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Fixed Brain Dissection

Surgical Correlation

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Fixed Brain Dissection. A, The aspect of the specimen dissected should be as shown in the picture, with the roof of the temporal horn opened by the cuts toward the inferior circular sulcus of the insula. The Ammon’s horn, the collateral eminence, the choroid fissure, choroids plexus and the ventricular and atrial walls are exposed, by the dissection. With a number 10 blade, the posterior extension of the temporal horn and atrium should be opened. B, The option B described in the text is shown in this picture. A sagittal cut was made in the insular lobe. The relations of the ventricular structures with the insular lobe are clear in this dissection. The cuts should be made progressively from lateral to medial, with the long knife, and every cut should be studied before the more medial next one is done. That’s because the relations between the structures in the central core are changed in different sagittal planes. The amygdala, located at the anterior wall of the temporal horn, is evident in this picture, and its relations with the globus pallidum, internal capsule and ventricular structures should be done. In these cuts, the different portions of the internal capsule are also evident. C, Basal surface of the brain. The uncal notch at the uncal apex is used as an initial landmark for the incision in the basal surface of the temporal lobe. This curved incision, shown by the red dotted line in the picture, doesn’t have to be made in only one movement. Instead, progressively medial to lateral curve cuts should be made toward the collateral sulcus. The objective is to remove the inferior or basal part of the uncus. There is an arachnoid plane and vessels coming from the crural and ambient cistern in the uncal notch which helps the identification of the correct plane of dissection. Posteriorly, the incision removes the subiculum, making more evident the choroid fissure from below. If the correct plane of the dissection was carried on, the dentate gyrus and fimbriae should be exposed without damage in the posterior part of the temporal lobe. D, The uncal notch of the right temporal lobe is shown in an inferior and medial angle. The uncal notch at the uncal apex, just anterior to the dissector in the picture, is the point where the incision should begin, and is the correct depth of the incision as well. E and F, After the removal of the inferior part of the uncus and the subiculum, the dentate gyrus and the fimbria just medial to it should be exposed. The identification of the dentate gyrus is made by the unique aspect of this structure, with transversal stripes, and the arachnoid membrane and vessels between it and the uncus and subiculum, evident in the picture. The fimbria is found in the dissection as a white structure medial and superior to the dentate gyrus from above. The fasciolar gyrus is shown in E. The lateral geniculate body and the choroid fissure turns clearly exposed after the removing of the subiculum, showing the relations of the temporal horn and the mesial temporal lobe with the thalamus. The optic tract, as the roof of the crural cistern, is evident. The uncinate gyrus, band of Giacomini and intralimbic gyrus are evident in this specimen, after the dissection described. (Images courtesy of E de Oliveira)

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