Flame sign (carotid)
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The flame sign refers to a gradual tapering of contrast opacification in the mid-cervical internal carotid artery, sparing the carotid bulb. The sign can be observed on angiography (digital subtraction angiography 1, CT angiography 1, or contrast-enhanced MR angiography 2) in either of two scenarios 3:
- occlusion due to cervical internal carotid artery dissection
- pseudo-occlusion (flow-related contrast stagnation) due to downstream (intracranial internal carotid artery) occlusion
Delayed images distinguish these two possibilities: cervical internal carotid artery occlusion would show a lack of contrast opacification, while pseudo-occlusion would show advancing contrast filling in the cervical segment 4.
The flame sign should be distinguished from blunt or beak-shaped (abrupt tapering) contrast involving the carotid bulb, which is likely to represent true extracranial internal carotid artery occlusion 4.
In carotid dissection without complete occlusion, the flame sign may be followed by a thin lumen known as the string sign.
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