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We were pleased to read the informative article by Rene et al.1 The authors refer to “Odoni cells” as, “aerated posterior ethmoid air cells along the optic canal.” Could it be that they meant to refer to the cells as “Onodi cells”? Onodi described a number of variations of posterior ethmoid anatomy.2 Endoscopic sinus surgeons refer to the pattern of extramural pneumatisation of the ethmoid lateral or superolateral to the sphenoid, where the posterior ethmoid is indented by the optic canal, as an Onodi cell.3 More recently it has been suggested that this cell is better characterised as a “sphenoethmoidal” cell.4
The main significance of the Onodi or sphenoethmoid cell is that while sinus surgeons expect to find the optic nerve in the sphenoid sinus, they are not routinely looking for it in the posterior ethmoid. Consequently, the chance of iatrogenic injury is likely to be higher in patients with Onodi cells and even higher in patients with extensively pneumatised Onodi cells.5 The exact incidence of Onodi cells is unclear. Endoscopic dissection studies suggest an incidence as high as 39%5 or 42%.3 CT imaging studies suggest a lower incidence of 7%.5 Driben et al5 feel that the likelihood of a sphenoethmoid cell increases with increasing obliquity of the anterior sphenoid wall. Racial factors may also have a role as Onodi cells appear to be more common in Asian patients.6
Every effort should be made to identify sphenoethmoid cells preoperatively and to be aware of intraoperative clues such as anterior sphenoid wall alignment, which may point to the presence of an Onodi cell. Attention to these important details will increase the likelihood of uncomplicated endoscopic sinus surgery at the sphenoethmoidal junction.