Lavina Chaubey BHU

A Case Study : Acardiac Twin (Acardius anceps)
Dr. Lavina Chaubey (Dept. of Obgyn), Dr. Madhu Jain (Dept. of Obgyn),
Dr. Ashish Verma (Dept. of Radiology), Dr. Shivi Jain (Dept. of Radiology)
Institute Of Medical Sciences, Banaras Hindu University, Varanasi (U.P.), India
BACKGROUND
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Twin Reversed Arterial Perfusion sequence (TRAP) is a complication of
monochorionic twin pregnancy in which one twin with an absent or nonfunctioning heart e.i. non-viable acardiac twin is perfused by the other
“pump” twin via placental artery to artery anastomoses resulting in
growth and the characteristic anomalies of the acardiac twin with
possible heart failure of the pump twin.
TRAP sequence occurs in about 1% of monochorionic pregnancies and
1 in 35,000 deliveries
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CASE HISTORY
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A 25 year old second gravida (previous 1 spontaneous abortion of 1
month gestation) was booked for antenatal care during current
pregnancy from 6 weeks of gestation
LMP 21/09/2012, EDD 28/06/2013 ,previous cycles normal and regular
Patient had an ultrasound from a private centre showing a single live
intra-uterine pregnancy of 6+3 weeks with CRL 6.4 and +ve cardiac
activity
Past history
Family history
Revealed
Personal history
no abnormality
General examination
Baseline antenatal investigations
In the first trimester of her current pregnancy, patient had a single
episode of mild antepartum haemorrhage
Serial ultrasounds showed monochorionic diamniotic twin pregnancy
with one live twin at 12+6 weeks , liquor adequate and another twin of 10
weeks with no cardiac activity. Placenta was left anterolateral reaching
upto the margin of the os. A subchorionic bleed of 2.7 x 0.7 cm was noted
at the placental margin located over the os . Cervical length was 4.1 cm
with no evidence of funneling. Subsequently, the subchorionic bleed was
seen to be resolving and the live pregnancy progressing.
Follow up MRI showed monochorionic pregnancy with a live twin having
normal biometric parameters corresponding to gestational age of 17+0
weeks. Amniotic fluid was normal and heart rate 132 bpm. No
abnormality , structural or otherwise, was seen.
Twin 2, however, was hydropic with malformations. The femur was
present with a length of 1.82 cm corresponding to a GA of 15+3
weeks.The brain showed multiple cysts. Abdominal and thoracic organs
could not be delineated at all. A primitive looking heart tube and aortic
arch were present. Pulsations from the area could be seen with a rate of
139 bpm (difference of <10 bpm from the first twin)
Placenta was single with inter-placental venous lakes. The lower
segment was free. An intertwinning membrane could be seen
Color Doppler of the normal twin (first) showed a four chambered view of
the heart with high amplitude triphasic arterial waveform from the cardiac
area and a normal flow. But the hydropic twin(second) showed only a
tubular heart and low amplitude attenuated waveform, possibly arterial,
which at the time was thought to be originating from the heart.
A provisional diagnosis of monochorionic twin pregnancy with twin 1
normal and twin 2 grossly malformed , both live, was made at the time
based on the reports of USG, MRI and color doppler (doppler scan of the
placental circulation was not done since the abnormal twin was thought
to be live).
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Leading twin (acardius) being delivered
at caesarean section( thin arrow) followed
by after-coming sac of normal twin
( thick arrow)
Acardius anceps with head (thick arrow),
meningomyelocoele (thin arrow) and
lower limb bud
Normal twin being delivered at caesarean
section after the abnormal one (thick
arrow)
Front view of abnormal fetus showing
attachment of the cord
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Normal Twin
Abnormal Twin
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Visible vascular anastomoses between
the two cords on placental surface (thick
arrow)
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The pregnancy was followed under close supervision and it proceeded
uneventfully. However, only one fetal heart could be heard at a time
clinically.
At 28 weeks, patient reported to labour room with pain abdomen. She
was found to be in labour with the abnormal twin leading. However, it’s
presentation or heart rate could not be determined . The normal twin
was smaller, transverse and having a heart rate of 136 bpm.
Due to failed progress of labour patient was shifted for emergency
caesarean section
Twin 1 (1070 gms) was dead, grossly malformed (acardiac twin)
Twin 2 (910 gms/F) was apparently normal, APGAR 5/10, 6/10 and had
to be resuscitated. She was shifted to NICU where she was put on
mechanical ventilation, surfactants and I/V antibiotics. However the
baby developed refractory shock and died on day 3 of life due to
complications of prematurity.
Placenta was single with close insertion of the two cords and visible
anastomoses in between.
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Vascular connection between two cords
being cut open
From there, the ductus venosus shunts 80 percent of the placental blood
flow into the inferior vena cava, where it mixes with venous return from
the lower extremities and kidneys before entering the right atrium. Once
the blood enters the right atrium, the two sides of the fetal heart act in
parallel through intra- and extra-cardiac shunts (foramen ovale, ductus
arteriosus) to fill the aorta and provide systemic circulation. The distal
aorta terminates in the left and right common iliac arteries, which each
divide into internal and external iliac branches. The umbilical arteries
carry blood from the internal iliac arteries back to the placenta.
In TRAP sequence, the pump twin maintains this normal pattern of fetal
circulation. In addition, a portion of its cardiac output travels through
placental arterial-arterial anastomoses to the umbilical artery and
eventually the systemic circulation of the recipient co-twin, thus creating
“reversed” circulation in this twin. This is possible because the acardiac
twin lacks a functional heart, whose pumping would normally provide
forward flow and high systemic pressure. The presence of placental
vascular anastomoses is common in monochorionic twins and alone is
not sufficient for the development of TRAP sequence.
The abnormal circulatory pattern provides perfusion of deoxygenated
blood from the pump twin to the lower half of the recipient twin via its iliac
arteries, but poor perfusion of the upper torso and head. Unequal
vascular perfusion from the pump twin may contribute to the evolution of
a variety of structural abnormalities in the recipient twin.
The acardiac twin has been classified according to the degree of
abnormal development. The most common anomaly is acardiac
acephalus, in which the fetal thoracic organs and head are absent.
Other rarer types are acardius acormus, in which only the fetal head
develops; acardius amorphus, consisting of a shapeless mass of tissue
with no recognizable human parts; and acardius myelacephalus, in
which the head and one or more extremities are partially developed.
CONCLUSION
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Communicating channel between the two
cords showing blood clot
AP and Lateral view of x-ray of acardiac
twin
DISCUSSION
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Acardia was first described in the sixteenth century referred to as
chorioangiopagus parasiticus
It is the most extreme form of twin to twin transfusion syndrome now
referred to as twin reversed arterial perfusion sequence.
In the normal fetal circulation, blood from the placenta flows through the
umbilical vein to the fetus.
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This was a case of acardiac twin pregnancy which was missed in the
antenatal period due to erroneous finding of pulsations in the cardiac
area of the abnormal twin
The pulsation and abnormal waveform from the cardiac area of the
abnormal twin on doppler was probably the transmitted wave from the
heart of the normal twin. It became attenuated because of the long
distance it travelled retrograde through the circulation of the acardiac
fetus
The abnormal twin is acardiac anceps ( most developed among all)
since the x-ray shows the presence of the skull, vertebral column, ribs,
lower limbs
The upper limbs were not formed
Brain was replaced by cystic spaces as seen on the ultrasound.
Thoracic and abdominal organs could not be delineated.

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