|Chiari Type||Anatomical Anomaly||Frequency of Hydrocephalus||Associated CNS Anoimalies|
|I||Tonsillar herniation ≥5 mm below plane of foramen magnum with moderate frequency of syringomyelia||Low||Multiple|
|II||Caudal herniation of vermis, brainstem, and fourth ventricle with high frequency of syringomyelia||High||Associated with myelomeningocele and multiple brain anomalies|
|III||Occipital encephalocele containing dysmorphic cerebellum and brainstem||N/A||N/A|
|IV||Hypoplasia or aplasia of cerebellum||N/A||N/A|
- Syndromic craniosynostosis: These disorders include Apert’s and Crouzon’s syndromes
- Endocrinopathies: These include achondroplasia, acromegaly growth hormone deficiency, and osteopetrosis or Paget’s disease.
- Neurocutaneous disorders: These disorders include NF1, acanthosis nigricans, blue rubber bleb nevus syndrome, giant congenital melanocytic nevi, LEOPARD syndrome, and Waardenburg syndrome.
- Beckwith-Wiedemann syndrome
- Ehlers-Danlos syndrome
- Craniocervical anomalies: These include basilar invagination, atlantoaxial assimilation and Klippel-Feil syndrome.
- Acquired tonsillar descent: Elevation in ICP due to conditions such as brain tumors and hydrocephalus may cause acquired tonsillar descent (56).