The sinuses frequently show variable anatomy. There are multiple 'critical' variations that surgeons like to be aware of prior to operating, hence the importance for assessing the sinuses carefully prior to surgery.
1. Agger nasi cell: Anterior ethmoid cell which may block the frontal recess.
2. Ethmoid Bulla: most posterior cell in the anterior ethmoid complex with significant variation in size and morphology.
3. Onodi cells: variation of the posterior ethmoid cells superior to the sphenoid sinus secondary to hyperpneumatisation. These onodi cells can be in close relation with the optic nerve.
4. Haller cells: infraorbital ethmoid cells. These may obstruct the infundibulum which is part of the ostiomeatal complex of the maxillary sinuses.
5. Concha bullosa: extension of a ethmoid cell in the middle concha. >50% of pneumatisation in the coronal plane. This may obstruct the infunibulum or middle meatus. Associated with nasal deviation, mucosal swelling, exudate, retention cysts or an osteoma.
5. Deep olfactory fossa: the cribriform plate can not only be asymmetric but also be in a more caudal position. If a fracture of the fragile/deep cribriform plate occurs during surgery there is a risk of CSF leak or meningitis.
6. Defect within the lamina papyracea: a defect with in the medial orbital wall. Which may give rise to intraorbital bleeding fibrosis or damage to the intra occular muscle.
I love this easy to use check list from "StartRadiology" (reference below) on how to approach the sinuses:
Are all sinuses present?
Are the sinuses clear? Mucosal swelling or air-fluid level?
What is the aspect of the bone? Bone thickening or destruction?
Is the ostiomeatal complex patent?
Is the cause for obstructed drainage visible?
Are there any abnormalities outside the ENT area?
'CT sinuses', StartRadiology, Available from: http://www.startradiology.com/internships/otolaryngology/paranasal-sinuses/ct-sinus/