Anatomy of the Optic Canal: A Computed Tomography Study of Endoscopic Nerve Decompression

Objectives: Endoscopic optic nerve decompression has variable success rates for trauma. Little is known of its use in skull base tumors. Our goal is to further delineate the radiographic anatomy of the optic canal to understand if the variable success can be explained on anatomical principles.

Study Design: Optic canal dimensions and the degree of optic canal exposure to the sphenoid sinus were measured on sinus CT images of 96 patients.

Results: A total of 191 optic canals were analyzed (111 females, 80 males). The average medial canal wall length was 1.48 cm (range, 0.7–2.3 cm). The length in males was 1.61 cm (1.1–2.3) compared with 1.39 cm (range, 0.7–2.0 cm) in females (P = 8.0–7). Onodi cells and pneumatized anterior clinoids were present on 14 and 16 images, respectively. The average degree of exposure of the optic canal to the sphenoid sinus without Onodi cells or clinoid pneumatization was 99.3 degrees; with both Onodi cells and clinoid pneumatization, it was 117.7 degrees. The potential area of canal exposed was 0.66 cm², or 28% of total surface area.

Conclusions: A wide range in medial canal wall length and exposure of the optic canal to the sphenoid sinus exists on CT images. Variation in medial canal wall length and optic canal exposure may limit the surface area of nerve available for endoscopic optic nerve decompression. Case examples are presented.