This study protocol adheres to the SQUIRE 2.0 guidelines.
Ethics approval:
The study protocol was conducted in compliance with the Declaration of Helsinki and approved by the ethics committee of the Otto-von-Guericke University Magdeburg. (Ethics vote number: RENOVA 94/20)
Statement of Human and Animal Rights:
This article does not contain any studies with human or animal subjects.
Statement of Informed Consent:
Written informed consent was obtained from the patient for their anonymized information to be published in this article.
Data Acquisition
After obtaining the approval of the local ethics committee, imaging datasets (computed tomography angiography [CTA], and magnetic resonance imaging [MRI]) of a 52-year-old male with an incidental aneurysm of the left middle cerebral artery (MCA) were used for thresholding-based segmentation and reconstruction of the skull, brain and the circulus arteriosus willisi (CAW).
Construction of the Phantom
The creation of the Phantom combined digital reconstructions and post-processing with additive manufacturing, material research and handcrafting.
The skull was reconstructed from the patient’s CT-angiography data by greysclae boundaries using the freely available 3D reoncstruction software InVesalius3 (Centro de Tecnologia da Informação Renato Archer (CTI)) and subsequently refined with the open-source graphics software tools MeshMixer (Autodesk, Inc.), and Blender (Blender Foundation - Nonprofit organization) to reduce production costs and time expenditure by incorporating reusable and detachable parts via slide and plug-in mechanisms. (Fig. 1A)
The CAW was segmented from the patient’s contrast-enhanced T1 MRI dataset on the free cross-plattform application MeVisLab (MeVis Medical Solutions AG, Bremen, Germany) employing threshold-based techniques. Subsequent mesh smoothing and adjustments were permormed with MeshMixer and Sculptris 1.02 (Pixologic, Inc., www.sculpteo.com). The CAW was designed to remainin in the centrale console of the skull with magnetic connectors integrated into the proximal M1-segments to facilitate a swift attachment and detachment of the aneurysm models. (Fig. 1B)
The reconstruction of the brain from the patient’s MRI datatset was executed with the open-source software Fressurfer (Harvard University, Cambridge, Massachusetts, USA). Additional manual segmentation was required to accurately replicate the lateral sulcus and generate an anatomically precise negative mold and facilitate the subsequent casting of the Sylvian fissure (SF) models. To achieve this, the SF mesh was manually divided into two segments in Blender, determined by hand-selected points demarcating the pial surfaces of the temporal and frontal lobes within the sulcus. (Fig. 1C)
Additive manufacturing of the skull, CAW and SF models were executed on a desktop 3D Printer (Raise3D Pro2 dual extrusion by Raise 3D Technologies, Inc.) using standard 1,75 mm PLA filaments. The rigidity disparities between compact and cancellous bone druing the drilling process were ensured by adjusting the infill density of the skull at 15%.
Mimicking the tactile properties of the living brain was a challenging process based on previous studies and involving a substudy with subjective and objective material research and evaluations. Candle gel, identified by six experienced neurosurgeons for its similar tactile properties to the brain tissue as encountered during surgery, circumvents the limitations associated with previous gelatin-based models while offering a more sustainable and ethically sound option. The result was an anatomically and tactilly accurate, reusable replication of the SF. (Fig. 2A) The subjective evaluation was further validated through rheological assessments. (Fig. 2B)
MCA models with identical aneurysms located at M1 and MCA-birfucarrtion were handcrafted using paraffin wax and coated with two thin layers of liquid latex. After a detaliled shaping process, the models were then bathed in water with temperatures between 65°-70° C to wash out the paraffin wax. (Fig. 3A - C)
The simulation of the meninges involved applying a latex layer to mimic the dura mater, enhanced with a coalescing agent for better adhesion. (Fig. 4A) The web-like texture of the arachnoid mater was recreated using a blend of synthetic resin adhesive, latex, and glycerin, meticulously applied to the SF to achieve a natural, wet look. (Fig. 4B)
Simulator assembly:
The initial step of the assembly involves attaching the dura mater to the interchangeable lateral skull base models. Concurrently, the middle cerebral artery aneurysm models, and optionally cerebral veins, are carefully placed within the SF models. After applying the arachnoid membrane, the SF models are positioned in the lateral skull bases which are then connected to the central console via clip mechanisms. During this process, the aneurysm model establishes a magnetic connection with the CAW model placed on the central console. In the final assembly stage, the skull base and central console are securely attached to the rest of the Phantom via integrated rail-slide systems. The assembly process is depicted in Fig. 5.
Study design
Three groups of participants (n = 22) with varying levels of neurosurgical experience were recruited for this study. (Table 1)
-
Novice Group (n = 12): 4th - and 5th -year medical students (MS)
-
Advanced Group (n = 6): 4th - and 5th -year neurosurgical residents (NR)
-
Expert Group (n = 4): neurosurgeons (NS) specialized in vascular neurosurgery
Simulation setting:
The simulation took place at the microneurosurgical laboratories of the department of neurosurgery, where a training environment with a full-functioning operating theatre is provided. Simulations were executed using a ZEISS OPMI Neuro NC-4. (Fig. 6) A full set of neurosurgical instruments including drills, scalpels, forceps, scissors, bone punches, aneurysm clips, and clip appliers were organized on a surgical tray within a hand’s reach.
To allow a direct comparison between the two approaches, identical MCA models fitted with two aneurysms placed in the M1- and MCA-bifurcation segments, were used in this study. The length of the M1-segment was set at 14 mm20 where the MCA-bifurcation aneurysm was placed. A second aneurysm was placed at 8 mm length, representing an MCA-bifurcation aneurysm with a shorter M1-segment. (Fig. 7)
Simulation Process:
The simulation was preceded by an introduction explaining the principles and key steps of MCA aneurysm clipping. The surgical approach was predefined to the standard pterional and the lateral supraorbital approaches. All medical students received additional instruction on the operating microscope and microsurgical instruments. The participants started the simulation with the positioning of the head in a 3-pin immobilization device. Craniotomy and dural incision were performed. After visualizing the aneurysm a clip was chosen and placed on the neck of the aneurysm. Each participant performed the procedure twice, with either approach on one side of the Phantom. Both approaches were repeated after a period of three to five days. Per attempt, each participant was given one chance to clip each aneurysm with either one or two clips of choice. (Fig. 8)
Simulation assessment:
The simulations were directly followed by a questionnaire for the assessment of face and content validity derived on 5-point Likert scales. All participants (n = 22) were asked to gauge their attitude towards the simulator. Neurosurgical residents and neurosurgeons rated the simulators’ usefulness in developing technical skills. Experienced neurosurgeons rated the simulators’ realism and accuracy.
The expert group further compared both approaches regarding the surgical exposure of key anatomical structures, accessibility of MCA-bifurcation aneurysms, the ease of surgical manipulation, and overall surgical experience.
All participants were observed during the simulations and assessed by two independent neurosurgeons based on the Objective Structured Assessment of Aneurysm Clipping Skills (OSAACS)15,19 (Table 2) OSAACS rates surgical clipping skills based on user performance during simulation to evaluate progress in training and differentiate between novice and advanced surgeons (construct validity). The tool was modified to include specific assessment criteria for correct head positioning and craniotomy placement.