| Arnold Chiari Malformation
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Etiology
•Both Chiari type l and ll may be due to a malformed
posterior fossa.
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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.,
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Epidemiology
•Both Arnold Chiari l and ll are sporadic although type
l can be inherited
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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:
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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:
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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.
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| Arnold Chiari Malformation
| | Synopsis by: M.L. Grunnet M.D. (TX2000M20150)[64]
| |