By prenatal ultrasound, cerebellar hypoplasia is diagnosed if the cerebellum measures more than two standard deviations below the mean. In adults, cerebellar hypoplasia is typically diagnosed by computer tomography or magnetic resonance imaging. Cerebellar hypoplasia can be diagnosed if there is a small cerebellum with fissures of normal size compared with the folia (this is a distinguishing characteristic compared with cerebellar atrophy).