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Sequential Dissection of Temporal Region

Surgical Correlation

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Sequential Dissection of Temporal Region. A, Superior view of the right temporal lobe and horn with the frontal and parietal lobes and the thalamus removed. The medial temporal region can be divided in three parts: anterior, middle, and posterior. The anterior portion of the medial temporal region is limited anteriorly by the anterior end of the rhinal sulcus and posteriorly by a transverse line at the level of inferior choroidal point, located at the posterior edges of the uncus and hippocampal head. The junction of the middle and posterior parts is located at the level of the quadrigeminal plate. The posterior limit of the posterior part is positioned at the level of the basal parietotemporal line, which connects the preoccipital notch to the inferior end of the parietooccipital sulcus. The anterior part includes both the anterior and posterior segments of the uncus. The anterior segment of the uncus faces the carotid and sylvian cistern and the posterior segment faces the crural cistern. The middle portion is formed by the parahippocampal and dentate gyri and fimbria and forms the lateral wall of the ambient cistern. The posterior portion is formed by the most posterior portion of the parahippocampal gyrus, the isthmus of cingulate gyrus, and the anteriormost portion of the lingula and forms the lateral wall of the quadrigeminal cistern. The anterior segment of the uncus contains the amygdala. The apex of the uncus is located medial to the uncal recess of the temporal horn and lateral to the oculomotor nerve. The uncal recess extends medially between the amygdala and the head of the hippocampus. The head of the hippocampus sits in the upper part of the posterior segment of the uncus. The middle part of the medial temporal region is composed, from below to above, by the parahippocampal gyrus, dentate gyrus, fimbria, choroid plexus, body of the hippocampus, and the collateral eminence. The posterior part includes the choroid plexus, choroidal fissure, tail of the hippocampus, and the collateral trigone, in addition to the cortical surface facing the quadrigeminal cistern. The crural, ambient, and quadrigeminal cisterns are located on the medial side of the temporal lobe. B, Upper part of the right cerebral hemisphere has been removed to expose the temporal horn, atrium, and the basal cisterns. The internal carotid and middle cerebral arteries cross the anterior segment of the uncus. The M1 segment of the middle cerebral artery courses on the upper surface of the temporal pole, and the M2 segment crosses the insula just above and lateral to the temporal horn. The posterior cerebral arteries pass posteriorly in the crural and ambient cisterns to reach the quadrigeminal cistern. The P2A segment of the posteriorcerebral artery courses medial to the uncus in the crural cistern, the P2P courses in the ambient cistern, and the P3 courses in the quadrigeminal cistern. The anterior choroidal artery passes around the upper part of the uncus to enter the temporal horn and choroid plexus at the inferior choroidal point. The sylvian point is located where the most posterior branch of the M2 segment turns away from the insular surface and toward the lateral convexity. 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. C, Inferior view of the lower surface of the medial temporal lobe and midbrain. The part of the posterior uncal segment below the uncal notch and the medial part of the parahippocampal gyrus on the left side have been removed to expose the lower surface of the upper half of the posterior segment of uncus and the dentate gyrus, fimbria, and lateral geniculate body. Colored pins have been placed around the midbrain to identify the surface facing the adjacent perimesencephalic cisterns. Red pins face the interpeduncular cistern, yellow pins face the crural cistern, green pins face the ambient cistern, and gray pins face the quadrigeminal cistern. D–F, Stepwise dissection of another medial temporal lobe demonstrating the relationships of the anterior, middle, and posterior portions of the medial temporal region. D, Structures below the roof of the right temporal horn have been removed to expose the course of posterior cerebral artery through the cisterns on the medial side of the temporal horn. E, Right posterior cerebral artery has been removed to expose the anterior choroidal artery. The inferior choroidal point marks the lower end of the choroidal fissure. The anterior choroidal artery enters and the inferior ventricular vein exits the temporal horn at the inferior choroidal point. The inferior choroid point is located at the posterior edge of the posterior segment of the uncus, and the crural cistern is located at the junction of the anterior and middle parts of the medial temporal region. F, Right anterior choroidal artery has been removed to expose the most superior portion of the crural and ambient cisterns and the basal vein. Both the inferior ventricular and inferior choroidal veins empty into the basal vein at the inferior choroidal point. The left posterior cerebral artery has been removed to expose the anterior choroidal artery. (Images courtesy of AL Rhoton, Jr.)

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