Twin reversed arterial perfusion sequence: acardiac-acephalic twin - a case report

Acardiac-acephalic twin is one of the bizarre complications of monozygotic, monochorionic twin pregnancies. It is commonly referred to as Twin Reversed Arterial Perfusion (TRAP) sequence, in which the primary malformation is the lack of a well -defined cardiac structure in one twin (acardiac), which is kept alive by its structurally normal co-twin (pump twin) through abnormal placental vascular anastomosis. The anomalous twin appears as a heterogenous mass simulating a teratoma, with absence of head, neck and upper limbs. Thoracic organs are either absent or underdeveloped. The majority of the acardiac twins are of female sex and have no chance of survival, and more than 50% of the fetuses have some chromosomal anomalies. The perinatal mortality rate of pump twin may be as high as 50 75%, mainly due to polyhydramnios, preterm labor and high-output cardiac failure. The diagnosis of the TRAP sequence can be established as early as 9 week by regular gray-scale ultrasonography and transvaginal Doppler ultrasonography. Assessment of extent of cardiac failure in the pump fetus and timing of the delivery are the key factors in the pregnancy management and in the survival of the normal cotwin. The majority of the pregnancies are managed conservatively, but in a minority group a minimally invasive procedure was needed to arrest the vascular anastomosis to improve the outcome of pump twins. The case presented here reports on an acardiac-acephalic twin; it describes variable clinical presentations, pathophysiology and treatment modalities. It also reviews pertinent literature.