Think of it when a headache, seizure or haemorrhage does not fit an arterial territory. Look at the sinuses themselves: a dense sinus on CT, a filling defect on CT venography, and loss of flow void or clot signal on MRI.
Orient first
- Venous infarcts cross arterial territories, are often haemorrhagic, and are bilateral parasagittal with superior sagittal sinus thrombosis or temporal with transverse sinus thrombosis.
- Hypoplastic transverse sinuses (usually the left) and arachnoid granulations mimic thrombosis.
- Clot signal changes with age on MRI, so no single sequence is reliable on its own.
Acquire the study
- Non-contrast CT (narrow window) and CT venography with thin-slice multiplanar reformats.
The manoeuvre
- Non-contrast: dense (hyperattenuating) superior sagittal, transverse or sigmoid sinus or cortical vein ("cord sign").
- CT venography: empty delta sign (a triangular filling defect in the superior sagittal sinus) and filling defects along each sinus on reformats.
- Parenchyma: parasagittal or temporal oedema, haemorrhage crossing arterial territories.
What confirms it
- A filling defect within a sinus on a contrast study, in two planes.
What licenses you to exclude it
- A normal non-contrast CT does not exclude it; a normal contrast venogram does, for the major sinuses.
The classic misread
- Calling a haematocrit-high dense sinus (dehydration, polycythaemia) a thrombus without the venogram.