Arnold-Chiari Malformation

The Arnold-Chiari malformation is a malformation of the brain in which part of the brainstem and cerebellum are herniated into the cervical vertebral canal through the foramen magnum.

Arnold-Chiari malformations are classified anatomically:

• Type I
• downward displacement of cerebellar tonsils only
• associated with syringomyelia in up to 80% of cases
• many patients are asymptomatic
• mean age of onset 25
• Type II
• downward displacement of cerebellum, lower pons and medulla
• commonest form
• tends to present in childhood
• associated with spina bifida and hydrocephalus
• more severe form
• Type III
• cerebellar herniation into a high cervical meningocele
• Type IV
• Hypoplasia/aplasia of the cerebella hemispheres

Clinical manifestions of Arnold-Chiari include:

• Downbeat nystagmus
• Headaches – made worse by valsalva manoeuvres
• Vertigo
• Tinnitus
• Dysarthria
• Dysphagia
• Parasthesias
• Facial pain

References:

OMIM: Chiari malformation type I. Available at http://omim.org/entry/118420

OMIM: Chiari malformation type II. Available at http://omim.org/entry/207950

Pieh, C. and Gottlob, I. Arnold-Chiari malformation and nystagmus of skew. J Neurol Neurosurg Psychiatry. 2000; 69(1): 124-126.