Chronic rhinosinusitis and pre-operative sinus CT

ACR AC Sinonasal Disease; NICE NG79 (acute sinusitis)

CT does not diagnose sinusitis; it maps it. Acute uncomplicated rhinosinusitis is a clinical diagnosis and imaging it changes nothing, so the two questions worth scanning for are chronic disease that has failed maximal medical therapy and is heading for endoscopic surgery, where the study doubles as the navigation roadmap, and suspected orbital or intracranial complication, where contrast, wider coverage and an MRI question all enter at once.

Persistent nasal obstruction, discharge, facial pressure or hyposmia beyond twelve weeks despite treatment, usually reaching radiology from ENT with surgery in mind — or, quite differently, a patient with periorbital swelling, painful or restricted eye movements, proptosis, visual change, severe headache or altered consciousness during a sinus infection.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

GCS

Focal neurological deficit

Where is the patient?

Some pathways change in the emergency department — an acutely threatened limb is not an elective work-up.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Paranasal Sinuses — Unenhanced, Low Dose

CT Paranasal Sinuses

What we'd amend, and why

Two jobs, one acquisition, and neither of them is making the diagnosis — the diagnosis was made in clinic from twelve weeks of symptoms and an endoscopy. The first job is to confirm that there is objective sinus disease left after maximal medical therapy and to grade its distribution, because a patient with disabling symptoms and clear sinuses is not helped by an operation. The second is to be the map the surgeon navigates from: the depth of the olfactory fossa and its Keros class, the integrity and position of the lamina papyracea, the course of the anterior ethmoidal artery across the ethmoid roof, the sphenoid septations and whether one inserts onto the carotid canal, and the presence of an Onodi cell overlying the optic nerve. That second job is why the study is unenhanced, sub-millimetre and reconstructed in bone algorithm with true coronal reformats: contrast adds nothing to bone, and a thick reformat blurs precisely the structures whose breach is the complication being avoided. Low-dose parameters are appropriate and well validated for this, with the caveat that extensive polyposis or a revision case distorts the landmarks enough that standard dose is the safer choice.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwaychronic-preoperative — Chronic rhinosinusitis after failed medical therapy — pre-operative roadmap
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.

Worth asking the referrer (3)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Has the patient completed a documented course of maximal medical therapy — intranasal steroid, saline irrigation and, where indicated, a prolonged antibiotic course — and is surgery being considered?
This is what separates an appropriate pre-operative roadmap from imaging that will not change management. If medical therapy has not been tried, or nobody is contemplating an operation, the scan usually answers a question no one is going to act on, and the answer is to treat first and image afterwards.
Are there any features of orbital or intracranial complication: periorbital swelling, proptosis, painful or restricted eye movements, reduced visual acuity or colour vision, severe unremitting headache, seizure, focal deficit or altered consciousness?
A single one of these changes the study, the protocol and the timescale — from an unenhanced elective bone study to an urgent contrast-enhanced acquisition covering the orbits and frontal lobes, with MRI where intracranial extension is a real possibility. The tool cannot read these from the request, so they are asked explicitly.
Is the disease unilateral, and is there epistaxis, a visible mass or bone destruction?
Unilateral sinonasal disease carries a neoplastic differential that bilateral inflammatory disease does not. It changes what the report has to comment on and usually adds an MRI, which separates tumour from obstructed secretions in a way CT cannot.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Focal deficit or altered consciousness — the intracranial question leads

Role	Study & protocol	Why this answers the question
First line	MRI Brain MRI Brain — with gadolinium usually appropriate	A seizure, a focal deficit or drowsiness during a sinus infection has stopped being a sinus question. Subdural empyema, cerebritis, early abscess, cavernous sinus thrombosis and dural venous involvement are what is being looked for, and they are routinely occult or badly under-called on CT — a thin extra-axial collection along the falx is exactly the finding a contrast CT reports as normal. Diffusion is the sequence that earns the study: restricted diffusion separates empyema from a sterile effusion and an abscess from a necrotic mass. Neurosurgery and ENT are involved on clinical grounds while it is being arranged, and antibiotics do not wait for it.
Second line	CT Paranasal Sinuses CT Sinuses and Orbits — Contrast-Enhanced	Still wanted, and no longer first. It answers the orbital half of the question in the same breath — the preseptal cellulitis that is treated medically against the subperiosteal or postseptal collection that is drained — and it maps the sinus source for the surgeon, with coverage extended up through the orbits and frontal lobes and enough dose to call a small collection. Where MRI cannot be delivered within a few hours, do this first and accept that a negative study does not exclude an intracranial collection.

A frontal sinusitis with forehead swelling is a Pott puffy tumour until proven otherwise and carries a high rate of intracranial extension — that patient needs both studies, not a choice between them.

Acute presentation to hospital — suspected orbital or intracranial complication

Role	Study & protocol	Why this answers the question
First line	CT Paranasal Sinuses CT Sinuses and Orbits — Contrast-Enhanced usually appropriate	Everything about the elective sinus protocol is wrong for this patient. The question is no longer where the ostiomeatal complex drains but whether there is pus outside the sinus, and pus is a soft-tissue finding: it needs iodine to show an enhancing rim, it needs the coverage extended from the standard sinus block up through the orbits and frontal lobes, and it needs enough dose to call a small subperiosteal collection rather than the low-dose bone parameters that make the elective study defensible. The distinction that actually decides management is between a preseptal cellulitis, which is treated medically, and a postseptal or subperiosteal collection, which is drained — and that distinction is invisible clinically once the lids are swollen shut. Scan the same day; visual loss from an orbital abscess is measured in hours.
Second line	MRI Brain MRI Brain — with gadolinium	The intracranial half of the question, and the half CT answers worst. Subdural empyema, cerebritis, early cerebral abscess, cavernous sinus thrombosis and dural venous involvement are all routinely occult or badly under-called on CT, and a thin extra-axial collection along the falx is exactly the finding that a contrast CT reports as normal. Diffusion-weighted imaging is the specific sequence that earns the study: restricted diffusion in an extra-axial collection distinguishes empyema from a sterile effusion, and does the same for an intraparenchymal abscess against a necrotic tumour. It is second rather than first only because CT is faster and answers the orbital question in the same breath — where the presentation is neurological rather than orbital, going straight to MRI is the better sequence, not a deviation from it.

The setting is a proxy for the thing that matters, which is the presence of orbital or intracranial signs. Confirm them: painful or restricted eye movements, proptosis, any change in acuity or colour vision, severe headache, seizure, focal deficit or drowsiness.
Ophthalmology and ENT are involved on clinical grounds while the scan is being arranged. The imaging defines the collection and its drainability; it does not decide whether the patient is unwell.
A frontal sinusitis with forehead swelling is a Pott puffy tumour until proven otherwise, and it carries a high rate of intracranial extension — that patient needs the MRI as well, not instead.

Chronic rhinosinusitis after failed medical therapy — pre-operative roadmap

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Paranasal Sinuses CT Paranasal Sinuses — Unenhanced, Low Dose usually appropriate	Two jobs, one acquisition, and neither of them is making the diagnosis — the diagnosis was made in clinic from twelve weeks of symptoms and an endoscopy. The first job is to confirm that there is objective sinus disease left after maximal medical therapy and to grade its distribution, because a patient with disabling symptoms and clear sinuses is not helped by an operation. The second is to be the map the surgeon navigates from: the depth of the olfactory fossa and its Keros class, the integrity and position of the lamina papyracea, the course of the anterior ethmoidal artery across the ethmoid roof, the sphenoid septations and whether one inserts onto the carotid canal, and the presence of an Onodi cell overlying the optic nerve. That second job is why the study is unenhanced, sub-millimetre and reconstructed in bone algorithm with true coronal reformats: contrast adds nothing to bone, and a thick reformat blurs precisely the structures whose breach is the complication being avoided. Low-dose parameters are appropriate and well validated for this, with the caveat that extensive polyposis or a revision case distorts the landmarks enough that standard dose is the safer choice.
Problem solving	MRI Head and Neck (Soft Tissue Neck) MRI Neck — soft tissue	Reserved for the request that is not really about inflammatory disease. Unilateral opacification, bone remodelling rather than sclerosis, epistaxis, cheek or palatal numbness, or a mass at endoscopy all move the question towards neoplasia and towards fungal disease, and CT cannot separate a tumour from the obstructed secretions sitting behind it — both are soft-tissue density, and the tumour is regularly reported as extensive sinusitis. On MRI the distinction is usually straightforward, inspissated secretions behaving very differently on T2 from a cellular mass, and MRI is also what shows perineural spread, orbital invasion and dural involvement before surgery. It supplements the CT rather than replacing it: the bone map is still needed.

Scan after, not during, maximal medical therapy. An exacerbation-timed study over-states chronic disease and the surgeon plans from an appearance that would have resolved.
If nobody is contemplating an operation and medical therapy has not been exhausted, the honest answer is usually to treat and review rather than to scan; the report will describe mucosal change that is present in a substantial minority of asymptomatic adults.
Acute uncomplicated rhinosinusitis is not on this ladder at all. It is a clinical diagnosis, it resolves, and the CT taken during it is both uninformative and a source of incidental findings.

Pitfalls

Imaging acute uncomplicated sinusitis. It is a clinical diagnosis, imaging does not distinguish viral from bacterial disease, and the mucosal thickening seen in the first two weeks is expected rather than diagnostic — a scan here is low-value care that generates incidental findings and reassures nobody.
Scanning during an exacerbation before medical therapy is complete, which over-states the extent of chronic disease and gives the surgeon a map of an appearance that would have resolved.
Reporting the disease and forgetting the map. A pre-operative sinus CT that does not comment on Keros depth, lamina papyracea integrity, anterior ethmoidal artery course, sphenoid septation insertions and the presence of an Onodi cell has omitted the reason the scan was done.
Treating unilateral opacification as sinusitis. Unilateral disease, bone remodelling, epistaxis or facial numbness raise neoplasia, and CT cannot separate tumour from the secretions trapped behind it.
Retaining the low-dose bone parameters for a soft-tissue question. In suspected complication the images become too noisy to call a small subperiosteal collection, which is the finding that decides whether the patient goes to theatre.
Cropping the coverage at the orbital roof in a complicated case, so the intracranial extension the referrer is actually worried about is outside the field.
Accepting a contrast-enhanced CT as excluding intracranial complication. A thin subdural empyema along the falx is regularly occult on CT, and diffusion-weighted MRI is what confirms or excludes it.
Cropping above the hard palate, which misses the odontogenic source of a unilateral maxillary opacity.

Priors — what to pull first

A previous sinus CT is decisive in a revision case: the anatomy the surgeon is navigating is post-surgical, and knowing which partitions have already been removed changes the operative risk far more than the mucosal findings do.
Any prior cross-sectional imaging that included the sinuses — a CT head, an MRI brain, a head and neck staging study — may already answer a unilateral-disease question without a further exposure.
Where a mass is suspected, previous imaging establishes whether bone remodelling is new or longstanding, which is one of the more useful discriminators between neoplasia and a chronic inflammatory process.

What makes a good request

Acute uncomplicated rhinosinusitis is diagnosed clinically. NICE guidance on acute sinusitis is built around symptom duration and antimicrobial stewardship and contains no imaging step at all, because the scan cannot separate viral from bacterial disease and mucosal thickening in the first fortnight of an infection is expected rather than informative.
The ACR rates CT of the paranasal sinuses without contrast as the appropriate study for chronic rhinosinusitis and for pre-operative planning, and reserves contrast-enhanced CT — with MRI alongside it — for suspected complications.
The pre-operative study is not a diagnostic test that happens to precede surgery. It is the intraoperative map: the surgeon reads the depth of the olfactory fossa and the Keros class, the height and dehiscence of the lamina papyracea, the course of the anterior ethmoidal artery, the sphenoid septations and their relationship to the carotid and optic nerve, and the presence of an Onodi cell. Those are the structures that get injured, and they are the reason the coronal plane and thin bone reformats are not optional.
Timing relative to treatment matters and is regularly got wrong. A scan taken during an acute exacerbation shows mucosal thickening that will resolve, over-stating the extent of chronic disease and misleading both the surgeon and the patient. The scan belongs after a documented course of maximal medical therapy, once the residual disease is what is being imaged.
Unilateral disease is a different card in all but name. Unilateral opacification, bone remodelling or destruction, epistaxis or a visible mass raises neoplasia, and the CT is then a first step towards MRI rather than towards surgery.
In a child, the same anatomy is smaller, the sinuses are incompletely pneumatised, incidental mucosal change is very common, and the dose argument is correspondingly stronger — but the paediatric patient is also the one who classically presents with an orbital complication, and that is an urgent scan rather than a deferred one.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MRI Brain — with gadolinium CT Sinuses and Orbits — Contrast-Enhanced CT Paranasal Sinuses — Unenhanced, Low Dose MRI Neck — soft tissue

Confirm locally

CT Paranasal Sinuses — Unenhanced, Low Dose: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.