CT imaging features of acute hemorrhage and active arterial hemorrhage
Hemorrhage may occur in any portion of the abdomen and pelvis, and generally appears on CT as nonenhancing high attenuation fluid, sometimes with a “hematocrit effect” as manifested by a dependent high attenuation layer and a low attenuation nondependent layer related to settling of red blood cells. Nonclotted acute hemorrhage generally has lower attenuation (30 to 45 HU) compared to clotted acute hemorrhage (45 to 70 HU). The presence of focal high attenuation clotted blood in the abdomen or pelvis may serve as an indicator of the source of hemorrhage (“sentinel clot” sign). In patients with anemia, however, acute hemorrhage may have similar attenuation to that of simple fluid.
Active arterial hemorrhage appears as a round or linear focus of extraluminal intravenous contrast material with very high attenuation similar to that of contrast material within arterial vessels, which does not conform to a known vascular structure. It persists or increases in size on more delayed phase image acquisitions and is often surrounded by high attenuation acute hemorrhage