Optic nerve course and its association with lateral lamella: relevance for endoscopic sinus surgery

Abstract

Purpose To investigate the association between the anatomical course of the optic nerve within the sphenoid and posterior ethmoid sinuses (Delano classification) and anterior skull base morphology, particularly lateral lamella length and olfactory fossa depth. Methods Paranasal sinus CT scans from 192 patients (384 hemi-sinuses) were retrospectively reviewed. The course of the optic nerve was categorized using the Delano classification (types 1–4). Lateral lamella length and Keros classification were assessed for each case. Statistical comparisons were performed using ANOVA, post-hoc Tukey tests, and Chi-square analysis. Results Lateral lamella length significantly differed among the Delano types (p=0.001). Delano type 3 and type 4 sinuses demonstrated significantly longer lateral lamella compared to type 1 (p=0.026 and p=0.016, respectively). Additionally, a significant variation in Keros classification was observed across Delano groups (p=0.025), with higher Delano types showing increased prevalence of Keros type 3. These findings suggest that optic nerve protrusion is associated with elongation of the lateral lamella and deepening of the olfactory fossa. Conclusion This is the first study to demonstrate a significant anatomical correlation between Delano classification and anterior skull base morphology. As optic nerve protrusion into the sphenoid sinus increases, adjacent skull base structures—particularly the lateral lamella—become elongated, potentially heightening the risk of iatrogenic injury during endoscopic sinus surgery. Combined use of Keros and Delano classifications in preoperative imaging may enhance surgical risk stratification and improve patient safety.