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Subarachnoid Seeding from Medulloblastoma

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This was a scan of a child that was being

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evaluated for recurrence of medulloblastoma.

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On the T1-weighted scan,

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before contrast,

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we note that the signal intensity of the

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vertebral body is just a little bit more

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bright on the T1-weighted scan

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than one would expect.

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This is yellow fatty marrow replacement for

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from radiation therapy.

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I noticed that also that the skull base,

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the patient has had surgery for the

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medulloblastoma. But even on the T1-weighted

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scan, if we just magnify a little bit,

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we see in the thoracic region that there are

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these areas of nodularity on the surface of

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the spinal cord with some widening of the

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subarachnoid space. As I mentioned,

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for subarachnoid seeding, really,

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we need post-gadolinium-enhanced scans,

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the T1-weighted and T2-weighted scans,

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unless it's pretty gross

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disease like this, are often negative.

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So when go to the post-gadolinium-enhanced images,

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you can see very thick contrast enhancement on

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the posterior portion surface of the spinal

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cord, indicative of subarachnoid seeding.

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There are some areas also on the anterior

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aspect at the C6 level.

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So I went back to look at the prior studies on

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this patient to see where the subarachnoid

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seeding was in the past that they were looking for.

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So if we go back to the patient's earliest

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most study and just pull up some

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representative images, pre and post-contrast.

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This is the flare scan.

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We see this large infiltrative

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mass in the posterior fossa,

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predominantly in the midline,

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but extending to the right side.

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And it just looks kind of aggressive the way

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it has enhancing areas, as well as non

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enhancing areas, but just sort of

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infiltrating the fourth ventricle

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and leading to hydrocephalus.

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So medulloblastomas are grade four,

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the most malignant of the brain tumors.

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Usually on the ADC maps,

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they're going to be dark in signal intensity.

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So this is diffusion-weighted scan.

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I'll bring up the diffusion-weighted image.

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So bright on the diffusion-weighted image,

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but dark signal intensity on the ADC map,

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reflecting low ADC,

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which is usually a marker of hypercellularity.

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And this is very typical of a medulloblastoma

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in the posterior fossa. On this scan,

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the patient did have surveillance for

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subarachnoid seeding, and on the post

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gadolinium-enhanced scans, while you see some

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of the enhancement of the

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posterior fossa mass,

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the scans through the spinal cord looked

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pretty normal. However, the CSF was positive.

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So this is an example of a patient

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who had medullobastoma,

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who had a relatively negative cord

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evaluation, pre and post-contrast,

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but had positive CSF in there.

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And then in follow up, and again,

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the follow up that I was looking at was four

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years after the initial resection of the tumor,

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had all of this bad subarachnoid seeding.

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Just to make the point on the examination of

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the brain, the only area of concern on the study.

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It looks like they got the primary tumor pretty well,

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except there was this one small area of

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enhancement which could represent subarachnoid

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seeding of the ependymal surface of the

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fourth ventricle, and then an additional seed

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at the interpeduncular cistern of the midbrain.

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So in this case,

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the primary tumor was taken care of,

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but unfortunately,

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the subarachnoid bread of the tumor was what

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was the main issue in four year follow up.

Report

Description

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Spine

Neuroradiology

Neoplastic

Musculoskeletal (MSK)

MRI

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