Relationship Between the Insular Cortex and Deep Landmarks. A, Superolateral view of the insula and lateral ventricle. The upper portion of the cerebral hemisphere was removed using an axial cut approximately 1 cm above the posterior ramus of the sylvian fissure. The frontoparietal operculum has been removed to expose the insula lateral to the frontal horn and the body of the lateral ventricle. The anterior portion of the superior limiting sulcus is separated from the frontal horn by the anterior isthmus, and the posterior portion of the limiting sulcus is separated from the atrium by the posterior isthmus. The choroid plexus is attached along the choroidal fissure, located between the fornix and thalamus. The foramen of Monro is located deep to the posterior short gyrus. B, Enlarged lateral view. The M2 branches course along the insula. Most of the branching occurs near the insular pole. The central insular sulcus is the site most replete with insular perforating arteries. C, Posterolateral view of the same hemisphere. The lateral wall of the atrium and the roof of the temporal horn have been removed by dividing the white matter along the inferior limiting sulcus. The posterosuperior insular angle at the junction of the superior and inferior limiting sulci is superficial to the junction of the tail of the hippocampus, calcar avis, and anterior wall of the atrium. The choroid plexus has been elevated to expose the floor of the temporal horn, which is formed by the collateral eminence overlying the collateral sulcus laterally and the hippocampus medially. D, The incision along the inferior limiting sulcus has been extended forward to where the incision begins for the transinsular approach into the temporal horn for a selective amygdalohippocampectomy. The choroidal fissure in the temporal horn has been opened by separating the fimbria of the fornix and choroid plexus to expose the basal vein and PCA in the posterior portion of the ambient cistern below the thalamus. The fimbria of the fornix arises on the surface of the hippocampal formation. The parahippocampal gyrus extends medially below the choroidal fissure. E, The opening along the choroidal fissure has been extended anteriorly without disturbing the attachment of the choroid plexus to the thalamus. The PCA and the basal vein course through the ambient cistern on the medial side of the choroidal fissure. F, The exposure along the choroidal fissure has been extended forward to the back edge of the amygdala. The head of the hippocampus blends into the posterior segment of the uncus. The lateral geniculate body protrudes from the lower surface of the thalamus, just medial to the choroidal fissure and body of the hippocampus, into the upper portion of the ambient cistern. (Images courtesy of AL Rhoton, Jr.)