Bottom line: Arnold-Chiari malformations refer to a group of congenital malformations at the base of the brain where part of the cerebellum protrudes through the opening at the base of the skull. Clinical manifestations in Type I malformation include headache, cerebellar ataxia, spastic quadriparesis, downbeating nystagmus, or symptoms of cervical syringomyelia (segmental amyotrophy and sensory loss in the hands and arms). Sometimes these symptoms do not appear until adolescence or adulthood.
For details, see Neurologic Disorders Associated with Craniospinal Deformities. In: Adams and Victors’ Neurology. [AccessMedicine]