Development Of Fetal Hippocampal Formation In The Second Trimester: Assessment With 7.0T MRI

Objective:To study the changes of the hippocampal formation morphology and its infolding angle during the second trimester pregnancy and analyze the developmental pattern.Method:51 fetal specimens (male 24, female 27) of 14 to 22 weeks gestational age (GA) were selected. All fetuses showed normal central nerve system on sonography examinations. Images were obtained by 7.0T Bruker scanner made in Germany, the morphological changes of the hippocampal was analyzed by eFilm software. Hippocampal infolding angle (HIA) was defined as the angle between the line connecting the lateral margin of the cornu ammonis with the medial superior margin of the subiculum and the line passing through the midline structures. The coronal section encompassing the pons was used to perform the measurement of HIAResult:During 14W GA, there was almost no infolding of hippocampal formation, and the cortex had three layers:periventricular layer, intermediate layer and cotical plate. During 15-17W GA, dentate gyrus and hippocampal horn started to infold inside the temporal lobe. Hippocampal formation showed typical characteristic of obvious layer structures. Cortex of CA2 and CA3 became narrower while the marginal layer of hippocampal formation became thicker. During 18-22W GA, dentate gyrus and hippocampal horn had infolded into the temporal lobe and formed a C-type. Layer structures became narrow. Bilateral hippocampal infolding angles increased linearly with GA. No statistically significant difference was noted in gender and hemispheres.Conclusion:The second trimester is the key period of fetus hippocampal formation development. The 7.0T MRI of high-field with high signal-to-noise ratio and high count pulse receive coil, can improve the image of the spatial resolution and organization contrast. Using specimens by MRI scan with high-field, small vision, long collection period, can get the advantages of clear images, display the internal fine structure of hippocampal formation, to define the hippocampus boundary. So With 7.0T MRI, we could obtain clear developmental changes of hippocampal formation and accurate changes of hippocampal infolding angle. The data had consulted significance on evaluating the diseases relative to abnormal development of hippocampal formation in utero or postnatal development.Conclusion and SignificanceConclusion:The second trimester is the key period of fetus hippocampal formation development. The 7.0T MRI high-field with high signal-to-noise ratio and high count pulse receive coil, can improve the image of the spatial resolution and organization contrast. Using specimens of MRI scan with high-field, small vision, long collection period, so can get the advantages of clear images, display the internal fine structure of hippocampal formation, to define the hippocampus boundary. So with 7.0T MRI, we could obtain clear developmental changes of hippocampal formation and accurate changes of hippocampal infolding angle. The data had consulted significance on evaluating the diseases relative to abnormal development of hippocampal formation in utero or postnatal development.Significance:High field specimen of MRI can clearly shown the hippocampal formation's morphological changes and its folding angle developmental changes during the second trimester, reveal the hippocampus developmental changes features, help better understand the hippocampus structure development in clinical using 1.5 T and 3.0 T low field MRI showed on the image feature, enrich and perfect developing brain imaging and embryology knowledge, improve abnormal fetuses clinical diagnosis level, in order to improve population quality, beneficial to the healthy birth, while improving premature survival.