During the second and third trimesters, the fetal brain develops rapidly and complexly in the womb. During gestation, the fetal cerebrum undergoes intricate yet 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.
Given its better qualities than ultrasonography, in-utero MRI has become one of the most extensively used medical imaging modalities for prenatal evaluation. Despite the difficulties of fetal brain MRI, which is prone to fetal and maternal mobility, advanced acquisition and post-processing methods have been developed over the last decade to make 3D imaging of the fetal brain possible.
At each gestational age (GA), a developing atlas of the healthy fetal brain provides a consistent anatomical reference, which is critical for quantitative image analysis.
Scientists suggested a spatiotemporal atlas of the Chinese fetus based on 3T high-resolution in-utero MRI of healthy babies imaged at 22.57 to 39.00 weeks of gestational age (GA) and compared it to existing atlases from Caucasian/mixed populations in this study. The study characterized cortical morphological trajectories to quantify the growth rate among distinct cortical regions, which resulted in a cortical development gradient.
The fetal cerebral cortex is asymmetric in different functional regions
The growth of the normal embryonic cerebral cortex may represent the underlying cellular processes. For the study scientists gathered 219 healthy gestational age fetuses between 20 and 40 weeks.
The rebuilt Chinese atlas revealed significant developmental changes in size and structure, particularly in the cortex; for example, cortical folding evolved fast throughout the second-third trimester. At 23w of GA, the Sylvian fissure was well visible, indicating that it formed before 23w GA. The central sulcus was visible as early as 24w GA, and it was visible on curvature maps. The precentral gyrus and postcentral gyrus eventually evolved between 26w and 28w GA. Throughout GA, cortical thickness underwent biphasic change (first increasing, then decreasing). Sulcal depth, which shows the degree of gyrification, increased linearly with GA. The earliest development of the central and postcentral sulcus was associated with the fastest increase in sulcal depth in the parietal lobe. Early in GA, the occipital lobe had the deepest sulcus, but due to slow growth, it lagged later.
During the GA period, the posterior part of the superior temporal gyrus, also known as Wernicke’s region, expanded fast and showed apparent developmental asymmetry, while the parahippocampal gyrus remained relatively steady. The underlying cellular events throughout development reflect changes in cortical morphological features.
The researchers showed an in-depth analysis of cortical asymmetry in fetal brains. The current study presents a detailed picture of fetal brain development and an atlas, which could be significant as a normative reference for brain developmental and diagnostic purposes, particularly in the Chinese population.
The fetal brain atlas and well-characterized neuro-developmental patterns of the fetal cortex could help us better understand development in utero and is helpful for prenatal diagnosis.