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Figure 2: Case 1: Schematic illustrations of the surgical technique: (a) A right-sided pterional craniotomy and a fronto-temporal approach is adopted. The aneurysm (*) has a broad neck and is lifting up the optic nerve (II). The proximal aspect of its neck is not visible as it is covered by both the optic nerve (II) and the anterior clinoid process (ACP). (b) After an intradural clinoidectomy, the distal dural ring (DDR), the carotid collar (CC) covering the clinoidal segment of the internal carotid artery (ICA) are exposed. The excision of these fascial layers exposes the clinoidal ICA proximally curving laterally towards the cavernous sinus. The ophthalmic artery (arrow) is visible just distal to the DDR. The drilling of the planum sphenoidale (PS) that forms the roof of the optic foramen exposes the distal 8-10mm of optic nerve (E II) covered by the falciform ligament. The mobilized optic nerve may be gently displaced medially to access proximal and distal aspects of the broad neck of the medially directed aneurysm (*) and clipped. No attempt is made to mobilize the fundus of this giant aneurysm as it is surrounded by perforators to the hypothalamus. ACA: Anterior cerebral artery; MCA: Middle cerebral artery; E II: Exposed distal part of the optic nerve within the optic foramen; #: Exposed and drilled planum sphenoidale bone after reflecting the dura overlying it; L: Membrane of Liliequist

Figure 2: Case 1: Schematic illustrations of the surgical technique: (a) A right-sided pterional craniotomy and a fronto-temporal approach is adopted. The aneurysm (*) has a broad neck and is lifting up the optic nerve (II). The proximal aspect of its neck is not visible as it is covered by both the optic nerve (II) and the anterior clinoid process (ACP). (b) After an intradural clinoidectomy, the distal dural ring (DDR), the carotid collar (CC) covering the clinoidal segment of the internal carotid artery (ICA) are exposed. The excision of these fascial layers exposes the clinoidal ICA proximally curving laterally towards the cavernous sinus. The ophthalmic artery (arrow) is visible just distal to the DDR. The drilling of the planum sphenoidale (PS) that forms the roof of the optic foramen exposes the distal 8-10mm of optic nerve (E II) covered by the falciform ligament. The mobilized optic nerve may be gently displaced medially to access proximal and distal aspects of the broad neck of the medially directed aneurysm (*) and clipped. No attempt is made to mobilize the fundus of this giant aneurysm as it is surrounded by perforators to the hypothalamus. ACA: Anterior cerebral artery; MCA: Middle cerebral artery; E II: Exposed distal part of the optic nerve within the optic foramen; #: Exposed and drilled planum sphenoidale bone after reflecting the dura overlying it; L: Membrane of Liliequist