CT - Cerebellar atrophy: A 51-year-old woman with a long-standing seizure disorder treated with Dilantin was admitted for worsening gait. On examination her speech was dysarthric and she was unable to walk due to severe truncal ataxia. The non-contrasted CT scan in the left demonstrates marked cerebellar atrophy with enlargement of the cisterna magna and the more anteriorly located vallecula between the cerebellar tonsils. In the panel on the right, note the prominent pattern of cerebellar folia. Although the brain stem is mildly atrophic the remaining structures appear normal. Her cerebellar atrophy was most likely due to long-standing Dilantin use, but the differential of cerebellar atrophy includes paraneoplastic disease, vitamin E deficiency and neurodegenerative disorders such as olivopontocerebellar atrophy.