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 Table of Contents  
Year : 2020  |  Volume : 25  |  Issue : 2  |  Page : 116-118

Siamese twins: Thoracopagus – A rare congenital anomaly

1 Department of Obstetrics and Gynecology, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India
2 Department of Radiodiagnosis, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India

Date of Submission07-Nov-2017
Date of Acceptance24-Feb-2020
Date of Web Publication15-Dec-2020

Correspondence Address:
Dr. Mohd Ilyas
Department of Radiodiagnosis, Sher-i-Kashmir Institute of Medical Sciences, Srinagar - 190 011, Jammu and Kashmir
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmgims.jmgims_60_17

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A case report of conjoined twins (thoracopagus-conjoined neck, thorax, and upper abdomen) diagnosed by routine ultrasonography in a 26-year-old G2 P1 pregnant female at 19 weeks of gestation is discussed. The pregnancy was terminated at this gestation with explained prognosis to the patient and consent of the family.

Keywords: Siamese twins, thoracopagus, ultrasonography

How to cite this article:
Khan I, Ilyas M, Shah SA, Saldanha CL. Siamese twins: Thoracopagus – A rare congenital anomaly. J Mahatma Gandhi Inst Med Sci 2020;25:116-8

How to cite this URL:
Khan I, Ilyas M, Shah SA, Saldanha CL. Siamese twins: Thoracopagus – A rare congenital anomaly. J Mahatma Gandhi Inst Med Sci [serial online] 2020 [cited 2023 Jun 4];25:116-8. Available from: https://www.jmgims.co.in/text.asp?2020/25/2/116/303423

  Introduction Top

Conjoined twins represent one of the rarest forms of twin gestation. They occur in roughly 1 in 200 identical twin pregnancies. The incidence ranges from 1 in 50,000 to 1 in 100,000 live births.[1] If the twinning is initiated after the embryonic disc and amniotic sac have formed and if the division of the embryonic disc is complete, conjoined twins result.[2]

  Case Report Top

A 26-year-old G2 P1 pregnant female with last childbirth as a full-term normal vaginal delivery female baby, with 5 month amenorrhea was referred to the radiology department for routine ultrasonography (USG) and to rule out any gross congenital anomalies. She had no previous ultrasound records. USG was performed using Logic-200 (GE-Healthcare). USG revealed two fetuses with two arms, two legs, and one head each [Figure 1]. The twins were joined at the neck, thorax, and upper abdomen with one umbilical cord and single fetal heart [Figure 2]. A single anterior wall upper segment placenta was seen. The biparietal diameters and femur lengths revealed the average gestational age of 19 weeks. The diagnosis of Siamese twin of the type thoracopagus was formulated and referred back to the Department of Gynecology and Obstetrics. After explaining the prognosis to the mother and family, the pregnancy was terminated by Cesarian section and findings confirmed postdelivery [Figure 2].
Figure 1: Cross-section of the ultrasound imaging showing the fused neck region and basal parts of the two fetal heads

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Figure 2: Immediate postdelivery photograph demonstrating fused neck, thorax, and upper abdomen of the conjoined twin, thus confirming the ultrasonography findings

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  Discussion Top

The Conjoined twins are classified according to the most prominent site of conjunction: thorax (thoracopagus), abdomen (omphalopagus), sacrum (pyopagus), pelvis (ischiopagus), skull (cephalopagus), and back (rachipagus). Depending on the aspect of embryonic disc, the most common type is thoracopagus (19%).[3]

The condition is more commonly found in females, with a ratio of 3:1 (female: male).[4] Two theories have been proposed to explain this observation: the process of X-inactivation overlaps with the timing of monozygotic twinning and thus may directly contribute to the development of monozygotic twins, and the XX karyotype may confer a survival benefit.[5]

Two contradicting theories exist to explain the origin of conjoined twins. The traditional theory is fission in which the fertilized egg splits partially, and conjoined twins represent delayed separation of the embryonic mass after day 12 of fertilization. The second theory is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together.[6],[7]

Early diagnosis of conjoined twins was previously reported, but not before the 10th week of gestation.[8] Once conjoined twins have been diagnosed, the characterization of the type and severity of the abnormality can be performed with ultrasound, computed tomography, or magnetic resonance imaging (MRI).[9],[10] In our case, the prognosis was explained to the family, and since the family chose to terminate the pregnancy, no further diagnostic intervention was considered. Surgery to separate conjoined twins may range from relatively simple to extremely complex, depending on the point of attachment and the internal parts that are shared. Most cases of separation are extremely risky and life threatening. Ultrasound enables an early and accurate diagnosis of conjoined twins, which is vital for the obstetric management. MRI is reserved for better tissue characterization.[11]

  Conclusion Top

Conjoined twins are a rare type of congenital anomaly with a high degree of perinatal mortality. The thoracopagus is the most common type. Early diagnosis by ultrasound is beneficial for the patient which gives parents a chance for the termination of pregnancy and avoids late complications.

Learning points

  1. Thoracopagus involves fusion of the thorax and upper abdomen, also called Type A conjoined twins
  2. Accurate and early prenatal diagnosis is necessary for the proper management of the patient and to prevent the complications to the mother if a delay in diagnosis occurs
  3. The ultrasound is one of the easily available and accurate methods for the diagnosis prenatally after 10 weeks of gestation as it helps in the diagnosis as well as characterization and to assess the severity of the malformation, although MRI remains the investigation of choice
  4. Although Cesarian section is indicated in cases detected after 24 weeks, if a complicated case is there or if the patient requests, it should be performed for the convenience of the patient
  5. Since the separation postdelivery is very risky and extremely life threatening to the patient, it is better to terminate the pregnancy once diagnosed
  6. The later the diagnosis is made, the more are the chances of complications to the mother.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initial will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Rees AE, Vujanic GM, Williams WM. Epidemic of conjoined twins in Cardiff. Br J Obstet Gynaecol 1993;100:388-91.  Back to cited text no. 1
Cunningham FG, MacDonald PC, Gant NF. Williams Obstetrics. 21st ed. New York: McGraw-Hill; 2003.  Back to cited text no. 2
Schnaufer L. Conjoined twins. In: Raffensperger JG, editor. Swenson's Pediatric Surgery. 4th ed. New York, NY, USA: Appleton Century-Crofts; 1980. p. 910-20.  Back to cited text no. 3
Abossolo T, Dancoisne P, Tuaillon J, Orvain E, Sommer JC, Rivière JP. Early prenatal diagnosis of asymmetric cephalothoracopagus twins. J Gynecol Obstet Biol Reprod (Paris) 1994;23:79-84.  Back to cited text no. 4
Chitnis S, Derom C, Vlietinck R, Derom R, Monteiro J, Gregersen PK. X chromosome-inactivation patterns confirm the late timing of monoamniotic-MZ twinning. Am J Hum Genet 1999;65:570-1.  Back to cited text no. 5
Spencer R. Theoretical and analytical embryology of conjoined twins: Part I: Embryogenesis. Clin Anat 2000;13:36-53.  Back to cited text no. 6
Spencer R. Theoretical and analytical embryology of conjoined twins: Part II: Adjustments to union. Clin Anat 2000;13:97-120.  Back to cited text no. 7
Hubinont C, Kollmann P, Malvaux V, Donnez J, Bernard P. First-trimester diagnosis of conjoined twins. Fetal Diagn Ther 1997;12:185-7.  Back to cited text no. 8
Kuroda K, Kamei Y, Kozuma S, Kikuchi A, Fujii T, Unno N, et al. Prenatal evaluation of cephalopagus conjoined twins by means of three-dimensional ultrasound at 13 weeks of pregnancy. Ultrasound Obstet Gynecol 2000;16:264-6.  Back to cited text no. 9
Kingston CA, McHugh K, Kumaradevan J, Kiely EM, Spitz L. Imaging in the preoperative assessment of conjoined twins. Radiographics 2001;21:1187-208.  Back to cited text no. 10
Mathew RP, Francis S, Basti RS, Suresh HB, Rajarathnam A, Cunha PD, et al. Conjoined twins – Role of imaging and recent advances. J Ultrason 2017;17:259-66.  Back to cited text no. 11


  [Figure 1], [Figure 2]


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