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Perisylvian and Temporal Cortical Relationships

Surgical Correlation

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Perisylvian and Temporal Cortical Relationships. A, Lateral view of the right cerebral hemisphere. The lateral temporal surface is divided by the superior and inferior temporal sulci into the superior, middle, and inferior temporal gyri. Both the temporal gyri and sulci are parallel to the sylvian fissure. The sylvian fissure and central sulcus are the most important landmarks on the lateral surface of the brain. The sylvian fissure extends backward and turns up into the supramarginal gyrus at its posterior end. The inferior frontal gyrus is composed of the pars orbitalis, pars triangularis, and pars opercularis. The angular gyrus wraps around the upturned posterior end of the superior temporal sulcus. The temporal lobe is separated from the parietal lobe by the sylvian fissure and the extended sylvian line, which extends backward along the long axis of the sylvian fissure; from the occipital lobe on the lateral convexity, by the inferior part of the lateral parietotemporal line, which runs from the impression of the parieto-occipital sulcus on the superior margin of the hemisphere to the preoccipital notch; from the occipital lobe on the lower surface by the basal parietotemporal line, which extends from the junction of the calcarine and parieto-occipital sulcus to the preoccipital notch; and from insula, by the inferior portion of the limiting sulcus of the insula. B, Opercular lips of the sylvian fissure have been retracted to expose the insula and superior surface of the temporal lobe. The insula has a triangular shape with its apex directed anterior and inferior toward the limen insulae. The insula is encircled and separated from the frontal, parietal, and temporal opercula by a shallow limiting sulcus. The lower part of the limiting sulcus that borders the temporal lobe is referred to as the inferior limiting sulcus. The central sulcus of the insula separates the short gyri anteriorly from the long gyri posteriorly. The superior surface of the temporal lobe has two parts: the posteriorly placed planum polare, formed by the transverse temporal gyri, the most anterior of which is Heschl’s gyrus, and the planum temporale, which forms the floor of the anterior part of the sylvian fissure. The temporal lobe is connected superiorly to the insula by the temporal stem and anteriorly to the basal frontal lobe by the limen insulae. C, Basal view of the right temporal lobe. The basal temporal surface is traversed longitudinally by the occipitotemporal, collateral, and rhinal sulci that divide it from lateral to medial into the lower surface of the inferior temporal gyrus and the occipitotemporal (fusiform) and parahippocampal gyri. The anterior end of the parahippocampal gyrus deviates medially to form the uncus. The rhinal sulcus is located lateral to the uncus. The collateral sulcus may or may not be continuous anteriorly with the rhinal sulcus. The uncus has an anterior segment, an apex, and a posterior segment. The medial part of the uncus usually projects medial to and is often grooved (red arrow) by the tentorial edge. D, Medial surface of the right cerebral hemisphere. The medial surface of the temporal lobe is the most complex of the medial cortical areas. It is composed of three longitudinal strips of neural tissue, one located above the other. The most inferior strip is formed by the parahippocampal gyrus, the middle strip by the dentate gyrus, and the superior strip by the fimbria of the fornix. The choroid fissure in the temporal horn is located between the fimbria and the lower surface of the thalamus. The parahippocampal gyrus forms most of the medial surface of the temporal lobe. Anteriorly, the parahippocampal gyrus deviates medially to form the uncus. Posteriorly, it is intersected by the calcarine sulcus, which divides the posterior portion of the parahippocampal gyrus into an upper part that is continuous with the isthmus of the cingulate gyrus and a lower part that is continuous with the lingula. E, Enlarged view of D. The parahippocampal gyrus has been retracted to expose the dentate gyrus. The parahippocampal and dentate gyri are separated by the hippocampal sulcus, and the dentate gyrus and fimbria are separated by the fimbriodentate sulcus. In the temporal horn, the choroid fissure is located between thalamus and fimbria of fornix. The medial temporal region is divided into three parts: anterior, middle, and posterior. The anterior part (green brackets) extends posteriorly from the anterior end of the rhinal sulcus and uncus to a transverse line at the level of the inferior choroidal point. The middle part (red brackets) extends posteriorly from the inferior choroidal point to a transverse line passing at the level of the quadrigeminal plate. The posterior part (blue brackets) extends from the quadrigeminal plate to the level of the basal parietotemporal line, which connects the preoccipital notch to the lower end of the parieto-occipital sulcus. F, Superior view of the right temporal lobe with the anterior, middle, and posterior part bracketed as in E. The upper surface of the temporal lobe forms the floor of the sylvian fissure and presents two distinct parts: the planum polare anteriorly and the planum temporale posteriorly. The planum polare is free of gyri, and its lateral edge is formed by the superior temporal gyrus. The planum temporale is formed by the transverse temporal gyri. The inferior choroidal point, the lower end of the choroidal fissure, is located just behind the uncus and head of the hippocampus. The amygdala, located predominantly within the boundaries of the uncus, forms most of the anterior segment of the uncus and the anterior wall of the temporal horn. Superiorly, the amygdala blends into the globus pallidus without any clear demarcation. The hippocampus sits in the floor of the temporal horn. The head of the hippocampus is directed anteriorly and medially and is buried in the upper half of the posterior segment of the uncus. G, Coronal section of a right temporal lobe at the level of the apex of the uncus (insert). The temporal stem, the layer of white and gray matter that connects the temporal lobe to the lower insula, is positioned above the temporal horn. H, Coronal section of a right temporal lobe at the level of the inferior choroidal point (insert), which is positioned at the junction of the anterior and middle portions of the medial temporal lobe. The inferior choroidal point is located at the posterior edge of the uncus and at the anterior end of the choroid plexus and choroidal fissure in the temporal horn. (Images courtesy of AL Rhoton, Jr.)

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