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Non-Aneurysmal Perimesencephalic SAH

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Another entity that is important to understand

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as a resident reading emergency department

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neuroradiology studies is non-aneurysmal

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perimesencephalic subarachnoid hemorrhage.

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This is an entity which is thought to be due

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to bleeding from small veins, as opposed to

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arteries. However, it presents in a similar fashion

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to a basilar artery tip subarachnoid hemorrhage.

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That is, you have hemorrhage that is in the

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perimesencephalic or interpeduncular cistern on CT that

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looks, for all the world, like a clot that may

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be associated with a basilar artery aneurysm.

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So, subarachnoid hemorrhage

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in the perimesencephalic cistern usually doesn't

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extend very far into interhemispheric or sylvian

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fissures, if at all, and there shouldn't be any

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layering of intraventricular hemorrhage, and

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there should be no intraparenchymal hemorrhage.

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Now, these patients will likely get a

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CTA, despite the fact that they may have a

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characteristic appearance on the non-contrast CT.

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The CTA will not show an aneurysm,

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and it won't show the bleeding vein.

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Yes.

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The question then is, in the face of this subarachnoid

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hemorrhage, are you still going to need to go to

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the gold standard of conventional arteriography?

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Most people would say no.

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If it has this characteristic criteria, you can

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simply do a follow-up CTA rather than having

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to do a more invasive conventional arteriogram.

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So, in patients with perimesencephalic

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subarachnoid hemorrhage...

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There were found two aneurysms out of the 71

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patients and one case of vasculitis, but the

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source of the hemorrhage was not identified.

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No source of hemorrhage in

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68 of the 71 patients, or 96%.

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So, this is from an 11-year

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experience in looking at CT-negative

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subarachnoid hemorrhage.

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So again, depending upon the comfort level of

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the clinicians or the patient's history, you may

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be able to stop with a CTA and just recommend

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a follow-up to ensure that you're not missing a

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basilar artery aneurysm, or in some people's hands,

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they will still do a conventional arteriogram.

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These are three different patients, all of

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whom had negative arteriograms and yet positive

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subarachnoid hemorrhage as evidenced by CT.

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Here, we have hemorrhage just behind the dorsum

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sella, in front of the pons, with a little bit of

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extension into the wings of the sylvian region.

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Here, we have a more dramatic area of hemorrhage at the

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pons-midbrain junction, and here, we

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have hemorrhage in the interpeduncular

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cistern—less dense, but still hemorrhage.

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All of these patients had negative arteriograms,

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and the diagnosis was non-aneurysmal

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subarachnoid hemorrhage due to weeping

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veins, if you will, as most people believe.

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In this case, these patients have a very good prognosis.

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They don't have an arterial bleed,

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they don't get into issues with vasospasm, and they

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don't have the usual complications of hydrocephalus

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or otherwise associated with subarachnoid hemorrhage.

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This pattern on a CT is one that you

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should recognize as a resident and suggest

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that the differential diagnosis not only

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includes a basilar tip aneurysm, but also

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non-aneurysmal subarachnoid

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hemorrhage from non-arterial sources.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Neuroradiology

Idiopathic

Emergency

CT

Brain

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