An axial CT image of the brain in a trauma patient shows a hyperdense epidural hematoma (arrowheads) with a small rounded area of low attenuation (arrow) internally.
Facts: The Swirl Sign
- An area of low attenuation within the extra-axial hematoma, usually in epidural hematoma, seen on nonenhanced CT scan
- Represents an actively extravasating unclotted blood
- The area is surrounded by clotted blood (50-70 Hounsfield Units). Clotted blood is hyperdense on CT because of protein component of hemoglobin
Al-Nakshabandi NA. The swirl sign. Radiology 2001; 218:433.