The swirl sign refers to the non-contrast CT appearance of acute extravasation of blood into a haematoma, for example an extradural haematoma or subdural haematoma. It represents unclotted fresh blood which is of lower attenuation than the clotted blood which surrounds it 1.
It is the corollary of the spot sign on CTA which represents the same phenomenon, but in that case caused by contrast extravasation 2.
- 1. Al-Nakshabandi NA. The swirl sign. Radiology. 2001;218 (2): 433. doi:10.1148/radiology.218.2.r01fe09433 - Pubmed citation
- 2. Wada R, Aviv RI, Fox AJ et-al. CT angiography "spot sign" predicts hematoma expansion in acute intracerebral hemorrhage. Stroke. 2007;38 (4): 1257-62. doi:10.1161/01.STR.0000259633.59404.f3 - Pubmed citation