Fig. 1

Measurements of the paranasal sinuses and the reference measurements included in calculation of ratio of the mean of maxillary and sphenoid sinus diameters, diameter ratio measurement, (DRM) described in the “Methods” section. The middle widths were measured perpendicular to the depth (the middle longitudinal diameter in the axial plane) or the height (the middle longitudinal diameter in the coronal plane). a Diameter measurements in the suborbital axial plane of the maxillary sinuses, where the sinus area usually is greatest. b Diameter measurements in the coronal plane where the maxillary sinus area is at the greatest usually at the level of the uncinate process. c Diameter measurements in the axial plane of the sphenoid sinuses at the level directly cranial to foramen rotundum. d Diameter measurements in the coronal plane of the sphenoid sinuses at the level of the internal carotic artery crossing the anterior clinoid process. The depth and the height were measured parallel to the septum between the sphenoid sinuses. e Reference diameter measurement in the axial plane: The distance between the lateral orbital walls at the level of the dorsum sellae and the eye lenses. f Reference diameter measurement in the coronal plane: The width of the skull immediately above the orbit in the CT slice at the level of the axial reference measurement