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Case 26: Basilar Artery Aneurysm on CT, CTA

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In general, anterior circulation aneurysms are more

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common than posterior circulation aneurysms, and we

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usually look for those aneurysms most commonly in

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the posterior communicating artery in the internal

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carotid artery distal segment, as well as in the anterior

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communicating artery. Middle cerebral artery aneurysms

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uh, also occur and they usually

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bleed into the Sylvian fissure.

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Let's look at this case, however. This was a

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patient again who presented with thunderclap

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headache with severe pain in the back of the head.

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On this non-contrast CT scan, what we

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see is hyperdensity in the subarachnoid

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space of the interpeduncular cistern.

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This is the midbrain.

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This is the interpeduncular cistern.

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It looks like it's relatively well-localized

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to the interpeduncular cistern.

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No intraventricular hemorrhage.

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No hemorrhage extending along the Sylvian fissures.

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And in this location, what sits in the interpeduncular

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cistern just adjacent to it, is the basilar artery.

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So we would be concerned about

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a basilar artery aneurysm.

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This patient has had previous

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enucleation for trauma to that eye, so—

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It is uncommon to have the non-contrast

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CT scan followed immediately by CTA.

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So at this juncture in imaging, most patients

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who have concern for subarachnoid hemorrhage

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are going to get a non-contrast CT and a

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CTA if that non-contrast CT is positive.

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Conventional arteriography for diagnosing

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aneurysm is much less common nowadays.

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Due to the high quality of CTA, we

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have with modern thin-section imaging.

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So a CTA was indeed performed, and as you can

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see, not too subtly, as we come up from below and

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come to the basilar artery, we see the contrast

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enhancing stain of this aneurysm, which is deviating

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to the right side and posteriorly.

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The evaluation of aneurysm with CTA is similar to

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the evaluation with conventional arteriography,

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in that we want to characterize the size of the

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aneurysm, the width of the neck, whether or not

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it's involving adjacent blood vessels, and whether

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or not there's coil associated with it, and if we

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can identify the site of where it has ruptured,

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particularly if you're dealing with multiple aneurysms.

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You wanna know which one of the aneurysms

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bled because that's the one we're obviously

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going to treat, because the incidence of re-

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hemorrhage in the immediate 24 to 48 hours is

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relatively high with an aneurysm which has bled.

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So let's take a look at my favorite,

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which is our coronal MIP imaging.

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Here we see our anterior cerebral arteries anteriorly.

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Here we see the distal internal carotid artery

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with the A1 segments and the M1 segments.

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And the middle cerebral artery.

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You can see whether or not there's an aneurysm

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of the MCA bifurcation in this location.

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And as we go further posteriorly, we identify

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the vertebrobasilar artery circulation.

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Let's magnify this so that way

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we get our best quality imaging.

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Okay, so this is the left vertebral artery.

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This is probably the right vertebral artery.

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Let's make sure—no, the right vertebral artery

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is here.

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So this is our vertebrobasilar junction.

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This little blood vessel here is our

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anterior inferior cerebellar artery.

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As we come up superiorly, we come to the

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superior cerebellar artery and the posterior

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cerebral artery branches of the basilar artery.

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This aneurysm is sitting in between the posterior

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cerebral and superior cerebellar arteries,

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with likely involvement of the origin

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of that superior cerebellar artery.

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You could sort of see that coming right

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here, and we would measure the width here.

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Pretty easy to measure the width of that

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aneurysm, which measures six millimeters

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at the base, and then the overall dimension

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around 5.5 millimeters of the aneurysm.

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Posterior circulation

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aneurysms nowadays are pretty much exclusively treated

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with neurointerventional procedures, with coiling

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and/or stenting or pipeline intervention procedures.

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Surgery in the posterior fossa aneurysm is

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very complicated and runs the risk of injuring

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those vital brainstem or cerebellar structures.

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So here we have the aneurysm.

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Obviously, you're going to continue to evaluate

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this patient for the potential for multiple

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aneurysms because multiple aneurysms occur in

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25% of patients who have a single aneurysm.

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So we're gonna characterize this.

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You can look at it in multiple planes to give

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better definition of the size of the aneurysm.

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You can see that this is projecting posteriorly,

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as I mentioned, in intimate association with the

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superior cerebellar artery.

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It has an irregular contour to it, so

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it likely has bled, and as we saw,

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it bled into the interpeduncular cistern.

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When you do a CTA for the intracranial

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circulation for aneurysm, quite frequently,

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we're also combining that with

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the neck vessels.

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Why? This is used for guidance for the

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neurointerventionalists. They wanna know, in

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order to get to that basilar artery aneurysm,

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which vertebral artery should I catheterize?

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We wanna catheterize, obviously, the larger

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of the two vertebral arteries.

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Here's your right side.

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Your left side over here is the larger one.

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And that will be helpful, again, if there are

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kinks to that vessel or stenosis of that vessel

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or dissections of that blood vessel.

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It should be known in advance of planning the

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intervention to address the basilar artery aneurysm.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Vascular

Neuroradiology

Emergency

CTA

CT

Brain

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