Prenatal Development Of Occipital Laminar Organization Of Human Cerebral Cortex

In recent years, improvement in diagnostic techniques has led to better recognition of "disorders of cortical development". These disorders constitute a significant cause of epilepsy, mental retardation, developmental delay and neurological deficits in childhood, and may also contribute to the pathogenesis of psychological and neurodegenerative diseases in adults. Hitherto, however, few systematic studies of the human fetal cortex have been performed, and little is known about the ontogenetic processes of the neocortex in man.The main radiological technologies which applied commonly to prenatal examination and evaluation of human fetal brain are in vivo ultrasound (US) and MRI. The advantages of US are safe, convenience, real time imaging, so US is the first choice to evaluate the development of human fetus at present. MRI examination is non-radiative, with high contrast and resolution ratio, and the fast imaging sequences decrease the artifact while imaging, so MRI is the best auxiliary diagnosis method. However, these two technologies also have boundedness when examine the brain cortex of fetal. The US has low resolution ratio of spatial and tissue, it has poor imaging effect to the pregnant women which fat, oligoamnios and with obviously skull ossification fetus. The field intensity collected by in vivo fetal MRI usually lower than 1.5T, which also disturbed by collection sequence, scanning thickness, fetal movement and so on. Fetal specimens (in vitro) MRI scanning can avoid these interference factors, and it can be studied by histology, so postmortem MRI becomes an effective means to explore the development and maturation of fetal cerebrum.Previous studies have found that some temporary laminar organization appear on the cerebral cortex of embryo and fetus along with the complex histogenesis process of human cerebral cortex, and these laminar organization are changing along with the gestational weeks (GW). Therefore, it is necessary to reveal the change of laminar organization of human fetal cerebral cortex on post-mortem MRIs of high magnetic strgenth with specimens of large sample and great GA span, and contrast with histological studies, the results of this study can supply reference comments for the development mechanism of human cerebral cortex, it can also provide assessment guidance for cerebral development situation of in utero fetus, and increase the quality of newborns.Part 1:The prenatal development of occipital laminar organization of human cerebral cortex:assessment with MRI of high magnetic strengthObjective:To explore the demonstrating and development changes of occipital laminar organization of human cerebral cortex along with the increasing of GW on 3.0T and 7.0T post-mortem MRI.Materials and methods:Choose 26 fetal specimens which were devided into ten gestational age groups to scan with 3.0T and 7.0T MR, the sequential development of the occipital laminar organization was analyzed on different field intensity transverse MRIs.Results:According to 3.0T and 7.0T postmortem MRIs, Four to six laminations can be observed in occipital cortex on 14 to 18 GW; seven laminations were revealed on 20 to 22 GW which the laminar organization were typical; it changed to atypical on 24 to 30 GW; the occipital laminar organization were gradually disappear and changed to three laminations after 30 GW. The ventricular zone (VZ), the subventricular zone (SVZ) and the cortical plate (CP) were showed as low signal on T2 MRI while the periventricular zone (PVZ), the intermediate zone (IZ) and the marginal zone (MZ) were showed as high signal on T2 MRI, the signal of subplate zone (SP) on T2 MRI was changed while development process. All these lamination were showed as opposite signal on T1 MRI with T2 MRI.Conclusion:Ti-weighted 3.0T MRI and T2-weighted 7.0T MRI could well demonstrate the laminar organization, and the development of the laminar organization followed a specific regularity.Part 2:The morphological quantitative study for prenatal development of occipital laminar organization of human cerebral cortexPurpose:To explore the development rule of thickness and cell density of laminar structures in occipital pole of human fetal brain cortex, in order to provide morphological basis for prenatal diagnosis of human fetal brain cortex disease.Materials and Methods:Choose 26 fetal specimens which were devided into ten gestational age groups to scan with 3.0T and 7.0T MR, then choose 3 cases which were 14,20,30 GW respectively to take out the brain and with HE stain in occipital pole cortex. We measured the thickness and cell density of laminar structures with Amira and Image Pro Plus (IPP), and observed the development rule along with gestational ages.Results:The thickness of intermediate zone and subplate zone increased faster in 22 GW, and declined in 28 GW, then gradually increase. The thickness of the other zones reached the peak in 20 GW, then gradually decline. The thickness of fetal brain cortex increased while the cell density declined with the increase of gestational age.Conclusion:The increasing of thickness and cell density of laminar structures in occipital pole of human fetal brain cortex follow a particular rule, the macroscopic development of laminar structures have no connection with cell number.