Fetal Cerebral Lobes Development Between20and28Weeks Gestational Age:Postmortem MR Study

Magnetic resonance imaging has now become the best imaging protocol for evaluation of the development of fetal brain, reaching a new level of recognition of the developing brain’s morphology. Using MRI we could get any section of different part of the fetal brain, and tracking its development covering a large scale of gestational weeks.The brain grows quite asynchronously, indicated by its marvelous changes in its morphology. As the structure is the basis for function, this significant change obviously has its potential effect for the internal development of the brain function, thus possessing prodigious research value. Hence the most principal question is to find out what changes had actually happened especially when correlated with the gestational weeks, which is very important in determining whether the brain development is normal in clinical management. During the second and third trimester the brain morphology changes greatly, especially after the Sylvian fissure formed, the primary sulcus and fissure gradually formed while the secondary sulci haven’t formed yet, the brain appearance shifts from the original tubular antrum to the initially folded lobular cerebrum.This study focus on this critical period for morphology transforming using normal fetus specimen. By quantitative measurement of the normal fetus brain, effectively reflect the relative growth order at the early stage of cerebral lobes developing and supply with more meaningful quantitative parameters.ObjectiveTo investigate the fetal cerebral lobes development between20and28weeks gestational age and obtain quantitative parameters for development asynchrony evaluation. Analyze the temporal and spacial development pattern of the primitive cerebral lobes with gestational weeks.Materials and methods36fetus specimen without brain development abnormality, gestational age ranging20to28weeks and4for each week, were collected from hospitals in Shandong Province after induced abortion for abnormalities out of brain. After fixation using formalin these specimen were scanned with GE(general electric, milwaukee, USA)3.0T MR scanner using3D PDWI MR sequence. Images were reformatted perpendicular to the longitudinal axis of hippocampus body and the plane across the base of cerebral peduncle were chosen as the standard plane for lobular development parameters measurement. The overall diameters were also measured, including cerebral biparietal diameter (CBPD), cerebral frontooccipital diameter (CFOD) and the inter-insular diameter(BID).Lobular Development Measurement:1. The parenchyma thickness of the frontoparietal lobe and the temporal lobes (TF, TT);2. The margin length of the frontoparietal, the insula and the temporal lobes (MF, MI, MT);3. The margin length of the Sylvian fissure (MS);4. The perimeter of hippocampus (PH). Relative development ratios calculation:1. Ratio of the lobular parenchyma thickness frontoparietal to temporal lobe (RT);2. One side hemisphere margin length (MH) were calculated and each lobes’length ratio to the same side hemisphere were calculated(RF, RI, RT) as well as the relative ration to each other(RFT, RFI, RIT);3. Sylvian fissure length ratio to the same side hemisphere (RSH) as well as the temporal lobe (RST);4. Ratio of the hippocampus perimeter to the same side hemisphere (RHH) and the temporal lobe (RHT).Relation analysis with gestational weeks were done as well as regression analysis with scatter plots and fitting curve generated.Result:The overall parameters of for the fetus specimen brain ranging20to28GWs were positively correlated with gestational weeks (P<0.001) as well as the lobular parameters measured directly on the reformatted plane (P<0.001).1. Ratio of the lobular parenchyma thickness showed no significant relevance with GW (P>0.05);2. The frontooccipital lobe length ratio decreased while Temporal one increased before24weeks GA and then the two reversed, the ratio of the two fits a parabola curve toward the upside;3. The Sylvian fissure length ratio increased (P<0.001) all through this period.;4. The hippocampus decreased (P<0.001) all through this period.Conclusion:It’s sensible to quantitatively evaluate the development asynchrony of the emerging cerebral lobes by measuring the margin length on the reformatted oblique plane. Before24GWs the frontooccipital lobe grows slower than the temporal lobe and then faster than the latter, and the sylvian fissure remains a higher growth rate than the overall hemisphere while the hippocampus grows slower.24weeks GA could be a turning point for cerebrum development pattern changing from primitive to mature.