Preoperative and intraoperative brain mapping for the resection of eloquent-area tumors. A prospective analysis of methodology, correlation, and usefulness based on clinical outcomes

Transoperative Magnetic Resonance Imaging in Awake Glioma Surgery: Experience in a Latin American Tertiary-Level Center

OBJECTIVE

Analyze the usefulness, efficacy, and safety of transoperative magnetic resonance imaging (tMRI) in glioma surgery in awake patients.

METHODS

Retrospective, single-center, analytical study of a cohort of patients who underwent awake surgery for gliomas by the same surgeon in a third-level Argentine center, in the period between 2012 and 2022. Only patients with pathology-confirmed gliomas, with 6-month follow-up, who had preoperative and postoperative volumetric magnetic resonance imaging, were included in this sample. Subsequently, we analyzed which patients received surgery with the tMRI protocol and the results using multivariate regression analysis.

RESULTS

A total of 71 patients were included. A tMRI study was performed on 22 (31%) of these patients. The use of tMRI increased the percentage of resection by 20% (P = 0.03), thereby increasing the possibility of gross total resection. However, using tMRI significantly extended surgical time by 84 minutes (P < 0.001). In 55% of the patients in whom tMRI was performed, the resection was continued after it. The use of tMRI did not increase the rate of infections or the development of surgically associated neurological deficits in the long term, despite the fact that 47% of the patients showed the development of a new deficit or worsening of a previous one during the intraoperative period.

CONCLUSIONS

The use of tMRI in awake glioma surgery proved to be a safe tool that contributes to increasing the degree of tumor resection, compared to the use of neurophysiological mapping and neuronavigation, at the expense of increased surgical times and costs. We consider tMRI in awake glioma surgery should be used in properly selected cases.

Hemodynamic response function description in patients with glioma

INTRODUCTION

Functional magnetic resonance imaging is a powerful tool that has provided many insights into cognitive sciences. Yet, as its analysis is mostly based on the knowledge of an a priori canonical hemodynamic response function (HRF), its reliability in patients' applications has been questioned. There have been reports of neurovascular uncoupling in patients with glioma, but no specific description of the Hemodynamic Response Function (HRF) in glioma has been reported so far. The aim of this work is to describe the HRF in patients with glioma.

METHODS

Forty patients were included. MR images were acquired on a 1.5T scanner. Activated clusters were identified using a fuzzy general linear model; HRFs were adjusted with a double-gamma function. Analyses were undertaken considering the tumor grade, age, sex, tumor location, and activated location.

RESULTS

Differences are found in the occipital, limbic, insular, and sub-lobar areas, but not in the frontal, temporal, and parietal lobes. The presence of a glioma slows the time-to-peak and onset times by 5.2 and 3.8 % respectively; high-grade gliomas present 8.1 % smaller HRF widths than low-grade gliomas.

DISCUSSION AND CONCLUSION

There is significant HRF variation due to the presence of glioma, but the magnitudes of the observed differences are small. Most processing pipelines should be robust enough for this magnitude of variation and little if any impact should be visible on functional maps. The differences that have been observed in the literature between functional mapping obtained with magnetic resonance vs. that obtained with direct electrostimulation during awake surgery are more probably due to the intrinsic difference in the mapping process: fMRI mapping detects all recruited areas while intra-surgical mapping indicates only the areas indispensable for the realization of a certain task. Surgical mapping might not be the gold standard to use when trying to validate the fMRI mapping process.

Experience in awake glioma surgery in a South American center. Correlation between intraoperative evaluation, extent of resection and functional outcomes

Introduction

Gliomas are the second most frequent primary brain tumors. Surgical resection remains a crucial part of treatment, as well as maximum preservation of neurological function. For this reason awake surgery has an important role.The objectives of this article are to present our experience with awake surgery for gliomas in a South American center and to analyze how intraoperative functional findings may influence the extent of resection and neurological outcomes.

Materials and methods

Retrospective single center study of a cohort of adult patients undergoing awake surgery for brain glioma, by the same neurosurgeon, between 2012 and 2022 in the city of Buenos Aires, Argentina.

Results

A total of 71 patients were included (mean age 34 years, 62% males). Seventy seven percent of tumors were low grade, with average extent of resection reaching 94% of preoperative volumetric assessment. At six months follow up, 81.7% of patients presented no motor or language deficit.Further analysis showed that having a positive mapping did not have a negative impact in the extent of resection, but was associated with short term postoperative motor and language deficits, among other variables, with later improvement.

Conclusion

Awake surgery for gliomas is a safe procedure, with the proper training. In this study it was observed that guiding the resection by negative mapping did not worsen the results and that positive subcortical mapping correlated with short term postoperative neurological deficits with posterior improvement within six months in most cases.

Neuropsychological Evaluation and Functional Magnetic Resonance Imaging Tasks in the Preoperative Assessment of Patients with Brain Tumors: A Systematic Review

BACKGROUND

Current surgical treatment of gliomas relies on a function-preserving, maximally safe resection approach. Functional Magnetic Resonance Imaging (fMRI) is a widely employed technology for this purpose. A preoperative neuropsychological evaluation should accompany this exam. However, only a few studies have reported both neuropsychological tests and fMRI tasks for preoperative planning-the current study aimed to systematically review the scientific literature on the topic.

METHODS

PRISMA guidelines were followed. We included studies that reported both neuropsychological tests and fMRI. Exclusion criteria were: no brain tumors, underage patients, no preoperative assessment, resting-state fMRI only, or healthy sample population/preclinical studies.

RESULTS

We identified 123 papers, but only 15 articles were included. Eight articles focused on language; three evaluated cognitive performance; single papers studied sensorimotor cortex, prefrontal functions, insular cortex, and cerebellar activation. Two qualitative studies focused on visuomotor function and language. According to some authors, there was a strong correlation between performance in presurgical neuropsychological tests and fMRI. Several papers suggested that selecting well-adjusted and individualized neuropsychological tasks may enable the development of personalized and more efficient protocols. The fMRI findings may also help identify plasticity phenomena to avoid unintentional damage during neurosurgery.

CONCLUSIONS

Most studies have focused on language, the most commonly evaluated cognitive function. The correlation between neuropsychological and fMRI results suggests that altered functions during the neuropsychological assessment may help identify patients who could benefit from an fMRI and, possibly, functions that should be tested. Neuropsychological evaluation and fMRI have complementary roles in the preoperative assessment.

Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging for Language Mapping in Brain Tumor Surgery: Validation With Direct Cortical Stimulation and Cortico-Cortical Evoked Potential

OBJECTIVE

Functional magnetic resonance imaging (fMRI) and diffusion tensor imaging-derived tractography (DTI-t) contribute to the localization of language areas, but their accuracy remains controversial. This study aimed to investigate the diagnostic performance of preoperative fMRI and DTI-t obtained with a simultaneous multi-slice technique using intraoperative direct cortical stimulation (DCS) or corticocortical evoked potential (CCEP) as reference standards.

MATERIALS AND METHODS

This prospective study included 26 patients (23-74 years; male:female, 13:13) with tumors in the vicinity of Broca's area who underwent preoperative fMRI and DTI-t. A site-by-site comparison between preoperative (fMRI and DTI-t) and intraoperative language mapping (DCS or CCEP) was performed for 226 cortical sites to calculate the sensitivity and specificity of fMRI and DTI-t for mapping Broca's areas. For sites with positive signals on fMRI or DTI-t, the true-positive rate (TPR) was calculated based on the concordance and discordance between fMRI and DTI-t.

RESULTS

Among 226 cortical sites, DCS was performed in 100 sites and CCEP was performed in 166 sites. The specificities of fMRI and DTI-t ranged from 72.4% (63/87) to 96.8% (122/126), respectively. The sensitivities of fMRI (except for verb generation) and DTI-t were 69.2% (9/13) to 92.3% (12/13) with DCS as the reference standard, and 40.0% (16/40) or lower with CCEP as the reference standard. For sites with preoperative fMRI or DTI-t positivity (n = 82), the TPR was high when fMRI and DTI-t were concordant (81.2% and 100% using DCS and CCEP, respectively, as the reference standards) and low when fMRI and DTI-t were discordant (≤ 24.2%).

CONCLUSION

fMRI and DTI-t are sensitive and specific for mapping Broca's area compared with DCS and specific but insensitive compared with CCEP. A site with a positive signal on both fMRI and DTI-t represents a high probability of being an essential language area.

Surgical management of Glioma Grade 4: technical update from the neuro-oncology section of the Italian Society of Neurosurgery (SINch®): a systematic review

PURPOSE

The extent of resection (EOR) is an independent prognostic factor for overall survival (OS) in adult patients with Glioma Grade 4 (GG4). The aim of the neuro-oncology section of the Italian Society of Neurosurgery (SINch®) was to provide a general overview of the current trends and technical tools to reach this goal.

METHODS

A systematic review was performed. The results were divided and ordered, by an expert team of surgeons, to assess the Class of Evidence (CE) and Strength of Recommendation (SR) of perioperative drugs management, imaging, surgery, intraoperative imaging, estimation of EOR, surgery at tumor progression and surgery in elderly patients.

RESULTS

A total of 352 studies were identified, including 299 retrospective studies and 53 reviews/meta-analysis. The use of Dexamethasone and the avoidance of prophylaxis with anti-seizure medications reached a CE I and SR A. A preoperative imaging standard protocol was defined with CE II and SR B and usefulness of an early postoperative MRI, with CE II and SR B. The EOR was defined the strongest independent risk factor for both OS and tumor recurrence with CE II and SR B. For intraoperative imaging only the use of 5-ALA reached a CE II and SR B. The estimation of EOR was established to be fundamental in planning postoperative adjuvant treatments with CE II and SR B and the stereotactic image-guided brain biopsy to be the procedure of choice when an extensive surgical resection is not feasible (CE II and SR B).

CONCLUSIONS

A growing number of evidences evidence support the role of maximal safe resection as primary OS predictor in GG4 patients. The ongoing development of intraoperative techniques for a precise real-time identification of peritumoral functional pathways enables surgeons to maximize EOR minimizing the post-operative morbidity.

The current state of the art of primary motor mapping for tumor resection: A focused survey

INTRODUCTION

Cortical and subcortical motor mapping has advanced the notion of maximal safe resection of intra-axial brain tumours, thereby preserving neurological functions as well as improving survival. Despite being an age-old and established neurosurgical procedure across the world, the strategy and techniques involved in motor mapping have a gamut of variation due to a lack of defined standard protocols.

METHODS

We disseminated a structured survey among focused group of neurosurgeons with established practices involving brain mapping. It consisted of 40 questions, split into five sections assessing the practice description, general approach for motor mapping, preference for asleep versus awake mapping, operative techniques and approach to representative tumor cases. Practice-patterns during primary motor mapping for brain tumours were analysed from responses of 51 neurosurgeons.

RESULTS

60.8 % felt that any lesion even near (without infiltration) was suffice to define "involvement" of the cortical/subcortical motor pathways. 82.4 % felt that motor mapping was necessary for brain tumours involving motor pathways, irrespective of the tumor histology or patient age. 90.2 % opined that tumor location was the predominant factor affecting their choice between awake or asleep mapping. 31.4 % believed that all cases should be performed awake unless patient-related medical, psychological, or anaesthetic contraindications exist, whereas 45.1 % felt that all cases should be performed asleep unless language mapping is required. MRI, DTI-based tractography and intra-operative fluorescence were the most commonly employed surgical adjuncts.

CONCLUSIONS

The data from this survey may serve as a preliminary foundation for a more standardized approach to patient selection and the approach to motor mapping for brain tumors.

Supramarginal Gyrus and Angular Gyrus Subcortical Connections: A Microanatomical and Tractographic Study for Neurosurgeons

Background and Objectives: This article aims to investigate the subcortical microanatomy of the supramarginal gyrus (SMG) and angular gyrus (AnG) using a microfiber dissection technique and diffusion tensor imaging (DTI)/fiber tractography (FT). The cortical and subcortical structures of this region are highly functional, and their lesions often present clinically. For this reason, the possibility of post-surgical deficits is high. We focused on the supramarginal gyrus and the angular gyrus and reviewed their anatomy from a topographic, functional and surgical point of view, and aimed to raise awareness especially for neurosurgeons. Methods: Four previously frozen, formalin-fixed human brains were examined under the operating microscope using the fiber dissection technique. Four hemispheres were dissected from medial to lateral under the surgical microscope. Brain magnetic resonance imaging (MRI) of 20 healthy adults was examined. Pre-central and post-central gyrus were preserved to achieve topographic dominance in dissections of brain specimens. Each stage was photographed. Tractographic brain magnetic resonance imaging of 10 healthy adults was examined radiologically. Focusing on the supramarginal and angular gyrus, the white matter fibers passing under this region and their intersection areas were examined. These two methods were compared anatomically from the lateral view and radiologically from the sagittal view. Results: SMG and AnG were determined in brain specimens. The pre-central and post-central gyrus were topographically preserved. The superior and medial temporal gyrus, and inferior and superior parietal areas were decorticated from lateral to medial. U fibers, superior longitudinal fasciculus II (SLF II), superior longitudinal fasciculus III (SLF III), arcuat fasciculus (AF) and middle longitudinal fasciculus (MdLF) fiber groups were shown and subcortical fiber structures belonging to these regions were visualized by the DTI/FT method. The subcortical fiber groups under the SMG and the AnG were observed anatomically and radiologically to have a dense and complex structure. Conclusions: Due to the importance of the subcortical connections of SMG and AnG on speech function, tumoral lesions and surgeries of this region are of particular importance. The anatomical architecture of the complex subcortical structure, which is located on the projection of the SMG and AnG areas, was shown with a DTI/FT examination under a topographic dominance, preserving the pre-central and post-central gyrus. In this study, the importance of the anatomical localization, connections and functions of the supramarginal and angular gyrus was examined. More anatomical and radiological studies are needed to better understand this region and its connections.

Cortical mapping in glioma surgery: correlation of fMRI and direct electrical stimulation with Human Connectome Project parcellations

OBJECTIVE

Noninvasive brain mapping with functional MRI (fMRI) and mapping with direct electrical stimulation (DES) are important tools in glioma surgery, but the evidence is inconclusive regarding the sensitivity and specificity of fMRI. The Human Connectome Project (HCP) proposed a new cortical parcellation that has not been thoroughly tested in a clinical setting. The main goal of this study was to evaluate the correlation of fMRI and DES mapping with HCP areas in a clinical setting, and to evaluate the performance of fMRI mapping in motor and language tasks in patients with glioma, using DES as the gold standard.

METHODS

Forty patients with supratentorial gliomas were examined using preoperative fMRI and underwent awake craniotomy with DES. Functional activation maps were visualized on a 3D representation of the cortex, classified according to HCP areas, and compared with surgical mapping.

RESULTS

Functional MRI was successful in identifying language and motor HCP areas in most cases, including novel areas such as 55b and the superior longitudinal fasciculus (SLF). Functional MRI had a sensitivity and specificity of 100% and 71%, respectively, for motor function in HCP area 4. Sensitivity and specificity were different according to the area and fMRI protocol; i.e., semantic protocols performed better in Brodmann area (BA) 55b/peri-sylvian language areas with 100% sensitivity and 20% specificity, and word production protocols in BAs 44 and 45 with 70% sensitivity and 80% specificity. Some compensation patterns could be observed, such as motor activation of the postcentral gyrus in precentral gliomas.

CONCLUSIONS

HCP areas can be detected in clinical scenarios of glioma surgery. These areas appear relatively stable across patients, but compensation patterns seem to differ, allowing occasional resection of activating areas. Newly described areas such as 55b and SLF can act as critical areas in language networks. Surgical planning should account for these parcellations.

Wide Dissection Trans-Sulcal Approach for Resection of Deep Intra-Axial Lesions in Eloquent Brain Areas

Introduction: Resection of intra-axial tumors (IaT) in eloquent brain regions risks major postoperative neurological deficits. Awake craniotomy is often used to navigate these areas; however, some patients are ineligible for awake procedures. The trans-sulcal approach (TScal) was introduced to reduce parenchymal trauma during tumor resection. We report our experiences utilizing TScal for resection of deep IaT located in eloquent areas. Materials and Methods: This is a single-center retrospective analysis of patients who underwent IaT resection in eloquent areas via TScal from January 2013 to April 2021. Seventeen cases were reviewed, and relevant data was collected. Fluorescence-guided surgery with 5-aminolevulinic acid (ALA) and intraoperative ultrasound was performed in some cases. Results: Seventeen patients (10 males, 7 females) averaging 61.2 years-old (range, 21-76) were included in this study. Average length of stay was 4.8 days, and only 2 patients (11.8%) required hospital readmission within 30 days. Gross total resection (GTR) was achieved in 15 patients (88.2%), while subtotal resection occurred in 2 patients (11.8%). Eleven patients (64.7%) reported full resolution of symptoms, 4 patients (23.5%) reported deficit improvement, and 2 patients (11.8%) experienced no change from their preoperative deficits. No patient developed new permanent deficits postoperatively. Discussion: GTR, preoperative deficit reduction, and complications were comparable to awake craniotomy and other TScal studies. Ancillary intraoperative techniques, such as brain mapping, 5-ALA and intraoperative ultrasound, are afforded by TScal to improve resection rates and overall outcomes. Conclusions: TScal can be an option for patients with deep lesions in eloquent areas who are not candidates for awake surgeries.

Correlation of Preoperative Functional Magnetic Resonance Imaging (fMRI) with Intraoperative Cortical Stimulation in Surgeries of Eloquent Brain Lesions

Background

Direct Cortical Stimulation (DCS) represents the gold standard for mapping of eloquent brain cortex. However, DCS is an invasive and time-consuming procedure. fMRI has become a useful tool to delineate motor and sensory eloquent cortex from the areas of planned neurosurgical resection. In our study, we will be studying the reliability of preoperative imaging when compared with the intraoperative DCS.

Objectives

The aim of this study was to assess the reliability of fMRI by comparing it with DCS.

Methods and Materials

Thirty patients with eloquent cortex lesions were admitted. Preoperative fMRI sequences were loaded into a neuro-navigational system. Intraoperative motor mapping was done by DCS. The location of all cortical stimulated points was correlated with the cortical functional structures. Based on it, specificity, sensitivity, positive predictive value, negative predictive value of fMRI was calculated. Preoperative and postoperative Karnofsky score and MRC grading was then noted.

Results

Concordance between fMRI and DCS was noted in 26 cases. Overall mean sensitivity, specificity, positive and negative predictive value of fMRI as compared to DCS was 95%, 92.48%, 85.56%, and 96.08%, respectively. Preoperative and Postoperative Karnofsky score stayed same in most of the cases [25/30].

Conclusions

DCS remains the gold standard for mapping eloquent cortex in-spite of its invasiveness, side effects such as seizures and cost concerns. Although fMRI cannot replace DCS, it can guide and increase the efficacy in resection, select high-risk patients for intraoperative monitoring, help in preoperative stratification of risk counseling and preservation of neurological status in eloquent brain lesions.

A New Functional Magnetic Resonance Imaging Localizer for Preoperative Language Mapping Using a Sentence Completion Task: Validity, Choice of Baseline Condition, and Test–Retest Reliability

To avoid post-neurosurgical language deficits, intraoperative mapping of the language function in the brain can be complemented with preoperative mapping with functional magnetic resonance imaging (fMRI). The validity of an fMRI “language localizer” paradigm crucially depends on the choice of an optimal language task and baseline condition. This study presents a new fMRI “language localizer” in Russian using overt sentence completion, a task that comprehensively engages the language function by involving both production and comprehension at the word and sentence level. The paradigm was validated in 18 neurologically healthy volunteers who participated in two scanning sessions, for estimating test–retest reliability. For the first time, two baseline conditions for the sentence completion task were compared. At the group level, the paradigm significantly activated both anterior and posterior language-related regions. Individual-level analysis showed that activation was elicited most consistently in the inferior frontal regions, followed by posterior temporal regions and the angular gyrus. Test–retest reliability of activation location, as measured by Dice coefficients, was moderate and thus comparable to previous studies. Test–retest reliability was higher in the frontal than temporo-parietal region and with the most liberal statistical thresholding compared to two more conservative thresholding methods. Lateralization indices were expectedly left-hemispheric, with greater lateralization in the frontal than temporo-parietal region, and showed moderate test-retest reliability. Finally, the pseudoword baseline elicited more extensive and more reliable activation, although the syllable baseline appears more feasible for future clinical use. Overall, the study demonstrated the validity and reliability of the sentence completion task for mapping the language function in the brain. The paradigm needs further validation in a clinical sample of neurosurgical patients. Additionally, the study contributes to general evidence on test–retest reliability of fMRI.

[Functional magnetic resonance imaging in neurosurgery]

The study is a short review of articles concerning functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery. Advantages and disadvantages of the methods are considered, the results of surgical treatment of patients using functional navigation are presented. Separate attention is paid to fMRI precision, a new resting-state method of visualization. Practical advices of fMRI application in neurooncology and surgery of arteriovenous malformations are given.

[Functional magnetic resonance imaging in neurosurgery]

The review of publications on functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery is presented. Advantages and disadvantages are selected taking pathogenesis into account. Results of surgical treatment with use of functional navigation are described. Separate attention is paid to fMRI precision by its comparing with direct cortical stimulation. New resting-state method of visualization is observed. Practical advices are given of fMRI application in neurooncology and surgery of arteriovenous malformations.

The Relationship Between Stimulation Current and Functional Site Localization During Brain Mapping

BACKGROUND

Gliomas are often in close proximity to functional regions of the brain; therefore, electrocortical stimulation (ECS) mapping is a common technique utilized during glioma resection to identify functional areas. Stimulation-induced seizure (SIS) remains the most common reason for aborted procedures. Few studies have focused on oncological factors impacting cortical stimulation thresholds.

OBJECTIVE

To examine oncological factors thought to impact stimulation threshold in order to understand whether a linear relationship exists between stimulation current and number of functional cortical sites identified.

METHODS

We retrospectively reviewed single-institution prospectively collected brain mapping data of patients with dominant hemisphere gliomas. Comparisons of stimulation threshold were made using t-tests and ANOVAs. Associations between oncologic factors and stimulation threshold were made using multivariate regressions. The association between stimulation current and number of positive sites was made using a Poisson model.

RESULTS

Of the 586 patients included in the study, SIS occurred in 3.92% and the rate of SIS events differed by cortical location (frontal 8.5%, insular 1.6%, parietal 1.3%, and temporal 2.8%; P = .009). Stimulation current was lower when mapping frontal cortex (P = .002). Stimulation current was not associated with tumor plus peritumor edema volume, world health organization) (WHO grade, histology, or isocitrate dehydrogenase (IDH) mutation status but was associated with tumor volume within the frontal lobe (P = .018). Stimulation current was not associated with number of positive sites identified during ECS mapping (P = .118).

CONCLUSION

SISs are rare but serious events during ECS mapping. SISs are most common when mapping the frontal lobe. Greater stimulation current is not associated with the identification of more cortical functional sites during glioma surgery.

Altered sense of self during seizures in the posteromedial cortex

In this manuscript, we report a rare case of a patient with localized seizures originating from the right anterior and dorsal posteromedial cortex (PMC). We mapped the electrophysiological and neuroimaging connectivity of the ictal onset site and replicated seizure auras by stimulating the homotopical PMC site in the left hemisphere. Our findings provide a causal link between PMC and the sense of self and provide unique clues about the pathophysiology of self-dissociation in neuropsychiatric conditions.

The posteromedial cortex (PMC) is known to be a core node of the default mode network. Given its anatomical location and blood supply pattern, the effects of targeted disruption of this part of the brain are largely unknown. Here, we report a rare case of a patient (S19_137) with confirmed seizures originating within the PMC. Intracranial recordings confirmed the onset of seizures in the right dorsal posterior cingulate cortex, adjacent to the marginal sulcus, likely corresponding to Brodmann area 31. Upon the onset of seizures, the patient reported a reproducible sense of self-dissociation—a condition he described as a distorted awareness of the position of his body in space and feeling as if he had temporarily become an outside observer to his own thoughts, his “me” having become a separate entity that was listening to different parts of his brain speak to each other. Importantly, 50-Hz electrical stimulation of the seizure zone and a homotopical region within the contralateral PMC induced a subjectively similar state, reproducibly. We supplement our clinical findings with the definition of the patient’s network anatomy at sites of interest using cortico-cortical–evoked potentials, experimental and resting-state electrophysiological connectivity, and individual-level functional imaging. This rare case of patient S19_137 highlights the potential causal importance of the PMC for integrating self-referential information and provides clues for future mechanistic studies of self-dissociation in neuropsychiatric populations.

Can Preoperative Mapping with Functional MRI Reduce Morbidity in Brain Tumor Resection? A Systematic Review and Meta-Analysis of 68 Observational Studies

Background Preoperative functional MRI (fMRI) is one of several techniques developed to localize critical brain structures and brain tumors. However, the usefulness of fMRI for preoperative surgical planning and its potential effect on neurologic outcomes remain unclear. Purpose To assess the overall postoperative morbidity among patients with brain tumors by using preoperative fMRI versus surgery without this tool or with use of standard (nonfunctional) neuronavigation. Materials and Methods A systematic review and meta-analysis of studies across major databases from 1946 to June 20, 2020, were conducted. Inclusion criteria were original studies that (a) included patients with brain tumors, (b) performed preoperative neuroimaging workup with fMRI, (c) investigated the usefulness of a preoperative or intraoperative functional neuroimaging technique and used that technique to resect cerebral tumors, and (d) reported postoperative clinical measures. Pooled estimates for adverse event rate (ER) effect size (log ER, log odds ratio, or Hedges g) with 95% CIs were computed by using a random-effects model. Results Sixty-eight studies met eligibility criteria (3280 participants; 58.9% men [1555 of 2641]; mean age, 46 years ± 8 [standard deviation]). Functional deterioration after surgical procedure was less likely to occur when fMRI mapping was performed before the operation (odds ratio, 0.25; 95% CI: 0.12, 0.53; P < .001]), and postsurgical Karnofsky performance status scores were higher in patients who underwent fMRI mapping (Hedges g, 0.66; 95% CI: 0.21, 1.11; P = .004]). Craniotomies for tumor resection performed with preoperative fMRI were associated with a pooled adverse ER of 11% (95% CI: 8.4, 13.1), compared with a 21.0% ER (95% CI: 12.2, 33.5) in patients who did not undergo fMRI mapping. Conclusion From the currently available data, the benefit of preoperative functional MRI planning for the resection of brain tumors appears to reduce postsurgical morbidity, especially when used with other advanced imaging techniques, such as diffusion-tensor imaging, intraoperative MRI, or cortical stimulation. © RSNA, 2021 Online supplemental material is available for this article.

Feasibility, Contrast Sensitivity and Network Specificity of Language fMRI in Presurgical Evaluation for Epilepsy and Brain Tumor Surgery

Language fMRI has become an integral part of the planning process in brain surgery. However, fMRI may suffer from confounding factors both on the patient side, as well as on the provider side. In this study, we investigate how patient-related confounds affect the ability of the patient to perform language fMRI tasks (feasibility), the task sensitivity from an image contrast point of view, and the anatomical specificity of expressive and receptive language fMRI protocols. 104 patients were referred for language fMRI in the context of presurgical procedures for epilepsy and brain tumor surgery. Four tasks were used: (1) a verbal fluency (VF) task to map vocabulary use, (2) a semantic description (SD) task to map sentence formation/semantic integration skills, (3) a reading comprehension (RC) task and (4) a listening comprehension (LC) task. Feasibility was excellent in the LC task (100%), but in the acceptable to mediocre range for the rest of the tasks (SD: 87.50%, RC: 85.57%, VF: 67.30%). Feasibility was significantly confounded by age (p = 0.020) and education level (p = 0.003) in VF, by education level (p = 0.004) and lesion laterality (p = 0.019) in SD and by age (p = 0.001), lesion laterality (p = 0.007) and lesion severity (p = 0.048) in RC. All tasks were comparable regarding sensitivity in generating statistically significant image contrast (VF: 90.00%, SD: 92.30%, RC: 93.25%, LC: 88.46%). The lobe of the lesion (p = 0.005) and the age (p = 0.009) confounded contrast sensitivity in the VF and SD tasks respectively. Both VF and LC tasks demonstrated unilateral lateralization of posterior language areas; only the LC task showed unilateral lateralization of anterior language areas. Our study highlights the effects of patient-related confounding factors on language fMRI and proposes LC as the most feasible, less confounded, and efficiently lateralizing task in the clinical presurgical context.

The Use of Standardized Intraoperative Language Tests in Awake Craniotomies: A Scoping Review

Assessment of speech and language functions is an essential part of awake craniotomies. Although standardized and validated tests have several advantages compared to homemade (or mixed) batteries, in the literature it is unclear how such tests are used or whether they are used at all. In this study, we performed a scoping review in order to locate standardized and validated intraoperative language tests. Our inquiry included two databases (PubMED and MEDLINE), gray literature, and snowball referencing. We discovered 87 studies reporting use of mixed batteries, which consist of homemade tasks and tests borrowed from other settings. The tests we found to meet the validation and standardization criteria we set were ultimately three (n = 3) and each one has its own advantages and disadvantages. We argue that tests with high sensitivity and specificity not only can lead to better outcomes postoperatively, but they can also help us to gain a better understanding of the neuroanatomy of language.

Novel intraoperative online functional mapping of somatosensory finger representations for targeted stimulating electrode placement: technical note

Defining eloquent cortex intraoperatively, traditionally performed by neurosurgeons to preserve patient function, can now help target electrode implantation for restoring function. Brain-machine interfaces (BMIs) have the potential to restore upper-limb motor control to paralyzed patients but require accurate placement of recording and stimulating electrodes to enable functional control of a prosthetic limb. Beyond motor decoding from recording arrays, precise placement of stimulating electrodes in cortical areas associated with finger and fingertip sensations allows for the delivery of sensory feedback that could improve dexterous control of prosthetic hands. In this study, the authors demonstrated the use of a novel intraoperative online functional mapping (OFM) technique with high-density electrocorticography to localize finger representations in human primary somatosensory cortex. In conjunction with traditional pre- and intraoperative targeting approaches, this technique enabled accurate implantation of stimulating microelectrodes, which was confirmed by postimplantation intracortical stimulation of finger and fingertip sensations. This work demonstrates the utility of intraoperative OFM and will inform future studies of closed-loop BMIs in humans.

Impact of combined use of intraoperative MRI and awake microsurgical resection on patients with gliomas: a systematic review and meta-analysis

Microsurgical resection of primary brain tumors located within or near eloquent areas is challenging. Primary aim is to preserve neurological function, while maximizing the extent of resection (EOR), to optimize long-term neurooncological outcomes and quality of life. Here, we review the combined integration of awake craniotomy and intraoperative MRI (IoMRI) for primary brain tumors, due to their multiple challenges. A systematic review of the literature was performed, in accordance with the Prisma guidelines. Were included 13 series and a total number of 527 patients, who underwent 541 surgeries. We paid particular attention to operative time, rate of intraoperative seizures, rate of initial complete resection at the time of first IoMRI, the final complete gross total resection (GTR, complete radiological resection rates), and the immediate and definitive postoperative neurological complications. The mean duration of surgery was 6.3 h (median 7.05, range 3.8-7.9). The intraoperative seizure rate was 3.7% (range 1.4-6; I^2 = 0%, P heterogeneity = 0.569, standard error = 0.012, p = 0.002). The intraoperative complete resection rate at the time of first IoMRI was 35.2% (range 25.7-44.7; I^2 = 66.73%, P heterogeneity = 0.004, standard error = 0.048, p < 0.001). The rate of patients who underwent supplementary resection after one or several IoMRI was 46% (range 39.8-52.2; I^2 = 8.49%, P heterogeneity = 0.364, standard error = 0.032, p < 0.001). The GTR rate at discharge was 56.3% (range 47.5-65.1; I^2 = 60.19%, P heterogeneity = 0.01, standard error = 0.045, p < 0.001). The rate of immediate postoperative complications was 27.4% (range 15.2-39.6; I^2 = 92.62%, P heterogeneity < 0.001, standard error = 0.062, p < 0.001). The rate of permanent postoperative complications was 4.1% (range 1.3-6.9; I^2 = 38.52%, P heterogeneity = 0.123, standard error = 0.014, p = 0.004). Combined use of awake craniotomy and IoMRI can help in maximizing brain tumor resection in selected patients. The technical obstacles to doing so are not severe and can be managed by experienced neurosurgery and anesthesiology teams. The benefits of bringing these technologies to bear on patients with brain tumors in or near language areas are obvious. The lack of equipoise on this topic by experienced practitioners will make it difficult to do a prospective, randomized, clinical trial. In the opinion of the authors, such a trial would be unnecessary and would deprive some patients of the benefits of the best available methods for their tumor resections.

Accuracy analysis of fMRI and MEG activations determined by intraoperative mapping

OBJECTIVE

By looking at how the accuracy of preoperative brain mapping methods vary according to differences in the distance from the activation clusters used for the analysis, the present study aimed to elucidate how preoperative functional neuroimaging may be used in such a way that maximizes the mapping accuracy.

METHODS

The eloquent function of 19 patients with a brain tumor or cavernoma was mapped prior to resection with both functional MRI (fMRI) and magnetoencephalography (MEG). The mapping results were then validated using direct cortical stimulation mapping performed immediately after craniotomy and prior to resection. The subset of patients with equivalent MEG and fMRI tasks performed for motor (n = 14) and language (n = 12) were evaluated as both individual and combined predictions. Furthermore, the distance resulting in the maximum accuracy, as evaluated by the J statistic, was determined by plotting the sensitivities and specificities against a linearly increasing distance threshold.

RESULTS

fMRI showed a maximum mapping accuracy at 5 mm for both motor and language mapping. MEG showed a maximum mapping accuracy at 40 mm for motor and 15 mm for language mapping. At the standard 10-mm distance used in the literature, MEG showed a greater specificity than fMRI for both motor and language mapping but a lower sensitivity for motor mapping. Combining MEG and fMRI showed a maximum accuracy at 15 mm and 5 mm-MEG and fMRI distances, respectively-for motor mapping and at a 10-mm distance for both MEG and fMRI for language mapping. For motor mapping, combining MEG and fMRI at the optimal distances resulted in a greater accuracy than the maximum accuracy of the individual predictions.

CONCLUSIONS

This study demonstrates that the accuracy of language and motor mapping for both fMRI and MEG is heavily dependent on the distance threshold used in the analysis. Furthermore, combining MEG and fMRI showed the potential for increased motor mapping accuracy compared to when using the modalities separately.Clinical trial registration no.: NCT01535430 (clinicaltrials.gov).

Diffusion Tensor Imaging Color-Coded Maps: An Alternative to Tractography

INTRODUCTION

White matter tracts can be observed using tractograms generated from diffusion tensor imaging (DTI). However, the dependence of these white matter tract images on subjective variables, including how seed points are placed and the preferred level of fractional anisotropy, introduces interobserver inconsistency and potential lack of reliability. We propose that color-coded maps (CCM) generated from DTI can be a preferred method for the visualization of important white matter tracts, circumventing bias in preoperative brain tumor resection planning.

METHODS

DTI was acquired retrospectively in 25 patients with brain tumors. Lesions included 15 tumors of glial origin, 9 metastatic tumors, 2 meningiomas, and 1 cavernous angioma. Tractograms of the pyramidal tract and/or optic radiations, based on tumor location, were created by marking seed regions of interest using known anatomical locations. We compared the degree of tract involvement and white matter alteration between CCMs and tractograms. Neurological outcomes were obtained from chart reviews.

RESULTS

The pyramidal tract was evaluated in 20/25 patients, the visual tracts were evaluated in 10/25, and both tracts were evaluated in 5/25. In 19/25 studies, the same patterns of white matter alternations were found between the CCMs and tractograms. In the 6 patients where patterns differed, 2 tractograms were not useful in determining pattern alteration; in the remaining 4/6, no practical difference was seen in comparing the studies. Two patients were lost to follow-up. Thirteen patients were neurologically improved or remained intact after intervention. In these, 10 of the 13 patients showed tumor-induced white matter tract displacement on CCM. Twelve patients had no improvement of their preoperative deficit. In 9 of these 12 patients, CCM showed white matter disruption.

CONCLUSION

CCMs provide a convenient, practical, and objective method of visualizing white matter tracts, obviating the need for potentially subjective and time-consuming tractography. CCMs are at least as reliable as tractograms in predicting neurological outcomes after neurosurgical intervention.

Perioperative Management of Patients with Glioblastoma

The clinical presentation of glioblastomas is varied, and definitive diagnosis requires pathologic examination and study of the tissue. Management of glioblastomas includes surgery and adjuvant chemotherapy and radiotherapy, with surgery playing an important role in the prognosis of these patients. Awake craniotomy plays a crucial role in tumors in or adjacent to eloquent areas, allowing surgeons to maximize resection, while minimizing iatrogenic deficits. However, the prognosis remains dismal. This article presents the perioperative management of patients with glioblastoma including tools and surgical adjuncts to maximize extent of resection and minimize poor outcomes.

Electrophysiology of the Human Superior Temporal Sulcus during Speech Processing

The superior temporal sulcus (STS) is a crucial hub for speech perception and can be studied with high spatiotemporal resolution using electrodes targeting mesial temporal structures in epilepsy patients. Goals of the current study were to clarify functional distinctions between the upper (STSU) and the lower (STSL) bank, hemispheric asymmetries, and activity during self-initiated speech. Electrophysiologic properties were characterized using semantic categorization and dialog-based tasks. Gamma-band activity and alpha-band suppression were used as complementary measures of STS activation. Gamma responses to auditory stimuli were weaker in STSL compared with STSU and had longer onset latencies. Activity in anterior STS was larger during speaking than listening; the opposite pattern was observed more posteriorly. Opposite hemispheric asymmetries were found for alpha suppression in STSU and STSL. Alpha suppression in the STS emerged earlier than in core auditory cortex, suggesting feedback signaling within the auditory cortical hierarchy. STSL was the only region where gamma responses to words presented in the semantic categorization tasks were larger in subjects with superior task performance. More pronounced alpha suppression was associated with better task performance in Heschl's gyrus, superior temporal gyrus, and STS. Functional differences between STSU and STSL warrant their separate assessment in future studies.

Importance and Evidence of Extent of Resection in Glioblastoma

Maximal safe resection is an essential part of the multidisciplinary care of patients with glioblastoma. A growing body of data shows that gross total resection is an independent prognostic factor associated with improved clinical outcome. The relationship between extent of glioblastoma (GB) resection and clinical benefit depends critically on the balance between cytoreduction and avoiding neurologic morbidity. The definition of the extent of tumor resection, how this is best measured pre- and postoperatively, and its relation to volume of residual tumor is still discussed. We review the literature supporting extent of resection in GB, highlighting the importance of a standardized definition and measurement of extent of resection to allow greater collaboration in research projects and trials. Recent developments in neurosurgical techniques and technologies focused on maximizing extent of resection and safety are discussed.

Anatomo-radiological correlation between diffusion tensor imaging and histologic analyses of glial tumors: a preliminary study

BACKGROUND AND PURPOSE

The challenge of the neurosurgical management of gliomas lies in achieving a maximal resection without persistent functional deficit. Diffusion tensor imaging (DTI) allows non-invasive identification of white matter tracts and their interactions with the tumor. Previous DTI validation studies were compared with intraoperative cortical stimulation, but none was performed based on the tumor anatomopathological analysis. This preliminary study evaluates the correlation between the preoperative subcortical DTI tractography and histology in terms of fiber direction as well as potential tumor-related fiber disruption.

METHODS

Eleven patients harboring glial tumors underwent preoperative DTI images. Correlations were performed between the visual color-coded anisotropy (FA) map analysis and the tumor histology after "en bloc" resection. Thirty-one tumor areas were classified according to the degree of tumor infiltration, the destruction of myelin fibers and neurofilaments, the presence of organized white matter fibers, and their orientation in space.

RESULTS

After histologic comparison, the DTI sensitivity and specificity to predict disrupted fiber tracts were respectively of 89% and 90%. The positive and negative predicted values of DTI were 80% and 95%. The DTI data were in line with the histologic myelin fiber orientation in 90% of patients. In our series, the prevalence of destructed fiber was 31%. Glioblastoma WHO grade IV harbored a higher proportion of destructed white matter tracts. Lower WHO grades were associated with higher preservation of subcortical fiber tracts.

CONCLUSION

This DTI/histology study of "en bloc"-resected gliomas reported a high and reproducible concordance of the visual color-coded FA map with the histologic examination to predict subcortical fiber tract disruption. Our series brought consistency to the DTI data that could be performed routinely for glioma surgery to predict the tumor grade and the postoperative clinical outcomes.

Awake glioma surgery: technical evolution and nuances

INTRODUCTION

Multiple studies have demonstrated that improved extent of resection is associated with longer overall survival for patients with both high and low grade glioma. Awake craniotomy was developed as a technique for maximizing resection whilst preserving neurological function.

METHODS

We performed a comprehensive review of the literature describing the history, indications, techniques and outcomes of awake craniotomy for patients with glioma.

RESULTS

The technique of awake craniotomy evolved to become an essential tool for resection of glioma. Many perceived contraindications can now be managed. We describe in detail our preferred technique, the testing paradigms utilized, and critically review the literature regarding functional and oncological outcome.

CONCLUSIONS

Awake craniotomy with mapping has become the gold standard for safely maximizing extent of resection for tumor in or near eloquent brain. Cortical and subcortical mapping methods have been refined and the technique is associated with an extremely low rate of complications.

Tractography in Neurosurgery: A Systematic Review of Current Applications

The ability to visualize the brain's fiber connections noninvasively in vivo is relatively young compared with other possibilities of functional magnetic resonance imaging. Although many studies showed tractography to be of promising value for neurosurgical care, the implications remain inconclusive. An overview of current applications is presented in this systematic review. A search was conducted for (("tractography" or "fiber tracking" or "fibre tracking") and "neurosurgery") that produced 751 results. We identified 260 relevant articles and added 20 more from other sources. Most publications concerned surgical planning for resection of tumors (n = 193) and vascular lesions (n = 15). Preoperative use of transcranial magnetic stimulation was discussed in 22 of these articles. Tractography in skull base surgery presents a special challenge (n = 29). Fewer publications evaluated traumatic brain injury (TBI) (n = 25) and spontaneous intracranial bleeding (n = 22). Twenty-three articles focused on tractography in pediatric neurosurgery. Most authors found tractography to be a valuable addition in neurosurgical care. The accuracy of the technique has increased over time. There are articles suggesting that tractography improves patient outcome after tumor resection. However, no reliable biomarkers have yet been described. The better rehabilitation potential after TBI and spontaneous intracranial bleeding compared with brain tumors offers an insight into the process of neurorehabilitation. Tractography and diffusion measurements in some studies showed a correlation with patient outcome that might help uncover the neuroanatomical principles of rehabilitation itself. Alternative corticofugal and cortico-cortical networks have been implicated in motor recovery after ischemic stroke, suggesting more complex mechanisms in neurorehabilitation that go beyond current models. Hence tractography may potentially be able to predict clinical deficits and rehabilitation potential, as well as finding possible explanations for neurologic disorders in retrospect. However, large variations of the results indicate a lack of data to establish robust diagnostical concepts at this point. Therefore, in vivo tractography should still be interpreted with caution and by experienced surgeons.

The role of diffusion tractography in refining glial tumor resection

Primary brain tumors are notoriously hard to resect surgically. Due to their infiltrative nature, finding the optimal resection boundary without damaging healthy tissue can be challenging. One potential tool to help make this decision is diffusion-weighted magnetic resonance imaging (dMRI) tractography. dMRI exploits the diffusion of water molecule along axons to generate a 3D modelization of the white matter bundles in the brain. This feature is particularly useful to visualize how a tumor affects its surrounding white matter and plan a surgical path. This paper reviews the different ways in which dMRI can be used to improve brain tumor resection, its benefits and also its limitations. We expose surgical tools that can be paired with dMRI to improve its impact on surgical outcome, such as loading the 3D tractography in the neuronavigation system and direct electrical stimulation to validate the position of the white matter bundles of interest. We also review articles validating dMRI findings using other anatomical investigation techniques, such as postmortem dissections, manganese-enhanced MRI, electrophysiological stimulations, and phantom studies with known ground truth. We will be discussing the areas of the brain where dMRI performs well and where the future challenges are. We will conclude this review with suggestions and take home messages for neurosurgeons, tractographers, and vendors for advancing the field and on how to benefit from tractography's use in clinical practice.

Novel Deep Learning Network Analysis of Electrical Stimulation Mapping-Driven Diffusion MRI Tractography to Improve Preoperative Evaluation of Pediatric Epilepsy

OBJECTIVE

To investigate the clinical utility of deep convolutional neural network (DCNN) tract classification as a new imaging tool in the preoperative evaluation of children with focal epilepsy (FE).

METHODS

A DCNN tract classification deeply learned spatial trajectories of DWI white matter pathways linking electrical stimulation mapping (ESM) findings from 89 children with FE, and then automatically identified white matter pathways associated with eloquent functions (i.e., primary motor, language, and vision). Clinical utility was examined by 1) measuring the nearest distance between DCNN-determined pathways and ESM, 2) evaluating the effectiveness of DCNN-determined pathways to optimize surgical margins via Kalman filter analysis, and 3) evaluating how accurately changes in DCNN-determined language pathway volume can predict changes in language ability via canonical correlation analysis.

RESULTS

DCNN tract classification outperformed other existing methods, achieving an excellent accuracy of 98 % while non-invasively detecting eloquent areas within the spatial resolution of ESM (i.e., 1 cm). The Kalman filter analysis found that the preservation of brain areas within a surgical margin determined by DCNN tract classification predicted lack of postoperative deficit with a high accuracy of 92 %. Postoperative change of DCNN-determined language pathway volume showed a significant correlation with postoperative changes in language ability (R = 0.7, p   0.001).

CONCLUSION

Our findings demonstrate that postoperative functional deficits substantially differ according to the extent of resected white matter, and that DCNN tract classification may offer key translational information by identifying these pathways in pediatric epilepsy surgery.

SIGNIFICANCE

DCNN tract classification may be an effective tool to improve surgical outcome of children with FE.

Stimulation-related intraoperative seizures during awake surgery: a review of available evidences

Awake surgery is a well-defined procedure with a very low morbidity. In particular, stimulation-related intraoperative seizure (IOS) is a commonly discussed and serious complication associated with awake surgery. Here, we reviewed the literature on awake surgery and IOS and sought to obtain evidences on the predictive factors of IOS and on the effect of IOS on postoperative outcomes. We conducted a comprehensive search of the Embase, MEDLINE, and Cochrane Central Register of Controlled Trials databases to identify potentially relevant articles from 2000 to 2019. We used combinations of the following search terms: "intraoperative seizure awake craniotomy," "awake surgery seizures," and pertinent associations; the search was restricted to publications in English and only to papers published in the last 20 years. The search returned 141 articles, including 39 papers that reported the IOS rate during awake craniotomy. The reported IOS rates ranged between 0 and 24% (mean, 7.7%). Only few studies have assessed the relationships between awake surgery and IOS, and hence, drawing clear conclusions is difficult. Nevertheless, IOS does not cause permanent and severe postoperative deficits, but can affect the patient's status perioperatively and the hospitalization duration. Anterior tumor location is an important perioperative factor associated with high IOS risk, whereas having seizures at tumor diagnosis does not seem to influence. However, the role of antiepileptic drug administration and prophylaxis remains unclear. In conclusion, given the difficulty in identifying predictors of IOS, we believe that prompt action at onset and awareness of appropriate management methods are vital.

Real-time presurgical resting-state fMRI in patients with brain tumors: Quality control and comparison with task-fMRI and intraoperative mapping

Resting-state functional magnetic resonance imaging (rsfMRI) is a promising task-free functional imaging approach, which may complement or replace task-based fMRI (tfMRI) in patients who have difficulties performing required tasks. However, rsfMRI is highly sensitive to head movement and physiological noise, and validation relative to tfMRI and intraoperative electrocortical mapping is still necessary. In this study, we investigate (a) the feasibility of real-time rsfMRI for presurgical mapping of eloquent networks with monitoring of data quality in patients with brain tumors and (b) rsfMRI localization of eloquent cortex compared with tfMRI and intraoperative electrocortical stimulation (ECS) in retrospective analysis. Five brain tumor patients were studied with rsfMRI and tfMRI on a clinical 3T scanner using MultiBand(8)-echo planar imaging (EPI) with repetition time: 400 ms. Moving-averaged sliding-window correlation analysis with regression of motion parameters and signals from white matter and cerebrospinal fluid was used to map sensorimotor and language resting-state networks. Data quality monitoring enabled rapid optimization of scan protocols, early identification of task noncompliance, and head movement-related false-positive connectivity to determine scan continuation or repetition. Sensorimotor and language resting-state networks were identifiable within 1 min of scan time. The Euclidean distance between ECS and rsfMRI connectivity and task-activation in motor cortex, Broca's, and Wernicke's areas was 5-10 mm, with the exception of discordant rsfMRI and ECS localization of Wernicke's area in one patient due to possible cortical reorganization and/or altered neurovascular coupling. This study demonstrates the potential of real-time high-speed rsfMRI for presurgical mapping of eloquent cortex with real-time data quality control, and clinically acceptable concordance of rsfMRI with tfMRI and ECS localization.

Risk factors for intraoperative stimulation-related seizures during awake surgery: an analysis of 109 consecutive patients

INTRODUCTION

During surgery for lesions in eloquent areas the goal is to achieve the widest resection possible, without loss of neurological function. Intraoperative seizures may lead to abandonment of the procedure or damages to the patient. Awareness regarding the predictors of IOS would help the surgeon. The aim of this retrospective study was to identify the factors associated with the occurrence of IOS in patients who underwent awake surgery for removal of gliomas in eloquent areas.

METHODS

This was a retrospective analysis of prospectively collected data of 109 patients who underwent awake craniotomy between January 2010 and December 2017 for removal of gliomas. IOS were defined as tonic-clonic seizures or loss of consciousness resulting in communication difficulties with the patient occurring during cortical and subcortical mapping.

RESULTS

A total of 109 patients were included in this study and IOS occurred in 9 (8.2%) patients. Demographic and clinical factors were comparable between patients with and without IOS. In the IOS group, 7 (77.8%) patients had seizures preoperatively and 4 (57.1%) were on more than one perioperative antiepileptic drugs (AED).

CONCLUSIONS

The current series add some hints to the poorly studied IOS risk during awake surgery. The risk of IOS appears to be relatively higher in patients with anteriorly located tumors and in patients operated without intraoperative brain activity monitoring and different patterns of stimulation for language and sensory-motor mapping. Further studies are needed to clarify the role of intraoperative techniques.

A novel neural prosthesis providing long-term electrocorticography recording and cortical stimulation for epilepsy and brain-computer interface

OBJECTIVE

Wireless technology is a novel tool for the transmission of cortical signals. Wireless electrocorticography (ECoG) aims to improve the safety and diagnostic gain of procedures requiring invasive localization of seizure foci and also to provide long-term recording of brain activity for brain-computer interfaces (BCIs). However, no wireless devices aimed at these clinical applications are currently available. The authors present the application of a fully implantable and externally rechargeable neural prosthesis providing wireless ECoG recording and direct cortical stimulation (DCS). Prolonged wireless ECoG monitoring was tested in nonhuman primates by using a custom-made device (the ECoG implantable wireless 16-electrode [ECOGIW-16E] device) containing a 16-contact subdural grid. This is a preliminary step toward large-scale, long-term wireless ECoG recording in humans.

METHODS

The authors implanted the ECOGIW-16E device over the left sensorimotor cortex of a nonhuman primate (Macaca fascicularis), recording ECoG signals over a time span of 6 months. Daily electrode impedances were measured, aiming to maintain the impedance values below a threshold of 100 KΩ. Brain mapping was obtained through wireless cortical stimulation at fixed intervals (1, 3, and 6 months). After 6 months, the device was removed. The authors analyzed cortical tissues by using conventional histological and immunohistological investigation to assess whether there was evidence of damage after the long-term implantation of the grid.

RESULTS

The implant was well tolerated; no neurological or behavioral consequences were reported in the monkey, which resumed his normal activities within a few hours of the procedure. The signal quality of wireless ECoG remained excellent over the 6-month observation period. Impedance values remained well below the threshold value; the average impedance per contact remains approximately 40 KΩ. Wireless cortical stimulation induced movements of the upper and lower limbs, and elicited fine movements of the digits as well. After the monkey was euthanized, the grid was found to be encapsulated by a newly formed dural sheet. The grid removal was performed easily, and no direct adhesions of the grid to the cortex were found. Conventional histological studies showed no cortical damage in the brain region covered by the grid, except for a single microscopic spot of cortical necrosis (not visible to the naked eye) in a region that had undergone repeated procedures of electrical stimulation. Immunohistological studies of the cortex underlying the grid showed a mild inflammatory process.

CONCLUSIONS

This preliminary experience in a nonhuman primate shows that a wireless neuroprosthesis, with related long-term ECoG recording (up to 6 months) and multiple DCSs, was tolerated without sequelae. The authors predict that epilepsy surgery could realize great benefit from this novel prosthesis, providing an extended time span for ECoG recording.

Functional MRI and direct cortical stimulation: Prediction of postoperative language decline

OBJECTIVE

To assess the ability of functional MRI (fMRI) to predict postoperative language decline compared to direct cortical stimulation (DCS) in epilepsy surgery patients.

METHODS

In this prospective case series, 17 patients with drug-resistant epilepsy had intracranial monitoring and resection from 2012 to 2016 with 1-year follow-up. All patients completed preoperative language fMRI, mapping with DCS of subdural electrodes, pre- and postoperative neuropsychological testing for language function, and resection. Changes in language function before and after surgery were assessed. fMRI activation and DCS electrodes in the resection were evaluated as potential predictors of language decline.

RESULTS

Four of 17 patients (12 female; median [range] age, 43 [23-59] years) experienced postoperative language decline 1 year after surgery. Two of 4 patients had overlap of fMRI activation, language-positive electrodes in basal temporal regions (within 1 cm), and resection. Two had overlap between resection volume and fMRI activation, but not DCS. fMRI demonstrated 100% sensitivity and 46% specificity for outcome compared to DCS (50% and 85%, respectively). When fMRI and DCS language findings were concordant, the combined tests showed 100% sensitivity and 75% specificity for language outcome. Seizure-onset age, resection side, type, volume, or 1 year seizure outcome did not predict language decline.

SIGNIFICANCE

Language localization overlap of fMRI and direct cortical stimulation in the resection influences postoperative language performance. Our preliminary study suggests that fMRI may be more sensitive and less specific than direct cortical stimulation. Together they may predict outcome better than either test alone.

Electrical Stimulation Mapping of the Brain: Basic Principles and Emerging Alternatives

The application of electrical stimulation mapping (ESM) of the brain for clinical use is approximating a century. Despite this long-standing history, the value of ESM for guiding surgical resections and sparing eloquent cortex is documented largely by small retrospective studies, and ESM protocols are largely inherited and lack standardization. Although models are imperfect and mechanisms are complex, the probabilistic causality of ESM has guaranteed its perpetuation into the 21st century. At present, electrical stimulation of cortical tissue is being revisited for network connectivity. In addition, noninvasive and passive mapping techniques are rapidly evolving to complement and potentially replace ESM in specific clinical situations. Lesional and epilepsy neurosurgery cases now offer different opportunities for multimodal functional assessments.

A comparison of three fiber tract delineation methods and their impact on white matter analysis

Diffusion magnetic resonance imaging (dMRI) is an important method for studying white matter connectivity in the brain in vivo in both healthy and clinical populations. Improvements in dMRI tractography algorithms, which reconstruct macroscopic three-dimensional white matter fiber pathways, have allowed for methodological advances in the study of white matter; however, insufficient attention has been paid to comparing post-tractography methods that extract white matter fiber tracts of interest from whole-brain tractography. Here we conduct a comparison of three representative and conceptually distinct approaches to fiber tract delineation: 1) a manual multiple region of interest-based approach, 2) an atlas-based approach, and 3) a groupwise fiber clustering approach, by employing methods that exemplify these approaches to delineate the arcuate fasciculus, the middle longitudinal fasciculus, and the uncinate fasciculus in 10 healthy male subjects. We enable qualitative comparisons across methods, conduct quantitative evaluations of tract volume, tract length, mean fractional anisotropy, and true positive and true negative rates, and report measures of intra-method and inter-method agreement. We discuss methodological similarities and differences between the three approaches and the major advantages and drawbacks of each, and review research and clinical contexts for which each method may be most apposite. Emphasis is given to the means by which different white matter fiber tract delineation approaches may systematically produce variable results, despite utilizing the same input tractography and reliance on similar anatomical knowledge.

Evaluation of Diffusion Tensor Imaging-Based Tractography of the Corticospinal Tract: A Correlative Study With Intraoperative Magnetic Resonance Imaging and Direct Electrical Subcortical Stimulation

Background

The accuracy of intraoperative diffusion tensor imaging (DTI)–based tractography of the corticospinal tract (CST) is crucial for its use in neurosurgical planning and its implementation in image-guided surgery. To the best of our knowledge, this is the largest prospective correlative study of the intraoperative DTI tractography of the CST and intraoperative direct electrical subcortical stimulation (DESS) of the CST, with application of intraoperative magnetic resonance imaging (iMR).

Objective

To evaluate intraoperatively acquired DTI-based tractography of the CST in correlation with DESS.

Methods

Twenty patients with gliomas (grades II-IV) adjacent to the CST were included in this prospective study. Bilateral DTI tractography of the CST was performed pre- and intraoperatively with application of 1.5-T iMRI and the results correlated and compared with the prevailing gold standard of DESS. Sensitivity, specificity, positive predictive value, and negative predictive value were considered to quantify the correlation of DTI tractography with DESS. The intensity of DESS was correlated with the distance from the CST. Moreover, the tissue quality of stimulation points at the wall of the resection cavity was evaluated with 5-aminolevulinic acid. The clinical and volumetric outcomes at postoperative and follow-up periods were also analyzed.

Results

The mean ± SD age of the patients was 54.9 ± 12 years. A total of 40 CSTs were reconstructed and 36 stimulations were included at 20 pathological CSTs, resulting in 18 true-positive, 5 false-positive, and 13 true-negative responses. The sensitivity, specificity, positive predictive value, and negative predictive value of DTI tractography to localize the CST were 100%, 72%, 78%, and 100%, respectively. DTI-based tractography correlated well at 86% of DESSs, and a linear correlation was detected between the intensity of DESS and the distance. All of the patients improved clinically, and the mean extent of resection was 97.2%. 5-Aminolevulinic acid was valuable in visualizing tumor infiltration in the false-positive cases, suggesting an infiltration of the CST at stimulation points.

Conclusion

CST visualization in the iMRI setting appears to have a high sensitivity in accurately localizing the area of the CST adjacent to the resection cavity in glioma surgery. More prospective studies with a large sample size are needed to further support the results.

Diffusion Weighted/Tensor Imaging, Functional MRI and Perfusion Weighted Imaging in Glioblastoma-Foundations and Future

In this article, we review the basics of diffusion tensor imaging and functional MRI, their current utility in preoperative neurosurgical mapping, and their limitations. We also discuss potential future applications, including implementation of resting state functional MRI. We then discuss perfusion and diffusion-weighted imaging and their application in advanced neuro-oncologic practice. We explain how these modalities can be helpful in guiding surgical biopsies and differentiating recurrent tumor from treatment related changes.

Practical prognostic score for predicting the extent of resection and neurological outcome of gliomas in the sensorimotor area

OBJECTIVE

In this prospective study, we assessed the utility of a novel prognostic score (PS) in guiding the surgical strategy of patients with sensorimotor area gliomas.

PATIENTS AND METHODS

Form December 2012 to April 2016, we collected data from patients diagnosed with brain gliomas in the sensorimotor area. All the patients had intraoperatively confirmed contiguity or continuity with sensorimotor cortical and subcortical structures. Several clinical and radiological factors were analyzed to generate a PS for each patient (range 1-8). The end-points included the extent of resection (EOR) and neurological outcome (modified Rankin Score; mRS). We assessed the predictive power of the PS using different analyses. Crosstabs analyses and Fisher's exact test (Fet) were used to evaluate the possible predictive parameters, and for the classification of positive or negative outcomes for the chosen proxies; the significance threshold was set at p<0.05.

RESULTS

Using independent t-tests, we compared the mRS at different time points (pre, post, and at 6 months) for 2 subgroups from the total sample using a cut-off PS value of 4. For the EOR, a PS value of ≥5 was predictive of successful outcome, a value of 4 indicated an uncertain outcome, and a value of ≤3 predicted a worse outcome.

CONCLUSIONS

This PS value can be easily used in clinical settings to help predict the functional outcome and EOR in sensorimotor area tumors. Integration with information from fMRI, DTI, and TMS, along with MRI spectroscopy could further enhance the value of this PS.

Accuracy of Presurgical Functional MR Imaging for Language Mapping of Brain Tumors: A Systematic Review and Meta-Analysis

Purpose To compare functional magnetic resonance (MR) imaging for language mapping (hereafter, language functional MR imaging) with direct cortical stimulation (DCS) in patients with brain tumors and to assess factors associated with its accuracy. Materials and Methods PubMed/MEDLINE and related databases were searched for research articles published between January 2000 and September 2016. Findings were pooled by using bivariate random-effects and hierarchic summary receiver operating characteristic curve models. Meta-regression and subgroup analyses were performed to evaluate whether publication year, functional MR imaging paradigm, magnetic field strength, statistical threshold, and analysis software affected classification accuracy. Results Ten articles with a total of 214 patients were included in the analysis. On a per-patient basis, the pooled sensitivity and specificity of functional MR imaging was 44% (95% confidence interval [CI]: 14%, 78%) and 80% (95% CI: 54%, 93%), respectively. On a per-tag basis (ie, each DCS stimulation site or "tag" was considered a separate data point across all patients), the pooled sensitivity and specificity were 67% (95% CI: 51%, 80%) and 55% (95% CI: 25%, 82%), respectively. The per-tag analysis showed significantly higher sensitivity for studies with shorter functional MR imaging session times (P = .03) and relaxed statistical threshold (P = .05). Significantly higher specificity was found when expressive language task (P = .02), longer functional MR imaging session times (P < .01), visual presentation of stimuli (P = .04), and stringent statistical threshold (P = .01) were used. Conclusion Results of this study showed moderate accuracy of language functional MR imaging when compared with intraoperative DCS, and the included studies displayed significant methodologic heterogeneity. ^© RSNA, 2017 Online supplemental material is available for this article.

Language functional MRI and direct cortical stimulation in epilepsy preoperative planning

OBJECTIVE

Presurgical language assessment can help minimize damage to eloquent cortex during resective epilepsy surgery. Two methods for presurgical language mapping are functional MRI (fMRI) and direct cortical stimulation (DCS) of implanted subdural electrodes. We compared fMRI results to DCS to help optimize noninvasive language localization and assess its validity.

METHODS

We studied 19 patients referred for presurgical evaluation of drug-resistant epilepsy. Patients completed four language tasks during preoperative fMRI. After subdural electrode implantation, we used DCS to localize language areas. For each stimulation site, we determined whether language positive electrode pairs intersected with significant fMRI activity clusters for language tasks.

RESULTS

Sensitivity and specificity depended on electrode region of interest radii and statistical thresholding. For patients with at least one language positive stimulation site, an auditory description decision task provided the best trade-off between sensitivity and specificity. For patients with no language positive stimulation sites, fMRI was a dependable method of excluding eloquent language processing.

INTERPRETATION

Language fMRI is an effective tool for determining language lateralization before electrode implantation and is especially useful for excluding unexpected critical language areas. It can help guide subdural electrode implantation and narrow the search for eloquent cortical areas by DCS. Ann Neurol 2017;81:526-537.

Functional Magnetic Resonance Imaging for Preoperative Planning in Brain Tumour Surgery

BACKGROUND

Functional magnetic resonance imaging (fMRI) is being increasingly used for the preoperative evaluation of patients with brain tumours.

METHODS

The study is a retrospective chart review investigating the use of clinical fMRI from 2002 through 2013 in the preoperative evaluation of brain tumour patients. Baseline demographic and clinical data were collected. The specific fMRI protocols used for each patient were recorded.

RESULTS

Sixty patients were identified over the 12-year period. The tumour types most commonly investigated were high-grade glioma (World Health Organization grade III or IV), low-grade glioma (World Health Organization grade II), and meningioma. Most common presenting symptoms were seizures (69.6%), language deficits (23.2%), and headache (19.6%). There was a predominance of left hemispheric lesions investigated with fMRI (76.8% vs 23.2% for right). The most commonly involved lobes were frontal (64.3%), temporal (33.9%), parietal (21.4%), and insular (7.1%). The most common fMRI paradigms were language (83.9%), motor (75.0%), sensory (16.1%), and memory (10.7%). The majority of patients ultimately underwent a craniotomy (75.0%), whereas smaller groups underwent stereotactic biopsy (8.9%) and nonsurgical management (16.1%). Time from request for fMRI to actual fMRI acquisition was 3.1±2.3 weeks. Time from fMRI acquisition to intervention was 4.9±5.5 weeks.

CONCLUSIONS

We have characterized patient demographics in a retrospective single-surgeon cohort undergoing preoperative clinical fMRI at a Canadian centre. Our experience suggests an acceptable wait time from scan request to scan completion/analysis and from scan to intervention.