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Exploring Deep Space - Uncovering the Anatomy of Periventricular Structures to Reveal the Lateral Ventricles of the Human Brain
Chapters
Summary October 22nd, 2017
This paper demonstrates the effective use of a fiber dissection method to reveal the superficial white matter tracts and periventricular structures of the human brain, in three-dimensional space, to aid student comprehension of ventricular morphology.
Transcript
The first step of this brain dissection is to first identify if there is any arachnoid mater left in the specimen. If there is, we will need to remove it using a pair of forceps. In this case, we will move on to our next step.
We then need to remove the cerebellum. Firstly, we need to look at the ventroposterior view of the brain, looking for the inferior colliculi. Using a size 22 blade, we will make a straight incision at the level below the inferior colliculi.
An assistant will help by gently pulling the cerebellum to facilitate the process. We are now ready to start our brain dissection. In order to do this, we will employ the Klingler dissection technique.
First, we will need to identify some structures on the lateral view of the left side of the brain. We can see the frontal lobe, the parietal and temporal lobes, as well as the lateral fissure. The Klingler dissection technique requires the use of the blunt end of the scalpel to remove or scape off the gray matter fibers to reveal the association fibers underneath.
The first step of our blunt dissection is to remove a portion of the parietal lobe, using the blunt end of the scalpel to scrape off some gray matter fibers. As we can see here, when we remove the cortex using the blunt end of the scalpel, we can follow the tracts of the superficial association of fibers underneath. These fibers travel in a rostrocaudal direction.
Now we will have a look at what we have revealed so far. We can see the superficial association fibers here, going in the rostrocaudal direction, and by gently lifting some of the superficial white matter, we can highlight the direction of the superficial longitudinal fasciculus tracts a lot better. The next step is to reveal the superior and inferior longitudinal fasciculus.
We will continue with our blunt dissection, removing the remaining parts of the parietal lobe, as well as the superficial gray matter of the temporal lobe. As we can see in this step, we are gently removing the superficial gyri of the temporal lobe to reveal the inferior longitudinal fasciculus underneath. In this part of the dissection, we have a band of fibers which connect the superior longitudinal and inferior longitudinal fasciculi together.
This is called the arcuate fasciculus, and it is found arching posteriorly to the insula. This is what we have revealed so far in this part of the dissection. We have the frontal lobe, the parietal lobe, and the temporal lobe, and we can see the insular cortex right in the middle.
What we can see here are the rostrocaudal fibers of the superior longitudinal fasciculus as well as the inferior longitudinal fasciculus in the temporal lobe. And here, we have removed the arcuate fasciculus, which connects those two fasciculi together. Damage on any of these pathways can result in aphasia.
For our next step, we will continue with a blunt dissection, but this time, in a dorsoventral direction to reveal fibers of a different orientation. These dorsoventral fibers represent the corona radiata. The corona radiata contains projection fibers traveling between the cerebral cortex and the subcortical structures in the spinal cord.
What we are now showing here is the removal of fibers around the orbitofrontal region to show the uncinate fasciculus, which connects the limbic system to the orbitofrontal gyrus. Now, we have highlighted the corona radiata, as well as showing the insular cortex in the middle. The next step is to use the blunt end of the scalpel to remove the insular cortex and the underlying, to reveal the external capsule underneath.
We have now exposed the external capsule after removing the insular. We can appreciate the dorsoventral fibers as shown here. We can see the corona radiata, shown earlier, which continues to become the internal capsule underneath the striatum.
And this is revealed by that small window I've cut that we can see here. Now, we will repeat the same steps shown earlier on the other cerebral hemisphere. Once we have dissected both the sides of the cerebral hemispheres, we can now reveal the cingulate gyri by removing the superficial gyri of the parietal and frontal lobes.
We have now removed the dorsal aspect of the parietal and frontal lobes of the right hemisphere, and we can appreciate how much gray matter we will have to remove to reach the cingulate gyrus. We will then do the same step on the other side. Once we have exposed the cingulate gyrus, it is now time to bluntly dissect this area to reveal the underlying corpus callosum.
Once the cingulate cortex is removed, we can see the belt of association fibers called the cingulum, which connects the frontal and parietal with the temporal and parahippocampal cortices. We will now dissect away the cingulum to better reveal the corpus callosum, which forms the roof of the lateral ventricle. Now we can see the dorsal view of the corpus callosum, with the cingulate gyrus removed on either side.
The body of the corpus callosum, and we can see the splenium and the genu of the corpus callosum. Now we will open up the lateral ventricles. Before we make the cut, we first need to gently push against the collateral trigone where the three horns of the lateral ventricles meet.
Using a probe, gently push against this area until a loss of resistance is felt. Using a size 22 blade, use this hole as a guide to extend the cut. First, in a rostral direction, and then dorsally.
We will extend this cut across the corpus callosum to join the cut we have made on the other side. We can use a probe to check if we have successfully opened the lateral ventricle. We will again use the scalpel to extend the cut we made ventrally into the inferior horn of the lateral ventricle.
Once we have joined the two incisions in the midline, we will now extend the cut ventrally towards the genu of the corpus callosum. We will make two parallel incisions on the lateral sides of the corpus callosum. Now gently lift the corpus callosum from the midline cut, and using a scalpel, gently cut underneath the corpus callosum.
At this level, we are removing the corpus callosum from the septum pellucidum, a structure which forms part of the medial wall of the lateral ventricle. Our cut is perpendicular to the orientation of the callosal fibers. As we remove the corpus callosum, we can notice the commissural fibers being disrupted, highlighting their orientation.
Once we have removed the corpus callosum, we can have a glimpse of the structures that surround the lateral ventricle. We can identify the two thalami, which forms the majority of the floor of the body of the lateral ventricle. We have the choroidal vessels, which supply the choroid plexus that makes cerebrospinal fluid.
In this area, we can see the columns of the fornices, which will eventually split to project to the mammillary bodies. And here we can see the remnants of the septum pellucidum. We can also appreciate the chordate nucleus, which makes a part of the lateral wall of the lateral ventricle.
These structures will be highlighted even better once we have fully opened the lateral ventricles. In this view, we can see the trigone of the lateral ventricle, again containing choroid plexus, which makes CSF. And here, we can examine the corpus callosum that we have removed with the fibers of the fornix underneath.
Here, we can see the two crura of the fornix located in its inferior part. Once we have made the cuts, it is now time to pull the brain apart to reveal the internal structures related to the lateral ventricle. Now we are looking at the posterior view of the anterior half of the brain.
And we can highlight some very important anatomical structures. We can see the two thalami with the overlying choroid plexus, shown here in the left thalamus. We can see the superior and inferior colliculi of the midbrain.
The pineal gland. And the habenula, which are associated with the pineal gland. If we gently pull the two halves apart, we are looking at the third ventricle, the walls of which are made of the two thalami.
We can see the interthalamic adhesion join the two thalami together, as highlighted here with the probe. And if we put the probe through a foramen in its anterior part, we go through the interventricular foramen, which connects the lateral and third ventricles together. And we can see the columns of the fornix, as we have identified earlier.
Now we are looking at the anterior view of the posterior half of our dissected brain. As we can see, if we put a probe through this area, we can find the posterior horn of the lateral ventricle projecting to the occipital lobe. Also, we can identify these listening structures here, which make up the hippocampi.
This forms part of the floor of the lateral ventricle in the temporal lobe. If we follow this region in the hippocampus called the fimbria, we can see the fimbria as it forms the crus of the fornix. The crura will join to form the body of the fornix, lying underneath the corpus callosum.
These two structures form the roof of the lateral ventricle, and are important parts of the limbic system. Here we can see the choroidal vessels, which we have shown earlier. And if we examine the curvatures of the hippocampi, we can see that these curvatures fit nicely with the curvatures of the thalami.
And we can show this by putting the two halves back together.
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