Ultrasonic evaluation of the size of the trigone of the fetal ventricle.

A well-demarcated hypoechoic area seen on routine fetal biparietal diameters (BPDs) was retrospectively reviewed in 101 routine obstetrical ultrasonograms. This region has been confirmed to represent the hippocampus with its lateral borders formed by the trigone of the lateral ventricle. Recognition of this structure in conjunction with other previously described structures is a useful method of obtaining easily reproducible BPD measurements. Measurements of the distance of the lateral wall to the midline and the diameter of the hypoechoic area are presented as possible useful indicators in predicting fetal intracranial abnormalities such as hydrocephalus.