Proposal of an Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Skull Base Using the Orbitosellar Line (OSL), Critical Oblique Foramen Line (COFL), and Paramedian Anterior Line (PAL) as Coordinates

Background Endoscopic endonasal approaches to access the sellar and parasellar regions are challenging in the face of anatomical variations or pathological conditions. Objective Propose an anatomically-based model including the orbito-sellar line (OSL), critical oblique foramen line (COFL), and paramedial anterior line (PAL) facilitating safe, superficial-to-deep dissection triangulating upon the medial opticocarotid recess (MOCR). Methods Five cadaveric heads were dissected to systematically expose the OSL, COFL, PAL illustrated with image-guidance. Application of the coordinate system and 6-step dissection sequence is described as well. Results The coordinate system consists of: 1) OSL, connecting a) anterior orbital point (AOP), junction of the anterior buttress of the middle turbinate with Agger nasi region, located 34.3 +/- 0.9 mm above the intersection of the vertical plane of the lacrimal crest and the orthogonal plane of the maxilloethmoidal suture, b) posterior orbital point (POP), junction of the optic canal (OC) with the lamina papyracea, located 4 +/- 0.7 mm below the posterior ethmoidal artery (PEA), and c) MOCR ; 2) COFL (15 +/- 2.8 mm) connecting the palatovaginal canal, vidian canal (VC) and foramen rotundum and 3) PAL (39 +/- 0.06 mm) connecting the VC with the posterior ethmoidal artery. Conclusions OSL, COFL, and PAL form an anatomically-based model for the systematic exposure when accessing the parasellar and sellar region. Preliminary anatomical data suggests that this model may be of value when normal anatomy is distorted by pathology or anatomic variations.