Fig. 7.

Transorbital exposure of the lateral anterior skull base. A The removal of the orbital roof provides exposure of the anterior cranial fossa dura (ACFD), which can be resected or incised to expose the inferior aspect of the frontal lobe and related neurovascular structures. Among transorbital endoscopic approaches, superior eyelid crease and precaruncular provide the best exposure of this portion of the cranial base and adjacent structures. The orbital beak (OBe) is the line located above ethmoidal foramina where the anterior cranial base turns from horizontal to cranially-convex (i.e., from the ethmoidal roof to the orbital roof, respectively). The lateral orbital wall (LOW) can be used as landmark to define the lateral limit of the craniectomy. B Posterior craniectomy can include the anterior clinoid process, medially, and lesser sphenoidal wing, laterally. This provides exposure of the intracanalicular portion of the optic nerve (ON), anterior clinoid process dura (ACPD), and meningo-orbital fold (MOF), which is the area where the dura of anterior and middle cranial fossae turns into periorbit. C Focusing on the posteromedial portion of the surgical corridor, the optic strut (OSt) between the optic nerve and the paraclinoid tract of the internal carotid artery (pcICA). D In the most medial and anterior portion of the surgical corridor, bone removal of the superomedial orbital wall provide access to the frontal sinus (FS), frontoethmoidal region, and anterior ethmoid (AE). AEF, anterior ethmoidal foramen; Pe, periorbit; PSp, planum sphenoidale; PEF, posteror ethmoidal foramen; Tr with white dashed line, position of the trochlea