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Articles » Multiple gestations » Twin reversed arterial perfusion syndrome

1993-10-22-17 Twin, acardiac, anceps © Nevils

Twin, acardiac, anceps

Bobby G. Nevils, MD*, James E. Maciulla, MD, Luis A. Izquierdo, MD, George J. Gilson, MD, Luis B. Curet, MD

Address correspondence to: Bobby G. Nevils, MD, University of New Mexico School of Medicine, Division of Maternal‑Fetal Medicine, Department of Obstetrics and Gynecology, 2211 Lomas Blvd., NE, Albuquerque, New Mexico 87131‑5286, Ph: 505‑272‑6907 Fax: 505‑272‑6385 *Captain MC USNR. The opinions presented are not the opinions of the United States Navy.

MESH Diseases‑in‑twins‑diagnosis; Fetofetal‑transfusion‑diagnosis; Heart defects; Pregnancy multiple; Monsters; Umbilical‑cord blood supply ICD9 761.5 CDC 759.456


The incidence of monozygotic twinning is 1 in 250 births and is independent of race, heredity, age and parity. The twin reversed arterial perfusion syndrome is a rare occurrence and is noted to be about 1% of monozygotic twins and one in 35,000 deliveries. 1‑7 The acardiac twin is dependent upon the normal twin to provide circulation by means of vascular anastomoses. Many of the bizarre defects are felt to be caused by low oxygen tension, and this causes dramatic alterations in the twin fetal physiology and high perinatal mortality. We present a case of acardiac anceps diagnosed and followed at our institution.

Case report

The patient is a 17‑year‑old Hispanic female, primigravida, who was referred to the University of New Mexico Hospital"s Women"s Ultrasound unit at 25 weeks gestation. The patient was a late obstetrical registrant and was noted to be large for dates. An ultrasound examination was performed by her primary care physician. The examination revealed a twin gestation “...with the fetus in the right being dead with monstrous changes consisting of marked diffuse subcutaneous cystic formations similar to a lymphatic channel anomaly... the left‑ sided live fetus appeared to be normal.”

On examination at our institution, she had a fundal height of 39 centimeters and an ultrasound examination was repeated. The twin gestation was confirmed with the following findings. The pump twin was in a vertex presentation. It presented as a “stuck twin” with oligohydramnios and was pushed to the uterine side wall in the left lower uterine cavity (fig. 1).

Figure 1: Sonogram of large cystic masses (arrow) and “stuck twin”.

This twin had normal anatomy, and biometric parameters were consistent with gestational age. This twin also had bradycardia around 70 beats per minute at the time of ultrasound. The recipient twin demonstrated marked abnormal features. There was no polyhydramnios surrounding the abnormal twin, but instead the large uterine size was accounted for by the massive cystic structures arising from the abnormal twin. No cardiac activity could be identified. There were definite fetal skull structures, and extremities could not be discerned. Information about early ultrasound identifying fetal heart activity was not available. These ultrasonic findings were consistent with a diagnosis of twin reversed arterial perfusion syndrome (TRAP) syndrome versus cystic hygroma with demise of one twin.

After extensive counseling and discussion with the perinatologist, it was recommended that a transabdominal tap of the massive cystic areas be done to decompress them in an effort to release the “stuck twin.” On the initial transabdominal tap procedure, 350 milliliters of yellowish clear fluid was obtained and sent for karyotyping. A second tap was attempted the following day and resulted in 120 milliliters of fluid. The live twin continued with brady­cardia. Seven hours later, no heart tones were audible by Doppler, and a demise was confirmed by ultrasound.

Labor was induced with a pitocin infusion after cervical ripening with Dilapan®. The patient delivered vaginally. The pump twin was a male with a birth weight of 700g and was grossly normal. The recipient twin was also a male with a birth weight of 1820g and with gross anomalies (figs. 2 and 3).

Figure 2: Products of conception: acardiac anceps twin and normal twin.

Figure 3: Close-up view of acardiac twin.


The karyotype on the fluid submitted from the transabdominal tap was 46, XY. The autopsy findings confirmed the diagnosis of monoamniotic, monochorionic placenta with abnormal cord vessels (fig. 4).

Figure 4: Placenta and cord showing aberrant umbilical vessel. 

The gross description of the placenta stated “...the cord from the pump twin contains 3 vessels... the cord of the recipient twin contains one visible vessel. One vessel is shared between the two cords and shows a "U‑shaped" turn near the insertion before entering the placenta” (fig. 4). The pump twin had no congenital anomalies, whereas the recipient twin revealed multiple congenital anomalies (Table 1).

Table 1: Autopsy findings in the acardiac twin.

g Congenital anomalies:

       1 multiple cystic hygroma

       1 cleft lip and palate

       1 incomplete formation of eyes

       1 malformed hands and feet

       1 absent heart, aorta, lungs, thymus liver and gallbladder

       1 incomplete rotation of large intestine

       1 single pelvic kidney

g Monoamniotic monochorionic placenta

       1 two-vessel umbilical cord

       1 twin-twin transfusion (recipient)

g Intrauterine fetal demise (26 weeks) with maceration.


The TRAP syndrome has been reported by a number of authors as a prenatal diagnosis. This patient was referred for a second opinion ultrasound because of the intrauterine demise of one anomalous twin. This report illustrates an acardiac twin of the “ANCEPS” variety (Table 2). This variety of acardiac twin has cranial structures and/or identifiable neural tissue. 

Table 2: Classification of acardiac twins.




No cephalic structures present


Some cranial structure and/or neural tissue present


Cephalic structures but no truncal structures


No discernible cephalic or truncal structures


The acardiac twin anomaly is also referred to as acardius, acardiac monster, acephalus, pseudocardiac anomaly acephalus acaradia, holocardius, and twin reversed arterial perfusion syndrome (TRAP).


The twin reversed arterial perfusion syndrome is a dramatic complication of monozygotic twin pregnancy. One fetus develops normally (the pump twin) and the second twin (recipient twin) demonstrates total or partial absence of the heart and reduction anomalies affecting all tissues.


The prevalence of the TRAP syndrome is one in 35,000 births or about 1% of monozygotic pregnancies.


The etiology of twin reversed arterial perfusion syndrome syndrome is anastomosis of the umbilical arteries in early embryogenesis leading to reversed circulation in the perfused twin. This case demonstrates the suggestion “that intrauterine growth is achieved by perfusion from the normal twin via large blood vessel anastomosis in the placenta." Here the blood vessel communication is apparent outside the placenta. Chromosomal errors are not the cause of the acardiac anomaly.


According to Benirschke5, perfusion of the anomalous twin is a result of a reversed flow through the umbilical artery of the recipient twin and the resultant anomalies are caused by decreased oxygenation with disruption of organogenesis.

Associated anomalies

In the recipient twin, associated anomalies are: total or partial absence of cranial vault, holoprosencephaly, absent facial structures, anophthalmia, microphthalmia, cleft lip, cleft palate, absent or rudimentary limbs, diaphragmatic defects, absent lungs and heart, esophageal atresia, ventral wall defects, ascites, absent liver and gallbladder, edema of the skin and single umbilical artery.

In the pump twin there is evidence of congestive heart failure (ascites, pleural effusions, polyhydramnios and skin edema).

Differential diagnosis

The diagnosis of acardia or TRAP syndrome should be suspected whenever a twin gestation presents with discordance and bizarre malformations. A difficult diagnostic dilemma is encountered when cranial structures are present, as illustrated by this case: massive cystic hygroma with fetal demised versus TRAP syndrome.


The anomaly is uniformly fatal for the recipient twin. The perinatal mortality for the pump twin has been reported to be 50% or greater. Moore et al7 reviewed 49 cases of acardiac twins and reported that perinatal outcome was related to the ratio of the weights of the twins. This Twin Weight Ratio is the weight of the acardiac twin divided by the weight of the normal twin.

When the Twin Weight Ratio was above 70% preterm labor, hydramnios and congestive heart failure in the pump twin were observed. Such data is useful in determining the prognosis of these unusual pregnancies.

Recurrence risk

The risk of recurrence is not increased.


The management of these pregnancies is concerned with a number of issues. Complications associated with the presence of an acardiac twin are twin‑to‑twin transfusion syndrome, polyhydramnios, preterm labor, cord accidents, dystocia, ruptured uterus, congestive heart failure and intrauterine death of the normal twin3,7,9,10. Once the diagnosis is made, serial ultrasound is required to assess the growth pattern of the normal twin and to look for evidence of congestive heart failure.

This patient presented with the “stuck twin” clinical picture as the large anomalous fetus had pushed the normal twin against the uterine side wall, and there was oligohydramnios of that twin. A number of interventional procedures have been speculated in the management of these pregnancies such as interrupting the circulation by clamping the umbilical cord of the acardiac twin.

This would require hysterotomy and is not practical. The development of an endoscopic/fetoscopic technique for occlusion of the cord is under current investigation. Hamade et al11 have reported placing a steel coil in the abdomen of an acardiac fetus under ultrasound. That pregnancy went to term with delivery of a 2237g normal baby. Selective feticide has been suggested, but the risk to the normal fetus would be great4.

We attempted to decompress the large cystic masses via transabdominal taps under ultrasound to relieve pressure on the stuck twin. This twin had a sudden intrauterine demise, which is consistent with the increased risk of sudden death even without ultrasound evidence of congestive heart failure as reported by Fusi et al. 9

At present, conservative management of TRAP syndrome consists of serial ultrasound to assess the growth rate and cardiovascular status of the normal twin. Once viability is reached, early delivery should be considered because of the high risk of sudden intrauterine fetal demise.


1. Izquierdo L, Smith J, Gilson G, et al. Twin, acardiac, acephalus. The Fetus  7615:1‑3, 1991.

2. Romero R, Pilu G, Jeanty P, et al. Prenatal diagnosis of congenital anomalies. New York, Appleton and Lange 409‑411, 1988.

3. Sherer DM, Armstrong R, Shah YG, et al. Prenatal sonographic diagnosis, Doppler velocimetric umbilical cord studies, and subsequent management of an acardiac twin pregnancy. Obstet Gynecol 74:472‑475, 1989.

4. Seeds JW, Herbert WNP, Richards DS. Prenatal sonographic diagnosis and management of a twin pregnancy with placenta previa and hemicardia. Am J Perinatol 4:313‑316, 1987.

5. Bernirschke K, Harper VDS. The acardiac anomaly. Teratology 15: 311‑316, 1977.

6. Stiller RJ, Romero R, Pace S, et al. Prenatal identification of twin reversed arterial perfusion syndrome in the first trimester. Am J Obstet Gynecol 160:1194‑1196, 1989.

7. Moore TR, Gale S, Benirschke K. Perinatal outcome of forty‑nine pregnancies complicated by acardiac twinning. Am J Obstet Gynecol 163:907‑912, 1990.  

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