CNS defects

[aspiringmd1015]

can anyone explain the assocation of arnold chiari and syringomyelia? is it type 1 and 2 that are associated with syringo? whats the mechanism?

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[Transposony]

http://forums.studentdoctor.net/threads/dandy-walker-hydrocephalus.1100744/

 

[aspiringmd1015]

Arnold Chiari:
A congenital anomaly resulting from a normal-sized cerebellum developing in an abnormally small posterior fossa with a low tentorial attachment. There is a narrow craniospinal junction and malformation of the posterior fossa leading to downward displacement of the medulla, fourth ventricle, and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle. This results in impaction of the foramen magnum, compression of the cervicomedullary junction by the ectopic tonsils, and interruption of normal flow of cerebrospinal fluid (CSF). Two types, type I is asymptomatic (till adulthood) and type II is symptomatic and commonly associated with meningomyelocele and syringomyelia. Symptoms arise from dysfunction of brainstem and lower cranial nerves.
epic, but the ectopic tonsils are referring to the actual displacement? or is it really ectopic meaning its tissue thats present thats not suppose to be there.

 

[aspiringmd1015]

and the "assocations" with lumbar meningomyelocele and syringomyelia, are those just assocations that we normally see, or is there an actual mechanism of the displaced tonsils causing something downstream?

 

[megaman123]

I think it is just mechanical during development: You push the cerebellum down, the spinal cord should go down with it (only in Chiari II tho). Chiari I is the only one associated w/ syringomyelocele.

 

[aspiringmd1015]

so with the chiari 1, you have the tonsils that are dsiplaced but NOT the vermis, so that leads to cavitation of the spinal cord?

 

[aspiringmd1015]

also, side question: sattar explains that alzheimers occurs because of the APP which undergoes beta cleavage giving you the B-app product which isnt degradable and accumulates and damages neurons, fair enough, but why does the tau protein get hyperphosphrylated?

 

[megaman123]

For Chiari 1, I don't think the tonsil displacement has a large part to do with it. It probably has to do with some narrowing of the central canal of the spinal cord, because most of the time you don't see symptoms of sphingomyelocele until 25 + y/o. Just a guess.

For AD, AD has many hypotheses for its pathogenesis. The two leading hypotheses are the Tau protein hypothesis and beta amyloid hypothesis. They are two separate hypotheses even though both are seen. They both create aggregates, but tau aggregates are microtubule proteins that have become hyperphosphorylated to a critical point causing aggregation vs the APP undergoing beta cleavage for beta amyloid. No one knows which is the right one for pathogenesis