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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.

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. The very first patient with agenesis I saw was already in his 60’s and presented with a small stroke. And when I did the CT scan it was an incidental finding.

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.

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. What’s very striking is it actually looks like a head filled with water, with a couple of eggs floating in it. If you ever saw a picture.

Microcephaly. Microcephaly is a complex thing. Microcephaly can have a variety of etiologies, depending on when you discover it. What I mean by that is some people are born microcephalic because they may have a chromosomal syndrome, or Cornelia de Lange or fetal alcohol, or one of the STORCH, meaning syphilis, toxo, rubella, and all that type of syndromes. On the other hand, it can become an acquired process if you have perinatal asphyxia.

Macrocephaly is kids with big heads. Here we have again a big differential. It can be metabolic disease, like Sturge, Tay-Sachs, Hurler’s, some of those. Leukodystrophies like Alexander and Canavan are known to create progressively large head. You can see it sometimes in neurocutaneous syndromes, or bone disease. There is a syndrome called Sotos syndrome.