Analysis of Optic Nerve Types in Relation to Posterior Paranasal Sinuses: A Computed Tomographic (CT) Study

Abstract

Objective: To assess the variations in the course of optic nerve (ON) in relation to sphenoid sinus with the help of CT scan. Methodology: A cross-sectional study was carried out using computed tomographic (CT) paranasal sinus scans of two hundred and seventy study participants between January 2017 and May 2017. Non-probability consecutive sampling technique was used and data was entered on SPSS version 23. Inclusion criteria comprised of adults coming for CT head and brain who did not have bony abnor- mality of sphenoid and ethmoid sinuses or adjacent structures. However, individuals with sinonasal tumors, chronic rhinosinusitis, prior sinus surgery, facial fracture, nasal polyposis and congenital craniofacial anomaly were excluded from this study. Analysis of optic nerve was carried out according to DeLano's classification. Results: Type 1 ON was found to be the most frequent type; 55.93%, followed by type 2 with a frequency of 26.85%. However, type 3 and type 4 appeared less frequently, that is 11.1% and 6.11%, re- spectively. When comparing right and left sides it was noted that the frequency of type 1 optic nerve was found to be higher on both right and left sides with a value of 56.30% and 55.5%, respectively. Type 2 showed a frequency of 26.67% on right side and 27% on left side. Type 3 was identified to be 11.4% and 10.7% on right and left sides, respectively. Type 4 optic nerve was found to be the least common type in our study on both sides, i.e. 5.56% on the right side and 6.67% on the left side. Conclusion: The combined percentage of type II and type III ON that is 37.96% in our sample brings us to this conclusion that fairly high percentage of our population is exposed to increased potential risk of iatrogenic optic nerve injury thus emphasising the need for careful evaluation of ON in relation to sphenoid sinus anatomy on CT scan prior to endoscopic sinus surgery.

Keywords

• X-ray CT scan, optic nerve, ethmoid sinus, sphenoid sinus, paranasal sinuses.