Defining Lateral Access Over the Optic Canal in Endoscopic Endonasal Approaches and Proposed Methods of Its Maximization: An Anatomical Study

Abstract To quantify lateral extension over the optic canal (OC) through endoscopic endonasal approaches (EEAs) and present techniques to maximize lateral extension. On 20 sides of 10 specimens, transplanum EEAs were performed. The OC roof was drilled maximally laterally. The lateral anterior cranial fossa (ACF) dura accessed was marked; its distance from lateral OC was measured at the proximal and distal OC. To enhance lateral drilling, we performed a posteromedial orbital decompression (POD)—removal of the posteromedial lamina papyracea and orbital apex bone—and continued lateral drilling. New lateral limits were marked and measured. At proximal OC, the transplanum approach accessed the full width of ACF dura overlying OC in 55% of sides; POD addition provided access in 100% of sides (p < 0.01). At proximal OC, the transplanum approach provided access to ACF dura an average of 0.7 mm lateral to OC; POD addition provided an average access of 6.0 mm lateral to OC (p < 0.01). At distal OC, the transplanum approach accessed the full width of ACF dura overlying OC in 30% of sides dissected; POD addition afforded access in 100% of sides (p < 0.01). At distal OC, the transplanum approach provided access to ACF dura an average of 1.1 mm medial to OC; adjunct POD provided an average access of 6.4 mm lateral to OC (p < 0.01). A transplanum approach affords inconsistent access to the full width of ACF dura overlying OC; adjunct POD consistently affords access to ACF dura lateral to OC and significantly increases lateral reach.