Arnold Chiari malformations classification

Arnold Chiari malformations classification

Type I: Downward displacement of the cerebellum with elongation of the medulla such that the cerebellar tonsils egress through the foramen. 

Type II: Associated with lumbosacral myelomeningocele and numerous other nervous system malformations including:

  • Small posterior fossa
  • Cerebellar tonsil herniation through the foramen magnum
  • Elongated and thinned medulla
  • Characteristic beaking appearance of the quadrigeminal plate
  • Hydrocephalus
  • Syringomyelia and occasionally syringobulbia
  • Interdigitation of gyri along the interhemispheric fissure

Type III: An occipital encephalocele with protrusion of cerebellar remnants into the overlying sac. 

Type IV: Isolated hypoplasia of the cerebellum not associated with other nervous system malformations.

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