Cortical dysplasia associated with massive ectopia of neurons and glial cells within the subarachnoid space.

A detailed neuropathological study of the brain of a 31-day-old premature newborn infant revealed the presence of massive ectopia of neurons and glial cells within the subarachnoid space. The extrusion of neural tissue into the subarachnoid space appeared to have taken place through multiple pial-glial bridges. The laminar cortical pattern was also severely disturbed at these sites. Narrow strips of normal and dysplastic cortex alternated in direct relationship to the presence or absence of the pial-glial gaps. Migration of postmitotic neurons and the final positioning of postmigratory neurons appear to take place within highly specified and restricted pathways entrained in a radial direction. Our findings suggest that the pial-glial barrier plays an important role in the control of neuronal migration, and that its disruption may lead to the development of neuronal and glial cell ectopias in the subarachnoid space. The crucial role played by radial glia, the glia limitans and the basal lamina during cortical neurogenesis is emphasized.