Fetus Acardiac Amorphous Presenting as Placental Tumor: A Rare Case and Differentiating the Two

Fetus acardius is a rare manifestation of twin reversed arterial perfusion and is a parasite due to vascular circulation from donor twin and lacks any resemblance to human embryos. Antenatal diagnosis is challenging as there are no well-defined features. We report here a case which presented as placental mass, the diagnosis of which was evident after delivery. Antenatal diagnosis, review of the literature, and differential diagnosis from the placental mass are discussed. A primigravida in the late third trimester had ultrasonography (USG) showing a 7 cm × 5 cm mass adjacent to the placenta. She had no complaints and fetal biometry was normal. She delivered a healthy baby; placenta showed an attached mass without identifiable fetal body or limbs, and was covered with skin having scanty hairs, which was identified as an amorphous fetus. Early diagnosis is possible by early USG; an acardiac amorphous fetus may present as placental mass. Characteristic feature on USG supplemented by magnetic resonance imaging may help in reaching a correct diagnosis and optimal management.