CT Paranasal Sinuses — Unenhanced, Low Dose
Frontal sinuses to the hard palate, including the ostiomeatal complexes and anterior 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
- Chronic or recurrent rhinosinusitis that has failed medical therapy, before endoscopic sinus surgery.
- Anatomical roadmap for functional endoscopic sinus surgery, including variants relevant to surgical risk.
- Suspected sinonasal mass or unilateral disease requiring further characterisation.
- Facial trauma where sinus and orbital wall integrity is in question.
Technique
- Low-dose parameters are appropriate for bony anatomy and have been shown to preserve identification of the anatomical landmarks that matter surgically.
- Reported ultra-low-dose protocols may be insufficient in patients with extensive polyposis or previous surgery, where landmarks are distorted; a standard-dose acquisition is reasonable in that group.
- Contrast is not part of this protocol and adds nothing to a bony assessment.
Where it goes wrong
- Scanning during an acute uncomplicated infection produces mucosal thickening that is not the chronic disease being asked about — timing relative to treatment matters.
- Excessively thick reformats blur the uncinate process and lamina papyracea, which is precisely the anatomy the surgeon needs.
- A study cropped above the hard palate misses odontogenic causes of unilateral maxillary disease.
Clinical questions that reach this study
Contrast
Acquisition
- Breathing
- Quiet respiration, no swallowing.
- Reconstruction
- Sub-millimetre volumetric acquisition reconstructed in bone algorithm with axial, coronal and sagittal reformats; the coronal plane is the one surgeons plan from.
- 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.
- Non-contrast (unenhanced)No injection. Acquired before any contrast is given.
Shows intrinsic tissue attenuation, and nothing else. The transferable principle is that contrast is anti-signal for anything that is already dense: calcification, acute haemorrhage, urinary and biliary calculi, iodine-containing or haemorrhagic fluid, and intrinsic fat all lose conspicuity, or become uninterpretable, once surrounding tissue enhances. It is also the only baseline against which enhancement can be measured, so any protocol that quantifies enhancement or washout (a lesion "enhances by X HU", adrenal absolute washout, renal mass characterisation) is arithmetically impossible without it. Conversely, an unenhanced series adds dose and no information whenever the question is purely about vascularity or perfusion.
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.
- Child-sized technique and contrast dose· radiographer at scan