Neurological surgery is characterized by technically sophisticated procedures requiring years of training to minimize risk to the patient. Therefore, improving training and education is of paramount importance to both neurosurgeons and their patients. Thanks to the exponential growth in information technology, simulation technologies are evolving rapidly. The aerospace industry pioneered the use of virtual environments for practicing technical skills without risk. Neurological surgeons have embraced the idea of learning through simulation. Studies have shown that simulation technologies are useful for training new surgical skills and for maintaining proficiency,1-4 but so far, only a few neurosurgical skills have been successfully simulated. ImmersiveTouch (IT) is an augmented reality (AR) system that integrates a haptic device and a high-resolution stereoscopic display. IT was developed as a joint effort between engineers and neurosurgeons at the University of Illinois at Chicago and the University of Chicago. This simulation platform uses multiple sensory modalities, including visual, aural, tactile, and kinesthetic, re-creating many of the environmental cues experienced during an actual procedure. It is a flexible system, allowing the development of different training applications for different types of surgical skills. Ventriculostomy was the first neurosurgical procedure programmed for the IT system. Currently, other cranial procedures such as bone hole drilling, temporal bone drilling, and percutaneous trigeminal rhizotomy are simulated. Spine surgery skills such as pedicle screw placement, vertebroplasty, and lumbar puncture are also simulated and practiced with this system. We present our experience with the development of such AR neurosurgical modules and the feedback from neurosurgical residents.
VIRTUAL REALITY TRAINING MODULES
Several AR applications have been developed. Among them, there are modules for cranial and spinal procedures.
Cranial Procedures Applications
Ventriculostomy is often considered the first neurosurgical procedure that surgical residents learn; it is one of the simplest and most commonly performed procedures. Yet, complications related to the insertion technique can be detrimental to patient outcome.5,6 The purpose of this module is to improve the ability of neurosurgery residents to perform a ventriculostomy by developing an innovative instructional and assessment program using a virtual reality (VR)/haptics ventriculostomy simulator. Consequently, many VR simulator modules have been developed to model this procedure. The first true haptic simulator developed, the Virtual Brain Project,7 which expanded on an already existing Internet-based ventriculostomy simulation, was initially met with excitement, but it was quickly shown to be an unrealistic simulation system. However, because of the simplicity of the procedure, it is the most commonly modeled procedure for VR simulation. Despite the number of VR simulators with ventriculostomy modules, IT provides the most complete and realistic simulation of this procedure.
In theory, IT could be used for many different types of surgical interventions. The test of the device, however, came in the form of the fairly simple ventriculostomy procedure that is often learned during the first year of residency. Luciano et al8 and Lemole et al9 used patient data to develop a VR module based on normal ventricular anatomy. The trainee was able to explore the exterior shape and to position the virtual head in space as necessary to plan the ventriculostomy trajectory. The software is equipped with an option to create virtual lines on the skin to aid the operator with selecting the trajectory (burr hole to midpupillary, burr hole to tragus). Although the first generation of VR ventriculostomy training was built with a predefined burr hole, the second generation was expanded with 3 burr hole options that the trainee can select on the basis of on his/her assessment of landmarks. The operator was able to see the corresponding computed tomography (CT) scan of the virtual head in which the ventriculostomy was performed. CT scans in 3 planes were displayed on the screen. The current application is equipped with an option of measuring the distance from the orbital rim/glabella to the presumed site of the burr hole placement (Figure 1A). The trainee has the ability to decide where to place the burr hole. Bone drilling is also introduced with a bone/voxel removing technique, as described in the next section (Figure 1B). Individual reconstructed CT scans of the modules used are projected on the top of the screen to guide surgical planning. As the catheter is introduced through the burr hole, real-time tactile feedback is provided, which corresponds to the consistency of brain and the ventricular space (Figure 1C). The trainee recognizes the giveaway “pop” feeling as the catheter is introduced into the ventricular system. The catheter turns green if the catheterization is successful or red if the catheter tip is outside the ventricular system. The trainee can virtually cut through the brain (virtual scissor) to identify the location of the catheter; this visual feedback is thought to enhance the ability to have a successful attempt if the first attempt fails (Figure 1D).
Neurosurgery faculty, residents, and medical students have tested the system. All users found the platform to have realistic visual, tactile, and handling characteristics. Additionally, it was found to be a viable alternative to standard training. Once the system was validated on normal anatomy, Lemole et al9 sought to prove that the system also could be used with abnormal anatomy. After several attempts, IT users were able to properly cannulate the abnormal ventricle as a proof of concept, once again showing that IT was a realistic training alternative. The applications have progressed with the development of newer modules, including a library of 15 different ventricular anatomies with normal (Figure 2A and 2B), shifted (Figure 3A and 3B), and slit/compressed ventricles.9 The addition of those modules expands the application of training on different anatomical variations of ventricles, including the most challenging ones.
The use of the ventriculostomy module by neurosurgery residents on numerous occasions9-11 tested and validated the use of VR simulators. At the 2006 annual meeting of the American Association of Neurological Surgeons (AANS), 78 neurosurgical fellows and residents were tested on IT during the 3-day Top Gun competition. IT was used to demonstrate VR simulation of ventriculostomy. Banerjee et al10 showed that the system allows accurate catheter placement that is comparable to retrospective evaluation of free-hand ventriculostomy catheter placement as measured by the mean distance of the catheter tip from the Foramen of Monroe.
Furthermore, VR simulators have been used for training of catheter placement in abnormal ventricle anatomy.9,11 Yudkowsky et al11 demonstrated, via the use of a multiple case library, that IT was a beneficial system for ventriculostomy training. This was tested with neurosurgery residents’ ability to successfully place a ventricular catheter into normal, shifted, and small ventricles using a virtual head library derived from patient data. Residents were allowed to practice on the IT system with each type of ventricle before being tested with novel image libraries. Yudkowsky et al11 further demonstrated not only that practice on the IT improved the residents’ ability to successfully place catheters but also that residents felt that IT provided appropriate tactile feedback and that it was a realistic learning alternative to actual ventriculostomy procedures.
The single common aspect among all open, intracranial neurosurgical procedures is the need to drill surrounding bone. Although simple in concept, bone drilling has the potential to cause serious surgical complications. For example, while drilling burr holes, the surgeon could drill past the cranium and penetrate the dura and potentially the brain parenchyma. Although the likelihood of this occurring is minute, it is a concern that should always be considered. Despite the ease of the craniotomy procedure, the ability to perform this technique without complications comes only from practice and experience. To know how to perform this procedure properly and accurately, the surgeon must be aware of the differences in tactile feedback that he or she will receive from the different components of the bone. This awareness, however, will be learned only through practicing drilling bone. Therefore, VR simulation of this technique provides an excellent platform for surgeons to practice drilling bone.
The most basic module for drilling simulates a high-speed drill for a burr hole in which bone is removed in a piecemeal fashion as the drilling proceeds (Figure 1B). The expanded application simulates craniectomy as it is performed in suboccipital craniectomy (Figure 4). In addition to bone drilling for the purposes of craniotomy, several other procedures call for the surgeon to drill bone. Two such instances involve temporal bone drilling for middle ear surgery and anterior clinoid drilling to provide access to the paraclinoid space for the management of paraclinoid lesions (either tumors or aneurysms). At present, the only system developed for temporal bone drilling simulation is the VOXEL-MAN Tempo VR system.12 This system provides both visual and haptic feedback for middle ear surgeries that require temporal bone drilling.
Development of an application for temporal bone drilling involves reconstructing the bony anatomy from thin-cut high-resolution CT scans (bony windows) and content of the internal auditory canal from magnetic resonance imaging. The combination of the 2 structures is essential to build up a temporal bone drilling module over the internal auditory canal. Real-time haptic feedback from bone drilling is obtained during drilling, which helps the trainee know where to stop. The trainee also has visual feedback when the contents of the internal auditory canal can be visualized. Any further drilling into the nerves will result in a failing score.
Clinoid drilling and anterior clinoidectomy are frequently performed during neurosurgical management of paraclinoid and parasellar lesions. By performing an anterior clinoidectomy, the neurosurgeon creates a much larger surgical field with greater visualization of the surrounding tissue and vasculature. However, because of the close proximity of various structures—most notably, the optic chiasm, infundibular stalk, and cavernous sinuses—to the anterior clinoid process, caution must be exercised when the bone is drilled. Experienced surgeons typically do this procedure, with little opportunity for residents to practice this technique. Therefore, a VR module that permits practicing this procedure creates a platform from which junior faculty and residents can learn.
Percutaneous Treatment for Trigeminal Neuralgia
Trigeminal neuralgia is a debilitating disease of unknown origin that affects approximately 40 000 people at a given time.13 The primary treatment method is pharmacologic agents, including anticonvulsants, muscle relaxants, and tricyclic antidepressants. However, surgical options are available to treat trigeminal neuralgia in patients who are refractory to medical therapy. The most commonly used techniques are percutaneous approaches, including radiofrequency rhizotomy, glycerol rhizotomy, and balloon compression. Both radiofrequency and glycerol rhizotomy are permanent, destructive procedures, whereas relief via balloon compression results from a temporary compression of the trigeminal nerve during the operation. All 3 procedures are done via percutaneous delivery of the therapeutic agent to the exit of the trigeminal nerve from the skull at the foramen ovale. The most common complications from these procedures are dysesthesia, corneal hypoesthesia, and transient motor weakness.14,15 With the use of a VR simulation of these percutaneous procedures, the ability to practice and master these techniques will help minimize the complications from the surgeries. The IT module involves finding the anatomic landmarks for needle entrance through the cheek. In addition, the trajectory of the needle (toward the foramen ovale) could be adjusted by a real-time fluoroscopic feedback (lateral x-ray) image that appears on the side of the screen (Figure 5A). The combination of the tactile feedback, feeling for the bone vs soft tissues, and x-ray guidance makes the module very representative of the real procedure. At the end of the insertion, the needle turns green if it is within the correct location or and red if it missed or bypassed the target. The trainee can use the virtual scissors to cut through the 3-dimensional model and visualize the location of the needle tip (Figure 5B).
Spinal Procedure Applications
Lumbar puncture is a procedure performed frequently to help establish a diagnosis and for therapeutic purposes such as epidural and spinal anesthesia. It is also used to help reduce elevated intracranial pressure.16 Despite the simple concept of lumbar puncture, it is one of the more difficult procedures to perform successfully because of the variation in size and anatomy of each patient, as well as the basic skills of the physician (mostly nonsurgical residents/faculty) performing the procedure with no real-time x-ray guidance. Often, a lumbar puncture is performed emergently for indications like meningitis in which case time is critical and waiting for guidance from more experienced personnel is not practical. Training in a simulation environment takes on a particular importance in this situation. Therefore, a simulation of this procedure, specific to individual patients, would allow surgeons not only to practice the technique but also to figure out any complications that may arise while performing the procedure. As with all of the above procedures, the success of the operation will depend on the amount of practice and the level of training that the surgeon has experienced. VR simulation presents 1 more advantage to help aid in that training. The IT module involves a 3-dimensional model of the spine, along with the overlying soft tissues. The trainee attempts to find the proper approach based on anatomic landmarks (Figure 6A and 6B). The trainee then attempts the needle insertion solely on the basis of tactile feedback. Once the trainee thinks the needle is at its target location, the needle turns green if it is in the correct position or red if it is outside the thecal sac.
Pedicle Screw Placement
Luciano et al17 recently described the use of their IT system for thoracic pedicle screw placement. Pedicle fixation is an effective and dependable technique for spinal stabilization. However, because of natural variation in pedicle anatomy between patients, accurate and safe placement of screws can be challenging. Screw placement in a suboptimal location can result in varying degrees of neurological deficits, eg, by impinging on the spinal cord if a screw invades the vertebral canal and losing the ability to stabilize the spine adequately.18 These complications, however, can be avoided with adequate training and practice of the procedure.19
Currently, the 2 most frequently used methods to place pedicle screws are visualization by the surgeon and intraoperative CT-guided screw placement.20,21 Intraoperative x-ray confirms screw placement for the former, whereas the latter technique allows real-time visualization of screw placement without the need for x-ray imaging. In centers without the ability to perform these procedures with intraoperative CT image guidance, the more standard technique of surgeon visualization is used. This procedure, although well established, may result in postsurgical complications resulting from inaccurate screw placement. Consequently, a VR simulation module designed to demonstrate pedicle screw placement would be a very helpful tool in allowing surgeons to hone their surgical acumen for this procedure. Thoracic and lumbar modules have been developed. In these modules, the trainee uses a pedicle finder to cannulate the pedicle based on bony landmarks. Similar to the technique used in the operating room, the trainee can visualize the location of the pedicle finder in real time x-ray fluoroscopy. The projection of the virtual x-ray can be adjusted and rotated from the anteroposterior to lateral projections (Figure 7A-7D). The thoracic pedicle screw placement module developed by Luciano et al17 provides users with the ability to practice this procedure. The module allows a feeling similar to the open surgery approaches in which the skin and muscles are retracted with self-retaining retractors, representing real-life approaches. Similar modules for cervical instrumentation for finding the corresponding trajectory and approach for cervical instrumentation are available in which the trainee is able to place lateral mass and pedicle screws within the cervical spine (Figure 8A and 8B).
Minimally invasive surgical approaches place a greater demand on surgeon familiarity with the anatomy and surgical precision. The simulation can be adapted to open, minimally open, or percutaneous approaches with modules available for each. The open module includes realistic presentation of open skin and muscles, whereas the percutaneous module allows dialing of tissue transparency and resistance as needed to gradually teach the trainee relevant surgical anatomy and approach. The system has the ability to allow the user to continuously monitor drill/pedicle finder projection via anteroposterior, transverse, and lateral fluoroscopic views. For more advanced training, the user can turn the views off. Additionally, IT provides haptic feedback and vibration feedback to represent the natural vibration of the electrical drill with corresponding changes in vibration feedback, depending on the speed of the drill. Furthermore, like the Top Gun competition held at the 2006 AANS annual meeting, another competition was held at the 2009 AANS annual meeting in which thoracic pedicle screw placement was one of the tasks that residents and fellows performed. Luciano et al17 described the results from the IT system and showed that the accuracy of thoracic pedicle screw placement with the IT system corresponds to the actual placement by comparing experimental data with a retrospective evaluation of operating room screw placement. On the basis of 156 test data sets preceded by 76 practice data sets at the 2012 AANS Top Gun competition, participants obtained better cumulative scores on their tests after practice, attributable primarily to significantly fewer fluoroscopy requests. The differences in accuracy scores were relatively insignificant (Table).
TABLE TopGun Residen...Image Tools
In addition to pedicle screw placement, IT has a spine module that simulates percutaneous vertebroplasty. Properly executed vertebroplasty requires the surgeon to rely on both sight and touch.22 Therefore, if a surgeon trains for this procedure using a VR simulator, surgical errors presumably can be minimized. The module designed for this procedure allows the user to perform the vertebroplasty while getting immediate visual and haptic feedback, similar to the procedure on a real patient. The module is designed with a 3-dimensional representation of the procedure being performed, as well as anteroposterior and lateral view x-ray information, providing real-time imaging of the surgical instrument location. Consequently, the system operator has a realistic environment in which to practice this technique (Figure 7A-7C).
The vertebroplasty module is a variant of the percutaneous pedicle screw placement training system. It is an example of the adaptation and exaptation of IT simulation to relevant variants of procedures.
In the last decade, surgical training has faced both legal and ethical concerns regarding patient safety, work hour constraints, and the cost of operating room time. To remain proficient, surgeons must work to maintain their skills in addition to learning new and more advanced techniques. In neurosurgery, the majority of technical learning is accomplished through the observation of more senior surgeons. Furthermore, resident duty hour limitations are increasing the challenge of mastering the necessary surgical techniques. Consequently, training programs are exploring alternative simulated training modalities so that neurosurgery residents have adequate exposure to essential surgical techniques and scenarios before being exposed to the unforgiving reality of the operating room. VR and AR simulation with haptic feedback holds great promise for addressing the new training mandate for safe, consequence-free operative learning.
Despite the rapid development and promise of VR and AR simulation, several issues need to be addressed before simulator training becomes standard protocol for neurosurgery training programs. First, neurosurgical residents are not a homogeneous group. Residents vary in their hand-eye coordination and inherent ability to learn technically demanding skills. The residents tested on this system are at varying stages in their surgical training. Furthermore, there is an innate learning curve associated with the VR technology itself, and some have difficulty becoming acclimated to the virtual environment. Therefore, it is not clear whether simulator proficiency will translate into the operating and procedure rooms. Mastering a sophisticated flight simulator to the satisfaction of a Federal Aviation Administration examiner does not mean that the individual will be a good real-world pilot. It is our opinion that simulator training will be of benefit to surgeons of all levels of skill and experience and that those with poorer coordination and natural ability will benefit most.10
Testing and validation are a second issue requiring further attention through thoughtful study design and randomization. So far, the majority of studies designed to examine the efficacy of VR simulation, especially those of IT,9,10,23 have used nonrandomized techniques and have not explored the translation from VR training to actual operating experience with a real patient. To determine the efficacy of VR effectively, novice test subjects need to be randomized into at least 2 groups—1 group that trains on the VR system and 1 group that does not—to determine which group performs better under true operating conditions with actual patient health at stake. Chaer et al24 have performed the only such study to date. They demonstrated that individuals trained with the Procedicus VIST endoscopy system (Mentice Inc) performed procedures in real patients faster and made fewer mistakes. However, this has not been demonstrated for any other VR system. Therefore, further studies are needed to demonstrate this same efficacy for other VR systems and modalities that include cranial and spine applications and are not limited to endoscope-based procedures.
It is also unclear to what extent simulator training will benefit physicians at more advanced levels of training and expertise. For example, it has been demonstrated on the IT ventriculostomy module that novice surgeons outperform more senior residents.10,23,25 However, no other modalities have been tested. Additionally, these studies were based on data obtained at annual AANS conferences in which residents were selected to test the IT system. The accuracy of catheter placement into the lateral ventricles was measured and compared between residents with varying numbers of years of training. The numbers of test subjects in each group were not equal, and experience with ventriculostomy placement varied. The frequency with which each resident performed this procedure and the individual rate of complications were not taken into account. The observation that more junior residents performed better on IT suggests 1 of 2 possible explanations. Perhaps more senior residents perform this procedure less frequently and thus have lost their ability to place a ventricular drain accurately. Alternatively, senior residents may have become experts at this procedure in real patients, and the experience of a VR system is still too far removed from reality and lacks the many subtle environmental cues of a procedure performed in reality. So far, it seems that simulation training is more useful for novice participants than to physicians with extensive experience. For novices, VR systems establish a risk-free environment in which users not only acquire new skills but also learn the relevant anatomy for each procedure. Moreover, an already experienced surgeon can use these systems to learn new procedures. Because of these discrepancies, however, it is crucial that randomized studies be conducted that determine whether VR systems are beneficial for physicians of all expertise or are helpful only for novice surgeons. Despite the many uses of VR simulation, many studies need to be conducted to fully validate these systems. Although VR simulation provides a new approach to training residents, many questions remain. It appears that VR training is proving to be an effective alternative to observational learning and, in some cases, has proven to be a more efficient educational system.1,23,24,26-29
VR and AR environments represent a crucial advancement toward enriching the training of neurosurgical residents and providing a platform for experienced surgeons to maintain their skills. VR simulators are currently used to train surgeons, to preoperatively plan for the upcoming procedure, and to provide vital intraoperative information. For this reason, it is our hope that this technology will be incorporated into the new neurosurgery resident “boot camps” that indoctrinate new residents in the basic knowledge and skills they will need to successfully navigate the first years of their neurosurgical training. There is still more work to be done before VR simulation is a mainstay of neurosurgical training. Nevertheless, it is clear that VR simulation is the logical next step for de novo resident education and proficiency training for senior surgeons.
Drs Banerjee and Charbel are shareholders in IT. Drs Alaraj, Luciano, Rizzi, and Roitberg are coinvestigators on National Institutes of Health grants 1R21EB007650- 01A1 and 1R43NS066557 -01A1 awarded to IT. The other authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.
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