A new strategic neurosurgical planning tool for brainstem cavernous malformations using interactive computer graphics with multimodal fusion images

Efficacy of a Novel Augmented Reality Navigation System Using 3D Computer Graphic Modeling in Endoscopic Transsphenoidal Surgery for Sellar and Parasellar Tumors

In endoscopic transsphenoidal skull base surgery, knowledge of tumor location on imaging and the anatomic structures is required simultaneously. However, it is often difficult to accurately reconstruct the endoscopic vision of the surgical field from the pre-surgical radiographic images because the lesion remarkably displaces the geography of normal anatomic structures. We created a precise three-dimensional computer graphic model from preoperative radiographic data that was then superimposed on a visual image of the actual surgical field and displayed on a video monitor during endoscopic transsphenoidal surgery. We evaluated the efficacy of this augmented reality (AR) navigation system in 15 consecutive patients with sellar and parasellar tumors. The average score overall was 4.7 [95% confidence interval: 4.58-4.82], which indicates that the AR navigation system was as useful as or more useful than conventional navigation in certain patients. In two patients, AR navigation was assessed as less useful than conventional navigation because perception of the depth of the lesion was more difficult. The developed system was more useful than conventional navigation for facilitating an immediate three-dimensional understanding of the lesion and surrounding structures.

Real Stiffness and Vividness Reproduction of Anatomic Structures Into the 3D Printed Models Contributes to Improved Simulation and Training in Skull Base Surgery

BACKGROUND

Despite the advancement of 3-dimensional (3D) printing technology with medical application, its neurosurgical utility value has been limited to understanding the anatomy of bones, lesions, and their surroundings in the neurosurgical field.

OBJECTIVE

To develop a 3D printed model simulating the surgical technique applied in skull base surgery (SBS), especially to reproduce visually the surgical field together with the mechanical properties of tissues as perceived by the surgeon through procedures performance on a model.

METHODS

The Young modulus representing the degree of stiffness was measured for the tissues of anesthetized animals and printing materials. The stiffness and vividness of models were adjusted appropriately for each structure. Empty spaces were produced inside the models of brains, venous sinuses, and tumors. The 3D printed models were created in 7 cases of SBS planned patients and were used for surgical simulation.

RESULTS

The Young modulus of pig's brain ranged from 5.56 to 11.01 kPa and goat's brain from 4.51 to 13.69 kPa, and the dura of pig and goat values were 14.00 and 24.62 kPa, respectively. Although the softest printing material had about 20 times of Young modulus compared with animal brain, the hollow structure of brain model gave a soft sensation resembling the real organ and was helpful for bridging the gap between Young moduli values. A dura/tentorium-containing model was practical to simulate the real maneuverability at surgery.

CONCLUSION

The stiffness/vividness modulated 3D printed model provides an advanced realistic environment for training and simulation of a wide range of SBS procedures.

Efficacy of 3D evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® for determination of their intradural localization

BACKGROUND

Determination of the intradural unruptured paraclinoid aneurysm localization is difficult, but critical for selection of the optimal treatment strategy.

OBJECTIVE

To assess efficacy of the three-dimensional (3D) evaluation of unruptured paraclinoid aneurysms within Leksell GammaPlan® (LGP; Elekta AB; Stockholm, Sweden) for determination of their intradural localization.

METHODS

Overall, 125 incidentally diagnosed unruptured paraclinoid aneurysms in 118 patients (mean age, 55 years) underwent 3D evaluation of their localization within LGP using post-contrast thin-slice constructive interference in steady state (CISS) images, which in 41 cases were additionally co-registered and fused with the axial computed tomography angiography (CTA) source images.

RESULTS

According to the evaluation within LGP, paraclinoid aneurysms were considered intradural, transitional, and extradural in 75, 25, and 25 cases respectively. Overall, 51 of 75 aneurysms deemed to be intradural, underwent microsurgical management, and intraoperative visual inspection confirmed their intradural localization in 45 cases, whereas it was transitional in 3, and extradural in 3. If during preoperative 3D evaluation within LGP only post-contrast CISS images were used, prediction of the pure intradural localization of aneurysm was correct in 88 % of cases (95 % CI: 79-97 %), and of the pure or partial (i.e., transitional) intradural localization in 94 % of cases (95 % CI: 88-100 %), whereas it was 100 % if co-registration and fusion of the contrast-enhanced CISS and CTA source images was done.

CONCLUSION

Intradural localization of the unruptured paraclinoid aneurysms may be effectively predicted based on their 3D evaluation within LGP using post-contrast thin-slice CISS and CTA source images, which may help with clinical decision-making.

Three-Dimensional Printing in Neurosurgery: A Review of Current Indications and Applications and a Basic Methodology for Creating a Three-Dimensional Printed Model for the Neurosurgical Practice

Introduction Three-dimensional (3D) printing is an affordable aid that is useful in neurosurgery. It allows for better visualization and tactile appreciation of the individual anatomy and regions of interest and therefore potentially lowers the risk of complications. There are various applications of this technology in the field of neurosurgery. Materials and methods In this paper, we present a basic methodology for the creation of a 3D printed model using only open-source software for medical image editing, model generation, pre-printing preparation, and analysis of the literature concerning the practical use of this methodology. Results The literature review on the current applications of 3D printed models in neurosurgery shows that they are mostly used for preoperative planning, surgical training, and simulation, closely followed by their use in patient-specific implants and instrumentation and medical education. Materialise^TM Mimics is the most frequently used commercial software for a 3D modeling for preoperative planning and surgical simulation, while the most popular open-source software for the same applications is 3D Slicer. In this paper, we present the algorithm that we employ for 3D printing using Horos^TM, Blender, and Cura software packages which are all free and open-source. Conclusion Three-dimensional printing is becoming widely available and of significance to neurosurgical practice. Currently, there are various applications of this technology that are less demanding in terms of technical knowledge and required fluency in medical imaging software. These predispositions open the field for further research on the possible use of 3D printing in neurosurgery.

Threshold field painting saves the time for segmentation of minute arteries

PURPOSE

It is often time-consuming to segment fine structures, such as the cerebral arteries from magnetic resonance imaging (MRI). Moreover, extracting anatomically abnormal structures is generally difficult. The segmentation workflow called threshold field painting was tested for its feasibility in morbid minute artery segmentation with special emphasis on time efficiency.

METHODS

Seven patients with meningioma with ten-sided feeding arteries (n = 10) originating from middle meningeal arteries (MMA) were investigated by three experts of the conventional method for segmentation. The MRI time-of-flight sequence was utilized for the segmentation of each procedure. The tasks were accomplished using both the conventional method and the proposed method in random order. The task completion time and usability score were analyzed using the Wilcoxon signed-rank test.

RESULTS

Except for one examinee (P = 0.06), the completion time significantly decreased (both P < 0.01) with the use of the proposed method. The average task completion time among the three examinees for the conventional method was 2.8 times longer than that for the proposed method. The usability score was generally in favor of the proposed method.

CONCLUSION

The normally nonexistent minute arteries, such as the MMA feeders, were deemed more efficiently segmented with the proposed method than with the conventional method. While automatic segmentation might be the ultimate solution, our semiautomatic method incorporating expert knowledge is expected to work as the practical solution.

Case Report: “Clipping” an Internal Carotid Artery Aneurysm With a Duplicated Middle Cerebral Artery and the Anterior Choroidal Artery Arising From the Dome

Background

A duplicated middle cerebral artery (DMCA) is an anatomical variant that includes duplication of the middle cerebral artery (MCA) and an anomalous vessel originating between the anterior choroidal artery (AChA) and the distal end of the internal carotid artery (ICA). Here, we present a case report of an ICA aneurysm with a DMCA and the AChA originating from the dome, which was successfully treated with clipping.

Case Description

In a 64-year-old man, preoperative angiography revealed an unruptured right ICA aneurysm with a maximum diameter of 4.3 mm, and fusion three-dimensional computer graphics revealed that a DMCA and the AChA originated from the dome. The aneurysm enlarged; therefore, clipping was performed. The closure of the aneurysm while preserving the patency of the DMCA and AChA was identified using intraoperative microvascular Doppler ultrasonography and indocyanine green video angiography. The postoperative course was uneventful, and no ischemic lesions were confirmed on MR imaging.

Conclusion

To the best of our knowledge, this is the first report of an ICA aneurysm with a DMCA and the AChA arising from the dome. In such cases, the anatomy of the DMCA and AChA should be well-characterized before treatment.

Development of a New Image-Guided Neuronavigation System: Mixed-Reality Projection Mapping Is Accurate and Feasible

BACKGROUND

Image-guided systems improve the safety, functional outcome, and overall survival of neurosurgery but require extensive equipment.

OBJECTIVE

To develop an image-guided surgery system that combines the brain surface photographic texture (BSP-T) captured during surgery with 3-dimensional computer graphics (3DCG) using projection mapping.

METHODS

Patients who underwent initial surgery with brain tumors were prospectively enrolled. The texture of the 3DCG (3DCG-T) was obtained from 3DCG under similar conditions as those when capturing the brain surface photographs. The position and orientation at the time of 3DCG-T acquisition were used as the reference. The correct position and orientation of the BSP-T were obtained by aligning the BSP-T with the 3DCG-T using normalized mutual information. The BSP-T was combined with and displayed on the 3DCG using projection mapping. This mixed-reality projection mapping (MRPM) was used prospectively in 15 patients (mean age 46.6 yr, 6 males). The difference between the centerlines of surface blood vessels on the BSP-T and 3DCG constituted the target registration error (TRE) and was measured in 16 fields of the craniotomy area. We also measured the time required for image processing.

RESULTS

The TRE was measured at 158 locations in the 15 patients, with an average of 1.19 ± 0.14 mm (mean ± standard error). The average image processing time was 16.58 min.

CONCLUSION

Our MRPM method does not require extensive equipment while presenting information of patients' anatomy together with medical images in the same coordinate system. It has the potential to improve patient safety.

The Use of Fusion Images as a Diagnostic and Neurosurgical Planning Tool in Microvascular Decompression

Preoperative assessment of surgery using high-quality images can help surgeons to achieve best result of treatment. With the advances in computer technology, interactive multimodality fusion images have been developed. The use of fusion images as a preoperative planning tool is described with its examples in illustrative cases of trigeminal neuralgia and hemifacial spasm microvascular decompression (MVD). Interactive computer graphics such as multimodality fusion method is a useful tool to preoperatively predict the need of bone exposure and configuration of blood vessels with its correlation to cranial nerves in MVD.

Microsurgical management of midbrain cavernous malformations: does lesion depth influence the outcome?

Background

The purpose of this study was to clarify whether the intrinsic depth of midbrain cavernous malformations (MCMs) influenced the surgical outcome.

Methods

The authors conducted a retrospective study of 76 consecutive patients who underwent microsurgical resection of a MCM. The vascular lesions were categorized into 4 distinct groups based on how these lesions had altered the brainstem surface. Additionally, it was verified whether the actual aspect of the brainstem surface could be predicted only by evaluating the pertinent preoperative MRI slices. Clinical outcome was assessed by determining the modified Rankin Scale Score (mRS) before and after surgery.

Results

Twenty-three MCMs (30.3%) were located deeply within the midbrain. The overlying midbrain surface appeared to be normal (group nl). In 33 patients (43.4%), the midbrain surface showed only a yellowish discoloration (group yw). In another 14 individuals (18.4%), the midbrain surface was distorted by the underlying MCM and bulging out while the vascular lesion still remained covered by a thin parenchymal layer (group bg). In the smallest group comprising 6 patients (7.9%), the exophytic MCM had disrupted the midbrain surface and was clearly visible at microsurgical exposure (group ex). The mean mRS decreased in the group nl from 1.43 preoperatively to 0.61 at follow-up.

Conclusion

This study demonstrates in a large patient population that a deep intrinsic MCM location is not necessarily associated with an unfavorable clinical outcome after microsurgical lesionectomy. Predicting the aspect of the midbrain surface by evaluating preoperative MR images alone was not sufficiently reliable.

Evolution of microneurosurgical anatomy with special reference to the history of anatomy, surgical anatomy, and microsurgery: historical overview

This article reviews the evolution of microneurosurgical anatomy (MNA) with special reference to the development of anatomy, surgical anatomy, and microsurgery. Anatomy can be said to have started in the ancient Greek era with the work of Hippocrates, Galen, and others as part of the pursuit of natural science. In the sixteenth century, Vesalius made a great contribution in reviving Galenian knowledge while adding new knowledge of human anatomy. Also in the sixteenth century, Ambroise Paré can be said to have started modern surgery. As surgery developed, more detailed anatomical knowledge became necessary for treating complicated diseases. Many noted surgeons at the time were also anatomists eager to spread anatomical knowledge in order to enhance surgical practice. Thus, surgery and anatomy developed together, with advances in each benefiting the other. The concept of surgical anatomy evolved in the eighteenth century and became especially popular in the nineteenth century. In the twentieth century, microsurgery was introduced in various surgical fields, starting with Carl O. Nylen in otology. It flourished and became popularized in the second half of the century, especially in the field of neurosurgery, following Jacobson and Suarez's success in microvascular anastomosis in animals and subsequent clinical application as developed by M.G. Yasargil and others. Knowledge of surgical anatomy as seen under the operating microscope became important for surgeons to perform microneurosurgical procedures accurately and safely, which led to the fuller development of MNA as conducted by many neurosurgeons, among whom A.L. Rhoton, Jr. might be mentioned as representative.

Immersive 3-Dimensional Virtual Reality Modeling for Case-Specific Presurgical Discussions in Cerebrovascular Neurosurgery

BACKGROUND

Adequate surgical planning includes a precise understanding of patient-specific anatomy and is a necessity for neurosurgeons. Although the use of virtual reality (VR) technology is emerging in surgical planning and education, few studies have examined the effectiveness of immersive VR during surgical planning using a modern head-mounted display.

OBJECTIVE

To investigate if and how immersive VR aids presurgical discussions of cerebrovascular surgery.

METHODS

A multiuser immersive VR system, BananaVisionTM, was developed and used during presurgical discussions in a prospective patient cohort undergoing cerebrovascular surgery. A questionnaire/interview was administered to multiple surgeons after the surgeries to evaluate the effectiveness of the VR system compared to conventional imaging modalities. An objective assessment of the surgeon's knowledge of patient-specific anatomy was also conducted by rating surgeons' hand-drawn presurgical illustrations.

RESULTS

The VR session effectively enhanced surgeons' understanding of patient-specific anatomy in the majority of cases (83.3%). An objective assessment of surgeons' presurgical illustrations was consistent with this result. The VR session also effectively improved the decision-making process regarding minor surgical techniques in 61.1% of cases and even aided surgeons in making critical surgical decisions about cases involving complex and challenging anatomy. The utility of the VR system was rated significantly higher by trainees than by experts.

CONCLUSION

Although rated as more useful by trainees than by experts, immersive 3D VR modeling increased surgeons' understanding of patient-specific anatomy and improved surgical strategy in certain cases involving challenging anatomy.

Development of Integrated 3-Dimensional Computer Graphics Human Head Model

BACKGROUND

Understanding the complex anatomy of neurostructures is very important in various stages of medical education, from medical students to experienced neurosurgeons, and, ultimately, for the knowledge of human beings.

OBJECTIVE

To develop an interactive computer graphics (CG) anatomic head model and present the current progress.

METHODS

Based on the prior head 3-dimensional CG (3DCG) polygon model, 23 additional published papers and textbooks were consulted, and 2 neurosurgeons and 1 CG technician performed revision and additional polygon modeling. Three independent neurosurgeons scored the clear visibility of anatomic structures relevant to neurosurgical procedures (anterior petrosal and supracerebellar infratentorial approaches) in the integrated 3DCG model (i model) and patients' radiological images (PRIs) such as those obtained from computed tomography, magnetic resonance imaging, and angiography.

RESULTS

The i model consisted of 1155 parts (.stl format), with a total of 313 763 375 polygons, including 10 times more information than the foundation model. The i model was able to illustrate complex and minute neuroanatomic structures that PRIs could not as well as extracranial structures such as paranasal sinuses. Our subjective analysis showed that the i model had better clear visibility scores than PRIs, particularly in minute nerves, vasculatures, and dural structures.

CONCLUSION

The i model more clearly illustrates minute anatomic structures than PRIs and uniquely illustrates nuclei and fibers that radiological images do not. The i model complements cadaveric dissection by increasing accessibility according to spatial, financial, ethical, and social aspects and can contribute to future medical education.

Identification of the Facial Colliculus in Two-dimensional and Three-dimensional Images

The facial colliculus (FC), an important landmark for planning a surgical approach to brainstem cavernous malformation (BCM), is a microstructure; therefore, it may be difficult to identify on magnetic resonance imaging (MRI). Three-dimensional (3D) images may improve the FC-identification certainty; hence, this study attempted to validate the FC-identification certainty between two-dimensional (2D) and 3D images of patients with a normal brainstem and those with BCM.

In this retrospective study, we included 10 patients with a normal brainstem and 10 patients who underwent surgery for BCM. The region of the FC in 2D and 3D images was independently identified by three neurosurgeons, three times in each case, using the method for continuously distributed test results (0–100). The intra- and inter-rater reliability of the identification certainty were confirmed using the intraclass correlation coefficient (ICC). The FC-identification certainty for 2D and 3D images was compared using the Wilcoxon signed-rank test.

The ICC (1,3) and ICC (3,3) in both groups ranged from 0.88 to 0.99; therefore, the intra- and inter-rater reliability were good. In both groups, the FC- identification certainty was significantly higher for 3D images than for 2D images (normal brainstem group; 82.4 vs. 61.5, P = .0020, BCM group; 40.2 vs. 24.6, P = .0059 for the unaffected side, 29.3 vs. 17.3, P = .0020 for the affected side).

In the normal brainstem and BCM groups, 3D images had better FC-identification certainty. 3D images are effective for the identification of the FC.

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.

Surgical Simulation with Three-Dimensional Fusion Images in Patients with Arteriovenous Malformation

In arteriovenous malformation (AVM) surgery, vessel structures should be well evaluated with angiography. However, with conventional angiography, it is sometimes difficult to distinguish each feeder and its feeding territory in the nidus. In this study, we used two software systems to create three-dimensional (3D) fusion images using multiple imaging modalities and evaluated their clinical use. In the AVM patient, data were obtained from 3D rotational angiography, rotational venography, computed tomography (CT), and magnetic resonance imaging (MRI) and superimposed into 3D fusion images using imaging software (iPLAN and Avizo). Virtual surgical fields that were quite similar to the real ones were also created with these software programs. Compared with fusion images by iPLAN, those by Avizo have higher resolution and can demarcate not only each feeder but also its supplying territory in the nidus with different colors.In conclusion, 3D fusion images in AVM surgery are helpful for simulation, even though it takes time and requires special skill to create them.

Endoscopic transnasal resection of the CP angle schwannoma

Cerebellopontine (CP) angle tumors are often resected via retrosigmoid craniotomy; however, sometimes cranial nerves (CNs) make their resection more complex. In such cases, the endoscopic transnasal approach can avoid such manipulations as delivering surgical instruments over CNs or peeling off CNs from the tumor, minimizing the risk of postoperative deficits. A 35-year-old man presented with a 37-mm cystic tumor in the right CP angle, and preoperative 3D fusion images revealed that multiple CNs (VII, VIII, and lower CNs) were running on the tumor posteriorly. The endoscopic transnasal approach enabled safe subtotal resection without causing neurological deficits, and the patient underwent stereotactic radiosurgery for the residual schwannoma.

The video can be found here: https://youtu.be/xKLwdDsLpWA.

Three-dimensional angioarchitecture and microsurgical treatment of arteriovenous fistulas at the craniocervical junction

Digital subtraction angiography (DSA) is the gold standard for diagnosing vascular malformations; however, difficulties are associated with visualizing the angioarchitecture of arteriovenous fistulas at the craniocervical junction (CCJ AVFs) using DSA because of their complex regional neurovascular anatomy. The present study evaluated the application of 3-dimensional computer graphics (3D CG) to the surgical planning of CCJ AVFs. Six patients with CCJ AVFs who underwent microsurgery and/or endovascular treatment were included. The results of DSA and 3D CG were compared in the last 3 patients. The visibility of important anatomical structures were evaluated using visibility grading scores. Clinical outcomes were assessed based on the rate of occlusion of AVFs, surgical complications, neurological status, and recurrence in long-term follow-ups. The 3D CG images could combine arteries, veins, the spinal cord and dura mater in one single picture to evaluate the anatomy of CCJ AVFs. The image interpretation of vascular structures, particularly narrow arterial feeders, was significantly better using 3D CG than DSA (overall visibility scores, 97% vs 51%, p = 0.001). In all patients, the complete occlusion of AVFs was achieved by microsurgery except for 2 patients without surgical planning with 3D CG. Postoperatively, the neurological status of all patients improved or stabilized without the recurrence of AVFs (median, 5.4 years). 3D CG may help to improve the quality of the microsurgical procedures in complex AVFs. However, it should be used as a complementary diagnostic modality rather than the alternative of DSA because 3D CG has no hemodynamic information at this time.

Virtual Reality and Simulation in Neurosurgical Training

Recent biotechnological advances, including three-dimensional microscopy and endoscopy, virtual reality, surgical simulation, surgical robotics, and advanced neuroimaging, have continued to mold the surgeon-computer relationship. For developing neurosurgeons, such tools can reduce the learning curve, improve conceptual understanding of complex anatomy, and enhance visuospatial skills. We explore the current and future roles and application of virtual reality and simulation in neurosurgical training.

Microsurgery Simulator of Cerebral Aneurysm Clipping with Interactive Cerebral Deformation Featuring a Virtual Arachnoid

BACKGROUND

A virtual reality simulator for aneurysmal clipping surgery is an attractive research target for neurosurgeons. Brain deformation is one of the most important functionalities necessary for an accurate clipping simulator and is vastly affected by the status of the supporting tissue, such as the arachnoid membrane. However, no virtual reality simulator implementing the supporting tissue of the brain has yet been developed.

OBJECTIVE

To develop a virtual reality clipping simulator possessing interactive brain deforming capability closely dependent on arachnoid dissection and apply it to clinical cases.

METHODS

Three-dimensional computer graphics models of cerebral tissue and surrounding structures were extracted from medical images. We developed a new method for modifiable cerebral tissue complex deformation by incorporating a nonmedical image-derived virtual arachnoid/trabecula in a process called multitissue integrated interactive deformation (MTIID). MTIID made it possible for cerebral tissue complexes to selectively deform at the site of dissection. Simulations for 8 cases of actual clipping surgery were performed before surgery and evaluated for their usefulness in surgical approach planning.

RESULTS

Preoperatively, each operative field was precisely reproduced and visualized with the virtual brain retraction defined by users. The clear visualization of the optimal approach to treating the aneurysm via an appropriate arachnoid incision was possible with MTIID.

CONCLUSION

A virtual clipping simulator mainly focusing on supporting tissues and less on physical properties seemed to be useful in the surgical simulation of cerebral aneurysm clipping. To our knowledge, this article is the first to report brain deformation based on supporting tissues.

Skull Base Tumors and Tumor-Like Lesions: A Pictorial Review

A number of tumors and tumor-like non-neoplastic lesions with different cell types on histology occur in the skull base. A wide variety in disease and lesion appearance often complicates the process of radiological diagnosis. The main role of radiographic imaging is the detection and characterization of skull base lesions, with evaluation of the extent of invasion or preservation of adjacent critical organs. Evaluation of the skull base anatomy and surgical planning by using image guidance are also important for surgeons. Computed tomography (CT) and magnetic resonance (MR) imaging are the preferred modalities for the evaluation of skull base lesions. CT and MR are used for lesion detection, tissue characterization and assessment of neurovascular and bone involvement by the lesions. Both modalities provide useful information, one sometimes of greater value than the other. T1-weighted MR imaging is useful in detecting skull base lesions, typically surrounded by abundant fatty bone marrow. T2-weighted MR imaging is generally useful for tumor tissue characterization. CT surpasses MR imaging in evaluating intratumoral calcification and bone destruction or hyperostosis. To date, imaging features have been well-reported in individual skull base tumors; however, correct diagnosis by imaging alone still presents a challenge. Knowledge of clinical issues and awareness of variants of skull base tumors are of help in making a diagnosis. The purpose of this article is to review pertinent clinical issues, typical imaging appearances and certain imaging variations of common skull base lesions.

Usefulness of high-resolution 3D multifusion medical imaging for preoperative planning in patients with posterior fossa hemangioblastoma: technical note

Successful resection of hemangioblastoma depends on preoperative assessment of the precise locations of feeding arteries and draining veins. Simultaneous 3D visualization of feeding arteries, draining veins, and surrounding structures is needed. The present study evaluated the usefulness of high-resolution 3D multifusion medical imaging (hr-3DMMI) for preoperative planning of hemangioblastoma. The hr-3DMMI combined MRI, MR angiography, thin-slice CT, and 3D rotated angiography. Surface rendering was mainly used for the creation of hr-3DMMI using multiple thresholds to create 3D models, and processing took approximately 3–5 hours. This hr-3DMMI technique was used in 5 patients for preoperative planning and the imaging findings were compared with the operative findings. Hr-3DMMI could simulate the whole 3D tumor as a unique sphere and show the precise penetration points of both feeding arteries and draining veins with the same spatial relationships as the original tumor. All feeding arteries and draining veins were found intraoperatively at the same position as estimated preoperatively, and were occluded as planned preoperatively. This hr-3DMMI technique could demonstrate the precise locations of feeding arteries and draining veins preoperatively and estimate the appropriate route for resection of the tumor. Hr-3DMMI is expected to be a very useful support tool for surgery of hemangioblastoma.

Neurosurgical Virtual Reality Simulation for Brain Tumor Using High-definition Computer Graphics: A Review of the Literature

Simulation and planning of surgery using a virtual reality model is becoming common with advances in computer technology. In this study, we conducted a literature search to find trends in virtual simulation of surgery for brain tumors. A MEDLINE search for “neurosurgery AND (simulation OR virtual reality)” retrieved a total of 1,298 articles published in the past 10 years. After eliminating studies designed solely for education and training purposes, 28 articles about the clinical application remained. The finding that the vast majority of the articles were about education and training rather than clinical applications suggests that several issues need be addressed for clinical application of surgical simulation. In addition, 10 of the 28 articles were from Japanese groups. In general, the 28 articles demonstrated clinical benefits of virtual surgical simulation. Simulation was particularly useful in better understanding complicated spatial relations of anatomical landmarks and in examining surgical approaches. In some studies, Virtual reality models were used on either surgical navigation system or augmented reality technology, which projects virtual reality images onto the operating field. Reported problems were difficulties in standardized, objective evaluation of surgical simulation systems; inability to respond to tissue deformation caused by surgical maneuvers; absence of the system functionality to reflect features of tissue (e.g., hardness and adhesion); and many problems with image processing. The amount of description about image processing tended to be insufficient, indicating that the level of evidence, risk of bias, precision, and reproducibility need to be addressed for further advances and ultimately for full clinical application.

A neurosurgical simulation of skull base tumors using a 3D printed rapid prototyping model containing mesh structures

BACKGROUND

Deep regions are not visible in three-dimensional (3D) printed rapid prototyping (RP) models prepared from opaque materials, which is not the case with translucent images. The objectives of this study were to develop an RP model in which a skull base tumor was simulated using mesh, and to investigate its usefulness for surgical simulations by evaluating the visibility of its deep regions.

METHODS

A 3D printer that employs binder jetting and is mainly used to prepare plaster models was used. RP models containing a solid tumor, no tumor, and a mesh tumor were prepared based on computed tomography, magnetic resonance imaging, and angiographic data for four cases of petroclival tumor. Twelve neurosurgeons graded the three types of RP model into the following four categories: 'clearly visible,' 'visible,' 'difficult to see,' and 'invisible,' based on the visibility of the internal carotid artery, basilar artery, and brain stem through a craniotomy performed via the combined transpetrosal approach. In addition, the 3D positional relationships between these structures and the tumor were assessed.

RESULTS

The internal carotid artery, basilar artery, and brain stem and the positional relationships of these structures with the tumor were significantly more visible in the RP models with mesh tumors than in the RP models with solid or no tumors.

CONCLUSIONS

The deep regions of PR models containing mesh skull base tumors were easy to visualize. This 3D printing-based method might be applicable to various surgical simulations.

Anatomy and approaches along the cerebellar-brainstem fissures

OBJECT Fissure dissection is routinely used in the supratentorial region to access deeply situated pathology while minimizing division of neural tissue. Use of fissure dissection is also practical in the posterior fossa. In this study, the microsurgical anatomy of the 3 cerebellar-brainstem fissures (cerebellomesencephalic, cerebellopontine, and cerebellomedullary) and the various procedures exposing these fissures in brainstem surgery were examined. METHODS Seven cadaveric heads were examined with a microsurgical technique and 3 with fiber dissection to clarify the anatomy of the cerebellar-brainstem and adjacent cerebellar fissures, in which the major vessels and neural structures are located. Several approaches directed along the cerebellar surfaces and fissures, including the supracerebellar infratentorial, occipital transtentorial, retrosigmoid, and midline suboccipital approaches, were examined. The 3 heads examined using fiber dissection defined the anatomy of the cerebellar peduncles coursing in the depths of these fissures. RESULTS Dissections directed along the cerebellar-brainstem and cerebellar fissures provided access to the posterior and posterolateral midbrain and upper pons, lateral pons, floor and lateral wall of the fourth ventricle, and dorsal and lateral medulla. CONCLUSIONS Opening the cerebellar-brainstem and adjacent cerebellar fissures provided access to the brainstem surface hidden by the cerebellum, while minimizing division of neural tissue. Most of the major cerebellar arteries, veins, and vital neural structures are located in or near these fissures and can be accessed through them.

A Microscopic Optically Tracking Navigation System That Uses High-resolution 3D Computer Graphics

Three-dimensional (3D) computer graphics (CG) are useful for preoperative planning of neurosurgical operations. However, application of 3D CG to intraoperative navigation is not widespread because existing commercial operative navigation systems do not show 3D CG in sufficient detail. We have developed a microscopic optically tracking navigation system that uses high-resolution 3D CG. This article presents the technical details of our microscopic optically tracking navigation system. Our navigation system consists of three components: the operative microscope, registration, and the image display system. An optical tracker was attached to the microscope to monitor the position and attitude of the microscope in real time; point-pair registration was used to register the operation room coordinate system, and the image coordinate system; and the image display system showed the 3D CG image in the field-of-view of the microscope. Ten neurosurgeons (seven males, two females; mean age 32.9 years) participated in an experiment to assess the accuracy of this system using a phantom model. Accuracy of our system was compared with the commercial system. The 3D CG provided by the navigation system coincided well with the operative scene under the microscope. Target registration error for our system was 2.9 ± 1.9 mm. Our navigation system provides a clear image of the operation position and the surrounding structures. Systems like this may reduce intraoperative complications.

Combined use of diffusion tensor tractography and multifused contrast-enhanced FIESTA for predicting facial and cochlear nerve positions in relation to vestibular schwannoma

OBJECT

The authors assessed whether the combined use of diffusion tensor tractography (DTT) and contrast-enhanced (CE) fast imaging employing steady-state acquisition (FIESTA) could improve the accuracy of predicting the courses of the facial and cochlear nerves before surgery.

METHODS

The population was composed of 22 patients with vestibular schwannoma in whom both the facial and cochlear nerves could be identified during surgery. According to DTT, depicted fibers running from the internal auditory canal to the brainstem were judged to represent the facial or vestibulocochlear nerve. With regard to imaging, the authors investigated multifused CE-FIESTA scans, in which all 3D vessel models were shown simultaneously, from various angles. The low-intensity areas running along the tumor from brainstem to the internal auditory canal were judged to represent the facial or vestibulocochlear nerve.

RESULTS

For all 22 patients, the rate of fibers depicted by DTT coinciding with the facial nerve was 13.6% (3/22), and that of fibers depicted by DTT coinciding with the cochlear nerve was 63.6% (14/22). The rate of candidates for nerves predicted by multifused CE-FIESTA coinciding with the facial nerve was 59.1% (13/22), and that of candidates for nerves predicted by multifused CE-FIESTA coinciding with the cochlear nerve was 4.5% (1/22). The rate of candidates for nerves predicted by combined DTT and multifused CE-FIESTA coinciding with the facial nerve was 63.6% (14/22), and that of candidates for nerves predicted by combined DTT and multifused CE-FIESTA coinciding with the cochlear nerve was 63.6% (14/22). The rate of candidates predicted by DTT coinciding with both facial and cochlear nerves was 0.0% (0/22), that of candidates predicted by multifused CE-FIESTA coinciding with both facial and cochlear nerves was 4.5% (1/22), and that of candidates predicted by combined DTT and multifused CE-FIESTA coinciding with both the facial and cochlear nerves was 45.5% (10/22).

CONCLUSIONS

By using a combination of DTT and multifused CE-FIESTA, the authors were able to increase the number of vestibular schwannoma patients for whom predicted results corresponded with the courses of both the facial and cochlear nerves, a result that has been considered difficult to achieve by use of a single modality only. Although the 3D image including these prediction results helped with comprehension of the 3D operative anatomy, the reliability of prediction remains to be established.

Case-control studies in neurosurgery

OBJECT

Observational studies, such as cohort and case-control studies, are valuable instruments in evidence-based medicine. Case-control studies, in particular, are becoming increasingly popular in the neurosurgical literature due to their low cost and relative ease of execution; however, no one has yet systematically assessed these types of studies for quality in methodology and reporting.

METHODS

The authors performed a literature search using PubMed/MEDLINE to identify all studies that explicitly identified themselves as "case-control" and were published in the JNS Publishing Group journals (Journal of Neurosurgery, Journal of Neurosurgery: Pediatrics, Journal of Neurosurgery: Spine, and Neurosurgical Focus) or Neurosurgery. Each paper was evaluated for 22 descriptive variables and then categorized as having either met or missed the basic definition of a case-control study. All studies that evaluated risk factors for a well-defined outcome were considered true case-control studies. The authors sought to identify key features or phrases that were or were not predictive of a true case-control study. Those papers that satisfied the definition were further evaluated using the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist.

RESULTS

The search detected 67 papers that met the inclusion criteria, of which 32 (48%) represented true case-control studies. The frequency of true case-control studies has not changed with time. Use of odds ratios (ORs) and logistic regression (LR) analysis were strong positive predictors of true case-control studies (for odds ratios, OR 15.33 and 95% CI 4.52-51.97; for logistic regression analysis, OR 8.77 and 95% CI 2.69-28.56). Conversely, negative predictors included focus on a procedure/intervention (OR 0.35, 95% CI 0.13-0.998) and use of the word "outcome" in the Results section (OR 0.23, 95% CI 0.082-0.65). After exclusion of nested case-control studies, the negative correlation between focus on a procedure/intervention and true case-control studies was strengthened (OR 0.053, 95% CI 0.0064-0.44). There was a trend toward a negative association between the use of survival analysis or Kaplan-Meier curves and true case-control studies (OR 0.13, 95% CI 0.015-1.12). True case-control studies were no more likely than their counterparts to use a potential study design "expert" (OR 1.50, 95% CI 0.57-3.95). The overall average STROBE score was 72% (range 50-86%). Examples of reporting deficiencies were reporting of bias (28%), missing data (55%), and funding (44%).

CONCLUSIONS

The results of this analysis show that the majority of studies in the neurosurgical literature that identify themselves as "case-control" studies are, in fact, labeled incorrectly. Positive and negative predictors were identified. The authors provide several recommendations that may reverse the incorrect and inappropriate use of the term "case-control" and improve the quality of design and reporting of true case-control studies in neurosurgery.

Gamma Knife radiosurgery for sellar and parasellar meningiomas: a multicenter study

Object

Parasellar and sellar meningiomas are challenging tumors owing in part to their proximity to important neurovascular and endocrine structures. Complete resection can be associated with significant morbidity, and incomplete resections are common. In this study, the authors evaluated the outcomes of parasellar and sellar meningiomas managed with Gamma Knife radiosurgery (GKRS) both as an adjunct to microsurgical removal or conventional radiation therapy and as a primary treatment modality.

Methods

A multicenter study of patients with benign sellar and parasellar meningiomas was conducted through the North American Gamma Knife Consortium. For the period spanning 1988 to 2011 at 10 centers, the authors identified all patients with sellar and/or parasellar meningiomas treated with GKRS. Patients were also required to have a minimum of 6 months of imaging and clinical follow-up after GKRS. Factors predictive of new neurological deficits following GKRS were assessed via univariate and multivariate analyses. Kaplan-Meier analysis and Cox multivariate regression analysis were used to assess factors predictive of tumor progression.

Results

The authors identified 763 patients with sellar and/or parasellar meningiomas treated with GKRS. Patients were assessed clinically and with neuroimaging at routine intervals following GKRS. There were 567 females (74.3%) and 196 males (25.7%) with a median age of 56 years (range 8–90 years). Three hundred fifty-five patients (50.7%) had undergone at least one resection before GKRS, and 3.8% had undergone prior radiation therapy. The median follow-up after GKRS was 66.7 months (range 6–216 months). At the last follow-up, tumor volumes remained stable or decreased in 90.2% of patients. Actuarial progression-free survival rates at 3, 5, 8, and 10 years were 98%, 95%, 88%, and 82%, respectively. More than one prior surgery, prior radiation therapy, or a tumor margin dose < 13 Gy significantly increased the likelihood of tumor progression after GKRS.

At the last clinical follow-up, 86.2% of patients demonstrated no change or improvement in their neurological condition, whereas 13.8% of patients experienced symptom progression. New or worsening cranial nerve deficits were seen in 9.6% of patients, with cranial nerve (CN) V being the most adversely affected nerve. Functional improvements in CNs, especially in CNs V and VI, were observed in 34% of patients with preexisting deficits. New or worsened endocrinopathies were demonstrated in 1.6% of patients; hypothyroidism was the most frequent deficiency. Unfavorable outcome with tumor growth and accompanying neurological decline was statistically more likely in patients with larger tumor volumes (p = 0.022) and more than 1 prior surgery (p = 0.021).

Conclusions

Gamma Knife radiosurgery provides a high rate of tumor control for patients with parasellar or sellar meningiomas, and tumor control is accompanied by neurological preservation or improvement in most patients.

Neurosurgical simulation by interactive computer graphics on iPad

PURPOSE

Presurgical simulation before complicated neurosurgery is a state-of-the-art technique, and its usefulness has recently become well known. However, simulation requires complex image processing, which hinders its widespread application. We explored handling the results of interactive computer graphics on the iPad tablet, which can easily be controlled anywhere.

METHODS

Data from preneurosurgical simulations from 12 patients (4 men, 8 women) who underwent complex brain surgery were loaded onto an iPad. First, DICOM data were loaded using Amira visualization software to create interactive computer graphics, and ParaView, another free visualization software package, was used to convert the results of the simulation to be loaded using the free iPad software KiwiViewer.

RESULTS

The interactive computer graphics created prior to neurosurgery were successfully displayed and smoothly controlled on the iPad in all patients. The number of elements ranged from 3 to 13 (mean 7). The mean original data size was 233 MB, which was reduced to 10.4 MB (4.4% of original size) after image processing by ParaView. This was increased to 46.6 MB (19.9%) after decompression in KiwiViewer. Controlling the magnification, transfer, rotation, and selection of translucence in 10 levels of each element were smoothly and easily performed using one or two fingers. The requisite skill to smoothly control the iPad software was acquired within 1.8 trials on average in 12 medical students and 6 neurosurgical residents.

CONCLUSIONS

Using an iPad to handle the result of preneurosurgical simulation was extremely useful because it could easily be handled anywhere.

Ptosis as partial oculomotor nerve palsy due to compression by infundibular dilatation of posterior communicating artery, visualized with three-dimensional computer graphics: case report

Oculomotor nerve palsy (ONP) due to internal carotid-posterior communicating artery (PcomA) aneurysm generally manifests as partial nerve palsy including pupillary dysfunction. In contrast, infundibular dilatation (ID) of the PcomA has no pathogenic significance, and mechanical compression of the cranial nerve is extremely rare. We describe a 60-year-old woman who presented with progressive ptosis due to mechanical compression of the oculomotor nerve by an ID of the PcomA. Three-dimensional computer graphics (3DCG) accurately visualized the mechanical compression by the ID, and her ptosis was improved after clipping of the ID. ID of the PcomA may cause ONP by mechanical compression and is treatable surgically. 3DCG are effective for the diagnosis and preoperative simulation.

Optimal setting of image bounding box can improve registration accuracy of diffusion tensor tractography

PURPOSE

When we register diffusion tensor tractography (DTT) to anatomical images such as fast imaging employing steady-state acquisition (FIESTA), we register the B0 image to FIESTA. Precise registration of the DTT B0 image to FIESTA is possible with non-rigid registration compared to rigid registration, although the non-rigid methods lack convenience. We report the effect of image data bounding box settings on registration accuracy using a normalized mutual information (NMI) method METHODS: MRI scans of 10 patients were used in this study. Registration was performed without modification of the bounding box in the control group, and the results were compared with groups re-registered using multiple bounding boxes limited to the region of interest (ROI). The distance of misalignment after registration at 3 anatomical characteristic points that are common to both FIESTA and B0 images was used as an index of accuracy.

RESULTS

Mean ([Formula: see text]SD) misalignment at the 3 anatomical points decreased significantly from [Formula: see text] to [Formula: see text] mm, [Formula: see text]), [Formula: see text] to [Formula: see text] mm, ([Formula: see text], and [Formula: see text] to [Formula: see text] mm, ([Formula: see text], each showing improvement compared to the control group CONCLUSION: Narrowing the image data bounding box to the ROI improves the accuracy of registering B0 images to FIESTA by NMI method. With our proposed methodology, accuracy can be improved in extremely easy steps, and this methodology may prove useful for DTT registration to anatomical image.

Presurgical planning of feeder resection with realistic three-dimensional virtual operation field in patient with cerebellopontine angle meningioma

BACKGROUND

To devascularize meningiomas, the precise location of tumor attachment must be known. However, when a cerebellopontine angle (CPA) meningioma is in contact with many surrounding structures, it can be difficult to distinguish the most vascularized attachment (MVA) from other contact surfaces.

OBJECTIVE

To validate the usefulness of a virtual operation field (VOF) of a CPA meningioma by high-spatial-resolution three-dimensional computer graphics (hs-3DCG).

METHODS

Presurgical simulation with VOF was performed for eight CPA meningiomas to assess the MVA and the appropriate route to the main feeder. For hs-3DCG, the necessary preoperative radiographic images were fused. A hybrid model of volume and surface rendering was created from the fused images. The simulation results were compared with the operative results, and the MVA estimation rate was compared between VOF and contrast-enhanced fast imaging employing steady-state acquisition.

RESULTS

By using VOF, the point at which the main feeder penetrated the tumor was estimated in all cases, and using this information, the MVA was detected. All patients underwent resection of the main feeder in the same way as simulated preoperatively. Estimation rates of MVA were 37.5% in CE-FIESTA and 100% in VOF (p = 0.02, Fisher's exact test).

CONCLUSION

The hs-3DCG method was of sufficiently high quality to enable VOF of CPA meningioma. This method may facilitate estimation of MVA and the main feeder penetration point, and may aid in the determination of the most appropriate approach to the main feeder.