Exencephaly-anencephaly sequence: proof by ultrasound imaging and amniotic fluid cytology.

We present and discuss major current theories about the developmental natural history of the anencephalic human fetus. We confirm previous observations made using transvaginal ultrasonography of exencephalic fetuses which were later imaged and/or delivered as anencephalic fetuses. We explore the possibility of proving the theory of the slowly rubbed-off exposed brain tissue by cytologic examination and special staining of aspirated cells in amniotic fluid. Three fetuses with a typical sonographic picture of exencephaly at 13-15 postmenstrual weeks underwent amniocentesis. The aspirated fluid contained pathognomonic neural cells. The same fetuses later showed the characteristic sonographic and postabortion picture of anencephaly. Our results support the theory that exencephaly is the forerunner of anencephaly.