Early prenatal diagnosis of holoprosencephaly: the value of transvaginal ultrasonography.

Holoprosencephaly is a rare condition characterized by different degrees of fused ventricles resulting from the failure of the prosencephalon to cleave during embryonic life. In this report we present a case of alobar holoprosencephaly diagnosed prenatally at 15 weeks' gestation in a woman with a family history of open neural tube defect. The diagnosis was initially missed because only suboptimal views of the fetal brain were obtained with transabdominal ultrasonography due to fetal position; however, a better depiction of brain anatomy was obtained using the transvaginal approach, allowing the detection of a single ventricle and fused thalami. We conclude that transvaginal ultrasonography is not only important for the early prenatal diagnosis of central nervous system abnormalities but also for enhancing brain visualization when transabdominal examination of the fetal head is limited due to maternal and fetal factors.