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Vestibular Schwannoma

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So, this case will illustrate not only the most common

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indication we image the cerebellopontine angle,

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but it'll also help identify the most common pathology

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that we'll see in the cerebellopontine angle,

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and that is the vestibular schwannoma.

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So in the next series of cases,

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what we'll do is we'll help identify the imaging

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characteristics of the vestibular schwannoma and also

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separate it from some of the other diseases

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that can involve this area.

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We've already talked about arachnoid cysts and epidermoids.

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Those are non-enhancing lesions that can be separated by

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diffusion sequences and the heavily T2-weighted

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sequences. Now we'll talk about the vestibular schwannoma.

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So vestibular schwannomas typically involve the cerebello

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pontine angle and they can either involve the fundus of

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the internal auditory canal where they can be isolated,

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they can have a bicompartmental involvement,

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which is the internal auditory canal

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and the cerebellopontine angle,

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or they can predominantly just involve the

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cerebellopontine angle. In general,

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what we would like to see is a vestibular schwannoma

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involving the medial aspect of the internal auditory canal

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and the cerebellopontine angle, as is seen here.

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So in this particular case,

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this is a T2-weighted sequence and we can see this mass

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that is an extra-axial mass that's medially displacing

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the right middle cerebellar peduncle.

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When we look at the non-contrast T1-weighted image,

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we can see this mass is low signal,

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but the low signal is not as low as we see in the fluid

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in the fourth ventricle. So it's low signal,

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but it doesn't have the signal intensity of the fluid

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in the fourth ventricle. Then we give contrast.

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So when we give contrast,

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we can see this mass is very homogeneously enhancing.

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Now, there are some areas that do not enhance.

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Sometimes this may be due to calcification

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or it may be due to hemorrhage,

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but in general it's still a very avidly enhancing mass.

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But two features that you should look for on the

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contrast-enhanced series are the following.

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Is there involvement of the internal auditory canal?

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And number two,

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does this mass have an acute angle with

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relationship to the posterior fossa?

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Or is it more of a wider angle suggesting

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what we will refer to as the dural tail?

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So in this particular case,

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we can see that there is a very sharp demarcation and a

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sharp angle with respect to the adjacent

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cerebellar hemisphere.

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So when we have a combination of an avidly enhancing mass

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that's extra-axial without evidence of a dural tail,

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and then we look at the coronal image and we can see that

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this mass is extending into the internal auditory canal.

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This confirms the diagnosis of a vestibular schwannoma.

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The other thing that we can identify based on this study

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is why patients present with either hearing loss

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or dizziness. Why? Because remember anatomy.

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The four nerves of the internal auditory canal

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are the cochlear nerve, the facial nerve,

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the superior vestibular nerve,

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or the inferior vestibular nerve.

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The superior vestibular nerve is felt to be the

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most likely origin of a vestibular schwannoma.

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If it gets large enough,

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it can involve the cochlear nerve.

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So because this is a contained space,

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as this mass grows larger and larger, as you can see here,

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it's starting to involve the internal auditory canal.

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It compresses these nerves.

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And that's why patients can either present with hearing

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loss or they can present with dizziness.

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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