1 Training Models in Neurosurgery • Neurological surgery is one of the most technically demanding medical specialties, with a steep learning curve. • Neurosurgery has benefited from several technical advancements in the last 3 decades that involved visualization, instrumentation, and approaches. • In recent years there has been the development of an increasing number of training models and courses to augment the training of new generations of surgeons and in an attempt to lessen the steep learning curve mentioned earlier. • Changes in regulations regarding working hours for neurosurgical trainees have challenged the neurosurgical community to develop methods to maintain high quality standards without compromising the neurosurgical training, which is a necessary component of each residency. This is extremely important when dealing with highly complex lesions that are not routinely encountered such as deep-seated tumors and vascular lesions. • To augment the clinical exposure to the pathology, an alternative option of reliable training that simulates life-like conditions is needed. • Laboratory training is usually advocated to master the intricate anatomy of the brain and micro-neurosurgical technique. • Both physical and computer-simulated training models are becoming increasingly available. These include models based on synthetic materials, animals, and human cadaver. • Human cadaveric models are still deemed the most beneficial as they resemble life-like anatomical and technical challenges however there is a lack of blood circulation. • Excellent spinal and cranial models have been created, focusing on performing surgical approaches with normal surgical anatomy. Some expose the residents to anatomy altered by pathological processes. • There have been widespread advancements over recent years when it comes to simulation in neurosurgery. • The majority of simulators are divided into either physical or virtual reality (VR) subtypes. • The physical simulators include cadaver models, live animal models, and synthetic models. Despite many recent advancements, the cadaver model has remained the most effective and most commonly used method for neurosurgical training. • Cadavers and mannequins are particularly useful for the practice of basic skills such as drilling techniques, neuroendoscopy, spinal decompression and instrumentation. • Microsurgical training is among the most practiced type of simulation, and it can involve the use of synthetic models such as silicon tubes, dead tissue models such as the chicken wing artery (Fig. 1.1), human and bovine placental vessels, and more recently three-dimensional printing. • Live models provide the most realistic method for many types of training with pulsatile blood flow, natural viscosity and coagulation. Utilizing these models, however, has become more difficult as institutional protocols and review boards continue to impose necessary but significant constraints regarding the use of live animals. • Computer generated graphics along with CT and MRI data have allowed for the re-creation of human anatomy in a virtual space. This has become particularly useful for understanding the complex anatomy of the central nervous system and the spatial relationship between anatomical structures in three dimensions. • Currently there are three main types of virtual simulators: they are simplified, augmented, and immersive. ◦ Simplified VR systems are the most basic consisting of only a computer-user interface with no sensory interaction by the user. ◦ Augmented VR systems allow for more interaction and manipulation by the user with the use of external props. The ‘Robo-Sim-Endoscopic neurosurgical simulator’ is an example. ◦ Immersive VR systems are the most technologically advanced and involve creating a physical presence in a virtual world utilizing primary sensory input/output and haptic and kinesthetic modalities. • Three-dimensional printing for neurosurgical training is a more recent advancement, which produces a multi-texture reconstruction and allows for the planning and training of specific and complex operative procedures (Fig. 1.2). Fig. 1.1 Chicken wing dissection. The brachial artery is 5-6 cm long. • The brachial artery is harvested from a chicken wing and can be used to practice end-to-end, end-to-side, or side-to-side anastomosis under a microscope (Fig. 1.1). • Shapes of the arteriotomy, type of sutures as well as incident angle of the bypass graft may vary between surgeons; however, the basic yet crucial principles of microsuturing are exercised in this model. • The distance the sutures are placed from the vessel edge is precise and the needle must penetrate the entire thickness of the vessel wall without touching the intima. It is important to keep the vessel and material moist throughout the anastomosis to prevent the structures from drying out. • The integrity of the anastomosis can be evaluated by injecting water into the vessel and looking for leaks. In addition, the technique can be evaluated by cutting the artery, placing it under a microscope, and looking at the intimal appearance surrounding the anastomosis in search of kinks or strangulation. • One of the drawbacks of this model is the variability in vessel diameter across different wings. Also, many of the wings suffer from freezing artifact after thawing which creates many difficulties when attempting to harvest the arteries. • Recently, the utility of both human and bovine placental vessels in microsurgical training has been explored and validated as an effective way to train neurosurgeons in low-flow and high-flow neurosurgical bypass techniques. • Human placental arteries have wall thicknesses, amounts of connective tissue and diameters that closely resemble those in the human brain. Bovine placenta can be readily used if human specimens are not available as acquisition it does not require institutional review board or Institutional Animal Care and Use Committee approval, which makes it an easy replacement. • The two umbilical arteries and the vein are cannulated and colored normal saline is incorporated into a flow circuit at around 100 to 180 mmHg. This allows for the trainee to encounter “bleeding” if a vessel is damaged and practice hemostatic techniques using bipolar coagulation or ligation. • The placenta is placed into a skull with a previously created bone window to simulate depth and the restrictions of a craniotomy. Vessels with diameters of 0.8 to 1.5 mm and 1.0 to 2.0 mm are used to mimic the human middle cerebral artery (MCA) and superficial temporal artery (STA), respectively. Vessels with diameters of 8.0 mm to 9.0 mm and 2.0 to 3.0 mm are used to model the human ICA and radial artery (RA), respectively. • End-to-side, end-to-end, and side-to-side bypasses with a long interposition graft are several of the microvascular techniques that can be practiced using this model. • Some of the limitations of this model include the viability of placentas, the exposure to potential infectious agents using human placentas and the absence of adjacent soft-tissue that would need to be dissected in a real case. • Recent advancements in endovascular surgery have changed the surgical indications for aneurysm clipping such that aneurysms not amenable to endovascular approaches are most often highly complex and challenging lesions. This decrease in the number of aneurysms considered amenable for surgery has led to an increase in the level of expertise required to handle those that need to be clipped. It is important that new methods are available for future neurosurgeons to practice and refine the techniques necessary to address these during their careers. • In this model, 3D models of aneurysms are printed based on real patient data and implanted in human cadavers at the same anatomical region as the modeled patient (Fig. 1.2). • The cadavers are connected to two liquid reservoirs inside pressure bags to simulate surgical bleeding during the simulation. • Benet et al demonstrated this method by printing both patient specific middle cerebral artery and basilar apex aneurysms, placing them in human cadavers using standard surgical techniques and evaluating their utility in the operative training as well as case management and planning. ◦ It was found that the flexibility of the neck and branches of the aneurysm were similar to those of the modeled patient. ◦ The aneurysm domes were also sufficiently rigid to produce mass effect without compromising the aneurysm’s integrity. ◦ To simulate mass effect, a Foley catheter was introduced beforehand and progressively inflated to allow room for implantation of the modeled giant aneurysm. • This 3D aneurysm implantation model may help supplement the declining number of aneurysms treated surgically by incorporating hands-on training for patient specific aneurysms considered for surgery. • In 2010, Gragnaniello et al proposed an injectable skull based tumor model, using Stratathane resin ST-504 polymer (SRSP), that could be used to train future neurosurgeons for the delicate dissection of a tumor from surrounding neural and vascular structures (Fig. 1.3). • Stratathane resin ST-504 polymer (SRSP) is used for its characteristics to emulate brain tumors different in consistency ranging from rubbery meningioma to suckable pituitary adenomas. The polymer, developed in cooperation with the scientists of the Nanotechnology Center, reflects most of the properties of real extra-axial central nervous system (CNS) tumors. • It causes displacement of surrounding neural and vascular structure, and because of its non-adhesive nature, it affords us a dissection plane very similar to the one described in the aforementioned tumors. It also has a consistency similar to these tumors; it can be incised by micro-instruments, but it cannot be suctioned like a jelly, which helps in imitating the exact conditions of live surgery. • The polymer has a distinct characteristic on T2-weighted MR images that enables its superb delineation and further assists the preoperative planning of the procedure. • The pressurized heads consisted of cadavers in whom an artificial circulation was established in the existing vasculature using a red solution imitating real blood infused via a mechanical pumping device. • As endoscopic approaches to intraventricular tumors become more common, there is an increasing demand for appropriate laboratory training models. • Ashour et al describe a model in which the polymer mentioned above is injected into the lateral ventricle of formalin-fixated, latex injected cadaveric heads under direct endoscopic and neuro-navigated guidance (Fig. 1.4).
1.1 Introduction
1.2 Simulation Models in Neurosurgery
1.2.1 Physical Simulators
1.2.2 Virtual Reality
Abbreviations: CBA = chicken brachial artery; EM = extensor muscle; FM = flexor muscle; MC = metacarpus.
1.3 Training Models in Vascular Neurosurgery
1.3.1 Chicken Wing Artery
1.3.2 Human and Bovine Placental Vessels
1.3.3 Three-Dimensional Printing
1.4 Training Models In Neuro-Oncology
1.4.1 Injectable Tumor Model
1.4.2 Intraventricular Tumor Model
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