Exploring Deep Space - Uncovering the Anatomy of Periventricular Structures to Reveal the Lateral Ventricles of the Human Brain

Summary

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.

Abstract

Anatomy students are typically provided with two-dimensional (2D) sections and images when studying cerebral ventricular anatomy and students find this challenging. Because the ventricles are negative spaces located deep within the brain, the only way to understand their anatomy is by appreciating their boundaries formed by related structures. Looking at a 2D representation of these spaces, in any of the cardinal planes, will not enable visualisation of all of the structures that form the boundaries of the ventricles. Thus, using 2D sections alone requires students to compute their own mental image of the 3D ventricular spaces. The aim of this study was to develop a reproducible method for dissecting the human brain to create an educational resource to enhance student understanding of the intricate relationships between the ventricles and periventricular structures. To achieve this, we created a video resource that features a step-by-step guide using a fiber dissection method to reveal the lateral and third ventricles together with the closely related limbic system and basal ganglia structures. One of the advantages of this method is that it enables delineation of the white matter tracts that are difficult to distinguish using other dissection techniques. This video is accompanied by a written protocol that provides a systematic description of the process to aid in the reproduction of the brain dissection. This package offers a valuable anatomy teaching resource for educators and students alike. By following these instructions educators can create teaching resources and students can be guided to produce their own brain dissection as a hands-on practical activity. We recommend that this video guide be incorporated into neuroanatomy teaching to enhance student understanding of the morphology and clinical relevance of the ventricles.

Introduction

Many students struggle to comprehend the negative spaces of the ventricular system, located deep within the human brain^1,2. Commonly used resources available for students to study the ventricles provide relatively crude representations of the intricate 3D relationships of these deep cerebral structures. Understanding the 3D anatomy of the ventricular system and related structures is particularly important in neurosurgery because access to the ventricular system is one of the most utilised techniques to measure intracranial pressure, decompress the ventricular system, and administer medications³. In addition, rapid advancements in medical imaging have necessitated the development of skills in the interpretation of 3D anatomy.

Two-dimensional (2D) sections of the brain in different planes are typically used to visualise the deep brain structures that form the boundaries of the negative ventricular spaces⁴. However, 2D slices of the brain alone are insufficient to enable students to understand the full extent of the 3D architecture of the ventricles and the fine details of the region such as fiber bundles connecting the cortex and subcortical structures⁵. Consequently, educators have to rely on the students' own ability to compute a comprehensible 3D conception of the ventricles⁴. Students who struggle with spatial awareness find it extremely difficult to create this 3D image. Whilst plastic models and ventricular casts provide a 3D representation of the ventricular system, they fail to demonstrate the comprehensive relationships that form the boundaries of the ventricles. Students often mindlessly remove parts of the plastic model to access the ventricular system and understand its interconnections. In this process, they frequently overlook the detailed relative positions of each structure and lose understanding of their relationships (e.g. formation of the roof of the lateral ventricles by the corpus callosum).

The development of new computerised teaching tools has addressed some of these limitations. However, many of these models are limited to static text and images and do not take advantage of the interactivity offered by these new technologies^7,8. Whilst interactive technologies enable the user to rotate 3D computer models to study multiple viewpoints, this can confuse some users especially novices who find it challenging to orientate structures⁶. Furthermore, interactive computer resources have been shown to be less effective in teaching more complex anatomical structures⁶. Thus, one of the challenges in neuroanatomy education is to provide students with resources that enable them to adequately visualize the ventricles and appreciate their 3D structure and anatomical relationships including the delicate associative, projection, and commissural fiber bundles that form complex relationships with the periventricular structures².

Dissection has been shown to be an excellent educational method for learning anatomy^7,8. A recent study provides evidence of the benefits of student dissection in learning neuroanatomy. In 2016, Rae et al. found improved short-term and long-term retention of neuroanatomy knowledge in students participating in dissections⁹. Whilst advances in technology continue to improve the accuracy and interactivity of 3D computer models, the knowledge acquired through hands-on dissection cannot be replicated digitally at the present time¹⁰.

In this study, we aimed to produce a reproducible dissection of a human brain. We chose a fiber dissection method because that allows preservation of the delicate fiber bundles and periventricular gray matter structures to better define the negative space of the ventricles.

Here we present a comprehensive step-by-step guide for creating a prosection model of the ventricles and periventricular structures together with an accompanying training video for use in neuroanatomy teaching and learning. These resources can be used for teaching and learning the neuroanatomy of the brain by both educators and students.

Protocol

All methods described here have been approved by the Human Research Ethics Committee of the Australian National University. To create the ventricular model we used the Klingler fiber dissection technique^12,14. The Klingler technique is a tactile dissection method that involves removing small portions of the gray matter of the cortex and peeling off bundles of nerve fibers, thus providing a step-by-step guide through the tissue layers from the surface to the deep structures of the brain.

NOTE: The brain specimen used to demonstrate this protocol in the accompanying video and images was carefully removed from a formalin-embalmed human cadaver obtained from the body donor program of the Medical School, Australian National University. The donor had no known history of neuropathological disease. After removal of the dura mater, the brain was stored in 10% ethanol solution at room temperature for three years.

1. Preparation

1. Obtain a whole brain from an embalmed human cadaver and remove the dura mater and store the brain in 10% ethanol at room temperature prior to dissection.
   Caution: Use personal protection equipment in a well-ventilated room in accordance to local guidelines when handling. Ensure all participants are familiar with the institutional procedures for the safe handling and disposal of a scalpel and sharp objects before commencing the dissection protocol.
2. Prepare the following instruments: scissors, forceps, scalpel blades (No. 15 and No. 22), metal probe, and the blunt end of a metal scalpel handle (Figure 1). Use the blunt end of the scalpel handle to minimise damage to the delicate nerve fibers and conserve the major white matter fiber tracts (Figure 2)¹³.
3. Position the brain so that its ventral surface is facing upwards.

2. Dissection Procedure

NOTE: The dissection takes approximately 2 to 3 h to complete

1. Remove the arachnoid mater and associated vasculature from both cerebral hemispheres using a pair of atraumatic (blunt) forceps.
2. Gently lift the cerebellum and locate the inferior colliculi. Place the scalpel blade (No. 15) attached to a long scalpel handle just caudal to the inferior colliculi and cut axially through the brainstem. Keep the blade as close to horizontal as possible to avoid damaging the cerebellum. Take care to preserve the tectum of the midbrain.
3. Position the brain to view the left or right lateral fissure. Starting at the supramarginal gyrus, use the blunt end of the scalpel handle to gently remove the superficial cortical layers. Gently move forward first above, then below the lateral sulcus to reveal the horizontal association fiber bundles running in the parietal, frontal, and temporal lobes, respectively.
4. Follow the direction of the fibers arching around the posterior border of the insula connecting the superior and inferior longitudinal fasciculi to reveal the arcuate fasciculus.
5. Anteriorly, gently remove the remaining superficial cortical layers of the middle temporal and inferior frontal gyri to reveal the uncinate fascicular fibers that connect the temporal and frontal lobes
6. Identify the short gyri of the insular cortex and then remove the insula. Next remove the extreme capsule and claustrum to reveal the underlying external capsule. Note the bulge formed by the lentiform nucleus deep to the capsule. Moving towards the dorsal surface of the cortex, reveal the fibers of the corona radiata (Figure 4).
7. Remove the remaining cortex and underlying white matter on the dorsal surface of the brain to reach the cingulate gyrus. Continue to use the blunt-end of the scalpel handle to remove the cingulate cortex to reveal the cingulum, the white matter tracts connecting the anterior perforated substance with the parahippocampal gyrus.
8. Use the same technique to remove the cingulum from posterior to anterior to reveal the corpus callosum, composed of commissural fibers connecting the two cerebral hemispheres. The dorsum of the body (trunk) of the corpus callosum will now be visible (Figure 6).
9. Repeat steps 2.3 to 2.8 on the contralateral cerebral hemisphere.
10. Palpate and identify the extent of the lateral ventricle on one of the hemispheres. Using a probe, puncture the lateral wall of the ventricle at the site of the collateral trigone. Using a size 24 blade (attached to a No. 4 scalpel handle) enter through the puncture-site and cut inferiorly to open up the entire length of the inferior horn of the lateral ventricle.
11. Now return to the ventricular collateral trigone to extend the cut superiorly towards the splenium of the corpus callosum (dotted line in Figure 5).
12. Repeat steps 2.10 and 2.11 on the other hemisphere.
13. Open the body of the lateral ventricle by continuing the incision from the trigone rostrally using a cut approximately 3 cm parallel to the corpus callosum in both hemispheres (dotted lines in Figure 6).
14. Join the two parallel incisions in each hemisphere rostrally at the level of the genu and caudally at the level of the splenium of the corpus callosum. Using forceps, held in the non-dominant hand, gently lift the corpus callosum at the splenium. With a small sharp pair of scissors, held in the dominant hand, separate the splenium from the underlying septum pellucidum. Once you have reached the rostral end of the body, cut the corpus callosum and remove it.
15. Nestle the ventral surface of the brain lengthwise on the palm of your non-dominant hand to stabilize the occipital and temporal areas (posterior part). At the same time, use your dominant hand to firmly but gently hold the anterior end of the brain by placing your opposed fingers and thumb on the lentiform nuclei of both sides of the brain.
16. Using gentle pulling and twisting motions, physically separate the anterior and posterior parts of the brain taking special care to keep the choroid plexus intact. It is recommended that a colleague be present to guide the separation and gently section any remaining connecting tissues during the process using a scalpel.

Results

This method of dissection exposes the ventricular system by separating the brain into an anterior and a posterior part (Figure 7 and Figure 8). The posterior part offers an internal view to the collateral trigone from which the posterior and inferior horns can be seen extending to the occipital and temporal lobes, respectively (Figure 8). In the inferior/temporal horn the hippocampus...

Discussion

The purpose of this paper was to devise a dissection guide for dissemination to teachers and students that could be used to enhance teaching and learning of the deep ventricular and periventricular structures of the human brain. We have devised a step-by-step guide with accompanying images, together with a video resource, that can be used to aid understanding of the morphology of the ventricles and their associated structures. The dissection technique itself is not new. Fiber dissection has been previously used for the s...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Scalpel Blade No 15	Swann-Morton	0205	Scalpel blade
Scalpel Blade No 11	Swann-Morton	0203	Scalpel blade
Scalpel Blade No 24	Swann-Morton	0211	Scalpel blade
Long Scalpel handle No3L	Swann-Morton	0913	Scalpel handle
Short Scalpel handle No4G	Swann-Morton	0934	Scalpel handle
Scissors			Scissors
Atraumatic Forceps			Atraumatic forceps
Toothed Forceps			Toothed forceps
Genelyn Arterial Enhanced	GMS Inovations	AE-475	Arterial embalming media