Variations of sphenoid and related structures.

The aim of this study was to delineate the precise relationship between the sphenoid sinus and internal carotid artery and the optic nerve, as well as to assess incidence of the anatomic variations of these structures. A review of 92 paranasal sinus tomographic scans was made for anatomic variations of the sphenoid sinus and related bony and neurovascular structures. Coronal and axial tomographic sections were obtained with 2.5-mm section thickness. We assessed the protrusion of the internal carotid artery (ICA) and the optic nerve (ON) into the sphenoid sinus, bone dehiscence of these structures, and pneumatization of the anterior clinoid process (ACP) and pterygoid recess (PR), as well as the variations of the sphenoid sinus septum. The protrusion of the ICA into the sphenoid sinus was found in 24 (26.1%) patients. An ON protrusion was present in 29 (31.5%) patients. Pneumatization of the PR was encountered in 27 (29.3%) patients. There was not a statistically significant relationship between the pneumatization of the PR and ICA protrusion into the sphenoid sinus (chi2 = 0.258, p = 0.168). A significant relationship between the ACP pneumatization and protrusion of the ON into the sphenoid sinus was found (chi2= 0.481,p = 0.007). Preoperative recognition of the anatomic variations by the radiologist is beneficial for identification of the limits of dissection. This is particularly important in the sphenoid sinus area where extensive pneumatization of the skull base bones may distort the anatomic configuration. Therefore, axial and coronal CT sections should always be obtained prior to any surgery in the sphenoid sinus area.