Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 
  • Users Online: 463
  • Home
  • Print this page
  • Email this page
Cover page of the Journal of Health Sciences

 Table of Contents  
Year : 2017  |  Volume : 10  |  Issue : 1  |  Page : 90-93

Twin reversed arterial perfusion sequence/syndrome - An insight into the ultrasonographic features for prenatal diagnosis and review of literature with obstetric importance: Case series of two reports

Department of Radiodiagnosis and Imaging, Government Medical College, SMGS Hospital, Jammu, Jammu and Kashmir, India

Date of Web Publication18-Jan-2017

Correspondence Address:
Dr. Mohd Ilyas
House No. 38 Lane No. 22, Tawi Vihar Sidhra, Jammu - 180 019, Jammu and Kashmir
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2349-5006.198597

Rights and Permissions

We present two case reports of twin reversed arterial perfusion sequence - a rare type of twin-twin transfusion syndrome, wherein there maldevelopment of one twin and is supplied by the normal twin. Then, we discuss the importance of this entity and various measures required if such a situation is encountered.

Keywords: Acardiac, acephalus, embolization, ligation, twin, twin-reversed arterial perfusion sequence/syndrome

How to cite this article:
Ilyas M, Bhat A. Twin reversed arterial perfusion sequence/syndrome - An insight into the ultrasonographic features for prenatal diagnosis and review of literature with obstetric importance: Case series of two reports. Indian J Health Sci Biomed Res 2017;10:90-3

How to cite this URL:
Ilyas M, Bhat A. Twin reversed arterial perfusion sequence/syndrome - An insight into the ultrasonographic features for prenatal diagnosis and review of literature with obstetric importance: Case series of two reports. Indian J Health Sci Biomed Res [serial online] 2017 [cited 2020 Jun 4];10:90-3. Available from: http://www.ijournalhs.org/text.asp?2017/10/1/90/198597

  Introduction Top

 "Tein Reversed Arterial Perfusion (TRAP)" wherein there is simultaneous presence of a normal (pump) fetus and an acardiac (perfuse) fetus. Although acardiac monsters have been known since 1533 when the condition was first described by Benedetti, appropriate definition was first provided by Grunewald in 1942. TRAP syndrome is a rare obstetric condition unique to monozygotic monochorionic twin pregnancies, in which there is the coexistence of a normal pump (donor) fetus and an acardiac recipient (perfuse) fetus.[1] The incidence of TRAP syndrome is 1 in 35,000 pregnancies, 1 in 100 monozygotic monochorionic twin gestation, and 1 in 30 monochorionic triplet gestation.[2] Most cases are seen in twins with only 8% in triplets.[3] The risk in multiple pregnancies of a higher order is even greater.[4] The acardiac fetus or chorangiopagus parasiticus or TRAP syndrome is one of the forms of twin to twin transfusion. Diagnosis is necessary for proper prenatal management and can be established by ultrasonography (USG) and color Doppler examination of the umbilical artery of abnormal twin.

  Case Reports Top

Case 1

A 30-year-old primigravida female patient presented to our department for the second trimester anomaly scan. Her blood parameters were within normal range. USG with color Doppler study was performed. The study revealed a live fetus with biparietal diameter and femoral length corresponding to gestational age of 19 weeks, 2 days and another heterogeneous mass lesion in the amniotic cavity. On careful examination, the mass lesion was seen connected to normal fetus through umbilical artery. Further examination revealed the mass to be fetal liver and gut loops surrounded by membranes with absent upper torso, i.e., fetal head, thorax, and upper limbs [Figure 1]a. Color Doppler study revealed high pulsatility index of the involved umbilical arteries [Figure 1]b and c. Single anterior wall placenta was visualized. The diagnosis of twin pregnancy with one normal fetus and other acardiac acephalic twin was made with a demonstration of TRAP sequence on color Doppler was given and patient to obstetrics for further management.
Figure 1: (a) Longitudinal ultrasonography showing the heart of pump twin and heterogeneous mass on the side (perfuse twin) without head and upper torso. (b) Color/pulsed Doppler waveform of umbilical artery of normal twin. (c) Color/pulsed Doppler waveform of umbilical artery of perfuse twin

Click here to view

Case 2

Another patient came to our department within a gap of 1 month for anomaly scan in the second trimester. USG with color Doppler was performed [Videos 1 and 2]. The study revealed one normal fetus with anomaly detected with another twin appearing as a heterogeneous mass comprising liver and gut loops without heart getting blood supply from the normal twin. Single anterior wall placenta was visualized. Color Doppler study revealed high PI and RI of the umbilical arteries and absent head, thorax of the acardiac twin [Figure 2]a and b. The diagnosis of twin pregnancy with TRAP was given and patient referred to obstetrics for further management.
Figure 2: (a and b) Ultrasonography demonstration of acardiac heterogeneous twin and normal twin with normal heart and the connection between two on color Doppler study

Click here to view

  Discussion Top

TRAP syndrome occurs in monochorionic gestation form, in which case one twin has acardia (the recipient) with no heart and the other is structurally normal (pump or donor twin). Due to the absence of heart, in the acardia twin, the pump twin supplies deoxygenated blood through vascular anastomoses to the cardiac twin. Acardiac twin does not send blood to placenta and all its blood comes from and goes back to the circulation of the pump twin, through the vascular connections on the surface of shared placenta. Therefore, it is structurally normal twin perfusing an anomalous recipient twin through an artery to artery anastomoses in a reverse direction. The reversed flow is through its umbilical artery and exits through umbilical vein, which is opposite to the normal fetal blood supply. The acardiac twin is usually grossly abnormal. The mortality of the pump twin is 50%-75% due to the result of heart failure (may be due to polyhydramnios or excessive cardiac load) and of the acardiac twin is 100%.

The upper half of the body of an acardiac twin is extremely poorly developed and sometimes not developed at all. Head, cervical spine, and upper limbs are usually absent. In contrast, the lower half of the body, although malformed, is better developed. Therefore, on USG, it appears as a heterogeneous mass simulating a teratoma or intrauterine fetal demise.[5]

The classification of the acardiac twin is according to the degree of cephalic and truncal maldevelopment.[6] Various types are:

  1. Acardius acephalus - No cephalic structure present (head and upper extremities lacking). This is the most common type
  2. Acardius anceps - Some cranial structures and neural tissue/brain tissue are present. The body and extremities are also developed. It is highly developed form
  3. Acardius acormus - Cephalic structure present but no truncal structures seen (head without a body). Umbilical cord is attached directly to the head. It is the rarest type of acardia
  4. Acardia amorphous - No distinguishable cephalic or truncal structure. It is the least developed and not recognizable as human form with minimal development. This differs from teratomas only by its attachment to an umbilical cord.

Another classification of acardiac twinning is as follows:

  1. Hemiacardius: If the heart is incompletely formed
  2. Holoacardius: If the heart is absent.

The TRAP sequence is explained by the two main hypotheses:

  1. Deep placental anastomoses in early embryogenesis cause malformation of the acardiac twin. The early pressure flow in one twin exceeds that of other and leads to reversed circulation in the twin who exhibits perfusion
  2. A primary defect in embryogenesis in one twin leads to failure of cardiac development. The normal twin perfuses the acardiac twin through artery to artery anastomoses. The anastomoses are not responsible for the cardiac anomaly.[7]

Congenital anomalies are present in about 9% of pump twins.[2] Most commonly associated are VACTREL anomalies. When the ratio of the weight of the acardiac fetus to the weight of the donor fetus is more than 70%, the incidence of preterm delivery is 90% that of polyhydramnios is 40%, and that of congestive heart failure in the pump twin is 30%, in comparison, the corresponding rates are 75%, 30%, and 10%, respectively, when the ratio is <70%.[2] The weight of the acardiac twin cannot be measured by routine parameters and is calculated by the following formula:

(1.2 × longest length2 ) – (1.7 × longest length).[8]

Prenatal diagnosis is done using Gray-scale and color Doppler USG. TRAP syndrome is suspected when a twin gestation presents with discordance and bizarre malformations with retrograde blood flow in acardiac twin demonstrated by pulsed/color flow Doppler.[1] It is necessary so that proper prenatal management is done. The various prenatal treatment options for occlusion of blood flow to the acardiac twin so that normal twin is saved are;

  1. Endoscopic (fetoscopic) ligation of umbilical cord
  2. Laser coagulation of umbilical cord
  3. Bipolar cord cauterization or
  4. Intrafetal radiofrequency ablation.[9]

The various indications for prenatal treatment include;

  1. Polyhydramnios
  2. Cardiac dysfunction of pump twin
  3. Hydrops of the pump twin or
  4. Relatively large weight of the acardiac twin.

The obstetricians and radiologists need to be well versed with the condition so that timely diagnosis is made and the normal twin saved from complications.

Learning points

  1. TRAP is a rare anomalous sequence usually occurring in monochorionic twin gestations wherein one fetus is less developed/malformed and gets blood supply from other developed twin
  2. The prenatal diagnosis is necessary and is made by USG which shows monochorionic twin gestation with one normal fetus and another fetus as a heterogeneous mass lesion resembling a teratoma; however, umbilical cord attachment helps in differentiation
  3. Color Doppler study remains the main tool for the establishment of diagnosis by demonstrating retrograde flow in acardiac twin
  4. Most common type is acardia acephalus, and the acardia twin is also known as chorangiopagus parasiticus
  5. Early prenatal diagnosis is required for proper management to save the normal twin
  6. Radiologists and obstetricians must be well aware of the anomaly for proper diagnosis and early management
  7. When detected, a detailed Level-II scan of the normal fetus should be performed to rule out any anomaly in the normal fetus
  8. Prenatal treatment options as described above should be applied whenever required.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Wu CJ, Ding DC, Ren SS, Chang CC, Weng JT, Hwang KS. Prenatal diagnosis and management of twin reversed arterial perfusion (TRAP) syndrome. Taiwan J Obstet Gynecol 2008;47:126-8.  Back to cited text no. 1
Bartha RA, Crow HC. Ultrasound evaluation of multifetal gestation. In: Callen PW, editor. Callen Ultrasonography in Obstetrics and Gynecology. 4 th ed. Pennsylvania: W B Saunders; 2000. p. 196-8.  Back to cited text no. 2
Chen CC, Hsu YH, Chan TF, Yuan SS, Su JH. Poor long-term outcome in a survivor presenting with the twin reversed arterial perfusion sequence in utero: A case report. Kaohsiung J Med Sci 2003;19:526-30.  Back to cited text no. 3
Chaliha C, Schwarzler P, Booker M, Battash MA, Ville Y. Trisomy 2 in an acardiac twin in a triplet in-vitro fertilization pregnancy. Hum Reprod 1999;14:1378-80.  Back to cited text no. 4
Monteagudo A, Roman AS. Ultrasound in multiple gestations: Twins and other multifetal pregnancies. Clin Perinatol 2005;32:329-54, vi.  Back to cited text no. 5
Napolitani FD, Schreiber I. The acardiac monster. A review of the world literature and presentation of 2 cases. Am J Obstet Gynecol 1960;80:582-9.  Back to cited text no. 6
Van Allen MI, Smith DW, Shepard TH. Twin reversed arterial perfusion (TRAP) sequence: A study of 14 twin pregnancies with acardius. Semin Perinatol 1983;7:285-93.  Back to cited text no. 7
Egan JF, Borgida AF. Ultrasound evaluation of multiple pregnancies. In: Callen PW, editor. Ultrasonography in Obstetrics and Gynaecology. 5 th ed. Pennsylvania: W B Saunders; 2008. p. 286-8.  Back to cited text no. 8
Malone FD, D′Alton ME. Anomalies peculiar to multiple gestations. Clin Perinatol 2000;27:1033-46, x.  Back to cited text no. 9


  [Figure 1], [Figure 2]


Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
  Case Reports
   Article Figures

 Article Access Statistics
    PDF Downloaded94    
    Comments [Add]    

Recommend this journal