Ultrasound diagnosis of acrania with major low–lying placenta and polyhydramnios; case report

Acrania is a rare foetal anomaly in which the calvaria is absent, and the meninges come into direct contact with the amniotic fluid. Acrania is the most common anomaly in the acrania – exencephaly – anencephaly spectrum, with anincidence of 3.68 to 5.4 per 10,000 live births. We present a case of a primigravida who presented for an ultrasound on account of vaginal bleeding in early cyesis. Transabdominal ultrasound showed a viable foetus at 13 weeks without a calvaria, with the brain in direct contact with amniotic fluid. There was a low-lying placenta extending from the posterior to anterior part of the lower uterine segment, completely covering the internal cervical os (major low–lying placenta), a placental cyst and polyhydramnios (amniotic fluid index, AFI of 17 cm). A diagnosis of acrania with major low–lying placenta and polyhydramnios was made. Detailed ultrasound is required to detect acrania at 13 weeks. The diagnosis of acrania is required to help direct patient counselling and maternal expectation. When acrania and major low–lying placenta occur in the same patient, both diagnoses must be promptly made concurrently, regardless of gestational age and without waiting for placental trophotropism and migration to occur first.