Arnold-Chiari Malformation is a condition in which the cerebellum portion of the brain protrudes into the spinal canal. It may or may not be apparent at birth. Arnold-Chiari I type malformation usually causes symptoms in young adults and is often associated with syringomyelia, in which a tubular cavity develops within the spinal cord. Arnold-Chiari II type malformation is associated with myelomeningocele (a defect of the spine) and hydrocephalus (increased cerebrospinal fluid and pressure within the brain), which usually are apparent at birth. Myelomeningocele usually causes paralysis of the legs and, less commonly, the arms. If left untreated, hydrocephalus can cause mental impairment. Either type of Arnold-Chiari Malformation can cause symptoms of headache, vomiting, difficulty swallowing, and hoarseness.