A German physician, Dr. Hans von Chiari, who described his findings during a postmortem evaluation, first named the disorder in 1891. Now, a century later, there are several classifications of the condition with numerous surgical treatments to improve the associated symptoms.
Chiari malformation is a defect in the formation of the lower part of the brain and cranium.
Two parts of the brain, the brain stem and the cerebellum, are longer than normal and protrude into the top of the spinal canal. There is essentially more brain tissue than cranial space to accommodate the cerebellum and brain stem. I is a very mild form of the disorder and does not have the associated anomalies listed above. With Type I, there is an excess of cerebellar tissue for the cranial size. Portions of the brain called cerebellar tonsils abnormally extend through the upper opening of the spinal canal, known medically as the foramen magnum.