CT Sinuses and Orbits — Contrast-Enhanced
Extended above the standard sinus block to include the orbits and the frontal lobes, so intracranial and intraorbital complications are within the field.
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 complicated sinusitis: periorbital or orbital cellulitis, subperiosteal or orbital abscess.
- Suspected intracranial extension of sinonasal infection, including subdural empyema or venous sinus involvement.
- Characterisation of an aggressive-looking sinonasal mass before biopsy or MRI.
Technique
- A systemic venous-phase acquisition at roughly 60-80 s from the start of injection is the usual timing for soft-tissue and abscess wall enhancement.
- The dose-sparing rationale of the plain sinus protocol does not apply here: the question is soft tissue, not bone.
- MRI remains the better test for intracranial extension where it can be obtained.
Where it goes wrong
- Retaining the standard low-dose sinus parameters for a soft-tissue question yields images too noisy to call a small subperiosteal collection.
- Cropping the coverage at the orbital roof misses the intracranial complication the referrer is actually worried about.
- An arterial-timed acquisition under-shows the enhancing rim of an abscess.
Clinical questions that reach this study
Contrast
Typically 60-100 mL of non-ionic iodinated contrast at around 2-3 mL/s.
Acquisition
- Reconstruction
- Thin axial acquisition with soft-tissue and bone reformats in all three planes.
- Preparation
- No preparation. Remove dentures and facial piercings.
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.
- Systemic venous (soft-tissue) phaseTypically ~45–90 s after the start of injection, with most published soft-tissue protocols sitting at ~60–80 s. Region-specific: reported neck delays span roughly 50–90 s, and routine contrast-enhanced chest work is conventionally ~60 s. Confirm locally.
Arteries and veins have equalised, and soft tissue outside the liver is at or near peak interstitial enhancement. The transferable principle is that away from the liver the purpose of a venous acquisition has nothing to do with portal delivery: it is that (a) every vessel is now uniformly dense, so a vessel stops being mistaken for a node or a mass, and (b) contrast has had time to leak into the expanded interstitium of inflamed or neoplastic tissue, which is what makes an abscess wall, a necrotic node, a mucosal tumour or a phlegmon declare itself against normal tissue. This is therefore the general-purpose soft-tissue phase for neck, chest, extremities and superficial structures. It is deliberately NOT called portal venous: the portal venous phase is a liver-timed acquisition that merely happens to fall in the same window, and borrowing its name for a neck or limb study imports a hepatic timing rationale that does not apply and hides the fact that the right delay is set by the target tissue. The errors are symmetrical — too early and arteries are far denser than nodes while an abscess rim has not yet enhanced; too late and everything equilibrates, collapsing the lesion-to-background difference the study depends on.
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