Computed Tomography Anatomy of the Optic Canal

Abstract

Objective (1) Analyze the radiographic anatomy of the optic canal in relationship to the sphenoid sinus. (2) Understand the role variation in optic canal anatomy may have in the variability of outcomes in optic nerve decompression. Methods Fine cut computed tomography images of the sinuses were obtained with an IRB waiver. Optic canal dimensions were measured on sinus computed tomography images of 96 patients. 191 optic canals were analyzed (111 females, 80 males). Student T-test calculations were performed for statistical analysis on computer software. Results The average medial canal wall length was 1.48 centimeters (range 0.7–2.3). The length in males was 1.61 centimeters (1.1–2.3) as compared to 1.39 centimeters (0.7–2.0) in females (p=8.0–7). The average degree of exposure of the optic canal exposed to the sphenoid sinus was 101.3 degrees (56–176). The degree of exposure was 105.6 in males versus 98.2 in females (p=.01). The potential area of canal exposed to the sphenoid sinus was 0.66 centimeters squared or 28% of the total surface area. The potential area exposed to the sphenoid sinus in males was 0.76cm2 (28%) and 0.58 centimeters squared (27%) in females. Conclusions A wide range in medial canal wall length and exposure of the bony optic canal to the sphenoid sinus exists on CT images. The variation in medial canal wall length and in optic canal exposure to the sphenoid sinus may contribute to the variability in success rates of endoscopic optic nerve decompression for optic neuropathy.