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This is an MRI of the brain in a 13-year-old

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with developmental delay,

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as well as some seizures.

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And there are several things that we see.

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First of all,

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in this image,

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we do not see a septum pellucidum.

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If we go up,

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we actually see there's midline continuity of

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gray matter across the anterior aspect

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of the interhemispheric fissure.

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Now, if we go down lower,

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we see two separate thalami.

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So, remember we talked in the holoprosencephaly

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spectrum disorder that the thalami

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are a part of the diencephalon,

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whereas the cerebral hemispheres are

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a part of the telencephalon.

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So together,

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the diencephalon and telencephalon

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are the prosencephalon.

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Well, we don't have a prosencephalic abnormality

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because the diencephalon is normal.

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So this is an isolated telencephalic abnormality.

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Well, what else do we see that's abnormal?

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Well, in this sagittal image,

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we see segmental dysgenesis of the mid

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portion of the corpus callosum.

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There's some gray matter heterotopia here,

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abnormal gray matter in this location.

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And if we go out to the side,

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there's almost vertical

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extension of the sylvian fissures here.

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And this right here is an abnormality that's

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known as Syntelencephaly.

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Syn meaning like synapse

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coming together of the telencephalon.

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It's a milder version even of a whole

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prosencephaly spectrum disorder.

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We still see what's an azygous,

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or unpaired anterior cerebral artery

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and midline continuity of the telencephalon.

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But we're not seeing all the other features

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that would make this a true prosencephalic abnormality.

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So, Syntelencephaly is an even milder

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hemispheric cleavage abnormality than

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lobar holoprosencephaly.