Arnold-Chiari Syndrome: Defect in the formation of the lower
portion of the medulla (posterior fossa). Can be associated, according to
the type, with hydrocephalus, raised intracranial pressure, and respiratory
and cardiac center dysfunction. Infants may present with vomiting, mental
impairment, and weakness. Limb paralysis is possible. The presence in
adolescents usually is milder. Dizziness, weakness of the legs, headaches,
double vision, or deafness may be present. Raised intracranial pressure. In
type I, cerebellar displacement into the spinal canal occurs; however,
hydrocephalus and syringomyelia are variable.