Development and developmentaldisorders of the human cerebellum

The human cerebellum develops over a long time, extendingfrom the early embryonic period until the first postnatal years.This protracted development makes the cerebellum vulnerable to abroad spectrum of developmental disorders. The development ofthe cerebellum occurs in four basic steps: 1) characterizationof the cerebellar territory at the midbrain-hindbrain boundary;2) formation of two compartments for cell proliferation: first,the Purkinje cells and the deep cerebellar nuclei arise from theventricular zone of the metencephalic alar plate; second,granule cell precursors are formed from a second compartment ofproliferation, i. e. the upper rhombic lip; 3) inward migrationof the granule cells: granule precursor cells form the externalgranular layer, from which (and continuing into the firstpostnatal year), granule cells migrate inwards to their definiteposition in the internal granular layer, and 4) formation ofcerebellar circuitry and further differentiation. Theprecerebellar nuclei, i. e. the pontine nuclei and the inferiorolive, arise from the lower rhombic lip. Developmental disordersof the cerebellum are often accompanied by malformations of theprecerebellar nuclei. In this review the development of thecerebellum and some of its more frequent developmentaldisorders, such as the Dandy-Walker and related midlinemalformations, and the pontocerebellar hypoplasias, arediscussed.