Signal flare phenomenon as active bleeding in retroperitoneal hematoma with hematocrit effect on dynamic CT scan: three clinical cases and experimental study based on a specific gravity theory.

The contrast medium was observed as a thin line indicating active bleeding in the cellular component and stayed at the boundary between the plasma and cellular components in liquefied hematomas. We could also reproduce the same phenomenon in an experimental study using human blood. The characteristic dynamic motion of the contrast medium demonstrated in the liquefied hematoma, which we have called the "signal flare" phenomenon, is a significant sign indicating active bleeding.