Arnold-Chiari malformation: a diagnostic challenge.

Arnold-Chiari malformation is a disorder of embryologic development. In Type I, there is cerebellar displacement into the spinal canal, but hydrocephalus and syringomyelia are variable. Type II usually is manifested by severe hydrocephalus and myelomeningocele in infancy. Type I malformations may pose diagnostic challenges because they often produce bizarre and vague symptoms. A careful history and physical examination, coupled with neurologic testing, especially magnetic resonance imaging, will lead to the correct diagnosis.