**3.1 PVC rat model**

Using the PVC rat model for 'unbloody training' of microsurgical techniques and improvement of practical skills is a perfect example of the replacement of living animals (**Figure 14**). The number of live animals used for in-vivo training will likely be reduced in the future, therefore these in-vitro methods will be needed to make the transition to in-vivo models easier. The PVC rat model (Microsurgical Developments Foundation, Maastricht, The Netherlands) should be the first step in the practical education and allow various microsurgical training situations. The replacement of the plastic vessels is easy and relatively cheap [19]. Using a specific nozzle at the back of the rat model, the colored vessels can be filled with water, thus permitting an easy check of patency and quality of the anastomosis.

In the prospective part of our published study [18], end-to-end and end-to-side anastomoses were performed with three different levels of difficulty in the PVC rat model. In total six surgeons with different expertises and different levels of vascular training and surgical skills performed these microsurgical procedures. Different sizes of plastic tubes of various lengths and diameters were used for reduction of the surgical approach and the workspace, to adapt the experimental set-up to a scenario with different degrees of difficulty (**Figure 15**). Those plastic tubes reduce the operative field and consecutively the surgical working space and determine the trajectory and

#### **Figure 12.**

*The navigational data set for the 3D model of an MCA aneurysm.*

#### **Figure 13.**

*The operating microscope (Neuro NC4, Carl Zeiss) was linked and registered with the navigation system (Brainlab VectorVision). After the combined craniotomy and opening of the dura, AR overlay head-up display depicts the dominant sigmoid and transverse sinus (green), the basilar artery (magenta) and the clival meningioma below.*

#### **Figure 14.**

*In-vitro model with plastic vessels of the abdominal cavity of the PVC rat (Microsurgical Developments Foundation, Maastricht, The Netherlands).*

#### **Figure 15.**

*A transparent plastic tube was brought into the operative field and fixed to a conventional flexible retractor system to reduce the working space and mimic surgical conditions in deeper approaches. In this narrow workspace, the level of difficulty to perform an anastomosis significantly increases.*

the direction for the instruments. Due to this focused working channel, the degree of freedom for using the instruments is restricted and therefore, the level of difficulty to perform an adequate anastomosis increases significantly (**Figure 15**). The different sizes of the plastic tubes mimic intraoperative conditions in a narrow and deep surgical field. Plastic tube I (Advanced) has a diameter of 40 mm and a depth of 15 mm. Tube II (Expert) has a diameter of 30 mm and a depth of 35 mm (**Figure 15**). Tube III (Master) has a diameter of 25 mm and a depth of 45 mm. For the anastomoses, we used conventional microsurgical instruments and monofile polyamid sutures 8/0 (BV 2 needle), respectively, 10/0 (BV 100-4 needle) Ethilon (Ethicon, Johnson & Johnson MEDICAL GmbH, Norderstedt, Germany).

In this experimental set-up, the increase of surgical complexity by reducing the workspace with the different plastic tubes clearly demonstrates that the time of surgery to perform the anastomosis increased significantly (**Figure 15**). In addition, the rate of incorrect sutures of the vessel wall increased, the narrower the surgical field

*Training Models for Skull-Base and Vascular Micro-Neurosurgery DOI: http://dx.doi.org/10.5772/intechopen.101924*

#### **Figure 16.**

*This plastic skull and silicone brain model shows an extended pterional approach with slight retraction and opening of the Sylvian fissure. An end-to-side anastomosis was performed using highly elastic PVA-vessels (Kezlex, Ono & Co., Ltd., Tokyo, Japan). This set-up allows for a realistic scenario and the handling of the vessels during the anastomosis, closely mimicking human conditions during bypass surgery.*

became due to the decreasing diameter of the tube. Therefore, the overall patency rate of the anastomosis was clearly reduced with increasing grade of complexity [18].

#### **3.2 PVA vessel with craniotomy site**

The wet PVA vessels of the vascular anastomosis practice kit are transparent, highly flexible and soft [20]. However, they have to be kept moist and tend to dry out and lose their elasticity, especially under the high-energy xenon light of the operating microscope. At present, we have used the PVA vessels of the vascular anastomosis practice kit for various experimental anastomoses. Compared to the PVC vessels in the rat model, the preparation and handling of the PVA vessels, especially the grasping with a forceps or the insertion of the needle into the vessel wall is much more realistic and closely mimics human conditions.

An even more realistic scenario is provided by the plastic skull model with relatively soft and deformable silicone brain material and the vascular anastomosis practice kit with highly elastic plastic (PVA) vessels (Kezlex, Ono & Co., Ltd., Tokyo, Japan). The very soft and elastic plastic vessels of the vascular anastomosis practice kit are available in three different diameters: 1 mm, 2 mm and 3 mm. The vascular kit with the humid PVA vessels has a perfect haptic feeling during preparation, cutting and suturing of the vessels. The whole set-up with the deformable plastic brain, the realistic feeling of retraction and especially the optical impression under the microscope generate an overall aspect of a real microsurgical scenario closely mimicking human conditions.

The 3D model with pterional craniotomy and the deformable frontal and temporal lobe (Kezlex, Ono & Co., Ltd., Tokyo, Japan) is a perfect in-vitro model to simulate an opened Sylvian fissure for experimental bypass, as well as aneurysm surgery training.

#### **Figure 17.**

*In-vitro model in a rabbit. An end-to-side anastomosis of both carotid arteries was created using 10/0 sutures to generate an arterial bifurcation.*

#### **Figure 18.**

*The insertion of a venous pouch into the bifurcation finally results in an experimental bifurcation aneurysm, comparable to a 6 mm MCA aneurysm with a broad neck. The in-vivo bifurcation aneurysm model is a perfect training tool for clip application, especially if a plastic tube (schematic drawing) creates a narrow workspace with limited access for the clip applicator. Due to the determined trajectory, the clip occlusion of the aneurysm mimics human conditions. This set-up is a sophisticated in-vivo training model for active teaching and practical training for bypass surgery, as well as aneurysm clipping.*

*Training Models for Skull-Base and Vascular Micro-Neurosurgery DOI: http://dx.doi.org/10.5772/intechopen.101924*

This set-up allows a realistic retraction of the Sylvian fissure, its handling and preparation closely imitating human conditions (**Figure 16**).

We also used 3D printed aneurysms made from soft PVA tubing that could be clipped for training purposes. The 3D printed hollow aneurysms were positioned in the depth of the Sylvian fissure and so microsurgical clip application could be simulated adequately (Videos 1 and 2, https://bit.ly/3AeRgNk). Then the experimental plastic aneurysm could be removed from the site to assess the success of the clipping maneuver (Video 3, https://bit.ly/3AeRgNk). These realistic human skull and brain models are relatively expensive but could be used repeatedly [24, 25]. If the models are integrated into practical teaching and training, they help to establish a realistic microsurgical scenario and are definitively superior to computer-based animations alone [26].

### **4. In-vivo microsurgical models**

#### **4.1 Rabbit model for experimental bifurcation aneurysms**

The materials and methods of the experimental aneurysm bifurcation model in rabbits (**Figure 17**) were described in great detail in previous publications [21–23]. The developed and previously described animal bifurcation aneurysm model is a perfect and highly realistic vivisection model for education and practical training for microsurgical handling and preparation of cerebral vessels. However, this model should be used as a final education tool in an advanced stage of training. The blood flow, the vessel diameter, the haptic feedback, even the induced vasospasms by manipulating too roughly, and the tension of the vessel walls, all of this can be compared to vascular microsurgery in humans (**Figures 17** and **18**). Therefore, it is an optimal training tool for all cerebrovascular reconstructive surgical procedures and maintains expert status in bypass surgery [27].

Additionally, this experimental aneurysm model allows an optimal practical training of clip application and is a realistic teaching model for optimizing clip occlusion of cerebral aneurysms. As described in the PVC rat model study conditions, the different sizes of plastic tubes were also integrated into our experimental animal model (**Figure 18**). The tubes were fixed to a conventional and flexible retractor system and could be removed easily if difficulties arise, especially inadvertent bleeding intraoperatively. The transparent plastic tubes create a narrow and deep surgical approach by restricting the angle of view and determining the trajectory of the clip occlusion of the aneurysm as in real aneurysm surgery. After clipping of the experimental bifurcation aneurysm, the plastic tube was removed and the aneurysm could be inspected easily from all sides and the clip position could be checked adequately.

For repeated training, the clip was removed from the experimental aneurysm and the procedure could be repeated, for example, with a narrower, longer or differently angled plastic tube, creating a completely new situation with a different view and access to the experimental bifurcation aneurysm. This high-end in-vitro animal model is an excellent and realistic set-up for intensive practical training and teaching of aneurysm clipping. However, it takes a great deal of logistical and technical effort to produce such an experimental animal aneurysm.

### **5. Conclusion**

VR and AR are currently established in many areas of medical education and should increasingly become the standard in modern neurosurgical advanced

teaching and training as well. Therefore, these tools should also be used regularly for surgical training and further education of young neurosurgeons. With modern navigation systems, diverse software and hardware components are generally available and should consequently be used and strictly integrated into our daily clinical routine. This technology thus forms the basis for highly qualified practical training in skull base surgery. In addition, it facilitates the necessary interdisciplinary cooperation between faculties and offers the opportunity for lifelong learning for all surgically active colleagues in skull base surgery.

In-vitro models, like the AR 3D models, the PVC rat model or the PVA vascular model combined with the realistic brain and craniotomy site, allow for a perfect setup for the advanced training of microsurgery and microvascular anastomoses. The main advantages of these artificial plastic models are their overall availability, the low price and the lack of a specific OR set-up or instruments, compared to training in in-vivo models. The costs and logistical considerations, as well as the ethical and legal aspects involved in maintaining living animals for education and training, make in-vivo models a relatively impractical tool.

These in-vitro models are easily adaptable to the respective circumstances and allow unhindered practical training under almost realistic operating conditions. The surgical complexity with end-to-end and end-to-side anastomoses could be adapted in models and the success rate is easy to check. Parameters like the time of surgery, the rate of incorrect sutures of the vessel wall and the overall patency rate of the anastomoses can be clearly monitored, as well as the learning curve. Therefore, these in-vitro models form the basis for the first step in basic practical training and are a prerequisite for a successful career in vascular neurosurgery and skull base surgery.

In-vivo models should be the last step of practical education. Like our experimental animal model with the insertion of a venous pouch within the microsurgically created arterial bifurcation represents an advanced training model very close to realistic human conditions. In the first step of this model, microvascular anastomoses are trained and secondly, the resulting bifurcation aneurysm is a perfect training tool to learn clip application. Especially, if a plastic tube is positioned over the surgical field and creates a narrow approach with restricted workspace and limited scope for manipulation for the correct clip occlusion of the aneurysm. Our experimental animal model represents a higher level of surgical vascular expertise and additionally is a perfect model to practice bypass surgery, as well as the appropriate handling of clip application and clip occlusion of cerebral aneurysms.
