Arnold-Chiari malformation (Type II)

A type II Arnold-Chiari malformation is characterised by descent of part of the cerebellum and fourth ventricle into the spinal canal, often to the midcervical region. The lower nerves are stretched and the cervical nerve roots run horizontally or in an upward direction.

It is associated with:

• spinal disease:
  • meningomyelocoele
  • syringomyelia
  • Klippel Feil
    
    
• cranial disorders:
  • principally hydrocephalus - 85% of cases
  • aqueduct stenosis, small posterior fossa, basilar impression, fusion of the superior and inferior colliculi, hypoplastic tentorium cerebelli and falx
    
    
• others:
  • developmental anomalies of the cardiovascular, GI and GU systems in 10% of cases