(e.g., awake craniotomies and endonasal endoscopic procedures) [70–76]. Patients expect utmost proficiency and mastery from their neurosurgeons. Neurosurgical mastery requires comprehensive anatomical knowledge and hours of deliberate practice in the operating room and skill lab. Unfortunately, the case volume and overall surgical exposure during neurosurgical training (for each trainee) have declined as a result of strict duty-hour restrictions and the current global pandemic [77, 78]. Now more than ever, surgical simulation with 3D-printed models plays a pivotal role in neurosurgery training and anatomy teaching [72, 79]. Physical 3D printed models that recreate patient-specific anatomy and pathology can be readily manipulated to help better understand approach-specific and complex pathoanatomical relationships that are otherwise hard to visualize using other traditional means and allow for practicing the different phases of the operation in a safe environment (Figure 2). One area of growing interest is open cerebrovascular neurosurgery—a daunting field that requires immediate action [80] and unique surgical dexterity. Numerous studies have shown the utility of 3D-printed models for presurgical planning, approach selection (e.g., feasibility of using smaller “keyhole” craniotomies), aneurysm clip selection, configuration, and simulation [72, 73, 79, 81]. Other reported applications are brain arteriovenous malformation resection [79, 82] and endovascular techniques [83, 84]. Applications in skull base neurosurgery are 3Dprinted models for simulating endoscopic techniques such as endonasal transphenoidal approaches and tumor resections and open techniques such as transtemporal approaches, anterior clinoidectomies, middle, and posterior fossa approaches [72, 79, 85–87]. Applications in hydrocephalus treatment and pediatric neurosurgery are models simulating neuroendoscopic third ventriculostomies and pineal biopsies, external ventriculostomy, and craniosynostosis repair [72, 79]. Noteworthy applications in spine surgery are planning of complex spinal deformity cases, simulators of pedicle screw placement with accurate haptic feedback of cortico-cancellous interface, C2 laminar screw placement, and research [70, 88–90]. Finally, macroscopic and microscopic pathological 3D-printed models can also be used for research by reproducing complex physiology and flow dynamics as in arteriovenous malformation niduses [91] and brain aneurysms even with endothelial lining [74]. 3DP allows for rapid and inexpensive prototype manufacturing of surgical instruments (such as microforceps), devices such as patient-specific navigation molds, headrests for frameless gamma knife surgery, synthetic custom-made cranioplasties for covering bony defects, and spinal implants [90, 92, 93]. 3D printed scaffolds can be engineered for biological ingrowth or engrafting with applications in research and transplantation [94]. The complex 3D extracellular microenvironment [95] of human tissues can be replicated using 3DP techniques by providing a physical matrix and incorporating cell-supporting molecules for culturing human and cancer cells, developing tumor models, and manufacturing implantable tissue grafts [96]. The desired external geometry and internal structure of tissue scaffolds are readily controlled. (a) (b) (c) Figure 2: Postprinting result. (a, b) The printed brain can be combined with the tumor print (red) in order to establish the relationships of the adjacent anatomic structures. (c) The tumor can be painted to determine the separation from the brain parenchyma. This is a costeffective procedure that can help to improve the three-dimensional visualization of the brain tumors to improve the management [71]. Used with permission from Elsevier. 5 BioMed Research International JUNE 2022 | The Surgical Technologist | 257
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