Landmarks during Sylvian Fissure Dissection. A, Anterobasal view of the cerebrum. The arrowheads indicate the frontotemporal arachnoid reflection bridging the orbital surface of the frontal lobe to the planum polare. 1, anterior orbital gyrus; 2, lateral orbital gyrus; 3, rectus gyrus; 4, posterior orbital gyrus; 5, medial orbital gyrus. B, Intraoperative photograph showing the basal surface of the right hemisphere after the pterional craniotomy and dural opening. The frontotemporal arachnoid membrane (arrows) in this figure has been stretched between the tip of the bipolar forceps and the suction tube. The frontotemporal arachnoid membrane is continuous with the carotid, chiasmatic, and olfactory cisterns. In this figure, the olfactory tract is shown at the right side of the tip of the suction tube, and the optic nerve is shown at the right side of the olfactory tract. C, Sagittal MRI scan. The arrows indicate the intermediate plane of the sylvian fissure on the basal surface, located between the posterior portion of the orbital gyri and the planum polare. The arrowheads indicate the anterior operculoinsular compartment of the sylvian fissure. D, Superolateral view of the left hemisphere. A spatula has been placed in the horizontal ramus of the sylvian fissure that continues medially with the anterior limiting sulcus of the insula. The precentral gyrus is usually related to the midposterior portion of the insula. 1, precentral gyrus; 2, frontal horn; 3, anterior limiting sulcus of the insula; 4, junction between the inferior and the superior limiting sulci of the insula; 5, anterior portion of the insula; 6, pars orbitalis; 7, Heschl’s gyrus. (Images courtesy of AL Rhoton, Jr.)