Model-based surgical planning and simulation of cranial base surgery

Clinical situations for which 3D printing is considered an appropriate representation or extension of data contained in a medical imaging examination: neurosurgical and otolaryngologic conditions

BACKGROUND

Medical three dimensional (3D) printing is performed for neurosurgical and otolaryngologic conditions, but without evidence-based guidance on clinical appropriateness. A writing group composed of the Radiological Society of North America (RSNA) Special Interest Group on 3D Printing (SIG) provides appropriateness recommendations for neurologic 3D printing conditions.

METHODS

A structured literature search was conducted to identify all relevant articles using 3D printing technology associated with neurologic and otolaryngologic conditions. Each study was vetted by the authors and strength of evidence was assessed according to published guidelines.

RESULTS

Evidence-based recommendations for when 3D printing is appropriate are provided for diseases of the calvaria and skull base, brain tumors and cerebrovascular disease. Recommendations are provided in accordance with strength of evidence of publications corresponding to each neurologic condition combined with expert opinion from members of the 3D printing SIG.

CONCLUSIONS

This consensus guidance document, created by the members of the 3D printing SIG, provides a reference for clinical standards of 3D printing for neurologic conditions.

Skull base dural reflection models: tool for teaching neuroanatomy at resource-scarce centers

Skull base dural reflections are complex, and along with various ligaments joining sutures of the skull base, are related to most important vessels like internal carotid arteries (ICA), vertebral arteries, jugular veins, cavernous sinus, and cranial nerves which make surgical approaches difficult and need thorough knowledge and anatomy for a safe dissection and satisfactory patient outcomes. Cadaver dissection is much more important for the training of skull base anatomy in comparison to any other subspecialty of neurosurgery; however, such facilities are not available at most of the training institutes, more so in low- and middle-income countries (LMICs). A glue gun (100-Watt glue gun, ApTech Deals, Delhi, India) was used to spread glue over the superior surface of the bone of the skull base over desired area (anterior, middle, or lateral skull base). Once glue was spread over the desired surface uniformly, it was cooled under running tap water and the glue layer was separated from the skull base. Various neurovascular impressions were colored for ease of depiction and teaching. Visual neuroanatomy of the inferior surface of dural reflections of the skull base is important for understanding neurovascular orientations of various structures entering or exiting the skull base. It was readily available, reproducible, and simple for teaching neuroanatomy to the trainees of neurosurgery. Skull base dural reflections made up of glue are an inexpensive, reproducible item that may be used for teaching neuroanatomy. It may be useful for trainees and young neurosurgeons, especially at resource-scarce healthcare facilities.

Operative Anatomy of the Human Skull: A Virtual Reality Expedition

INTRODUCTION

The human cranial vault possesses an incredible, complex anatomical intricacy. Bridging the divide between 2-dimensional (2D) learning resources and the 3-dimensional (3D) world in which the anatomy becomes clinically relevant poses an intellectual challenge. Advances in computer graphics and modelling technologies have allowed increasingly accurate and representative resources to supplement cadaveric dissection specimens.

OBJECTIVE

To create accurate virtual models of all cranial bones to augment education, research, and clinical endeavours.

METHODS

Through a careful analysis of osteological specimens and high-resolution radiographic studies, a highly accurate virtual model of the human skull was created and annotated with relevant anatomical landmarks.

RESULTS

The skull was divided into 6 major segments including frontal, ethmoid, sphenoid, temporal, parietal, and occipital bones. These bones were thoroughly annotated to demonstrate the intricate anatomical features.

CONCLUSION

This virtual model has the potential to serve as a valuable resource for educational, research, and clinical endeavours, and demonstrates the significance of advances in computer modelling that can contribute to our understanding of neurosurgical anatomical substrates.

A Systematic Review of the Educational Effectiveness of Simulation Used in Open Surgery

STATEMENT

The role of simulation to teach and access open surgical skills has become more prevalent in recent years. This systematic review synthesizes the totality of evidence with respect to the educational effectiveness of simulators used in open surgical training. A systematic literature search was conducted in PubMed, Embase, CINAHL, Scopus, and Web of Science. Only randomized controlled trials were included that explored the educational efficacy of theses simulators. Six randomized controlled trials were included from the 9934 studies found. The methodological quality of the included studies was variable. Overall, the use of the simulators was more educationally effective compared with standard teaching of the skill without a simulator (P < 0.05). Two studies showed that the simulator was as good as an animal model of much higher fidelity. Further studies are needed to secure higher evidence for the educational value, validity, and transferability of the skills to the hospital setting for all simulators.

Review of 3-Dimensional Printing on Cranial Neurosurgery Simulation Training

OBJECTIVE

Shorter working times, reduced operative exposure to complex procedures, and increased subspecialization have resulted in training constraints within most surgical fields. Simulation has been suggested as a possible means of acquiring new surgical skills without exposing patients to the surgeon's operative "learning curve." Here we review the potential impact of 3-dimensional printing on simulation and training within cranial neurosurgery and its implications for the future.

METHODS

In accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, a comprehensive search of PubMed, OVID MEDLINE, Embase, and the Cochrane Database of Systematic Reviews was performed.

RESULTS

In total, 31 studies relating to the use of 3-dimensional (3D) printing within neurosurgery, of which 16 were specifically related to simulation and training, were identified. The main impact of 3D printing on neurosurgical simulation training was within vascular surgery, where patient-specific replication of vascular anatomy and pathologies can aid surgeons in operative planning and clip placement for reconstruction of vascular anatomy. Models containing replicas of brain tumors have also been reconstructed and used for training purposes, with some providing realistic representations of skin, subcutaneous tissue, bone, dura, normal brain, and tumor tissue.

CONCLUSION

3D printing provides a unique means of directly replicating patient-specific pathologies. It can identify anatomic variation and provide a medium in which training models can be generated rapidly, allowing the trainee and experienced neurosurgeon to practice parts of operations preoperatively. Future studies are required to validate this technology in comparison with current simulators and show improved patient outcomes.

Development of a modelled anatomical replica for training young neurosurgeons

INTRODUCTION

The Modelled Anatomical Replica for Training Young Neurosurgeons (MARTYN) is a novel simulation model developed by the Royal College of Surgeons England (RCSEng). This study describes the development of the model and aims to determine its feasibility as a potential future training tool.

METHODS AND MATERIALS

Traditional model-making methods were used to develop a prototype. Initial procedural trials tested the feasibility of the model. Eighteen participants, grouped by experience (nine novices, four intermediates and five experienced), completed two tasks: a craniotomy and a burr hole followed by insertion of an external ventricular drain (EVD). Subjective data on confidence, usefulness, realism and preference to other training modalities were collected via a standardised questionnaire and a 5-point Likert scale.

RESULTS

Preliminary trials of the model prototype demonstrated feasibility. The novice group had the greatest self-reported benefit from MARTYN training, with significant increases in self-rated confidence in both the craniotomy (p < 0.01) and EVD insertion (p < 0.05) procedures. MARTYN was reported to having good visual and tactile realism overall with the bone component being considered highly realistic. The model was reported to be a useful training tool. When asked to rank preferred training modalities, operative experience was chosen first with cadaveric training and MARTYN consistently scoring a second choice.

CONCLUSIONS

MARTYN was developed with the intention to fill the current niche for an inexpensive synthetic model head. This study shows that the use of MARTYN for training is both feasible and realistic. We demonstrate a preliminary face and construct validity of the model in this pilot study. With the reduction in working hours, we believe this model will be a suitable supplement to the current ST 1-3 level cadaveric training and will have a positive impact on patient safety.

Shortening the learning curve in endoscopic endonasal skull base surgery: a reproducible polymer tumor model for the trans-sphenoidal trans-tubercular approach to retro-infundibular tumors

BACKGROUND

Endoscopic endonasal skull base surgery attracts an increasing number of young neurosurgeons. This recent technique requires specific technical skills for the approaches to non-pituitary tumors (expanded endoscopic endonasal surgery). Actual residents' busy schedules carry the risk of compromising their laboratory training by limiting significantly the dedicated time for dissections.

OBJECTIVE

To enhance and shorten the learning curve in expanded endoscopic endonasal skull base surgery, we propose a reproducible model based on the implantation of a polymer via an intracranial route to provide a pathological retro-infundibular expansive lesion accessible to a virgin expanded endoscopic endonasal route, avoiding the ethically-debatable need to hundreds of pituitary cases in live patients before acquiring the desired skills.

METHODS

A polymer-based tumor model was implanted in 6 embalmed human heads via a microsurgical right fronto-temporal approach through the carotido-oculomotor cistern to mimic a retro-infundibular tumor. The tumor's position was verified by CT-scan. An endoscopic endonasal trans-sphenoidal trans-tubercular trans-planum approach was then carried out on a virgin route under neuronavigation tracking.

RESULTS

Dissection of the tumor model from displaced surrounding neurovascular structures reproduced live surgery's sensations and challenges. Post-implantation CT-scan allowed the pre-removal assessment of the tumor insertion, its relationships as well as naso-sphenoidal anatomy in preparation of the endoscopic approach.

CONCLUSION

Training on easily reproducible retro-infundibular approaches in a context of pathological distorted anatomy provides a unique opportunity to avoid the need for repetitive live surgeries to acquire skills for this kind of rare tumors, and may shorten the learning curve for endoscopic endonasal surgery.

CAD-CAM Prosthesis in Maxillo-Facial Surgery

To improve the maxillofacial surgery outcome, modern manufacturing methods such as rapid prototyping (RP), reverse engineering (RE) and medical imaging data have been utilised to manufacture custom-made prostheses after previous failed reconstructive surgery. After acquisition of data, an individual computer-based 3D model of the bony defect was generated and transferred into RE software to create the prosthesis CAD model. Then the physical model of the prosthesis was fabricated by RP technique. The precise fit of the prosthesis was evaluated using the prosthesis and skull models. The prosthesis was then directly used in investment casting such as “Quick Cast” pattern to produce the titanium model. In the clinical reports presented here, reconstructions of one patient with large mandible bone defects were performed using this method. The custom prostheses perfectly fit the defects during the operations, and surgery time was reduced. These cases showed that the prefabrication of a prosthesis using modern manufacturing technology is an effective method for maxillofacial defect reconstruction.

VIRTUAL TEMPORAL BONE: AN INTERACTIVE 3‐DIMENSIONAL LEARNING AID FOR CRANIAL BASE SURGERY

OBJECTIVE

We have developed an interactive virtual model of the temporal bone for the training and teaching of cranial base surgery.

METHODS

The virtual model was based on the tomographic data of the Visible Human Project. The male Visible Human's computed tomographic data were volumetrically reconstructed as virtual bone tissue, and the individual photographic slices provided the basis for segmentation of the middle and inner ear structures, cranial nerves, vessels, and brainstem. These structures were created by using outlining and tube editing tools, allowing structural modeling either directly on the basis of the photographic data or according to information from textbooks and cadaver dissections. For training and teaching, the virtual model was accessed in the previously described 3-dimensional workspaces of the Dextroscope or Dextrobeam (Volume Interactions Pte, Ltd., Singapore), whose interfaces enable volumetric exploration from any perspective and provide virtual tools for drilling and measuring.

RESULTS

We have simulated several cranial base procedures including approaches via the floor of the middle fossa and the lateral petrous bone. The virtual model suitably illustrated the core facts of anatomic spatial relationships while simulating different stages of bone drilling along a variety of surgical corridors. The system was used for teaching during training courses to plan and discuss operative anatomy and strategies.

CONCLUSION

The Virtual Temporal Bone and its surrounding 3-dimensional workspace provide an effective way to study the essential surgical anatomy of this complex region and to teach and train operative strategies, especially when used as an adjunct to cadaver dissections.

Individually Prefabricated Prosthesis for Maxilla Reconstuction

The reconstruction of maxillofacial bone defects by the intraoperative modeling of implants may reduce the predictability of the esthetic result, leading to more invasive surgery and increased surgical time. To improve the maxillofacial surgery outcome, modern manufacturing methods such as rapid prototyping (RP) technology and methods based on reverse engineeing (RE) and medical imaging data are applicable to the manufacture of custom-made maxillary prostheses. After acquisition of data, an individual computer-based 3D model of the bony defect is gernerated. These data are tranferrred into RE software to create the prosthesis using a computer-aided design (CAD) model, which is directed into the RP machine for the production of the physical model. The precise fit of the prosthesis is evaulated using the prosthesis and skull model. The prosthesis is then directly used in investment casting such as "Quick Cast" pattern to produce the titanium model. In the clincical reports presented here, reconstructions of two patients with large maxillary bone defects during the operations, and surgery time was reduced. These cases show that the prefabrication of a prosthesis using modern manufacturing technology is an effective method for maxillofacial defect reconstruction.

Study on Integrated Method of Medical Implant Manufacture Based on Rapid Prototyping Technology

The traditional method to manufacture the medical implant or prosthesis is based on sculpting and on the tissue site,or takes impressions of the entire face about human. The accuracy and efficiency of medical implant or prosthesis produced by conventional method is heavily relied on the skill and experience of both designer and manufacturer. In this paper, an integrated method of medical implant manufacture is approached. This integrated strategy was to establish a system that allows fabrication of facial prosthesis from digital information, and integrates the rapid prototyping with modeling technology of complex three-dimensional geometry from high-resolution non-invasive imaging, reverse engineering and computer aided design. The research results have shown that the integrated method can produce more exact-fit medical implant, that is, the physical model of the implant is more exactly fitted on the skull model. The advantages of this method are that the surgeon can plan and rehearse the surgery in advance, and a less invasive surgical procedure, and less time-consuming reconstructive, and an adequate esthetic can result.

Stereolithography for Craniofacial Surgery

Advances in computer technology have aided in the diagnostic and clinical management of complex congenital craniofacial deformities. The use of stereolithographic models has begun to replace traditional milled models in the treatment of craniofacial deformities. Research has shown that stereolithography models are highly accurate and provide added information in treatment planning for the correction of craniofacial deformities. These include the added visualization of the complex craniofacial anatomy and preoperative surgical planning with a highly accurate three-dimensional model. While the stereolithographic process has had a beneficial impact on the field of craniofacial surgery, the added cost of the procedure continues to be a hindrance to its widespread acceptance in clinical practice. With improved technology and accessibility the utilization of stereolithography in craniofacial surgery is expected to increase. This review will highlight the development and current usage of stereolithography in craniofacial surgery and provide illustration of it use.

Three-dimensional computational reconstruction of lateral skull base with plastinated slices

The goals of this study were to build the 3D reconstructed model of lateral skull base and to explore the spatial relationships of the important structures for providing the morphological basis for lateral skull base surgery and clinical image diagnosis. Blocks with edges of about 80 mm containing the lateral skull base region and adjacent structures were sawn out from both sides of the heads and sectioned on transverse plane at a thickness of 700 microm using a plastination technique. On an SGI workstation, a Contours-Marching cubes algorithm was selected to reconstruct the 3D model of the lateral skull base. Accurate alignment of the structures in the serial macroscopic sections was obtained by the employment of the plastination technique. The quality of the reconstructed images was distinct and perfect, specifically, the spatial positions and complicated adjacent relationships of various structures of the lateral skull base can be shown in direct viewing when they are displayed in background of the cranial bony substance. The time spent in displaying or rotating one image including 50 sections was 1.5 sec; all reconstructed structures can be represented individually or jointly and rotated in any plane. The plastination technique and computer-aided 3D reconstruction have an obvious advantage in the study of the complex anatomy of the lateral skull base. Plastination technique provides cross-section images of a higher resolution than those obtained from CT scanning. The computerized 3D reconstruction is important in studying the spatial anatomy of the lateral skull base and can serve as a standard for models created with other techniques.

Stereolithography: neurosurgical and medical implications

We present material to define and understand the concept of Stereolithography (STL) and its potential benefits to the field of neurosurgery and other medical specialties. A historical and scientific review of the literature on stereolithography, its evolution and uses in neurosurgery, forensic medicine, and other medical specialties are described. Considerations regarding different techniques used to obtain STL are discussed. The reproduction of cranial and vascular structures using this technique is evaluated. Data acquisition and model fabrication are the two basic steps required for stereolithography to create custom models for multiple applications in cranio-facial surgery, vascular studies, orthopedic surgery, urology and forensic medicine, among others. Stereolithography is a relatively new technique which continues to grow in many medical fields. Pre-operative education of patients, better understanding of patient anatomy, and the creation of custom-made prostheses are proven benefits of this technique.

A three-dimensional interactive virtual dissection model to simulate transpetrous surgical avenues

OBJECTIVE

This project involves the development of a three-dimensional surgical simulator called interactive virtual dissection, which is designed to teach surgeons the visuospatial skills required to navigate through a transpetrosal approach.

METHODS

A robotically controlled microscope is used for surgical planning and data collection. The spatial anatomic data are recorded from sequentially deeper cadaveric head dissections as a series of superimposed anatomic pictures in stereoscopic digital format. The sequential series of images are then merged to form the final virtual representation.

RESULTS

The current three-dimensional virtual reality simulator allows the user to drill the petrous bone progressively deeper and to identify crucial structures much like an experienced surgeon drilling the petrous bone. The program allows surgeons and trainees to manipulate the virtual "surgical field" by interacting with the surgical anatomy. The interactive system functions on a desktop computer.

CONCLUSION

The ability to visualize and understand anatomic spatial relationships is crucial in surgical planning, as is a surgeon's confidence in performing the surgery. The virtual reality simulator does not replace the need for practicing surgery on cadavers. However, it is designed to facilitate, via stereoscopic projection, learning how to manipulate a drill in complicated or unfamiliar surgical approaches (e.g., a transpetrosal approach).

Cranial base kyphosis and the surface morphology of the anterior cranial fossa

We investigated the relationship between the surface morphology of the anterior cranial fossa and cranial base kyphosis (sphenoid angle) in 52 cephalometric craniograms. Among them there were 25 female (mean age 54 +/- 15; range 31-82) and 27 male (mean age 43 +/- 18, range 19-85) skulls. The sphenoid angle and the altitudes of the highest elevation of the endofrontal eminence (cranial base over the orbital roof in the anterior cranial fossa) and the middle point of the sphenoid planum, measured according to the Frankfort horizontal, were analysed using classical cephalometric and morphometric analysis. Statistical analysis was performed by Pearson's product-moment correlation and simple linear regression. The sphenoid angle ranged from 97 degrees to 137 degrees (mean 118 +/- 9 degrees). The altitude ratio of the highest elevation of the endofrontal eminence and the middle point of the sphenoid planum ranged from 1.5 to 1.8 (mean 1.6 +/- 0.1). A significant correlation was found between this ratio and the sphenoid angle (r = -0.65; p < 0.001; coefficient of determination = 0.43). The elevation of the endofrontal eminence relative to the sphenoid planum was higher in skulls with increased cranial base kyphosis, whereas reduced sphenoid angle was associated with an increase in the elevations of the endofrontal eminence. Although the sphenoid angle has a significant effect on the morphology of the anterior cranial fossa, only 43% of the variance in altitude of the endofrontal eminence is likely to be explained by its relationship with the sphenoid angle.