====== Swirl sign ======

The swirl sign refers to the non-[[contrast]] [[CT]] appearance of acute extravasation of [[blood]] into a [[hematoma]], for example an [[extradural hematoma]] or [[subdural hematoma]]. It represents unclotted fresh blood which is of lower attenuation than the clotted blood which surrounds it
((Al-Nakshabandi NA. The swirl sign. Radiology. 2001 Feb;218(2):433. PubMed
PMID: 11161158.
)).

{{::swirlsign.png?200|}}

Black curved arrow

It is the corollary of the [[spot sign]] on [[CTA]] which represents the same phenomenon, but in that case caused by contrast extravasation
((Wada R, Aviv RI, Fox AJ, Sahlas DJ, Gladstone DJ, Tomlinson G, Symons SP. CT
angiography "spot sign" predicts hematoma expansion in acute intracerebral
hemorrhage. Stroke. 2007 Apr;38(4):1257-62. Epub 2007 Feb 22. PubMed PMID:
17322083.
)).


see Gupta VK, Seth A. "Swirl Sign" in Extradural Hematoma. World Neurosurg. 2018
Oct 10. pii: S1878-8750(18)32302-7. doi: 10.1016/j.wneu.2018.10.010. [Epub ahead 
of print] PubMed PMID: 30315986.