Error analysis in cranial neuronavigation

Safety and efficacy of frameless stereotactic robot-assisted intraparenchymal brain lesion biopsies versus image-guided biopsies: a bicentric comparative study

PURPOSE

User-friendly robotic assistance and image-guided tools have been developed in the past decades for intraparenchymal brain lesion biopsy. These two methods are gradually becoming well accepted and are performed at the discretion of the neurosurgical teams. However, only a few data comparing their effectiveness and safety are available.

METHODS

Population-based parallel cohorts were followed from two French university hospitals with different surgical methods and defined geographical catchment regions (September 2019 to September 2022). In center A, frameless robot-assisted stereotactic intraparenchymal brain lesion biopsies were performed, while image-guided intraparenchymal brain lesion biopsies were performed in center B. Pre-and postoperative clinical, radiological, and histomolecular features were retrospectively collected and compared.

RESULTS

Two hundred fifty patients were included: 131 frameless robot-assisted stereotactic intraparenchymal brain lesion biopsies in center A and 119 image-guided biopsies in center B. The clinical, radiological, and histomolecular features were comparable between the two groups. The diagnostic yield (96.2% and 95.8% respectively; p = 1.000) and the overall postoperative complications rates (13% and 14%, respectively; p = 0.880) did not differ between the two groups. The mean duration of the surgical procedure was longer in the robot-assisted group (61.9 ± 25.3 min, range 23-150) than in the image-guided group (47.4 ± 11.8 min, range 25-81, p < 0.001). In the subgroup of patients with anticoagulant and/or antiplatelet therapy administered preoperatively, the intracerebral hemorrhage > 10 mm on postoperative CT scan was higher in the image-guided group (36.8%) than in the robot-assisted group (5%, p < 0.001).

CONCLUSION

In our bicentric comparative study, robot-assisted stereotactic and image-guided biopsies have two main differences (shorter time but more frequent postoperative hematoma for image-guided biopsies); however, both techniques are demonstrated to be safe and efficient.

Assessment of Motor Evoked Potentials in Multiple Sclerosis

Transcranial magnetic stimulation (TMS) is a noninvasive technique mainly used for the assessment of corticospinal tract integrity and excitability of the primary motor cortices. Motor evoked potentials (MEPs) play a pivotal role in TMS studies. TMS clinical guidelines, concerning the use and interpretation of MEPs in diagnosing and monitoring corticospinal tract integrity in people with multiple sclerosis (pwMS), were established almost ten years ago and refer mainly to the use of TMS implementation; this comprises the magnetic stimulator connected to a standard EMG unit, with the positioning of the coil performed by using the external landmarks on the head. The aim of the present work was to conduct a narrative literature review on the MEP assessment and outcome measures in clinical and research settings, assessed by TMS Methodological characteristics of different TMS system implementations (TMS without navigation, line-navigated TMS and e-field-navigated TMS); these were discussed in the context of mapping the corticospinal tract integrity in MS. An MEP assessment of two case reports, by using an e-field-navigated TMS, was presented; the results of the correspondence between the e-field-navigated TMS with MRI, and the EDSS classifications were presented. Practical and technical guiding principles for the improvement of TMS studies in MEP assessment for MS are discussed, suggesting the use of e-field TMS assessment in the sense that it can improve the accuracy of corticospinal tract integrity testing by providing a more objective correspondence of the neurophysiological (e-field-navigated TMS) and clinical (Expanded Disability Status Scale-EDSS) classifications.

Accuracy and precision of navigated transcranial magnetic stimulation

Objective.Transcranial magnetic stimulation (TMS) induces an electric field (E-field) in the cortex. To facilitate stimulation targeting, image-guided neuronavigation systems have been introduced. Such systems track the placement of the coil with respect to the head and visualize the estimated cortical stimulation location on an anatomical brain image in real time. The accuracy and precision of the neuronavigation is affected by multiple factors. Our aim was to analyze how different factors in TMS neuronavigation affect the accuracy and precision of the coil-head coregistration and the estimated E-field.Approach.By performing simulations, we estimated navigation errors due to distortions in magnetic resonance images (MRIs), head-to-MRI registration (landmark- and surface-based registrations), localization and movement of the head tracker, and localization of the coil tracker. We analyzed the effect of these errors on coil and head coregistration and on the induced E-field as determined with simplistic and realistic head models.Main results.Average total coregistration accuracies were in the range of 2.2-3.6 mm and 1°; precision values were about half of the accuracy values. The coregistration errors were mainly due to head-to-MRI registration with average accuracies 1.5-1.9 mm/0.2-0.4° and precisions 0.5-0.8 mm/0.1-0.2° better with surface-based registration. The other major source of error was the movement of the head tracker with average accuracy of 1.5 mm and precision of 1.1 mm. When assessed within an E-field method, the average accuracies of the peak E-field location, orientation, and magnitude ranged between 1.5 and 5.0 mm, 0.9 and 4.8°, and 4.4 and 8.5% across the E-field models studied. The largest errors were obtained with the landmark-based registration. When computing another accuracy measure with the most realistic E-field model as a reference, the accuracies tended to improve from about 10 mm/15°/25% to about 2 mm/2°/5% when increasing realism of the E-field model.Significance.The results of this comprehensive analysis help TMS operators to recognize the main sources of error in TMS navigation and that the coregistration errors and their effect in the E-field estimation depend on the methods applied. To ensure reliable TMS navigation, we recommend surface-based head-to-MRI registration and realistic models for E-field computations.

Current status of augmented reality in cerebrovascular surgery: a systematic review

Augmented reality (AR) is an adjuvant tool in neuronavigation to improve spatial and anatomic understanding. The present review aims to describe the current status of intraoperative AR for the treatment of cerebrovascular pathology. A systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The following databases were searched: PubMed, Science Direct, Web of Science, and EMBASE up to December, 2020. The search strategy consisted of "augmented reality," "AR," "cerebrovascular," "navigation," "neurovascular," "neurosurgery," and "endovascular" in both AND and OR combinations. Studies included were original research articles with intraoperative application. The manuscripts were thoroughly examined for study design, outcomes, and results. Sixteen studies were identified describing the use of intraoperative AR in the treatment of cerebrovascular pathology. A total of 172 patients were treated for 190 cerebrovascular lesions using intraoperative AR. The most common treated pathology was intracranial aneurysms. Most studies were cases and there was only a case-control study. A head-up display system in the microscope was the most common AR display. AR was found to be useful for tailoring the craniotomy, dura opening, and proper identification of donor and recipient vessels in vascular bypass. Most AR systems were unable to account for tissue deformation. This systematic review suggests that intraoperative AR is becoming a promising and feasible adjunct in the treatment of cerebrovascular pathology. It has been found to be a useful tool in the preoperative planning and intraoperative guidance. However, its clinical benefits remain to be seen.

FLAIRectomy in Supramarginal Resection of Glioblastoma Correlates With Clinical Outcome and Survival Analysis: A Prospective, Single Institution, Case Series

BACKGROUND

Extent of tumor resection (EOTR) in glioblastoma surgery plays an important role in improving survival.

OBJECTIVE

To analyze the efficacy, safety and reliability of fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) images used to guide glioblastoma resection (FLAIRectomy) and to volumetrically measure postoperative EOTR, which was correlated with clinical outcome and survival.

METHODS

A total of 68 glioblastoma patients (29 males, mean age 65.8) were prospectively enrolled. Hyperintense areas on FLAIR images, surrounding gadolinium-enhancing tissue on T1-weighted MR images, were screened for signal changes suggesting tumor infiltration and evaluated for supramaximal resection. The surgical protocol included 5-aminolevulinic acid (5-ALA) fluorescence, neuromonitoring, and intraoperative imaging tools. 5-ALA fluorescence intensity was analyzed and matched with the different sites on navigated MR, both on postcontrast T1-weighted and FLAIR images. Volumetric evaluation of EOTR on T1-weighted and FLAIR sequences was compared.

RESULTS

FLAIR MR volumetric evaluation documented larger tumor volume than that assessed on contrast-enhancing T1 MR (72.6 vs 54.9 cc); residual tumor was seen in 43 patients; postcontrast T1 MR volumetric analysis showed complete resection in 64 cases. O6-methylguanine-DNA methyltransferase promoter was methylated in 8/68 (11.7%) cases; wild type Isocytrate Dehydrogenase-1 (IDH-1) was found in 66/68 patients. Progression free survival and overall survival (PFS and OS) were 17.43 and 25.11 mo, respectively. Multiple regression analysis showed a significant correlation between EOTR based on FLAIR, PFS (R2 = 0.46), and OS (R2 = 0.68).

CONCLUSION

EOTR based on FLAIR and 5-ALA fluorescence is feasible. Safety of resection relies on the use of neuromonitoring and intraoperative multimodal imaging tools. FLAIR-based EOTR appears to be a stronger survival predictor compared to gadolinium-enhancing, T1-based resection.

Framed and non-framed robotics in neurosurgery: A 10-year single-center experience

BACKGROUND

Safety, efficacy and efficiency of neurosurgical robots are defined by their design (i.e., framed and non-framed) and procedural workflow (PW) (from image to surgery). The present study describes the quality indicators of three different robots in brain and spine surgery.

METHODS

This single-centre study enrolled 252 patients over a 10-year period. Safety (complication rate) and efficacy (diagnostic yield, pedicle screw placement) were determined. Predictors of workflow efficiency (e.g., skin-to-skin) were evaluated and compared to conventional techniques (neuronavigation, stereotaxy).

RESULTS

All robots showed excellent reliability (97.5%-100%) with low complication rates (4.5%-5.3%) and high efficacy (94.7%-97.7%). Robotics demonstrated a better time-efficiency than neuronavigation. However, there was no shortening of surgery time compared to conventional stereotaxy. Time-efficiency differed significantly between framed and non-framed workflows.

CONCLUSION

While all neurosurgical robots were reliable, safe and efficacious, there were significant differences in time-efficiency. PWs should be improved to increase the acceptance of robotics in neurosurgery.

Detecting small conflicting drainages with contrast-enhanced magnetic resonance venography for surgical planning: a technical description and quantified analysis

BACKGROUND

Recent studies have shown the challenges involved in detecting small conflicting vessels (1.0-1.5 mm) on contrast-enhanced (CE) T1 images during stereoelectroencephalography (SEEG) planning. Improving the resolution of non-invasive approaches to identify these vessels is possible and important. We present a superior sagittal sinus mapping-based CE-magnetic resonance venography (CE-MRV) protocol calibrated by craniotomies.

METHOD

Seven patients with epileptic symptoms who received craniotomy were enrolled. CE-MRV was acquired with a bolus mapping of the superior sagittal sinus. Together with the T1 image, 3D veins and the brain surface were visualized. The resolution of the CE-MRV was quantified by measuring the diameter of superficial drainages after exposure of the brain surface during craniotomy.

RESULTS

A total of 37 superficial drainages were exposed in the bone windows. CE-MRV visualized all these drainages. On average, one superficial drainage could be found in every 13.2 mm diameter of the bone window. The boundary resolution of the CE-MRV was 0.58-0.8 mm in vessel diameter, while drainages larger than 0.8 mm were visualized consistently.

CONCLUSIONS

The resolution of the CE-MRV in the present study met the requirement for detection of small conflicting vessels during SEEG planning. The visualized venous landmarks could be used for visual guidance to the surgical zone. As a non-invasive approach, CE-MRV is practical to use in the clinical setting.

A new application of ultrasound-magnetic resonance multimodal fusion virtual navigation in glioma surgery

Background

Long-term survival and high-quality life of patients with gliomas depends on the extent of resection (EOR) and the protection of functional white matter fibers. The navigation system provides precise positioning for surgery based on preoperative magnetic resonance imaging (MRI) but the precision decreases when intraoperative brain drift occurs. Ultrasound (US) can support real-time imaging and correct brain shift. The real-time US-MRI multimodal fusion virtual navigation system (UMNS) is a new technique for glioma surgery. In order to obtain a maximum EOR and functional protection, this study aimed to explore the feasibility, efficiency, and safety of real-time UMNS for glioma surgery, and to evaluate the benefit of the new application by UMNS presetting markers between the tumor and functional white matter fiber surgery.

Methods

A retrospective analysis included 45 patients who underwent glioma surgery, 19 patients with only intraoperative US, and 26 patients with UMNS. A preoperative plan was made by 3D-slicer software based on preoperative MRI. This was combined with a reconstruction of diffusion tensor imaging (DTI) that designed the important locations as "warning points" between functional white matter fibers and tumor. Following patient registration, markers were injected into preset "warning points" under image-guided UMNS in order to give us a warning during surgery in case of postoperative function deficits. The operating time, volumetric assessment in glioma resection, and postoperative complications were evaluated and used to compared those surgeries using intraoperative US (iUS) with those surgeries using intraoperate MRI (iMRI) navigation.

Results

A total of 45 patients underwent glioma surgery. Gross total removal (GTR) of iUS alone was achieved in 6 of 19 cases, while this was achieved in 22 of 26 cases with UMNS alone, demonstrating an improvement in rate of GTR from 31.58% to 84.62%, respectively. This may be attributable to the superior US image quality provided by UMNS. In 13 of 26 cases, there was improved image quality (from poor/moderate to moderate/good) with the aid of UMNS. In addition, the consistency of EOR of postoperative MRI evaluated by UMNS (92.31%) was higher than when using iUS alone (42.11%). The whole process of intraoperative scanning time and marker injection did not lead to a significant delay of the operating time compared to using iUS alone, and has been reported to be shorter than with iMRI as well. Furthermore, the percentage of postoperative morbidity in the UMNS group was lower than that in the iUS group (motor deficit: 11.54% vs. 42.11%; aphasia: P =3.85% vs. 31.58%, respectively).

Conclusions

Real-time UMNS is an effective, timesaving technology that offers high quality intraoperative imaging. Injection markers between functional white matter fibers and tumor by UMNS can help to obtain a maximum EOR of glioma and functional protection postoperatively. The integration of iUS into the neuronavigation system offered quick and helpful intra-operative images.

Presurgical and Intraoperative Augmented Reality in Neuro-Oncologic Surgery: Clinical Experiences and Limitations

Virtual reality (VR) and augmented reality (AR) represent novel adjuncts for neurosurgical planning in neuro-oncology. In addition to established use in surgical and medical training, VR/AR are gaining traction for clinical use preoperatively and intraoperatively. To understand the utility of VR/AR in the clinical setting, we conducted a literature search in Ovid MEDLINE and EMBASE with various search terms designed to capture the use of VR/AR in neurosurgical procedures for resection of cranial tumors. The search retrieved 302 articles, of which 35 were subjected to full-text review; 19 full-text articles were included in the review. Key findings highlighted by the individual authors were extracted and summarized into themes to present the value of VR/AR in the clinical setting. These studies included various VR/AR systems applied to surgeries involving heterogeneous pathologies and outcome measures. Overall, VR/AR were found to be qualitatively advantageous due to enhanced visualization of complex anatomy and improved intraoperative lesion localization. When these technologies were compared with existing neuronavigation systems, quantitative clinical benefits were also reported. The capacity to visualize three-dimensional images superimposed on patient anatomy is a potentially valuable tool in complex neurosurgical environments. Surgical limitations may be addressed through future advances in image registration and tracking as well as intraoperatively acquired imaging with the ability to yield real-time virtual models.

Position and Orientation Errors in a Neuronavigation Procedure: A Stepwise Protocol Using a Cranial Phantom

OBJECTIVE

Neuronavigation procedures demand high precision and accuracy. Despite this need, there are still few studies analyzing errors in such procedures. The aim of this study was to use a custom-built cranial phantom to measure target position and orientation errors in different phases of a simulated neuronavigation procedure.

METHODS

A cranial phantom with 10 target sites was designed and imaged with computed tomography and magnetic resonance. A segmentation of a cloud of points of the phantom (ground truth) was obtained using an optical tracking system and compared with the images (imaging phase). Targets and trajectories were then planned with neuronavigation software and compared with the ground truth (planning phase). The same plan was used to identify the points in real space after image-to-phantom registration and calculate the final error of the procedure by comparison with the ground truth (registration and execution phase).

RESULTS

The mean errors after the imaging phase were 1.11 ± 0.42 mm and 3.23° ± 1.69° for position and orientation, respectively. After planning the mean errors were 1.10 ± 0.39 mm and 5.55° ± 2.91°. The global errors after the registration and mechanical execution were 3.93 ± 1.70 mm and 3.65° ± 1.29°.

CONCLUSIONS

After a stepwise analysis, registration and mechanical execution were the main contributors to the global position error.

Accurate external localization of the left frontal cortex in dogs by using pointer based frameless neuronavigation

BACKGROUND

In humans, non-stereotactic frameless neuronavigation systems are used as a topographical tool for non-invasive brain stimulation methods such as Transcranial Magnetic Stimulation (TMS). TMS studies in dogs may provide treatment modalities for several neuropsychological disorders in dogs. Nevertheless, an accurate non-invasive localization of a stimulation target has not yet been performed in this species.

HYPOTHESIS

This study was primarily put forward to externally locate the left frontal cortex in 18 healthy dogs by means of a human non-stereotactic neuronavigation system. Secondly, the accuracy of the external localization was assessed.

ANIMALS

A total of 18 healthy dogs, drawn at random from the research colony present at the faculty of Veterinary Medicine (Ghent University), were used.

METHODS

Two sets of coordinates (X, Y, Z and X″, Y″, Z″) were compared on each dog their tomographical dataset.

RESULTS

The non-stereotactic neuronavigation system was able to externally locate the frontal cortex in dogs with accuracy comparable with human studies.

CONCLUSION AND CLINICAL IMPORTANCE

This result indicates that a non-stereotactic neuronavigation system can accurately externally locate the left frontal cortex and paves the way to use guided non-invasive brain stimulation methods as an alternative treatment procedure for neurological and behavioral disorders in dogs. This technique could, in analogy with human guided non-invasive brain stimulation, provide a better treatment outcome for dogs suffering from anxiety disorders when compared to its non-guided alternative.

[Application of intraoperative electromagnetic frameless navigation in transcranial and endoscopic neurosurgical interventions]

The paper summarizes the experience in using a system of electromagnetic intraoperative frameless navigation in various neurosurgical pathologies of the brain. The electromagnetic navigation technique was used for 102 operations in 98 patients, including 36 transnasal endoscopic interventions. There were no intraoprtative and postoperative complications associated with the use of the system. In the process of using the system, factors influencing the accuracy of navigation and requiring additional control by the surgeon were identified.

PURPOSE

The study purpose was to evaluate the use of electromagnetic navigation in surgical treatment of patients with various brain lesions.

MATERIAL AND METHODS

The system of electromagnetic navigation was used for 102 operations in 98 patients (42 males and 56 females, including 18 children; median age, 34.8 years (min, 2.2 years; max, 69 years)) in the period from December 2012 to December 2016. In 36 patients, the system was used for endoscopic interventions. In 19 patients, electromagnetic navigation was used in combination with neurophysiological monitoring.

RESULTS

In our series of cases, the frameless electromagnetic navigation system was used in 66 transcranial operations. The mean error of navigation was 1.9±0.5 mm. In 5 cases, we used the data of preoperative functional MRI (fMRI) and tractography for navigation. At the same time, in all 7 operations with simultaneous direct stimulation of the cortex, there was interference and significant high-frequency noise, which distorted the electrophysiological data. A navigation error of more than 3 mm was associated with the use of neuroimaging data with an increment of more than 3 mm, image artifacts from the head locks, high rate of patient registration, inconsequence of touching points on the patient's head, and unsatisfactory fixation to the skin or subsequent displacement of a non-invasive localizer of the patient. In none of the cases, there was a significant effect of standard metal surgical tools (clamps, tweezers, aspirators) located near the patient's head on the navigation system. In two cases, the use of massive retractors located near the patient's localizer caused noise in the localizer and navigation errors of more than 10 mm due to significant distortions of the electromagnetic field. Thirty-six transnasal endoscopic interventions were performed using the electromagnetic frameless navigation system. The mean navigation error was 2.5±0.8 mm.

CONCLUSION

In general, electromagnetic navigation is an accurate, safe, and effective technique that can be used in surgical treatment of patients with various brain lesions. The mean navigation error in our series of cases was 1.9±0.5 mm for transcranial surgery and 2.5±0.8 mm for endoscopic surgery. Electromagnetic navigation can be used for different, both transcranial and endoscopic, neurosurgical interventions. Electromagnetic navigation is most convenient for interventions that do not require fixation of the patient's head, in particular for CSF shunting procedures, drainage of various space-occupying lesions (cysts, hematomas, and abscesses), and optimization of the size and selection of options for craniotomy. In repeated interventions, disruption of the normal anatomical relationships and landmarks necessitates application of neuronavigation systems in almost mandatory manner. The use of electromagnetic navigation does not limit application of the entire range of necessary intraoperative neurophysiological examinations at appropriate surgical stages. Succession in application of neuronavigation should be used to get adequate test results.

The accuracy of computer-aided surgery in neurotologic approaches to the temporal bone: A cadaver study

OBJECTIVE

To assess the accuracy of computer-aided surgery for common neurotologic approaches to the temporal bone.

STUDY DESIGN AND SETTING

Cadaveric heads were dissected by using standard neurotologic approaches to the temporal bone including translabyrinthine, middle fossa, and retrosigmoid. Dissected anatomic landmarks from each approach were compared with CT images that were obtained before dissection on the VectorVision 2 system (BrainLAB Corp, Munich, Germany) and the variability measured from digital images. Each approach was performed 5 times, with each anatomic landmark measured 3 times from each approach.

RESULTS

The accuracy of the computer-aided surgery system was less than 1 mm for all anatomic points measured. Forty-two of the 49 measured points were accurate to less than 0.5 mm.

CONCLUSIONS

Computer-aided surgery of the temporal bone using common neurotologic approaches can be performed accurately and reliably in cadaver specimens.

SIGNIFICANCE

The utility and limitations of computer-aided surgery in the temporal bone are discussed.

EBM RATING

B-2.

Surgical implantation of STN-DBS leads using intraoperative MRI guidance: technique, accuracy, and clinical benefit at 1-year follow-up

BACKGROUND

Improvement of surgical accuracy during DBS-lead implantation has been described recently, leading to "frameless" or "MRI-verified" techniques. However, combining a high-quality definition of the STN using intraoperative 1.5 MRI with the possibility to reduce errors due to co-registration and to monitor lead progression during surgical insertion while checking the absence of surgical complication is an appealing method. We report here surgical methodology, safety, application accuracy, and clinical benefit of STN-lead implantation under MRI guidance.

METHODS

Two patients with a severe PD state were treated by bilateral STN-DBS. Leads were implanted under general anesthesia using intraoperative MRI guidance (ClearPoint system). Lead implantation accuracy was measured on T1 axial images at the level of the target. Clinical improvement was measured on the pre- and post-UPDRS 3 scale at 1-year follow-up.

RESULTS

Surgery was safe and uneventful in both cases. Radial error was 0.36 (right) and 0.86 mm (left) in case 1, and 0.41 (right) and 0.14 mm (left) in case 2. No edema or hemorrhage were noticed.

CONCLUSIONS

Intraoperative MRI guidance allows DBS lead implantation with high accuracy and with great clinical efficacy. A larger cohort of patients is needed to confirm these initial results.

Neuronavigation in the surgical management of brain tumors: current and future trends

Neuronavigation has become an ubiquitous tool in the surgical management of brain tumors. This review describes the use and limitations of current neuronavigational systems for brain tumor biopsy and resection. Methods for integrating intraoperative imaging into neuronavigational datasets developed to address the diminishing accuracy of positional information that occurs over the course of brain tumor resection are discussed. In addition, the process of integration of functional MRI and tractography into navigational models is reviewed. Finally, emerging concepts and future challenges relating to the development and implementation of experimental imaging technologies in the navigational environment are explored.

Application and machine accuracy of a new frameless computed tomography-guided stereotactic brain biopsy system in dogs

The purpose of this study was to describe application and machine accuracy for a new computed tomography (CT) guided, frameless, stereotactic brain biopsy system in dogs. Heads from ten canine cadavers were secured to a bite-plate with six attached fiducial markers and imaged using CT. Fiducialized CT images were imported into stereotactic software and spherical phantom lesions between 3.9 and 5.5 mm in diameter were created in six locations. Infrared cameras and reflective markers were used to register fiducials to the reconstructed image set. Coordinates in the X, Y, and Z planes were identified for each lesion center. Iohexol (1.5 μl of 240 mgI/ml) was injected into the center of each lesion and CT scans were repeated. Pre- and postinjection CT images for each cadaver were fused using the system software. Application accuracy was calculated using the center of each phantom lesion and the center of each injected contrast material location. Machine accuracy was calculated using a phantom with known distances between four fixed points in the X, Y, and Z planes. Mean application accuracy in the first 5 cadavers was 4.3 mm (95% confidence interval [CI] 2.9-4.3 mm) and in the second 5 cadavers was 2.9 mm (95% CI 2-3.9 mm). The more superficial lesions were targeted significantly less accurately than the deeper lesions (P = 0.0183). Median machine accuracy was 0.1 mm and the range was 0.1-0.2 mm. Findings supported use of the new biopsy system for canine brain lesions >3.9 mm in diameter.

Clinical use of a neuronavigation system in hemangioblastoma resection of posterior cranial fossa

The aim of this study was to retrospectively evaluate the effectiveness of the Stryker Leibinger neuronavigation system in surgical resection of hemangioblastomas of the posterior fossa. The study included 16 cases of solid hemangioblastoma of posterior cranial fossa treated since we began using Stryker Leibinger neuronavigation system-assisted microneurosurgery in 2003. These cases were compared on the basis of time, blood loss, and complications to 19 similar cases of solid hemangioblastoma that underwent conventional microneurosurgical resection prior to 2003. All patients in the experimental (neuronavigation-assisted) group underwent surgical resection without complications while the control groups' resections all involved blood loss related to the longer operation time. Neuronavigation also resulted in a clear field of surgical vision and clear lesion boundaries, making it easier to remove lesions and reduce accidental injury of adjacent normal structures. The application of navigation technology is very valuable for solid hemangioblastoma operations not only by shortening operative time, thereby significantly reducing operative blood loss, but also by making surgical excision easier, reducing damage to adjacent normal structures, and decreasing surgical complications and mortality.

[Modern skull base surgery from the perspective of neurosurgeons]

At present, modern skull base surgery is a highly sophisticated interdisciplinary collaboration of various diagnostic and therapeutic disciplines. The overall goal is the treatment of complex tumorous, traumatic, vascular and inflammatory processes or developmental disorders of the skull base with preservation of function. The paper presents modern concepts, procedures and minimally invasive strategies in skull base surgery and also critically discusses the current trend to endoscopic and robot-assisted surgical techniques.

Stand-alone 3D-ultrasound navigation after failure of conventional image guidance for deep-seated lesions

Image guidance has proven to be an important tool in surgery for deep-seated or eloquently located cavernomas. However, neuronavigation depending on preoperative images can fail. Thus, the displayed anatomy might be distorted already during the approach. This report demonstrates the use of three-dimensional intraoperative ultrasound (3D-US) as a rescue tool, when conventional navigation is erroneous. Two patients with symptomatic cavernomas, the one located subcortically in the right peritrigonum, the other in the left thalamus, were operated in our clinic via an image-guided approach. An integrated ultrasound-navigation system was used for neuronavigation. In both cases, navigation based on preoperative MRI failed after the craniotomy because patient-to-image registration was lost. In both cases, a simple registration of the patient's orientation was performed. Then a 3D-US volume was acquired and navigation was performed using the 3D-US data set. This is accurate as image acquisition and navigation are done in the same system. The cavernoma was visualized without difficulties in both cases. It could be reached directly via the ultrasound-guided approach. Patients' symptoms improved postoperatively and a complete resection could be documented. Two cavernomas were successfully resected using 3D-US guidance. In our experience, stand-alone 3D-US navigation is an effective option if conventional MRI-based navigation fails.

Transcranial magnetic stimulation and the challenge of coil placement: a comparison of conventional and stereotaxic neuronavigational strategies

The combination of transcranial magnetic stimulation (TMS) with functional neuroimaging has expanded the potential of TMS for human brain mapping. The precise and reliable positioning of the TMS coil is not a simple task, however. Modern frameless stereotaxic systems allow investigators to base navigation either on the subject's structural magnetic resonance imaging (MRI), functional MRI data, or the use of functional neuroimaging data from the literature, so-called "probabilistic approach." The latter assumes consistency across individuals in the location of task-related "activations" in standardized stereotaxic space. Conventional nonstereotaxic localization of brain areas is also a common method for defining the coil position. Our aim was to evaluate the accuracy of five different localization strategies in one single study. The left primary motor cortex (left M1-Hand) was used as target region. Three approaches were based on real-time frameless stereotaxy using information based on either anatomical or functional MRI. The remaining two strategies relied either on standard cranial landmarks (i.e., the International 10-20 EEG system) or a standardized function-guided procedure (i.e., the spatial relationship between the left and right M1-Hand). The results were compared to a TMS-based mapping of the primary motor cortex; center of gravity of motor-evoked potentials (MEP-CoG) was calculated for each subject (n = 10). Our findings suggest that highest precision can be achieved with fMRI-guided stimulation, which was accurate within the range of millimeters. Very consistent results were also obtained with the "probabilistic" approach. In view of these findings, we discuss the methods and special characteristics of each localization strategy.

High-resolution three-dimensional T2-weighted sequence for neuronavigation: a new setup and clinical trial

OBJECT

Conventional imaging for neuronavigation is performed using high-resolution computerized tomography (CT) scanning or a T1-weighted isovoxel magnetic resonance (MR) sequence. The extension of some lesions, however, is depicted much better on T2-weighted MR images. A possible fusion process used to match low-resolution T2-weighted MR image set with a referenced CT or T1-weighted data set leads to poor resolution in the three-dimensional (3D) reconstruction and decreases accuracy, which is unacceptable for neuronavigation. The object of this work was to develop a 3D T2-weighted isovoxel sequence (3D turbo-spin echo [TSE]) for image-guided neuronavigation of the whole brain and to evaluate its clinical application.

METHODS

The authors performed a phantom study and a clinical trial on a newly developed T2-weighted isovoxel sequence, 3D TSE, for image-guided neuronavigation using a common 1.5-tesla MR imager (Siemens Sonata whole-body imager). The accuracy study and intraoperative image guidance were performed with the aid of the pointer-based Medtronic Stealth Station Treon. The 3D TSE data set was easily applied to the navigational setup and demonstrated a high registration accuracy during the experimental trial and during an initial prospective clinical trial in 25 patients. The sequence displayed common disposable skin fiducial markers and provided convincing delineation of lesions that appear hyperintense on T2-weighted images such as low-grade gliomas and cavernomas in its clinical application.

CONCLUSIONS

Three-dimensional TSE imaging broadens the spectrum of navigational and intraoperative data sets, especially for lesions that appear hyperintense on T2-weighted images. The accuracy of its registration is very reliable and it enables high-resolution reconstruction in any orientation, maintaining the advantages of image-guided surgery.

Navigated transoral approach to the cranial base and the craniocervical junction: technical note

OBJECTIVE

The transoral approach is an elegant reliable surgical procedure that provides anterior exposure of the cranial base and the craniocervical junction. Our objective was to demonstrate the advantages of neuronavigation in planning and performing the transoral approach.

METHODS

Three patients with chordomas and one patient with rheumatoid atlantoaxial subluxation were considered for a neuronavigated transoral procedure. For image guidance, the Stryker navigation system (Stryker Instruments, Kalamazoo, MI) was used. Registration was performed with individually constructed occlusal splints with four markers.

RESULTS

The transoral approach was successfully used for two patients with chordomas involving the cranial base and the upper spine and for one patient with dislocation of the dens and medullary compression. In one case, preoperative simulation of the approach and trajectory planning demonstrated that adequate resection could not be achieved via the transoral route, and a paracondylar suboccipital approach was used. The registration accuracy achieved with the occlusal splint was less than 1 mm.

CONCLUSION

Neuronavigation is a useful tool for planning and performing a transoral approach. It optimizes preoperative planning, clarifies and secures resection limits, and reduces overall surgical morbidity. Registration with an occlusal splint with four markers proved to be an attractive alternative to conventional systems.