Training for brain tumour resection: a realistic model with easy accessibility

Sheep's Head as an Anatomic Model for Basic Training in Endoscopic Sinus Surgery

Background and Objectives: This study aims to establish the sheep head as a viable anatomical model for training in functional endoscopic sinus surgery through comprehensive anatomical examination and training-based assessment of participants' satisfaction. Materials and Methods: Participants were divided into three groups according to their prior experience in endoscopic sinus surgery; in total, 24 participants were included. Each participant in the study was assigned to perform the designated procedures on a single sheep's head. Following the completion of the procedures, each participant was provided with a 14-item comprehensive satisfaction questionnaire with a scale attributed from 1 to 5. The normality of distribution was checked by applying the Shapiro-Wilk Test. The Kruskal-Wallis test was applied to compare study group sentiment of agreement towards individual procedures. Results: No significant differences were noted between the answers of the different groups. For the resident group, the average satisfaction score was 4.09 ± 0.54; junior specialist group 4.00 ± 0.55; for the senior specialist group overall satisfaction average score was 4.2 ± 0.77. Conclusions: The sheep's head can be successfully used for learning and practicing manual skills and the use of instruments specific to functional endoscopic sinus surgery. Moreover, the sheep head model can be used for training in other diagnostic or surgical procedures in the field of otorhinolaryngology, such as endoscopy of the salivary glands, open laryngotracheal surgery, or in otologic surgery, but also in other different surgical fields such as neurosurgery, ophthalmology or plastic surgery. Despite the differences between the ovine model and human anatomy, it provides a resourceful and cost-effective model for beginners in endoscopic nasal surgery.

Morphometric study of the ventricular indexes in healthy ovine BRAIN using MRI

Background

Sheep (Ovis aries) have been largely used as animal models in a multitude of specialties in biomedical research. The similarity to human brain anatomy in terms of brain size, skull features, and gyrification index, gives to ovine as a large animal model a better translational value than small animal models in neuroscience. Despite this evidence and the availability of advanced imaging techniques, morphometric brain studies are lacking. We herein present the morphometric ovine brain indexes and anatomical measures developed by two observers in a double-blinded study and validated via an intra- and inter-observer analysis.

Results

For this retrospective study, T1-weighted Magnetic Resonance Imaging (MRI) scans were performed at 1.5 T on 15 sheep, under general anaesthesia. The animals were female Ovis aries, in the age of 18-24 months. Two observers assessed the scans, twice time each. The statistical analysis of intra-observer and inter-observer agreement was obtained via the Bland-Altman plot and Spearman rank correlation test.

The results are as follows (mean ± Standard deviation):

Indexes: Bifrontal 0,338 ± 0,032 cm; Bicaudate 0,080 ± 0,012 cm; Evans’ 0,218 ± 0,035 cm; Ventricular 0,241 ± 0,039 cm; Huckman 1693 ± 0,174 cm; Cella Media 0,096 ± 0,037 cm; Third ventricle ratio 0,040 ± 0,007 cm.

Anatomical measures: Fourth ventricle length 0,295 ± 0,073 cm; Fourth ventricle width 0,344 ± 0,074 cm; Left lateral ventricle 4175 ± 0,275 cm; Right lateral ventricle 4182 ± 0,269 cm; Frontal horn length 1795 ± 0,303 cm; Interventricular foramen left 1794 ± 0,301 cm; Interventricular foramen right 1,78 ± 0,317 cm.

Conclusions

The present study provides baseline values of linear indexes of the ventricles in the ovine models. The acquisition of these data contributes to filling the knowledge void on important anatomical and morphological features of the sheep brain.

Best Practices Using Ex Vivo Animal Brain Models in Neurosurgical Education to Assess Surgical Expertise

BACKGROUND

Ex vivo animal brain simulation models are being increasingly used for neurosurgical training because these models can replicate human brain conditions. The goal of the present report is to provide the neurosurgical community interested in using ex vivo animal brain simulation models with guidelines for comprehensively and rigorously conducting, documenting, and assessing this type of research.

METHODS

In consultation with an interdisciplinary group of physicians and researchers involved in ex vivo models and a review of the literature on the best practices guidelines for simulation research, we developed the "ex vivo brain model to assess surgical expertise" (EVBMASE) checklist. The EVBMASE checklist provides a comprehensive quantitative framework for analyzing and reporting studies involving these models. We applied The EVBMASE checklist to the studies reported of ex vivo animal brain models to document how current ex vivo brain simulation models are used to train surgical expertise.

RESULTS

The EVBMASE checklist includes defined subsections and a total score of 20, which can help investigators improve studies and provide readers with techniques to better assess the quality and any deficiencies of the research. We classified 18 published ex vivo brain models into modified (group 1) and nonmodified (group 2) models. The mean total EVBMASE score was 11 (55%) for group 1 and 4.8 (24.2%) for group 2, a statistically significant difference (P = 0.006) mainly attributed to differences in the simulation study design section (P = 0.003).

CONCLUSIONS

The present findings should help contribute to more rigorous application, documentation, and assessment of ex vivo brain simulation research.

Microsurgical subpial resections for diffuse gliomas-old wine in a new bottle

BACKGROUND

Maximizing resection is an oft-sought-after albeit challenging goal in diffuse gliomas. Microsurgical technique remains the mainstay.

METHOD

By virtue of their pattern of growth and spread, gliomas respect anatomical boundaries like the pia. Using subpial dissection, en bloc resections provide the most optimal surgical technique. This paper revisits this technique and describes the rationale and basic principles integrating it in the modern multimodal glioma surgery workflow.

CONCLUSION

Subpial resection is a very useful and "anatomical" technique for en bloc resection of diffuse gliomas which is easy to master and execute and optimizes the extent of resection and minimizes complications effectively.

Development and initial evaluation of a novel simulation model for comprehensive brain tumor surgery training

Background

Increasing technico-manual complexity of procedures and time constraints necessitates effective neurosurgical training. For this purpose, both screen- and model-based simulations are under investigation. Approaches including 3D printed brains, gelatin composite models, and virtual environments have already been published. However, quality of brain surgery simulation is limited due to discrepancies in visual and haptic experience. Similarly, virtual training scenarios are still lacking sufficient real-world resemblance. In this study, we introduce a novel simulator for realistic neurosurgical training that combines real brain tissue with 3D printing and augmented reality.

Methods

Based on a human CT scan, a skull base and skullcap were 3D printed and equipped with an artificial dura mater. The cerebral hemispheres of a calf’s brain were placed in the convexity of the skullcap and tumor masses composed of aspic, water, and fluorescein were injected in the brain. The skullcap and skull base were placed on each other, glued together, and filled up with an aspic water solution for brain fixation. Then, four surgical scenarios were performed in the operating room as follows: (1) simple tumor resection, (2) complex tumor resection, (3) navigated biopsy via burr hole trepanation, and (4) retrosigmoidal craniotomy. Neuronavigation, augmented reality, fluorescence, and ocular—as well as screen-based (exoscopic)—surgery were available for the simulator training. A total of 29 participants performed at least one training scenario of the simulator and completed a 5-item Likert-like questionnaire as well as qualitative interviews. The questionnaire assessed the realism of the tumor model, skull, and brain tissue as well as the capability for training purposes.

Results

Visual and sensory realism of the skull and brain tissue were rated,”very good,” while the sensory and visual realism of the tumor model were rated “good.” Both overall satisfaction with the model and eligibility of the microscope and neurosurgical instruments for training purposes were rated with “very good.” However, small size of the calf’s brain, its limited shelf life, and the inability to simulate bleedings due to the lack of perfusion were significant drawbacks.

Conclusion

The combination of 3D printing and real brain tissue provided surgical scenarios with very good real-life resemblance. This novel neurosurgical model features a versatile setup for surgical skill training and allows for efficient training of technological support like image and fluorescence guidance, exoscopic surgery, and robotic technology.

Electronic supplementary material

The online version of this article (10.1007/s00701-020-04359-w) contains supplementary material, which is available to authorized users.

The use of non-living animals as simulation models for cranial neurosurgical procedures: a literature review

Simulation plays a pivotal role in neurosurgical training by allowing trainees to develop the requisite expertise to enhance patient safety. Several models have been used for simulation purposes. Non-living animal models offer a range of benefits, including affordability, availability, biological texture, and a comparable similarity to human anatomy. In this paper, we review the available literature on the use of non-living animals in neurosurgical simulation training. We aim to answer the following questions: (1) what animals have been used so far, (2) what neurosurgical approaches have been simulated, (3) what were the trainee tasks, and (4) what was the experience of the authors with these models. A search of the PubMed Medline database was performed to identify studies that examined the use of non-living animals in cranial neurosurgical simulation between 1990 and 2020. Our initial search yielded a total of 70 results. After careful screening, we included 22 articles for qualitative analysis. We compared the reports in terms of the (1) animal used, (2) type of surgery, and (3) trainee tasks.

All articles were published between 2003 and 2019. These simulations were performed on three types of animals, namely sheep, cow, and swine. All authors designed specific, task-oriented approaches and concluded that the models used were adequate for replicating the surgical approaches. Simulation on non-living animal heads has recently gained popularity in the field of neurosurgical training. Non-living animal models are an increasingly attractive option for cranial neurosurgical simulation training. These models enable the acquisition and refinement of surgical skills, with the added benefits of accessibility and cost-effectiveness. To date, 16 different microneurosurgical cranial approaches have been replicated on three non-living animal models, including sheep, cows, and swine. This review summarizes the experience reported with the use of non-living animal models as alternative laboratory tools for cranial neurosurgical training, with particular attention to the set of tasks that could be performed on them.

In vivo Diffusion Tensor Magnetic Resonance Tractography of the Sheep Brain: An Atlas of the Ovine White Matter Fiber Bundles

Diffusion Tensor Magnetic Resonance Imaging (DTI) allows to decode the mobility of water molecules in cerebral tissue, which is highly directional along myelinated fibers. By integrating the direction of highest water diffusion through the tissue, DTI Tractography enables a non-invasive dissection of brain fiber bundles. As such, this technique is a unique probe for in vivo characterization of white matter architecture. Unraveling the principal brain texture features of preclinical models that are advantageously exploited in experimental neuroscience is crucial to correctly evaluate investigational findings and to correlate them with real clinical scenarios. Although structurally similar to the human brain, the gyrencephalic ovine model has not yet been characterized by a systematic DTI study. Here we present the first in vivo sheep (ovis aries) tractography atlas, where the course of the main white matter fiber bundles of the ovine brain has been reconstructed. In the context of the EU's Horizon EDEN2020 project, in vivo brain MRI protocol for ovine animal models was optimized on a 1.5T scanner. High resolution conventional MRI scans and DTI sequences (b-value = 1,000 s/mm², 15 directions) were acquired on ten anesthetized sheep o. aries, in order to define the diffusion features of normal adult ovine brain tissue. Topography of the ovine cortex was studied and DTI maps were derived, to perform DTI tractography reconstruction of the corticospinal tract, corpus callosum, fornix, visual pathway, and occipitofrontal fascicle, bilaterally for all the animals. Binary masks of the tracts were then coregistered and reported in the space of a standard stereotaxic ovine reference system, to demonstrate the consistency of the fiber bundles and the minimal inter-subject variability in a unique tractography atlas. Our results determine the feasibility of a protocol to perform in vivo DTI tractography of the sheep, providing a reliable reconstruction and 3D rendering of major ovine fiber tracts underlying different neurological functions. Estimation of fiber directions and interactions would lead to a more comprehensive understanding of the sheep's brain anatomy, potentially exploitable in preclinical experiments, thus representing a precious tool for veterinaries and researchers.

Development of a Simulation Model for Fluorescence-Guided Brain Tumor Surgery

Objective: Fluorescence dyes are increasingly used in brain tumor surgeries, and thus the development of simulation models is important for teaching neurosurgery trainees how to perform fluorescence-guided operations. We aimed to create a tumor model for fluorescence-guided surgery in high-grade glioma (HGG).

Methods: The tumor model was generated by the following steps: creating a tumor gel with a similar consistency to HGG, selecting fluorophores at optimal concentrations with realistic color, mixing the fluorophores with tumor gel, injecting the gel into fresh pig/sheep brain, and testing resection of the tumor model under a fluorescence microscope. The optimal tumor gel was selected among different combinations of agar and gelatin. The fluorophores included fluorescein, indocyanine green (ICG), europium, chlorin e6 (Ce6), and protoporphyrin IX (PpIX). The tumor model was tested by neurosurgeons and neurosurgery trainees, and a survey was used to assess the validity of the model. In addition, the photobleaching phenomenon was studied to evaluate its influence on fluorescence detection.

Results: The best tumor gel formula in terms of consistency and tactile response was created using 100 mL water at 100°C, 0.5 g of agar, and 3 g of gelatin mixed thoroughly for 3 min. An additional 1 g of agar was added when the tumor gel cooled to 50°C. The optimal fluorophore concentration ranges were fluorescein 1.9 × 10⁻⁴ to 3.8 × 10⁻⁴ mg/mL, ICG 4.9 × 10⁻³ to 9.8 × 10⁻³ mg/mL, europium 7.0 × 10⁻² to 1.4 × 10⁻¹ mg/mL, Ce6 2.2 × 10⁻³ to 4.4 × 10⁻³ mg/mL, and PpIX 1.8 × 10⁻² to 3.5 × 10⁻² mg/mL. No statistical differences among fluorophores were found for face validity, content validity, and fluorophore preference. Europium, ICG, and fluorescein were shown to be relatively stable during photobleaching experiments, while chlorin e6 and PpIX had lower stability.

Conclusions: The model can efficiently highlight the “tumor” with 3 different colors—green, yellow, or infrared green with color overlay. These models showed high face and content validity, although there was no significant difference among the models regarding the degree of simulation and training effectiveness. They are useful educational tools for teaching the key concepts of intra-axial tumor resection techniques, such as subpial dissection and nuances of fluorescence-guided surgery.

The Microneurosurgical Training Model for Intrinsic and Extrinsic Brain Tumor Surgery Using Polyurethane Foam and Fresh Cadaveric Cow Brain: An Experimental Study

Objective

To evaluate the feasibility of an experimentally designed brain tumor model consisting of polyurethane foam and fresh cadaveric cow brain for the surgical training of the technique for tumor ablation.

Methods

A laboratory-training model was created for microneurosurgical intervention of intrinsic brain tumor ablation covering microdissection of the brain tissue and opening of the pia mater, dissection and separation of the sulcal and cisternal structures, and dissection and removal of the tumor tissue. The left front parietal lobe was used as the area of interest for this experimental study. One-centimeter cube polyurethane foam was injected 2-cm deep inside the brain tissue using a plastic injection tube. After 5 minutes, the model was ready to use under the operating microscope for dissection, separation, and removal of the tumor tissue. The compatibility of the training model also was evaluated as poor, acceptable, and perfect.

Results

Ten stripped fresh cadaveric cow brains were used in this experimental feasibility study. The compatibility of the model was evaluated as poor, acceptable, and perfect in 1, 6, and 3 subjects, respectively.

Conclusions

In intrinsic brain tumor ablation, surgical manipulations of sulcal, cisternal, and fissural dissection must be undertaken while preserving vital neural and vascular structures. We believe that our model holds promise in developing the technical skills of neurosurgeons in training.