The Prevalence of an Onodi Cell in Adult Thai Cadavers

Abstract

Endoscopic sinus surgery in patients who have an Onodi cell (sphenoethmoid cell) carries a high risk f or optic nerve injury. We meticulously dissected 65 embalmed cadaver adult half-heads and attempted to identify an optic canal bulge in each with a nasal endoscope. Our aims were to determine the prevalence ofan Onodi cell in adult Thai cadavers, to ascertain the prevalence of an overriding ethmoid cell, and to measure the length ofan overriding ethmoid cell's superio r and posterior extensions in relation to the anterior sphenoid wall. Moreover, we attempted to determine the minimum amount ofbone thickness betwee n an Onodi cell and the optic nerve. We fo und that an Onodi cell was present in 39 of the 65 specimens (60.0 %). We also fo und that an overriding ethmoid cell was present in 14 spec imens, which accounted f or 21.5 % of the total numb er of specimens and 36.8% of38 Onodi cell-pos itive speci mens (the presence or absence of an overriding ethmoid cell was not recorded in one of the 39 Onodi cell-pos itive specimens). The distance of the overriding ethmoid cell 's superior and posterior extensions f rom the anterior sphenoid wall rangedfro m 3 to 13 mm (median: 7) andfrom 4 to 16mm (median: 9.5), respectively. Measurements of the minimum amount ofbone thicknesses between each Onodi cell and optic nerve ranged fro m 0.03 to 0.54 mm (median: 0.08). Our study demonstrated that the prevalence ofan Onodi cell in adult Thai cadavers was as great as the

High‐resolution computed tomography analysis of the prevalence of onodi cells

“…The reported prevalence of Onodi cells varies greatly. Studies of computed tomography (CT) scans report that Onodi cell prevalence ranges from 8% to 24%,14–18 whereas cadaveric studies show an increased incidence of 42% to 60% 19–22. A recent study by Shin et al23 analyzing 162 preoperative CTs and intraoperative endoscopic endonasal findings demonstrated the incidence of Onodi cells on preoperative CT to be 32.7% and 33.3%, during trans‐sphenoidal surgery, thus illustrating a good correlation between CT and intraoperative findings.…”

The central Onodi Cell: A Previously Unreported Anatomic Variation

“…Overriding ethmoid cells have been found to coexist in 36.8% of Onodi cell–positive specimens (defined as the most posterior ethmoid cell that features an endoscopically identifiable optic canal bulge). 12 No overriding ethmoid air cells have been found in Onodi cell–negative specimens. 9 Posterior ethmoid cells may expand beyond the ethmoid bone and grow into the sphenoid bone, usually superolaterally, 17 possibly surrounding the optic canal or completely overgrowing the sphenoid sinus and extending posterior to it.…”

“…6,8,11 These definitions distinguish the Onodi cell from the overriding posterior ethmoid cell as defined by Thanaviratananich et al because of the close association of the optic nerve with the Onodi cell. 12 …”

Visual loss in patients with sphenoethmoidal cells

“…4 These prevalence figures are based on CT findings, and are generally accepted within the literature; however, a recent paper reported a much higher prevalence of 65.3 per cent based on 170 CT scans. 6,7 The discrepancy may reflect a lack of resolution on imaging. 6,7 The discrepancy may reflect a lack of resolution on imaging.…”