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Magnified Views of the Medial Temporal Region

Surgical Correlation

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Magnified Views of the Medial Temporal Region. a, Enlarged view of the anterior and middle segments of the medial temporal region (MTR). The anterior segment is formed by the uncus and the entorhinal area. The uncus is divided into anterior and posterior segments meeting at the medially directed apex. The entorhinal area shown with green stars occupies the inferior surfaces of the anterior and posterior segments of the uncus but does not have a clearly demarcated borders. The parahippocampal gyrus forming the cortical component of the middle segment of the MTR has 3 surfaces: inferior, medial, and superior. The superior surface faces the lower surface of the pulvinar across the upper part of the ambient cistern and has superiorly the dentate gyrus and the fimbria of the fornix. b, Enlarged view of the anterior segment of the MTR. The anterior segment of the uncus contains the semilunar gyrus and the ambient gyrus. The semilunar gyrus covers the cortical nucleus of the amygdala. The ambient gyrus located anterior and inferior to the semilunar gyrus is separated by the semiannular sulcus from it. The posterior segment of the uncus is divided into an upper and lower part by the uncal sulcus. The upper part is formed by the medially folded extraventricular (cisternal) head of the hippocampus, and the lower part is formed by the anterior part of the parahippocampal gyrus. The intralimbic gyrus forms the posterior end of the uncus and is the site of attachment of the fimbria. c–f, Stepwise dissection of the basal surface of the temporal lobe. c, The anterior segment of the uncus faces the carotid cistern, and posterior segment faces the crural cistern and the cerebral peduncle. The uncal apex is positioned lateral to the oculomotor nerve. The cortical component of the middle MTR formed by the parahippocampal gyrus faces the midbrain across the ambient cistern. d, The part of the posterior uncal segment located below the uncal notch has been removed to expose the lower surface of the upper part of the posterior uncal segment formed by the extraventricular head of the hippocampus. The fimbria is situated above the dentate gyrus. The choroidal fissure, located between the thalamus and fimbria, extends along the lateral edge of the lateral geniculate body and pulvinar. e, The hippocampus and dentate gyrus have been removed while preserving the fimbria and the choroid plexus attached along the choroidal fissure. The amygdala forms the anterior wall of the temporal horn and fills most of the anterior segment of the uncus. The inferior choroidal point, located at the lower end of the attachment of the choroid plexus in the temporal horn, is positioned behind the head of the hippocampus, anterior to the lateral geniculate body, and lateral to the posterior edge of the cerebral peduncle. f, The fimbria and choroid plexus have been removed to expose the roof of the temporal horn. The tapetum fibers forming the roof of the temporal horn have been removed to expose the optic radiations arising from the lateral geniculate body and passing across the roof and around the lateral wall of the temporal horn. (Images courtesy of AL Rhoton, Jr.)

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