| Arnold Chiari Malformation
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Etiology
Unknown
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Pathogenesis
There are a number of theories of pathogenesis of A-C
malformation including Traction on the spinal cord and
brainstem by a meningomyelocoele pulling into the
spinal canal, pushing the cerebellum and brainstem
downward by the hydrocephalus or an abnormally small
posterior fossa. These are helpful ways to think of
pathogenesis but no one is sure of the real cause.,
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Epidemiology
Arnold Chiari Malformation type II is the most comman
type and is characterized by elongation of the
cerebellar tonsils and malformation of the brainstem
so that both structures extend through the foramen
Magnum into the upper cervical region of the spinal
cord. It is usually associated with meningomyelocoele
and hydrocephalus. A-C malformation type I is less
severe and can cause brainstem signs in adults. Type
III consists of a cerebellar encephalocoele and is
very rare.
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General Gross Description
In type II the cerebellar tonsils and abnormally formed
brainstem are seen in the foramen magnum and upper
cervical spinal canal. This is associated with
hydrocephalus and usually a lumbar meningomyleocoele.
In type on only the cerebellar tonsils are impacted in
the foramen magnum.
•Examples:
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General Microscopic Description
Microscopically the cerebellar tonsils are gliotic and
have lost normal neuronal patterns. The hydrocephalus
is due to aquaductal atresia or gliosis or impaction of
the tonsils and brainstem in the foramen magnum blocking
normal passage of CSF out of the foramina of Luschka
and Magendie.
•Examples:
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Clinical Correlation
The Arnold Chiari malformation may be associated with
normal intellagence if the hydrocephalus is shunted or
mental retardation. It is also associated with lower
limb paralysis and urinary and fecal incontinence due
to the meningomyelocoele. Type I can cause neck pain
and cranial nerve signs and may sometimes have to be
treated with surgical decompression.
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References
1. Poirier, Gray, and Escourolle. Manual of Basic
Neuropathology 1990. pp 203-204.
2. Cotran, Kumar and Robbins. Pathologic Basis of
Disease. pp 1302-1303.
3. Graham and Lantos. Greenfield's Neuropathology.
pp 418-422.
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| Arnold Chiari Malformation
| | Synopsis by: Dr MLGrunnet (Tx2000M20150)[362]
| |