Operative Anatomy of the Human Skull: A Virtual Reality Expedition

Photorealistic 3-Dimensional Models of the Anatomy and Neurosurgical Approaches to the V2, V3, and V4 Segments of the Vertebral Artery

BACKGROUND

The vertebral artery (VA) has a tortuous course subdivided into 4 segments (V1-V4). For neurosurgeons, a thorough knowledge of the 3-dimensional (3D) anatomy at different segments is a prerequisite for safe surgery. New technologies allowing creation of photorealistic 3D models may enhance the anatomic understanding of this complex region.

OBJECTIVE

To create photorealistic 3D models illustrating the anatomy and surgical steps needed for safe neurosurgical exposure of the VA.

METHODS

We dissected 2 latex injected cadaver heads. Anatomic layered dissections were performed on the first specimen. On the second specimen, the two classical approaches to the VA (far lateral and anterolateral) were realized. Every step of dissection was scanned using photogrammetry technology that allowed processing of 3D data from 2-dimensional photographs by a simplified algorithm mainly based on a dedicated mobile phone application and open-source 3D modeling software. For selected microscopic 3D anatomy, we used an operating microscope to generate 3D models.

RESULTS

Classic anatomic (n=17) and microsurgical (n=12) 3D photorealistic models based on cadaver dissections were created. The models allow observation of the spatial relations of each anatomic structure of interest and have an immersive view of the approaches to the V2-V4 segments of the VA. Once generated, these models may easily be shared on any digital device or web-based platforms for 3D visualization.

CONCLUSIONS

Photorealistic 3D scanning technology is a promising tool to present complex anatomy in a more comprehensive way. These 3D models can be used for education, training, and potentially preoperative planning.

Examining the utility of a photorealistic virtual ear in otologic education

BACKGROUND

Otolaryngology-head and neck surgical (OHNS) trainees' operating exposure is supplemented by a combination of didactic teaching, textbook reading, and cadaveric dissections. Conventional teaching, however, may not adequately equip trainees with an understanding of complex visuospatial relationships of the middle ear. Both face and content validation were assessed of a novel three-dimensional (3D) photorealistic virtual ear simulation tool underwent face and content validation as an educational tool for OHNS trainees.

METHODS

A three-dimensional mesh reconstruction of open access imaging was generated using geometric modeling, which underwent global illumination, subsurface scattering, and texturing to create photorealistic virtual reality (VR) ear models were created from open access imaging and comiled into a educational platform. This was compiled into an educational VR platform which was explored to validate the face and content validity questionnaires in a prospective manner. OHNS post-graduate trainees were recruited from University of Toronto and University of Calgary OHNS programs. Participation was on a voluntary basis.

RESULTS

Total of 23 OHNS post-graduate trainees from the two universities were included in this study. The mean comfort level of otologic anatomy was rated 4.8 (± 2.2) out of 10. Senior residents possessed more otologic surgical experience (P < 0.001) and higher average comfort when compared to junior residents [6.7 (± 0.7) vs. 3.6 (± 1.9); P = 0.001]. Face and content validities were achieved in all respective domains with no significant difference between the two groups. Overall, respondents believed OtoVIS was a useful tool to learn otologic anatomy with a median score of 10.0 (8.3-10.0) and strongly agreed that OtoVIS should be added to OHNS training with a score of 10.0 (9.3-10.0).

CONCLUSIONS

OtoVIS achieved both face and content validity as a photorealistic VR otologic simulator for teaching otologic anatomy in the postgraduate setting. As an immersive learning tool, it may supplement trainees' understanding and residents endorsed its use.

Operative Anatomy of the Skull Base: 3D Exploration with a Highly Detailed Interactive Atlas

Objective We evaluated the usefulness of a three-dimensional (3D) interactive atlas to illustrate and teach surgical skull base anatomy in a clinical setting.

Study Design A highly detailed atlas of the adult human skull base was created from multiple high-resolution magnetic resonance imaging (MRI) and computed tomography (CT) scans of a healthy Caucasian male. It includes the parcellated and labeled bony skull base, intra- and extracranial vasculature, cranial nerves, cerebrum, cerebellum, and brainstem. We are reporting retrospectively on our experiences with employing the atlas for the simulation and teaching of neurosurgical approaches and concepts in a clinical setting.

Setting The study was conducted at the University Hospital Mainz, Germany, and Hirslanden Hospital, Zürich, Switzerland.

Participants Medical students and neurosurgical residents participated in this study.

Results Handling the layered graphical user interface of the atlas requires some training; however, navigating the detailed 3D content from intraoperative perspectives led to quick comprehension of anatomical relationships that are otherwise difficult to perceive. Students and residents appreciated the collaborative learning effect when working with the atlas on large projected screens and markedly improved their anatomical knowledge after interacting with the software.

Conclusion The skull base atlas provides an effective way to study essential surgical anatomy and to teach operative strategies in this complex region. Interactive 3D computer graphical environments are highly suitable for conveying complex anatomy and to train and review surgical concepts. They remain underutilized in clinical practice.

The Extended Pterional Craniotomy: A Contemporary and Balanced Approach

Pterional craniotomy is the workhorse approach among cranial operative corridors. It is a highly flexible skull base approach that affords excellent exposure of the anterior cranial fossa, the circle of Willis, and the interpeduncular region. Its strategic use via dynamic retraction can obviate the need to use a more extensive skull base route, such as orbitozygomatic osteotomy, in select cases. The focus of the surgeon should be reaching the surgical target effectively while minimizing disruption of normal anatomy. In other words, the focus should be less on "how to get there" and more on "what to do when you are there." This multimedia presentation summarizes an efficient execution of this route and its expansion and demonstrates the surgical corridor via 3-dimensional virtual reality models.

Stereoscopy in Surgical Neuroanatomy: Past, Present, and Future

Since the dawn of antiquity, scientists, philosophers, and artists have pondered the nature of optical stereopsis-the perception of depth that arises from binocular vision. The early 19th century saw the advent of stereoscopes, devices that could replicate stereopsis by producing a 3D illusion from the super-imposition of 2D photographs. This phenomenon opened up a plethora of possibilities through its usefulness as an educational tool-particularly in medicine. Before long, photographers, anatomists, and physicians were collaborating to create some of the first stereoscopic atlases available for the teaching of medical students and residents. In fields like neurosurgery-where a comprehensive visuospatial understanding of neuro-anatomical correlates is crucial-research into stereoscopic modalities are of fundamental importance. Already, medical institutions all over the world are capitalizing on new and immersive technologies-such as 3D intraoperative recording, and 3D endoscopes-to refine their pedagogical efforts as well as improve their clinical capacities. The present paper surveys the history of stereoscopy from antiquity to the modern era-with a focus on its role in neurosurgery and medical education. Through the tracking of this evolution, we can discuss potential benefits, future directions, and highlight areas in which further research is needed. By anticipating these factors, we may strive to take full advantage of an emergent field of technology, for our ultimate goal of improving patient care.

The Neurosurgical Atlas: advancing neurosurgical education in the digital age

OBJECTIVE

The advent of the internet and the popularity of e-learning resources has promoted a shift in medical and surgical education today. The Neurosurgical Atlas has sought to capitalize on this shift by providing easily accessible video and online education to its users on an international scale. The rising popularity of social media has provided new avenues for expanding that global reach, and the Atlas has sought to do just that. In this study, the authors analyzed user demographics and web traffic patterns to quantify the international reach of the Atlas and examined the potential impact of social media platforms on the expansion of that reach.

METHODS

Twitter, Facebook, and Instagram metrics were extracted using each respective service's analytics tool from the date of their creation through October 2019. Google Analytics was used to extract website traffic data from September 2018 to September 2019 and app data from January 2019 to October 2019. The metrics extracted included the number of platform users/followers, user demographic information, percentage of new versus returning visitors, and a number of platform-specific values.

RESULTS

Since the authors' previous publication in 2017, annual website viewership has more than doubled to greater than 500,000 viewing sessions in the past year alone; international users accounted for more than 60% of the visits. The Atlas Twitter account, established in August 2012, has more than 12,000 followers, primarily hailing from the United States, the United Kingdom, Canada, and Saudi Arabia. The Atlas Facebook account, established in 2013, has just over 13,000 followers, primarily from India, Egypt, and Mexico. The Atlas Instagram account (established most recently, in December 2018) has more than 16,000 followers and the highest percentage (31%) of younger users (aged 18-24 years). The Atlas app was officially launched in May 2019, largely via promotion on the Atlas social media platforms, and has since recorded more than 60,000 viewing sessions, 80% of which were from users outside the United States.

CONCLUSIONS

The Neurosurgical Atlas has attempted to leverage the many e-learning resources at its disposal to assist in spreading neurosurgical best practice on an international scale in a novel and comprehensive way. By incorporating multiple social media platforms into its repertoire, the Atlas is able to ensure awareness of and access to these resources regardless of the user's location or platform of preference. In so doing, the Atlas represents a novel way of advancing access to neurosurgical educational resources in the digital age.

Cerebral Anatomy Detection and Surgical Planning in Patients with Anterior Skull Base Meningiomas Using a Virtual Reality Technique

Anterior skull base meningiomas represent a wide cohort of tumors with different locations, extensions, configurations, and anatomical relationships. Diagnosis of these tumors and review of their therapies are inseparably connected with cranial imaging. We analyzed the influence of three-dimensional-virtual reality (3D-VR) reconstructions versus conventional computed tomography (CT) and magnetic resonance imaging (MRI) images (two-dimensional (2D) and screen 3D) on the identification of anatomical structures and on the surgical planning in patients with anterior skull base meningiomas. Medical files were retrospectively analyzed regarding patient- and disease-related data. Preoperative 2D-CT and 2D-MRI scans were retrospectively reconstructed to 3D-VR images and visualized via VR software to detect the characteristics of tumors. A questionnaire of experienced neurosurgeons evaluated the influence of the VR visualization technique on identification of tumor morphology and relevant anatomy and on surgical strategy. Thirty patients were included and 600 answer sheets were evaluated. The 3D-VR modality significantly influenced the detection of tumor-related anatomical structures (p = 0.002), recommended head positioning (p = 0.005), and surgical approach (p = 0.03). Therefore, the reconstruction of conventional preoperative 2D scans into 3D images and the spatial and anatomical presentation in VR models enabled greater understanding of anatomy and pathology, and thus influenced operation planning and strategy.

Virtual Exploration of Safe Entry Zones in the Brainstem: Comprehensive Definition and Analysis of the Operative Approach

BACKGROUND

A detailed and accurate understanding of the intrinsic brainstem anatomy and the interrelationship between its internal tracts and nuclei and external landmarks is of paramount importance for safe and effective brainstem surgery. Using anatomical models can be an important step in increasing such understanding. In the present study, we have shown the applicability of our developed virtual 3-dimensional (3D) model in depicting the safe entry zones (SEZs) to the brainstem.

METHODS

Accurate 3D virtual models of brainstem elements were created using high-resolution magnetic resonance imaging and computed tomography to depict the brainstem SEZs.

RESULTS

All the described SEZs to different parts of the brainstem were successfully depicted using our 3D virtual models.

CONCLUSIONS

The virtual models provide an immersive experience of brainstem anatomy, allowing users to understand the intricacies of the microdissection that is necessary to appropriately work through the brainstem nuclei and tracts toward a particular target. The models provide an unparalleled learning environment to understand the SEZs into the brainstem that can be used for training and research.

Virtual reality technology for teaching neurosurgery of skull base tumor

BACKGROUND

Neurosurgery represents one of the most challenging and delicate of any surgical procedure. Skull base tumors in particular oftentimes present as a very technically difficult procedures in the setting of neurosurgical teaching. Virtual reality technology is one of the most promising surgical planning tools. It can perform fast three-dimensional (3D) reconstruction of computed tomography (CT), magnetic resonance imaging (MRI) and other imaging data sets under conditions of virtual reality (VR). Surgical simulation can more intuitively understand the anatomical relationship of the surgical area in significantly greater detail.

METHODS

Thirty clinical undergraduates from the class of 2016 were randomly divided into two groups: the traditional teaching group and the virtual reality teaching group. After the study concluded, the teaching effectiveness was evaluated by combining basic theoretical knowledge, case analysis and questionnaire survey methods.

RESULTS

Comparative analysis between both groups showed the response effect of the virtual reality teaching group was better than that of the traditional teaching group (P < 0.05). There was also no difference between both groups in terms of the design of the surgical approach and the listing of surgical matters that required attention (P > 0.05).The results of theoretical knowledge assessment between both groups showed that the scores of basic theory, location, adjacent structure, clinical manifestation, diagnosis and analysis, surgical methods and total scores in the VR group exceeded those in the traditional teaching group (P < 0.05).

CONCLUSIONS

This study showed that VR technology might improve neurosurgical skull base teaching quality, which should be promoted in the teaching of clinical subjects.

Cerebrovascular Operative Anatomy: An Immersive 3D and Virtual Reality Description

BACKGROUND

The innate detail of the cerebrovasculature is a demonstration of the structural complexity exhibited within the nervous system and highlights the challenges intrinsic to surgically influencing this system. Bridging the knowledge gap between the 2-dimentional learning environment and the 3-dimensional (3D) clinical setting is a challenge requiring experience. Computer graphic technology provides an opportunity for the learner to step into a new era of learning via the use of interactive 3D models and virtual reality.

OBJECTIVE

To create virtually anatomically accurate cerebrovascular models with superior detail and visual appeal.

METHODS

High-resolution angiographic radiological studies were utilized to create virtual 3D models which were edited for anatomical accuracy and artistry post-processing.

RESULTS

We have created anatomically realistic and detailed 3D virtual models of the cerebrovascular structures including the arterial and venous systems. The relevant surgical anatomy of the bony and brain structures was also included. In addition, these models were used to illustrate the pathoanatomy of a deep vascular malformation to demonstrate the potential of this technology. These models allow user interactivity in the 3D environment for improved understanding of anatomical relationships.

CONCLUSION

Advances in computer graphics have invited a new era of education and experiential learning. The authors have created an immersive virtual 3D model of the cerebrovasculature to augment education, research, and clinical applications.

Exploration of temporal bone anatomy using mixed reality (HoloLens): development of a mixed reality anatomy teaching resource prototype

Mixed reality (MR), a technology which supplements the real world with virtual objects, is increasingly becoming available as a teaching tool in medical education. The Microsoft HoloLens device allows operators to experience MR using a head-mounted device without interfering with their physical reality, stimulating a realistic learning experience using virtual objects. This project aimed to develop a MR anatomy teaching application with HoloLens for exploring the anatomy of the temporal bone. The educational application was developed from a multidisciplinary collaboration between undergraduate and postgraduate students across several academic disciplines with Medtronic, a medical technology company. 3D anatomical models were built using ZBrush and Blender, while the HoloLens1 application was developed using Windows 10, Visual Studio 2017, Unity and Mixed Reality Toolkit (MRTK). Modules developed within the application included a basic HoloLens tutorial, a virtual temporal bone with surgical anatomy landmarks and free drilling of the temporal bone. The basic tutorial allows the operator to adapt to the MR environment prior to exploring the anatomical landmarks of the 3D temporal bone. The free drilling of the temporal bone using vertex displacement and texture stretching replicates a real-time bone drilling experience and allows the operator to explore the anatomical relationship between different otological structures.

The Benefits of Limited Orbitotomy on the Supraorbital Approach: An Anatomic and Morphometric Study in Virtual Reality

BACKGROUND

Cadaveric studies on surgical anatomy and approaches are hampered by the limited number of specimens. Virtual reality (VR) technology can overcome this limitation, allowing for more in-depth statistical analysis of the data.

OBJECTIVE

To determine the benefit of a supraorbital ridge osteotomy in a supraorbital craniotomy targeting (1) the anterior communicating artery complex (ACOM), and (2) a lesion 25 mm above tuberculum sellae, using a large dataset generated by VR.

METHODS

Computed tomography scans of 30 subjects without cranial osseous pathology were identified for use with VR technology. After correlating VR and DICOM datasets, supraorbital craniotomies were simulated without and with removal of supraorbital ridge, bilaterally (n = 60). Area of freedom (AOF) from the outer table to the targets and the vertical center angle (VCA) to targets were calculated, before and after the orbitotomy.

RESULTS

For the ACOM, AOF averaged 496 mm2 (range: 322-805) and increased 8.9% to an average of 547 mm2 with the removal of the supraorbital ridge (P &lt; .001). VCA increased from 18.5 to 20.3 degrees. For the suprasellar target, AOF averaged 507 mm2 (range 324-772) and increased 42.5% to 722 mm2 after orbitotomy (P &lt; .001). VCA increased from 22.1 to 30.8 degrees.

CONCLUSION

VR technology is an emerging tool to study neurosurgical approaches. Here, we demonstrate with VR that the removal of the supraorbital ridge in a supraorbital craniotomy affords greater access to superiorly located lesions of the anterior fossa floor; however, deeper and lower lesions require a more aggressive orbital roof osteotomy to widen the exposure.

Acquisition of Volumetric Models of Skull Base Anatomy Using Endoscopic Endonasal Approaches: 3D Scanning of Deep Corridors Via Photogrammetry

OBJECTIVE

In this study we aim to evaluate the feasibility of creating volumetric models of highly intricate skull-base anatomy-previously not amenable to volumetric reconstruction-using endoscopic endonasal approaches.

METHODS

Ten human cadaveric heads were dissected through the nasal corridor to expose anterior, middle, and posterior cranial fossi structures and the pterygopalatine and infratemporal fossi. A rigid endoscope with a 30° lens was used to capture the images. Subsequently, a photogrammetry software was used to align, smooth, and texturize the images into a complete 3-dimensional model.

RESULTS

An average of 174 photographs were used to construct each model (n = 10). In the end, we achieved high-definition stereoscopic volumetric models of the nasal corridor; paranasal fossae; and anterior, middle and posterior fossae structures that preserved structural integrity. Strategic points of interests were labeled and animated for educational use.

CONCLUSIONS

Endoscopic volumetric models represent a new way to depict the anatomy of the skull base; their use with 3-dimensional technologies could potentially improve the visuospatial understanding of narrow surgical corridors for education and surgical-planning purposes.

A general theory of genital homologies for the Hexapoda (Pancrustacea) derived from skeletomuscular correspondences, with emphasis on the Endopterygota

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from medially-fused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which fine-grained transition series are hypothesized given observed skeletomuscular correspondences.