Study of the relationship between sphenoid sinus volume and protrusions in the sphenoid sinus

The relationship between the volume of sphenoid sinus (SS) and the prevalence of internal carotid artery (ICA) and optic nerve (ON) protrusions in the SS was studied by using high-resolution CT imaging. The ICA and ON protrusions in SS were observed in randomly selected normal head CT scanning images from 350 adult subjects. According to the incidence of ICA protrusion, three groups were divided into no ICA protrusion (70.75%), unilateral protrusion (8.68%) and bilateral protrusions (20.57%). The ON protrusion accounted for 16% in 350 subjects and accompanied absolutely with ICA protrusion, but ICA protrusion appeared without accompanying with ON protrusion. The SS volume depended upon the protrusions in it and showed statistical differences, without ICA protrusion, the smallest size (11.16 ± 1.60) cm; the unilateral protrusion, medium size (14.20 ± 1.80) cm and the bilateral protrusion, the largest size (25.03 ± 2.21) cm. By observing 3D reconstructed models of ON and SS, we found ON was adjacent to SS (46%) and to posterior ethmoid sinuses (44%). The current study indicates that SS volume is varied with numbers of the protrusions and that ON location varies with the pneumatization of SS. Our results provide an anatomical basis to the surgeries for SS and its surrounding structures.