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Retrovermian/Infravermian Arachnoid Cyst

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This is an MRI of the brain

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in a six-year-old child with seizures,

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that at an outside institution

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was referred to as a Dandy-Walker variant.

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Now, if we look,

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we see the normal development

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of the cerebellar vermis,

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and that normal development of

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the cerebellar vermis tells us

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that this is not a Dandy-Walker

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spectrum malformation.

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There is no hypoplasia or

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intrinsic developmental abnormality

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within the cerebellar vermis.

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Now, there is prominence of CSF

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posterior and inferior to

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the cerebellar vermis.

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And if we look on this axial image,

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this CSF prominence is on both

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sides of the falx cerebelli,

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and it goes behind both

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cerebellar hemispheres.

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It's hyperintense on T2-weighted imaging,

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suppresses on FLAIR imaging,

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and demonstrates facilitated diffusion.

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So, this is an arachnoid cyst.

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There is no significant mass

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effect upon the cerebellum.

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I think this more likely is,

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given the absence of contra abnormality,

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just chronic remodeling and

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chronic slight expansion of the

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posterior cranial fossa.

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We also see chronic elevation of

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the torcula and the superior

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angulation of the posterior

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aspect of the straight sinus

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related to this.

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So, this is a retrovermian arachnoid cyst

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that's also infravermian.

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But there is no Dandy-Walker spectrum malformation.

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So, that's very important

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that there is not a malformation.

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Now, we do see CSF slightly prominent

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in the folia of both cerebellar hemispheres.

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And in a child with chronic anti-epileptic medications,

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you sometimes can see that.

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But that's not an intrinsic

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developmental abnormality.

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So, this patient does not have

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an intrinsic developmental abnormality.

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Therefore, there's no need to do a genetic

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workup for a cerebellar malformation.

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This is a retrovermian and

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infravermian arachnoid cyst.

Report

Description

Faculty

Asim F Choudhri, MD

Chief, Pediatric Neuroradiology

Le Bonheur Children's Hospital

Tags

Pediatrics

Neuroradiology

MRI

Idiopathic

Congenital

Brain

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