et al.: Triventricular heart with three atrioventricular valves in a conjoined twin. Arch Pathol Lab Med 102:414-7, 1978.

21. Ornoy A, Navot D, Menashi M, et al.: Asymmetry and discordance for congenital anomalies in conjoined twins: A report of six cases. Teratology 22:145-54, 1980.

22. Tandon R, Sterns LP, Jesse E, et al.: Thoraco-omphalopagus twins: Report of a case. Arch Pathol 98:248, 1974.

23. Micheli JL, Sadeghi J, Freeman C, et al.: An attempt to separate xiphogapus twins sharing a common heart, liver, and duodenum. J Pediat Surg 13:139, 1978.

24. Koontz WL, Herbert WN, Seeds JW, et al.: Ultrasonography in the antepartum diagnosis of conjoined twins: A report of two cases. J Reprod Med 28:627, 1983.

25. Schmidt W, Herberling D, Kubli F: Antepartum ultrasonic diangosis of conjoined twins in early pregnancy. Am J Obstet Gynecol 139:961, 1981.

26. Wilson RL, Shaub MS, Cetrulo CJ: The antepartum finding of conjoined twins. JCU 5:35-37, 1977.

27. Vaughn TC, Powell LC: Obstetric management of conjoined twins. Obstet Gynecol 53:675, 1979.

28. Nichols BL, Blattner RJ, Rudolph AJ: General clinical management of thoraco-omphalopagus twins, in Bergsma D (ed): Conjoined Twins. Birth defects original article series, New York, National Foundation March of Dimes, 3: 38-51, 1967.

29. Gray CM, Nix HG, Wallas AJ: Thoraco-omphalopagus twins: Prenatal diagnosis. Radiology 54:398, 1950.

30. Nyberg DA, Mahonby BS, Pretorius DH: Diagnostic ultrasound of fetal anomalies: Text and atlas. Year Book Medical Publishers p661, Chicago, 1990.

31. Gould GM, Pyle WL: Anomalies and curiosities of medicine. W.B. Saunders p 174-190, 1896.

32. Buyse ML: Birth Defects Encyclopedia. Blackwell Scientific Publications p1719, Cambridge, MA, 1990.

33. Finberg HJ: Ultrasound evaluation in multiple gestation. Chapter 8 in Callen PW: Ultrasonography in obstetrics and gynecology. W.B. Saunders Company Philadelphia p121, 1994.