[Development of human cerebellar granular layer: a morphometric study].

Abstract

Development of the cerebellar granular layer, the external granular layer (EGL) and the internal granular layer (IGL), was studied morphologically to make complete serial sections of the brain from human fetuses ranging 12 to 40 weeks' gestation (WG). To examine the chronological changes and the regional differences, we measured the thickness of the layer microscopically among five different parts of the cerebellum: anterior lobe/hemisphere (AH), anterior lobe/vermis (AV), posterior lobe/hemisphere (PH), posterior lobe/vermis (PV) and flocculus (FL). EGL was the most superficial layer composed of densely packed undifferentiated cells. Its thickness showed little changes during the fetal period of 12-40 WG for all parts except FL where EGL was thicker than those in other parts and made a gradual attenuation with development. We noticed at least three stages in the fetal development of IGL: 1) the primary or undifferentiated stage (before 18 WG) when IGL was hardly distinguishable from the layer of immature Purkinje cells (PCL); 2) the secondary or intermediate stage (18 to 30 or 35 WG) when it was clearly visible and almost stable in thickness for all parts; 3) the tertiary or developing stage (30 or 35 to 40 WG) when it showed a dramatic increase in thickness as the formation of cerebellar folia was proceeding. During the intermediate stage the Lamina dissecans was observed between PCL and IGL typically in PH. Regional differences were detected in a period of transition from the intermediate to the developing stage among each part: the developing stage appeared earliest in AV and FL and latest in PH.(ABSTRACT TRUNCATED AT 250 WORDS)