Chiari malformation

1-There is three types.

2-Chiari malformation type 1 is considered a normal variant.

A-The descent here is cerebellar tonsils in foramen magnum.

B-No compression of the fourth ventricle, no hydrocephalic changes.

C-Tonsillar position

-first decade---6 mm.

-second decade---5 mm.

-Fourth decade---4 mm.

-8 decade---3 mm.

3-Chiari malformation type 2

-Small sized posterior fossa.

-100% lumbar myelomeningocele.

-Downward displacement of the medulla and vermis.

-Supra tentorial hydrocephalus due to compression of the fourth ventricle.

-Manifestation seen in three levels

*At the posterior fossa

#Small posterior fossa.

#Gapping of the edges of foramen magnum.

#Concavity of the clivus.

#The fourth ventricle may be totally attenuated(can not be seen) or stretched giving tube like appearance.

#It gives dilatation of the lateral and third ventricle with no dilatation of the fourth ventricle simulating appearance of hydrocephalus due to aqueduct of sylvius obstruction but there are major difference in which in case of the latter the dilatation of the third ventricle is ballooned and dilatation of the lateral ventricle is symmetrical while in the former the third ventricle is not ballooned and the lateral ventricle is not symmetrical giving appearance of colpocephaly in which posterior horns of the lateral ventricle are much dilated than anterior ones.

*Supra tentorial changes:

#Colpocephaly.

#Large basal ganglia indenting lateral ventricles forming inverted 3 sign.

#Peaking of the quadrigeminal cistern due descend of tectum.

#Fenestrated falx, in the midline you can see the brain tissue crossing the midline and coming back across the midline once again.

4-Chiari malformation type 3

-More of the posterior contents descent into cervical canal.

-Chiari 2 + low occipital or cervical encephalocele.

-Contents of encephalocele : cerebellum, occipital lobes, medulla, pons and fourth ventricle.

-The herniated tissue is abnormal.
-It is better to be called cervical encephalocele rather than type 3 Chiari malformation.