The growth and development of microvasculature in human cerebral cortex.

Sections of the occipital cortex from 31 fetuses, infants and children, ranging in age from 15 weeks gestation to ten years postnatal, were stained to demonstrate alkaline phosphatase activity in intracortical vessels. At 15 weeks gestation intracortical positively staining vessels, assumed to be arterial precursors, were radially oriented, originating from leptomeningeal arteries. Most radial vessels coursed through the cerebral cortex without branching to vascularize the subcortical tissue. By 20 weeks gestation horizontal branches arose from radial vessels, most frequently in the lower half of the cortex. Occasionally, recurrent collaterals ascended from these horizontal branches to more superficial cortex. From 20-27 weeks gestation, the number of horizontal branches and recurrent collaterals increased in the lower half of the cortex, horizontal branches appeared in the upper half. From 27 weeks to term, shorter radial vessels, terminating in the more superficial cortical laminae increased in number. After birth a network of fine vessels, presumable precursors of capillaries, increased, particularly vascular layer 3 (neuronal lamina IV and Va). The number of radially oriented vessels per mm2 of pial surface (NA) decreased throughout development, with the most dramatic decrease occurring prenatally. In five cases of trisomy values of NA decreased less rapidly than in the normal.