An Anatomically-Based Endoscopic Endonasal Model to Navigate the Anterior Ventral Skull Base

Endoscopic endonasal approaches to access the sellar and parasellar regions are challenging in the face of anatomical variations or pathologic conditions. We propose an anatomically-based model including the orbitosellar line (OSL), critical oblique foramen line (COFL), and paramedial anterior line (PAL) facilitating safe, superficial-to-deep dissection triangulating upon the medial opticocarotid recess. Five cadaveric heads were dissected to systematically expose the OSL, COFL, and PAL, illustrated with image guidance. Application of the coordinate system and a 6-step dissection sequence is described. The coordinate system consists of 1) the OSL, connecting a) the anterior orbital point, junction of the anterior buttress of the middle turbinate with the 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 maxillo-ethmoidal suture; b) the posterior orbital point, junction of the optic canal with the lamina papyracea, located 4 ± 0.7 mm below the posterior ethmoidal artery; and c) the medial opticocarotid recess; 2) COFL (15 ± 2.8 mm), connecting the palatovaginal canal, vidian canal, and foramen rotundum; and 3) PAL (39 ± 0.06 mm), connecting the vidian canal with the posterior ethmoidal artery. OSL, COFL, and PAL form an anatomically-based model for the systematic exposure when accessing the parasellar and sellar regions. Preliminary anatomical data suggest that this model may be of value when normal anatomy is distorted by pathology or anatomic variations.