Craniotomy for tumor treatment in an intraoperative magnetic resonance imaging unit

Intraoperative MRI: A Review of Applications Across Neurosurgical Specialties

Intraoperative MRI (iMRI) made its debut to great fanfare in the mid-1990s. However, the enthusiasm for this technology with seemingly obvious benefits for neurosurgeons has waned. We review the benefits and utility of iMRI across the field of neurosurgery and present an overview of the evidence for iMRI for multiple neurosurgical disciplines: tumor, skull base, vascular, pediatric, functional, and spine. Publications on iMRI have steadily increased since 1996, plateauing with approximately 52 publications per year since 2011. Tumor surgery, especially glioma surgery, has the most evidence for the use of iMRI contributing more than 50% of all iMRI publications, with increased rates of gross total resection in both adults and children, providing a potential survival benefit. Across multiple neurosurgical disciplines, the ability to use a multitude of unique sequences (diffusion tract imaging, diffusion-weighted imaging, magnetic resonance angiography, blood oxygenation level-dependent) allows for specialization of imaging for various types of surgery. Generally, iMRI allows for consideration of anatomic changes and real-time feedback on surgical outcomes such as extent of resection and instrument (screw, lead, electrode) placement. However, implementation of iMRI is limited by cost and feasibility, including the need for installation, shielding, and compatible tools. Evidence for iMRI use varies greatly by specialty, with the most evidence for tumor, vascular, and pediatric neurosurgery. The benefits of real-time anatomic imaging, a lack of radiation, and evaluation of surgical outcomes are limited by the cost and difficulty of iMRI integration. Nonetheless, the ability to ensure patients are provided by a maximal yet safe treatment that specifically accounts for their own anatomy and highlights why iMRI is a valuable and underutilized tool across multiple neurosurgical subspecialties.

Intraoperative MRI use in transsphenoidal surgery for pituitary tumors: Trends and healthcare utilization

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) use in transsphenoidal approach (TSA) for pituitary tumors (PTs) has been reported to improve the extent of resection (EOR). The aim of this study is to report the trends and the impact of iMRI on healthcare utilization in patients who underwent TSA for PTs.

MATERIALS AND METHODS

MarketScan database were queried using the ICD-9/10 and CPT-4, from 2004 to 2020. We included patients ≥ 18 years of age PTs with > 1 year follow-up. Outcomes were length of stay (LOS), discharge disposition, hospital/emergency room (ER) re-admissions, outpatient services, medication refills and corresponding payments.

RESULTS

A cohort of 10,192 patients were identified from the database, of these 141 patients (1.4%) had iMRI used during the procedure. Use of iMRI for PTs remained stable (2004-2007: 0.85%; 2008-2011: 1.6%; 2012-2015:1.4% and 2016-2019: 1.46%). No differences in LOS (median 3 days each), discharge to home (93% vs. 94%), complication rates (7% vs. 13%) and payments ($34604 vs. $33050) at index hospitalization were noted. Post-discharge payments were not significantly different without and with iMRI use at 6-months ($8315 vs. $ 7577, p = 0.7) and 1-year ($13,654 vs. $ 14,054, p = 0.70), following the index procedure.

CONCLUSION

iMRI use during TSA for PTs remained stable with no impact on LOS, complications, discharge disposition and index payments. Also, there was no difference in combined index payments at 6-months, and 1-year after the index procedure in patients with and without iMRI use for PTs.

Impact of Intraoperative Magnetic Resonance Imaging (i-MRI) on Surgeon Decision Making and Clinical Outcomes in Cranial Tumor Surgery

Background  Although intraoperative magnetic resonance imaging (iMRI) has an established role in guiding intraoperative extent of resection (EOR) in cranial tumor surgery, the details of how iMRI data are used by the surgeon in the real-time decision-making process is lacking.

Materials and Methods  The authors retrospectively reviewed 40 consecutive patients who underwent cranial tumor resection with the guidance of iMRI. The tumor volumes were measured by volumetric software. Intraoperative and postoperative EOR were calculated and compared. Surgeon preoperative EOR intention, intraoperative EOR assessment, and how iMRI data impacted surgeon decisions were analyzed.

Results  The pathology consisted of 29 gliomas, 8 pituitary tumors, and 3 other tumors. Preoperative surgeon intention called for gross total resection (GTR) in 28 (70%) cases. After resection and before iMRI scanning, GTR was 20 (50.0%) cases based on the surgeon's perception. After iMRI scanning, the results helped identify 19 (47.5%) cases with unexpected results consisting of 5 (12.5%) with unexpected locations of residual tumors and 14 (35%) with unexpected EOR. Additional resection was performed in 24 (60%) cases after iMRI review, including 6 (15%) cases with expected iMRI results. Among 34 cases with postoperative MRI results, iMRI helped improve EOR in 12 (35.3%) cases.

Conclusion  In cranial tumor surgery, the surgeon's preoperative and intraoperative assessment is frequently imprecise. iMRI data serve several purposes, including identifying the presence of residual tumors, providing residual tumor locations, giving spatial relation data of the tumor with nearby eloquent structures, and updating the neuro-navigation system for the final stage of tumor resection.

Use of intraoperative MRI for resection of intracranial tumors: A nationwide analysis of short-term outcomes

OBJECTIVE

Recent evidence supports the use of intraoperative MRI (iMRI) during resection of intracranial tumors due to its demonstrated efficacy and clinical benefit. Though many single-center investigations have been conducted, larger nationwide outcomes have yet to be characterized.

METHODS

We used the American College of Surgeons National Surgical Quality Improvement Program database to examine baseline characteristics and 30-day postoperative outcomes among patients undergoing craniotomy for tumor resection with and without iMRI. Comparisons between outcomes were accomplished after propensity matching using chi-square tests for categorical variables and Welch two-sample t-tests for continuous variables.

RESULTS

A total of 38,003 patients met inclusion criteria. Of this population, 54 (0.1%) received iMRI, while 37,949 (99.9%) did not receive iMRI. After propensity score matching, the resulting groups consisted of an iMRI group (n = 54) and a matched non-iMRI group (n = 54). Procedures involving iMRI were associated with significantly increased operation length compared to those without (p < 0.01). Length of hospital stay was higher in patients without iMRI, with this difference trending towards significance (p = 0.05) in the unmatched comparison. Patients undergoing craniotomy without iMRI had a higher rate of readmission (p = 0.04). There was no significant difference in occurrence of other adverse events between the two patient groups.

CONCLUSION

Despite increasing operative length, iMRI is not associated with higher infection rate and may have a clinical benefit associated with reducing readmissions and a trend towards reducing inpatient length of stay. Additional nationwide analyses including more iMRI patients would provide further insight into the strength of these findings.

Evaluating the Impact of Intraoperative MRI in Neuro-Oncology by Scientometric Analysis

(1) Objective—Intraoperative Magnetic Resonance Imaging (IOMRI) guided surgery has revolutionized neurosurgery and has especially impacted the field of Neuro-Oncology, with randomized controlled trails demonstrating improved resection, fewer postoperative deficits and enhanced survival rates. Bibliometric analysis allows for analysing chronological trends and measuring the impact and directions of research in a particular field. To the authors’ knowledge, this is the first Bibliometric analysis conducted on IOMRI. (2) Methods—a title specific search of the Web of Science database was executed using the keywords ‘intraoperative MRI’, ‘intraoperative magnetic resonance imaging’, and “IOMRI’ on 23rd April 2021. Results—663 articles met the inclusion criteria and were included in the final analysis. In addition, the 100 most cited were analysed as well. Among these 100 articles, 76 were original research papers, while 14 others were review articles. Amongst all the authors, Ganslandt contributed the maximum number of articles, with USA being the largest single source of these articles, followed by Germany. Interestingly, a shift of trends from “Image guided surgery’ and ‘accuracy’ in the early 2000s to ‘extent of resection’, ‘impact’, and ‘survival’ in the later years was noted. (3) Conclusions—IOMRI has now become an integral part of neurosurgery, especially in neuro-oncology. Focus has now shifted from implementation to refinement of technique in the form of functional and oncological outcomes. Therefore, future research in this direction is imperative and will be of more impact that in any other sub-field related to IOMRI.

An insight into electrical resistivity of white matter and brain tumors

BACKGROUND

There is a lack of information regarding electrical properties of white matter and brain tumors.

OBJECTIVE

To investigate the feasibility of in-vivo measurement of electrical resistivity during brain surgery and establish a better understanding of the resistivity patterns of brain tumors in correlation to the white matter.

METHODS

A bipolar probe was used to measure electrical resistivity during surgery in a prospective cohort of patients with brain tumors. For impedance measurement, the probe applied a constant current of 0.7 μA with a frequency of 140 Hz. The measurement was performed in the white matter within and outside peritumoral edema as well as in non-enhancing, enhancing and necrotic tumor areas. Resistivity values expressed in ohmmeter (Ω∗m) were compared between different intracranial tissues and brain tumors.

RESULTS

Ninety-two patients (gliomas WHO II:16, WHO III:10, WHO IV:33, metastasis:33) were included. White matter outside peritumoral edema had higher resistivity values (13.3 ± 1.7 Ω∗m) than within peritumoral edema (8.5 ± 1.6 Ω∗m), and both had higher values than brain tumors including non-enhancing (WHO II:6.4 ± 1.3 Ω∗m, WHO III:6.3 ± 0.9 Ω∗m), enhancing (WHO IV:5 ± 1 Ω∗m, metastasis:5.4 ± 1.3 Ω∗m) and necrotic tumor areas (WHO IV:3.9 ± 1.1 Ω∗m, metastasis:4.3 ± 1.3 Ω∗m), p=<0.001. No difference was found between low-grade and anaplastic gliomas, p = 0.808, while resistivity values in both were higher than the highest values found in glioblastomas, p = 0.003 and p = 0.004, respectively.

CONCLUSIONS

The technique we applied enabled us to measure electrical resistivity of white matter and brain tumors in-vivo presumably with a significant effect with regard to dielectric polarization. Our results suggest that there are significant differences within different areas and subtypes of brain tumors and that white matter exhibits higher electrical resistivity than brain tumors.

Historical Perspective on Surgery and Survival with Glioblastoma: How Far Have We Come?

BACKGROUND

Glioblastoma multiforme remains a therapeutic challenge. We offer a historical review of the outcomes of patients with glioblastoma from the earliest report of surgery for this lesion through the introduction of modern chemotherapeutics and aggressive approaches to tumor resection.

METHODS

We reviewed all major surgical series of patients with glioblastoma from the introduction of craniotomy for glioma (1884) to 2020.

RESULTS

The earliest reported craniotomy for glioblastoma resulted in the patient's death less than a month after surgery. Improved intracranial pressure management resulted in improved outcomes, reducing early postoperative mortality from 50% to 6% in Harvey Cushing's series. In the first major surgical series (1912), the mean survival was 10.1 months. This figure did not improve until the introduction of radiotherapy in the 1950s, which doubled survival relative to those who had surgery alone. The most recent significant advance, chemotherapy with the alkylating agent temozolomide, extended survival by 2.5 months compared with surgery and radiotherapy alone (14.6 and 12.1 months, respectively). This protocol remains the standard regimen for newly diagnosed glioblastoma. The innovative treatments being investigated have yet to show a survival benefit.

CONCLUSIONS

With advancements in localization, imaging, anesthesia, surgical technique, control of cerebral edema, and adjuvant therapies, outcomes in glioblastoma improved incrementally from Cushing's time until the introduction of magnetic resonance imaging enabled better degrees of resection in the 1990s. Modest improvements came with the advent of biomarker-driven targeted chemotherapy in the first decade of the current century.

Physical approaches to treat glioblastoma

PURPOSE OF REVIEW

Glioblastoma (GBM) patients have a poor prognosis despite the use of modern synergistic multimodal treatment strategies, with a progression-free survival estimated at 7-8 months, a median survival of 14-16 months and 5-year overall survival of 9.8%.

RECENT FINDINGS

Physical methods hold the promise to act synergistically with classical treatments to improve the outcome of GBM patients. Fluorescent guided surgery with 5-aminolevulinic acid and tumor-treating fields therapy have already shown positive results in randomized phase III trials and have been incorporated in the standard management. Other techniques such as photodynamic therapy (PDT) and focused ultrasound, often combined whit microbubbles, are reaching clinical development.

SUMMARY

Several clinical trials to evaluate the feasibility and efficacy of ultrasound devices to disrupt the blood-brain barrier are ongoing. PDT enables the creation of a safety margin or treatment of non-resecable tumors. However, randomized trials are urgently required to validate the efficacy of these promising approaches. We aim to critically review physical approaches to treat GBM, focusing on available clinical trial data.

Intraoperative 3-T Magnetic Resonance Spectroscopy for Detection of Proliferative Remnants of Glioma

BACKGROUND

Few studies have examined the usefulness of intraoperative magnetic resonance spectroscopy (iMRS) for identifying abnormal signals at the resection margin during glioma surgery. The aim of this study was to assess the value of iMRS for detecting proliferative remnants of glioma at the resection margin.

METHODS

Fifteen patients with newly diagnosed glioma underwent single-voxel 3-T iMRS concurrently with intraoperative magnetic resonance imaging-assisted surgery. Volumes of interest (VOIs) were placed at T2-hyperintense or contrast-enhancing lesions at the resection margin. In addition to technical verification, the correlation between the MIB-1 labeling index (a pathologic feature) and metabolites measured using iMRS (N-acetyl-L-aspartate [NAA], choline [Cho], and Cho/NAA ratio) was analyzed.

RESULTS

iMRS was performed for 20 VOIs in 15 patients. Fourteen (70%) of these VOIs were confirmed to be MIB-1-positive. There was a significant positive correlation between the Cho/NAA ratio and MIB-1 index (r = 0.46, P = 0.04). Cho level (P = 0.003) and Cho/NAA ratio (P = 0.002) were significantly higher in VOIs that were MIB-1-positive than in those that were MIB-1-negative. Detection of a Cho level >1.074 mM and a Cho/NAA ratio >0.48 using iMRS resulted in high diagnostic accuracy for MIB-1-positive remnants (Cho level: sensitivity 86%, specificity 100%; Cho/NAA ratio: sensitivity 79%, specificity 100%).

CONCLUSIONS

This study provides evidence that 3-T iMRS can detect proliferative remnants of glioma at the resection margin using the Cho level and Cho/NAA ratio, suggesting that intraoperative magnetic resonance imaging-assisted surgery with iMRS would be practicable in glioma.

Use of an Offsite Intraoperative MRI Operating Theater for Pediatric Brain Tumor Surgery: Experience from a Singapore Children's Hospital

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) has been recognized as a useful adjunct for brain tumor surgery in pediatric patients. There is minimal data on the use of an offsite intraoperative magnetic resonance imaging operating theater (iMRI OT), whereby vehicle transfer of patients is involved. The primary aim of this study is to validate the feasibility of perioperative patient transfer to use an offsite iMRI OT for patients with pediatric brain tumor. Secondary objectives include the assessment of tumor resection efficacy and perioperative outcomes in our patient cohort.

METHODS

This is a retrospective, single-institution clinical study of prospectively collected data from Singapore's largest children hospital. Variables of interest include issues encountered during interhospital transfer, achievement of surgical aims, length of stay in hospital, and postoperative complications. Our findings were compared with results of related studies published in the literature.

RESULTS

From January 1, 2009 to December 31, 2018, a total of 35 pediatric operative cases were performed in our offsite iMRI OT. Within this cohort, 24 of these were brain tumor surgery cases. For all the patients in this study, use of the iMRI OT influenced intraoperative decisions. Average ambulance transport time from parent hospital to the iMRI OT was 30.5 minutes, and from iMRI OT back to the parent hospital after surgery was 27.7 minutes. The average length of hospitalization stay was 7.9 days per patient. There were no ferromagnetic accidents during perioperative iMRI scanning and no airway/hemodynamic incidents in patients encountered during interhospital transfer.

CONCLUSIONS

In our local context, the use of interhospital transfers for access to iMRI OT is a safe and feasible option in ensuring good patient outcomes for a select group of patients with pediatric brain tumors.

Intraoperative fluorescence diagnosis in the brain: a systematic review and suggestions for future standards on reporting diagnostic accuracy and clinical utility

Background

Surgery for gliomas is often confounded by difficulties in distinguishing tumor from surrounding normal brain. For better discrimination, intraoperative optical imaging methods using fluorescent dyes are currently being explored. Understandably, such methods require the demonstration of a high degree of diagnostic accuracy and clinical benefit. Currently, clinical utility is determined by tissue biopsies which are correlated to optical signals, and quantified using measures such as sensitivity, specificity, positive predictive values, and negative predictive values. In addition, surgical outcomes, such as extent of resection rates and/or survival (progression-free survival (PFS) and overall survival (OS)) have been measured. These assessments, however, potentially involve multiple biases and confounders, which have to be minimized to ensure reproducibility, generalizability and comparability of test results. Test should aim at having a high internal and external validity. The objective of this article is to analyze how diagnostic accuracy and outcomes are utilized in available studies describing intraoperative imaging and furthermore, to derive recommendations for reliable and reproducible evaluations.

Methods

A review of the literature was performed for assessing the use of measures of diagnostic accuracy and outcomes of intraoperative optical imaging methods. From these data, we derive recommendations for designing and reporting future studies.

Results

Available literature indicates that potential confounders and biases for reporting the diagnostic accuracy and usefulness of intraoperative optical imaging methods are seldom accounted for. Furthermore, methods for bias reduction are rarely used nor reported.

Conclusions

Detailed, transparent, and uniform reporting on diagnostic accuracy of intraoperative imaging methods is necessary. In the absence of such reporting, studies will not be comparable or reproducible. Future studies should consider some of the recommendations given here.

Electronic supplementary material

The online version of this article (10.1007/s00701-019-04007-y) contains supplementary material, which is available to authorized users.

Hyperacute Infarct on Intraoperative Diffusion Imaging of Pediatric Brain Tumor Surgery

BACKGROUND

Brain neoplasms are the second-most prevalent cancer of childhood for which surgical resection remains the main treatment. Intraoperative MRI is a useful tool to optimize brain tumor resection. It is, however, not known whether intraoperative MRI can detect complications such as hyperacute ischemic infarcts.

METHODS

A retrospective analysis of pre- and intraoperative MRIs including DWI sequence and correlation with early and 3-month postoperative MRIs was conducted to evaluate the incidence of hyperacute arterial infarct during pediatric brain tumor resection. Patient demographics, pathological type, tumor location, resection type as well as preoperative tumoral vessel encasement, evolution of the area of restricted diffusion were collected and analyzed comparatively between the group with acute infarct and the control group. Extent of the hyperacute infarct was compared to both early postsurgical and 3-month follow-up MRIs.

RESULTS

Of the 115 cases, 13 (11%) developed a hyperacute arterial ischemic infarct during brain tumor resection. Tumoral encasement of vessels was more frequent in the infarct group (69%) compared to 25.5% in the control group. Four cases showed additional vessel irregularities on intraoperative MRI. On early follow-up, the infarcted brain area had further progressed in six cases and was stable in seven cases. No further progression was noted after the first week post-surgery.

CONCLUSIONS

Hyperacute infarcts are not rare events to complicate pediatric brain tumor resection. Tumoral encasement of the circle of Willis vessels appears to be the main risk factor. Intraoperative DWI underestimates the final extent of infarcted tissue compared to early postsurgical MRI.

How to Build a Neurosurgical Oncology Practice Specializing in Gliomas

For the neurosurgical oncologist, a specialty practice in gliomas represents an intersection of tailored surgical approaches, emerging intraoperative technologies, expanding surgical trial portfolios, and new paradigms in glioma biology. Assembling these disparate pieces into a cohesive career trajectory is a difficult task but ultimately enables the subspecialist to navigate all domains relevant to improving glioma patient outcomes. Within the larger clinical and basic science community, thoughtful integration and intensive collaborations are essential mechanisms when building a multidisciplinary glioma program.

Clinical application of 3.0 T intraoperative magnetic resonance combined with multimodal neuronavigation in resection of cerebral eloquent area glioma

Glioma is the most common tumor among central nervous system tumors; surgical intervention presents difficulties. This is especially the case for gliomas in so-called "eloquent areas," as surgical resection threatens vital structures adjacent to the tumor. Intraoperative magnetic resonance imaging (iMRI) combined with multimodal neuronavigation may prove beneficial during surgery. This study explored the applicability of 3.0 T high field iMRI combined with multimodal neuronavigation in the resection of gliomas in eloquent brain areas.We reviewed 40 patients with a glioma located in the eloquent brains areas who underwent treatment in the Neurosurgery Department of Peking University International Hospital between December 2015 and August 2017. The experimental group included 20 patients treated using iMRI assistance technology (iMRI group). The remaining 20 patients underwent treatment by conventional neuronavigation (non-iMRI group). Tumor resection degree, preoperative and postoperative ability of daily living scale (Barthel index), infection rate, and operative time were compared between the 2 groups.No difference in infection rate was observed between the 2 groups. However, compared with the non-iMRI group, the iMRI group had a higher resection rate (96.55 ± 4.03% vs 87.70 ± 10.98%, P = .002), postoperative Barthel index (90.75 ± 12.90 vs 9.25 ± 16.41, P = .018), as well as a longer operation time (355.85 ± 61.40 vs 302.45 ± 64.09, P = .011).The use of iMRI technology can achieve a relatively higher resection rate among cases of gliomas in eloquent brain areas, with less incidence of postoperative neurological deficits. Although the operative time using iMRI was longer than that taken to perform conventional navigation surgery, the surgical infection rate in these 2 procedures showed no significant difference.

Surgical Management of Incidental Gliomas

Detailed brain imaging studies discover gliomas incidentally before clinical symptoms or signs show. These tumors represent an early stage in the natural history of gliomas. Left untreated, they are likely to progress to a symptomatic stage and transform to malignant gliomas. A greater extent of resection delays the onset of malignant transformation and prolongs patient survival. Because incidental gliomas are typically smaller and less likely to be in eloquent brain locations, there is a strong case for early surgical intervention to maximize resection and improve outcomes. This article discusses developments in the surgical management of low-grade gliomas.

Anesthetic management and human factors in the intraoperative MRI environment

PURPOSE OF REVIEW

The use of intraoperative MRI technology during neurosurgery has become increasingly more common over the past several years. These surgical procedures require a specialized operating room designed to accommodate an MRI machine, as well as MRI-compatible anesthesia equipment and monitors. The MRI environment also poses unique risks and challenges to both patients and medical staff.

RECENT FINDINGS

General anesthesia in the MRI operating room suite poses several challenges not routinely experienced in a conventional operating room suite, and anesthesia providers delivering care in these suites must complete specialized training and screening. The presence of a magnetic field, as well as reduced access to the patient during the MRI scan, require high levels of vigilance.

SUMMARY

The use of checklists and teamwork training can maximize both patient and provider safety in the intraoperative MRI environment.

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.

An MRS- and PET-guided biopsy tool for intraoperative neuronavigational systems

OBJECTIVE Glioma heterogeneity and the limitations of conventional structural MRI for identifying aggressive tumor components can limit the reliability of stereotactic biopsy and, hence, tumor characterization, which is a hurdle for developing and selecting effective treatment strategies. In vivo MR spectroscopy (MRS) and PET enable noninvasive imaging of cellular metabolism relevant to proliferation and can detect regions of more highly active tumor. Here, the authors integrated presurgical PET and MRS with intraoperative neuronavigation to guide surgical biopsy and tumor sampling of brain gliomas with the aim of improving intraoperative tumor-tissue characterization and imaging biomarker validation. METHODS A novel intraoperative neuronavigation tool was developed as part of a study that aimed to sample high-choline tumor components identified by multivoxel MRS and 18F-methylcholine PET-CT. Spatially coregistered PET and MRS data were integrated into structural data sets and loaded onto an intraoperative neuronavigation system. High and low choline uptake/metabolite regions were represented as color-coded hollow spheres for targeted stereotactic biopsy and tumor sampling. RESULTS The neurosurgeons found the 3D spherical targets readily identifiable on the interactive neuronavigation system. In one case, areas of high mitotic activity were identified on the basis of high 18F-methylcholine uptake and elevated choline ratios found with MRS in an otherwise low-grade tumor, which revealed the possible use of this technique for tumor characterization. CONCLUSIONS These PET and MRI data can be combined and represented usefully for the surgeon in neuronavigation systems. This method enables neurosurgeons to sample tumor regions based on physiological and molecular imaging markers. The technique was applied for characterizing choline metabolism using MRS and 18F PET; however, this approach provides proof of principle for using different radionuclide tracers and other MRI methods, such as MR perfusion and diffusion.

"Next Door" intraoperative magnetic resonance imaging for awake craniotomy: Preliminary experience and technical note

BACKGROUND

During glioma surgery "maximal safe resection" must be the main goal. Intraoperative magnetic resonance imaging (iMRI) associated with awake craniotomy (AC) is a valuable tool to achieve this objective. In this article, AC with a "next-door" iMRI concept is described in a stepwise protocol.

METHODS

This is a retrospective analysis of 18 patients submitted to AC using iMRI; a stepwise protocol is also discussed.

RESULTS

The mean age was 41.7 years. Hemiparesis, aphasia, and seizures were the main initial symptoms of the patients. Sixty-six percent of the tumors were located in the left hemisphere. All tumors were near or within eloquent areas. Fifty-three percent of the cases were glioblastomas multiforme and 47% of the patients had low grade gliomas. The mean surgical time and iMRI time were 4 h 4 min and 30 min, respectively. New resection was performed in 33% after iMRI. Extent of resection (EOR) higher than 95% was possible in 66.7% of the patients. The main reason of EOR lower than 95% was positive mapping of eloquent areas (6 patients). Eighty percent of the patients experienced improvement of their deficits immediately after the surgery or had a stable clinical status whereas 20% had neurological deterioration, however, all of them improved after 30 days.

CONCLUSION

AC associated with "next-door" iMRI is a complex procedure, but if performed using a meticulous technique, it may improve the overall tumor resection and safety of the patients.

An MRS- and PET-guided biopsy tool for intraoperative neuronavigational systems

OBJECTIVE Glioma heterogeneity and the limitations of conventional structural MRI for identifying aggressive tumor components can limit the reliability of stereotactic biopsy and, hence, tumor characterization, which is a hurdle for developing and selecting effective treatment strategies. In vivo MR spectroscopy (MRS) and PET enable noninvasive imaging of cellular metabolism relevant to proliferation and can detect regions of more highly active tumor. Here, the authors integrated presurgical PET and MRS with intraoperative neuronavigation to guide surgical biopsy and tumor sampling of brain gliomas with the aim of improving intraoperative tumor-tissue characterization and imaging biomarker validation. METHODS A novel intraoperative neuronavigation tool was developed as part of a study that aimed to sample high-choline tumor components identified by multivoxel MRS and ¹⁸F-methylcholine PET-CT. Spatially coregistered PET and MRS data were integrated into structural data sets and loaded onto an intraoperative neuronavigation system. High and low choline uptake/metabolite regions were represented as color-coded hollow spheres for targeted stereotactic biopsy and tumor sampling. RESULTS The neurosurgeons found the 3D spherical targets readily identifiable on the interactive neuronavigation system. In one case, areas of high mitotic activity were identified on the basis of high ¹⁸F-methylcholine uptake and elevated choline ratios found with MRS in an otherwise low-grade tumor, which revealed the possible use of this technique for tumor characterization. CONCLUSIONS These PET and MRI data can be combined and represented usefully for the surgeon in neuronavigation systems. This method enables neurosurgeons to sample tumor regions based on physiological and molecular imaging markers. The technique was applied for characterizing choline metabolism using MRS and ¹⁸F PET; however, this approach provides proof of principle for using different radionuclide tracers and other MRI methods, such as MR perfusion and diffusion.

Astrocytic gliomas WHO grades II and III

World Health Organization grades II and III lower-grade astrocytomas are a challenging area in neuro-oncology. One the one hand, for proper diagnosis, the analysis of molecular factors, especially mutation status of isocitrate dehydrogenase and 1p/19q status in the tumor status needs to be done in addition to classical neuropathology. Further, the high clinical and prognostic value of a maximal safe resection requires a profound knowledge of presurgical diagnosis and surgical as well as imaging techniques to ensure optimal outcome for patients. Also medical treatment may be more intensive than previously believed, with randomized trials providing evidence for a benefit in overall survival by combined chemoradiation versus radiation alone. A critical problem concerns the considerable undesirable effects of therapeutic interventions on long-term health-related quality of life, cognitive and functional outcome as well as future developments in this still difficult disease that will need to be addressed in future trials.

Orbit-associated tumors: navigation and control of resection using intraoperative computed tomography

OBJECT Treatment of skull base lesions is complex and usually requires a multidisciplinary approach. In meningioma, which is the most common tumor entity in this region, resection is considered to be the most important therapeutic step to avoid tumor recurrence. However, resection of skull base lesions with orbital or optic nerve involvement poses a challenge due to their anatomical structure and their proximity to eloquent areas. Therefore the main goal of surgery should be to achieve the maximum extent of resection while preserving neurological function. In the postoperative course, medical and radiotherapeutic strategies may then be successfully used to treat possible tumor residues. Methods to safely improve the extent of resection in skull base lesions therefore are desirable. The current study reports the authors' experience with the use of intraoperative CT (iCT) combined with neuronavigation with regard to feasibility and possible benefits of the method. METHODS Those patients with tumorous lesions in relationship to the orbit, sphenoid wing, or cavernous sinus who were surgically treated between October 2008 and December 2013 using iCT-based neuronavigation and in whom an intraoperative scan was obtained for control of resection were included. In all cases a second iCT scan was performed under sterile conditions after completion of navigation-guided microsurgical tumor resection. The surgical strategy was adapted accordingly; if necessary, resection was continued. RESULTS Twenty-three patients (19 with WHO Grade I meningioma and 4 with other lesions) were included. The most common clinical symptoms were loss of visual acuity and exophthalmus. Intraoperative control of resection by iCT was successfully obtained in all cases. Intraoperative imaging changed the surgical approach in more than half (52.2%) of these patients, either because iCT demonstrated unexpected residual tumor masses or because the second scan revealed additional tumor tissue that was not detected in the first scan due to overlay by osseous tumor parts; in these cases resection was continued. In the remaining cases resection was concluded as planned because iCT verified the surgeon's microscopic estimation of tumor resection status. Postoperative visual outcome was favorable in more than 80% of patients. CONCLUSIONS Intraoperative CT allows control of resection in case of uncertainty and can help to improve the extent of maximal safe resection, especially in case of osseous tumor parts and masses within the orbit.

Intraoperative MRI in pediatric brain tumors

Intraoperative magnetic resonance imaging (iMRI) has emerged as an important tool in guiding the surgical management of children with brain tumors. Recent advances have allowed utilization of high field strength systems, including 3-tesla MRI, resulting in diagnostic-quality scans that can be performed while the child is on the operating table. By providing information about the possible presence of residual tumor, it allows the neurosurgeon to both identify and resect any remaining tumor that is thought to be safely accessible. By fusing the newly obtained images with the surgical guidance software, the images have the added value of aiding in navigation to any residual tumor. This is important because parenchyma often shifts during surgery. It also gives the neurosurgeon insight into whether any immediate postoperative complications have occurred. If any complications have occurred, the child is already in the operating room and precious minutes lost in transport and communications are saved. In this article we review the three main approaches to an iMRI system design. We discuss the possible roles for iMRI during intraoperative planning and provide guidance to help radiologists and neurosurgeons alike in the collaborative management of these children.

From Grey Scale B-Mode to Elastosonography: Multimodal Ultrasound Imaging in Meningioma Surgery-Pictorial Essay and Literature Review

The main goal in meningioma surgery is to achieve complete tumor removal, when possible, while improving or preserving patient neurological functions. Intraoperative imaging guidance is one fundamental tool for such achievement. In this regard, intra-operative ultrasound (ioUS) is a reliable solution to obtain real-time information during surgery and it has been applied in many different aspect of neurosurgery. In the last years, different ioUS modalities have been described: B-mode, Fusion Imaging with pre-operative acquired MRI, Doppler, contrast enhanced ultrasound (CEUS), and elastosonography. In this paper, we present our US based multimodal approach in meningioma surgery. We describe all the most relevant ioUS modalities and their intraoperative application to obtain precise and specific information regarding the lesion for a tailored approach in meningioma surgery. For each modality, we perform a review of the literature accompanied by a pictorial essay based on our routinely use of ioUS for meningioma resection.

Preliminary experience with an intraoperative MRI-compatible infant headholder: technical note

The development of high-quality intraoperative MRI (iMRI) capability has offered a major advance in the care of patients with complex intracranial disease. To date, this technology has been limited by the need for pin fixation of the calvaria. The authors report their preliminary experience with an MRI-compatible horseshoe headrest that allows for the following: 1) iMRI in patients too young for pin fixation; 2) iMRI in patients with large calvarial defects; 3) the ability to move the head during iMRI surgery; and 4) the use of neuronavigation in such cases. The authors report 2 cases of infants in whom the Visius Surgical Theatre horseshoe headrest (IMRIS Inc.) was used. Image quality was equivalent to that of pin fixation. The infants suffered no skin issues. The use of neuronavigation with the system remained accurate and could be updated with the new iMRI information. The Visius horseshoe headrest offers a technical advance in iMRI technology for infants, for patients with cranial defects or prior craniotomies in whom pin fixation may not be safe, or for patients in whom the need to move the head during surgery is required. The image quality of the system remains excellent, and the ability to merge new images to the neuronavigation system is helpful.

Advances in the Surgical Management of Low-Grade Glioma

Over the past 2 decades, extent of resection has emerged as a significant prognostic factor in patients with low-grade gliomas (LGGs). Greater extent of resection has been shown to improve overall survival, progression-free survival, and time to malignant transformation. The operative goal in most LGG cases is to maximize extent of resection, while avoiding postoperative neurologic deficits. Several advanced surgical techniques have been developed in an attempt to better achieve maximal safe resection. Intraoperative magnetic resonance imaging, fluorescence-guided surgery, intraoperative functional pathway mapping, and neuronavigation are some of the most commonly used techniques with multiple studies to support their efficacy in glioma surgery. By using these techniques either alone or in combination, patients harboring LGGs have a better prognosis with less surgical morbidity following tumor resection.

Multimodal imaging for improved diagnosis and treatment of cancers

The authors review methods for image-guided diagnosis and therapy that increase precision in the detection, characterization, and localization of many forms of cancer to achieve optimal target definition and complete resection or ablation. A new model of translational, clinical, image-guided therapy research is presented, and the Advanced Multimodality Image-Guided Operating (AMIGO) suite is described. AMIGO was conceived and designed to allow for the full integration of imaging in cancer diagnosis and treatment. Examples are drawn from over 500 procedures performed on brain, neck, spine, thorax (breast, lung), and pelvis (prostate and gynecologic) areas and are used to describe how they address some of the many challenges of treating brain, prostate, and lung tumors. Cancer 2015;121:817-827. © 2014 American Cancer Society.

3T intraoperative MRI for management of pediatric CNS neoplasms

BACKGROUND AND PURPOSE

High-field-strength intraoperative MR imaging has emerged as a powerful adjunct for resection of brain tumors. However, its exact role has not been firmly established. We sought to determine the impact of 3T-intraoperative MRI on the surgical management of childhood CNS tumors.

MATERIALS AND METHODS

We evaluated patient data from a single academic children's hospital during a consecutive 24-month period after installation of a 3T-intraoperative MRI. Tumor location, histology, surgical approach, operating room time, presence and volume of residual tumor, need for tumor and non-tumor-related reoperation, and anesthesia- and MR imaging-related complications were evaluated. Comparison with pre-intraoperative MRI controls was performed.

RESULTS

One hundred ninety-four patients underwent intraoperative MRI-guided surgery. Of these, 168 were 18 years or younger (mean, 8.9 ± 5.0 years; 108 males/60 females). There were 65 posterior fossa tumors. The most common tumors were pilocytic astrocytoma (n = 31, 19%), low-grade glioma (n = 31, 19%), and medulloblastoma (n = 20, 12%). An average of 1.2 scanning sessions was performed per patient (maximum, 3). There were no MR imaging-related safety issues. Additional tumor was resected after scanning in 21% of patients. Among patients with a preoperative goal of gross total resection, 93% achieved this goal. The 30-day reoperation rate was <1% (n = 1), and no patient required additional postoperative MR imaging during the same hospital stay.

CONCLUSIONS

Intraoperative MRI is safe and increases the likelihood of gross total resection, albeit with increased operating room time, and reduces the need for early reoperation or repeat sedation for postoperative scans in children with brain tumors.

Principles of surgery for malignant astrocytomas

Malignant astrocytomas constitute the most aggressive and common primary tumors of the central nervous system. The standard treatment protocol for these tumors involves maximum safe surgical resection with adjuvant chemoradiotherapy. Despite numerous advances in surgical techniques and adjuncts, as well as the ongoing renaissance in the genetic and molecular characterization of these tumors, malignant astrocytomas continue to be associated with poor prognosis, with median overall survival averaging 15 months for grade IV astrocytomas after standard-of-care treatment. In this article, the goals, principles, techniques, prognostic factors, and modern outcomes of malignant astrocytoma surgery are reviewed. Particular attention is paid to contemporary methods of neuronavigation and functional mapping, the prognostic significance of the extent of resection, surgically delivered adjunctive therapies, and future avenues of research.

Use of high-field intraoperative magnetic resonance imaging during endoscopic transsphenoidal surgery for functioning pituitary microadenomas and small adenomas located in the intrasellar region

The usefulness of 1.5-T high-field intraoperative magnetic resonance (iMR) imaging during transsphenoidal surgery for functioning pituitary adenomas was retrospectively evaluated based on long-term endocrine remission from the records of 14 patients who underwent transsphenoidal surgery with iMR imaging for functioning pituitary microadenomas and small adenomas located in the intrasellar region. The maximum tumor diameter was 9.3 ± 2.6 mm. Patients were diagnosed with acromegaly (n = 7), prolactinoma (n = 4), and Cushing's disease (n = 3). If iMR imaging detected tumor remnants after resection, the resection cavity was reexamined and further resection was performed. Postoperative endocrine follow-up period was mean 33.7 ± 13.3 months. Tumor remnants were detected after the first resection in seven patients. Further resection was performed in five of these patients, and three achieved long-term endocrine remission. As a result, the overall long-term endocrine remission rate was 78.5% (11/14), instead of the 57.1% (8/14) that would be expected if iMR imaging had not been performed. Long-term endocrine remission had a tendency to be associated with the absence of tumor remnants on the final iMR images, but this was not significant (p = 0.09). Long-term endocrine remission was associated with presence of tumor remnants in the cavernous sinus on the final iMR images (p = 0.03). High-field iMR imaging is useful for depicting tumor remnants after resection, and increased the long-term endocrine remission rate for patients with functioning pituitary microadenomas and small adenomas.

Role of surgical resection in low- and high-grade gliomas

OPINION STATEMENT

Central nervous system tumors are a major cause of morbidity and mortality in the United States. Outside of brain metastasis, low- and high-grade gliomas are the most common intrinsic brain tumors. Low-grade gliomas have a 5- and 10-year survival rate of 97 % and 91 %, respectively, when extent of resection is greater than 90 %. High-grade gliomas are extremely aggressive with the vast majority of patients experiencing recurrence and a median survival of 1 to 3 years. Survival of patients with both low- and high-grade gliomas is enhanced with maximal tumor resection. The pursuit of more aggressive extent of resection must be balanced with preservation of functional pathways. Several innovations in neurosurgical oncology have expanded our understanding of individualized patient neuroanatomy, physiology, and function. Emerging imaging technologies as well as intraoperative techniques have expanded our ability to resect maximal amounts of tumor while preserving essential function. Stimulation mapping of language and motor pathways is well-established for the safe resection of intrinsic brain lesions. Additional techniques including neuro-navigation, fluorescence-guided microsurgery using 5-aminolevulinic acid, intraoperative magnetic resonance imaging, and high-frequency ultrasonography can all be used to improve extent of resection in glioma patients.

Early re-do surgery for glioblastoma is a feasible and safe strategy to achieve complete resection of enhancing tumor

Background

Complete resection of enhancing tumor as assessed by early (<72 hours) postoperative MRI is regarded as the optimal result in glioblastoma surgery. As yet, there is no consensus on standard procedure if post-operative imaging reveals unintended tumor remnants.

Objective

The current study evaluated the feasibility and safety of an early re-do surgery aimed at completing resections with the aid of 5-ALA fluorescence and neuronavigation after detection of enhancing tumor remnants on post-operative MRI.

Methods

From October 2008 to October 2012 a single center institutional protocol offered a second surgery within one week to patients with unintentional incomplete glioblastoma resection. We report on the feasibility of the use 5-ALA fluorescence guidance, the extent of resection (EOR) rates and complications of early re-do surgery.

Results

Nine of 151 patients (6%) with glioblastoma resections had an unintentional tumor remnant with a volume >0.175 cm³. 5-ALA guided re-do surgery completed the resection (CRET) in all patients without causing neurological deficits, infections or other complications. Patients who underwent a re-do surgery remained hospitalized between surgeries, resulting in a mean length of hospital stay of 11 days (range 7-15), compared to 9 days for single surgery (range 3-23; p=0.147).

Conclusion

Our early re-do protocol led to complete resection of all enhancing tumor in all cases without any new neurological deficits and thus provides a similar oncological result as intraoperative MRI (iMRI). The repeated use of 5-ALA induced fluorescence, used for identification of small remnants, remains highly sensitive and specific in the setting of re-do surgery. Early re-do surgery is a feasible and safe strategy to complete unintended subtotal resections.

Mass spectrometry imaging as a tool for surgical decision-making

Despite significant advances in image-guided therapy, surgeons are still too often left with uncertainty when deciding to remove tissue. This binary decision between removing and leaving tissue during surgery implies that the surgeon should be able to distinguish tumor from healthy tissue. In neurosurgery, current image-guidance approaches such as magnetic resonance imaging (MRI) combined with neuronavigation offer a map as to where the tumor should be, but the only definitive method to characterize the tissue at stake is histopathology. Although extremely valuable information is derived from this gold standard approach, it is limited to very few samples during surgery and is not practically used for the delineation of tumor margins. The development and implementation of faster, comprehensive, and complementary approaches for tissue characterization are required to support surgical decision-making--an incremental and iterative process with tumor removed in multiple and often minute biopsies. The development of atmospheric pressure ionization sources makes it possible to analyze tissue specimens with little to no sample preparation. Here, we highlight the value of desorption electrospray ionization as one of many available approaches for the analysis of surgical tissue. Twelve surgical samples resected from a patient during surgery were analyzed and diagnosed as glioblastoma tumor or necrotic tissue by standard histopathology, and mass spectrometry results were further correlated to histopathology for critical validation of the approach. The use of a robust statistical approach reiterated results from the qualitative detection of potential biomarkers of these tissue types. The correlation of the mass spectrometry and histopathology results to MRI brings significant insight into tumor presentation that could not only serve to guide tumor resection, but that is also worthy of more detailed studies on our understanding of tumor presentation on MRI.

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.

Intraoperative visualization for resection of gliomas: the role of functional neuronavigation and intraoperative 1.5 T MRI

OBJECTIVE

To investigate how functional neuronavigation and intraoperative high-field magnetic resonance imaging (MRI) influence glioma resection.

METHODS

One hundred and thirty-seven patients [World Health Organization (WHO) grade I: 20; II: 19; III: 41; IV: 57] underwent resection for supratentorial gliomas in an operative suite equipped with intraoperative high-field MRI and microscope-based neuronavigation. Besides standard anatomical image data including T1- and T2-weighted sequences, various functional data from magnetoencephalography (n=37), functional MRI (n=65), positron emission tomography (n=8), MR spectroscopy (n=28) and diffusion tensor imaging (n=55) were integrated in the navigational setup.

RESULTS

Intraoperative MRI showed primary complete resection in 27% of all patients (I: 50%; II: 53%; III: 2%; IV: 28%). In 41% of all patients (I: 40%; II: 26%; III: 66%; IV: 28%) the resection was extended owing to intraoperative MRI increasing the percentage of complete resections to 40% (I: 70%; II: 58%; III: 17%; IV: 40%). Integrated application of functional navigation resulted in low post-operative morbidity with a transient new neurological deficit in 10.2% (paresis: 8.8% and speech disturbance: 1.4%) decreasing to a permanent deficit in 2.9% (four of 137 patients with a new or increased paresis).

CONCLUSIONS

The combination of intraoperative MRI and functional navigation allows safe extended resections in glioma surgery. However, despite extended resections, still in the majority of the grade III and IV gliomas no gross total resection could be achieved owing to the extension of the tumor into eloquent brain areas. Intraoperative MRI data can be used to localize the tumor remnants reliably and compensate for the effects of brain shift.

Feasibility of anaesthetic provision for paediatric patients undergoing off-site intraoperative MRI-guided neurosurgery: the Singapore experience from 2009 to 2012

The benefits of using intraoperative magnetic resonance imaging (iMRI) for neurosurgery have been recognised. However, iMRI facilities are not available in all hospitals. For example, in Singapore iMRI is currently available only at the Singapore General Hospital, an adult hospital without facilities for intensive care management of patients less than 12 years of age. KK Women's and Children's Hospital is a dedicated children's hospital situated 6.3 km away from this facility. In order to obtain iMRI services for our paediatric patients, transport to Singapore General Hospital is required, with return to our hospital for postoperative management. Since July 2009 we have managed nine paediatric patients in this manner: three children with arteriovenous malformations and six children with brain tumours. There was no morbidity or mortality that could be attributed to the transport of patients either to or from Singapore General Hospital. Our experience suggests that with adequate planning and preparation, providing anaesthetic care and transporting children for off-site iMRI-guided neurosurgery is feasible and safe for selected children.

Intraoperative Visualization of Residual Tumor: The Role of Perfusion-Weighted Imaging in a High-Field Intraoperative Magnetic Resonance Scanner

BACKGROUND:

High-field, intraoperative magnetic resonance imaging (iMRI) achieves free tumor margins in glioma surgery by involving anatomic neuronavigation and sophisticated functional imaging.

OBJECTIVE:

To evaluate the role of perfusion-weighted iMRI as an aid to detect residual tumor and to guide its resection.

METHODS:

Twenty-two patients undergoing intraoperative scanning (in a dual-room 1.5-T magnet setting) during the resection of high-grade gliomas were examined with perfusion-weighted iMRI. The generated relative cerebral blood volume (rCBV) maps were scrutinized for any hot spots indicative of tumor remnants, and region-of-interest analysis was performed. Differences among the rCBV region-of-interest estimates in residual tumor, free tumor margins, and normal white matter were analyzed. Histopathology of the tissue specimens and the neurosurgeon's intraoperative macroscopic estimations were considered the reference standards.

RESULTS:

In all cases, diagnostic rCBV perfusion maps were generated. Interpretation of perfusion maps demonstrated that gross total resection of gliomas was achieved in 4 of 22 cases (18%), which was macroscopically and histopathologically verified, whereas in 18 of 22 cases (82%), the perfusion-weighted iMRI revealed hot spots indicating subtotal tumor removal. The latter proved to be true in all but 1 case. The receiver-operating characteristic curves of the qualitative visual and quantitative analyses showed excellent sensitivity and specificity rates. Statistical analysis demonstrated statistically significant differences for the mean rCBV and maximum rCBV between residual disease and tumor-free margins (P = .002 for both).

CONCLUSION:

Perfusion-weighted iMRI may be implemented easily into imaging protocols and may assist the surgeon in detecting residual tumor volume.

Usefulness of multimodal examination and intraoperative magnetic resonance imaging system in glioma surgery

Extensive surgical removal of tumor tissue can contribute to longer survival for patients with gliomas. Intraoperative magnetic resonance (iMR) imaging is important for safe and maximal resection of brain tumors. A new operating room equipped with a 1.5-T MR imaging system and neuronavigation opened at Yamagata University Hospital in 2008. Using this new suite, we have safely treated over 200 cases. Use of iMR imaging improved glioma resection rates in 25 (34%) of 73 cases, and gross total resection was achieved in 48 patients (66%). Motor evoked potential (MEP) monitoring was performed in combination with iMR imaging for 32 gliomas. MEP monitoring was successful in 30 cases (94%). Transient decreases in MEP amplitude were seen in two patients. One patient showed transient motor weakness and another showed improvement of motor function. The iMR imaging system provides useful information for tumor resection that allows intraoperative modification of surgical strategies. Combining MEP monitoring with iMR imaging appears to offer the most effective method for safe glioma surgery near eloquent areas.

Emerging operative strategies in neurosurgical oncology

PURPOSE OF REVIEW

In recent years, the safety and efficacy of neurosurgical intervention has rapidly improved for brain tumor patients. Technological advances, combined with refined intraoperative techniques, now enable well tolerated surgical access to any region of the human brain. For patients with gliomas, these improvements have redefined the clinical possibilities, and here we review several emerging operative strategies that are essential for next-generation neurosurgical oncologists and major brain tumor centers.

RECENT FINDINGS

The value of glioma extent of resection remains controversial, but review of the modern literature reveals important opportunities for early neurosurgical intervention. Although microsurgical resection must be balanced by the risk of neurological compromise, improvements in intraoperative stimulation techniques now enable resection of highly eloquent tumors with minimal morbidity. Additionally, the emergence of fluorescence-guided surgery as a new operative paradigm provides a unique opportunity to resect tumors to the margins of microscopic infiltration.

SUMMARY

Neurosurgical intervention remains the first step in effective glioma management. With intraoperative mapping techniques, aggressive microsurgical resection can be safely pursued even when tumors occupy essential functional pathways. With the development of tumor-specific fluorophores, such as 5-aminolevulinic acid, real-time microscopic visualization of tumor infiltration can be surgically targeted prior to adjuvant therapy.