To establish normative dimensions for the depth of the olfactory fossa, the length and angulation of the lateral lamella of the cribriform plate, and the height of the ethmoid roof, in adult males and females.

The study assessed 300 high resolution, multislice computed tomography scans of the paranasal sinuses, which were evaluated using Merge Efilm software (version 2.0.0, build 37).

According to the original Keros classification, the type II olfactory fossa was the commonest type in men (66.7 per cent), while the type I fossa was commonest in women (53 per cent). A difference of 3 mm or more between the depths of the right and left olfactory fossae was present in 11 per cent of men and 2 per cent of women. The lateral lamella of the cribriform plate was significantly shorter and less oblique in men than in women. The length of the lateral lamella was greater anteriorly than posteriorly in both sexes. There was a statistically significant difference between the angle of the lateral lamellae, comparing right and left sides. The ethmoid roof was lower in women than men.

The observed differences between men and women and between the right and left sides are of surgical importance, and should alert surgeons to the need for thorough, systematic pre-operative evaluation of computed tomography scans.