4 types of Chiari malformation: 

1. Displacement of cerebellar tonsils 3-5mm caudal of the foramen magnum
– can be asymptomatic 

2. Cerebellar + brainstem + 4th ventricle displacement through foramen magnum 
– Most pts will have a lumbosacral meningocele or meningomeylocele 
Agensis of the corpus callosum and abnormal gyral patterns are also common 

3. High cervical meningocelphalocele on imaging 

4. Profound cerebellar hypoplasia on imaging 

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