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Retrovermian Arachnoid Cyst

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This is a 16-year-old child

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who was in a car accident, hit their head,

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and a head CT was performed to look for signs of

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intracranial traumatic injury.

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Fortunately,

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there were no signs of traumatic injury.

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No fractures, no bleeding or anything like that.

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But one thing that caught people's attention was

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this cystic appearing area here does not

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look like an acute traumatic etiology,

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but it definitely was puzzling,

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and it resulted in a brain MRI being performed.

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An MRI of the brain was performed and shows a

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normal development of the cerebellar vermis.

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We see the superior medullary velum,

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the inferior medullary velum,

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that little angle where they come together

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is called the fastigium,

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and there's a normal fastigial angle.

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Overall,

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the cerebellar vermis looks on this mid-sagittal

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image, like the video game character Pac-Man,

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directed towards the brainstem.

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So the cerebellar vermis is normal,

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but there is prominence of CSF posterior

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to the cerebellar vermis.

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It's pushing slightly to the right,

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the falx cerebelli.

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This is demonstrating hyperintense

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signal on T2-weighted imaging.

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It suppresses on FLAIR imaging.

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It's hypointense on T1-weighted imaging,

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and it demonstrates facilitated diffusion.

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All of those other features help us know

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that this is just an arachnoid cyst.

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It's an arachnoid cyst behind

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the cerebellar vermis.

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So, it's known as a retrovermian arachnoid cyst.

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This is normal.

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This is not a Dandy-Walker spectrum malformation.

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This does not require imaging follow-up.

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This does not require neurosurgical consultation.

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This does not require consternation

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on the part of the clinical team.

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This does not require anxiety on the part of the patient.

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This is a normal finding.

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Now, notice this retrovermian arachnoid cyst results

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in slight elevation of the torcula.

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So, the position of the torcula alone actually is

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not a feature to diagnose

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or exclude a Dandy-Walker spectrum malformation.

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This patient does not have a Dandy

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Walker spectrum malformation.

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This patient does not have any

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pathologic abnormality.

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They have a retrovermian arachnoid cyst,

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which is a normal variant.

Report

Description

Faculty

Asim F Choudhri, MD

Chief, Pediatric Neuroradiology

Le Bonheur Children's Hospital

Tags

Pediatrics

Neuroradiology

MRI

Idiopathic

Congenital

CT

Brain

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