Dating the development of human cerebellum.

Abstract

A histological study of normal cerebella in 72 human autopsies allowed defining several readily identifiable landmarks by which cerebellar development was dated for vermis and for hemispheres respectively: Disappearance of the lamina dissecans at 28 and 32 weeks gestation; Purkinje cells first discernible at the same age for both; onset of growth of inner granular layer at 30 and 32 weeks; sharp boundary between inner granular layer and white matter at approximately 36 weeks and about term; onset of marked growth of molecular layer at 30 and 38 weeks; adult thickness of molecular layer at approximately the 8th postnatal month for both; and accelerated involution of outer granular layer between the 2nd and 4th postnatal months, remnants persisting up to 9 and 13 months. Nests of matrix cells in the cerebellar nuclei were found in 28% of the cases less than 4 months old. These cell nests appear to undergo involution by the 4th month—that is, at the same time as the outer granular layer. The significance of these developmental events for the interpretation of pathological alterations in the developing cerebellum is discussed.