Abstract
Objective:
The pediatric skull base may present anatomic challenges to the skull base surgeon including limited sphenoid pneumatization and a narrow nasal corridor. The rare nature of pediatric skull base pathology makes it difficult to gain experience with these anatomic challenges. The objective of this study was to create a 3D printed model of the pediatric skull base and assess its potential as a training tool.
Methods:
28 participants at various stages of training and practice were included in our study. They completed a pre- and post-dissection questionnaire assessing challenges with endoscopic endonasal skeletonization of the carotid arteries and sella face using the 3D printed model.
Results:
The majority of participants had completed a skull base surgery fellowship (60.7%), were <5 years into practice (60.7%), and had < 10 cases of pediatric skull base experience (82.1%). Anticipated challenges included limitation of maneuverability of instruments (71.4%), narrow nasal corridor and non-pneumatized bone (57.1%). On a scale of 0 to 10, 10 being very difficult, the average participant expected level of difficulty with visualization was 6.89 and expected level of difficulty with instrumentation was 7.3. On post-dissection assessment, there was a non-statistically significant change to 6.93 and 7.5, respectively. Participants endorsed on a scale of 0 to 10, 10 being very realistic an overall model realism of 7.0 and haptic realism of 7.1.
Conclusions:
A 3D printed model of the pediatric skull base may provide a realistic model to help participants gain experience with anatomic limitations characteristic of the pediatric anterior skull base.
Keywords: Pediatric skull base, simulation, 3D printed model
Introduction
Expanded endonasal approaches (EEA) to the skull base have been rapidly developing over the last two decades1. These approaches allow minimally-invasive access to complex anatomic subsites with high resolution for the dissection and manipulation for skull base tumors, replacing traditional open approaches. With the rapid growth in this field, there is a need for simulations to provide a platform for young trainees to gain experience in endoscopic skills.
Anatomic challenges for EEA to the skull base are particularly apparent in young children2–3. This may include limited sphenoid pneumatization, making it difficult to identify the sella and critical neurovascular structures such as the optic nerves and carotid arteries. A narrow pyriform aperture and/or small nasal cavities can also limit maneuverability4. Furthermore, pathology of the pediatric skull base is rare, which can decrease learning opportunities to become familiar with these anatomic challenges2,5–6. Therefore, models to practice these techniques may aid in improving one’s comfort level and skill as it relates to EEA to the pediatric skull base.
Utilization of skull base models has become increasingly popular to train skull base surgeons in challenging techniques or situations in endonasal skull base surgery7–9. With the advent and increased accessibility to 3D printing, the use of laser sintered technology has been increasingly applied to training, pre-operative planning, and reconstruction of the skull base10–12. Multiple advantages of 3D printing include reproducibility, ease of accessibility, and cost-effectiveness. The goal of this study was to create a 3D printed model of the pediatric skull base and assess its potential as a training tool.
Materials and methods
Model Development
Digital Imaging and Communications in Medicine (DICOM) images from a de-identified, high-resolution CT scan from a pediatric patient with a craniopharyngioma were used to segment the pediatric sinonasal and skull base anatomy, including bones, carotid artery (pharyngeal to supraclinoid), optic nerves and chiasm, and pituitary gland in a 3D modeling software (Figure 1) (Materialise Mimics Software, Materialise; Plymouth, Michigan). Once fully segmented, the images were built into a 3D rendered skull base, including the above-mentioned anatomy. The Materialise 3-Matic software was then used to refine the model, smoothing the carotid, optic nerves, and pituitary gland as needed, and subtracting any overlap between the skull and the rest of the anatomy. As the model was initially generated from a patient with craniopharyngioma, the anatomy was slightly modified towards native anatomy as our intent was to generate a basic skills training simulator. The anatomic fidelity of the model was then verified with an expert otolaryngologist.
Figure 1.
Segmentation and design of the model
To manufacture the models, each part was assigned a different color: the bone was beige, the orbital cavity was dark yellow, the optic nerves and chiasm were light yellow, the carotid arteries were red, and the pituitary gland was pink. The complete assembly of the model was sent to 3D Systems On Demand Rapid Prototyping services (3D Systems, Rock Hill, SC) to be printed using the ColorJet Printing (CJP) process in VisiJet PXL material coated with ColorBond for color, and costs approximately $63 per model. This material was chosen for its bone-like drilling properties, with the color for easier visualization and identification of anatomical landmarks. VisiJet PXL core powder is primarily composed of calcium sulfate hemihydrate, which is closely related to plaster of Paris. Using various additives or epoxy in the binding resin, the material, when printed, can display vivid colors while retaining physical properties (flexural modulus and tensile strength) that begin to approximate human bone.
Study Population
Twenty-nine otolaryngologists and neurosurgeons at various stages of training and practice were invited to participate. This group included those participating in a skull base hands-on course and institutional trainees. Participants were asked to utilize endoscopic endonasal techniques and instrumentation to skeletonize the carotid arteries and sella of a non-pneumatized 3D printed pediatric skull base model. Each participant was given a new, identical 3D printed model for individual drilling. Subjects were asked to complete pre- and post-dissection questionnaires. 96.6% of participants completed both pre and post-dissection surveys. One participant did not submit a post-dissection survey and was thus excluded from the study.
Questionnaires
The pre-dissection questionnaire was designed to collect demographic information such as age range, specialty, highest level of training, years in practice and proportion of skull base surgery in that practice, as well as the participants experience with pediatric skull base surgery. Study subjects were also asked to identify challenges they expected with the model as well as the level of difficulty with visualization and instrumentation and expected time to complete carotid artery and sella skeletonization. After completion of the dissection, participants were asked to assess the realism of the model, level of difficulty with visualization, and level of difficulty with instrumentation on a scale of 0 to 10. Participants were asked to assess challenges with accessing the pediatric skull base, the actual time to skeletonize the carotids and sella, and their comfort level with the pediatric skull base corridor.
Statistics
A T test with two-tailed distribution was used to compare quantitative data as indicated, and a P < 0.05 was considered to be statistically significant.
Results
Pediatric skull base model generation and participant demographics
Models of a poorly pneumatized pediatric skull base model were created with a 3D printer and participants completed a pre-dissection questionnaire prior to carotid and sella skeletonization (Figures 2–5). Of the 28 subjects who completed the pre-dissection questionnaire and individually performed the dissection of the model, 10 identified as otolaryngologists, 17 as neurosurgeons, and 1 unspecified (Table 1). The majority of the participants were between the age of 18-35 (35.7%) and 36-45 (50.0%) with the highest level of training as fellowship (78.6%) or residency (17.9%) (Table 1). The majority of participants identified as <5 years in practice (60.7%) or between 5-10 years in practice (17.9%). Furthermore, the majority reported their current practice as <10% skull base surgery (50.0%) or between 10-50% skull base surgery (39.3%) (Table 1). In regards to pediatric patients, 71.4% of participants reported <10% of their practice with pediatric patients while 17.9% report 10-50% of their practice with pediatric skull base surgery. Respondents reported fewer than 10 pediatric cases in 82.1% of participants and between 11-50 cases in 17.9% (Table 1).
Figure 2.
Anterior view of 3D printed pediatric skull base model
Figure 5.
Endonasal view of 3D printed pediatric skull base model after drilling. Red stars – carotid arteries, long arrows – optic nerves, short arrows – pituitary gland
Table 1.
Study participant demographics
| Participant age | |
| 18-35 | 10 (35.7%) |
| 36-45 | 14 (50.0%) |
| 46-56 | 2 (7.1%) |
| >56 | 2 (7.1%) |
| Specialty | |
| Otolaryngology | 10 (35.7%) |
| Neurosurgery | 17 (60.7%) |
| Not specified | 1 (3.6%) |
| Highest level of training completed | |
| Medical school | 1 (3.6%) |
| Residency | 5 (17.9%) |
| Fellowship | 22 (78.6%) |
| Completion of a skull base fellowship | |
| Yes | 17 (60.7%) |
| No | 11 (39.3%) |
| Years in practice | |
| <5 | 17 (60.7%) |
| 5-10 | 5 (17.9%) |
| 10-15 | 4 (14.3%) |
| >15 | 2 (7.1%) |
| % of skull base surgery in your practice | |
| <10% | 14 (50.0%) |
| 10-50% | 11 (39.3%) |
| 51-75% | 2 (7.1%) |
| >75% | 1 (3.6%) |
| % of pediatric patients in your practice | |
| <10% | 20 (71.4%) |
| 10-50% | 5 (17.9%) |
| 51-75% | 0 (0%) |
| >75% | 3 (10.7%) |
| Experience with pediatric skull base surgery | |
| <10 cases | 23 (82.1%) |
| 11-50 | 5 (17.9%) |
| 51-100 | 0 (0%) |
| >100 | 0 (0%) |
Pre-dissection anticipated challenges
As part of the pre-dissection questionnaire, participants were also queried regarding anticipated challenges with accessing the pediatric skull base. Of these, limitations with maneuverability of instruments was the most commonly endorsed challenge (71.4%), followed by a narrow nasal corridor and non-pneumatized bone (57.1%), and limitation of visualization (53.6%) (Table 2). On a scale of 0 to 10, 0 being very simple and 10 being very difficult, the average expected level of difficulty with visualization was 6.89 and expected level of difficulty with instrumentation was 7.3 (Table 2). The average pre-dissection comfort level with the pediatric corridor was 6.0. The expected time to skeletonize the carotids and face of the sella was >40 minutes (39.3%) or 20-40 minutes (42.9%) (Table 2).
Table 2.
Pre-dissection anticipated challenges and expected levels of difficulty compared to post-dissection encountered challenges
| Anticipated | Encountered | |
|---|---|---|
| Challenges with accessing the pediatric skull base | ||
| Limitation of visualization | 15 (53.6%) | 16 (57.1%) |
| Limitation of maneuverability of instruments | 20 (71.4%) | 18 (64.3%) |
| Narrow nasal corridor | 16 (57.1%) | 18 (64.3%) |
| Narrow intercarotid distance | 14 (50.0%) | 11 (39.3%) |
| Non-pneumatized bone | 16 (57.1%) | 14 (50.0%) |
| Level of difficulty with visualization | 6.89 ± 1.69 (range 4-10) | 6.93 ± 2.36 (range 2-10) |
| 0 (very simple) – 10 (very difficult) | ||
| Level of difficulty with instrumentation | 7.3 ± 1.86 (range 4-10) | 7.5 ± 2.41 (range 2-10) |
| 0 (very simple) – 10 (very difficult) | ||
| Comfort level with the pediatric corridor | 6.0 ± 2.62 (range 0-10) | 5.3 ± 1.91 (range 2-10) |
| 0 (very comfortable) – 10 (very uncomfortable) | ||
| Time to skeletonize carotids and sella face (min) | ||
| <20 | 2 (7.1%) | 2 (7.1%) |
| 20-40 | 12 (42.9%) | 15 (53.6%) |
| >40 | 11 (39.3%) | 10 (35.7%) |
| Not indicated | 3 (10.7%) | 1 (3.6%) |
| Realism of the model | 7.0 ± 1.98 (range 2-10) | |
| 0 (very unrealistic) – 10 (very realistic) | ||
| Haptic realism | 7.1 ± 2.08 (range 2-10) | |
| 0 (very unrealistic) – 10 (very realistic) |
Post-dissection encountered challenges
After completing the dissection, participants were asked to assess the overall realism as well as the haptic realism of the model on a scale of 0-10 (10 being very realistic). The average score for overall realism was 7.0 and haptic realism was 7.1 (Table 2). The challenges noted were similar to the anticipated challenges with limitation of maneuverability of instruments and narrow nasal corridor (64.3%), limitation of visualization (57.1%), and non-pneumatized bone (50.0%) (Table 2). The encountered level of difficulty with visualization was 6.93 and difficulty with instrumentation was 7.5. The average comfort level with the pediatric corridor was 5.3 (Table 3). The most frequent actual time to skeletonize the carotids and sella face was for 20-40 minutes in 53.6% and >40 minutes in 35.7%.
Discussion
Pediatric patients present a unique set of anatomic challenges for the skull base surgeon including decreased sphenoid pneumatization, narrow nasal cavities, and narrow intercarotid distance2–4 While simulation with models cannot completely replace clinical hands-on experience with soft tissue handling in the nose and fluid dynamics related to management of bleeding and secretions, a high-fidelity bone analog model as utilized in the current study sought to replicate the characteristics of working within a pediatric nasal cavity and manipulating the bony anatomy to provide sufficient exposure for endonasal approaches. The study presented here demonstrates that a 3D printed model of the pediatric skull base can realistically model the challenges that face pediatric skull base surgeons, and participants rated the overall realism and haptic realism highly. While cadaveric specimens may routinely be obtained to practice endoscopic endonasal techniques in adult specimens, this is typically not feasible in the pediatric setting. The generation of 3D modeling of the pediatric skull base may be particularly beneficial to practice endonasal skull base techniques given these considerations. Given the advent of virtual reality technology, combination 3D modeling with virtual reality systems may continue to refine the realism of modeling the pediatric skull base13–16.
The average participant expected level of difficulty with visualization was 6.89 and expected level of difficulty with instrumentation was 7.3 while on post-dissection assessment, there was a non-statistically significant increase to 6.93 and 7.5 respectively. Furthermore, there were only small changes in pre-dissection anticipated and post-dissection encountered challenges such as limitation of maneuverability, visualization, narrow corridor, and sphenoid pneumatization (Table 2). One reason for the small changes seen may be due to the fact that resources only allowed each participant to drill one 3D printed model of the pediatric skull base in a single setting. It may be possible that drilling multiple models over time may enhance the training applicability, comfort level with the pediatric skull base, and allow for measurements of improved technique. This study provides proof of principle that a 3D printed model of the pediatric skull base is feasible and may provide a valuable training resource in the future, and appears to reasonably reflect the challenges of pediatric endonasal skull base surgery. The current study also identified areas for improvement in the model to improve realism and these changes would be expected to increase the realism of the model and its educational value in the future. To our knowledge, this is the first pediatric endonasal simulation model. It would be interesting in the future to generate advanced simulation models that include disease pathology that may be valuable for experienced learners. The model provides relatively good haptic feedback for bone (when using a high-speed electric drill with a hybrid or coarse diamond burr) but lacks the soft tissue components, i.e. mucosa, cartilage or tumor, that could be added following advancements in materials and 3D printing. This model also underwent digital refinements of the middle and inferior turbinates to help optimize the nasal corridor. Even so, many participants found that the middle turbinate had to be removed in this model to achieve adequate access. In a future iteration, it may be valuable to print thinner turbinate attachments that can be more easily lateralized or resected.
Limitations of this study include a small sample size (28 participants) at a single location. Many of those participating, however, were visiting from international locations both for the skull base course as well as for training. As such, the results reflect the experiences from multiple centers. An increased sample size as well as the ability to dissect multiple models over time will allow will help to strengthen the assessment of the applicability of this model in the future. An additional limitation of the study includes bias towards more junior participants with less perspective regarding pre-dissection estimations of challenges.
Conclusions
A 3D printed model of the pediatric skull base may provide a realistic model to help participants gain experience with anatomic limitations characteristic of the pediatric anterior skull base. Future studies will continue to assess the validity of this model and its application in training pediatric skull base surgeons.
Figure 3.
Posterior view of 3D printed pediatric skull base model. Red – carotid arteries, yellow – optic nerves, pink – pituitary gland, grey – anterior skull base
Figure 4.
Inferior view of 3D printed pediatric skull base model
Acknowledgments
A.P. was supported through a T32 NIH training grant. This study was presented as an oral presentation at the North American Skull Base Society Meeting on Saturday February 8, 2020 in San Antonio, Texas.
Abbreviations:
- DICOM
Digital Imaging and Communications in Medicine
- EEA
expanded endonasal approach
Footnotes
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This study was presented as an oral presentation at the North American Skull Base Society Meeting on Saturday February 8, 2020.
Conflict of interest: N.L. holds stock in Navigen Pharmaceuticals and was a consultant for Cooltech Inc., neither of which are relevant to this study. The other authors have no relevant conflicts of interest to disclose.
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