The signal flare phenomenon is a useful sign to identify active bleeding in a liquefied hematoma with hematocrit effect on dynamic CT scan images.
When active arterial hemorrhage is present in a liquefied hematoma that has a hematocrit effect, a signal flare phenomenon may be seen as a linear, high attenuating focus in the dependent layer as well as very high-attenuation foci at the boundary of the two fluid-fluid levels.
This is due to movement of very-high attenuation extravasated contrast material through the dependent cellular layer to the boundary of the cellular and liquid layers, based on differences in specific gravity.
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