Sphenoethmoidal air cell

Sphenoethmoidal (or Onodi) air cell is defined as an ethmoidal air cell that lies posteriorly to the sphenoid sinus. Rarely it may lay superiorly to the sphenoid sinus and is called a central Onodi air cell.

As a result of its location the optic nerve, and less commonly, the internal carotid artery, are very closely related with as little as 0.03 mm (median 0.08 mm) of bone separating them. 

The incidence is variable with sphenoethmoidal air cells present in up to 60% of cadavers in one series 1, although the figures usually quoted in Western populations is ~10% (range 8-13%).

Potential damage to the optic nerve and ICA occurs when attempts to enter the sphenoid sinus endoscopically are made by passing through what is thought to be the posterior most ethmoidal air cell, while it is instead an sphenoethmoidal cell.

Other pathology such as isolated mucocoeles, squamous cell carcinoma and sinusitis have all been reported in sphenoethmoidal air cells, leading to early optic nerve involvement.

See also

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Head and neck anatomy

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