Transcranial approach to the orbit: microsurgical anatomy.

An anatomical study of three microsurgical intraorbital routes to the optic nerve and orbital apex, which can be reached through a fronto-orbital craniotomy, was conducted on cadaver specimens. The structures that could be exposed via the medial, central, or lateral approaches directed through the orbital roof were defined. The medial approach, directed through the space between the superior oblique and the levator muscles, provides good access to all parts of the intraorbital optic nerve. The central approach, between the levator and the superior rectus muscles, provides the shortest route to the optic nerve. Two variants of the central approach were examined. In the first, the levator muscle and frontal nerve are retracted medially and the superior rectus muscle laterally. This variant provides access to only the midportion of the intraorbital segment of the optic nerve. In the second variant, the frontal nerve is retracted laterally together with the superior rectus muscle. This variant provides access to the posterior two-thirds of the intraorbital portion of the optic nerve. The lateral approach is directed between the levator and lateral rectus muscles. This approach also has two variants, depending on whether the superior ophthalmic vein is retracted medially or laterally. The variant in which the superior ophthalmic vein is retracted medially with the levator and superior rectus muscles provides access to the lateral side of the optic nerve except in the region adjacent to the superior orbital fissure. The variant in which the superior ophthalmic vein is retracted laterally together with the lateral rectus muscle provides excellent access to the optic nerve in the region of the superior orbital fissure. It is an ideal approach for lesions that involve both the cavernous sinus and orbit.