Should Complex Cognitive Functions Be Mapped With Direct Electrostimulation in Wide-Awake Surgery? A Network Perspective

Predictors of cognition after glioma surgery: connectotomy, structure-function phenotype, plasticity

Determining preoperatively the maximal extent of resection that would preserve cognitive functions is the core challenge of brain tumour surgery. Over the past decade, the methodological framework to achieve this goal has been thoroughly renewed: the population-level topographically-focused voxel-based lesion-symptom mapping has been progressively overshadowed by machine learning (ML) algorithmics, in which the problem is framed as predicting cognitive outcomes in a patient-specific manner from a typically large set of variables. However, the choice of these predictors is of utmost importance, as they should be both informative and parsimonious. In this perspective, we first introduce the concept of connectotomy: instead of parameterizing resection topography through the status (intact/resected) of a huge number of voxels (or parcels) paving the whole brain in the Cartesian 3D-space, the connectotomy models the resection in the connectivity space, by computing a handful number of networks disconnection indices, measuring how the structural connectivity sustaining each network of interest was hit by the resection. This connectivity-informed reduction of dimensionality is a necessary step for efficiently implementing ML tools, given the relatively small number of patient-examples in available training datasets. We further argue that two other major sources of interindividual variability must be considered to improve the accuracy with which outcomes are predicted: the underlying structure-function phenotype and neuroplasticity, for which we provide an in-depth review and propose new ways of determining relevant predictors. We finally discuss the benefits of our approach for precision surgery of glioma.

Systematic Review Between Resting-State fMRI and Task fMRI in Planning for Brain Tumour Surgery

As an alternative to task-based functional magnetic resonance imaging (T-fMRI), resting-state functional magnetic resonance imaging (Rs-fMRI) is suggested for preoperative mapping of patients with brain tumours, with an emphasis on treatment guidance and neurodegeneration prediction. A systematic review was conducted of 18 recent studies involving 1035 patients with brain tumours and Rs-fMRI protocols. This was accomplished by searching the electronic databases PubMed, Scopus, and Web of Science. For clinical benefit, we compared Rs-fMRI to standard T-fMRI and intraoperative direct cortical stimulation (DCS). The results of Rs-fMRI and T-fMRI were compared and their correlation with intraoperative DCS results was examined through a systematic review. Our exhaustive investigation demonstrated that Rs-fMRI is a dependable and sensitive preoperative mapping technique that detects neural networks in the brain with precision and identifies crucial functional regions in agreement with intraoperative DCS. Rs-fMRI comes in handy, especially in situations where T-fMRI proves to be difficult because of patient-specific factors. Additionally, our exhaustive investigation demonstrated that Rs-fMRI is a valuable tool in the preoperative screening and evaluation of brain tumours. Furthermore, its capability to assess brain function, forecast surgical results, and enhance decision-making may render it applicable in the clinical management of brain tumours.

An update on tests used for intraoperative monitoring of cognition during awake craniotomy

PURPOSE

Mapping higher-order cognitive functions during awake brain surgery is important for cognitive preservation which is related to postoperative quality of life. A systematic review from 2018 about neuropsychological tests used during awake craniotomy made clear that until 2017 language was most often monitored and that the other cognitive domains were underexposed (Ruis, J Clin Exp Neuropsychol 40(10):1081-1104, 218). The field of awake craniotomy and cognitive monitoring is however developing rapidly. The aim of the current review is therefore, to investigate whether there is a change in the field towards incorporation of new tests and more complete mapping of (higher-order) cognitive functions.

METHODS

We replicated the systematic search of the study from 2018 in PubMed and Embase from February 2017 to November 2023, yielding 5130 potentially relevant articles. We used the artificial machine learning tool ASReview for screening and included 272 papers that gave a detailed description of the neuropsychological tests used during awake craniotomy.

RESULTS

Comparable to the previous study of 2018, the majority of studies (90.4%) reported tests for assessing language functions (Ruis, J Clin Exp Neuropsychol 40(10):1081-1104, 218). Nevertheless, an increasing number of studies now also describe tests for monitoring visuospatial functions, social cognition, and executive functions.

CONCLUSIONS

Language remains the most extensively tested cognitive domain. However, a broader range of tests are now implemented during awake craniotomy and there are (new developed) tests which received more attention. The rapid development in the field is reflected in the included studies in this review. Nevertheless, for some cognitive domains (e.g., executive functions and memory), there is still a need for developing tests that can be used during awake surgery.

Structural networking of the developing brain: from maturation to neurosurgical implications

Modern neuroscience agrees that neurological processing emerges from the multimodal interaction among multiple cortical and subcortical neuronal hubs, connected at short and long distance by white matter, to form a largely integrated and dynamic network, called the brain "connectome." The final architecture of these circuits results from a complex, continuous, and highly protracted development process of several axonal pathways that constitute the anatomical substrate of neuronal interactions. Awareness of the network organization of the central nervous system is crucial not only to understand the basis of children's neurological development, but also it may be of special interest to improve the quality of neurosurgical treatments of many pediatric diseases. Although there are a flourishing number of neuroimaging studies of the connectome, a comprehensive vision linking this research to neurosurgical practice is still lacking in the current pediatric literature. The goal of this review is to contribute to bridging this gap. In the first part, we summarize the main current knowledge concerning brain network maturation and its involvement in different aspects of normal neurocognitive development as well as in the pathophysiology of specific diseases. The final section is devoted to identifying possible implications of this knowledge in the neurosurgical field, especially in epilepsy and tumor surgery, and to discuss promising perspectives for future investigations.

Dynamics in cognition and health-related quality of life in grade 2 and 3 gliomas after surgery

BACKGROUND

The focus of clinical management and research in gliomas has been on survival, but the interest in the treatment effects on cognition and health-related quality of life (HRQoL) is emerging. The primary aim of this study was to investigate the dynamics in cognition after brain tumor surgery for astrocytomas and oligodendrogliomas grade 2 and 3. The secondary aim was to investigate the association of postoperative changes in cognition with changes HRQoL.

METHODS

In this observational study, 48 patients operated for an astrocytoma or oligodendrogliomas, grade 2 or 3, at the Department of Neurosurgery, Uppsala, Sweden, 2016-2021, were included. Cognitive and language skills were assessed with a selected test battery and HRQoL was patient-reported as assessed with RAND-36 pre- and approximately 3 months postoperatively.

RESULTS

There was a significant postoperative decrease in attention span and verbal learning, but the patients improved in the test for visual memory. There was no change in visual attention, executive function, verbal memory, visual organization and construction, verbal fluency, and confrontation naming. The RAND-36 variables physical function, role physical, general health, vitality, and social functioning decreased significantly after surgery. Patients operated for tumor recurrence exhibited greater deterioration in attention and a greater extent of resection correlated with a less pronounced decrease in verbal memory, but there were otherwise weak associations between the dynamics in cognition and patient-, tumor-, and treatment-variables. A decline in cognitive variables was not associated with worse HRQoL.

CONCLUSIONS

Although both several cognitive and HRQoL domains deteriorated postoperatively, these changes did not correlate with each other. This highlights the complexity of cognitive and HRQoL dynamics in the early postoperative phase.

Frontal aslant tract in the non-dominant hemisphere: A systematic review of anatomy, functions, and surgical applications

Knowledge of both the spatial organization and functions of white-matter fiber tracts is steadily increasing. We report here the anatomy and functions of the frontal aslant tract (FAT) in the non-dominant hemisphere (usually the right hemisphere). Despite the structural symmetry between the right and left FAT, these two tracts seem to display functional asymmetry, with several brain functions in common, but others, such as visuospatial and social cognition, music processing, shifting attention or working memory, more exclusively associated with the right FAT. Further studies are required to determine whether damage to the right FAT causes permanent cognitive impairment. Such studies will constitute the best means of testing whether this tract is a critical pathway that must be taken into account during neurosurgical procedures and the essential tasks to be incorporated into intraoperative monitoring during awake craniotomy.

Group-level stability but individual variability of neurocognitive status after awake resections of right frontal IDH-mutated glioma

Awake surgery for low-grade gliomas is currently considered the best procedure to improve the extent of resection and guarantee a "worth living life" for patients, meaning avoiding not only motor but also cognitive deficits. However, tumors located in the right hemisphere, especially in the right frontal lobe, are still rarely operated on in awake condition; one of the reasons possibly being that there is little information in the literature describing the rates and nature of long-lasting neuropsychological deficits following resection of right frontal glioma. To investigate long-term cognitive deficits after awake surgery in right frontal IDH-mutated glioma. We retrospectively analyzed a consecutive series of awake surgical resections between 2012 and 2020 for right frontal IDH-mutated glioma. We studied the patients' subjective complaints and objective neuropsychological evaluations, both before and after surgery. Our results were then put in perspective with the literature. Twenty surgical cases (including 5 cases of redo surgery) in eighteen patients (medium age: 42.5 [range 26-58]) were included in the study. The median preoperative volume was 37 cc; WHO grading was II, III and IV in 70%, 20%, and 10% of cases, respectively. Preoperatively, few patients had related subjective cognitive or behavioral impairment, while evaluations revealed mild deficits in 45% of cases, most often concerning executive functions, attention, working memory and speed processing. Immediate postoperative evaluations showed severe deficits of executive functions in 75% of cases but also attentional deficits (65%), spatial neglect (60%) and behavioral disturbances (apathy, aprosodia/amimia, emotional sensitivity, anosognosia). Four months after surgery, although psychometric z-scores were unchanged at the group level, individual evaluations showed a slight decrease of performance in 9/20 cases for at least one of the following domains: executive functions, speed processing, attention, semantic cognition, social cognition. Our results are generally consistent with those of the literature, confirming that the right frontal lobe is a highly eloquent area and suggesting the importance of operating these patients in awake conditions.

Subcortical Stimulation in Brain Tumor Surgery: A closer look beneath the surface

INTRODUCTION

Maximizing a patient's onco-functional balance is the central tenet of brain tumor surgery. As a result, numerous surgical adjuncts have been developed to facilitate identification of the tumor-brain interface and preservation of functional anatomy. Among these, intraoperative neurophysiologic monitoring (IONM) with direct cortical and subcortical stimulation remains the gold standard for real time, functional mapping of motor and language activity. However, stimulation techniques are not standardized and vary significantly across institutions. This is particularly true with subcortical stimulation for mapping of motor function.

METHODS

We review the state of subcortical IONM and mapping techniques. Historical and predicate literature were reviewed as well as new and emerging techniques. We discuss their evolution, clinical utility, and limitations to direct future research and application.

RESULTS

We evaluate and discuss the background and current clinical use of direct cortical and subcortical stimulation techniques and protocols and identify current trends and limitations. We focus specifically on methods of subcortical stimulation given the heterogeneity in the published literature. We also suggest directions to optimize the clinical utility of these tools.

CONCLUSION

Despite significant heterogeneity in published techniques, trends support the use of the Taniguchi method for subcortical stimulation. Novel dynamic stimulation techniques may improve accuracy. Prospective studies to define standardized guidelines are needed.

Eigenvector PageRank difference as a measure to reveal topological characteristics of the brain connectome for neurosurgery

PURPOSE

Applying graph theory to the human brain has the potential to help prognosticate the impacts of intracerebral surgery. Eigenvector (EC) and PageRank (PR) centrality are two related, but uniquely different measures of nodal centrality which may be utilized together to reveal varying neuroanatomical characteristics of the brain connectome.

METHODS

We obtained diffusion neuroimaging data from a healthy cohort (UCLA consortium for neuropsychiatric phenomics) and applied a personalized parcellation scheme to them. We ranked parcels based on weighted EC and PR, and then calculated the difference (EP difference) and correlation between the two metrics. We also compared the difference between the two metrics to the clustering coefficient.

RESULTS

While EC and PR were consistent for top and bottom ranking parcels, they differed for mid-ranking parcels. Parcels with a high EC centrality but low PR tended to be in the medial temporal and temporooccipital regions, whereas PR conferred greater importance to multi-modal association areas in the frontal, parietal and insular cortices. The EP difference showed a weak correlation with clustering coefficient, though there was significant individual variation.

CONCLUSIONS

The relationship between PageRank and eigenvector centrality can identify distinct topological characteristics of the brain connectome such as the presence of unimodal or multimodal association cortices. These results highlight how different graph theory metrics can be used alone or in combination to reveal unique neuroanatomical features for further clinical study.

Polarimetric visualization of healthy brain fiber tracts under adverse conditions: ex vivo studies

We suggest using the wide-field imaging Mueller polarimetry to contrast optically anisotropic fiber tracts of healthy brain white matter for the detection of brain tumor borders during neurosurgery. Our prior studies demonstrate that this polarimetric imaging modality detects correctly the in-plane orientation of brain white matter fiber tracts of a flat formalin-fixed thick brain specimen in reflection geometry [IEEE Trans. Med. Imaging39, 4376 (2020)10.1109/TMI.2020.3018439]. Here we present the results of ex vivo polarimetric studies of large cross-sections of fresh calf brain in reflection geometry with a special focus on the impact of the adverse measurement conditions (e.g. complex surface topography, presence of blood, etc.) on the quality of polarimetric images and the detection performance of white matter fiber tracts and their in-plane orientation.

Disrupting self-evaluative processing with electrostimulation mapping during awake brain surgery

Brain awake surgery with cognitive monitoring for tumor removal has become a standard of treatment for functional purpose. Yet, little attention has been given to patients' interpretation and awareness of their own responses to selected cognitive tasks during direct electrostimulation (DES). We aim to report disruptions of self-evaluative processing evoked by DES during awake surgery. We further investigate cortico-subcortical structures involved in self-assessment process and report the use of an intraoperative self-assessment tool, the self-confidence index (SCI). Seventy-two patients who had undergone awake brain tumor resections were selected. Inclusion criteria were the occurrence of a DES-induced disruption of an ongoing task followed by patient's failure to remember or criticize these impairments, or a dissociation between patient's responses to an ongoing task and patient's SCI. Disruptions of self-evaluation were frequently associated with semantic disorders and critical sites were mostly found along the left/right ventral semantic streams. Disconnectome analyses generated from a tractography-based atlas confirmed the high probability of the inferior fronto-occipital fasciculus to be transitory 'disconnected'. These findings suggest that white matters pathways belonging to the ventral semantic stream may be critically involved in human self-evaluative processing. Finally, the authors discuss the implementation of the SCI task during multimodal intraoperative monitoring.