Central nervous system microangioarchitecture in the human foetus.

It is thought that arterioles penetrating the central nervous system behave as terminal arteries and lack for anastomosys. The purpose of our study was to define the angiogenesys in the fetal encephalon at different stages of development. To this purpose, we examinated 13 fetal and newborn encephalons between the 10th and 33rd week. To label blood vessels, we used an immunohistochemical procedure based on the detection of two antigens located within endothelial cells: CD31 and CD34. The cerebral vascularization modifies in quantity and in structure during pregnancy, with important topographic differences between cerebral cortex and striatal-limbic areas. We observed two microarchitectural patterns: 1. Rectangular mesh pattern, characterized by capillaries that join transversally to one or more branches that deepen orthogonally from the surface of the meninges; 2. Hexagonal mesh pattern, which surrounds small groups of neurons and develops with a honeycomb shape. The rectangular mesh pattern is mostly observed from the 13th to 26th week in the white matter, in the hippocampus and in the cortex. The hexagonal mesh pattern is typical of the basal nuclei, and of the cerebral cortex during the 10th-12th week and after the 26th-27th week. Until the 26th week the vascularization increases mainly in the hippocampus and in the basal nuclei. The cortex shows a vascularization increment, greater than in the limbic system, with a pattern prevalently hexagonal in areas were the neurons' number increases. Our data demonstrate that, in the human fetus, cerebral capillaries are not of terminal type. On the contrary, they show a rich anastomotic network that has different patterns in white matter (rectangular pattern) or in grey matter (hexagonal pattern). The functional meaning of this difference is unknown, but we can suppose that its role is to warrant availability of nutritional substances within regions where a high number of neurons is present. Recent findings in computational neuroanatomy show that computer simulated axonall symmetric bifurcation can generate a dendritic tree with close similarities with real observed vascular patterns in fetal cortex.