A sonographic sign which predicts which fetuses with hydrocephalus have an associated neural tube defect.

We report a sonographic sign which reliably distinguishes those hydrocephalic fetal heads associated with a neural tube defect from those which are not, particularly in the second trimester. This sign involves a "pointed" deformity of the frontal aspect of the skull in fetuses with hydrocephalus, indicating the presence of a neural tube defect. A retrospective review of 36 cases of hydrocephalus demonstrates that this sign is particularly helpful in the second trimester, where it was present in all the fetuses with hydrocephalus and neural tube defect. It was less reliable in the third trimester; however, this sign was not present in any of the fetuses with hydrocephalus who did not have a neural tube defect. Angulation or pointing of the fetal frontal bone when hydrocephalus is present, particularly in the second trimester, seems to be a reliable predictor of an associated neural tube defect and mandates a careful search for this defect.