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
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.|
|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.|
- Greenberg Handbook of Neurosurgery
- Fernández AA, Guerrero AI, Martínez MI, et al. Malformations of the craniocervical junction (Chiari type I and syringomyelia: classification, diagnosis and treatment). BMC Musculoskelet Disord. 2009;10 Suppl 1(Suppl 1):S1. Published 2009 Dec 17. doi:10.1186/1471-2474-10-S1-S1 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2796052/
- Hidalgo JA, Varacallo M. Arnold Chiari Malformation. [Updated 2019 Nov 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK431076/
- Chiari malformation type III: Case report and review of the literature. Christina Andica, Ristaniah D. Soetikno. Radiology Case Reports, 8, 3, 2013 https://doi.org/10.2484/rcr.v8i3.831
- The Chiari malformations. Donald M. Hadley. Neurology in Practice, 72, 2, 2002 http://dx.doi.org/10.1136/jnnp.72.suppl_2.ii38