The relationship of the natural sphenoid ostium to the skull base.

OBJECTIVES/HYPOTHESIS Various intranasal landmarks have been described to aid in the localization of the natural sphenoid sinus ostium. The objectives of this study are to identify the ostium location relative to the skull base and assess the relationships between the location of the ostium and sphenoid disease or pneumatization pattern. DESIGN Descriptive study. METHODS Consecutive Xoran Mini-CAT (Ann Arbor, MI) scans of patients with no history of sinus surgery (n = 202) were evaluated. The natural sphenoid ostium was identified in axial, coronal, and sagittal planes. Distances from the planum to the ostium and from the planum to the sinus floor were calculated. Lund-Mackay score and pneumatization pattern were recorded for each sphenoid sinus. RESULTS The mean distance from planum to ostium was 11.2 ± 2.6 mm (range 4.4-19.2). On average, this encompassed 45.5% ± 10% of the total sphenoid height. ANOVA with posthoc Tukey analysis revealed that the ostium was closer to the planum in sinuses with sellar (P = 0.05) or presellar (P = 0.02) pneumatization, compared to those with postsellar pneumatization. There was no significant relationship between the ostium location and degree of sinus disease. There was a significant difference in the pneumatization pattern between males and females (P = .04). More males had postsellar pneumatization than expected, and more females had sellar pneumatization than expected. CONCLUSIONS The natural ostium of the sphenoid sinus is located at approximately the midpoint of the sphenoid face. Nevertheless, significant variability can be observed based on the pneumatization pattern. Surgeons should recognize that the ostium may be closer to the skull base when the sinus is less pneumatized.