During the second and third trimesters, the fetal brain develops rapidly and in a complex way in the womb. During gestation, the fetal brain undergoes complex but well-orchestrated growth, particularly in the cerebral cortex. The intricacies of fetal cortical development are difficult to understand due to a lack of in vivo assessment methods.
Spatial-temporal structural atlas of fetal brains. Credit: BioRxiv
Given its better qualities than ultrasound, in utero MRI has become one of the most widely used medical imaging modalities for prenatal evaluation. Despite the difficulties of fetal brain MRI, subject to fetal and maternal mobility, advanced acquisition and post-processing methods have been developed over the past decade to make 3D imaging of the fetal brain possible.
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At each gestational age (GA), a developing atlas of the healthy fetal brain provides a consistent anatomical reference, which is essential for quantitative image analysis.
Scientists suggested a spatio-temporal atlas of the Chinese fetus based on high-resolution 3T in utero MRI of healthy babies imaged between 22.57 and 39.00 weeks of gestational age (GA) and compared it to existing atlases of Caucasian/mixed populations in this study. The study characterized cortical morphological trajectories to quantify the rate of growth between distinct cortical regions, resulting in a gradient of cortical development.
The fetal cerebral cortex is asymmetrical in different functional regions
The growth of the normal embryonic cerebral cortex may represent the underlying cellular processes. For the study, the scientists collected 219 healthy fetuses with a gestational age of between 20 and 40 weeks.
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The reconstructed Chinese atlas revealed significant developmental changes in size and structure, particularly in the cortex; for example, cortical folding evolved rapidly throughout the second-third trimester. At 23w GA, the Sylvian fissure was clearly visible, indicating that it formed before 23w GA. The central groove was visible from 24w GA, and it was visible on the curvature maps. The precentral gyrus and the postcentral gyrus eventually evolved between 26w and 28w GA. Throughout GA, cortical thickness underwent a biphasic change (first increasing, then decreasing). The depth of the furrows, which shows the degree of gyrification, increases linearly with GA. Earliest central and postcentral sulcus development was associated with the fastest increase in sulcus depth in the parietal lobe. At the beginning of GA, the occipital lobe had the deepest groove, but due to slow growth it fell behind later.
During the GA period, the posterior part of the superior temporal gyrus, also known as Wernicke’s region, grew rapidly and showed apparent developmental asymmetry, while the parahippocampal gyrus remained relatively stable. Underlying cellular events throughout development reflect changes in cortical morphological characteristics.
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Clinical significance
The researchers showed an in-depth analysis of cortical asymmetry in the brains of fetuses. The current study presents a detailed picture of fetal brain development and an atlas, which could be important as a normative reference for brain development and diagnosis purposes, especially in the Chinese population.
Conclusion
The fetal brain atlas and well-characterized neurodevelopmental models of the fetal cortex could help us better understand in utero development and are useful for prenatal diagnosis.
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References
Spatiotemporal Atlas of Fetal Brain Describes Gradient of Cortical Development in Chinese Population