Pneumatization of the sphenoid sinus, dorsum sellae and posterior clinoid processes in computed tomography

Purpose
Assessment of sphenoid sinus (SS), posterior clinoid process (PCP), and dorsum sellae (DS) pneumatisation is significant when planning surgical approaches both to intra- and extrasellar pathologies. The authors analysed pneumatisation of the SS, with particular attention paid to pneumatisation of the PCP and DS.

Material and methods
The study was based on 100 computed tomography angiography examinations. SS, PCP, and DS pneumatisation grades were assessed using the classification system proposed by Hardy. The analyses were conducted in sagittal planes: midline plane (MP), sagittal posterior clinoid plane right (SPCP-R), and sagittal posterior clinoid plane left (SPCP-L). The occurrence of the highest pneumatisation grade (IVB according to Hardy), which encompasses DS and PCP, prompted the authors to conduct a further analysis in the coronal plane. In this way, seven DS and PCP pneumatisation symmetry types were identified.

Results
In the MP and SPCP-R, the most frequent pneumatisation grade was grade III (41% and 38%, respectively). In the SPCP-L, grade IVA prevailed (41%). Grade IVB was found in 12% of the SPCP-R images, 10% of the SPCP-L images, and in 12% of the MP images. Consistent pneumatisation grades in all analysed planes were found for 64% of cases. This was usually grade III noted in 28% of cases.

Conclusions
SS pneumatisation is characterised by considerable individual variability. There are a number of SS pneumatisation classification systems, but the system proposed by Hardy is the most useful for assessment of DS and PCP pneumatisation. Grade III of SS pneumatisation is the most common. Pneumatisation encompassing DS and PCP was found in 10-12% of cases.