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This is an MRI of the brain

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performed in a one day old child

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that had a known posterior fossa

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developmental abnormality in utero.

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The head is on its side right now

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due to this abnormality.

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So if we zoom out,

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we can see there is this occipital encephalocele,

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and we have protrusion of brain parenchyma

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into this encephalocele.

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And we have cystic membranes in there and

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a large CSF collection posteriorly.

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I'm going to rotate this to a more

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standard anatomic orientation,

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and I'm going to show this sagittal image,

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which shows we see the occipital

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lobes protruding into this,

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through this defect and the cerebellum.

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In addition to that,

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we see actually a large massa intermedia.

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There is actually sort of posterior

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displacement of the tectoplate.

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And additionally,

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we have syringohydromyelia

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in the lower cervical cord.

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So, these are features of an occipital

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and cerebellar encephalocele

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with intracranial developmental abnormalities,

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which form a constellation of features

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that can be referred to as a Chiari type 3 malformation.

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A Chiari type 2 malformation is intracranial

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developmental abnormality that is secondary

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to a myelomeningocele in the spine.

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Typically, lumbosacral.

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And because of that,

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you get a constant CSF leak that results in low

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intracranial pressures and result in sagging

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of the brainstem and cerebellum

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into the foramen magnum.

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That sagging takes place during development.

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So you get an enlarged foramen magnum.

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In this case,

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we have some of the same features of

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a defect,

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but instead of it being a spinal defect,

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it's a defect in the posterior

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cranial fossa here.

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So, an encephalocele that results

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in some of the features that you sometimes see

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in a Chiari type 2 malformation,

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is something that can result in a clinical phenotype

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referred to as a Chiari type 3 malformation.

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Now, a Chiari type 3 malformation is a

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characterization of what's going on,

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but is not uniquely descriptive of each patient.

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In each patient,

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you have to decide what is involved,

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what is normal, what is abnormal,

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and you have to determine how big is the abnormality.

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So, we measure the craniocaudal extent

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and the transverse extent of the defect.

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We have to determine whether major

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blood vessels go in there.

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In this case,

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we have the internal cerebral veins and straight

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sinus that's protruding back into this.

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So, I believe the torcula is going to be within

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this herniated, protruding area of brain.

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Well, that's important,

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because a neurosurgeon can't just say,

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well, this is a treacle-brain,

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I'm going to transect it at the defect.

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They need to find out what

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is protruding into there.

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They also benefit from us being able

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to determine what membranes exist,

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whether some of these membranes need shunting,

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need marsupialization or other treatment.

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So, this is an occipital encephalocele

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resulting in, among other things,

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features of a Chiari type 3 phenotype.