Stage the disease (Lund–Mackay), map the drainage pathways (ostiomeatal unit, frontal recess, sphenoethmoidal recess), and flag the anatomical danger points — Keros depth, lamina papyracea, Onodi cell, dehiscent optic nerve or ICA — for the surgeon.
Orient first
- CT is done after medical treatment; it maps anatomy rather than diagnosing symptoms.
- Lund–Mackay scores each sinus 0–2 and the ostiomeatal complex 0/2 (verify).
- Keros classification of the olfactory fossa depth predicts skull base injury risk.
Acquire the study
- Non-contrast CT paranasal sinuses, 0.6–1 mm, coronal and sagittal reformats, bone window (low-dose protocol).
The manoeuvre
- Coronal bone window: ostiomeatal unit patency; uncinate process and infundibulum.
- Score each sinus (Lund–Mackay); note polyps and hyperdense content (fungal, allergic).
- Olfactory fossa depth in mm on coronal slices: Keros type 1–3; asymmetry.
- Lamina papyracea dehiscence; anterior ethmoidal artery position.
- Sagittal reformat: frontal recess cells; sphenoid: Onodi cell, optic nerve and ICA dehiscence.
What confirms it
- Mucosal disease with obstructed drainage pathways in a patient with chronic symptoms after medical therapy.
What licenses you to exclude it
- Clear sinuses and patent drainage pathways after treatment make chronic rhinosinusitis unlikely as the cause of symptoms.
The classic misread
- Unilateral opacification with bone erosion or calcification — consider inverted papilloma or tumour, not simple sinusitis.