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Case: Overshunting

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This was a child in which I'm going to show you

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three separate studies over the course of time.

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This was the initial presentation of the

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child who was being evaluated for an enlarged

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head circumference as part of the pediatric

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evaluation of the child in the first year of life.

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And what we see is marked enlargement

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of the lateral ventricles.

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We want to sort of try to give an estimate of

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why this patient has big ventricles, and for that,

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we will look at the sagittal scan and identify

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whether or not there appears to be a web at

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the cerebral aqueduct as a source of lateral

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ventricular and third ventricular enlargement.

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In this case, the fourth ventricle also

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appears to be enlarged, and there is a large

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CSF space below the cerebellum. So, this

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is more likely to be a communicating

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hydrocephalus, which could occur secondary

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to perinatal bleeding at the time of birth,

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or meningitis, or a functional obstruction

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for whatever reason in the arachnoid villi.

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The next study that was performed was the

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study that was done after the patient had

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placement of the ventriculostomy catheter.

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So, the ventriculostomy catheter has been inserted

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in the occipital region on the right side.

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In general, ventriculostomies are placed

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on the right side because that's usually the

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non-dominant hemisphere, and usually, they come

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through the parietal occipital region because

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that has fewer functional potential problems than,

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for example, inserting it through the frontal

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lobe, where you may affect the motor strip.

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36 00:01:42,570 --> 00:01:46,995 So, ventriculostomy catheter has been placed initially

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after placement of the ventriculostomy catheter.

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We don't expect very much change

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in the ventricles in this child.

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We're not seeing a lot of transpendymal CSF

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flow, which suggests that this is a chronic.

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Hydrocephalus.

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It's not as if there's an acute

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obstruction of the ventricles.

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This is a longstanding process in, in this

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particular child, probably from a perinatal

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injury that led to the ventricular enlargement.

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They don't want to rapidly decompress the ventricles.

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'Cause if they were to do so rapidly, it

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sometimes will tear the bridging veins.

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And whenever you hear the term "tearing of

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the bridging veins," you might think about

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subdural hematomas.

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So, if you decompress the ventricles quickly,

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what happens is you rip those bridging veins

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'cause suddenly they're collapsing inward, and

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you can lead to bilateral subdural hematomas.

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So here, this is the appropriate location of

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the ventriculostomy with no significant

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change in the lateral ventricular system.

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The patient presented shortly

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thereafter with mental status changes.

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And here is the problem.

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This is the same patient who has the

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ventriculostomy catheter here in the occipital

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region, and the ventricles are really small.

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Now, you might say, "Oh, that's a good thing.

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You know, they treated the hydrocephalus."

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But what happened?

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You've got these big subdural collections bilaterally

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now, and this is what is referred to as overdrainage.

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Of the lateral ventricles.

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In this case, whatever the pressure setting that was

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placed for the pressure in the ventriculostomy catheter

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was too low, and that led to collapse of the ventricles.

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And as I said, when that happens, you get these

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subdural collections because of issues with hydrostatic

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pressure and potentially ripping of the bridging veins.

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Now, this looks predominantly like CSF, so these may be

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subdural hygromas rather than

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hematomas from the blood products.

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But in any case, this is secondary to over-

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drainage of the lateral ventricles in a

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patient who had chronic hydrocephalus.

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We actually don't want to see these small ventricles.

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We wanna see larger ventricles

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that allow the hydrostatic pressure

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between what's in the brain versus what's

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outside the brain to be in equilibrium.

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So, when you're looking at patients for shunt failure,

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you can have shunt failure because the patient's

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ventricles blow up and the shunt is obstructed.

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But you may also have shunt failure from over-

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drainage, slit ventricle syndrome, which may lead to

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patient symptomatology and/or subdural collections.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Neuroradiology

MRI

Iatrogenic

Emergency

Brain

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