Development and Implementation of an Inexpensive, Easily Producible, Time Efficient External Ventricular Drain Simulator Using 3-Dimensional Printing and Image Registration

Development and Implementation of an Inexpensive, Easily Producible, Time Efficient External... Abstract BACKGROUND External ventricular drain (EVD) placement is one of the most commonly performed procedures in neurosurgery, frequently by the junior neurosurgery resident. Simulators for EVD placement are often costly, time-intensive to create, and complicated to set up. OBJECTIVE To describe creation of a simulator that is inexpensive, time-efficient, and simple to set up. METHODS This simulator involves printing a hollow head using a desktop 3-dimensional (3D) printer. This head is registered to a commercially available image-guidance system. A total of 11 participants volunteered for this simulation module. EVD placement was assessed at baseline, after verbal teaching, and after live 3D view instruction. RESULTS Accurate placement of an EVD on the right side at the foramen of Monro or the frontal horn of the lateral ventricle increased from 44% to 98% with training. Similarly, accurate placement on the left increased from 42% to 85% with training. CONCLUSION During participation in the simulation, accurate placement of EVDs increased significantly. All participants believed that they had a better understanding of ventricular anatomy and that this module would be useful as a teaching tool for neurosurgery interns. 3D printing, External ventricular drain, Image registration, Simulation ABBREVIATIONS ABBREVIATIONS CT computed tomography EVD external ventricular drain Insertion of an external ventricular drain (EVD) is one of the oldest and most commonly performed procedures in neurosurgery.1 It is frequently one of the first procedures that junior neurosurgery residents learn.2 Currently, at many institutions neurosurgery interns learn how to insert an EVD first by observation and then under direct senior resident supervision.3 Although the procedure may be life saving, incorrect placement may result in catastrophic consequences, including hemorrhage, paralysis, and death.4-7 Free-hand EVD placement does not always result in the EVD tip being at an ideal location. In 1 study, 10% were in the subarachnoid space and another 10% were in the brain parenchyma.8 Similarly, in another study, 22% of passes were in nonventricular spaces, and an average of 2 passes were required for successful placement.9 Additionally, junior residents may need to perform more passes for successful placement compared to senior residents.10 The additional number of passes may increase the risk for bleeding. Hemorrhage has been associated with up to 41% of EVD placements.4 Additional simulated practice with selection of EVD entrance location, trajectory, and depth may aid in junior resident understanding of anatomy and decrease the number of passes to successfully cannulate the ventricle. Simulators for EVD placement have been available for at least a decade.11 However, few are widely adopted. Challenges include cost, complexity in setup, and time needed for preparation. Three representative examples include systems that were used at the University of Illinois at Chicago, University of Michigan, and the University of Florida. The ImmersiveTouch system that the University of Illinois at Chicago uses involves virtual reality but costs about $75k.11,12 University of Michigan developed a sophisticated physical simulator replicating many of the physical steps in EVD placement.13 Specifically, it involves casting a plastic brain, connecting a water reservoir, and creating a multilayer disposable insert for the skull and skin. However, the time needed for setup and the complexity of manufacturing may hinder its adoption at other programs. Lastly, the innovative University of Florida simulator uses in-house developed software and hardware that may be difficult to transfer to other programs.14,15 In this paper, we describe an EVD simulation module that is very accessible with respect to cost, complexity in manufacturing, and preparation time. Our hypothesis is that hands-on practice with a 3-dimensional (3D) model and real-time verbal feedback will increase accuracy of EVD placement more than verbal instruction alone. METHODS We have developed a simulator that involves a hollow 3D printed head registered to an image-guidance workstation. We obtained Institutional Review Board approval. Creation of Hollow 3D Printed Head We obtained a computed tomography (CT) scan of a “normal” person's head from an online DICOM image library (OsiriX, Pixmeo, Bernex, Switzerland) in accordance with their permissions of use.16 The 2-dimensional DICOM images were converted to 3D STL form using InVesalius 3.0 (InVesalius, Information Technology Center Renato Archer, Amarais, Brazil). The images were then edited with respect to the selection of relevant anatomy using Meshmixer (Autodesk, San Rafael, California). We then used Cura (Ultimaker, Geldermalsen, Netherlands) to convert the edited STL file into a file our 3D printer could interpret. Parameters were selected that allowed for the creation of a hollow contoured 3D head with normal surface anatomy. All of the software that we used was free. The printer that we used is the MakerGear M2, which costs around $1500 (MakerGear, Beachwood, Ohio). The filament that is used is polylactic acid in white, $23/kg (Hatchbox, Pomona, California), which is biodegradable and derived from renewable resources. Each head requires approximately 225 g of filament, resulting in a cost of $5 per printed head. Setup and supervision of the printer take approximately 5 min. It takes 12 h for the printer to create a model head, a process that can be completed overnight without supervision. When the print is ready, an additional 5 min is required to remove excess supporting material. In summary, approximately 10 min of in-person time is required to produce each print (Figure 1). FIGURE 1. View largeDownload slide Printout of a hollow head using the MakerGear M2 printer. The computed tomography that the model was created from was obtained from an online DICOM image library.16 FIGURE 1. View largeDownload slide Printout of a hollow head using the MakerGear M2 printer. The computed tomography that the model was created from was obtained from an online DICOM image library.16 Simulation Setup Our institution uses the Medtronic Axiem StealthStation (Medtronic, Dublin, Ireland), which is one of the several commercially available systems. A subset of the downloaded DICOM files including only the head was selected and put on a USB thumb drive. The files were then loaded onto the system per the manufacturer's standard instructions. The probe, cannula, and radiofrequency (RF) button required for use were obtained from an abandoned ventriculoperitoneal shunt operation. Setup of the StealthStation generally followed the steps required for the setup of a ventriculoperitoneal shunt placement. Briefly, the RF button was taped on the left cheek of the 3D printed head. We then used the probe to trace the bridge of the nose, forehead, and top of the head to register the 3D printed head to the StealthStation. We took an EVD catheter and cut it at 10 cm. We slid it over the StealthStation cannula equipped with navigation sensors and glued it in place. Setup and registration of the StealthStation takes fewer than 15 min (Figure 2). According to prior literature involving a similar setup with a phantom, the accuracy of the Medtronic Axiem StealthStation system has a target localization error of 2.1 mm.17 FIGURE 2. View largeDownload slide Simulation setup using the Medtronic Axiem StealthStation. FIGURE 2. View largeDownload slide Simulation setup using the Medtronic Axiem StealthStation. Participant Recruitment and Instructions We believe this simulation would mostly benefit participants who lack adequate experience to insert an EVD independently but who are likely to be responsible for this procedure in the near future. We intend for this simulation to be used for neurosurgery interns at our institution prior to starting their neurosurgical rotation. For this reason, we recruited the 3 neurosurgery interns starting at our institution and 8 consecutive subinterns during the months of July and August 2017. We did not recruit more senior neurosurgery residents, as they were less likely to benefit from the experience. We also did not recruit medical students without a clear intention of pursuing neurosurgery, as we did not believe they would have adequate baseline knowledge of the procedure. Prior to starting the module, informed consent was obtained from each participant and a survey was completed regarding the participant's prior observations and experience with placement of EVDs. The module involved 5 sets of 5 EVD passes each. The first 3 sets involved the right side of the head, and the last 2 sets involved the left side of the patient's head. At no point during each recorded pass was the participant able to see the image-guidance screen. No verbal feedback was given during or between each set. The following are the 5 sets of trials. Right Side – Set 1: 5 attempts at baseline, prior to any instruction from neurosurgical instructor – Set 2: 5 attempts after verbal tutorial on EVD placement – Set 3: 5 attempts after hands-on practice using image-guidance with contemporaneous feedback by neurosurgical instructor Left Side – Set 4: 5 attempts after knowledge gained from placements on the right side – Set 5: 5 attempts after hands-on practice on the left side while using image-guidance with contemporaneous feedback by neurosurgical instructor Right Side Set 1: In the first set, the participant was instructed to insert a right-sided EVD based on what she previously knew about EVD insertion. The participant picked an entrance location on an unmarked head: the participant was given a marking pen and a ruler to pick a location consistent with her estimate of Kocher's point. A hole was then created at that location using a soldering iron to melt the plastic. Using the EVD catheter on the RF stylet, the participant was then asked to place the EVD based on a self-selected trajectory and depth for final EVD termination at the foramen of Monro. When the participant believed that the EVD placement was ideal, the guidance screen was frozen and a photograph was taken. Only the neurosurgical instructor running the simulation (not the participant) was able to view the guidance screen at any time during this or any other set. Insertion was then repeated 4 more times. The participant was allowed to change the entrance location. Verbal Tutorial: After Set 1, the participant was verbally taught a standard method of EVD insertion. This tutorial takes approximately 10 min. Set 2: After the verbal tutorial, the participant was instructed to repeat the same steps as in Set 1. A total of 5 passes were performed. Hands-on Practice on the Right: The participant was allowed to view the image-guidance screen and try various trajectories. The monitor showed coronal, sagittal, and axial views of the patient's CT angiogram. The participant was then given as long as she wanted to try different entrance locations, trajectories, and depths. During this time, the participant was given feedback and commentary regarding each trajectory. After she felt comfortable in her knowledge, the live image-guidance views were then turned away from the participant. Set 3: Prior to this set, the image-guidance screen was obscured from the participant. At no point during Set 3’s testing phase could the participant see the live view of the image-guidance screen. The participant then repeated the same steps as in Set 1. Left Side Set 4: The participant was instructed to perform 5 passes on the patient's left side. Set 4 involved picking an entrance location and trajectory based on what was learned during the previous exercises. Measurements to Kocher's point on the patient's left were made, and a new entrance location was created on the head's left side. The participants then repeated the same steps as in Set 1. Hands-on Practice on the Left: The participant was allowed to view the image-guidance screen and try various trajectories on the patient's left side. Set 5: The image-guidance screen was obscured from the participant. The participant then repeated the same steps as in Set 1. Statistical Analysis IBM SPSS version 23 (IBM SPSS Statistics for Macintosh, Version 23.0, IBM Inc, Armonk, New York) was used for statistical analysis. The Wilcoxon Signed Rank Test for Matched Pairs was used to analyze the outcomes of the different trials. Participant Survey After the simulation, participants completed a survey regarding their experience. The survey was created as a Google Form (Google, Mountain View, California), and participants could complete it anonymously: participants were texted a link to the form. Results were tabulated at the end of this study. The questions asked can be found in the appendix (Supplemental Digital Content). The survey sought to identify how well the simulator approximated procedures that the participant had observed on actual patients. It also asked participants how helpful they believed the simulation would be in teaching interns how to place EVDs. After the conclusion of the study, we contacted participants by email to ask about handedness. RESULTS We had a total of 11 consecutive participants taking part in the simulation: 3 neurosurgery interns and 8 medical students who rotated at our institution during the months of July and August 2017. All participants had seen an EVD placed before; 8 had observed EVD insertion between 1 and 5 times and 3 participants had observed EVD insertion between 6 and 25 times. No participant had placed an EVD independently before, and 3 participants had performed insertion with supervision from a neurosurgery resident. Ten of 11 participants responded to an email survey conducted after the simulation, all of whom stated they were right-handed. Based on notes taken during the simulation, all participants used their right hand to pass the EVD. Photographs of the navigation screen for each EVD pass were reviewed. They were separated into 3 categories: clearly in the frontal horn or at the foramen of Monro, in a ventricle but not clearly in the frontal horn or at the foramen of Monro, or not in any ventricle (Figure 3). Without training, 64% of passes were successful in contacting a ventricle and 36% were not. After the verbal tutorial, 49% were successful in contacting a ventricle and 51% were not. The P-value between these 2 trials was 0.20. The EVDs were placed closer to the foramen of Monro with respect to depth, but many deviated laterally and contacted structures like the basal ganglia, internal capsule, and thalamus. After hands-on practice, 98% of placements were in the frontal horn or at the foramen of Monro. The P-value between this set and after verbal tutorial was .017. FIGURE 3. View largeDownload slide Location of external ventricular drain (EVD) catheter tip when the participant placed the EVD on the patient's RIGHT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. In this chart, the red represents an EVD trajectory where the tip is not in a ventricle. Yellow is an EVD where tip is in a ventricle but not in the frontal horn or the foramen of Monro. Green is an EVD that is either in the frontal horn or at the foramen of Monro. FIGURE 3. View largeDownload slide Location of external ventricular drain (EVD) catheter tip when the participant placed the EVD on the patient's RIGHT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. In this chart, the red represents an EVD trajectory where the tip is not in a ventricle. Yellow is an EVD where tip is in a ventricle but not in the frontal horn or the foramen of Monro. Green is an EVD that is either in the frontal horn or at the foramen of Monro. For left-sided EVDs, on initial placement attempts, 47% were in the ventricle (Figure 4). With visual practice, 87% of left-sided EVD’s were then placed in the ventricle. The P-value between these 2 sets was .084. FIGURE 4. View largeDownload slide Location of EVD insertion when the participant placed the EVD on the patient's LEFT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. FIGURE 4. View largeDownload slide Location of EVD insertion when the participant placed the EVD on the patient's LEFT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. With respect to subjective feedback regarding the simulation, 8 of the 11 participants believed that the selection of entrance location was comparable to what they had witnessed while viewing an actual insertion on a patient. Three of the 11 believed that it was similar to the selection of an entrance location on a patient but lacked various features to make it realistic. These features may include the tactile feedback provided by the coronal suture. All participants felt that their understanding of anatomy needed to place an EVD increased, and all participants believed that this simulation module would be helpful to interns starting neurosurgery. Additional comments regarding the simulation include the fact that upon insertion of the EVD catheter, no sudden decrease in resistance could be felt upon entering the ventricle. Also, upon insertion the catheter could pivot with respect to the entrance location due to the inside of the head being hollow. DISCUSSION Participants in the simulation were either neurosurgery interns or subinterns. We chose this particular cohort, because we believed that the simulation module would be most helpful for those who did not have sufficient experience to place an EVD independently but were likely to be responsible for its insertion in the near future. Hands-on Simulator Experience Improves Accuracy of EVD Placement The proportion of successful EVD placements at baseline and after the verbal tutorial slightly decreased: 64% vs 49%, in contrast to our expectation that accuracy would increase. However the P-value between these 2 trials was 0.20, suggesting that the results were not statistically significant. In our opinion, this lack of improvement illustrates the insufficiency of verbal instruction alone in teaching safe and proper EVD insertion. One challenge is the ability of the instructor to impart 3D spatial awareness to the trainee. Verbal instruction alone, thus, led to more attempts that were close to the ventricle, along the long axis of the narrow ventricular corridor leading to the frontal horn but not actually into the ventricle. However, verbal instruction alone is frequently what most neurosurgery interns receive prior to their first EVD placement. In our study, the proportion of successful attempts after hands-on practice with image-guidance increased to 98%. This improvement highlights the role that simulator training may provide in improving safety, efficacy, and outcomes of patients. Left-sided EVD Placement also Benefits from Specific Hands-on Training With respect to left-sided EVDs, a large proportion initially deviated laterally and contacted the caudate, internal capsule, or basal ganglia. The 98% accuracy on the right side after training did not translate to the contralateral side, with only 47% of initial attempts resulting in successful placement. According to an email survey conducted after the study, 10/11 participants responded and all identified as right-handed. According to our notes, all of the participants passed the EVD with the right hand. Subjective observation during the experiment suggested that many participants underestimated the degree of right forearm pronation when placing an EVD on the left side with their right hand. After hands-on training, this proportion of successful passes increased to 87%. This again illustrates the benefit of practical simulator-based learning to gain the spatial anatomic orientation necessary for successful placement of EVDs. Specifically, the simulator aided with correcting the amount of forearm pronation needed for right-handed passes on the left side. One of the points of feedback involved the lack of tactile feedback during insertion of the EVD. Filling the head with material to make it solid and have a consistency similar to brain was investigated. One such material is the solidifier used in the operating room. However, these steps added too much complication and time for model production, and we felt that it did not substantially improve the participant experience. Another point of feedback is the inability to palpate the coronal suture to locate Kocher's point. This is an inherent limitation of creating a rigid, nondeformable plastic head. However, an artificial depression or ridge at the location of the coronal suture can be easily created on the model head using Meshmixer, the computer-aided design software mentioned earlier. Future directions involve creating simulations that distort the normal intracranial anatomy, such as subdural hematoma, intraparenchymal hemorrhage, and intraventricular hemorrhage. Additionally, we plan on investigating the impact of this simulation on the accuracy of our interns’ EVD placement. Lastly, we will incorporate this simulation into our EVD quality improvement protocol. One of our goals for this project is to provide guidance for an easily replicable simulator model that can be used across all neurosurgical training programs. There are 2 main steps for setup: loading the DICOM files onto the surgical navigation system and printing a hollow 3D head. Loading the DICOM files can be done with either a CD or USB containing the files, following standard procedures for an actual operation. The STL file for the hollow head can be shared electronically, to be printed at the local training program. Many institutions, similar to ours, have a 3D printing center, where 3D prints can be obtained by submission of a file. Alternatively, as discussed earlier, the materials for replicating this simulation in total cost less than $1600, with $1500 for the 3D printer. In addition to this specific simulation, we believe the investment in hardware will enable creation of additional neurosurgical simulations and anatomic models. Through contacting the authors, we can share both the DICOM files and the STL file electronically. CONCLUSION In conclusion, we have created an inexpensive, time-efficient, and easily disseminated EVD simulation module. Specifically, the production of the disposable simulation head costs approximately $5 and takes approximately 10 min of person-time to produce, after purchase of the 3D printer. We have shown that it is possible to register this head to a commercially available image-guidance system, already in use at neurosurgical programs. Our simulation results indicate that by practice, participants were able to improve accuracy of EVD placement. Feedback that we got from the participants was uniformly positive, and all participants believed that this simulation would be helpful as a teaching tool for interns. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. Notes Portions of this work were presented in oral presentation form at the Tennessee Neurosurgical Society 2017 Meeting in Nashville, Tennessee, August 12, 2017. REFERENCES 1 Srinivasan VM , O’Neill BR , Jho D , Whiting DM , Oh MY . The history of external ventricular drainage: historical vignette . J Neurosurg . 2014 ; 120 ( 1 ): 228 – 236 . Google Scholar CrossRef Search ADS PubMed 2 Sneldon NR , Origitano TC , Burchiel KJ et al. A national fundamentals curriculum for neurosurgery PGY1 residents: the 2010 Society of Neurological Surgeons boot camp courses . Neurosurgery . 2012 ; 70 ( 4 ): 971 – 981 . Google Scholar CrossRef Search ADS PubMed 3 Kalarka UK , Kim LJ , Chang SW , Theodore N , Spetzler RF . Safety and accuracy of bedside external ventricular drain placement . Neurosurgery . 2008 ; 63 ( 1 suppl 1 ): 162 – 166 . 4 Gardner PA , Engh J , Atteberry D , Moossy JJ . Hemorrhage rates after external ventricular drain placement . J Neurosurg . 2009 ; 110 ( 5 ): 1021 – 1025 . Google Scholar CrossRef Search ADS PubMed 5 Maniker AH , Vaynman AY , Karimi RJ , Sabit AO , Holland B . Hemorrhagic complications of external ventricular drainage . Neurosurgery . 2006 ; 59 ( 4 suppl 2 ): 419 – 424 . 6 Dasic D , Hanna SJ , Bojanic S , Kerr RS . External ventricular drain infection: the effect of a strict protocol on infection rates and a review of the literature . Br J Neurosurg . 2006 ; 20 ( 5 ): 296 – 300 . Google Scholar CrossRef Search ADS PubMed 7 Wong GK , Poon WS , Wai S , Yu LM , Lyon D , Lam JM . Failure of regular external ventricular drain exchange to reduce cerebrospinal fluid infection: result of a randomised clinical trial . J Neurol Neurosurg Psychiatry . 2002 ; 73 ( 6 ): 759 – 761 . Google Scholar CrossRef Search ADS PubMed 8 Toma AK , Camp S , Watkins LD , Grieve J , Kitchen ND . External ventricular drain insertion accuracy: is there a need for change in practice? Neurosurgery . 2009 ; 65 ( 6 ): 1197 – 1200 . Google Scholar CrossRef Search ADS PubMed 9 Huyette DR , Turnbow BJ , Kaufman C , Vaslow DF , Whiting BB , Oh MY . Accuracy of the freehand pass technique for ventriculostomy catheter placement: retrospective assessment using computed tomography scans . J Neurosurg . 2008 ; 108 ( 1 ): 88 – 91 . Google Scholar CrossRef Search ADS PubMed 10 O’Neill BR , Velez DA , Braxton EE , Whiting D , Oh MY . A survey of ventriculostomy and intracranial pressure monitor placement practices . Surg Neurol . 2008 ; 70 ( 3 ): 268 – 273 . Google Scholar CrossRef Search ADS PubMed 11 Banerjee PP , Luciano CJ , Lemole GM , Charbel FT , Oh MY . Accuracy of ventriculostomy catheter placement using a head- and hand-tracked high-resolution virtual reality simulator with haptic feedback . J Neurosurg . 2007 ; 107 ( 3 ): 515 – 521 . Google Scholar CrossRef Search ADS PubMed 12 Schirmer CM , Elder JB , Roitberg B , Lobel DA . Virtual reality-based simulation training for ventriculostomy: an evidence-based approach . Neurosurgery . 2013 ; 73 (s uppl 1 ): 66 – 73 Google Scholar CrossRef Search ADS PubMed 13 Tai BL , Rooney D , Stephenson F et al. Development of a 3D-printed external ventricular drain placement simulator: technical note . J Neurosurg . 2015 ; 123 ( 4 ): 1070 – 1076 Google Scholar CrossRef Search ADS PubMed 14 Hooten KG , Lister JR , Lombard G et al. Mixed reality ventriculostomy simulation: experience in neurosurgical residency . Neurosurgery . 2014 ; 10 ( suppl 4 ): 576 – 581 . Google Scholar CrossRef Search ADS PubMed 15 Bova FJ , Rajon DA , Friedman WA et al. Mixed-reality simulation for neurosurgical procedures . Neurosurgery . 2013 ; 73 ( Suppl 1 ): 138 – 145 . Google Scholar CrossRef Search ADS PubMed 16 Pixmeo. OsiriX DICOM Image Library. DICOM image sample sets. Available at: http://www.osirix-viewer.com/resources/dicom-image-library/ Accessed June 15, 2016 . 17 Rosenow JM , Sootsman WK . Application accuracy of an electromagnetic field-based image-guided navigation system . Stereotact Funct Neurosurg . 2007 ; 85 ( 2-3 ): 75 – 81 . Google Scholar CrossRef Search ADS PubMed Supplemental digital content is available for this article at www.operativeneurosurgery-online.com. Supplemental Digital Content. Appendix. Preparticipation and postparticipation surveys. COMMENT In almost all our residency training programs worldwide, junior residents learn how to tap the frontal or occipital horns of the lateral ventricles by trial and error, based on guidelines prescribed in neurosurgical textbooks. The investigators of this submission propose a simple and practical module which could be used by our residents on how to insert an intraventricular catheter for EVD or a shunt system in multiple settings such as trauma or elective neurosurgery when we know the ventricles are slit-like and hard to hit. Insertion of such a ventricular catheter blindly could end up in the thalamus, internal capsule, the other ventricle or basal cisterns predisposing to neurological deficit and intraparenchymal hemorrhage. Such complications are inherently dangerous and expensive. The technical design proposed in this submission is to convert 2-dimensional DICOM CT digital data into 3D digital data useable by a 3D printer. The printer will construct a hollow skull with invisible internal anatomy. In addition, the 3D printer digital data are fed into a Medtronic stealth navigation system. The practicing resident will observe the track of his/her IVC and its approach into the ventricular system on a stealth monitor. Eleven students or residents practiced using the system and had significant gain in their practical expertise in tapping the lateral ventricles without deviating into the corpus callosum, basal ganglia, internal capsule, or thalamus. If affordable, this system could be available in residency training programs so that junior residents might practice tapping the ventricular system before their neurotrauma rotation. For sure the module will reduce the complication rate of insertion of an intraventricular cannula for ventricular drainage in severe head injury. Alternatively, the practice is helpful in tapping the ventricular system in extreme conditions such as slit ventricle syndrome or pseudotumor. Bizhan Aarabi Baltimore, Maryland Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

Development and Implementation of an Inexpensive, Easily Producible, Time Efficient External Ventricular Drain Simulator Using 3-Dimensional Printing and Image Registration

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Oxford University Press
Copyright
Copyright © 2018 by the Congress of Neurological Surgeons
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2332-4252
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2332-4260
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10.1093/ons/opy142
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Abstract

Abstract BACKGROUND External ventricular drain (EVD) placement is one of the most commonly performed procedures in neurosurgery, frequently by the junior neurosurgery resident. Simulators for EVD placement are often costly, time-intensive to create, and complicated to set up. OBJECTIVE To describe creation of a simulator that is inexpensive, time-efficient, and simple to set up. METHODS This simulator involves printing a hollow head using a desktop 3-dimensional (3D) printer. This head is registered to a commercially available image-guidance system. A total of 11 participants volunteered for this simulation module. EVD placement was assessed at baseline, after verbal teaching, and after live 3D view instruction. RESULTS Accurate placement of an EVD on the right side at the foramen of Monro or the frontal horn of the lateral ventricle increased from 44% to 98% with training. Similarly, accurate placement on the left increased from 42% to 85% with training. CONCLUSION During participation in the simulation, accurate placement of EVDs increased significantly. All participants believed that they had a better understanding of ventricular anatomy and that this module would be useful as a teaching tool for neurosurgery interns. 3D printing, External ventricular drain, Image registration, Simulation ABBREVIATIONS ABBREVIATIONS CT computed tomography EVD external ventricular drain Insertion of an external ventricular drain (EVD) is one of the oldest and most commonly performed procedures in neurosurgery.1 It is frequently one of the first procedures that junior neurosurgery residents learn.2 Currently, at many institutions neurosurgery interns learn how to insert an EVD first by observation and then under direct senior resident supervision.3 Although the procedure may be life saving, incorrect placement may result in catastrophic consequences, including hemorrhage, paralysis, and death.4-7 Free-hand EVD placement does not always result in the EVD tip being at an ideal location. In 1 study, 10% were in the subarachnoid space and another 10% were in the brain parenchyma.8 Similarly, in another study, 22% of passes were in nonventricular spaces, and an average of 2 passes were required for successful placement.9 Additionally, junior residents may need to perform more passes for successful placement compared to senior residents.10 The additional number of passes may increase the risk for bleeding. Hemorrhage has been associated with up to 41% of EVD placements.4 Additional simulated practice with selection of EVD entrance location, trajectory, and depth may aid in junior resident understanding of anatomy and decrease the number of passes to successfully cannulate the ventricle. Simulators for EVD placement have been available for at least a decade.11 However, few are widely adopted. Challenges include cost, complexity in setup, and time needed for preparation. Three representative examples include systems that were used at the University of Illinois at Chicago, University of Michigan, and the University of Florida. The ImmersiveTouch system that the University of Illinois at Chicago uses involves virtual reality but costs about $75k.11,12 University of Michigan developed a sophisticated physical simulator replicating many of the physical steps in EVD placement.13 Specifically, it involves casting a plastic brain, connecting a water reservoir, and creating a multilayer disposable insert for the skull and skin. However, the time needed for setup and the complexity of manufacturing may hinder its adoption at other programs. Lastly, the innovative University of Florida simulator uses in-house developed software and hardware that may be difficult to transfer to other programs.14,15 In this paper, we describe an EVD simulation module that is very accessible with respect to cost, complexity in manufacturing, and preparation time. Our hypothesis is that hands-on practice with a 3-dimensional (3D) model and real-time verbal feedback will increase accuracy of EVD placement more than verbal instruction alone. METHODS We have developed a simulator that involves a hollow 3D printed head registered to an image-guidance workstation. We obtained Institutional Review Board approval. Creation of Hollow 3D Printed Head We obtained a computed tomography (CT) scan of a “normal” person's head from an online DICOM image library (OsiriX, Pixmeo, Bernex, Switzerland) in accordance with their permissions of use.16 The 2-dimensional DICOM images were converted to 3D STL form using InVesalius 3.0 (InVesalius, Information Technology Center Renato Archer, Amarais, Brazil). The images were then edited with respect to the selection of relevant anatomy using Meshmixer (Autodesk, San Rafael, California). We then used Cura (Ultimaker, Geldermalsen, Netherlands) to convert the edited STL file into a file our 3D printer could interpret. Parameters were selected that allowed for the creation of a hollow contoured 3D head with normal surface anatomy. All of the software that we used was free. The printer that we used is the MakerGear M2, which costs around $1500 (MakerGear, Beachwood, Ohio). The filament that is used is polylactic acid in white, $23/kg (Hatchbox, Pomona, California), which is biodegradable and derived from renewable resources. Each head requires approximately 225 g of filament, resulting in a cost of $5 per printed head. Setup and supervision of the printer take approximately 5 min. It takes 12 h for the printer to create a model head, a process that can be completed overnight without supervision. When the print is ready, an additional 5 min is required to remove excess supporting material. In summary, approximately 10 min of in-person time is required to produce each print (Figure 1). FIGURE 1. View largeDownload slide Printout of a hollow head using the MakerGear M2 printer. The computed tomography that the model was created from was obtained from an online DICOM image library.16 FIGURE 1. View largeDownload slide Printout of a hollow head using the MakerGear M2 printer. The computed tomography that the model was created from was obtained from an online DICOM image library.16 Simulation Setup Our institution uses the Medtronic Axiem StealthStation (Medtronic, Dublin, Ireland), which is one of the several commercially available systems. A subset of the downloaded DICOM files including only the head was selected and put on a USB thumb drive. The files were then loaded onto the system per the manufacturer's standard instructions. The probe, cannula, and radiofrequency (RF) button required for use were obtained from an abandoned ventriculoperitoneal shunt operation. Setup of the StealthStation generally followed the steps required for the setup of a ventriculoperitoneal shunt placement. Briefly, the RF button was taped on the left cheek of the 3D printed head. We then used the probe to trace the bridge of the nose, forehead, and top of the head to register the 3D printed head to the StealthStation. We took an EVD catheter and cut it at 10 cm. We slid it over the StealthStation cannula equipped with navigation sensors and glued it in place. Setup and registration of the StealthStation takes fewer than 15 min (Figure 2). According to prior literature involving a similar setup with a phantom, the accuracy of the Medtronic Axiem StealthStation system has a target localization error of 2.1 mm.17 FIGURE 2. View largeDownload slide Simulation setup using the Medtronic Axiem StealthStation. FIGURE 2. View largeDownload slide Simulation setup using the Medtronic Axiem StealthStation. Participant Recruitment and Instructions We believe this simulation would mostly benefit participants who lack adequate experience to insert an EVD independently but who are likely to be responsible for this procedure in the near future. We intend for this simulation to be used for neurosurgery interns at our institution prior to starting their neurosurgical rotation. For this reason, we recruited the 3 neurosurgery interns starting at our institution and 8 consecutive subinterns during the months of July and August 2017. We did not recruit more senior neurosurgery residents, as they were less likely to benefit from the experience. We also did not recruit medical students without a clear intention of pursuing neurosurgery, as we did not believe they would have adequate baseline knowledge of the procedure. Prior to starting the module, informed consent was obtained from each participant and a survey was completed regarding the participant's prior observations and experience with placement of EVDs. The module involved 5 sets of 5 EVD passes each. The first 3 sets involved the right side of the head, and the last 2 sets involved the left side of the patient's head. At no point during each recorded pass was the participant able to see the image-guidance screen. No verbal feedback was given during or between each set. The following are the 5 sets of trials. Right Side – Set 1: 5 attempts at baseline, prior to any instruction from neurosurgical instructor – Set 2: 5 attempts after verbal tutorial on EVD placement – Set 3: 5 attempts after hands-on practice using image-guidance with contemporaneous feedback by neurosurgical instructor Left Side – Set 4: 5 attempts after knowledge gained from placements on the right side – Set 5: 5 attempts after hands-on practice on the left side while using image-guidance with contemporaneous feedback by neurosurgical instructor Right Side Set 1: In the first set, the participant was instructed to insert a right-sided EVD based on what she previously knew about EVD insertion. The participant picked an entrance location on an unmarked head: the participant was given a marking pen and a ruler to pick a location consistent with her estimate of Kocher's point. A hole was then created at that location using a soldering iron to melt the plastic. Using the EVD catheter on the RF stylet, the participant was then asked to place the EVD based on a self-selected trajectory and depth for final EVD termination at the foramen of Monro. When the participant believed that the EVD placement was ideal, the guidance screen was frozen and a photograph was taken. Only the neurosurgical instructor running the simulation (not the participant) was able to view the guidance screen at any time during this or any other set. Insertion was then repeated 4 more times. The participant was allowed to change the entrance location. Verbal Tutorial: After Set 1, the participant was verbally taught a standard method of EVD insertion. This tutorial takes approximately 10 min. Set 2: After the verbal tutorial, the participant was instructed to repeat the same steps as in Set 1. A total of 5 passes were performed. Hands-on Practice on the Right: The participant was allowed to view the image-guidance screen and try various trajectories. The monitor showed coronal, sagittal, and axial views of the patient's CT angiogram. The participant was then given as long as she wanted to try different entrance locations, trajectories, and depths. During this time, the participant was given feedback and commentary regarding each trajectory. After she felt comfortable in her knowledge, the live image-guidance views were then turned away from the participant. Set 3: Prior to this set, the image-guidance screen was obscured from the participant. At no point during Set 3’s testing phase could the participant see the live view of the image-guidance screen. The participant then repeated the same steps as in Set 1. Left Side Set 4: The participant was instructed to perform 5 passes on the patient's left side. Set 4 involved picking an entrance location and trajectory based on what was learned during the previous exercises. Measurements to Kocher's point on the patient's left were made, and a new entrance location was created on the head's left side. The participants then repeated the same steps as in Set 1. Hands-on Practice on the Left: The participant was allowed to view the image-guidance screen and try various trajectories on the patient's left side. Set 5: The image-guidance screen was obscured from the participant. The participant then repeated the same steps as in Set 1. Statistical Analysis IBM SPSS version 23 (IBM SPSS Statistics for Macintosh, Version 23.0, IBM Inc, Armonk, New York) was used for statistical analysis. The Wilcoxon Signed Rank Test for Matched Pairs was used to analyze the outcomes of the different trials. Participant Survey After the simulation, participants completed a survey regarding their experience. The survey was created as a Google Form (Google, Mountain View, California), and participants could complete it anonymously: participants were texted a link to the form. Results were tabulated at the end of this study. The questions asked can be found in the appendix (Supplemental Digital Content). The survey sought to identify how well the simulator approximated procedures that the participant had observed on actual patients. It also asked participants how helpful they believed the simulation would be in teaching interns how to place EVDs. After the conclusion of the study, we contacted participants by email to ask about handedness. RESULTS We had a total of 11 consecutive participants taking part in the simulation: 3 neurosurgery interns and 8 medical students who rotated at our institution during the months of July and August 2017. All participants had seen an EVD placed before; 8 had observed EVD insertion between 1 and 5 times and 3 participants had observed EVD insertion between 6 and 25 times. No participant had placed an EVD independently before, and 3 participants had performed insertion with supervision from a neurosurgery resident. Ten of 11 participants responded to an email survey conducted after the simulation, all of whom stated they were right-handed. Based on notes taken during the simulation, all participants used their right hand to pass the EVD. Photographs of the navigation screen for each EVD pass were reviewed. They were separated into 3 categories: clearly in the frontal horn or at the foramen of Monro, in a ventricle but not clearly in the frontal horn or at the foramen of Monro, or not in any ventricle (Figure 3). Without training, 64% of passes were successful in contacting a ventricle and 36% were not. After the verbal tutorial, 49% were successful in contacting a ventricle and 51% were not. The P-value between these 2 trials was 0.20. The EVDs were placed closer to the foramen of Monro with respect to depth, but many deviated laterally and contacted structures like the basal ganglia, internal capsule, and thalamus. After hands-on practice, 98% of placements were in the frontal horn or at the foramen of Monro. The P-value between this set and after verbal tutorial was .017. FIGURE 3. View largeDownload slide Location of external ventricular drain (EVD) catheter tip when the participant placed the EVD on the patient's RIGHT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. In this chart, the red represents an EVD trajectory where the tip is not in a ventricle. Yellow is an EVD where tip is in a ventricle but not in the frontal horn or the foramen of Monro. Green is an EVD that is either in the frontal horn or at the foramen of Monro. FIGURE 3. View largeDownload slide Location of external ventricular drain (EVD) catheter tip when the participant placed the EVD on the patient's RIGHT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. In this chart, the red represents an EVD trajectory where the tip is not in a ventricle. Yellow is an EVD where tip is in a ventricle but not in the frontal horn or the foramen of Monro. Green is an EVD that is either in the frontal horn or at the foramen of Monro. For left-sided EVDs, on initial placement attempts, 47% were in the ventricle (Figure 4). With visual practice, 87% of left-sided EVD’s were then placed in the ventricle. The P-value between these 2 sets was .084. FIGURE 4. View largeDownload slide Location of EVD insertion when the participant placed the EVD on the patient's LEFT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. FIGURE 4. View largeDownload slide Location of EVD insertion when the participant placed the EVD on the patient's LEFT. The numbers in the bars are a count of the number of times that event happened. A total of 55 insertions were performed for each set. With respect to subjective feedback regarding the simulation, 8 of the 11 participants believed that the selection of entrance location was comparable to what they had witnessed while viewing an actual insertion on a patient. Three of the 11 believed that it was similar to the selection of an entrance location on a patient but lacked various features to make it realistic. These features may include the tactile feedback provided by the coronal suture. All participants felt that their understanding of anatomy needed to place an EVD increased, and all participants believed that this simulation module would be helpful to interns starting neurosurgery. Additional comments regarding the simulation include the fact that upon insertion of the EVD catheter, no sudden decrease in resistance could be felt upon entering the ventricle. Also, upon insertion the catheter could pivot with respect to the entrance location due to the inside of the head being hollow. DISCUSSION Participants in the simulation were either neurosurgery interns or subinterns. We chose this particular cohort, because we believed that the simulation module would be most helpful for those who did not have sufficient experience to place an EVD independently but were likely to be responsible for its insertion in the near future. Hands-on Simulator Experience Improves Accuracy of EVD Placement The proportion of successful EVD placements at baseline and after the verbal tutorial slightly decreased: 64% vs 49%, in contrast to our expectation that accuracy would increase. However the P-value between these 2 trials was 0.20, suggesting that the results were not statistically significant. In our opinion, this lack of improvement illustrates the insufficiency of verbal instruction alone in teaching safe and proper EVD insertion. One challenge is the ability of the instructor to impart 3D spatial awareness to the trainee. Verbal instruction alone, thus, led to more attempts that were close to the ventricle, along the long axis of the narrow ventricular corridor leading to the frontal horn but not actually into the ventricle. However, verbal instruction alone is frequently what most neurosurgery interns receive prior to their first EVD placement. In our study, the proportion of successful attempts after hands-on practice with image-guidance increased to 98%. This improvement highlights the role that simulator training may provide in improving safety, efficacy, and outcomes of patients. Left-sided EVD Placement also Benefits from Specific Hands-on Training With respect to left-sided EVDs, a large proportion initially deviated laterally and contacted the caudate, internal capsule, or basal ganglia. The 98% accuracy on the right side after training did not translate to the contralateral side, with only 47% of initial attempts resulting in successful placement. According to an email survey conducted after the study, 10/11 participants responded and all identified as right-handed. According to our notes, all of the participants passed the EVD with the right hand. Subjective observation during the experiment suggested that many participants underestimated the degree of right forearm pronation when placing an EVD on the left side with their right hand. After hands-on training, this proportion of successful passes increased to 87%. This again illustrates the benefit of practical simulator-based learning to gain the spatial anatomic orientation necessary for successful placement of EVDs. Specifically, the simulator aided with correcting the amount of forearm pronation needed for right-handed passes on the left side. One of the points of feedback involved the lack of tactile feedback during insertion of the EVD. Filling the head with material to make it solid and have a consistency similar to brain was investigated. One such material is the solidifier used in the operating room. However, these steps added too much complication and time for model production, and we felt that it did not substantially improve the participant experience. Another point of feedback is the inability to palpate the coronal suture to locate Kocher's point. This is an inherent limitation of creating a rigid, nondeformable plastic head. However, an artificial depression or ridge at the location of the coronal suture can be easily created on the model head using Meshmixer, the computer-aided design software mentioned earlier. Future directions involve creating simulations that distort the normal intracranial anatomy, such as subdural hematoma, intraparenchymal hemorrhage, and intraventricular hemorrhage. Additionally, we plan on investigating the impact of this simulation on the accuracy of our interns’ EVD placement. Lastly, we will incorporate this simulation into our EVD quality improvement protocol. One of our goals for this project is to provide guidance for an easily replicable simulator model that can be used across all neurosurgical training programs. There are 2 main steps for setup: loading the DICOM files onto the surgical navigation system and printing a hollow 3D head. Loading the DICOM files can be done with either a CD or USB containing the files, following standard procedures for an actual operation. The STL file for the hollow head can be shared electronically, to be printed at the local training program. Many institutions, similar to ours, have a 3D printing center, where 3D prints can be obtained by submission of a file. Alternatively, as discussed earlier, the materials for replicating this simulation in total cost less than $1600, with $1500 for the 3D printer. In addition to this specific simulation, we believe the investment in hardware will enable creation of additional neurosurgical simulations and anatomic models. Through contacting the authors, we can share both the DICOM files and the STL file electronically. CONCLUSION In conclusion, we have created an inexpensive, time-efficient, and easily disseminated EVD simulation module. Specifically, the production of the disposable simulation head costs approximately $5 and takes approximately 10 min of person-time to produce, after purchase of the 3D printer. We have shown that it is possible to register this head to a commercially available image-guidance system, already in use at neurosurgical programs. Our simulation results indicate that by practice, participants were able to improve accuracy of EVD placement. Feedback that we got from the participants was uniformly positive, and all participants believed that this simulation would be helpful as a teaching tool for interns. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. Notes Portions of this work were presented in oral presentation form at the Tennessee Neurosurgical Society 2017 Meeting in Nashville, Tennessee, August 12, 2017. REFERENCES 1 Srinivasan VM , O’Neill BR , Jho D , Whiting DM , Oh MY . The history of external ventricular drainage: historical vignette . J Neurosurg . 2014 ; 120 ( 1 ): 228 – 236 . Google Scholar CrossRef Search ADS PubMed 2 Sneldon NR , Origitano TC , Burchiel KJ et al. A national fundamentals curriculum for neurosurgery PGY1 residents: the 2010 Society of Neurological Surgeons boot camp courses . Neurosurgery . 2012 ; 70 ( 4 ): 971 – 981 . Google Scholar CrossRef Search ADS PubMed 3 Kalarka UK , Kim LJ , Chang SW , Theodore N , Spetzler RF . Safety and accuracy of bedside external ventricular drain placement . Neurosurgery . 2008 ; 63 ( 1 suppl 1 ): 162 – 166 . 4 Gardner PA , Engh J , Atteberry D , Moossy JJ . Hemorrhage rates after external ventricular drain placement . J Neurosurg . 2009 ; 110 ( 5 ): 1021 – 1025 . Google Scholar CrossRef Search ADS PubMed 5 Maniker AH , Vaynman AY , Karimi RJ , Sabit AO , Holland B . Hemorrhagic complications of external ventricular drainage . Neurosurgery . 2006 ; 59 ( 4 suppl 2 ): 419 – 424 . 6 Dasic D , Hanna SJ , Bojanic S , Kerr RS . External ventricular drain infection: the effect of a strict protocol on infection rates and a review of the literature . Br J Neurosurg . 2006 ; 20 ( 5 ): 296 – 300 . Google Scholar CrossRef Search ADS PubMed 7 Wong GK , Poon WS , Wai S , Yu LM , Lyon D , Lam JM . Failure of regular external ventricular drain exchange to reduce cerebrospinal fluid infection: result of a randomised clinical trial . J Neurol Neurosurg Psychiatry . 2002 ; 73 ( 6 ): 759 – 761 . Google Scholar CrossRef Search ADS PubMed 8 Toma AK , Camp S , Watkins LD , Grieve J , Kitchen ND . External ventricular drain insertion accuracy: is there a need for change in practice? Neurosurgery . 2009 ; 65 ( 6 ): 1197 – 1200 . Google Scholar CrossRef Search ADS PubMed 9 Huyette DR , Turnbow BJ , Kaufman C , Vaslow DF , Whiting BB , Oh MY . Accuracy of the freehand pass technique for ventriculostomy catheter placement: retrospective assessment using computed tomography scans . J Neurosurg . 2008 ; 108 ( 1 ): 88 – 91 . Google Scholar CrossRef Search ADS PubMed 10 O’Neill BR , Velez DA , Braxton EE , Whiting D , Oh MY . A survey of ventriculostomy and intracranial pressure monitor placement practices . Surg Neurol . 2008 ; 70 ( 3 ): 268 – 273 . Google Scholar CrossRef Search ADS PubMed 11 Banerjee PP , Luciano CJ , Lemole GM , Charbel FT , Oh MY . Accuracy of ventriculostomy catheter placement using a head- and hand-tracked high-resolution virtual reality simulator with haptic feedback . J Neurosurg . 2007 ; 107 ( 3 ): 515 – 521 . Google Scholar CrossRef Search ADS PubMed 12 Schirmer CM , Elder JB , Roitberg B , Lobel DA . Virtual reality-based simulation training for ventriculostomy: an evidence-based approach . Neurosurgery . 2013 ; 73 (s uppl 1 ): 66 – 73 Google Scholar CrossRef Search ADS PubMed 13 Tai BL , Rooney D , Stephenson F et al. Development of a 3D-printed external ventricular drain placement simulator: technical note . J Neurosurg . 2015 ; 123 ( 4 ): 1070 – 1076 Google Scholar CrossRef Search ADS PubMed 14 Hooten KG , Lister JR , Lombard G et al. Mixed reality ventriculostomy simulation: experience in neurosurgical residency . Neurosurgery . 2014 ; 10 ( suppl 4 ): 576 – 581 . Google Scholar CrossRef Search ADS PubMed 15 Bova FJ , Rajon DA , Friedman WA et al. Mixed-reality simulation for neurosurgical procedures . Neurosurgery . 2013 ; 73 ( Suppl 1 ): 138 – 145 . Google Scholar CrossRef Search ADS PubMed 16 Pixmeo. OsiriX DICOM Image Library. DICOM image sample sets. Available at: http://www.osirix-viewer.com/resources/dicom-image-library/ Accessed June 15, 2016 . 17 Rosenow JM , Sootsman WK . Application accuracy of an electromagnetic field-based image-guided navigation system . Stereotact Funct Neurosurg . 2007 ; 85 ( 2-3 ): 75 – 81 . Google Scholar CrossRef Search ADS PubMed Supplemental digital content is available for this article at www.operativeneurosurgery-online.com. Supplemental Digital Content. Appendix. Preparticipation and postparticipation surveys. COMMENT In almost all our residency training programs worldwide, junior residents learn how to tap the frontal or occipital horns of the lateral ventricles by trial and error, based on guidelines prescribed in neurosurgical textbooks. The investigators of this submission propose a simple and practical module which could be used by our residents on how to insert an intraventricular catheter for EVD or a shunt system in multiple settings such as trauma or elective neurosurgery when we know the ventricles are slit-like and hard to hit. Insertion of such a ventricular catheter blindly could end up in the thalamus, internal capsule, the other ventricle or basal cisterns predisposing to neurological deficit and intraparenchymal hemorrhage. Such complications are inherently dangerous and expensive. The technical design proposed in this submission is to convert 2-dimensional DICOM CT digital data into 3D digital data useable by a 3D printer. The printer will construct a hollow skull with invisible internal anatomy. In addition, the 3D printer digital data are fed into a Medtronic stealth navigation system. The practicing resident will observe the track of his/her IVC and its approach into the ventricular system on a stealth monitor. Eleven students or residents practiced using the system and had significant gain in their practical expertise in tapping the lateral ventricles without deviating into the corpus callosum, basal ganglia, internal capsule, or thalamus. If affordable, this system could be available in residency training programs so that junior residents might practice tapping the ventricular system before their neurotrauma rotation. For sure the module will reduce the complication rate of insertion of an intraventricular cannula for ventricular drainage in severe head injury. Alternatively, the practice is helpful in tapping the ventricular system in extreme conditions such as slit ventricle syndrome or pseudotumor. Bizhan Aarabi Baltimore, Maryland Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Operative NeurosurgeryOxford University Press

Published: Jun 5, 2018

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