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This is an MRI of the brain in a seven-month-old

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child with macrocephaly or enlarged head.

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And we can see, if we go down,

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there's cystic enlargement of the

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posterior cranial fossa.

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And not only is there cystic enlargement

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of the posterior cranial fossa,

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that cystic area is in free continuity

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with the fourth ventricle,

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and the cerebellar hemispheres are splayed.

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We're not seeing an intervening cerebellar vermis.

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So, if we look at this sagittal image,

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we can see the cerebellar vermis is hypoplastic,

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is uplifted.

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We see this is the superior medullary velum.

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But then, normally, that would reach the

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fastigium of the fourth ventricle,

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the little pointed portion of the fourth ventricle.

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We don't see that,

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and we do not see the intramedullary velum.

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So this is a hypoplastic,

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uplifted cerebellar vermis.

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In this configuration,

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where the nose and the face

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is pointed this direction,

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some people sometimes refer to this as

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counterclockwise rotation of the cerebellar vermis.

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Now,

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there's other abnormalities that we see as well.

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We can see this is the straight sinus

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leading to the torcula.

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That is elevated.

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The torcula is usually much lower in position.

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In particular,

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this right here is the nuchal ligament.

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The nuchal ligament attaches to the occipital bone,

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and there is a slight little protrusion known

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as the external occipital protuberance,

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where the torcula is at the confluence

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of the superior sagittal sinus

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and the straight sinus,

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laterally forming the transverse sinuses,

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there is an internal occipital protuberance.

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Now, if we look on this CT scan,

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we can see the internal occipital protuberance,

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but that is markedly elevated from the location of

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the nuchal ligament or where the external

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occipital protuberance would be.

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That right there is actually a finding that in the

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days of radiographs prior to CT scans and MRIs,

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a lateral skull radiograph could be used to show

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this massive enlargement of the posterior cranial fossa

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because of elevation of the

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internal occipital protuberance.

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Well, this, therefore,

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is massive cystic dilation of the posterior

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cranial fossa in the setting of a hypoplastic

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cerebellar vermis and elevation of the internal

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occipital protuberance and its associated to torcula.

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This is referred to as a classic Dandy Walker malformation.

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In addition to a classic Dandy Walker malformation,

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we see there's developmental abnormality

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of the corpus callosum,

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there's AP shortening of the corpus callosum,

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and we see marked thinning of the posterior body

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isthmus and splenium of the corpus callosum.

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So this patient has, as their primary malformation,

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a Dandy Walker's malformation,

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but they additionally have some posterior

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corpus callosal dysgenesis.