Cerebellar hypoplasia is a type of congenital morphological cerebellar abnormality in which the cerebellum has reduced volume, but a normal shape, and is stable over time . The pattern of volume loss may be regional (affecting only part of the cerebellum) or global.
Global cerebellar hypoplasia can appear indistinguishable from diffuse cerebellar atrophy on a single study and can only be distinguished from the latter by demonstrating or implying (clinically) that there has been no change over time .
The primary causes of global cerebellar atrophy are chromosomal abnormalities, metabolic disorders, genetic syndromes, and migrational disorders while congenital infections (cytomegalovirus followed by rubella and varicella viruses) are considered as secondary causes .
All imaging modalities show a generalized reduction in size and volume of the cerebellum (involving both hemispheres and vermis) however its shape is preserved.