title: The prevalence and pattern of pneumatization of Onodi cell in Thai patients.
abstract: BACKGROUND
  The Onodi cell (sphenoethmoidal cell) is an anatomical variation of the most posterior ethmoid air cell the pneumatizes laterally and/or superiorly to the sphenoid sinus and is intimately in contact with the optic nerve. If it is infected or goes unrecognized during surgery it may result in serious damage to the optic nerve. Nowadays, computed tomographic scans of paranasal sinuses (CT PNS) have been used to detect variations in paranasal sinus anatomy However there is a lack of data about the variations of Onodi cell.
  
  
  OBJECTIVE
  To determine the prevalence and various patterns of Onodi cell.
  
  
  METHODS
  Axial, coronal, sagittal and sagittal oblique (parallel to the optic canal) CT scans of the paranasal sinuses, nasopharynx, neck and orbit performed at Srinagarind Hospital between January 1, 2004 and November 30, 2006 were reviewed A pilot study was carried out to investigate the inter-rater reliability of the identification of Onodi cell between the radiologist and rhinologist until the kappa value was 0.74. During the main study, the radiologist and rhinologist interpreted the CT scans independently. If there was a discordant opinion concerning the presence of Onodi cell, a consensus was reached by discussion between the rhinologist and the radiologist.
  
  
  RESULTS
  187 CT scans (374 sides) were included Sagittal oblique view detected Onodi cell in 185 sides 49.5% (95% CI: 44.4-54.5). The patterns of Onodi cell were classified into three patterns. In the first pattern, the Onodi cell extended only superiorly to sphenoid sinus (46%; 95% CI: 38.9-53.1). In the second pattern, it extended only laterally to sphenoid sinus (1%; 95% CI: 0.3-3.9). The last pattern was a combined type, lateral and superior to sphenoid sinus (53%; 95% CI: 45.8-60.0).
  
  
  CONCLUSIONS
  The prevalence of Onodi cell diagnosed by CT scans was 49.5% (95% CI 44.4-54.5) and the most common pattern was the combined type. This information may be useful for those who perform endoscopic sinus surgery.
authors.affiliation: Department of Otorhinolaryngology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Pornthep
authors.initials: P
authors.lastname: Kasemsiri
authors.forename: Sanguansak
authors.initials: S
authors.lastname: Thanaviratananich
authors.forename: Warinthorn
authors.initials: W
authors.lastname: Puttharak
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People / Q000706:statistics & numerical data; D005005:Ethmoid Sinus / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D020221:Optic Nerve Injuries / Q000517:prevention & control; D010256:Paranasal Sinuses / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D010361:Patients / Q000706:statistics & numerical data*; D015995:Prevalence; D015203:Reproducibility of Results; D013101:Sphenoid Sinus / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D013785:Thailand; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult