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Calculation of an Optic Nerve Injury Risk Profile Before Sphenoid Sinus Surgery

Objectives: Our objective was to analyze variations in the optic nerve (ON) course and surrounding structures in an effort to construct an optic nerve injury risk profile before endoscopic intranasal sphenoidal, or endoscopic endonasal transphenoidal, skull-base surgery, and eventually to construct and formulate a common classification by combining the known classes. The authors used computed tomography (CT) toward this end. Methods: The authors retrospectively reviewed 200 consecutive CT scans (400 sides) of the paranasal sinuses. The pneumatization of the anterior clinoid process, the relationships of the ONs to the sphenoidal sinuses, and ON dehiscence were evaluated. The authors then created a formula by which risk profiles can be constructed for patients for whom sphenoid or parasellar surgery is planned. Results: Pneumatization of the anterior clinoid process was evident in 28.25%. Dehiscence of the bony wall of the ON was evident in 9.5%. The ON course lay adjacent to the sphenoidal sinus, causing sinus wall indentation, in 23%. Cumulative optic nerve injury risk scoring showed that, radiologically, surgery on 8.5% and 1.5% of sphenoid sinuses described here carried severe or critical risk of ON injury, respectively. Conclusions: Head-and-neck surgeons and neurosurgeons should be aware of variations in ON course. The authors composed an optic nerve injury risk classification category based on the sum of individual weights of each of these classes. Reductions in ON injuries require careful evaluation of potential variant anatomies. Preoperative CT scans must be meticulously reviewed to avoid ON injury.