Growth trajectories of the human fetal brain tissues estimated from 3D reconstructed in utero MRI

Abstract

In the latter half of gestation (20 to 40 gestational weeks), human brain growth accelerates in conjunction with cortical folding and the deceleration of ventricular zone progenitor cell proliferation. These processes are reflected in changes in the volume of respective fetal tissue zones. Thus far, growth trajectories of the fetal tissue zones have been extracted primarily from 2D measurements on histological sections and magnetic resonance imaging (MRI). In this study, the volumes of major fetal zones—cortical plate (CP), subplate and intermediate zone (SP+IZ), germinal matrix (GMAT), deep gray nuclei (DG), and ventricles (VENT)—are calculated from automatic segmentation of motion-corrected, 3D reconstructed MRI. We analyzed 48 T2-weighted MRI scans from 39 normally developing fetuses in utero between 20.57 and 31.14 gestational weeks (GW). The supratentorial volume (STV) increased linearly at a rate of 15.22% per week. The SP+IZ (14.75% per week) and DG (15.56% per week) volumes increased at similar rates. The CP increased at a greater relative rate (18.00% per week), while the VENT (9.18% per week) changed more slowly. Therefore, CP increased as a fraction of STV and the VENT fraction declined. The total GMAT volume slightly increased then decreased after 25 GW. We did not detect volumetric sexual dimorphisms or total hemispheric volume asymmetries, which may emerge later in gestation. Further application of the automated fetal brain segmentation to later gestational ages will bridge the gap between volumetric studies of premature brain development and normal brain development in utero.

Mimicking Cortex Convolutions Through the Wrinkling of Growing Soft Bilayers

“…Then knowing the initial thickness value H which is about 0.1 mm at 11 weeks [46], we deduce the cortex thickness at 27 weeks : J 1 H ∼ 0.34 mm and at birth J 1 H ∼ 20H ∼ 2 mm. Comparison with MRI studies in vitro are satisfactory since estimation from the figure (4) of [49] gives approximatively 0.5 mm at 27 weeks, in reasonable agreement with our zero-order approximation of purely axial growth. However, very recent measurements, also achieved with MRI [40,41] indicate that the average thickness of newborn cortex is 1.99 ± 0.1 mm for the left hemisphere, 2.03 ± 0.12 for the right hemisphere, values which will increase by 42%, in the first year, much less in the second year.…”

“…The experimental data, given in [1,68], concern the whole brain growth and not separately the cortex and the white matter. Data concerning size increases, layer per layer, are only known for the pre-gyrification period, unfortunately [49]. The good agreement we have obtained for the growing cortex thickness indicates that the growth mismatch between both layers of the brain is not really significant, since we take, for the cortex, these data normalized by the initial size.…”

Prenatal growth in humans and postnatal brain maturation into late adolescence

“…The cerebral cortex undergoes especially rapid growth during in utero life (19) and represents a key biological substrate for many of the postnatal outcomes that are sensitive to normative BW variation. Prospective ultrasound studies of fetal growth indicate that prenatal influences on eventual BW are already operative by the second trimester of pregnancy (20,21), when a number of foundational aspects of cortical development are underway, including: (i) a growing role for the subventricular zone in generation of new cortically bound progenitor neurons (22); and (ii) subsequent migration of these neurons into the cortical plate via the expanding subplate (23), which plays a pivotal role in formation of early neuronal circuits (24).…”

Cerebrospinal Fluid and Parenchymal Brain Development and Growth in the Healthy Fetus

“…Advances in quantitative MRI techniques for fetal brain evaluation have spurred recent studies using three-dimensional (3D) volumetry to investigate in vivo development of the fetal brain [10][11][12][13][14][15][16][17][18][19][20][21] . 3D volumetric techniques provide more accurate results compared to the standard 2-dimensional (2D) biometric measures [16,22,23] . Together these techniques provide a multifaceted understanding of the developing brain, its regional and tissue-specific growth, microarchitecture, and evolving connectivity [12,[24][25][26] .…”

“…A number of studies have used quantitative 3D MRI techniques to measure brain growth and to evaluate the developing fetal brain [12,13,16,17] . However, very few studies have done so in the healthy fetus, and these have been limited by small sample sizes over relatively narrow gestational age periods.…”