Clinical utility and cost-effectiveness of interactive image-guided craniotomy: clinical comparison between conventional and image-guided meningioma surgery

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.

Assessment of necessity of neuronavigation in localization of calvarial extra-axial lesions in the setting of limited resources

Background

Neuronavigation is a very beneficial tool in modern neurosurgical practice. However, the neuronavigation is not available in most of the hospitals in our country raising the question about its importance in localizing the calvarial extra-axial lesions and to what extent it is safe to operate without it.

Methods

We studied twenty patients with calvarial extra-axial lesions who underwent surgical interventions. All lesions were preoperatively located with both neuronavigation and the usual linear measurements. Both methods were compared regarding the time consumed to localize the tumor and the accuracy of each method to anticipate the actual center of the tumor.

Results

The mean error of distance between the planned center of the tumor and the actual was 6.50 ± 1.762 mm in conventional method, whereas the error was 3.85 ± 1.309 mm in IGS method. Much more time was consumed during the neuronavigation method including booting, registration, and positioning. A statistically significant difference was found between the mean time passed in the conventional method and IGS method (2.05 ± 0.826, 24.90 ± 1.334, respectively), P-value < 0.001.

Conclusion

In the setting of limited resources, the linear measurement localization method seems to have an accepted accuracy in the localization of calvarial extra-axial lesions and it saves more time than neuronavigation method.

Review of Atypical and Anaplastic Meningiomas: Classification, Molecular Biology, and Management

Although the majority of meningiomas are slow-growing and benign, atypical and anaplastic meningiomas behave aggressively with a penchant for recurrence. Standard of care includes surgical resection followed by adjuvant radiation in anaplastic and partially resected atypical meningiomas; however, the role of adjuvant radiation for incompletely resected atypical meningiomas remains debated. Despite maximum treatment, atypical, and anaplastic meningiomas have a strong proclivity for recurrence. Accumulating mutations over time, recurrent tumors behave more aggressively and often become refractory or no longer amenable to further surgical resection or radiation. Chemotherapy and other medical therapies are available as salvage treatment once standard options are exhausted; however, efficacy of these agents remains limited. This review discusses the risk factors, classification, and molecular biology of meningiomas as well as the current management strategies, novel therapeutic approaches, and future directions for managing atypical and anaplastic meningiomas.

Improved accuracy of hemimandibular reconstructions involving the condyle by utilizing hydroformed reconstruction plates rather than hand-bent stock plates

BACKGROUND

Computer-aided design/computer-aided manufacturing (CAD/CAM) surgical templates allow precise mandibular reconstructive surgery. However, their clinical accuracy is limited by manual plate bending. Digitally hydroformed plates maintain a digital workstream in virtual planning.

METHODS

Twelve patients with Brown's class IIc mandibular defects were randomized into two groups: group I (experimental), the reconstruction plate was digitally hydroformed, and group II (control), surgeries were performed CAD/CAM guided with the reconstruction plate manually prebent. The linear and angular deviations of reconstruction outcomes were compared to surgical simulation in both groups.

RESULTS

The mean linear and angular deviations of middle and posterior segments were 2.14 ± 0.79 mm, 3.71 ± 0.95 mm, 8.73° ± 1.91°, and 9.06° ± 0.96° in group I and 4.31 ± 0.78 mm, 6.74 ± 1.40 mm, 16.35° ± 0.72°, and 31.48° ± 3.38° in group II, respectively. Measurements in group I were significantly lower than group II (P < .005).

CONCLUSION

Digital hydroforming for plate prebent is a reliable method that helps improving the clinical accuracy of CAD/CAM-guided mandibular reconstruction surgery.

Using the variogram for vector outlier screening: application to feature-based image registration

PURPOSE

Matching points that are derived from features or landmarks in image data is a key step in some medical imaging applications. Since most robust point matching algorithms claim to be able to deal with outliers, users may place high confidence in the matching result and use it without further examination. However, for tasks such as feature-based registration in image-guided neurosurgery, even a few mismatches, in the form of invalid displacement vectors, could cause serious consequences. As a result, having an effective tool by which operators can manually screen all matches for outliers could substantially benefit the outcome of those applications.

METHODS

We introduce a novel variogram-based outlier screening method for vectors. The variogram is a powerful geostatistical tool for characterizing the spatial dependence of stochastic processes. Since the spatial correlation of invalid displacement vectors, which are considered as vector outliers, tends to behave differently than normal displacement vectors, they can be efficiently identified on the variogram.

RESULTS

We validate the proposed method on 9 sets of clinically acquired ultrasound data. In the experiment, potential outliers are flagged on the variogram by one operator and further evaluated by 8 experienced medical imaging researchers. The matching quality of those potential outliers is approximately 1.5 lower, on a scale from 1 (bad) to 5 (good), than valid displacement vectors.

CONCLUSION

The variogram is a simple yet informative tool. While being used extensively in geostatistical analysis, it has not received enough attention in the medical imaging field. We believe there is a good deal of potential for clinically applying the proposed outlier screening method. By way of this paper, we also expect researchers to find variogram useful in other medical applications that involve motion vectors analyses.

Microvascular Decompression for Glossopharyngeal Neuralgia: Clinical Analyses of 30 Cases

Objective

We present our experience of microvascular decompression (MVD) for glossopharyngeal neuralgia (GPN) and evaluate the postoperative outcomes in accordance with four different operative techniques during MVD.

Methods

In total, 30 patients with intractable primary typical GPN who underwent MVD without rhizotomy and were followed for more than 2 years were included in the analysis. Each MVD was performed using one of four different surgical techniques: interposition of Teflon pieces, transposition of offending vessels using Teflon pieces, transposition of offending vessels using a fibrin-glue-coated Teflon sling, and removal of offending veins.

Results

The posterior inferior cerebellar artery was responsible for neurovascular compression in 27 of 30 (90%) patients, either by itself or in combination with other vessels. The location of compression on the glossopharyngeal nerve varied; the root entry zone (REZ) only (63.3%) was most common, followed by both the REZ and distal portion (26.7%) and the distal portion alone (10.0%). In terms of detailed surgical techniques during MVD, the offending vessels were transposed in 24 (80%) patients, either using additional insulation, offered by Teflon pieces (15 patients), or using a fibrin glue-coated Teflon sling (9 patients). Simple insertion of Teflon pieces and removal of a small vein were also performed in five and one patient, respectively. During the 2 years following MVD, 29 of 30 (96.7%) patients were asymptomatic or experienced only occasional pain that did not require medication. Temporary hemodynamic instability occurred in two patients during MVD, and seven patients experienced transient postoperative complications. Neither persistent morbidity nor mortality was reported.

Conclusion

This study demonstrates that MVD without rhizotomy is a safe and effective treatment option for GPN.

Deformation correction for image guided liver surgery: An intraoperative fidelity assessment

BACKGROUND

Although systems of 3-dimensional image-guided surgery are a valuable adjunct across numerous procedures, differences in organ shape between that reflected in the preoperative image data and the intraoperative state can compromise the fidelity of such guidance based on the image. In this work, we assessed in real time a novel, 3-dimensional image-guided operation platform that incorporates soft tissue deformation.

METHODS

A series of 125 alignment evaluations were performed across 20 patients. During the operation, the surgeon assessed the liver by swabbing an optically tracked stylus over the liver surface and viewing the image-guided operation display. Each patient had approximately 6 intraoperative comparative evaluations. For each assessment, 1 of only 2 types of alignments were considered: conventional rigid and novel deformable. The series of alignment types used was randomized and blinded to the surgeon. The surgeon provided a rating, R, from -3 to +3 for each display compared with the previous display, whereby a negative rating indicated degradation in fidelity and a positive rating an improvement.

RESULTS

A statistical analysis of the series of rating data by the clinician indicated that the surgeons were able to perceive an improvement (defined as a R > 1) of the model-based registration over the rigid registration (P = .01) as well as a degradation (defined as R < -1) when the rigid registration was compared with the novel deformable guidance information (P = .03).

CONCLUSION

This study provides evidence of the benefit of deformation correction in providing an accurate location for the liver for use in image-guided surgery systems.

Intraoperative Imaging Modalities and Compensation for Brain Shift in Tumor Resection Surgery

Intraoperative brain shift during neurosurgical procedures is a well-known phenomenon caused by gravity, tissue manipulation, tumor size, loss of cerebrospinal fluid (CSF), and use of medication. For the use of image-guided systems, this phenomenon greatly affects the accuracy of the guidance. During the last several decades, researchers have investigated how to overcome this problem. The purpose of this paper is to present a review of publications concerning different aspects of intraoperative brain shift especially in a tumor resection surgery such as intraoperative imaging systems, quantification, measurement, modeling, and registration techniques. Clinical experience of using intraoperative imaging modalities, details about registration, and modeling methods in connection with brain shift in tumor resection surgery are the focuses of this review. In total, 126 papers regarding this topic are analyzed in a comprehensive summary and are categorized according to fourteen criteria. The result of the categorization is presented in an interactive web tool. The consequences from the categorization and trends in the future are discussed at the end of this work.

Intracranial MR-guided laser-induced thermal therapy: single-center experience with the Visualase thermal therapy system

OBJECTIVE MR-guided laser-induced thermal therapy (MRgLITT) can be used to treat intracranial tumors, epilepsy, and chronic pain syndromes. Here, the authors report their single-center experience with 102 patients, the largest series to date in which the Visualase thermal therapy system was used. METHODS A retrospective analysis of all patients who underwent MRgLITT between 2010 and 2014 was performed. Pathologies included glioma, recurrent metastasis, radiation necrosis, chronic pain, and epilepsy. Laser catheters were placed stereotactically, and ablation was performed in the MRI suite. Demographics, operative parameters, length of hospital stay, and complications were recorded. Thirty-day readmission rates were calculated by using the standard method according to America's Health Insurance Plans Center for Policy and Research guidelines. RESULTS A total of 133 lasers were placed in 102 patients who required intervention for intracranial tumors (87 patients), chronic pain syndrome (cingulotomy, 5 patients), or epilepsy (10 patients). The procedure was completed in 98% (100) of these patients. Ninety-two patients (90.2%) had undergone previous treatment for their intracranial tumors. The average (± SD) total procedural time was 170.5 ± 34.4 minutes, and the mean laser-on time was 8.7 ± 6.8 minutes. The average intensive care unit (ICU) and hospital stays were 1.8 and 3.6 days, respectively, and the median length of stay for both the ICU and the hospital was 1 day. By postoperative Day 1, 54% of the patients (n = 55) were neurologically stable for discharge. There were 27 cases of morbidity, including new-onset neurological deficits, and 2 perioperative deaths. Fourteen patients (13.7%) developed new deficits after the MRgLITT procedure, and of those 14 patients, 64.3% (n = 9) had complete resolution of deficits within 1 month, 7.1% (n = 1) had partial resolution of symptoms within 1 month, 14.3% (n = 2) had not had resolution of symptoms at the most recent follow-up, and 14.3% (n = 2) died without resolution of symptoms. The 30-day readmission rate was 5.6% CONCLUSIONS MRgLITT, although minimally invasive, must be used with caution. Thermal damage to critical and eloquent structures can occur despite MRI guidance. Once the learning curve is overcome, the overall procedural complication rate is low, and most patients can be discharged within 24 hours, with a relatively low readmission rate. In cases in which they occurred, most neurological deficits were temporary. The therapeutic role of MRgLITT in various intracranial diseases will require larger and more rigorous studies.

Comparative effectiveness and safety of image guidance systems in neurosurgery: a preclinical randomized study

OBJECT

Over the last decade, image guidance systems have been widely adopted in neurosurgery. Nonetheless, the evidence supporting the use of these systems in surgery remains limited. The aim of this study was to compare simultaneously the effectiveness and safety of various image guidance systems against that of standard surgery.

METHODS

In this preclinical, randomized study, 50 novice surgeons were allocated to one of the following groups: 1) no image guidance, 2) triplanar display, 3) always-on solid overlay, 4) always-on wire mesh overlay, and 5) on-demand inverse realism overlay. Each participant was asked to identify a basilar tip aneurysm in a validated model head. The primary outcomes were time to task completion (in seconds) and tool path length (in mm). The secondary outcomes were recognition of an unexpected finding (i.e., a surgical clip) and subjective depth perception using a Likert scale.

RESULTS

The time to task completion and tool path length were significantly lower when using any form of image guidance compared with no image guidance (p < 0.001 and p = 0.003, respectively). The tool path distance was also lower in groups using augmented reality compared with triplanar display (p = 0.010). Always-on solid overlay resulted in the greatest inattentional blindness (20% recognition of unexpected finding). Wire mesh and on-demand overlays mitigated, but did not negate, inattentional blindness and were comparable to triplanar display (40% recognition of unexpected finding in all groups). Wire mesh and inverse realism overlays also resulted in better subjective depth perception than always-on solid overlay (p = 0.031 and p = 0.008, respectively).

CONCLUSIONS

New augmented reality platforms may improve performance in less-experienced surgeons. However, all image display modalities, including existing triplanar displays, carry a risk of inattentional blindness.

The current status of 5-ALA fluorescence-guided resection of intracranial meningiomas-a critical review

Meningiomas are the second most common primary tumors affecting the central nervous system. Surgical treatment can be curative in case of complete resection. 5-aminolevulinic acid (5-ALA) has been established as an intraoperative tool in malignant glioma surgery. A number of studies have tried to outline the merits of 5-ALA for the resection of intracranial meningiomas. In the present paper, we review the existing literature about the application of 5-ALA as an intraoperative tool for the resection of intracranial meningiomas. PubMed was used as the database for search tasks. We included articles published in English without limitations regarding publication date. Tumor fluorescence can occur in benign meningiomas (WHO grade I) as well as in WHO grade II and WHO grade III meningiomas. Most of the reviewed studies report fluorescence of the main tumor mass with high sensitivity and specificity. However, different parts of the same tumor can present with a different fluorescent pattern (heterogenic fluorescence). Quantitative probe fluorescence can be superior, especially in meningiomas with difficult anatomical accessibility. However, only one study was able to consistently correlate resected tissue with histopathological results and nonspecific fluorescence of healthy brain tissue remains a confounder. The use of 5-ALA as a tool to guide resection of intracranial meningiomas remains experimental, especially in cases with tumor recurrence. The principle of intraoperative fluorescence as a real-time method to achieve complete resection is appealing, but the usefulness of 5-ALA is questionable. 5-ALA in intracranial meningioma surgery should only be used in a protocolled prospective and long-term study.

Endoscopic and keyhole endoscope-assisted neurosurgical approaches: a qualitative survey on technical challenges and technological solutions

INTRODUCTION

The literature reflects a resurgence of interest in endoscopic and keyhole endoscope-assisted neurosurgical approaches as alternatives to conventional microsurgical approaches in carefully selected cases. The aim of this study was to assess the technical challenges of neuroendoscopy, and the scope for technological innovations to overcome these barriers.

MATERIALS AND METHODS

All full members of the Society of British Neurosurgeons (SBNS) were electronically invited to participate in an online survey. The open-ended structured survey asked three questions; firstly, whether the surgeon presently utilises or has experience with endoscopic or endoscope-assisted approaches; secondly, what they consider to be the major technical barriers to adopting such approaches; and thirdly, what technological advances they foresee improving safety and efficacy in the field. Responses were subjected to a qualitative research method of multi-rater emergent theme analysis.

RESULTS

Three clear themes emerged: 1) surgical approach and better integration with image-guidance systems (20%), 2) intra-operative visualisation and improvements in neuroendoscopy (49%), and 3) surgical manipulation and improvements in instruments (74%).

DISCUSSION

The analysis of responses to our open-ended survey revealed that although opinion was varied three major themes could be identified. Emerging technological advances such as augmented reality, high-definition stereo-endoscopy, and robotic joint-wristed instruments may help overcome the technical difficulties associated with neuroendoscopic approaches.

CONCLUSIONS

Results of this qualitative survey provide consensus amongst the technology end-user community such that unambiguous goals and priorities may be defined. Systems integrating these advances could improve the safety and efficacy of endoscopic and endoscope-assisted neurosurgical approaches.

The accuracy of computer-assisted primary mandibular reconstruction with vascularized bone flaps: iliac crest bone flap versus osteomyocutaneous fibula flap

Background

The intention of mandibular reconstruction is to restore the complex anatomy with maximum possible functionality and high accuracy. The aim of this study was to evaluate the accuracy of computer-assisted surgery in primary mandibular reconstruction with an iliac crest bone flap compared with an osteomyocutaneous fibula flap.

Materials and methods

Preoperative computed tomography data of the mandible and the iliac crest or fibula donor site were imported into a specific surgical planning software program. Surgical guides were manufactured using a rapid prototyping technique for translating the virtual plan, including information on the transplant dimensions and shape, into real-time surgery. Using postoperative computed tomography scans and an automatic surface-comparison algorithm, the actual postoperative situation was compared with the preoperative virtual simulation.

Results

The actual flap position showed a mean difference from the virtual plan of 2.43 mm (standard deviation [SD] ±1.26) and a surface deviation of 39% <2 mm and 15% <1 mm for the iliac crest bone flap, and a mean difference of 2.18 mm (SD ±1.93) and a surface deviation of 60% <2 mm and 37% <1 mm for the osteomyocutaneous fibula flap. The position of the neomandible reconstructed with an osteomyocutaneous fibula flap indicated a mean difference from the virtual plan of 1.25 mm (SD ±1.31) and a surface deviation of 82% <2 mm and 57% <1 mm, in contrast to a mean difference of 1.68 mm (SD ±1.25) and a surface deviation of 63% <2 mm and 38% <1 mm for the neomandible after reconstruction with an iliac crest bone flap. For shape analysis, a similarly high accuracy could be calculated for both flaps.

Conclusion

Virtual surgical planning is an effective method for mandibular reconstruction with vascularized bone flaps, and can help to restore the anatomy of the mandible with high accuracy in position and shape. It seems that primary mandibular reconstruction with the osteomyocutaneous fibula flap is more accurate compared with the vascularized iliac crest bone flap.

Evaluation of computer-assisted mandibular reconstruction with vascularized iliac crest bone graft compared to conventional surgery: a randomized prospective clinical trial

BACKGROUND

Computer-assisted surgery plays an increasingly important role in mandibular reconstruction, ensuring the best possible masticatory function and aesthetic outcome.

METHODS

Twenty patients were randomly assigned to computer-assisted or conventional mandibular reconstruction with vascularized iliac crest bone graft in a prospective study design.Virtual surgical planning was based on preoperative CT-data using specific surgical planning software. A rapid prototyping guide transferred the virtual surgery plan to the operation site. During surgery the transplant ischemic time, reconstruction time, time for shaping the transplant and amount of bone removed were measured. Additionally, the difference in the intercondylar distance before and after surgery was calculated.

RESULTS

Computer-assisted surgery shortened the time of transplant ischemia (P < 0.005) and defect reconstruction (P < 0.001) compared to conventional surgery. The time to saw and shape the transplant at the donor site was shorter using conventional surgery (P < 0.005); therefore, the overall time for surgery didn't change (P = 0.527). In the computer-assisted group, the amount of bone harvested equaled the defect size, whereas the transplant size in the conventional group exceeded the defect site by 16.8 ± 5.6 mm (P < 0.001) on average. The intercondylar distance before compared to after surgery was less affected in the computer-assisted than in the conventional group (P < 0.001).

CONCLUSIONS

The presented study shows that computer-assisted surgery can help reduce the time for mandibular defect reconstruction and consequently the transplant ischemic time. In the computer-assisted group, the iliac crest donor site defect was downsized and the postoperative condyle position was less altered, reducing possible risks of postoperative complications and donor site morbidity.

TRIAL REGISTRATION

DRKS00005181.

3D preoperative planning in the ER with OsiriX®: when there is no time for neuronavigation

The evaluation of patients in the emergency room department (ER) through more accurate imaging methods such as computed tomography (CT) has revolutionized their assistance in the early 80s. However, despite technical improvements seen during the last decade, surgical planning in the ER has not followed the development of image acquisition methods. The authors present their experience with DICOM image processing as a navigation method in the ER. The authors present 18 patients treated in the Emergency Department of the Hospital das Clínicas of the University of Sao Paulo. All patients were submitted to volumetric CT. We present patients with epidural hematomas, acute/subacute subdural hematomas and contusional hematomas. Using a specific program to analyze images in DICOM format (OsiriX^®), the authors performed the appropriate surgical planning. The use of 3D surgical planning made it possible to perform procedures more accurately and less invasively, enabling better postoperative outcomes. All sorts of neurosurgical emergency pathologies can be treated appropriately with no waste of time. The three-dimensional processing of images in the preoperative evaluation is easy and possible even within the emergency care. It should be used as a tool to reduce the surgical trauma and it may dispense methods of navigation in many cases.

Navigation in surgery

INTRODUCTION

"Navigation in surgery" spans a broad area, which, depending on the clinical challenge, can have different meanings. Over the past decade, navigation in surgery has evolved beyond imaging modalities and bulky systems into the rich networking of the cloud or devices that are pocket-sized.

DISCUSSION

This article will review various aspects of navigation in the operating room and beyond. This includes a short history of navigation, the evolution of surgical navigation, as well as technical aspects and clinical benefits with examples from neurosurgery, spinal surgery, and orthopedics.

CONCLUSION

With improved computer technology and a trend towards advanced information processing within hospitals, navigation is quickly becoming an integral part in the surgical routine of clinicians.

High-accuracy patient-to-image registration for the facilitation of image-guided robotic microsurgery on the head

Image-guided microsurgery requires accuracies an order of magnitude higher than today's navigation systems provide. A critical step toward the achievement of such low-error requirements is a highly accurate and verified patient-to-image registration. With the aim of reducing target registration error to a level that would facilitate the use of image-guided robotic microsurgery on the rigid anatomy of the head, we have developed a semiautomatic fiducial detection technique. Automatic force-controlled localization of fiducials on the patient is achieved through the implementation of a robotic-controlled tactile search within the head of a standard surgical screw. Precise detection of the corresponding fiducials in the image data is realized using an automated model-based matching algorithm on high-resolution, isometric cone beam CT images. Verification of the registration technique on phantoms demonstrated that through the elimination of user variability, clinically relevant target registration errors of approximately 0.1 mm could be achieved.

Image guidance for brain metastases resection

The primary goal in removing a metastatic brain tumor is to maximize surgical resection while minimizing the risk of neurological injury. Intraoperative image guidance is frequently used in the resection of both primary and metastatic brain tumors. Stereotactic volumetric techniques allow for smaller craniotomies, facilitate lesion localization, and help neurosurgeons avoid eloquent structures. In turn, this leads to decreased patient morbidity and shorter hospitalizations. Image guidance is not without shortcomings, however, perhaps the most significant of which is inaccuracy of tumor resection associated with intraoperative brain shifts. The goal of this review is to expound on the uses of image guidance and discuss avoidance of technical pitfalls in the resection of cerebral metastatic lesions.

Evaluation of Neuronavigation in Lesional and Non-Lesional Epilepsy Surgery

OBJECTIVE

For many patients, surgery for intractable epilepsy provides not only freedom or substantial relief from seizures, but also functional improvement and increased quality of life. Precise intraoperative localization of the underlying structural and functional processes is crucial in this regard. The aim of this study was to clinically evaluate whether neuronavigation leads to an improvement in the precision and safety of epilepsy surgery. In this paper, we also attempt to assess the navigation workstation as a platform for the integration of multimodal information (multimodal information guidance).

PATIENTS

Out of a series of 223 epilepsy surgery procedures, 140 were performed with the aid of neuronavigation. Patient and surgical data were prospectively collected.

METHODS

We used the neuronavigation device as a common platform to merge complementary information modalities. Correlation of anatomic and structural details with functional information contributed to the surgical script in non-lesional and localization-related epilepsy surgery. At least two different information modalities contributed to planning and surgical guidance in every patient. Immediately following the operative procedure, the surgeon answered a set of questions on the reasons for the application of neuronavigation, and the efficiency and safety of navigation. Detailed analysis of the location of the operative procedure, histopathological findings and outcome was performed.

RESULTS

The main benefits of neuronavigation in epilepsy surgery were precision of targeting even in small and deep-seated targets, safe manipulation in critical brain areas, accurate placement of electrodes, and correlation of electro-clinical information modalities with underlying structures. Furthermore, navigation provided individual tailoring of craniotomy and corticotomy. It was less reliable for verification of resection boundaries in the case of underlying glioma. Neuronavigational localization and its combination with image fusion and functional investigations greatly improved discussion within the epilepsy surgery team.

CONCLUSION

The neuronavigation concept proved its value in epilepsy surgery by linking anatomic, pathologic and functional data of the individual patient. Enhanced by the integration of multimodal information, neuronavigation significantly improved the available treatment options.

A surface registration method for quantification of intraoperative brain deformations in image-guided neurosurgery

Intraoperative brain deformations decrease accuracy in image-guided neurosurgery. Approaches to quantify these deformations based on 3-D reconstruction of cortectomy surfaces have been described and have shown promising results regarding the extrapolation to the whole brain volume using additional prior knowledge or sparse volume modalities. Quantification of brain deformations from surface measurement requires the registration of surfaces at different times along the surgical procedure, with different challenges according to the patient and surgical step. In this paper, we propose a new flexible surface registration approach for any textured point cloud computed by stereoscopic or laser range approach. This method includes three terms: the first term is related to image intensities, the second to Euclidean distance, and the third to anatomical landmarks automatically extracted and continuously tracked in the 2-D video flow. Performance evaluation was performed on both phantom and clinical cases. The global method, including textured point cloud reconstruction, had accuracy within 2 mm, which is the usual rigid registration error of neuronavigation systems before deformations. Its main advantage is to consider all the available data, including the microscope video flow with higher temporal resolution than previously published methods.

Image-guided, stereotactic perforator flap surgery: a prospective comparison of current techniques and review of the literature

BACKGROUND

Image-guided stereotaxy is a recent advancement in imaging technology, allowing computer guidance to aid surgical planning and accuracy. Despite the use of multiple techniques for patient registration in several surgical specialities, only fiducial marker registration has been described for use in soft tissue reconstructive surgery. The current study comprises an evaluation of the current techniques available for this purpose.

METHODS

A cohort of nine consecutive patients planned for elective free flaps were recruited, with the first five patients (four for the abdominal wall and one anterolateral thigh donor site) undergoing fiducial marker registration with a variable number of fiducial markers in order to determine the optimal number of fiducial markers to be used. Four subsequent patients undergoing perforator flap surgery underwent registration using three available registration modalities: fiducial marker registration, surface matching pointer/landmark and surface matching laser registration.

RESULTS

For the abdominal wall, registration was not able to be achieved with five fiducial markers, and was successfully achieved in all cases with either six or seven fiducial markers. For the anterolateral thigh, registration was achieved with either nine or ten markers. The four patients who also underwent surface-landmark registration and 'Z-touch' laser surface matching registration all failed the registration process.

CONCLUSION

Stereotactic navigation is a useful adjunct to the preoperative imaging of perforator flaps. Fiducial marker registration was able to be achieved in all cases, can be successfully achieved with a low and predictable number of fiducial markers, is highly accurate, and was the only reliable registration process in our experience.

Optimal port placement and enhanced guidance in robotically assisted cardiac surgery

BACKGROUND

Optimal port placement and enhanced guidance in robotically assisted cardiac surgery is required to improve preoperative planning and intraoperative navigation.

METHODS

Offline optimal port placement is planned on a three-dimensional virtual reconstruction of the patient's computed tomography scan. Using this data, an accurate in vivo port placement can be performed, which is achieved by augmented reality techniques superimposing virtual models of the thorax and the teleoperator arms on top of the real worldview.

RESULTS

A new system incorporating both port placement planning and intraoperative navigation in robotically assisted minimally invasive heart surgery was established to aid the operative workflow. A significant reduction of operation time by improved planning and intraoperative support is anticipated.

CONCLUSIONS

The enhanced intraoperative orientation possibilities may lead to further decrease in operation time and have the continuing ability to improve quality.

Neuronavigation and surgery of intracerebral tumours

Approximately four decades after the successful clinical introduction of framebased stereotactic neurosurgery by Spiegel and Wycis, frameless stereotaxy emerged to enable more elaborate image guidance in open neurosurgical procedures. Frameless stereotaxy, or neuronavigation, relies on one of several different localizing techniques to determine the position of an operative instrument relative to the surgical field, without the need for a coordinate frame rigidly fixed to the patients' skull. Currently, most systems are based on the optical triangulation of infrared light sources fixed to the surgical instrument. In its essence, a navigation system is a three-dimensional digitiser that correlates its measurements to a reference data set, i.e. a preoperatively acquired CT or MRI image stack. This correlation is achieved through a patient-to-image registration procedure resulting in a mathematical transformation matrix mapping each position in 'world space' onto 'image space'. Thus, throughout the remainder of the surgical procedure, the position of the surgical instrument can be demonstrated on a computer screen, relative to the CT or MRI images. Though neuronavigation has become a routinely used addition to the neurosurgical armamentarium, its impact on surgical results has not yet been examined sufficiently. Therefore, the surgeon is left to decide on a case-by-case basis whether to perform surgery with or without neuronavigation. Future challenges lie in improvement of the interface between the surgeon and the neuronavigator and in reducing the brainshift error, i.e. inaccuracy introduced by changes in tissue positions after image acquisition.

Effectiveness of neuronavigation in resecting solitary intracerebral contrast-enhancing tumors: a randomized controlled trial

Object

The goal of this study was to assess the impact of neuronavigation on the cytoreductive treatment of solitary contrast-enhancing intracerebral tumors and outcomes of this treatment in cases in which neuronavigation was preoperatively judged to be redundant.

Methods

The authors conducted a prospective randomized study in which 45 patients, each harboring a solitary contrast-enhancing intracerebral tumor, were randomized for surgery with or without neuronavigation. Peri- and postoperative parameters under investigation included the following: duration of the procedure; surgeon’s estimate of the usefulness of neuronavigation; quantification of the extent of resection, determined using magnetic resonance imaging; and the postoperative course, as evaluated by neurological examinations, the patient’s quality-of-life self-assessment, application of the Barthel index and the Karnofsky Performance Scale score, and the patient’s time of death.

The mean amount of residual tumor tissue was 28.9% for standard surgery (SS) and 13.8% for surgery involving neuronavigation (SN). The corresponding mean amounts of residual contrast-enhancing tumor tissue were 29.2 and 24.4%, respectively. These differences were not significant. Gross-total removal (GTR) was achieved in five patients who underwent SS and in three who underwent SN. Median survival was significantly shorter in the SN group (5.6 months compared with 9 months, unadjusted hazard ratio = 1.6); however, this difference may be attributable to the coincidental early death of three patients in the SN group. No discernible important effect on the patients’ 3-month postoperative course was identified.

Conclusions

There is no rationale for the routine use of neuronavigation to improve the extent of tumor resection and prognosis in patients harboring a solitary enhancing intracerebral lesion when neuronavigation is not already deemed advantageous because of the size or location of the lesion.

Comparison of the reliability of brain lesion localization when using traditional and stereotactic image-guided techniques: a prospective study

OBJECT

Accurate localization of brain lesions is of utmost importance. Traditional methods of localization that involve the use of neuroimaging and surface anatomy have been replaced in certain cases by using frameless stereotactic neuronavigational systems. Even though these systems have been found to be accurate, no studies have been conducted to investigate whether the systems provide improved localization accuracy compared with traditional methods.

METHODS

Twenty-two patients undergoing image-guided surgery with the aid of the Stealth Neuro-Station were prospectively enrolled in this study. All patients underwent standard magnetic resonance or computerized tomography imaging, as well as special Stealth-sequenced imaging acquired using scalp fiducial markers. Traditional and Stealth estimates of the surface projection of lesions were determined, digitally photographed, and later compared. The mean (+/- standard deviation) error associated with traditional localization of lesions was 1.1 +/- 0.7 cm in the mediolateral plane and 1.3 +/- 1.1 cm in the anteroposterior plane. This error was not significantly affected by the size or location of the lesion.

CONCLUSIONS

Findings of this study indicate that the conventional localization technique used to demarcate brain cortical and subcortical lesions has an error of approximately 1 to 1.5 cm in both the mediolateral and anteroposterior directions. This error can be reduced by judicious use of image-guided techniques.

Computer-aided navigation in neurosurgery

The article comprises three main parts: a historical review on navigation, the mathematical basics for calculation and the clinical applications of navigation devices. Main historical steps are described from the first idea till the realisation of the frame-based and frameless navigation devices including robots. In particular the idea of robots can be traced back to the Iliad of Homer, the first testimony of European literature over 2500 years ago. In the second part the mathematical calculation of the mapping between the navigation and the image space is demonstrated, including different registration modalities and error estimations. The error of the navigation has to be divided into the technical error of the device calculating its own position in space, the registration error due to inaccuracies in the calculation of the transformation matrix between the navigation and the image space, and the application error caused additionally by anatomical shift of the brain structures during operation. In the third part the main clinical fields of application in modern neurosurgery are demonstrated, such as localisation of small intracranial lesions, skull-base surgery, intracerebral biopsies, intracranial endoscopy, functional neurosurgery and spinal navigation. At the end of the article some possible objections to navigation-aided surgery are discussed.

Motor functional MRI for pre-operative and intraoperative neurosurgical guidance

Functional MRI (fMRI) may provide a means of locating areas of eloquent cortex that can be used to guide neurosurgeons in their quest to maximize intracerebral tumour resection whilst minimizing post-procedural neurological deficits. This work aimed to develop and provide an initial assessment of such a technique. 19 patients with mass lesions close to the primary motor cortex underwent fMRI at 1.5T. A single shot echo planar technique was used to acquire data corresponding to right and left hand movement. Resultant activation maps were used to aid pre-surgical planning. Data was used in conjunction with an intraoperative navigation system in 13 cases. Activation was attributed to primary motor, primary somatosensory or supplementary motor cortex in 17 of 19 subjects. No permanent changes in motor deficit were detected post surgery. The additional information provided by fMRI, particularly when incorporated into a neuronavigation guided craniotomy, was deemed highly valuable to the neurosurgeon as it enabled safe resection of tumour in anatomical locations previously deemed to be too high risk for safe resection using conventional (non-fMRI-guided) technique. This observation is reinforced by the fact that no patients suffered permanent neurological deficit after radical tumour debulking (surgical estimates >90% tumour resection).

Contemporary use of image-guided systems

Technologic advancements in radiographic imaging and interactive computers have allowed image-guided systems to be developed, which have been used to characterize surgical anatomy with greater accuracy and detail. Early generations of image-guided systems were difficult to use; however, recent modifications have allowed it to become more user friendly and less cumbersome. As a result, the application of image-guided systems has expanded and its use has become more frequent. Two major designs, optical and electromagnetic, have been used. Although most image-guided systems use computed tomography digital images, magnetic resonance image-based image-guided systems serve a unique and useful purpose. Future directions for image-guided surgery include smaller flexible instrumentation and simplified registration. As image-guided systems continue to evolve, they will enable otolaryngologist to broaden the horizon of minimally invasive techniques and operations.

Evaluation of factors predicting accurate resection of high-grade gliomas by using frameless image-guided stereotactic guidance

Object

Frameless image-guided stereotaxy is often used in the resection of high-grade gliomas. The authors of several studies, however, have suggested that brain shift may occur intraoperatively and result in inaccurate resection. To determine the usefulness of frameless stereotactic image-guided surgery of high-grade gliomas, the authors correlated factors predictive of brain shift, such as tumor size, periventricular location, and patient age (as an indicator of brain atrophy) with the extent of resection.

Methods

Inclusion criteria included the following: 1) stereotactic volumetric craniotomy for resection of tumor; 2) histologically proven high-grade glioma; 3) preoperative magnetic resonance (MR) imaging demonstration of an enhancing portion of tumor; 4) postoperative MR imaging within 48 hours to assess the extent of resection; and 5) preoperative intention to perform gross-total resection of the enhancing tumor. Fifty-four patients met these criteria between September 1997 and November 2002. Accurate resection was considered to be indicated by a lack of nodular enhancement on postoperative Gd-enhanced MR images obtained within 48 hours of surgery.

Frameless stereotactic image-guided surgery resulted in the successful resection of 46 (85%) of 54 high-grade gliomas. Accurate resection was significantly more likely with tumors less than 30 ml in volume than with those greater than 30 ml (93 and 58%, respectively [p < 0.05]). In addition, small periventricular tumors were associated with significant less successful resection compared with nonperiventricular tumor (77 and 96%, respectively [p = 0.5]). Patient age did not affect the likelihood of successful resection.

Conclusions

Frameless image-guided stereotactic techniques can be reliably used for accurate resection of high-grade gliomas when the tumor is less than 30 ml in volume and not adjacent to the ventricular system. In cases involving tumors larger in volume or located near the ventricles, intraoperative ultrasonography or MR imaging updates should be considered.

The process and development of image-guided procedures

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

Localisation of the sensorimotor cortex during surgery for brain tumours: feasibility and waveform patterns of somatosensory evoked potentials

OBJECTIVE

Intraoperative localisation of the sensorimotor cortex using the phase reversal of somatosensory evoked potentials (SEPs) is an essential tool for surgery in and around the perirolandic gyri, but unsuccessful and perplexing results have been reported. This study examines the effect of tumour masses on the waveform characteristics and feasibility of SEP compared with functional neuronavigation and electrical motor cortex mapping.

METHODS

In 230 patients with tumours of the sensorimotor region the SEP phase reversal of N20-P20 was recorded from the exposed cortex using a subdural grid or strip electrode. In one subgroup of 80 patients functional neuronavigation was performed with motor and sensory magnetic source imaging and in one subgroup of 40 patients the motor cortex hand area was localised by electrical stimulation mapping.

RESULTS

The intraoperative SEP method was successful in 92% of all patients, it could be shown that the success rate rather depended on the location of the lesion than on preoperative neurological deficits. In 13% of the patients with postcentral tumours no N20-P20 phase reversal was recorded but characteristic polyphasic and high amplitude waves at 25 ms and later made the identification of the postcentral gyrus possible nevertheless. Electrical mapping of the motor cortex took up to 30 minutes until a clear result was obtained. It was successful in 37 patients, but failed in three patients with precentral and central lesions. Functional neuronavigation indicating the tumour margins and the motor and sensory evoked fields was possible in all patients.

CONCLUSION

The SEP phase reversal of N20-P20 is a simple and reliable technique, but the success rate is much lower in large central and postcentral tumours. With the use of polyphasic late waveforms the sensorimotor cortex may be localised. By contrast with motor electrical mapping it is less time consuming. Functional neuronavigation is a desirable tool for both preoperative surgical planning and intraoperative use during surgery on perirolandic tumours, but compensation for brain shift, accuracy, and cost effectiveness are still a matter for discussion.