a posterior fossa dysplasia, mimicking a space-occupying lesion; it is also called dysplastic gangliocytoma of the cerebellum (see dysplastic cerebellar gangliocytoma), and is considered a complex hamartoma or malformation rather than a true neoplasm. The histological appearance is that of cellular disorganization, hypertrophied granular neurons, and axonal hypermyelination in the molecular layer of the cerebellum. It may occupy an entire cerebellar hemisphere; macroscopically the cerebellar folia appear hyperplastic. CT may be misleading since it shows a poorly delineated iso- or hypointense posterior fossa lesion without enhancement but with deformity of the fourth ventricle associated sometimes to hydrocephalus, that may mimic a posterior fossa neoplasm. MR shows a characteristic T2 pattern of laminated increased signal.