![]() ![]() The germinal matrices are initially composed only of a single region of proliferating cells (the ventricular zone), but as development proceeds, a more peripheral subventricular germinal zone develops, separated from the ventricular zone by a periventricular fiber-rich zone. As the vesicles expand, cellular layers develop within their walls, forming the germinal matrices from which the cells that form the cerebrum will eventually develop. The lamina terminalis does not grow as development proceeds however, the cerebral vesicles exhibit marked expansion laterally, rostrally, ventrally, and caudally. At the time of these outpouchings, the walls of the vesicles are uniformly thin and are connected in the midline by the lamina terminalis, a midline area derived from the roof plate that has shrunken due to apoptosis. The bilateral cerebral vesicles that will form the cerebral hemispheres first appear at about 35 days of gestation as outpouchings of the telencephalon from the regions of the foramina of Monro. ![]() Imaging correlations of these changes that occur during normal brain maturation will be described in this chapter. Finally, changes in regions of brain activity may be determined by looking at changes in local cerebral blood oxygenation resulting from the activity through the use of blood oxidation level-dependent (BOLD) imaging (sometimes called functional MRI or fMRI). Magnetic resonance spectroscopy (MRS) allows us to assess some of the chemical changes that occur as the brain develops. Myelination is an important component of brain maturation because it facilitates the transmission of neural impulses through the central nervous system myelination can be studied by the changes in the T1 and T2 relaxivity of the brain tissue, by assessing changes in magnetization transfer or, indirectly, by assessing changes in the degree and direction of microscopic motion (diffusion) of water in the brain. MR permits highly sensitive assessment of the maturation of gray and white matter, in addition to assessment of microstructural changes including those secondary to myelination. Although transfontanelle ultrasonography, x-ray computed tomography (CT), and magnetic resonance imaging (MRI) all show gross morphologic changes in the maturing brain, MR supplies the most information. Neuroimaging allows analysis of many aspects of brain maturation, including development of sulci, myelination, maturation of brain chemistry, changes in free water diffusion, changes in blood velocity, and changes in location of specific brain activities. Prior to the development of modern neuroimaging techniques, it was not possible to analyze normal brain maturation in vivo. The brain matures in an organized, predetermined pattern that correlates with the functions as the newborn or infant performs at various stages of development. ![]()
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