According to the National Institute of Neurological Disorders & Stroke, chiari malformations that can be acquired and are usually discovered during adulthood are classified as type 1 CMs. These CMs involve the lower part of the cerebellum extending into the foramen magnum (the hole in the base of the skull through which the spinal cord passes). The brainstem is not involved in this type. Type 2, also known as classic CM, occurs when both the cerebellum and the brainstem go into the foramen magnum. Type 2 CMs are usually accompanied by myelomeningocele (a form of spina bifida that occurs when the spinal canal and backbone don't close before birth). This can result in partial or complete paralysis.
