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Classification of Arnold Chiari Malformations

What are Arnold Chiari Malformations?


  • These comprise a group of abnormalities involving the rhombencephalon (hindbrain) and the contents of the CV junction 
  • With common feature of impaired CSF circulation through the foramen magnum  
  • May be Congenital or Acquired
  • Ranging from simple herniation of the cerebellar tonsils through the foramen magnum to complete agenesis of the cerebellum 
  • Presently there is no consensus regarding the precise definition, classification, etiology and the surgical management 
  • Five types 
  • No anatomical or embryological correlation between them 


Historical Background of Arnold Chiari Malformations

  • 1883, John Cleland (Professor of anatomy in Glasgow, Scotland) - described hindbrain hernia in a child with myelodysplasia.
  • 1891 and 1896, Hans Chiari- (Professor of Pathology at German University, Prague, Czechoslovakia): analyzed data from >40 postmortem examinations of patients with hindbrain malformations
  • Chiari malformations I, II and III were coined in the earlier work and Chiari malformation IV was added in 1896 publication. 
  • 1894, Julius A. Arnold(Professor of Pathology at Heidelberg, Germany)- described a single myelodysplastic patient with associated hindbrain herniation.
  • Schwalbe & Gerdig included Arnold name in the eponym & designated it ARNOLD –CHIARI malformation 
Historical Background of Arnold Chiari Malformations

What are the types of Chiari Malformations?

Chiari type 0 malformation

  • alteration in Cerebro Spinal Fluid (CSF) hydrodynamics at the level of the foramen magnum. 
  • they have syringomyelia either without tonsil herniation or with only mild tonsil herniation

Chiari Type I malformation

  • caudal herniation of the cerebellar tonsils more than 5 mm below the foramen magnum
  • typically associated with hydrosyringomyelia.
  • not usually accompanied by descent of the brain stem or IV ventricle, nor associated with the presence of hydrocephalus.
  • Most common type
  • Presents in young 

Chiari type II malformation

  • caudal herniation of the cerebellar vermis, brain stem, and IV ventricle through the foramen magnum. 
  • associated with myelomeningocele, hydrocephalus, and, less frequently, hydrosyringomyelia. 
  • hypoplastic tentorium cerebelli, cranial lacunae, anomalies of the Sylvius aqueduct may exist.

Chiari type III malformation

  • consists of occipital encephalocoele, with some of the intracranial defects associated with Chiari II malformation.

Chiari type IV malformation

  • cerebellar aplasia or hypoplasia, associated with aplasia of the tentorium cerebelli.

Images showing various Chiari malformations


Image of a Type 1 Arnold-Chiari Malformation. The cerebellum has descended 7mm and there are herniated cerebellar tonsils into the foramen magnum.
Image of a Type 1 Arnold-Chiari Malformation. The cerebellum has descended 7mm and there are herniated cerebellar tonsils into the foramen magnum.
Artist's representation of a Chiari II malformation showing the points of potential obstruction that yield different subtypes of hydrocephalus
Artist's representation of a Chiari II malformation showing the points of potential obstruction that yield different subtypes of hydrocephalus
Neonate with Chiari malformation type III.T2-weighted mid-sagittal MRI scan of the patient shows a small posterior fossa, an deep parieooccipitalis fissure (open arrow), ad a partial callosal agenesis (curved arrow), and a caudal herniation of part of the brain stem through the foramen magnum, with inferior tip appearing between C5 and C6 (closed arrow). (https://www.sciencedirect.com/science/article/pii/S1930043315302697)
T1 weighted sagittal MRI showing a so called “Chiari IV” or primary cerebellar agenesis. There is a tiny portion of residual quadrangular lobule just caudal to the tectum and a normal sized posterior fossa. No associated meningomyelocele is present.
T1 weighted sagittal MRI showing a so called “Chiari IV” or primary cerebellar agenesis. There is a tiny portion of residual quadrangular lobule just caudal to the tectum and a normal sized posterior fossa. No associated meningomyelocele is present.

References

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