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Epidermoid Cyst – Internal Characteristics

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So here's another example of an epidermoid.

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But in this particular case, we're going to focus on

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the addition of a specific sequence, and that's the

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heavily T2-weighted sequence, but also explain the

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importance of looking at all the sequences to avoid

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the potential pitfall of calling something a

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negative study when there's actually pathology.

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So on the top left sequence,

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this is a T2-weighted image, and when you draw a

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line down the middle and you compare

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one side to the other side,

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what I want you to do is focus on the cerebellopontine

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angle. Now, if we look at this,

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these really look pretty symmetric, and maybe with

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the leap of faith, there may be a little bit more

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impression on the flocculus, but I think

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that's a tough call to make.

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On the right-hand side is a contrast-enhanced T1

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weighted image with fat suppression. And on the T1

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weighted image with contrast with fat suppression,

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we can see that there's no enhancement

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in either cerebellopontine angle.

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So if we didn't look at all the sequences,

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in fact, if we didn't even include the sequences,

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we could call this study negative

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in a patient that presents with dizziness,

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the next thing that we have to do is take a

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look at our diffusion-weighted imaging.

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And when we look at our diffusion-weighted

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imaging located at the bottom left here,

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we can see the high diffusion signal which we

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learned in the last vignette was indicative of

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an epidermoid. So in general, we could say,

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aha, there is likely an epidermoid here. But really, in

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order to perform state-of-the-art imaging at your center,

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you really need to perform the heavily

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T2-weighted images.

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Because when you perform the heavily

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T2-weighted images,

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what you now see is this area of increased signal

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that's located in the cerebellopontine angle.

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And in fact,

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with a leap of faith, you can see that this mass is

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actually impinging on this external portion of the

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fifth nerve, and compare this to the normal

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appearance of the fifth nerve on the opposite side.

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So when we take a look a little bit more inferiorly,

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again, we can see this subtle area of increased

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diffusion signal. And again,

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I want to call your attention to the relatively

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normal appearance on our standard sequence.

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But remember,

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this patient presented with dizziness, and when we

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look at this heavily T2-weighted image, we can now

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explain the reason that this patient presented with

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dizziness. Why? Look at the patient's right side.

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We can see the internal auditory canal,

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we can see these two nerves which are

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extending from medial to lateral.

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And when we look at the porus acusticus at the

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cerebellopontine angle, we just see fluid.

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But when we look at the patient's left side,

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we can see that these two nerves,

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especially the inferior vestibular nerve,

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is extending into this frond-like mass which is

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the infrastructure of the epidermoid.

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So it's this mass effect on the epidermoid directly

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abutting the superior and the inferior vestibular

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nerve that is causing the patient's dizziness.

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And the only way we'll be able to confirm this

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diagnosis is with these heavily

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T2-weighted sequences.

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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