A, Bicoronal scalp flap has been reflected forward to expose the frontal bone and supraorbital margin. The supraorbital nerve has been released by removing bone from the lower margin of the supraorbital foramen. The craniotome has cut around the margin of the orbitofrontal bone flap, which includes the supraorbital ridge and part of the orbital roof. The temporalis muscle has been reflected backward to expose the keyhole, the site of a burr hole, which at its depth will expose periorbita in its lower edge and frontal dura in its upper edge. A zygomatic-temporal branch of the zygomatic nerve is exposed on the zygomatic process of the frontal bone. B, Removal of the bone flap exposes the periorbita of the orbital roof and the dura covering the frontal lobe. The medial edge of the bone cut should extend completely through the orbital rim and partially divide the thin part of the roof of the orbit behind the orbital rim to prevent the fracture across the orbital roof, which occurs as the bone flap is elevated, from extending medially into the cribriform plate or ethmoid air cells. C, The roof of the orbit has been removed, the frontal lobe elevated, and the dura and arachnoid opened to expose the optic nerve intracranially and in the optic canal. The optic canal has been unroofed to expose the intracanicular segment of the optic nerve. The falciform ligament is a dural fold, which extends from the anterior clinoid across the top of the optic nerve just proximal to the optic canal to the tuberculum sellae. At the site of this dural fold, the nerve is covered only by dura, rather than by dura and bone, as it is within the optic canal. The anterior clinoid artery, situated on the lateral side of the optic nerve, has been removed. The anterior cerebral artery courses above the optic chiasm. D, The periorbita has been opened and the orbital fat removed to expose the trochlear nerve, the supraorbital and supratrochlear branches of the frontal nerve, and the levator and superior oblique muscles. The trochlear nerve passes medially above the levator muscle to reach the superior oblique muscle. The superior ophthalmic vein passes through the lateral part of the superior orbital fissure. E, The medial approach is directed through the interval between the superior oblique and the levator muscles. In the medial route there are no neural and vascular structures between the ophthalmic artery and orbital apex, except the trochlear nerve, which crosses above the levator muscle in the extraconal area. The ophthalmic artery, superior ophthalmic vein, and nasociliary nerve are situated on the lateral side of the optic nerve at the orbital apex, but further forward they cross above the nerve to reach the medial part of the orbit. (Images courtesy of AL Rhoton, Jr.)