Preoperative mapping techniques for brain tumor surgery: a systematic review

Accurate preoperative mapping is crucial for maximizing tumor removal while minimizing damage to critical brain functions during brain tumor surgery. Navigated transcranial magnetic stimulation (nTMS), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI) are established methods for assessing motor and language function. Following PRISMA guidelines, this systematic review analyzes the reliability, clinical utility, and accessibility of these techniques. A total of 128 studies (48 nTMS, 56 fMRI, 24 MEG) were identified from various databases. The analysis finds nTMS to be a safe, standardized method with high accuracy compared to direct cortical stimulation for preoperative motor mapping. Combining nTMS with tractography allows for preoperative assessment of short-term and long-term motor deficits, which may not be possible with fMRI. fMRI data interpretation requires careful consideration of co-activated, non-essential areas (potentially leading to false positives) and situations where neural activity and blood flow are uncoupled (potentially leading to false negatives). These limitations restrict fMRI's role in preoperative planning for both motor and language functions. While MEG offers high accuracy in motor mapping, its high cost and technical complexity contribute to the limited number of available studies. Studies comparing preoperative language mapping techniques with direct cortical stimulation show significant variability across all methods, highlighting the need for larger, multicenter studies for validation. Repetitive nTMS speech mapping offers valuable negative predictive value, allowing clinicians to evaluate whether a patient should undergo awake or asleep surgery. Language function monitoring heavily relies on the specific expertise and experience available at each center, making it challenging to establish general recommendations.

Intraoperative DBS targeting of the globus pallidus internus by using motor evoked potentials

OBJECTIVES

Target localization for deep brain stimulation (DBS) is a crucial step that influences the clinical benefit of the DBS procedure together with the reduction of side effects. In this work, we address the feasibility of DBS target localization in the globus pallidus internus (GPi) aided by intraoperative motor evoked potentials (MEP) with emphasis on the reduction of capsular side effects.

MATERIAL AND METHODS

Micro-macroelectrode recordings were performed intraoperatively on 20 patients that underwent DBS treatment of the GPi (GPi-DBS). MEP were elicited intraoperatively by microelectrode stimulation during stereotactic DBS surgery. We studied the relationship between MEP thresholds and the internal capsule (IC) proximity.

RESULTS

We found a significant correlation between intraoperative MEP thresholds and IC proximity.

CONCLUSIONS

We provide further evidence of the role of MEPs for DBS target localization in the GPi, which extends and confirms the usefulness of MEPs as previously reported by DBS target localization studies dealing with the subthalamic and thalamic nuclei. Our approach is advantageous in that it provides criteria to determine the DBS target without the need to rely on a patient's response while avoiding capsular effects.

NTMS based tractography and segmental diffusion analysis in patients with brainstem gliomas: Risk stratification and clinical potential

Introduction

Surgery on the brainstem level is associated with a high-risk of postoperative morbidity. Recently, we have introduced the combination of navigated transcranial magnetic stimulation (nTMS) and diffusion tensor imaging (DTI) tractography to define functionally relevant motor fibers tracts on the brainstem level to support operative planning and risk stratification in brainstem cavernomas.

Research question

Evaluate this method and assess it's clinical impact for the surgery of brainstem gliomas.

Material and methods

Patients with brainstem gliomas were examined preoperatively with motor nTMS and DTI tractography. A fractional anisotropy (FA) value of 75% of the individual FA threshold (FAT) was used to track descending corticospinal (CST) and -bulbar tracts (CBT). The distance between the tumor and the somatotopic tracts (hand, leg, face) was measured and diffusion parameters were correlated to the patients' outcome.

Results

12 patients were enrolled in this study, of which 6 underwent surgical resection, 5 received a stereotactic biopsy and 1 patient received conservative treatment. In all patients nTMS mapping and somatotopic tractography were performed successfully. Low FA values correlated with clinical symptoms revealing tract alteration by the tumor (p = 0.049). A tumor-tract distance (TTD) above 2 mm was the critical limit to achieve a safe complete tumor resection.

Discussion and conclusion

nTMS based DTI tractography combined with local diffusion analysis is a valuable tool for preoperative visualization and functional assessment of relevant motor fiber tracts, improving planning of safe entry corridors and perioperative risk stratification in brainstem gliomas tumors. This technique allows for customized treatment strategy to maximize patients' safety.

Navigated Transcranial Magnetic Stimulation Motor Mapping and Diffusion Tensor Imaging Tractography for Diencephalic Tumor in Pediatric Patients

Background. In deep-seated brain tumors, adequate preoperative planning is mandatory to assess the best surgical corridor to obtain maximal safe resection. Functional diffusor tensor imaging (DTI) tractography based on navigated transcranial magnetic stimulation (nTMS) motor mapping has proven to be a valid preoperative examination method in adults. The aim of this paper is to present the application of nTMS and functional DTI tractography in a series of pediatric diencephalic tumors. Material and methods. Three patients affected by thalamic (one) and thalamopeduncular tumor (two) were successfully examined with nTMS motor mapping and DTI tractography between October 2020 and October 2021 (F:M 3:0, mean age 12 years ± 0.8). Cortical representation of leg, hand and mouth were determined in the affected hemisphere and the positive stimulation spots were set as seeds point for tractography. Results. Mapping of the motor cortex and tracts reconstruction for leg and hand were successful in all patients, while facial function was properly mapped in one patient only. In all cases, the procedure was well tolerated and no adverse events were recorded. Spatial relationships between tumor and functional tissue guided the surgical planning. Extent of the resection varied from 96.1% to 100% with a postoperative new motor deficit in one patient. Conclusions. nTMS and DTI fiber tracking is a feasible, effective and well-tolerated method to identify motor pathway in deep-seated lesion in pediatric population.

[Tractography in functional neuronavigation]

The review addresses the combined use of tractography and neuronavigation. Fundamentals of diffusion tensor imaging are given, technical aspects of fiber tracking in general and in depicting separate subcortical tracts are described. Main advantages of the method and possible causes of errors are highlighted. Precision assessment of this technology is given by comparing with results of subcortical neurostimulation. Surgical tactics is described depending on distance between the tumor and subcortical pathways.

Basis for error in stereotactic and computer-assisted surgery in neurosurgical applications: literature review

Technological advancements in optoelectronic motion capture systems have allowed for the development of high-precision computer-assisted surgery (CAS) used in cranial and spinal surgical procedures. Errors generated sequentially throughout the chain of components of CAS may have cumulative effect on the accuracy of implant and instrumentation placement - potentially affecting patient outcomes. Navigational integrity and maintenance of fidelity of optoelectronic data is the cornerstone of CAS. Error reporting measures vary between studies. Understanding error generation, mechanisms of propagation, and how they relate to workflow can assist clinicians in error mitigation and improve accuracy during navigation in neurosurgical procedures. Diligence in planning, fiducial positioning, system registration, and intra-operative workflow have the potential to improve accuracy and decrease disparity between planned and final instrumentation and implant position. This study reviews the potential errors associated with each step in computer-assisted surgery and provides a basis for disparity in intrinsic accuracy versus achieved accuracy in the clinical operative environment.

Motor evoked potentials versus Macrostimulation in predicting the postoperative motor threshold in STN Deep brain stimulation

INTRODUCTION

Accuracy is crucial in Deep Brain Stimulation (DBS). Electrophysiological and image-based techniques are used to avoid suboptimal positioning. Macrostimulation is the gold standard to delineate the therapeutic window intraoperatively. Despite this, electrode revision rates due to malpositioning are as high as 17%. The goal was to compare motor evoked potentials (MEPs) with the gold standard of Macrostimulation. We assessed accuracy and precision as well as the correlation in predicting motor side effects at the initial mapping 4 weeks postoperatively.

METHODS

In this prospective study intraoperative MEPs from 94 contacts in 16 patients undergoing STN DBS under local anesthesia were correlated to the postoperative threshold for stimulation-induced motor side effects and compared to intraoperative Macrostimulation. Analysis of accuracy, precision and correlation (Pearson) was performed.

RESULTS

MEPs of the upper extremity had a mean percentage error of 25% (SD 38.8%) and correlated significantly with the motor threshold at postoperative mapping (R=0.235). Macrostimulation was less accurate and precise with a mean percentage error of - 68% (SD 78.8%) but had a higher correlation (R=0.388). MEPs rarely (3%) overestimated the threshold by maximally 1 mA. In contrast, Macrostimulation overestimated the threshold by over 1 mA in 69% leading to a false sense of security.

CONCLUSION

MEPs are feasible in an awake setting during Deep Brain Stimulation in the STN for PD patients. MEPs of the upper extremity are more accurate and precise predicting the motor threshold and avoid a false sense of security in comparison to the gold standard of Macrostimulation.

Comparison of the interactions of flupyrimin and nitenpyram with serum albumins via multiple analysis methods

Flupyrimin and nitenpyram are emerging neonicotinoid insecticides that may cause potential harm to the human body. In the present work, the interactions of flupyrimin/nitenpyram with serum albumins under normal physiological conditions were thoroughly studied by using multiple spectroscopic techniques, DFT calculations and molecular docking. Flupyrimin/nitenpyram can quench the endogenous fluorescence of HSA/BSA and form a complex with HSA/BSA through a static process, causing conformational and secondary structure changes of HSA/BSA. Thermodynamic analysis shows that the combination of flupyrimin/nitenpyram with HSA/BSA is a spontaneous process, mainly driven by hydrogen bonds and hydrophobic forces. Site marking and molecular docking experiments indicated that flupyrimin/nitenpyram binds with HSA/BSA at site II (subdomain IIIA). The binding constant K_a in HSA-flupyrimin, HSA-nitenpyram, BSA-flupyrimin and BSA-nitenpyram systems at 298 K was 2.11 × 10⁵ M^-1, 2.35 × 10⁵ M^-1, 1.91 × 10⁵ M^-1 and 2.11 × 10⁵ M^-1, respectively. The binding constant K_a of nitenpyram with HSA/BSA was greater than flupyrimin, indicating that nitenpyram binds HSA/BSA was more stable than that of flupyrimin, which was consistent with the DFT calculation. In addition, the acute toxicity bioassay showed that flupyrimin and nitenpyram exhibited low toxicity to zebrafish, with 96 h LC₅₀ values of 181.662 and 250.658 mg a. i. L^-1, respectively. These results can help understand the interactions of flupyrimin/nitenpyram with HSA/BSA.

Bicentric validation of the navigated transcranial magnetic stimulation motor risk stratification model

OBJECTIVE

The authors sought to validate the navigated transcranial magnetic stimulation (nTMS)-based risk stratification model. The postoperative motor outcome in glioma surgery may be preoperatively predicted based on data derived by nTMS. The tumor-to-tract distance (TTD) and the interhemispheric resting motor threshold (RMT) ratio (as a surrogate parameter for cortical excitability) emerged as major factors related to a new postoperative deficit.

METHODS

In this bicentric study, a consecutive prospectively collected cohort underwent nTMS mapping with diffusion tensor imaging (DTI) fiber tracking of the corticospinal tract prior to surgery of motor eloquent gliomas. The authors analyzed whether the following items were associated with the patient's outcome: patient characteristics, TTD, RMT value, and diffusivity parameters (fractional anisotropy [FA] and apparent diffusion coefficient [ADC]). The authors assessed the validity of the published risk stratification model and derived a new model.

RESULTS

A new postoperative motor deficit occurred in 36 of 165 patients (22%), of whom 20 patients still had a deficit after 3 months (13%; n3 months = 152). nTMS-verified infiltration of the motor cortex as well as a TTD ≤ 8 mm were confirmed as risk factors. No new postoperative motor deficit occurred in patients with TTD > 8 mm. In contrast to the previous risk stratification, the RMT ratio was not substantially correlated with the motor outcome, but high RMT values of both the tumorous and healthy hemisphere were associated with worse motor outcome. The FA value was negatively associated with worsening of motor outcome. Accuracy analysis of the final model showed a high negative predictive value (NPV), so the preoperative application may accurately predict the preservation of motor function in particular (day of discharge: sensitivity 47.2%, specificity 90.7%, positive predictive value [PPV] 58.6%, NPV 86.0%; 3 months: sensitivity 85.0%, specificity 78.8%, PPV 37.8%, NPV 97.2%).

CONCLUSIONS

This bicentric validation analysis further improved the model by adding the FA value of the corticospinal tract, demonstrating the relevance of nTMS/nTMS-based DTI fiber tracking for clinical decision making.

Motor Evoked Potential Recordings During Segmented Deep Brain Stimulation-A Feasibility Study

BACKGROUND

Segmented deep brain stimulation (DBS) leads, which are capable of steering current in the direction of any 1 of 3 segments, can result in a wider therapeutic window by directing current away from unintended structures, particularly, the corticospinal tract (CST). It is unclear whether the use of motor evoked potentials (MEPs) is feasible during DBS surgery via stimulation of individual contacts/segments in order to quantify CST activation thresholds and optimal contacts/segments intraoperatively.

OBJECTIVE

To assess the feasibility of using MEP to identify CST thresholds for ring and individual segments of the DBS lead under general anesthesia.

METHODS

MEP testing was performed during pulse generator implantation under general anesthesia on subjects who underwent DBS lead implantation into the subthalamic nucleus (STN). Stimulation of each ring and segmented contacts of the directional DBS lead was performed until CST threshold was reached. Stereotactic coordinates and thresholds for each contact/segment were recorded along with the initially activated muscle group.

RESULTS

A total of 34 hemispheres were included for analysis. MEP thresholds were recorded from 268 total contacts/segments. For segmented contacts (2 and 3, respectively), the mean highest CST thresholds were 2.33 and 2.62 mA, while the mean lowest CST thresholds were 1.7 and 1.89 mA, suggesting differential thresholds in relation to CST. First dorsal interosseous and abductor pollicis brevis (34% each) were the most commonly activated muscle groups.

CONCLUSION

MEP threshold recording from segmented DBS leads is feasible. MEP recordings can identify segments with highest CST thresholds and may identify segment orientation in relation to CST.

Preoperative nTMS and Intraoperative Neurophysiology - A Comparative Analysis in Patients With Motor-Eloquent Glioma

Background

The resection of a motor-eloquent glioma should be guided by intraoperative neurophysiological monitoring (IOM) but its interpretation is often difficult and may (unnecessarily) lead to subtotal resection. Navigated transcranial magnetic stimulation (nTMS) combined with diffusion-tensor-imaging (DTI) is able to stratify patients with motor-eloquent lesion preoperatively into high- and low-risk cases with respect to a new motor deficit.

Objective

To analyze to what extent preoperative nTMS motor risk stratification can improve the interpretation of IOM phenomena.

Methods

In this monocentric observational study, nTMS motor mapping with DTI fiber tracking of the corticospinal tract was performed before IOM-guided surgery for motor-eloquent gliomas in a prospectively collected cohort from January 2017 to October 2020. Descriptive analyses were performed considering nTMS data (motor cortex infiltration, resting motor threshold (RMT), motor evoked potential (MEP) amplitude, latency) and IOM data (transcranial MEP monitoring, intensity of monopolar subcortical stimulation (SCS), somatosensory evoked potentials) to examine the association with the postoperative motor outcome (assessed at day of discharge and at 3 months).

Results

Thirty-seven (56.1%) of 66 patients (27 female) with a median age of 48 years had tumors located in the right hemisphere, with glioblastoma being the most common diagnosis with 39 cases (59.1%). Three patients (4.9%) had a new motor deficit that recovered partially within 3 months and 6 patients had a persistent deterioration (9.8%). The more risk factors of the nTMS risk stratification model (motor cortex infiltration, tumor-tract distance (TTD) ≤8mm, RMT_ratio <90%/>110%) were detected, the higher was the risk for developing a new postoperative motor deficit, whereas no patient with a TTD >8mm deteriorated. Irreversible MEP amplitude decrease >50% was associated with worse motor outcome in all patients, while a MEP amplitude decrease ≤50% or lower SCS intensities ≤4mA were particularly correlated with a postoperative worsened motor status in nTMS-stratified high-risk cases. No patient had postoperative deterioration of motor function (except one with partial recovery) when intraoperative MEPs remained stable or showed only reversible alterations.

Conclusions

The preoperative nTMS-based risk assessment can help to interpret ambiguous IOM phenomena (such as irreversible MEP amplitude decrease ≤50%) and adjustment of SCS stimulation intensity.

Motor Evoked Potentials Improve Targeting in Deep Brain Stimulation Surgery

OBJECTIVES

One of the main challenges posed by the surgical deep brain stimulation (DBS) procedure is the successful targeting of the structures of interest and avoidance of side effects, especially in asleep surgery. Here, intraoperative motor evoked potentials (MEPs) might serve as tool to identify the pyramidal tract. We hypothesized that intraoperative MEPs are useful to define the distance to the pyramidal tract and reduce the occurrence of postoperative capsular side effects.

MATERIALS AND METHODS

Motor potentials were evoked through both microelectrode and DBS-electrode stimulation during stereotactic DBS surgery on 25 subthalamic nuclei and 3 ventral intermediate thalamic nuclei. Internal capsule proximity was calculated for contacts on microelectrode trajectories, as well as for DBS-electrodes, and correlated with the corresponding MEP thresholds. Moreover, the predictivity of intraoperative MEP thresholds on the probability of postoperative capsular side effects was calculated.

RESULTS

Intraoperative MEPs thresholds correlated significantly with internal capsule proximity, regardless of the stimulation source. Furthermore, MEPs thresholds were highly accurate to exclude the occurrence of postoperative capsular side effects.

CONCLUSIONS

Intraoperative MEPs provide additional targeting guidance, especially in asleep DBS surgery, where clinical value of microelectrode recordings and test stimulation may be limited. As this technique can exclude future capsular side effects, it can directly be translated into clinical practice.

Pediatric navigated transcranial magnetic stimulation motor and language mapping combined with diffusion tensor imaging tractography: clinical experience

OBJECTIVE

In adults, navigated transcranial magnetic stimulation (nTMS) has been established as a preoperative examination method for brain tumors in motor- and language-eloquent locations. However, the clinical relevance of nTMS in children with brain tumors is still unclear. Here, the authors present their initial experience with nTMS-based surgical planning and family counseling in pediatric cases.

METHODS

The authors analyzed the feasibility of nTMS and its influence on counseling and surgical strategy in a prospective study conducted between July 2017 and September 2019. The main inclusion criterion was a potential benefit from functional mapping data derived from nTMS and/or nTMS-enhanced tractography in pediatric patients who presented to the authors' department prior to surgery for lesions close to motor- and/or speech-eloquent areas. The study was undertaken in 14 patients (median age 7 years, 8 males) who presented with different brain lesions.

RESULTS

Motor mapping combined with cortical seed area definition could be performed in 10 children (71%) to identify the corticospinal tract by additional diffusion tensor imaging (DTI). All motor mappings could be performed successfully without inducing relevant side effects. In 7 children, nTMS language mapping was performed to detect language-relevant cortical areas and DTI fiber tractography was performed to visualize the individual language network. nTMS examination was not possible in 4 children because of lack of compliance (n = 2), syncope (n = 1), and preexisting implant (n = 1). After successful mapping, the spatial relation between lesion and functional tissue was used for surgical planning in all 10 patients, and 9 children underwent nTMS-DTI integrated neuronavigation. No surgical complications or unexpected neurological deterioration was observed. In all successful nTMS cases, better function-based counseling was offered to the families. In 6 of 10 patients the surgical strategy was adapted according to nTMS data, and in 6 of 10 cases the extent of resection (EOR) was redefined.

CONCLUSIONS

nTMS and DTI fiber tracking were feasible for the majority of children. Presurgical counseling as well as surgical planning for the approach and EOR were improved by the nTMS examination results. nTMS in combination with DTI fiber tracking can be regarded as beneficial for neurosurgical procedures in eloquent areas in the pediatric population.

The value of diffusion tensor tractography delineating corticospinal tract in glioma in rat: validation via correlation histology

Background

An assessment of the degree of white matter tract injury is important in neurosurgical planning for patients with gliomas. The main objective of this study was to assess the injury grade of the corticospinal tract (CST) in rats with glioma using diffusion tensor imaging (DTI).

Methods

A total 17 rats underwent 7.0T MRI on day 10 after tumor implantation. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were acquired in the tumor, peritumoral and contralateral areas, and the ADC ratio (ipsilateral ADC/contralateral ADC) and rFA (relative FA = ipsilateral FA/contralateral FA) in the peritumoral areas were measured. The CST injury was divided into three grades and delineated by diffusion tensor tractography reconstruction imaging. The fiber density index (FDi) of the ipsilateral and contralateral CST and rFDi (relative FDi = ipsilateral FDi/contralateral FDi) in the peritumoral areas were measured. After the mice were sacrificed, the invasion of glioma cells and fraction of proliferating cells were observed by hematoxylin-eosin and Ki67 staining in the tumor and peritumoral areas. The correlations among the pathology results, CST injury grade and DTI parameter values were calculated using a Spearman correlation analysis. One-way analysis of variance was performed to compare the different CST injury grade by the rFA, rFDi and ADC ratio values.

Results

The tumor cells and proliferation index were positively correlated with the CST injury grade (r = 0.8857, 0.9233, P < 0.001). A negative correlation was demonstrated between the tumor cells and the rFA and rFDi values in the peritumoral areas (r = −0.8571, −0.5588), and the proliferation index was negatively correlated with the rFA and rFDi values (r = −0.8571, −0.5588), while the ADC ratio was not correlated with the tumor cells or proliferation index. The rFA values between the CST injury grades (1 and 3, 2 and 3) and the rFDi values in grades 1 and 3 significantly differed (P < 0.05).

Conclusions

Diffusion tensor imaging may be used to quantify the injury degrees of CST involving brain glioma in rats. Our data suggest that these quantitative parameters may be used to enhance the efficiency of delineating the relationship between fiber tracts and malignant tumor.

Targeted neural network interventions for auditory hallucinations: Can TMS inform DBS?

The debilitating and refractory nature of auditory hallucinations (AH) in schizophrenia and other psychiatric disorders has stimulated investigations into neuromodulatory interventions that target the aberrant neural networks associated with them. Internal or invasive forms of brain stimulation such as deep brain stimulation (DBS) are currently being explored for treatment-refractory schizophrenia. The process of developing and implementing DBS is limited by symptom clustering within psychiatric constructs as well as a scarcity of causal tools with which to predict response, refine targeting or guide clinical decisions. Transcranial magnetic stimulation (TMS), an external or non-invasive form of brain stimulation, has shown some promise as a therapeutic intervention for AH but remains relatively underutilized as an investigational probe of clinically relevant neural networks. In this editorial, we propose that TMS has the potential to inform DBS by adding individualized causal evidence to an evaluation processes otherwise devoid of it in patients. Although there are significant limitations and safety concerns regarding DBS, the combination of TMS with computational modeling of neuroimaging and neurophysiological data could provide critical insights into more robust and adaptable network modulation.

Surgery of language-eloquent tumors in patients not eligible for awake surgery: the impact of a protocol based on navigated transcranial magnetic stimulation on presurgical planning and language outcome, with evidence of tumor-induced intra-hemispheric plasticity

OBJECTIVES

Awake surgery and intraoperative monitoring represent the gold standard for surgery of brain tumors located in the perisylvian region of the dominant hemisphere due to their ability to map and preserve the language network during surgery. Nevertheless, in some cases awake surgery is not feasible. This could increase the risk of postoperative language deficit. Navigated transcranial magnetic stimulation (nTMS) and nTMS-based DTI fiber tracking (DTI-FT) provide a preoperative mapping and reconstruction of the cortico-subcortical language network. This can be used to plan and guide the surgical strategy to preserve the language function. The objective if this study is to describe the impact of a non-invasive preoperative protocol for mapping the language network through the nTMS and nTMS-based DTI-FT in patients not eligible for awake surgery and thereby operated under general anesthesia for suspected language-eloquent brain tumors.

PATIENTS AND METHODS

We reviewed clinical data of patients not eligible for awake surgery and operated under general anaesthesia between 2015 and 2016. All patients underwent nTMS language cortical mapping and nTMS-based DTI-FT of subcortical language fascicles. The nTMS findings were used to plan and guide the maximal safe resection of the tumor. The impact on postoperative language outcome and the accuracy of the nTMS-based mapping in predicting language deficits were evaluated.

RESULTS

Twenty patients were enrolled in the study. The nTMS-based reconstruction of the language network was successful in all patients. Interestingly, we observed a significant association between tumor localization and the cortical distribution of the nTMS errors (p = 0.004), thereby suggesting an intra-hemispheric plasticity of language cortical areas, probably induced by the tumor itself. The nTMS mapping disclosed the true-eloquence of lesions in 12 (60%) of all suspected cases. In the remaining 8 cases (40%) the suspected eloquence of the lesion was disproved. The nTMS-based findings guided the planning and surgery through the visual feedback of navigation. This resulted in a slight reduction of the postoperative language performance at discharge that was completely recovered after one month from surgery. The accuracy of the nTMS-based protocol in predicting postoperative permanent deficits was significantly high, especially for false-eloquent lesions (p = 0.04; sensitivity 100%, specificity 57.14%, negative predictive value 100%, positive predicitive value 50%).

CONCLUSIONS

The nTMS-based preoperative mapping allows for a reliable visualization of the language network, being also able to identify an intra-hemispheric tumor-induced cortical plasticity. It allows for a customized surgical strategy that could preserve post-operative language function. This approach should be considered as a support for neurosurgeons whenever approaching patients affected by suspected language-eloquent tumors but not eligible for awake surgery.

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level.

The Impact of Diffusion Tensor Imaging Fiber Tracking of the Corticospinal Tract Based on Navigated Transcranial Magnetic Stimulation on Surgery of Motor-Eloquent Brain Lesions

BACKGROUND

Navigated transcranial magnetic stimulation (nTMS) enables preoperative mapping of the motor cortex (M1). The combination of nTMS with diffusion tensor imaging fiber tracking (DTI-FT) of the corticospinal tract (CST) has been described; however, its impact on surgery of motor-eloquent lesions has not been addressed.

OBJECTIVE

To analyze the impact of nTMS-based mapping on surgery of motor-eloquent lesions.

METHODS

In this retrospective case-control study, we reviewed the data of patients operated for suspected motor-eloquent lesions between 2012 and 2015. The patients underwent nTMS mapping of M1 and, from 2014, nTMS-based DTI-FT of the CST. The impact on the preoperative risk/benefit analysis, surgical strategy, craniotomy size, extent of resection (EOR), and outcome were compared with a control group.

RESULTS

We included 35 patients who underwent nTMS mapping of M1 (group A), 35 patients who also underwent nTMS-based DTI-FT of the CST (group B), and a control group composed of 35 patients treated without nTMS (group C). The patients in groups A and B received smaller craniotomies (P = .01; P = .001), had less postoperative seizures (P = .02), and a better postoperative motor performance (P = .04) and Karnofsky Performance Status (P = .009) than the controls. Group B exhibited an improved risk/benefit analysis (P = .006), an increased EOR of nTMS-negative lesions in absence of preoperative motor deficits (P = .01), and less motor and Karnofsky Performance Status worsening in case of preoperative motor deficits (P = .02, P = .03) than group A.

CONCLUSION

nTMS-based mapping enables a tailored surgical approach for motor-eloquent lesions. It may improve the risk/benefit analysis, EOR and outcome, particularly when nTMS-based DTI-FT is performed.

Predicting brain tumor regrowth in relation to motor areas by functional brain mapping

Background

Due to frequent recurrences, high-grade gliomas still confer a poor prognosis. Several regrowth prediction models have been developed, but most of these models are based on cellular models or dynamic mathematical calculations, thus limiting direct clinical use. The present study aims to evaluate whether navigated transcranial magnetic stimulation (nTMS) or functional magnetic resonance imaging (fMRI) may be used to predict the direction of tumor regrowth.

Methods

Sixty consecutive patients with high-grade gliomas were enrolled prospectively and analyzed in a case-control design after tumor recurrence. All patients underwent serial MRI after surgery and suffered from recurrent tumors during a mean follow-up of 13.2 ± 14.9 months. Tumor regrowth speed and direction were measured in relation to motor areas defined by nTMS, nTMS-based tractography, and fMRI. Depending on initial resection, patients were separated into three groups (group 1: without residual tumor, group 2: residual tumor away from motor areas, and group 3: residual tumor facing motor areas).

Results

Sixty-nine percent of patients in group 1, 64.3% in group 2, and 66.7% in group 3 showed tumor recurrence towards motor eloquence on contrast-enhanced T1-weighted sequences (P = .9527). Average growth towards motor areas on contrast-enhanced T1-weighted sequences was 0.6 ± 1.5 (group 1), 0.6 ± 2.4 (group 2), and 2.3 ± 5.5 (group 3) mm/month (P = .0492).

Conclusion

This study suggests a new strategy to predict tumor regrowth patterns in high-grade glioma patients. Our approach could be directly applied in the clinical setting, thus having clinical impact on both surgical treatment and radiotherapy planning.

Ethics Committee Registration Number

2793/10.

Specific DTI seeding and diffusivity-analysis improve the quality and prognostic value of TMS-based deterministic DTI of the pyramidal tract

Object

Navigated transcranial magnetic stimulation (nTMS) combined with diffusion tensor imaging (DTI) is used preoperatively in patients with eloquent-located brain lesions and allows analyzing non-invasively the spatial relationship between the tumor and functional areas (e.g. the motor cortex and the corticospinal tract [CST]). In this study, we examined the diffusion parameters FA (fractional anisotropy) and ADC (apparent diffusion coefficient) within the CST in different locations and analyzed their interrater reliability and usefulness for predicting the patients' motor outcome with a precise approach of specific region of interest (ROI) seeding based on the color-coded FA-map.

Methods

Prospectively collected data of 30 patients undergoing bihemispheric nTMS mapping followed by nTMS-based DTI fiber tracking prior to surgery of motor eloquent high-grade gliomas were analyzed by 2 experienced and 1 unexperienced examiner. The following data were scrutinized for both hemispheres after tractography based on nTMS-motor positive cortical seeds and a 2nd region of interest in one layer of the caudal pons defined by the color-coded FA-map: the pre- and postoperative motor status (day of discharge und 3 months), the closest distance between the tracts and the tumor (TTD), the fractional anisotropy (FA) and the apparent diffusion coefficient (ADC). The latter as an average within the CST as well as specific values in different locations (peritumoral, mesencephal, pontine).

Results

Lower average FA-values within the affected CST as well as higher average ADC-values are significantly associated with deteriorated postoperative motor function (p = 0.006 and p = 0.026 respectively). Segmental analysis within the CST revealed that the diffusion parameters are especially disturbed on a peritumoral level and that the degree of their impairment correlates with motor deficits (FA p = 0.065, ADC p = 0.007). No significant segmental variation was seen in the healthy hemisphere. The interrater reliability showed perfect agreement for almost all analyzed parameters.

Conclusions

Adding diffusion weighted imaging derived information on the structural integrity of the nTMS-based tractography results improves the predictive power for postoperative motor outcome. Utilizing a second subcortical ROI which is specifically seeded based on the color-coded FA map increases the tracking quality of the CST independently of the examiner's experience. Further prospective studies are needed to validate the nTMS-based prediction of the patient's outcome.

•

ROI seeding based on nTMS-data and FA-maps improves DTI tractography of the CST.

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Perfect interrater reliability for DTI tractography of the CST was observed.

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The pattern of diffusivity disturbance predicts the postoperative motor outcome.

Implementing Functional Preoperative Mapping in the Clinical Routine of a Neurosurgical Department: Technical Note

BACKGROUND

Navigated transcranial magnetic stimulation (nTMS) is increasingly being used for mapping of various brain functions and in nTMS-based tractography in neurosurgical departments worldwide. When a department begins using nTMS data in the clinical workflow, smooth integration into the hospital's existing infrastructure is mandatory. Standardized approaches for this beyond the mapping or tractography procedures themselves have not yet been described.

METHODS

To create an effective workflow for neurosurgical nTMS mapping, we present the findings of our 7 years of experience and progressive integration into the clinical routine.

RESULTS

After indication for mapping is made, the workflow starts with patient admission and includes all preoperative steps until tumor resection. Importantly, only standard software and devices were used, enabling new centers to easily integrate data derived from nTMS mapping and nTMS-based tractography into their hospital's infrastructure. Registration of the patient, appointment planning, and documentation of results of the nTMS procedures within the hospital information system (HIS) can be achieved by a novel tailored software mask. As another important part of the workflow, nTMS data are imported into the picture archiving and communication system (PACS) via PACS integrator software. In addition, for surgical planning including nTMS-based tractography, nTMS data can be effectively included in surgical neuronavigation software.

CONCLUSIONS

Optimized integration of nTMS data can be achieved using a standardized workflow. The seamless integration and availability of nTMS data are crucial to the acceptance of these data in the clinical routine. This optimized workflow can serve as a guide for centers beginning to use nTMS data in patient care.

Comparison between electric-field-navigated and line-navigated TMS for cortical motor mapping in patients with brain tumors

BACKGROUND

For the navigation of transcranial magnetic stimulation (TMS), various techniques are available. Yet, there are two basic principles underlying them all: electric-field-navigated transcranial magnetic stimulation (En-TMS) and line-navigated transcranial magnetic stimulation (Ln-TMS). The current study was designed to compare both methods.

METHODS

To explore whether there is a difference in clinical applicability, workflow, and mapping results of both techniques, we systematically compared motor mapping via En-TMS and Ln-TMS in 12 patients suffering from brain tumors.

RESULTS

The number of motor-positive stimulation spots and the ratio of positive spots per overall stimulation numbers were significantly higher for En-TMS (motor-positive spots: En-TMS vs. Ln-TMS: 128.3 ± 35.0 vs. 41.3 ± 26.8, p < 0.0001; ratio of motor-positive spots per number of stimulations: En-TMS vs. Ln-TMS: 38.0 ± 9.2 % vs. 20.0 ± 14.4 %, p = 0.0031). Distances between the En-TMS and Ln-TMS motor hotspots were 8.3 ± 4.4 mm on the ipsilesional and 8.6 ± 4.5 mm on the contralesional hemisphere (p = 0.9124).

CONCLUSIONS

The present study compares En-TMS and Ln-TMS motor mapping in the neurosurgical context for the first time. Although both TMS systems tested in the present study are explicitly designed for application during motor mapping in patients with brain lesions, there are differences in applicability, workflow, and results between En-TMS and Ln-TMS, which should be distinctly considered during clinical use of the technique. However, to draw final conclusions about accuracy, confirmation of motor-positive Ln-TMS spots by intraoperative stimulation is crucial within the scope of upcoming investigations.

Functional MRI vs. navigated TMS to optimize M1 seed volume delineation for DTI tractography. A prospective study in patients with brain tumours adjacent to the corticospinal tract

BACKGROUND

DTI-based tractography is an increasingly important tool for planning brain surgery in patients suffering from brain tumours. However, there is an ongoing debate which tracking approaches yield the most valid results. Especially the use of functional localizer data such as navigated transcranial magnetic stimulation (nTMS) or functional magnetic resonance imaging (fMRI) seem to improve fibre tracking data in conditions where anatomical landmarks are less informative due to tumour-induced distortions of the gyral anatomy. We here compared which of the two localizer techniques yields more plausible results with respect to mapping different functional portions of the corticospinal tract (CST) in brain tumour patients.

METHODS

The CSTs of 18 patients with intracranial tumours in the vicinity of the primary motor area (M1) were investigated by means of deterministic DTI. The core zone of the tumour-adjacent hand, foot and/or tongue M1 representation served as cortical regions of interest (ROIs). M1 core zones were defined by both the nTMS hot-spots and the fMRI local activation maxima. In addition, for all patients, a subcortical ROI at the level of the inferior anterior pons was implemented into the tracking algorithm in order to improve the anatomical specificity of CST reconstructions. As intra-individual control, we additionally tracked the CST of the hand motor region of the unaffected, i.e., non-lesional hemisphere, again comparing fMRI and nTMS M1 seeds. The plausibility of the fMRI-ROI- vs. nTMS-ROI-based fibre trajectories was assessed by a-priori defined anatomical criteria. Moreover, the anatomical relationship of different fibre courses was compared regarding their distribution in the anterior-posterior direction as well as their location within the posterior limb of the internal capsule (PLIC).

RESULTS

Overall, higher plausibility rates were observed for the use of nTMS- as compared to fMRI-defined cortical ROIs (p < 0.05) in tumour vicinity. On the non-lesional hemisphere, however, equally good plausibility rates (100%) were observed for both localizer techniques. fMRI-originated fibres generally followed a more posterior course relative to the nTMS-based tracts (p < 0.01) in both the lesional and non-lesional hemisphere.

CONCLUSION

NTMS achieved better tracking results than fMRI in conditions when the cortical tract origin (M1) was located in close vicinity to a brain tumour, probably influencing neurovascular coupling. Hence, especially in situations with altered BOLD signal physiology, nTMS seems to be the method of choice in order to identify seed regions for CST mapping in patients.

Risk stratification in motor area-related glioma surgery based on navigated transcranial magnetic stimulation data

OBJECTIVE Navigated transcranial magnetic stimulation (nTMS) is a noninvasive method for preoperatively localizing functional areas in patients with tumors in presumed motor eloquent areas. The aim of this study was to establish an nTMS-based risk stratification model by examining whether the results of nTMS mapping and its neurophysiological data predict postoperative motor outcome in glioma surgery. METHODS Included in this study were prospectively collected data for 113 patients undergoing bihemispheric nTMS examination prior to surgery for gliomas in presumed motor eloquent locations. Multiple ordinal logistic regression analysis was performed to test for any association between preoperative nTMS-related variables and postoperative motor outcome. RESULTS A new motor deficit or deterioration due to a preexisting deficit was observed in 20% of cases after 7 days and in 22% after 3 months. In terms of tumor location, no new permanent deficit was observed when the distance between tumor and corticospinal tract was greater than 8 mm and the precentral gyrus was not infiltrated (p = 0.014). New postoperative deficits on Day 7 were associated with a pathological excitability of the motor cortices (interhemispheric resting motor threshold [RMT] ratio < 90% or > 110%, p = 0.031). Interestingly, motor function never improved when the RMT was significantly higher in the tumorous hemisphere than in the healthy hemisphere (RMT ratio > 110%). CONCLUSIONS The proposed risk stratification model, based on objective functional-anatomical and neurophysiological measures, enables one to counsel patients about the risk of functional deterioration or the potential for recovery.

Feasibility of nTMS-based DTI fiber tracking of language pathways in neurosurgical patients using a fractional anisotropy threshold

BACKGROUND

Navigated transcranial magnetic stimulation (nTMS) provides language maps in brain tumor patients. Yet, corresponding data on the visualization of language-related subcortical pathways is lacking. Therefore, this study evaluates the feasibility of nTMS-based diffusion tensor imaging fiber tracking (DTI FT) for subcortical language pathways by a fractional anisotropy (FA) protocol.

NEW METHOD

DTI FT was performed in 37 patients suffering from left-sided perisylvian brain lesions based on nTMS data exclusively, using the FA-based protocol originally established for the corticospinal tract (CST) by Frey et al. (2012): minimum fiber length was 110mm and the highest individual FA value leading to visualization of white matter tracts was determined as the FA threshold (FAT). Then, deterministic DTI FT using an FA value of 100%, 75%, 50%, and 25% of the individual FAT (with 25% as an additional setting to the original protocol) was performed.

RESULTS

Our approach visualized 9 language-related subcortical white matter pathways. By using 100% FAT, the mean percentage of visualized tracts was 13.5%, whereas DTI FT performed with 75%, 50%, and 25% FAT detected 30.6%, 61.3%, and 93.7% of language-related fiber tracts, respectively.

COMPARISON WITH EXISTING METHODS

nTMS language mapping alone is not able to visualize subcortical language-related pathways.

CONCLUSIONS

This study shows that nTMS language maps are feasible for DTI FT of language-related pathways within the scope of a FAT-based protocol. Although this approach is novel and might be helpful during scientific neuroimaging and tumor resection, intraoperative validation is needed to go beyond the level of feasibility.

Interhemispheric connectivity revealed by diffusion tensor imaging fiber tracking derived from navigated transcranial magnetic stimulation maps as a sign of language function at risk in patients with brain tumors

OBJECTIVE Resection of brain tumors in language-eloquent areas entails the risk of postoperative aphasia. It has been demonstrated via navigated transcranial magnetic stimulation (nTMS) that language function can partially shift to the unaffected hemisphere due to tumor-induced plasticity. Therefore, this study was designed to evaluate whether interhemispheric connectivity (IC) detected by nTMS-based diffusion tensor imaging-fiber tracking (DTI-FT) can be used to predict surgery-related aphasia in patients with brain tumors. METHODS Thirty-eight patients with left-sided perisylvian brain lesions underwent cortical language mapping of both hemispheres by nTMS prior to awake surgery. Then, nTMS-based DTI-FT was conducted with a fractional anisotropy (FA) of 0.01 and 0.2 to visualize nTMS-based IC. Receiver operating characteristics were calculated for the prediction of a postoperative (irrespective of the preoperative state) and a new surgery-related aphasia by the presence of detectable IC. RESULTS Language mapping by nTMS was possible in all patients. Seventeen patients (44.7%) suffered from surgery-related worsening of language performance (transient aphasia according to 3-month follow-up in 16 subjects [42.1%]; new permanent aphasia according to 3-month follow-up in 1 patient [2.6%]). Regarding the correlation of aphasia to nTMS-based IC, statistically significant differences were revealed for both evaluated FA values. However, better results were observed for tractography with an FA of 0.2, which led to a specificity of 93% (postoperative aphasia) and 90% (surgery-related aphasia). For postoperative aphasia, the corresponding OR was 0.1282 (95% CI 0.0143-1.1520), and for surgery-related aphasia the OR was 0.1184 (95% CI 0.0208-0.6754). CONCLUSIONS According to these results, IC detected by preoperative nTMS-based DTI-FT might be regarded as a risk factor for surgery-related aphasia, with a specificity of up to 93%. However, because the majority of enrolled patients suffered from transient aphasia postoperatively, it has to be evaluated whether this approach distinctly leads to similar results among patients with permanent language deficits. Despite this restriction, this approach might contribute to individualized patient consultation prior to tumor resection in clinical practice.

Improved nTMS- and DTI-derived CST tractography through anatomical ROI seeding on anterior pontine level compared to internal capsule

Imaging of the course of the corticospinal tract (CST) by diffusion tensor imaging (DTI) is useful for function-preserving tumour surgery. The integration of functional localizer data into tracking algorithms offers to establish a direct structure–function relationship in DTI data. However, alterations of MRI signals in and adjacent to brain tumours often lead to spurious tracking results. We here compared the impact of subcortical seed regions placed at different positions and the influences of the somatotopic location of the cortical seed and clinical co-factors on fibre tracking plausibility in brain tumour patients.

The CST of 32 patients with intracranial tumours was investigated by means of deterministic DTI and neuronavigated transcranial magnetic stimulation (nTMS). The cortical seeds were defined by the nTMS hot spots of the primary motor area (M1) of the hand, the foot and the tongue representation. The CST originating from the contralesional M1 hand area was mapped as intra-individual reference. As subcortical region of interests (ROI), we used the posterior limb of the internal capsule (PLIC) and/or the anterior inferior pontine region (aiP). The plausibility of the fibre trajectories was assessed by a-priori defined anatomical criteria. The following potential co-factors were analysed: Karnofsky Performance Scale (KPS), resting motor threshold (RMT), T1-CE tumour volume, T2 oedema volume, presence of oedema within the PLIC, the fractional anisotropy threshold (FAT) to elicit a minimum amount of fibres and the minimal fibre length.

The results showed a higher proportion of plausible fibre tracts for the aiP-ROI compared to the PLIC-ROI. Low FAT values and the presence of peritumoural oedema within the PLIC led to less plausible fibre tracking results. Most plausible results were obtained when the FAT ranged above a cut-off of 0.105. In addition, there was a strong effect of somatotopic location of the seed ROI; best plausibility was obtained for the contralateral hand CST (100%), followed by the ipsilesional hand CST (>95%), the ipsilesional foot (>85%) and tongue (>75%) CST. In summary, we found that the aiP-ROI yielded better tracking results compared to the IC-ROI when using deterministic CST tractography in brain tumour patients, especially when the M1 hand area was tracked. In case of FAT values lower than 0.10, the result of the respective CST tractography should be interpreted with caution with respect to spurious tracking results. Moreover, the presence of oedema within the internal capsule should be considered a negative predictor for plausible CST tracking.

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Somatotopic CST tractography was done in 32 patients with eloquent brain tumours.

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Seeding ROIs were defined by navigated TMS of the M1 hot spot (hand, foot, tongue).

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Using the anterior pons as a second ROI yielded more plausible tracts than the PLIC.

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Low FAT and oedema of the internal capsule were negative predictors.