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Arachnoid Cyst vs Epidermoid Cyst

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0:01

So, this case nicely illustrates the

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two principles of head-neck.

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When we're looking, especially

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at the posterior fossa,

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the purpose of the imaging is to define the

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anatomy, and eventually, the end

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goal is to see the anatomy.

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So here's an example of a patient that

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if you understand the anatomy,

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you can actually predict why they presented.

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So here's a heavily weighted T2-weighted image.

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And when we look at this heavily

0:28

weighted T2 image,

0:29

what we see is there's a cystic mass that's

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located right here in the left

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cerebellar pontine angle.

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Here is the porus Acusticus and extending

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through the porus Acusticus is

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the 7th-8th nerve complex.

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Now normally, the 7th-8th nerve complex gets from

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point A to point B in the straightest

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and shortest line.

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But look what's happening to the superior

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vestibular nerve. Instead of the superior

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vestibular nerve going straight,

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notice how it is being displaced

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anteriorly by this cystic mass that's

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located in the posterior fossa.

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So we see a cystic mass located

1:07

in the posterior fossa.

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This patient presents with some type of dizziness,

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which we can explain by the distortion in the

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normal course of the superior vestibular nerve.

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And the next thing that we want to be able to do

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is better characterize this on the

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T1 with and without contrast.

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So below is the non-contrast T1-weighted image.

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And we can see that this is a cystic mass.

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Again, from an anatomical standpoint,

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here is the porus Acusticus located here.

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And now we can see anterior displacement of the

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superior vestibular nerve when we give contrast.

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Notice how there is no enhancement whatsoever.

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So now we have to wonder,

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is this an arachnoid cyst or is it an epidermoid?

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Because as we'll see,

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epidermoids don't necessarily

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have to enhance either.

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But what allows us to differentiate

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between the arachnoid

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and the epidermoid is this sequence

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on your top right,

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which is the diffusion-weighted imaging sequence.

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So this DWI sequence obtained at the exact level

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of this T2-weighted image and the contrast-

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enhanced T1-weighted image showed that there's

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no increased diffusion signal on this sequence.

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And the lack of increased signal on the diffusion-

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weighted sequence confirms that this is

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an arachnoid cyst and not an epidermoid.

Report

Faculty

Suresh K Mukherji, MD, FACR, MBA

Clinical Professor, University of Illinois & Rutgers University. Faculty, Michigan State University. Director Head & Neck Radiology, ProScan Imaging

Tags

Temporal bone

Skull Base

Non-infectious Inflammatory

Neuroradiology

Neuro

MRI

Idiopathic

Head and Neck

Brain

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