Chiari malformations are usually described as Type I which consists of a downward displacement of the cerebellar tonsils out of the inferior opening of the skull into the spinal canal or Type II malformations which have greater displacement of brain structures into the spinal canal. In addition to the cerebellar tonsils, there is also displacement of the inferior vermis.

It is not unusual for the Chiari malformations to have an associated accumulation of fluid within the interior of the spinal cord. This condition is called syringomyelia.

The most frequent symptoms of Chiari malformation include headache with pain at the base of the skull and upper neck, progressive scoliosis, cerebral dysfunction (difficulty with balance, coordination, disequilibrium) and where there is compression of the lower brainstem, there can be an alteration in voice, frequent respiratory tract infections and coughing when swallowing foods and fluids.

Thirty (30) to fifty (50) percent of patients with Chiari malformation type I may include basilar impression, atlanto-occipital fusion, atlanto-axial assimilation, Klippel-Feil deformity, cervical spinabifida occulta and scoliosis. More information can be found at the Institute for Neurology and Neurosurgery in New York City.