The Arnold-Chiari malformation is a congenital malformation of the base of the skull with varying degrees of herniation of cerebellum and medulla into the spinal canal. Presentations include lower cranial nerve palsies, cerebellar limb signs, and upper motor neurone signs in the legs.
There are two common types of Arnold-Chiari malformation:
- type I:
- herniation of the cerebellar tonsils
- associated with syringomyelia
- type II:
- herniation of the cerebellar vermis and tonsils
- associated with meningomyeloceles and hydrocephalus