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Arnold Chiari Malformation
Etiology

Both Chiari type l and ll may be due to a malformed posterior fossa.
Pathogenesis

There many theories related to the causes of Arnold Chiari type ll including pulling of the brainstem and lower cerebellum into the foramen magnum by anchoring of the spinal cord by the meningomyelocoele. None really explains all the malformations.
Chiari l may be due to a small posterior fossa.,
Epidemiology

Both Arnold Chiari l and ll are sporadic although type l can be inherited
General Gross Description

Arnold Chiari type ll is almost always associated with a meningomyelocoele.
Consists of malformation of the brainstem and cerebellum leading to extension of the medulla and cerebellum through the foramen magnum where the cervical spinal cord should rest.
Usually associated with hydrocephalus
Arnold Chiari type l is not related to spina bifida, is often seen in adults and consists of herniation of the cerebellar tonsils through the foramen magnum around the cervical spinal cord.
•Examples:
Arnold-Chiari Malformation Arnold-Chiari Malformation Arnold Chiari Malformation
General Microscopic Description

Arnold Chiari ll shows variable malformations and repositioning of nuclei in the brainstem with disorganization and atrophy of the herniated cerebellum.
Arnold Chiari l shows some loss of neurons and gliosis of the herniated cerebellar tonsils.
•Examples:
References

Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp. 1302-3
Poirer J et.al. Manual of basic neuropathology. Philadelphia: Saunders, 1990, pp. 203-4.

For Most Current Information Search Medline at National Library of Medicine
This link will directly take you to the relevant new literature
Arnold Chiari Malformation
Synopsis by: M.L. Grunnet M.D. (TX2000M20150)[64]
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