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

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