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Arnold Chiari Malformation Radiology and Basic Concepts



Contents



What are Chiari Malformations?

  • Chiari Malformations are a group of abnormalities which involve the rhombencephalon which is also called as Hind brain and the contents of the CV junction.
  • We have 6 types of Chiari malformations

What are Chiari Malformations?

What is Chiari 1 Malformation?

  • In the MRI below, the foramen magnum has two points, the Basion and the opisthion. A line joining these points is called McRae's line. The herniation of tonsils and other brain structures is measured from this line.
  • 5-mm or more caudal displacement of the cerebellar tonsils inferior to the foramen magnum
  • This herniation and compression restricts normal CSF flow across the craniocervical junction
  • Commonly associated findings are cervical syringomyelia(50-75%) and, on occasion, hydrocephalus (10%)



What is Chiari 2 Malformation?


  • In Chiari 2 Malformation there is a greater amount of tissue that extends into the spinal canal compared to the chiari 1 malformation 
  • There is  characteristic displacement of the medulla, fourth ventricle, and cerebellum through the foramen magnum. 
  • almost all neonatal patients with Chari II have a  myelomeningocele
  • Can have tectal beaking


What is Chiari 3 Malformation?

  • Extremely rare 
  • Characterized by low occipital and high cervical encephalocele
  • There is herniation of posterior fossa contents, that is, the cerebellum and/or the brainstem, occipital lobe, and fourth ventricle. 



What is Chiari 4 Malformation?

  • This is characterized by marked cerebellar hypoplasia or aplasia and tentorial hypoplasia. 
  • There is no hindbrain herniation.
  • No hydrocephalus


What is Chiari type 0 and Chiari Type 1.5 ?

Chiari type 0
  • syringohydromyelia without hindbrain herniation that respond to posterior fossa decompression  (CSF flow across foramen magnum impaired)
Chiari type 1.5
  • Severe form of Chiari 
  • Entire cervicomedullary junction (and obex) is situated below the foramen magnum 



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