Endoscopy within the ventricular system is an accepted form of surgical access for problems such as obstructive hydrocephalus, biopsy, and excision of intraventricular lesions. The training of surgeons to perform these operations is more challenging than general microneurosurgery given the constraints of access and visualisation, as well as the ability to perform supervised training for juniors because of small margins for error.1–5
Current training in neuroendoscopy has been restricted to either cadaveric training or stepwise instructions during actual surgery.2,6 In the former, problems such as desiccation of tissue and absence of pathology make it a less than satisfactory training model to work with.7 Training during actual surgery, in contrast, is restricted by patient acceptance as well as safety and legal issues especially because this is a technique in which the trainer has limited control.2,8 Furthermore, in this technique, knowledge is gained in a stepwise fashion over a long period of apprenticeship.
There are a variety of simulators for endoscopic training in the other parts of human anatomy, for example, laparoscopy or endourology. These are usually in the form of box simulators or more complex computer-based virtual models.9 Although neurosurgical training has attempted to move toward simulation models similar to these simulators, the results have been far from satisfactory in terms of cost or realism.2,10,11
An optimal simulator for neuroendoscopy should have accurate representation of anatomic structures, realistic tissue handling characteristics, and the ability to interact with other instruments used in an endoscopic procedure such as navigation.11 Such a simulator should also accurately mimic common pathology encountered in this region such as a dilated ventricle or intraventricular tumors.7,12
By using a rapid prototyping 3-dimensional (3D) printer that is able to print in a variety of textures, we have been able to recreate a model of a patient with an enlarged ventricle secondary to a large pineal region tumor using actual patient data. The aim of this article was to share our experience with this model as a teaching aid for neuroendoscopic training.
Computed tomography and magnetic resonance imaging data from an existing patient with hydrocephalus were selected, and the various components including the skin, bone, dura, ventricle, and tumor were segmented. These data were then converted into STL format using an in-house software (BIOMODROID CBMTI UM) and subsequently used to print an actual replica of the head using a 3D printer (Stratasys Connex 500 USA).
Although the 3D printer was able to create tissues of varying consistency and density, we had to modify the ventricular wall by introducing a polymer layer to allow the ventricle to obtain elasticity, which allows the endoscope to perforate the ventricle with the appropriate “give.” The techniques involved in creating the various tissue layers such as the skin, bone, and dura were covered in a previous publication.13 The main challenges in the process of creating the model were to introduce fluid into the ventricular space and to keep it under appropriate tension. To enable this, we inserted an inlet and outlet valve onto the surface of the model, thus allowing the fluid to be continuously filled to the required tension (Fig. 1A, B).
The rest of the model was able to mimic the anatomy of an actual ventricle quite accurately including the interventricular septum, the fornices, the choroid plexus, vessels, and tumor. To increase the realism in an endoscopic procedure, we also introduced the concept of bleeding by injecting a red dye via an additional inlet and tube system into the “tumor” when necessary.
Finally, because this model was created based on actual patient data, it was possible to accurately register and navigate with 2 commonly used image guidance systems, namely, the BrainLab system using the Z touch laser registration technique and the Medtronic system using the surface-matching technique. The endoscope was registered to the respective navigation stations; after which suitable entry points and trajectories for performing the endoscopic third ventriculostomy (ETV) were identified. The accuracy of navigation registration of 3D rapid prototype models created via this technique has been presented previously.14,15
Three exact models were created and assessed in a qualitative manner by 3 independent neurosurgeons who were not involved in the design or production of the models. The surgeons were of varying seniority but experienced in performing endoscopic intraventricular procedures. All 3 surgeons were independently asked to perform a complete ETV and pineal biopsy procedure, from positioning, image guidance registration of the model and endoscope, planning of trajectory, creation of burr hole, and introduction of scope, up to ventriculostomy. The tumor biopsy was performed via the same burr hole by reorientating the scope under image guidance and direct vision. Standard equipment, including scalpel, retractors, high speed drill and endoscopes, were provided.
The surgeons assessed the models on a number of areas based on a 5-point Likert scale with 1 being unsatisfactory and 5 being outstanding representation of the actual procedure. In addition to scoring, the comments made by the surgeons were also documented.
Subsequent to the initial evaluation by the previously mentioned experienced surgeons, 6 models were used in an intraventricular endoscopy workshop attended by 12 participants at the level of senior trainees to junior neurosurgeons with minimal experience in intraventricular endoscopy. These participants were provided a series of lectures involving the various aspects of navigation-guided endoscopy, performing intraventricular endoscopy, third ventriculostomy, and finally an endoscopic biopsy of the pineal gland. The participants then performed the specified procedures on the models under the guidance of senior neurosurgeons. At the conclusion of the workshop, the participants evaluated the utility of the model to achieve the previously mentioned objectives as a training tool.
The 3 neurosurgeons independently set up the equipment and model with minimal assistance and subsequently performed the whole procedure with ease. Their overall score of the simulated third ventriculostomy procedure was 4 of 5 (Fig. 2). The process of performing image guidance was particularly cited as very realistic and useful, with an average score of 5 between the surgeons. The skin was noted to be not as pliant as in real tissue. However, the burr hole procedure including the use of clutch-enhanced perforator was noted to be “perfect.”
The surgical procedure scored an average of 4.6. Although most of the intraventricular structures were noted to be present, the surgeons felt that they were not fully represented in a realistic manner. The average surgical anatomy score among the surgeons was 3.2. The ventriculostomy procedure averaged a score of 3 because of the presence of a stiff floor, which did not respond as smoothly as in a surgical setting, and it was not possible to coagulate the floor; however, it provided the necessary simulation experience of performing a third ventriculostomy such as appearance of anatomy of third ventricle floor structures, instruments used, and overall method of performing a third ventriculostomy (Figs. 3–5). Finally, the surgeons found the biopsy procedure very satisfying, with an average score of 4 of 5 (Table 1).
All 3 surgeons agreed on the ease and usefulness of these models in the teaching of ETV, performing biopsies endoscopically, and the integration of navigation to ventriculoscopy (Video, Supplemental Digital Content 1, http://links.lww.com/SIH/A160, which demonstrates navigation-guided endoscopic third ventriculoscopy and biopsy of pineal tumor).
The bleeding mechanism, although in the early stages of development, was noted to add a sense of realism and urgency, which may enhance the training. The surgeons also commented that the models did not reflect accurately the problems of brain shift because of the release of cerebrospinal fluid during endoscopy, given the rigid nature of the ventricular walls of the model.
Subsequent to the initial trial, the models were used in an intraventricular endoscopy workshop, attended by 12 participants with an average of 6.75 years of experience in neurosurgery. These relatively junior surgeons were given a series of lectures on the theory and practical aspects of image-guided navigation and endoscopy. They then set up the equipment and performed the specified procedures with the help and guidance of senior neurosurgeons.
Their overall score of the usefulness of the workshop to learn intraventricular endoscopy and related procedures was 4.5 of 5. Contrary to the experienced neurosurgeons, the junior surgeons felt the intraventricular anatomy to be quite realistic and natural. Despite the drawbacks of a stiff third ventricular floor, the junior surgeons commented that the model provided the necessary simulation experience of performing a third ventriculostomy such as appearance of the anatomy of third ventricle floor structures, instruments used, and overall method of performing a third ventriculostomy. They averaged between a score of 4.0 to 4.6 for every individual step of the procedure, translating to an above average to outstanding representation of the realism of the procedure and anatomy (Table 2).
Although intracranial neuroendoscopy has become a mainstay in neurosurgery, training juniors to use these techniques remains a challenge. Presently, training consists of cadaveric workshops or the use of rudimentary box simulators.7,10,16 The challenge with cadavers other than the usual problems of availability and the need for special equipment includes desiccated ventricles and, more importantly, an absence of pathology.15 In contrast, training on the job potentially places patients at risk because the room for error is narrower than conventional microsurgery.2,16
A suitable simulator should be able to create an environment that is as realistic as possible while being anatomically accurate. It should represent actual pathology with realistic tactile sensation. Among the many new techniques suggested for optimizing training, simulated models with inbuilt pathology comes closest to fulfilling all the previously mentioned criteria. These simulated models containing pathology has recently come of interest to educators in the hope of enhancing training while shortening the time needed to acquire essential skills in surgery.16,17
Because of the relative small number of patients undergoing intraventricular endoscopic procedures in contrast to laparoscopic surgery, a simulator model such as this will allow trainees to develop the necessary hand-eye coordination. This is more so because of the training experience to operate based on an input appearing on a screen that is away from the operating site while manipulating instruments in a very delicate environment is not provided for in all other forms of conventional neurosurgery.
In addition to being able to provide the necessary experience, these models are also able to mimic certain tactile responses observed during actual surgery. The presence of pathology will also possibly allow the use of newer devices such as endoscopic ultrasonic aspirators on these models.
The model described in this article is derived from actual patient imaging data and therefore is anatomically and spatially accurate. This allows the trainee to perform the endoscopic procedures together with navigation techniques including registering the patient and the endoscope to the navigation system as well as planning a suitable trajectory, allowing it to be tracked throughout the procedure.14,15
The concept of trajectory planning as well as the benefits and problems of a single versus double burr hole technique for ETV and pineal biopsy can be well demonstrated with this model.18
Throughout the simulated procedure, the trainee finds himself or herself in a fluid-filled environment, which is kept at the appropriate tension, increasing the realism and providing the appropriate visual-optical feedback.
As reflected by the comments of the both the senior and junior surgeons, the use of these models was in creating a realistic simulation of a neuroendoscopy procedure that allows safe and effective teaching of navigation and endoscopy in a standardized and repetitive fashion, which can be used as a valuable training and assessment tool. The presence of pathology such as enlarged ventricles and intraventricular tumor can enhance the usefulness of this tool.
The surgeons agreed that using this model, the trainee is able to learn all the necessary steps that are involved in an ETV and pineal tumor biopsy from creating a burr hole to navigating through the lateral ventricle into the third ventricle and finally fenestrating the floor of the third ventricle. They were particularly satisfied with the ability to demonstrate the nuances of endoscopy including the use of different angled scopes in various situations to improve visualization and facilitate biopsy as well as the possibility to “stop” and “clear” blood within the ventricle by irrigation.
The drawback of this model presently is the inability to reproduce cerebrospinal fluid pulsations or allow the use of electrocoagulation equipment. Finer anatomic structures including the vessels and the Liliequest membrane need to be better represented.
Although previous authors have alluded to the usefulness of models created using 3D printing technology for training, this is possibly the first time such models have been developed with preexisting pathology and an built-in fluid system to accurately mimic real-time intraventricular surgery.
To keep the entire training model cost-efficient, the models have a reusable base segment consisting of the portion of the face that is used for image guidance system registration purposes that can be reused and a disposable segment consisting of the ventricular portion that is discarded after a training session. The former portion presently costs US $3000, and the latter costs US $800. The basic process of endoscopy and biopsy can be performed multiple times bilaterally, but the process of performing a third ventriculostomy can only be performed once effectively on the disposable portion.
This simulated model fulfils all the criteria that we think are necessary to supplement and eventually play an important role in training future neurosurgeons in the art of neuroendoscopic surgery.
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