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Empty delta sign

The empty delta sign is CT sign of dural venous sinus thrombosis of the superior sagittal sinus, where contrast outlines a triangular filling defect (clot). It is only described with contrast-enhanced CT-scan or MRI, not with NECT nor non-contrast MRI.

The exact mechanism for this appearance is uncertain, with possibilities including:

  • recanalisation around an organising clot
  • enlargement of the peri-dural 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 performed contrast bolus timing in CT venogram, otherwise a premature acquisition after contrast administration may create a false impression of sagittal sinus enhancement.

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