Does Extended Reality Simulation Improve Surgical/Procedural Learning and Patient Outcomes When Compared With Standard Training Methods?: A Systematic Review.

INTRODUCTION: The use of extended reality (XR) technologies, including virtual, augmented, and mixed reality, has increased within surgical and procedural training programs. Few studies have assessed experiential learning- and patient-based outcomes using XR compared with standard training methods. METHODS: As a working group for the Society for Simulation in Healthcare, we used Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and a PICO strategy to perform a systematic review of 4238 articles to assess the effectiveness of XR technologies compared with standard training methods. Outcomes were grouped into knowledge, time-to-completion, technical proficiency, reactions, and patient outcomes. Because of study heterogeneity, a meta-analysis was not feasible. RESULTS: Thirty-two studies met eligibility criteria: 18 randomized controlled trials, 7 comparative studies, and 7 systematic reviews. Outcomes of most studies included Kirkpatrick levels of evidence I-III (reactions, knowledge, and behavior), while few reported level IV outcomes (patient). The overall risk of bias was low. With few exceptions, included studies showed XR technology to be more effective than standard training methods in improving objective skills and performance, shortening procedure time, and receiving more positive learner ratings. However, XR use did not show significant differences in gained knowledge. CONCLUSIONS: Surgical or procedural XR training may improve technical skill development among trainees and is generally favored over standard training methods. However, there should be an additional focus on how skill development translates to clinically relevant outcomes. We recommend longitudinal studies to examine retention and transfer of training to clinical settings, methods to improve timely, adaptive feedback for deliberate practice, and cost analyses.

Common Iliac Artery to Below-Knee Popliteal Artery Bypass via Obturator Foramen in a Third-Time Reoperative Groin for Limb Salvage in Chronic Limb-Threatening Ischemia.

This case report presents the management of a 69-year-old man with an extensive history of peripheral vascular disease including 2 previous failed right femoral to distal bypasses and a left above-the-knee amputation who presented with right lower extremity rest pain and non-healing shin ulcers. A redo bypass was performed for limb salvage via the obturator foramen to avoid his extensively scarred femoral region. The postoperative course was uneventful and the bypass remained patent in the early period. This case demonstrates the usefulness of the obturator bypass to provide revascularization and avoid amputation in a patient with chronic limb-threatening ischemia and multiple failed bypasses.

Exposure to a Virtual Reality Mass-Casualty Simulation Elicits a Differential Sympathetic Response in Medical Trainees and Attending Physicians.

BACKGROUND: Previous studies have demonstrated the use of virtual reality (VR) in mass-casualty incident (MCI) simulation; however, it is uncertain if VR simulations can be a substitute for in-person disaster training. Demonstrating that VR MCI scenarios can elicit the same desired stress response achieved in live-action exercises is a first step in showing non-inferiority. The primary objective of this study was to measure changes in sympathetic nervous system (SNS) response via a decrease in heart rate variability (HRV) in subjects participating in a VR MCI scenario. METHODS: An MCI simulation was filmed with a 360º camera and shown to participants on a VR headset while simultaneously recording electrocardiography (EKG) and HRV activity. Baseline HRV was measured during a calm VR scenario immediately prior to exposure to the MCI scenarios, and SNS activation was captured as a decrease in HRV compared to baseline. Cognitive stress was measured using a validated questionnaire. Wilcoxon matched pairs signed rank analysis, Welch's t-test, and multivariate logistic regression were performed with statistical significance established at P <.05. RESULTS: Thirty-five subjects were enrolled: eight attending physicians (two surgeons, six Emergency Medicine [EM] specialists); 13 residents (five Surgery, eight EM); and 14 medical students (six pre-clinical, eight clinical-year students). Sympathetic nervous system activation was observed in all groups during the MCI compared to baseline (P <.0001) and occurred independent of age, sex, years of experience, or prior MCI response experience. Overall, 23/35 subjects (65.7%) reported increased cognitive stress in the MCI (11/14 medical students, 9/13 residents, and 3/8 attendings). Resident and attending physicians had higher odds of discordance between SNS activation and cognitive stress compared to medical students (OR = 8.297; 95% CI, 1.408-64.60; P = .030). CONCLUSIONS: Live-actor VR MCI simulation elicited a strong sympathetic response across all groups. Thus, VR MCI training has the potential to guide acquisition of confidence in disaster response.

Transcortical endoportal subchoroidal endoscope-assisted approach to the third ventricle: from virtual reality to anatomical laboratory.

BACKGROUND: Surgical approaches to the third ventricle (TV) have always represented a technical challenge in neurosurgery. Virtual reality (VR) is attaining increasing relevance in training programs and preoperative planning. The aim of this study is to demonstrate the worthwhile mutual contribution of VR simulations and specimen dissections to develop a new surgical approach to the TV. METHODS: The transcortical endoportal subchoroidal endoscope assisted (TEPSEA) approach was planned and simulated thanks to VR (Surgical Theater©, LLC, Cleveland, OH, USA), and then implemented on cadaver specimens by using the VBAS portal system (Viewsite™ Brain Access System TC Model, Vycor Medical™ Inc., Boca Raton, FL, USA). We assessed anthropometric measurements during VR planning and evaluated surgical operability during anatomical dissections. RESULTS: Surgical field depths measured between 75.6 and 85.3 mm to mammillary bodies and habenular commissure, which were in mean 20.2 mm away. An 18-mm movement was estimated for 15°-posterior tilting of a 70-mm long VBAS. Excellent exposure and maneuverability were achieved within the TV through a 2.47 cm2 portal working area. The 30°-endoscope assistance expanded the access towards the anterior and posterior walls of the TV particularly to the infundibular recess, mammillary bodies, habenular commissure and pineal recess. CONCLUSIONS: We documented the utility of a step-by-step VR planning and simulation followed by anatomical dissections to study surgical approaches to deep brain areas. The TEPSEA exploits the portal system and endoscopic assistance to access the entire TV minimizing cortical and white matter manipulation.

Disparities in utilization of robotic surgery for colon cancer: an evaluation of the U.S. National Cancer Database.

Despite the benefits of minimally invasive surgery for colorectal procedures, significant disparities in access to these techniques remain. While these gaps have been well-documented for laparoscopy, few studies have evaluated inequalities in access to robotic surgery. We analyze whether disparities exist in the use of robotic surgery in the management of colon cancer. The U.S. National Cancer Database was queried for patients with non-metastatic colon adenocarcinoma who underwent resection with the robotic platform (2010-2016). Demographic, clinicopathologic, and treatment facility-related variables were analyzed with respect to preferential utilization of robotic surgery with multivariable logistic regression. Patients with metastatic disease, missing or incomplete surgical information, and those who underwent local tumor excision were excluded. 74,984 patients were identified, 3001 (4%) of whom underwent robotic surgery. In multivariable analysis, patients who were older, Black, or were living in an urban area had decreased odds of receiving robotic surgery compared with open or laparoscopic surgery. Patients who were privately insured or living in areas with higher education had increased odds of receiving robotic surgery. Robotic surgery was also preferentially associated with lower clinical stage, more recent year of diagnosis, and hospitals with higher procedural volume. As advantages of the robotic platform are becoming better understood, use of this approach is increasing in popularity for treatment of non-metastatic colon cancer. Despite this, significant disparities exist with respect to patient demographics and socioeconomic factors, and access may only be limited to certain types of hospitals. Further studies are needed to define why these inequalities exist.

Open versus minimally invasive small bowel resection for Crohn's disease: a NSQIP retrospective review and analysis.

INTRODUCTION: Many patients with Crohn's Disease will require surgical resection. While many studies have described outcomes following ileocecectomy, few have evaluated surgical resection of other portions of small bowel. We sought to compare open and minimally invasive surgery (MIS) approaches for small bowel resection excluding ileocecectomy of patients with Crohn's Disease using the National Surgical Quality Improvement Program (NSQIP) database. METHODS: The NSQIP database was queried for patients with Crohn's disease or complications related to Crohn's disease who underwent segmental small bowel resection utilizing open or minimally invasive approaches between 2012 and 2018. Patients requiring ileocecectomy or diagnosed with ascites, disseminated cancer, pre-operative sepsis, ASA class 5, and patients requiring mechanical ventilation were excluded. The association of pre-operative variables including patient demographic information and comorbidities with surgical approach were examined using Fishers exact test. Intraoperative, and 30-day post-operative outcomes were compared between the groups using both univariate and multivariate logistical regression models. SAS was used for data analysis with p < 0.05 considered significant. RESULTS: After exclusions, we found 1697 patients with Crohn's disease who underwent segmental small bowel resection, 1252 of whom underwent open surgery and 445 of whom underwent MIS. After adjusting for possible confounders with multivariable analysis, patients who underwent MIS had a lower incidence of wound events (surgical site, organ space, or deep wound infection, or dehiscence), post-operative bleeding, need for return to the operating room, and shorter total hospital length of stay despite longer operative times compared with open surgery. CONCLUSIONS: This retrospective review of NSQIP shows that minimally invasive small bowel resection is associated with equivalent or improved morbidity over open surgery in select patients with small bowel Crohn's Disease. We show that in select patients minimally invasive small bowel resection can be safe and performed for patients with isolated small bowel Crohn's disease.

Surgical management of splenic flexure colon cancer: a retrospective propensity-matched study comparing open and minimally invasive approaches using the national cancer database.

PURPOSE: Minimally invasive resection of colon cancer at the splenic flexure can be technically challenging with concerns for a suboptimal oncologic outcome. We aimed to compare open and minimally invasive approaches following curative resection. METHODS: The National Cancer Database was queried for patients with non-metastatic colon adenocarcinoma at the splenic flexure who underwent resection from 2010 to 2016. Cohorts were separated into open and minimally invasive approaches, and demographic and clinicopathologic variables were compared. Propensity-score matching (PSM) was utilized to balance potential confounding covariates between cohorts to elucidate the independent association between surgical approach and outcomes. Kaplan-Meier estimation and Cox-proportional hazards regression were used to analyze survival. Secondary outcomes were analyzed by way of logistic regression or Mann-Whitney U test. RESULTS: After matching, 842 patients were compared between approaches. Patients who underwent minimally invasive surgery had no significant difference in regional nodes ≥ 12 examined, positive margins, negative circumferential margins, unplanned 30-day readmission, or time from surgery to initiation of chemotherapy when compared to patients who underwent open surgery. Minimally invasive surgery was significantly associated with decreased odds of 30-day mortality, 90-day mortality, and decreased mortality hazard for 5-year overall survival compared to open surgery. CONCLUSION: The optimal approach for surgical management of splenic flexure colon cancer has not been standardized given its rarity and exclusion from randomized controlled trials. Our retrospective review suggests that minimally invasive resection of splenic flexure colon cancers in carefully selected patients is associated with equivalent oncologic outcomes as well as improved short and long-term survival compared to an open approach.

Study of comparative surgical exposure to the petroclival region using patient-specific, petroclival meningioma virtual reality models.

OBJECTIVE: Despite advancement of surgical techniques, the attachments of petroclival meningiomas near the central clival depression (CCD) remain difficult to visualize. With existing methods, the amount of tumor near the CCD that is inaccessible through various approaches cannot be compared. Tumors distort the brainstem, changing the size of the operative corridor for some but not all approaches; therefore, using cadavers with normal posterior fossae makes it impossible to compare different approaches to the tumor. The authors used virtual reality (VR) models created from the imaging data of patients to compare various surgical approaches that have otherwise been incomparable in previous studies. METHODS: CT and MRI data obtained in 15 patients with petroclival meningiomas were used to create anatomically accurate 3D VR models. For each model, various surgical approaches were performed, and the surgical freedom to 6 targets of the regions were measured. Furthermore, portions of the tumor that were visually blocked by the brainstem or bony structures were segmented and recorded as blinded volumes for comparison. RESULTS: The extended retrosigmoid approach generated excellent exposure of the petroclival region, but for most specimens, there was inaccessible tumor volume adjacent to the brainstem (mean 641.3 mm3, SE 161.8). In contrast, the brainstem sides of the tumors were well-visualized by all the transpetrosal approaches. The blinded volume of the tumor was largest for the retrolabyrinthine approach, and this was statistically significant compared with all other approaches (mean 2381.3 mm3, SE 185.4). CONCLUSIONS: The authors performed a novel laboratory study by using patient CT and MRI data to generate 3D virtual models to compare surgical approaches. Since it is impossible to perform various approaches in separate surgeries in patients for comparison, VR represents a viable alternative for such comparative investigations.

Real-time navigation guidance with intraoperative CT imaging for pedicle screw placement using an augmented reality head-mounted display: a proof-of-concept study.

OBJECTIVE: Augmented reality (AR) has the potential to improve the accuracy and efficiency of instrumentation placement in spinal fusion surgery, increasing patient safety and outcomes, optimizing ergonomics in the surgical suite, and ultimately lowering procedural costs. The authors sought to describe the use of a commercial prototype Spine AR platform (SpineAR) that provides a commercial AR head-mounted display (ARHMD) user interface for navigation-guided spine surgery incorporating real-time navigation images from intraoperative imaging with a 3D-reconstructed model in the surgeon's field of view, and to assess screw placement accuracy via this method. METHODS: Pedicle screw placement accuracy was assessed and compared with literature-reported data of the freehand (FH) technique. Accuracy with SpineAR was also compared between participants of varying spine surgical experience. Eleven operators without prior experience with AR-assisted pedicle screw placement took part in the study: 5 attending neurosurgeons and 6 trainees (1 neurosurgical fellow, 1 senior orthopedic resident, 3 neurosurgical residents, and 1 medical student). Commercially available 3D-printed lumbar spine models were utilized as surrogates of human anatomy. Among the operators, a total of 192 screws were instrumented bilaterally from L2-5 using SpineAR in 24 lumbar spine models. All but one trainee also inserted 8 screws using the FH method. In addition to accuracy scoring using the Gertzbein-Robbins grading scale, axial trajectory was assessed, and user feedback on experience with SpineAR was collected. RESULTS: Based on the Gertzbein-Robbins grading scale, the overall screw placement accuracy using SpineAR among all users was 98.4% (192 screws). Accuracy for attendings and trainees was 99.1% (112 screws) and 97.5% (80 screws), respectively. Accuracy rates were higher compared with literature-reported lumbar screw placement accuracy using FH for attendings (99.1% vs 94.32%; p = 0.0212) and all users (98.4% vs 94.32%; p = 0.0099). The percentage of total inserted screws with a minimum of 5° medial angulation was 100%. No differences were observed between attendings and trainees or between the two methods. User feedback on SpineAR was generally positive. CONCLUSIONS: Screw placement was feasible and accurate using SpineAR, an ARHMD platform with real-time navigation guidance that provided a favorable surgeon-user experience.

Infra-Occipital Supra-Tentorial Approach for Resection of Low-Grade Tumor of the Left Lingual Gyrus: 2-Dimensional Operative Video.

Surgical treatment of lesions involving the postero-medial occipito-temporal region is challenging because of high risk of morbidity due to damage or excessive retraction of critical neuro-vascular structures, especially within the dominant hemisphere.1-3 Here, we describe the case of a 17-yr-old patient who underwent resection of an epileptogenic low-grade tumor located within the left-dominant lingual gyrus. Seizures were characterized, as a first symptom, by right-sided simple visual hallucination that pointed to the left pericalcarine region, corresponding to the lesion location. No signs of primary involvement of anterior temporo-mesial structures (hippocampus/amygdala) were found. As the anatomo-electroclinical correlation was concordant, direct tumor removal was indicated through an infra-occipital supratentorial approach. This route allowed direct access to the target through a safe extra-axial corridor, which limits intraparenchymal dissection until the tumor margin is identified and avoids critical vascular structures, such as the vein of Labbé.4,5 An external cerebrospinal fluid (CSF) drainage was used to facilitate brain relaxation, minimizing brain and venous retraction and, consequently, reducing the risk of postoperative neurological complications, especially for vision. Postoperative magnetic resonance imaging (MRI) demonstrated no surgical complications. Pathological examination revealed a ganglioglioma. At 9-mo follow-up, the neurological examination was normal, antiepileptic therapy was stopped, and the patient was seizure-free. The video describes the main surgical steps, using both intraoperative videos and advanced 3-dimensional modeling of neuroimaging pictures. Informed consent was obtained for surgery and video recording.

Progressive Orbitotomy and Graduated Expansion of the Supraorbital Keyhole: A Comparison with Alternative Minimally Invasive Approaches to the Paraclinoid Region.

BACKGROUND: Various minimally invasive approaches, such as supraorbital (SO), minipterional (MPT), and translateral orbital (TLO), can access the paraclinoid region. Studies have described these approaches individually but have not directly compared all of them in the same anatomic specimen. METHODS: Using virtual reality models generated from computed tomography studies of living subjects, we simulated TLO, MPT, and variations of SO approaches, without and with removal of the orbital rim and sphenoid wing. We measured the area of freedom (AOF), distance, and angle of attack to 4 paraclinoid targets: anterior clinoid process, optic foramen, lateral superior orbital fissure, and maxillary strut. RESULTS: For superiorly positioned targets, such as anterior clinoid process and optic foramen, MPT provided a larger AOF compared with the supraorbital approach. However, with progressive drilling of the orbital roof and lesser wing of the sphenoid, the SO corridor AOF was equivalent to MPT at the anterior clinoid process and larger at the optic foramen (P = 0.003). To the lateral superior orbital fissure, TLO had the most limited AOF, and MPT had the greatest (P < 0.01 for all comparisons). For the maxillary strut, MPT, TLO, and SO with orbitotomy and sphenoidectomy all provided a similar AOF. CONCLUSIONS: For surgical targets in the paraclinoid region, MPT provided a greater AOF and shorter distance compared with TLO and limited SO approaches. With progressive enlargement of the SO corridor, SO with orbitotomy and sphenoidectomy matched and occasionally superseded the AOF of MPT. However, the AOF to inferomedial targets such as the maxillary strut was similar among all approaches.

From CT to 3D Printed Models, Serious Gaming, and Virtual Reality: Framework for Educational 3D Visualization of Complex Anatomical Spaces From Within-the Pterygopalatine Fossa.

We describe the framework for capturing the internal view of complex anatomical spaces via multiple media and haptic platforms, exemplified by realistic and conceptual representations of the pterygopalatine fossa (PPF). A realistic three-dimensional (3D) mesh of the PPF was developed by segmenting the osseous anatomy on computed tomography (CT) using Materialize InPrint. Subsequently in Autodesk 3D Studio Max, the realistic mesh was enhanced with graphically designed neurovascular anatomy and additionally a conceptual representation of the PPF with its connections and contents was created. An interactive web-compatible Adobe Flash tutorial using ActionScript was developed, allowing users to advance through a series of educational slides that contained interactive rotatable interior camera views and scrollable CT cross-sectional content, incorporating both the realistic and conceptual models. Both models were also 3D printed using polyamide material. In the realistic model, the neurovasculature was colored with water-based acrylic paint. A 3-piece modular design with embedded magnets allows for internal visualization and seamless assembly. A serious gaming environment of the conceptual PPF was also developed using Truevision3D application programming interface, where users can freely move around rooms and hallways that represent various spaces. Lastly, the realistic model was incorporated into a headset-based virtual reality environment, Surgical Theater, allowing visualization and fly-through inside and outside the model. Multiple 3D techniques for visualization of complex 3D anatomical spaces from within were described, with the necessary software and skills detailed. A rough estimate of the time and cost needed to develop these tools as well as multiple supplementary source and end result files are also made available. Educators could utilize multiple advanced delivery methods to incorporate custom digital 3D models of complex anatomical spaces understood from inside.

Mini Fronto-Orbital Approach: "Window Opening" Towards the Superomedial Orbit - A Virtual Reality-Planned Anatomic Study.

BACKGROUND: Surgical approaches to the orbit are challenging and require combined multispecialist skills. Considering its increasing relevance in neurosurgical practice, keyhole surgery could be also applied to this field. However, mastering a minimally invasive approach necessitates an extended learning curve. For this reason, virtual reality (VR) can be effectively used for planning and training in this demanding surgical technique. OBJECTIVE: To validate the mini fronto-orbital (mFO) approach to the superomedial orbit, using VR planning and specimen dissections, conjugating the principles of skull base and keyhole neurosurgery. METHODS: Three-dimensional measurements were performed thanks to Surgical Theater (Surgical Theater© LLC), and then, simulated craniotomies were implemented on cadaver specimens. RESULTS: The mFO approach affords optimal exposure and operability in the target area and reduced risks of surrounding normal tissue injuries. The eyebrow skin incision, the minimal soft-tissue retraction, the limited temporalis muscle dissection and the single-piece craniotomy, as planned with VR, are the key elements of this minimally invasive approach. Furthermore, the "window-opening" cotton-tip intraorbital dissection technique, based on widening surgical corridors between neuromuscular bundles, provides a safe orientation and a deep access inside the orbit, thereby significantly limiting the risk of jeopardizing neurovascular structures. CONCLUSION: The mFO approach associated to the window-opening dissection technique can be considered safe, effective, suitable, and convenient for treating lesions located in the superomedial orbital aspect, up to the orbital apex.

The Benefits of Limited Orbitotomy on the Supraorbital Approach: An Anatomic and Morphometric Study in Virtual Reality.

BACKGROUND: Cadaveric studies on surgical anatomy and approaches are hampered by the limited number of specimens. Virtual reality (VR) technology can overcome this limitation, allowing for more in-depth statistical analysis of the data. OBJECTIVE: To determine the benefit of a supraorbital ridge osteotomy in a supraorbital craniotomy targeting (1) the anterior communicating artery complex (ACOM), and (2) a lesion 25 mm above tuberculum sellae, using a large dataset generated by VR. METHODS: Computed tomography scans of 30 subjects without cranial osseous pathology were identified for use with VR technology. After correlating VR and DICOM datasets, supraorbital craniotomies were simulated without and with removal of supraorbital ridge, bilaterally (n = 60). Area of freedom (AOF) from the outer table to the targets and the vertical center angle (VCA) to targets were calculated, before and after the orbitotomy. RESULTS: For the ACOM, AOF averaged 496 mm2 (range: 322-805) and increased 8.9% to an average of 547 mm2 with the removal of the supraorbital ridge (P < .001). VCA increased from 18.5 to 20.3 degrees. For the suprasellar target, AOF averaged 507 mm2 (range 324-772) and increased 42.5% to 722 mm2 after orbitotomy (P < .001). VCA increased from 22.1 to 30.8 degrees. CONCLUSION: VR technology is an emerging tool to study neurosurgical approaches. Here, we demonstrate with VR that the removal of the supraorbital ridge in a supraorbital craniotomy affords greater access to superiorly located lesions of the anterior fossa floor; however, deeper and lower lesions require a more aggressive orbital roof osteotomy to widen the exposure.

The Benefits of Progressive Occipital Condylectomy in Enhancing the Far Lateral Approach to the Foramen Magnum.

BACKGROUND: The portion of the occipital condyle that is safe to remove remains controversial in the transcondylar approach. We aimed to correlate the gain in exposure with incremental removal of the occipital condyle to determine if there is a point where further drilling yields diminishing gains. METHODS: Virtual reality rendering of the skull was generated from 25 subjects with no posterior fossa pathology. A suboccipital far lateral craniotomy was done in virtual reality space, stopping at the posterior edge of the occipital condyle. Angular measurements of surgical corridor were taken at this point and after removal of 25% and 50% of the condyle. Two surgical targets were used: at the anterior midline of the foramen magnum and the vertebrobasilar junction. RESULTS: Progressive removal of the occipital condyle increased exposure to both targets in a linear fashion. For the midline of the foramen magnum, the working angle increased from 12° to 18° for quarter condylectomy and then to 25° for half condylectomy. The corridor to the vertebrobasilar junction was much tighter, and the angle increased from 5.5° to 9° for quarter condylectomy and then to 12° for half condylectomy. The gain in exposure for the low target was greater than for the high target (P < 0.001). CONCLUSIONS: Progressive removal of the occipital condyle yielded a linear increase in exposure without an ideal point beyond which the drilling was futile. However, the impact of condylectomy was greater for our low target compared with our high target.

An anatomical study of the foramen of Monro: implications in management of pineal tumors presenting with hydrocephalus.

BACKGROUND: For pineal tumors presenting with hydrocephalus, simultaneous endoscopic third ventriculostomy (ETV) and tumor biopsy is commonly used as the initial step in management. To analyze the restriction which the foramen of Monro poses to this procedure, one must start with a detailed description of the microsurgical anatomy of the foramen in living subjects. However, the orientation and shape of the foramen of Monro make this description difficult with conventional imaging techniques. METHOD: Virtual reality technology was applied on MRIs on living subject without hydrocephalus, as well as patients with hydrocephalus, to generate precise anatomical models with sub-millimeter accuracy. The morphometry of the foramen of Monro was studied in each group. In addition, displacement of the margins of the foramen was studied in detail for simultaneous ETV and pineal tumor biopsy through a single burr hole. RESULTS: In 30 normal subjects, the foramen of Monro had oval-shaped openings averaging 5.23 mm2. The foramen was larger in people above age 55 (p = 0.007) and on the left side compared to the right (p = 0.002). For patients with clinical presentation of hydrocephalus, the average opening was 32.6 mm2. Simulated single burr hole simultaneous ETV and pineal tumor biopsy was performed in 10 specimens. Average displacement of the posterior and anterior margins of the foramen was 5.71 mm and 5.76 mm, respectively. However, maximum displacement reached 9.3 mm posteriorly and 10 mm anteriorly. CONCLUSIONS: The foramen of Monro is an oval-shaped cylinder that changes in size and orientation in the hydrocephalic patient. If universally applied to all patients regardless of foramen and tumor size, ETV/biopsy can displace structures around the Foramen of Monro up to 1 cm, which can potentially lead to neurological damage. Careful pre-operative assessment is critical to determine if a single burr hole approach is safe.