BACKGROUND: Surgeons must understand the complex anatomy of the cerebellum and brainstem and their 3-dimensional (3D) relationships with each other for surgery to be successful. To the best of our knowledge, there have been no fiber dissection studies combined with 3D models, augmented reality (AR), and virtual reality (VR) of the structure of the cerebellum and brainstem. In this study, we created freely accessible AR and VR simulations and 3D models of the cerebellum and brainstem.

OBJECTIVE: To create 3D models and AR and VR simulations of cadaveric dissections of the human cerebellum and brainstem and to examine the 3D relationships of these structures.

METHODS: Ten cadaveric cerebellum and brainstem specimens were prepared in accordance with Klingler’s method. The cerebellum and brainstem were dissected under the operating microscope, and two-dimensional (2D) and 3D images were captured at every stage. With a photogrammetry tool (Qlone, EyeCue Vision Technologies, Ltd.), AR and VR simulations and 3D models were created by combining several 2D pictures.

RESULTS: For the first time reported in the literature, high-resolution, easily accessible, free 3D models and AR and VR simulations of cerebellum and brainstem dissections were created.

CONCLUSIONS: Fiber dissection of the cerebellum-brainstem complex and 3D models with AR and VR simulations are a useful addition to the goal of training neurosurgeons worldwide.

The cerebellum and brainstem, and their relationship with each other, are some of the most complex parts of the human brain.^1-3 They are composed of both gray and white matter arranged in a 3-dimensional (3D) framework, and understanding the anatomy and relationships of structures in this critical area can be quite challenging.^4-7

Fortunately, 2 areas of development can help surmount this challenge. First, neurosurgeons can use the fiber microdissection technique to better understand the topographical organization of the cerebellum's essential contents, such as the deep cerebellar nuclei and cerebellar peduncles, and their relationship with the brainstem.^8-11 In addition, fiber dissection is useful for obtaining a strong knowledge of neuroanatomic structures in preparation for surgery. This technique, which includes removing white matter tracts to expose the brain's anatomic organization, was the first to provide surgeons with a true understanding of the brain's 3D features.¹² Second, photogrammetry is a method to capture, measure, and interpret photographs to obtain accurate information about physical objects and their surroundings.¹³ Recently, the use of photogrammetry, 3D modeling, and augmented reality (AR) and virtual reality (VR) technologies in anatomy studies has increased.^14-18

Previous research has enhanced our knowledge of cerebellar and brainstem architecture, as well as the value of Klingler’s method in modern neurosurgery.^6,11,19-23 However, the images obtained from these studies are 2-dimensional (2D) and 3D. For cerebellum and brainstem dissection, there is currently no 3D model or AR and VR simulations described in the literature. In this article, we demonstrate the delicate anatomy of the cerebellum and brainstem through fiber dissection and describe 3D models and AR and VR simulations of these structures.

According to the policy of the institution where this research was conducted, ethics committee approval is not mandatory for this type of study.

Ten adult human cadaver specimens (10% formalin-fixed) of the cerebellum and brainstem were studied at microsurgery-neuroanatomy laboratory. The specimens were frozen for at least 2 weeks at −15°C and thawed under water for 1 hour.

Under the operating microscope (Carl Zeiss Opmi 1 SH Surgical Microscope Contraves), at x6, x10, and x25 magnification and with the help of a microsurgical set (Rhoton dissector, wooden spatula, dissector, forceps), the specimens were dissected in stepwise fashion, and 2D and 3D images were captured at every stage. The anaglyph images were created using Adobe Photoshop CC and were viewed with red and blue glasses (Adobe). Each 3D image was placed next to or above a labeled 2D image.

As mentioned in a previous article from this laboratory,²⁴ each stage of dissection was captured with photogrammetry to create 3D models and AR and VR simulations. In brief, the application is used to find common points between images taken from various angles and then to overlay the images by matching the common points. Finally, the original images are overlaid on this mesh to give the final 3D model color and texture.

These models and simulations are freely available on The Neurosurgical Atlas website. Apple devices can open these files without the need for extra software. Any 3D, AR-viewing program (Qlone, Sketchfab, Emb3D, 3D Viewer, etc.) on an Android or Microsoft device can be used to view these models.

Anatomic dissection began with a detailed inspection of the cerebellum and brainstem surfaces. The fiber tract anatomy of the cerebellar peduncles, which wrap around and pass through the brainstem, the long brainstem tracts, and the intra-axial segment of the cranial nerves were reviewed.

The brainstem is composed of the mesencephalon, pons, and medulla oblongata. The oculomotor nerve fibers exit the midbrain and enter the interpeduncular cistern through the most medial region of the cerebral peduncle (Figure 1A and 1B, Video 1). The pons is located between the pontomesencephalic and pontomedullary sulci. It houses the trigeminal, abducens, facial, and vestibulocochlear nerves (Figure 1A and 1B, Video 1). At the middle of the pons, superior to the middle cerebellar peduncle, the trigeminal nerve enters the brainstem. Perpendicular to the transverse pontine fibers that reach the cerebellum through the middle cerebellar peduncle, trigeminal nerve fibers can be seen entering the upper margin of the anterior region of the pons (Figure 1A and 1B, Video 1). At the cerebellopontine angle, the facial nerve enters the brainstem from its ventrolateral side. On the lateral end of the pontomedullary sulcus, the vestibulocochlear nerve enters the brainstem (Figure 1A and 1B, Video 1).

Dissection continued with removal of the cranial nerves and visualization of the transverse pontine fibers, middle cerebellar peduncle, inferior cerebellar peduncle, and flocculus (Figure 1C and 1D, Video 1). The transverse pontine fibers were partially removed, and the corticospinal tract was exposed (Figure 1E and 1F, Video 1). The transverse pontine fibers were then completely removed, and the corticospinal tract was revealed (Figure 1G and 1H, Video 1).

Dissection continued with removal of the cranial nerves and visualization of the transverse pontine fibers, middle cerebellar peduncle, inferior cerebellar peduncle, and flocculus (Figure 1C and 1D, Video 1). The transverse pontine fibers were partially removed, and the corticospinal tract was exposed (Figure 1E and 1F, Video 1). The transverse pontine fibers were then completely removed, and the corticospinal tract was revealed (Figure 1G and 1H, Video 1).

The superior surface of the cerebellum was visualized (Figure 2A and 2B, Video 1), and its dissection began at the junction of the anterior quadrangular lobule and the middle cerebellar peduncle. The cortex of the anterior and posterior quadrangular lobules was separated from the underlying white matter in a lateral-to-medial manner, ending just short of the midline on both sides to preserve the vermis (Figure 2C-2F, Video 1).

The 3 cerebellar peduncles could be seen clearly on closer dissection, and the middle cerebellar peduncle was easily recognized (Figure 2E and 2F, Video 1). The superior cerebellar peduncle is formed by the lateral wall of the superior half of the fourth ventricle and arises from the dentate nucleus. The culmen and central lobule of the cerebellum cover the superior cerebellar peduncle in the midline, and the quadrangular lobule and wing of the central lobule cover it laterally. The culmen was partially removed (Figure 2G and 2H, Video 1).

The superior cerebellar peduncle, the cerebellum's principal efferent route, was dissected and removed to reveal the origin of the superior cerebellar peduncle from the dentate nucleus hilus. Based on their course, the inferior and middle cerebellar peduncles were identified (Figure 2G and 2H, Video 1), and the superior cerebellar peduncle was seen ascending into the midbrain, anterior to the inferior cerebellar peduncles. The inferior cerebellar peduncle runs dorsomedial around the dentate nucleus' upper two-thirds and hilus. This structure's rostral border runs dorsally at the level of the superior cerebellar peduncle's junction with the dentate nucleus and from lateral to medial in the area deep to the quadrangular lobule on the tentorial surface of the cerebellum. Deep transverse pontine fibers that run directly lateral to the inferior cerebellar peduncle cover it. The inferior cerebellar peduncles proceed upward and laterally, constituting part of the fourth ventricle's lateral walls, before directly bending backward and entering the cerebellum between the superior and middle peduncles.

Middle cerebellar peduncles are made entirely of fibers that originate in the pontine nuclei on the opposite side and end in the cerebellar cortex. These are the largest peduncles in the cerebellum. The main afferent pathway of the cerebellum is the middle cerebellar peduncle, the fibers of which migrate obliquely lateral and caudally from their origin in the pontine nuclei to create the floor of the cerebellopontine angle before entering the cerebellum. The anterior quadrangular lobule and posterior quadrangular lobule were removed (Figure 2I and 2J).

The middle cerebellar peduncle is where the transverse pontine fibers coming from the dispersed nuclei in the ventral pons reach the cerebellar cortex. At the point where the trigeminal nerve exits the pons, the transverse pontine fibers join to form the middle cerebellar peduncle. The superior cerebellar peduncles of each cerebellar hemisphere emerge from the medial section and ascend upwards to the tectum. The superior medullary velum is the connection between the 2 peduncles. As a result, they serve as both a lateral wall and a roof for the fourth ventricle. The superior cerebellar peduncle fibers are mostly produced from the cells of the cerebellum's dentate nucleus and exit from the hilus of the nucleus (Figure 2K and 2L, Video 1). The gray matter of the dentate nucleus was dissected from the tubercle and followed posteriorly and medially on both sides to the lateral margin of the pyramidal section of the vermis (Figure 2M-2P, Video 1).

The dentate nucleus bulge was now apparent behind the inferior cerebellar peduncle. The underlying white matter was examined before the dentate nucleus was dissected. This white matter was gradually separated from the underlying nucleus under high magnification. The longitudinal grooves on its surface were dissected and cleaned of all covering white matter, revealing practically the whole superior surface of the dentate nucleus. The fibers of the 2 peduncles cross ventral to the cerebral aqueduct as they continue upward beneath the corpora quadrigemina. The pons on the upper two-thirds and the medulla on the inferior one-third create the floor of the fourth ventricle, commonly known as the rhomboid fossa (Figure 3A, and 3B, Video 1).

The superior cerebellar peduncles provide a lateral boundary for the superior portion. Laterally, the inferior cerebellar peduncles constitute the inferior portion, and the superior and inferior sections form a triangle. The dorsal median sulcus and the sulcus limitans split the floor of the fourth ventricle longitudinally and laterally (Figure 3C and 3D, Video 1). The superior cerebellar peduncles and superior medullary velum can then be identified. The superior and inferior colliculi, also known as the quadrigeminal tubercles, are 4 round eminences of the midbrain fossa (Figure 2K and 2L, Video 1). Superior to the superior medullary velum, the quadrigeminal tubercles are prominences on either side of the midline. The cruciform sulcus separates the superior and inferior colliculi, and the subpineal triangle, which houses the pineal gland, is located between the upper ones.

The inferior aspect of the cerebellum was examined, and the biventral lobule, pyramid, tonsils, gracilis, superior semilunar lobule, and inferior semilunar lobule were visualized (Figure 4A and 4B, Video 1). The initial step was to dissect and remove the cortical surface of the tonsils, the biventral lobule, and the gracile lobule (partially) from the underlying white matter after evaluating the surface architecture (Figure 4C and 4D, Video 1). The dentate nucleus is covered by the base of the tonsil in an area just lateral to the dentate tubercle, and the medial end of the dentate nucleus is only a few millimeters below the pyramid's lateral margins. Next, the pyramid and uvula were removed, and the fourth ventricle was visualized from the inferior surface. The nucleus interpositus (emboliform and globose nuclei) was revealed when the white matter was separated from the underlying gray matter just lateral to the nodule (Figure 4E and 4F, Video 1).

The cerebellum-brainstem complex has a complicated structure, and understanding the 3D relationships of the structures in this region is imperative for successful surgery. Traditional anatomy educational materials include 2D anatomic atlases, lectures, and cadaveric dissection courses. However, it is difficult to understand the 3D structures of the cerebellum-brainstem complex from viewing 2D photos.    

Fiber dissection is one method that delineates the complex structures of the cerebrum, cerebellum, and brainstem.^8,25,26 This method was developed by Klingler and his colleagues.¹⁰ The procedure, which involves removing white matter tracts to reveal the brain's anatomic organization, was the first to provide surgeons a full view of the 3D features of the cerebrum, cerebellum, and brainstem.⁸ Studies done with this method have improved our knowledge of neuroanatomy.^11,25,27-29 However, these studies, which were limited to 2D and anaglyph photographs, were incomplete regarding understanding 3D structures.

Digital models of brain structure offer many advantages. They are more accessible than physical models because they can be used on mobile devices.^30,31 Because cadavers are available in only some places, neurosurgeons can access digital learning tools at any location worldwide.^30,31 This model can also be stored digitally, avoiding the difficulties of decay and discoloration that occur in cadaveric specimens over time. The ability to visualize the topography of the brain surface at various magnifications and angles provides a more accurate and interactive microsurgical simulation environment. Furthermore, dissections can be moved in any direction and turned 360 degrees around themselves in these models and simulations, allowing the relationship and depth of the structures to be examined in great detail. The 3D models and AR and VR simulations were perfect replicas of the genuine specimens. Although previous research has improved our understanding of cerebellum, brainstem, and fiber tract anatomy, they are scattered throughout the neurosurgical literature and do not provide a detailed, step-by-step 3D model or AR and VR simulations. These models and simulations are freely available on The Neurosurgical Atlas website for use in preoperative planning at facilities with limited cadaver access and in fundamental neuroanatomy and neurosurgery training.³²

This study describes a comprehensive 3D model and AR and VR simulation of cerebellum and brainstem dissection. As a result, we believe that systematic studies of the fiber dissection technique using 3D models and AR and VR simulations have the potential to uncover a new bank of knowledge that will aid our understanding of microneurosurgery, the development of techniques, and anatomic and radiological knowledge of the fiber tracts.

Although this method has many advantages, it also has disadvantages. Smooth or shiny surfaces can lower the resolution of 3D models, and the technique is quite susceptible to lighting and background issues. This method only offers surface scanning of the specimens.

The cerebellum and brainstem are complex structures. For surgery in these areas to be successful, a better understanding of the 3D anatomic architecture of the fiber pathways is necessary. These models can help us better understand the complicated anatomy of the cerebellum and brainstem. This research is available as a free, high-fidelity digital library of 3D cadaver models available to anyone around the world who is interested in cerebellum and brainstem anatomy.

Contributors: M. E. Gurses, A. Gungor, S. Rahmanov, E. Gökalp, S. Hanalioglu, M. Berker, A. A. Cohen-Gadol, and U. Türe

Content from Gurses ME, Gungor A, Rahmanov S, Gökalp E, Hanalioglu S, Berker M, Cohen-Gadol AA, Türe U. Three-dimensional modeling, and augmented reality, virtual reality simulation of fiber dissection of the cerebellum and brainstem. Oper Neurosurg (Hagerstown) 2022;23(5):345-354. doi.org/10.1227/ons.0000000000000358. With permission of Oxford University Press on behalf of the Congress of Neurological Surgeons. © Congress of Neurological Surgeons.