Chiari Malformation

The Chiari malformations consists of four types of hindbrain abnormalities, probably unrelated to each other. The majority of Chiari malformations are types 1 or 2. It is a heterogeneous group of conditions, with the underlying commonality of disruption of normal CSF flow through the foramen magnum (FM). It may be congenital or acquired. Cerebellar tonsillar herniation on MRI: criteria vary, > 5mm below the foramen magnum is often cited, but is neither essential nor diagnostic of the condition. Treatment, when indicated, is surgical.