Empty delta sign (dural venous sinus thrombosis)

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, which represents thrombus. It is only described in contrast-enhanced CT, not in unenhanced scans.

An equivalent appearance can be noted in the transverse sinus on sagittal or coronal planes.

Pathology

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

• recanalization around an organizing clot
• enlargement of the peridural small veins: a vascular mesh (dural cavernous spaces), and meningeal venous tributaries
• thickening of the dura with increased enhancement

History and etymology

'Δ' or delta is the name of the Greek letter with the sound of the English letter 'D' and clearly has a triangular shape. Hence river delta or delta-shaped wing.

Practical points

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 acquisition 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; if they are not, one should suspect premature acquisition.