A new method of locating the optic canal based on structures in sella region: computed tomography study

The location of optic canal and the intracranial segment of optic nerve is difficult because of the high possibility of the deficiency of optic protuberance as well as its complex relationship to sphenoid and ethmoidal sinus. A new method of locating the optic canal and a comprehensive analysis of it and the structures around is of great importance.

Our study aimed to provide a new method to locate the optic canal and analyze the relationship between optic canal and other structures in the sella region, which can be a guidance for endoscopic sinus surgery such as the optic nerve decompression and transsphenoidal approach to the pituitary adenoma and reduced complications caused by the injury of optic nerve.

Computed tomography images of 120 sphenoid sinuses in adults were reviewed, and multiplanar reconstruction was used to make it possible to make the measurement in coronal, sagittal, and axial plane at the same time. The positional relationship between optic canal and the stationary structures in sella region was analyzed.

The horizontal distance between the lowest point of sella bottom (SB) and sulcus prechiasmaticus in the sagittal plane was 8.08 (SD, 0.79) mm. The distance between the medial wall of optic canal and the midline of SB were 7.01 (SD, 1.43) mm in plane 1, 7.78 (SD, 0.86) mm in plane 2, 11.08 (SD, 0.82) mm in plane 3, and 13.81 (SD, 0.66) mm in plane 4; the angles between line BO and line BC were 87.99 (SD, 5.04) degrees in plane 1, 87.71 (SD, 4.98) degrees in plane 2, 82.54 (SD, 5.78) degrees in plane 3, and 82.57 (SD, 6.99) degrees in plane 4. As for the relationship between optic canal and the sphenoid sinus, there were 2.08% of sphenoid sinus of type A, 19.17% of type B, 45.00% of type C, 17.50% of type D, and 16.25% of type E.

Optic canal can be located by the structures or markers in sella region such as the midline of SB, the lowest point of SB, the midpoint in the top edge of sphenoid sinus, and tubercular recess. The analysis of the relationship between optic canal and the sphenoid sinus as well as the data measured in our study is helpful to make an accurate location of the optic canal when the bony landmarks of optic canal are not available.