Computed Tomography Analysis of Anatomic Variations of the Sphenoid Sinus

Background: The sphenoid sinus is a distinctly complex anatomic structure with great anatomic variation in the extent of pneumatization, number and position of septae, and the relationship of the sinus to adjacent structures, including the optic nerve, maxillary nerve, vidian nerve, and the internal carotid artery. These variations become especially important in transsphenoidal surgical approaches to the sella and parasellar regions. In this study, CT scans from 175 patients (age range, 19–81 years) with no sphenoid sinus fractures or associated masses were analyzed by two independent observers for the presence of these variations.

Methods: A retrospective radiographic analysis was performed.

Results: Four different classifications of sphenoid sinus pneumatization were defined—conchal, presellar, sellar, and postsellar—based on pneumatization relative to the anterior and posterior face of the sella. The distribution ranged from 2.8–3.4%, 6.8–7.4%, 44.6–46.9% and 41.1–43.4%, respectively. These data show a greater preponderance of sellar and postsellar variation than prior studies have demonstrated. When analyzed according to age, gender, and ethnicity, the distribution of the extent of pneumatization remained essentially the same. The prevalence of optic nerve, maxillary nerve, and internal carotid artery protrusion was found to be 24.3%, 25.4%, and 27.1%, respectively. The rate of dehiscence was found to be 3.4%, 7.4%, and 0.9%, respectively. Septa in the sphenoid were found to be present in 43.4% of cases. The lateral recesses were pneumatized in 34.3–35.7%, and the clinoid processes in 9.4–10% of patients.

Conclusions: This study further elucidates the prevalence of various types of anatomic variation of the sphenoid sinus in patients of different age, gender, and ethnicity, which has important implications for endoscopic endonasal sinus and endoscopic skull base surgery.