Onodi cell(sphenoethomoid cell):
- This is formed by lateral and posterior pneumatization of the most posterior ethmoid cells over the sphenoid sinus.
- Because the Onodi cells are posterior ethmoid cells that are positioned superolateral to the sphenoid sinus ,the optic nerve & carotid artery may often course through the lateral aspect of onodi cell instead of sphenoid sinus proper.
- Kainz and Stammberger defined an Onodi cell as a posterior ethmoid cell with an endoscopically visible bulge of the optic canal.
- The vulnerability of the optic nerve with or without the presence of an Onodi cell is further compounded by the thin lamina papyracea in the posterior ethmoid area .
- This anatomic variation is found in 8-14% of cases according to studies using CT in association with recent developments in endoscopic sinus surgery.
- The presence of Onodi cells increases the chance that the optic nerve and/or carotid artery would be exposed (or nearly exposed) in the pneumatized cell.
- The optic nerve, and more rarely, the internal carotid artery, may be exposed within or lie immediately adjacent to such an air cell.
- During endoscopic sinus surgery attempts to localise the sphenoidal sinus via instrumentation through the posterior most ethmoidal air cells can lead to optic nerve, and even, internal carotid artery, injury.
Haller cell (infraorbital cell or infraorbital extension of ethmoid cell):
- The Haller cell is usually situated below the orbit in the roof of the maxillary sinus.(i.e., in the orbital floor).
- It occurs in 10% of people.
- It is a pneumatized ethmoid cell that projects along the medial roof of the maxillary sinus.
- As it is closely related to ethmoidal infundibulum enlarged Haller cells may contribute to narrowing of the ethmoidal infundibulum and recurrent sinus disease.