Cob web sign in aortic dissection are slender linear areas of low attenuation seen occasionally in the false lumen in contrast enhanced computerized tomographic (CT) scans. They are specific for the false lumen and help in the identification of the false lumen [Sun Z. et al. Multislice CT virtual intravascular endoscopy of aortic dissection: A pictorial essay. World J Radiol. 2010; 2: 440–448].
It is thought to be a specific sign for the false lumen, but with low sensitivity as it is not seen very frequently.