Identification of the fetal hippocampus and fornix and role of 3-dimensional sonography

Objectives-The purposes of this study were to identify the fetal hippocampus and fornix using 3-dimensional sonography, to measure their curved length during pregnancy, and to describe a systematic method for volume data set analysis of the fetal hippocampus and fornix. Methods-Three-dimensional volumes of the fetal brain were acquired prospectively in 34 patients between 14 and 37 weeks' gestation. Volumes were acquired with transabdominal and transvaginal transducers. All volumes were analyzed offline by 2 examiners separately. The feasibility of identifying the fetal hippocampus and fornix was analyzed. The curved length of the hippocampus-fornix structure was measured on the right and left hemispheres. Results-The fetal hippocampus and fornix were identified bilaterally in 32 of 34 fetuses (94%) at gestational ages of 14 weeks 5 days to 37 weeks 1 day (mean, 23 weeks 3 days). In 1 fetus (3%), only one side was shown, and in another fetus (3%), both sides were obscured by acoustic shadows. A systematic approach for identification of the fetal hippocampus is described. Linear growth of the fetal hippocampus and fornix was shown during pregnancy and was correlated with both the gestational week and the head circumference (R = 0.71 and 0.74, respectively; P = .01). The length of the hippocampus and fornix did not differ between the left and the right hemispheres (P = .598). Conclusions-The fetal hippocampus and fornix can be identified by a systematic analysis of 3-dimensional data set volumes. The normal hippocampus and fornix show linear growth throughout pregnancy.