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Chiari Malformations

Chiari malformations. Type I Chiari is one where there is herniation of the cerebellar tonsils. That’s a very classic type of description, many of you probably recall Chiari malformations. Frequently Chiari’s are asymptomatic until later. Not everyone presents with major symptoms right away. Type II includes what’s said in type I, but there is an association of other anomalies. There is an elongation of caudal medulla, which is an important finding, and there is a kinking of the cervical medullary junction and type II always implies also a lumbosacral meningomyelocele. 

Type II involves spina bifida of the cervical spine whereby the defect extends to the bony area. And type IV is a variant with cerebellar hypoplasia and occipital encephalocele. But it turns out that type II is the most common one. So if anybody asks you, "What’s the most common neural tube problem, or the most common Chiari malformation?" it will be Chiari type II. So here we show you a picture that illustrates the major points. The blue structure here is the foramen magnum, here’s the foramen and this is the skull. Here we have the midbrain, this could be the cerebral peduncle, right here is the belly of the pons, and the medulla begins here and this would then be the medullo-cervical junction. And this may be distorted in an Chiari II. Here is some of the cerebellum herniating.

Then here is a syrinx that is often associated. So you have all these anomalies. So what happens then is at some point in the life of this youngster it may really interrupt cerebral fluid flow and therefore they may develop some hydrocephalus and headaches. They may have some motor problems. They may present kind of like a CP patients because there is constriction of the medullary pyramids when they get distorted, so you get paramental track signs.

Polymicrogyria is often due to some sort of acquired insult where the brain has a few too many neurons and there are too many gyri that are very very small. And it usually results in pretty severe seizure disorders. There is schizencephaly where there is a gray matter line cleft that may extend clear across the brain, from the pial lining to the ependymal lining. You may recall that the ependyma are the cells that line the ventricle. Agenesis of the corpus callosum is a fairly reasonably commonly encountered anomaly. It can be isolated, in which case you may not even know that a person has agenesis of the corpus callosum.

And when I did the CT scan it was an incidental finding. The person was a veteran, had been in World War II, and so on. On the other hand, it can be accompanied by other problems. It may be just a part of a bigger problem. In which case people could have significant mental retardation, seizures, so it may be part of non-ketotic hyperglycinemia, it could be part of neonatal ALD, meaning adrenal leukodystrophy, or pyro-dehydrogenase deficiency which is a mitochondrial problem. It could be part of Icardi syndrome. Icardi syndrome, by the way is a kid that has some eye problems, particularly retinal problems, presents with infantile spasms and you do the imaging and there’s no corpus callosum. It’s usually females, but I don’t think they’ll ask you to know all the features of Icardi syndrome.

Porencephaly is not really often a malformation. This can often be simply the residue of a small stroke. It is just a CSF-filled space where there ought to be brain. Should be distinguished from hydranencephaly. Hydranencephaly is a congenital absence of the cerebral hemispheres and we are not fully sure how this comes about, but it is very striking when you look at an MRI or a CT scan. Because the cerebral mantel is completely missing. What you normally see is well-formed basal ganglia.