CT Venogram — Dural Venous Sinuses
Foramen magnum to vertex, covering the superior sagittal, transverse, sigmoid and straight sinuses and the internal jugular veins to the skull base.
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Suspected cerebral venous sinus thrombosis when MR venography is unavailable, contraindicated or too slow.
- Equivocal hyperdense sinus or cord sign on an unenhanced head CT.
- Venous anatomy before skull base or posterior fossa surgery.
Technique
- A fixed delay is usual rather than bolus tracking. Published protocols cluster around 45-50 s from the start of injection, which is later than an arterial CTA and earlier than a true equilibrium phase; the `phase-portal-venous` slug is used here for that systemic venous return window.
- Some centres run a combined CTA/CTV, accepting a compromise timing; the venous acquisition is then the second pass.
- Filling of the sinuses can be delayed in raised intracranial pressure, and a longer delay may be needed.
Where it goes wrong
- Scanning too early leaves the sinuses incompletely opacified and manufactures a false-positive filling defect.
- Arachnoid granulations and hypoplastic transverse sinuses are the classic technique-independent mimics; a correctly timed study makes them easier, not harder, to recognise.
- Bone at the skull base obscures the sigmoid sinuses on thick reformats — thin sections or bone subtraction are needed.
Clinical questions that reach this study
Contrast
Typically 70-100 mL of non-ionic iodinated contrast at around 3-4 mL/s.
Acquisition
- Reconstruction
- Thin axial source images with multiplanar reformats along the plane of each major sinus; subtraction or bone-removal reconstructions help at the skull base.
- Preparation
- Power-injectable cannula, antecubital preferred.
Phases
Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.
- Cerebral venous phase (CT venography)Typically a fixed delay of ~45–50 s after the start of injection — later than an intracranial CTA, and EARLIER than a systemic venous or portal venous acquisition. Confirm locally.
The dural sinuses and cortical veins are uniformly opacified while arterial density is falling. The transferable principle is that the delay which opacifies a venous compartment is set by the CIRCULATION TIME OF THAT ORGAN, not by a universal clock: cerebral arteriovenous transit takes only a few seconds, so the intracranial venous window opens well before the systemic one, and a body venous delay catches the sinuses on the declining limb of the bolus. The second principle is that the finding sought here is a NEGATIVE one — a filling defect — which is only interpretable against a completely filled lumen. Incomplete opacification is therefore not a slightly degraded study but a study that manufactures false positives, and anything that slows venous outflow (raised intracranial pressure, low cardiac output) lengthens the delay needed. Flow-related and anatomical mimics — arachnoid granulations, a hypoplastic transverse sinus — are easier to recognise on a correctly timed study, not harder.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Prior contrast reaction and elective premedication· nurse pre scan
- Intravenous access adequate for the planned injection· radiographer at scan
- Metformin and iodinated contrast· radiographer at scan
- Child-sized technique and contrast dose· radiographer at scan
- Kidney function and intravenous iodinated contrast· radiographer at scan