Virtual reality-based evaluation of neurovascular conflict for the surgical planning of microvascular decompression in trigeminal neuralgia patients.

OBJECTIVE: Trigeminal neuralgia (TN) is a lightning bolt of violent, electrifying, and stinging pain, often secondary to the neurovascular conflict (NVC). The vessels involved in NVC are mostly arteries and rarely veins. Evaluation of NVC in the deep infratentorial region is inseparably connected with cranial imaging. We retrospectively analyzed the potential influence of three-dimensional (3D) virtual reality (VR) reconstructions compared to conventional magnetic resonance imaging (MRI) scans on the evaluation of NVC for the surgical planning of microvascular decompression in patients with TN. METHODS: Medical files were retrospectively analyzed regarding patient- and disease-related data. Preoperative MRI scans were retrospectively visualized via VR software to detect the characteristics of NVC. A questionnaire of experienced neurosurgeons evaluated the influence of VR visualization technique on identification of anatomical structures involved in NVC and on surgical strategy. RESULTS: Twenty-four patients were included and 480 answer sheets were evaluated. Compared to conventional MRI, image presentation using 3D-VR modality significantly influenced the identification of the affected trigeminal nerve (p = 0.004), the vascular structure involved in the NVC (p = 0.0002), and the affected side of the trigeminal nerve (p = 0.005). CONCLUSIONS: In patients with TN caused by NVC, the reconstruction of conventional preoperative MRI scans and the spatial and anatomical presentation in 3D-VR models offers the possibility of increased understanding of the anatomy and even more the underlying pathology, and thus influences operation planning and strategy.

Load-Bearing Capacity and Design Advantages of a Custom-Made, Thin Pure-Titanium Cranioplasty (CranioTop).

BACKGROUND: Adequate and stable coverage of cranial contour and continuity defects of any origin is a common challenge in neurosurgical clinics. This study presents the results of investigations concerning the mechanical load-bearing capacity and design advantages of custom-made implants made from a thin, pure-titanium sheet (CranioTop) (CLinstruments, Attendorn, Germany) for covering complex cranial defects. METHODS: In 9 test series, the stability of three differently shaped and sized thin titanium sheet implants was tested using vertical, uniaxial compression with 3 different compression stamps, to investigate the behaviour of these implants in relation to punctiform as well as planar forces. RESULTS: All 9 model implants showed elastic behavior in the synchronously recorded force/displacement diagrams at an impression of up to 2 mm. The forces at 2 mm deformation were between 170.1 and 702.7 Newton. CONCLUSION: Cranioplasty using CranioTop is a stable procedure for covering skull defects, even those of large dimensions. An added advantage is the significant reduction in effort required to prepare the area of the bone margins compared to other current techniques of cranioplasty.

Normal pressure hydrocephalus as a failure of ICP homeostasis mechanism: the hidden role of Monro-Kellie doctrine in the genesis of NPH.

OBJECTIVE: The theme of this paper is to outline that the genesis of normal pressure hydrocephalus (NPH) is governed by the intracranial pressure (ICP) homeostatic principle. The development of this new concept is based mainly on rethinking the well-known Monro-Kellie doctrine in the way that ICP homeostasis mechanism is not only a mechanism that works to prevent pathologically high ICP but also a mechanism that aims to protect from pathologically low ICP. METHODS: The NPH-related literatures are reviewed and reinterpreted to generate a new paradigm for the cascade of pathophysiological events that leads to the genesis NPH, as well as the mechanism of clinical beneficial effects and complications of the shunting procedure. RESULTS: According to this new paradigm, the suboptimal cerebral perfusion that is associated with the impairment of the cerebral autoregulation is the initial step in the genesis of NPH. When the overall volume of blood that circulates intracranially is diminished, a chronic low ICP with episodes of pathologically low ICP occurs. Since the cranial vault is not collapsible, those episodes of low ICP are compensated by the accumulation of cerebrospinal fluid (CSF) to keep the ICP in normal ideal range. The impairment of brain toxin-flushing mechanism because of CSF pooling combined with the already-established suboptimal cerebral perfusion leads to functional disinhibition of the cerebral cortex. CONCLUSION: Recognizing the importance of ICP homeostatic mechanisms in the genesis of the NPH is a simple yet novel view that could change the way we look at NP and can give a basic and fundamental theoretical frame work to achieve better understanding of NPH.

Placement of thoracolumbar pedicle screws using O-arm-based navigation: technical note on controlling the operational accuracy of the navigation system.

Suboptimal placements of pedicle screws may lead to neurological and vascular complications. Computer-assisted image guidance has been shown to improve accuracy in spinal instrumentation. Checking the accuracy of the navigation system during pedicle screw placement is fundamental. We describe a novel technique of using continuous accuracy check of the navigation system during O-arm-based neuronavigation to instrument the thoracolumbar region. Forty thoracic and 42 lumbar screws were inserted in 12 patients. The Mirza evaluation system was used to evaluate the accuracy of the inserted screws. There was no neurological injury and no need to reposition any screw. The accuracy of the screws placement was excellent. Our technique of continuous at will operational accuracy check of the neuronavigation system is associated with extreme accuracy of screw placement, no need to bring a patient back to the operating room to reposition a pedicle screw, and with excellent outcome.

A microanatomical map of the structures hidden in the middle fossa based on the facial nerve hiatus: measurements and their variability.

The aim of this study was to investigate the relationships/variations between the facial nerve hiatus (FNH) and middle cranial fossa neuro-vascular structures. Twenty CT-scanned middle cranial fossae of fresh adult cadavers were used; the greater superficial petrosal nerves, and critical neuro-vascular structures were identified. Using the FNH as a reference point, a neuronavigation system was used to measure the distance between each structure and the FNH. The coefficient of variation (CV) was used to quantify the degree of variation among each distance. The mean distances and standard deviations between the various landmarks and the FNH, and the associated CV were analyzed. Furthermore, a microanatomical map of the structures hidden in the middle fossa based on the greater superficial petrosal nerve was generated. The most reliable relationships of the FNH were with the internal auditory canal (CV = 14.59), and with the vertical portion of the intrapetrous internal carotid artery (CV = 15.54). Our data demonstrate that the FNH can be used as anatomical landmark to plot the position of several hidden neurovascular structures when performing a middle-fossa skull base approach. However, the pattern and the variation of these structures had to be recognized.

Setting up a microneurosurgical skull base lab: technical and operational considerations.

Microneurosurgical cadaveric dissections have become popular due to their usefulness in obtaining a working knowledge of the microneurosurgical anatomy in a controlled environment. This same controlled environment is also conducive to experiment with new surgical approaches. These factors have increased the number of microneurosurgical anatomic laboratories. Despite the increase in microneurosurgical laboratories, there is very little literature regarding the logistics of starting and maintaining a new neurosurgical laboratory. The aim of this paper is to provide a general road map and basic guidelines in starting and running a microneurosurgical dissection laboratory. The information in this paper is based on a review of the literature and on the experience we gained in organizing and managing the Dardinger Microneurosurgical Skull Base Laboratory at The Ohio State University.

Endoscopic orbital roof fenestration as an alternative treatment option for idiopathic intracranial hypertension: a cadaveric anatomical study.

BACKGROUND: We investigated a new minimally invasive surgical technique for the treatment of idiopathic intracranial hypertension in a cadaveric model. This technique aims at establishing a communication between the intraorbital and intracranial compartments by creating a bone, dural, and periorbital window in the anterior cranial fossa. This procedure is predicated on intraorbital absorptive capability that has been demonstrated in animals and discussed in humans. METHODS: Three fresh cadaver heads were fixed in a head holder so as to mimic the hyperextended supine position. The procedure was conducted bilaterally in each specimen. Our technique is as follows: 1) An incision is made in the eyebrow medial to the supraorbital notch; 2) using an endoscope and a periosteal elevator, the intraorbital surface of the orbital roof is separated from the periorbita in an anteroposterior direction for a length of 1.5-2.5 cm; 3) a 1 cm of the exposed orbital roof is removed, and the dura and arachnoid are opened; and 4) slits are made in the exposed periorbita. RESULTS: We were able to create a communication between the intracranial and the intraorbital compartments in all specimens. CONCLUSION: Our technique is new and does not require any foreign body implantation. Its applicability in humans needs to be evaluated in a clinical context.

Cerebral Anatomy Detection and Surgical Planning in Patients with Anterior Skull Base Meningiomas Using a Virtual Reality Technique.

Anterior skull base meningiomas represent a wide cohort of tumors with different locations, extensions, configurations, and anatomical relationships. Diagnosis of these tumors and review of their therapies are inseparably connected with cranial imaging. We analyzed the influence of three-dimensional-virtual reality (3D-VR) reconstructions versus conventional computed tomography (CT) and magnetic resonance imaging (MRI) images (two-dimensional (2D) and screen 3D) on the identification of anatomical structures and on the surgical planning in patients with anterior skull base meningiomas. Medical files were retrospectively analyzed regarding patient- and disease-related data. Preoperative 2D-CT and 2D-MRI scans were retrospectively reconstructed to 3D-VR images and visualized via VR software to detect the characteristics of tumors. A questionnaire of experienced neurosurgeons evaluated the influence of the VR visualization technique on identification of tumor morphology and relevant anatomy and on surgical strategy. Thirty patients were included and 600 answer sheets were evaluated. The 3D-VR modality significantly influenced the detection of tumor-related anatomical structures (p = 0.002), recommended head positioning (p = 0.005), and surgical approach (p = 0.03). Therefore, the reconstruction of conventional preoperative 2D scans into 3D images and the spatial and anatomical presentation in VR models enabled greater understanding of anatomy and pathology, and thus influenced operation planning and strategy.

Impact of Virtual Reality in Arterial Anatomy Detection and Surgical Planning in Patients with Unruptured Anterior Communicating Artery Aneurysms.

Anterior-communicating artery (ACoA) aneurysms have diverse configurations and anatomical variations. The evaluation and operative treatment of these aneurysms necessitates a perfect surgical strategy based on review of three-dimensional (3D) angioarchitecture using several radiologic imaging methods. We analyzed the influence of 3D virtual reality (VR) reconstructions versus conventional computed tomography angiography (CTA) scans on the identification of vascular anatomy and on surgical planning in patients with unruptured ACoA aneurysms. Medical files were retrospectively analyzed regarding patient- and disease-related data. Preoperative CTA scans were retrospectively reconstructed to 3D-VR images and visualized via VR software to detect the characteristics of unruptured ACoA aneurysms. A questionnaire was used to evaluate the influence of VR on the identification of aneurysm morphology and relevant arterial anatomy and on surgical strategy. Twenty-six patients were included and 520 answer sheets were evaluated. The 3D-VR modality significantly influenced detection of the aneurysm-related vascular structure (p = 0.0001), the recommended head positioning (p = 0.005), and the surgical approach (p = 0.001) in the planning of microsurgical clipping. Thus, reconstruction of conventional preoperative CTA scans into 3D images and the spatial presentation in VR models enabled greater understanding of the anatomy and pathology, provided realistic haptic feedback for aneurysm surgery, and influenced operation planning and strategy.

An endoscopic, cadaveric analysis of the roof of the fourth ventricle.

We performed endoscopic dissections of the roof of the fourth ventricle in eight fresh human cadaveric heads to characterize the endoscopic anatomy of the roof of the fourth ventricle and the anatomical configuration of the structures forming its roof. We also made three-dimensional (3D) silicone casts of the fourth ventricle in seven formalin-fixed specimens to evaluate the 3D configuration of the structures that create the roof of the fourth ventricle. The roof of the fourth ventricle can be divided into three zones. The upper zone is formed by the superior cerebellar peduncle and superior medullary velum and is associated with the lingula. The middle zone is formed by the inferior cerebellar peduncles and inferior medullary velum and is associated with the nodule in the midline and with the peduncle of the flocculus. The lower zone is formed by the tela choroidea and is associated with the tonsils. The 3D shape of the roof the fourth ventricle resembles that of a rhomboid-based pyramid; the edges of the base represent the borders of the ventricle, and the apex is the cerebellar fastigium. The lateral recess is shaped like a triangular-based pyramid, with its base connected to the cavity of the fourth ventricle and its tip opening into the lateral cerebellomedullary cistern through the foramen of Luschka. Our results may help in the endoscopic exploration of and microsurgical approaches to the fourth ventricle through its roof.

Real time parallel intraoperative integration of endoscopic, microscopic, and navigation images: a proof of concept based on laboratory dissections.

Endoscope, microscope, and neuronavigation systems are integrated in neurosurgical procedures mainly by using a serial combination algorithm, where, the user must switch his/her field of view from one platform display to another. The integration of theses devices could be optimized by incorporating different displays into one viewing platform thus achieving a parallel combination. In this study, we investigated the feasibility and the applicability of parallel integration of microscopic, endoscopic, and neuronavigation images by real time displaying the endoscope and neuronavigation image datasets in the main operative microscope oculars. The proposed set-up was effective in displaying the three images dataset in an operationally actionable mode. Ergonomically, the ability of using the different image dataset without the need of taking the eyes off the microscope oculars did not disrupt the flow or the tempo of the operative procedure. However, new endoscopes specific to this application are recommended.

A new methodology for laboratory evaluation of neurosurgical approaches based on the volume and shape of the surgical space with a mathematical model to quantify the surgical maneuverability in laboratory settings.

We conducted this study to validate the volume/shape of the surgical exposure and to introduce a mathematical model to quantify the maneuverability in a surgical space. We executed the pterional and lateral supraorbital approach four times in fresh cadavers in skull base laboratory. The surgical volumes were filled with a computed tomography (CT)-imageable mixture; CT scans were obtained to evaluate the volume and shape of the surgical space. The volume of the surgical space was 23.60 and 32.90 mL for the lateral supraorbital and pterional approach, respectively, (p < 0.05). The three-dimensional shape of the lateral supraorbital approach was cylindrical and that of the pterional approach pyramidal. The volume of the surgical approach can be used to define, together with other variables, the maneuverability (maneuvering in a surgical volume) by using the following formula [Formula: see text] where M, A, V, and L represent the maneuverability, the degree of the surgical freedom, the volume of the surgical exposure, and the surgical depth, respectively. Volume and shape of the surgical exposure are two objective parameters that can be used to define and contrast different microsurgical approaches in a laboratory setting. The volume of the surgical exposure may be integrated into a mathematical formula defining maneuverability.

Path to the Interpeduncular Fossa: Anatomical Comparison of Endoscopic-Assisted versus Standard Subtemporal Approach.

Objective The aim of this study was to assess the assumed advantage of endoscopic assistance to the standard subtemporal approach. The idea was to measure qualitatively and quantitatively visibility versus operability. Design We performed eight subtemporal dissections on four cadaver heads. Our dissections integrated an operating microscope, endoscope, and neuronavigation. Comparison was made between visibility and operability afforded by the microscope alone or by the microscope-endoscope combination. Visibility was recorded as complete or incomplete and was quantified for key structures using linear measurements taken by the navigation system. Operability was determined by whichever maneuvers could be safely and comfortably accomplished in the space afforded. Results From our survey, the structures whose visibility most benefitted from the addition of the endoscope include: contralateral third nerve, posterior perforated substance, mammillary bodies, and contralateral superior cerebellar artery. With regard to quantitative evaluation, we found increased visibility of both basilar artery and posterior cerebral artery. With regard to the operability, no objective advantage was afforded by the addition of the endoscope. Subjectively, the maneuvers were easier to perform while using the endoscope. Conclusion Using the endoscope as an assistance tool during conducting classical subtemporal approach can help in overcome a lot of the classical subtemporal approach limitations.

Deep brain stimulation for neurological disorders.

Deep brain stimulation (DBS) involves the delivery of precise electrical signals to specific deep anatomical structures of the central nervous system, with the objective of altering or modulating neural functioning and achieving a reversible, adjustable and therapeutic or clinically beneficial effect. The exact mechanism of action of DBS is still the subject of ongoing investigations. However, based on extensive clinical investigations, it has become an established modality for the surgical treatment of advanced and medication intractable movement disorders such as Parkinson's disease, essential tremor and dystonia. DBS is also being investigated for conditions such as intractable epilepsy, neurobehavioral and psychiatric disorders such as treatment resistant depression, obsessive compulsive disorders, addiction, obesity, Alzheimer's disease and traumatic brain injury. The advantage of DBS over older deep brain lesioning procedures is its reversibility and adjustability. The design of the DBS systems allows for dynamic adjustment of the effects of electrical stimulation by altering the contacts at which electrical pulses are delivered to the brain and changing the stimulation parameters of those pulses. The clinical results from studies on DBS show that it has great potential making it one of most promising fields which could be used to address challenging neurological problems.

Targeting the affective and cognitive aspects of chronic neuropathic pain using basal forebrain neuromodulation: rationale, review and proposal.

Chronic pain is a major health problem in developed countries where it may affect as much as 20% of the adult population. There have been no significant clinical breakthroughs in therapeutic options for persons with chronic neuropathic pain. These limitations underscore the importance of developing new therapies for this disabling pain syndrome. We have reviewed the limitations of the present treatment strategies for chronic pain, neurophysiology of somatosensory transmission and nociception, mechanisms of neuropathic pain, the concept of a "pain matrix" and the "top-down" modulation of pain, and the cognitive affective role in processing of the pain experience. We found that affective and cognitive aspects of pain constitute important considerations in achieving improvements in the outcomes of pain neuromodulation in patients with chronic neuropathic pain. Based on our review, we propose that future novel neuromodulatory therapeutic strategies should be directed at areas in the brain that are involved in the neural mechanisms of reward valuation and appetitive motivation such as nucleus accumbens, ventral tegmental area, and prefrontal cortex.

Effect of registration mode on neuronavigation precision: an exploration of the role of random error.

The aim of this paper is to analyze the variations in registration accuracy for computer-assisted surgical navigation using three different modes of registration, in order to explore the behavior of random error, and to highlight the precision of neuronavigation as a concept distinct from accuracy. The operational accuracy of three different registration modes (bone fiducials, scalp adhesive fiducials and an auto-registration mask) was evaluated in a total of 20 fresh cadaveric heads. The precision of the neuronavigation system was then assessed by evaluating the variation in the accuracy measurements associated with each registration mode. The coefficient of variation was employed to quantify the degree of variation in the attained accuracy using the following formula: Coefficient of variation = standard deviation/mean * 100. For external targets, the precision of the neuronavigation system was greatest with mask registration (43.75 and 51.41 for anterior and posterior external targets, respectively) and lowest with bone registration (65.30 and 67.17 for anterior and posterior external targets, respectively). For internal targets, the precision of the neuronavigation system was greatest with bone registration (47.69 and 42.6 for anterior and posterior internal targets, respectively) and lowest with mask registration (62.9 and 58.67 for anterior and posterior internal targets, respectively). The precision (reproducibility) of the neuronavigation system is another important quantity besides accuracy that characterizes the performance of the system. Understanding both of these quantities for a given registration mode enhances the use of a neuronavigation system in neurosurgery.

Microscopic and endoscopic anterior communicating artery complex anatomy as seen through keyhole approaches.

The purpose of this anatomical study is to illustrate the microscopic and endoscopic anatomy of the anterior communicating artery complex as viewed through three keyhole approaches (keyhole pterional, lateral supraorbital and supraorbital) and to compare them. Each approach was carried out once on each side in five glutaraldehyde-fixed human cadaveric heads. A microscope and microscope-endoscope combination were used to grade access and visualization of the structures qualitatively using a previously published surgical exposure grading system. All three approaches provided good access and visualization of ipsilateral structures in the anterior communicating artery complex, but the pterional keyhole and the lateral supraorbital approaches gave the best access. Exposure of contralateral structures was limited overall, but was enhanced somewhat by the use of the endoscope.