Clinical Data
97-year-old polymorbid female:
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Acute onset left hemiplegia (Time of last known well two hours ago)
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Code stroke activated
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Imaging in our institution constituted of:
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Non-contrast head CT
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CTA of aortocervical and intracranial vessels
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CT perfusion
Non-contrast head CT:
CT perfusion revealed a large ischemic core compared with the penumbra (approximately 2:1)
Based on the CTA and non-contrast head CT, which arteries were occluded?
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The CTP shows perfusion changes in the vascular territories of both the right MCA and ACA.
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We know that the MCA is also most certainly occluded because of the dense MCA sign.
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Based on this, there is either a simultaneous occlusion of both the MCA and the ACA or the occlusion is even more proximal – ICA.
CTA shows occlusion of the M1 segment of the right MCA, and the terminal segment of the ICA is patent
However, more proximal intracranial segments of the right ICA were not opacified with contrast
The cervical ICA segments were also not opacified with contrast.(ECA and vertebral artery on the right, no ICA)
Modified sagittal reformation of the bifurcation
Given the CTA appearance of the right ICA, which of the following are the reasonable differentials?
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Occlusion of the right carotid bulb with near total distal ICA occlusion
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ICA dissection
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ICA pseudo-occlusion
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Occlusion of the right carotid bulb with near total distal ICA occlusion – FALSE
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ICA dissection – TRUE
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ICA pseudo-occlusion – TRUE
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The carotid bulb is patent and contrast opacification stops 1 to 2 centimeters after the bulb. If the bulb would be really occluded, contrast opacification would stop (almost) at the level of the bulb and the atherosclerotic changes of the bulb would be more extensive.
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The sagittal images nicely show the gradual tapering of contrast opacification in the proximal cervical ICA, which is known as the flame sign.
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The flame sign can be seen in carotid artery dissections and pseudo-occlusions.
Solution:
Explanation:
How would you differentiate a pseudo-occlusion from a real dissection or ICA occlusion, while the patient is still lying in the CT scanner?
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Obtain a delayed CTA scan of the arteries.
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In other words, repeat the CTA scan at a later time point. Preferably tell the technician at the moment you see the flame sign on the console to just fire the CTA scan again (additional contrast application is not needed).
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(In our case, the clinical context might also have helped. Spontaneous carotid artery dissections are the leading cause of stroke in younger/middle-aged patients. Our patient was almost 100 years old, which made dissection not the most probable diagnosis.)
Normal vs delayed CTA: the unopacified parts of the ACI are now opacified:
Carotid artery pseudo-occlusion:
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A slightly confusing term, as the carotid artery is still occluded, just not in the extent you might think!
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Carotid artery pseudo-occlusion is seen, when there is an occlusion of a distal segment (usually one of the intracranial ones) of the ICA. This occlusion makes it harder for the contrast bolus to flow through the normal ICA – as the cervical ICA segment has no branches. So, using normal timings for the CTA bolus, the cervical segment might still be unopacifed, compared with the normal side. If we wait a little bit and obtain a delayed scan, we give the ICA time to fill up and can assess the extent of the occlusion more accurately. This can be achieved with a delayed CTA scan and is also easily identified with DSA (today mostly performed as the first part of mechanical thrombectomy).
The cavernous segment was unopacified in both the normal and delayed CTA – representing the true level of the occlusion
What are the final diagnoses?
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Right MCA and right cavernous segment ICA occlusion with resultant ischemic stroke
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Pseudo-occlusion of the proximal (mostly cervical) parts of the ICA