The empty delta sign is a CT sign of dural venous sinus thrombosis of the superior sagittal sinus, where contrast outlines a triangular filling defect (thrombus). It is only described with CECT-scan or MRI, not with NECT nor non-contrast MRI.
An equivalent appearance can be noted in the transverse sinus on sagittal or coronal planes.
The exact mechanism for this appearance is uncertain, with possibilities including:
- recanalisation around an organising clot
- enlargement of the peridural small veins: a vascular mesh (dural cavernous spaces), and meningeal venous tributaries
- thickening of the dura with increased enhancement
Caution must be taken to achieve a well timed acquisition in CT cerebral venography, particularly in cases of intracranial hypertension which can cause delayed filling of the venous sinus. A premature acquisiton may create a false impression of thrombosis, which is simply due to contrast not yet reaching the venous sinuses. The cerebral veins should also be opacified on a CT cerebral venogram, and if they are not, one should suspect premature acquisition.
- 1. Lee Emil J. Y. “The Empty Delta Sign.” Radiology 224, no. 3 (September 1, 2002): 788-789. doi:10.1148/radiol.2243990978.
- 2. Virapongse C, C Cazenave, R Quisling et al. “The empty delta sign: frequency and significance in 76 cases of dural sinus thrombosis.” Radiology 162, no. 3 (March 1, 1987): 779-785. [Link].