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

Influence of clinical and tumor-specific factors on the resting motor threshold in navigated transcranial magnetic stimulation

OBJECTIVE

Preoperative non-invasive mapping of motor function with navigated transcranial magnetic stimulation (nTMS) has become a widely used diagnostic procedure. Determination of the patient-individual resting motor threshold (rMT) is of great importance to achieve reliable results when conducting nTMS motor mapping. Factors which contribute to differences in rMT of brain tumor patients have not been fully investigated.

METHODS

We included adult patients with all types of de novo and recurrent intracranial lesions, suspicious for intra-axial brain tumors. The outcome measure was the rMT of the upper extremity, defined as the stimulation intensity eliciting motor evoked potentials with amplitudes greater than 50µV in 50 % of applied stimulations.

RESULTS

Eighty nTMS examinations in 75 patients (37.5 % female) aged 57.9 ± 14.9 years were evaluated. In non-parametric testing, rMT values were higher in patients with upper extremity paresis (p = 0.024) and lower in patients with high grade gliomas (HGG) (p = 0.001). rMT inversely correlated with patient age (rs=-0.28, p = 0.013) and edema volume (rs=-0.28, p = 0.012) In regression analysis, infiltration of the precentral gyrus (p<0.001) increased rMT values. Values of rMT were reduced in high grade gliomas (p<0.001), in patients taking Levetiracetam (p = 0.019) and if perilesional edema infiltrated motor eloquent brain (p<0.001). Subgroup analyses of glioma patients revealed similar results. Values of rMT did not differ between hand and forearm muscles.

CONCLUSION

Most factors confounding rMT in our study were specific to the lesion. These factors contributed to the variability in cortical excitability and must be considered in clinical work with nTMS to achieve reliable results with nTMS motor mapping.

Dose Reduction to Motor Structures in Adjuvant Fractionated Stereotactic Radiotherapy of Brain Metastases: nTMS-Derived DTI-Based Motor Fiber Tracking in Treatment Planning

Background: Resection of brain metastases (BM) close to motor structures is challenging for treatment. Navigated transcranial magnetic stimulation (nTMS) motor mapping, combined with diffusion tensor imaging (DTI)-based fiber tracking (DTI-FTmot.TMS), is a valuable tool in neurosurgery to preserve motor function. This study aimed to assess the practicability of DTI-FTmot.TMS for local adjuvant radiotherapy (RT) planning of BM. Methods: Presurgically generated DTI-FTmot.TMS-based corticospinal tract (CST) reconstructions (FTmot.TMS) of 24 patients with 25 BM resected during later surgery were incorporated into the RT planning system. Completed fractionated stereotactic intensity-modulated RT (IMRT) plans were retrospectively analyzed and adapted to preserve FTmot.TMS. Results: In regular plans, mean dose (Dmean) of complete FTmot.TMS was 5.2 ± 2.4 Gy. Regarding planning risk volume (PRV-FTTMS) portions outside of the planning target volume (PTV) within the 17.5 Gy (50%) isodose line, the DTI-FTmot.TMS Dmean was significantly reduced by 33.0% (range, 5.9−57.6%) from 23.4 ± 3.3 Gy to 15.9 ± 4.7 Gy (p < 0.001). There was no significant decline in the effective treatment dose, with PTV Dmean 35.6 ± 0.9 Gy vs. 36.0 ± 1.2 Gy (p = 0.063) after adaption. Conclusions: The DTI-FTmot.TMS-based CST reconstructions could be implemented in adjuvant IMRT planning of BM. A significant dose reduction regarding motor structures within critical dose levels seems possible.

Minimally invasive approach to a deep-seated motor eloquent brain tumour: a technical note

Deep-seated brain tumours represent a unique neurosurgical challenge as they are often surrounded by eloquent structures. We describe a minimally invasive technique using tubular retractors and intraoperative neurophysiology monitoring for open biopsy of a deep-seated lesion surrounded by the corticospinal tract. We used preoperative functional mapping with diffusion tensor imaging tractography and navigated transcranial magnetic stimulation to identify a safe surgical corridor. We also used 5-Aminolevulinic Acid induced fluorescence to identify the lesion intraoperatively and optimize tissue samples obtained for histopathological diagnosis. We found the use of these tools improved the safety of surgery and reduced the risk of surgical morbidity.

Dual-Task nTMS Mapping to Visualize the Cortico-Subcortical Language Network and Capture Postoperative Outcome-A Patient Series in Neurosurgery

BACKGROUND

Perioperative assessment of language function in brain tumor patients commonly relies on administration of object naming during stimulation mapping. Ample research, however, points to the benefit of adding verb tasks to the testing paradigm in order to delineate and preserve postoperative language function more comprehensively. This research uses a case series approach to explore the feasibility and added value of a dual-task protocol that includes both a noun task (object naming) and a verb task (action naming) in perioperative delineation of language functions.

MATERIALS AND METHODS

Seven neurosurgical cases underwent perioperative language assessment with both object and action naming. This entailed preoperative baseline testing, preoperative stimulation mapping with navigated Transcranial Magnetic Stimulation (nTMS) with subsequent white matter visualization, intraoperative mapping with Direct Electrical Stimulation (DES) in 4 cases, and postoperative imaging and examination of language change.

RESULTS

We observed a divergent pattern of language organization and decline between cases who showed lesions close to the delineated language network and hence underwent DES mapping, and those that did not. The latter displayed no new impairment postoperatively consistent with an unharmed network for the neural circuits of both object and action naming. For the cases who underwent DES, on the other hand, a higher sensitivity was found for action naming over object naming. Firstly, action naming preferentially predicted the overall language state compared to aphasia batteries. Secondly, it more accurately predicted intraoperative positive language areas as revealed by DES. Thirdly, double dissociations between postoperatively unimpaired object naming and impaired action naming and vice versa indicate segregated skills and neural representation for noun versus verb processing, especially in the ventral stream. Overlaying postoperative imaging with object and action naming networks revealed that dual-task nTMS mapping can explain the drop in performance in those cases where the network appeared in proximity to the resection cavity.

CONCLUSION

Using a dual-task protocol for visualization of cortical and subcortical language areas through nTMS mapping proved to be able to capture network-to-deficit relations in our case series. Ultimately, adding action naming to clinical nTMS and DES mapping may help prevent postoperative deficits of this seemingly segregated skill.

Neuronavigated repetitive transcranial magnetic stimulation as novel mapping technique provides insights into language function in primary progressive aphasia

Navigated repetitive transcranial magnetic stimulation (nrTMS) is an innovative technique that provides insight into language function with high accuracy in time and space. So far, nrTMS has mainly been applied in presurgical language mapping of patients with intracranial neoplasms. For the present study, nrTMS was used for language mapping in primary progressive aphasia (PPA). Seven patients (median age: 70 years, 4 males) with the non-fluent variant of PPA (nfvPPA) were included in this pilot study. Trains of nrTMS (5 Hz, 100% resting motor threshold) caused virtual lesions at 46 standardized cortical stimulation targets per hemisphere. Patients’ errors in a naming task during stimulation were counted. The majority of errors induced occurred during frontal lobe stimulation (34.3%). Timing errors and non-responses were most frequent. More errors were induced in the right hemisphere (58%) than in the left hemisphere (42%). Mapping was tolerated by all patients, however, discomfort or pain was reported for stimulation of frontal areas. The elevated right-hemispheric error rate in our study could be due to a partial shift of language function to the right hemisphere in neurodegenerative aphasia during the course of disease and therefore points to the existence of neuronal plasticity in nfvPPA. While this is an interesting finding for neurodegenerative disorders per se, its promotion might also harbor future therapeutic targets.

Tracking the Corticospinal Tract in Patients With High-Grade Glioma: Clinical Evaluation of Multi-Level Fiber Tracking and Comparison to Conventional Deterministic Approaches

While the diagnosis of high-grade glioma (HGG) is still associated with a considerably poor prognosis, neurosurgical tumor resection provides an opportunity for prolonged survival and improved quality of life for affected patients. However, successful tumor resection is dependent on a proper surgical planning to avoid surgery-induced functional deficits whilst achieving a maximum extent of resection (EOR). With diffusion magnetic resonance imaging (MRI) providing insight into individual white matter neuroanatomy, the challenge remains to disentangle that information as correctly and as completely as possible. In particular, due to the lack of sensitivity and accuracy, the clinical value of widely used diffusion tensor imaging (DTI)-based tractography is increasingly questioned. We evaluated whether the recently developed multi-level fiber tracking (MLFT) technique can improve tractography of the corticospinal tract (CST) in patients with motor-eloquent HGGs. Forty patients with therapy-naïve HGGs (mean age: 62.6 ± 13.4 years, 57.5% males) and preoperative diffusion MRI [repetition time (TR)/echo time (TE): 5000/78 ms, voxel size: 2x2x2 mm3, one volume at b=0 s/mm2, 32 volumes at b=1000 s/mm2] underwent reconstruction of the CST of the tumor-affected and unaffected hemispheres using MLFT in addition to deterministic DTI-based and deterministic constrained spherical deconvolution (CSD)-based fiber tractography. The brain stem was used as a seeding region, with a motor cortex mask serving as a target region for MLFT and a region of interest (ROI) for the other two algorithms. Application of the MLFT method substantially improved bundle reconstruction, leading to CST bundles with higher radial extent compared to the two other algorithms (delineation of CST fanning with a wider range; median radial extent for tumor-affected vs. unaffected hemisphere - DTI: 19.46° vs. 18.99°, p=0.8931; CSD: 30.54° vs. 27.63°, p=0.0546; MLFT: 81.17° vs. 74.59°, p=0.0134). In addition, reconstructions by MLFT and CSD-based tractography nearly completely included respective bundles derived from DTI-based tractography, which was however favorable for MLFT compared to CSD-based tractography (median coverage of the DTI-based CST for affected vs. unaffected hemispheres - CSD: 68.16% vs. 77.59%, p=0.0075; MLFT: 93.09% vs. 95.49%; p=0.0046). Thus, a more complete picture of the CST in patients with motor-eloquent HGGs might be achieved based on routinely acquired diffusion MRI data using MLFT.

Benefit of Action Naming Over Object Naming for Visualization of Subcortical Language Pathways in Navigated Transcranial Magnetic Stimulation-Based Diffusion Tensor Imaging-Fiber Tracking

Visualization of functionally significant subcortical white matter fibers is needed in neurosurgical procedures in order to avoid damage to the language network during resection. In an effort to achieve this, positive cortical points revealed during preoperative language mapping with navigated transcranial magnetic stimulation (nTMS) can be employed as regions of interest (ROIs) for diffusion tensor imaging (DTI) fiber tracking. However, the effect that the use of different language tasks has on nTMS mapping and subsequent DTI-fiber tracking remains unexplored. The visualization of ventral stream tracts with an assumed lexico-semantic role may especially benefit from ROIs delivered by the lexico-semantically demanding verb task, Action Naming. In a first step, bihemispheric nTMS language mapping was administered in 18 healthy participants using the standard task Object Naming and the novel task Action Naming to trigger verbs in a small sentence context. Cortical areas in which nTMS induced language errors were identified as language-positive cortical sites. In a second step, nTMS-based DTI-fiber tracking was conducted using solely these language-positive points as ROIs. The ability of the two tasks’ ROIs to visualize the dorsal tracts Arcuate Fascicle and Superior Longitudinal Fascicle, the ventral tracts Inferior Longitudinal Fascicle, Uncinate Fascicle, and Inferior Fronto-Occipital Fascicle, the speech-articulatory Cortico-Nuclear Tract, and interhemispheric commissural fibers was compared in both hemispheres. In the left hemisphere, ROIs of Action Naming led to a significantly higher fraction of overall visualized tracts, specifically in the ventral stream’s Inferior Fronto-Occipital and Inferior Longitudinal Fascicle. No difference was found between tracking with Action Naming vs. Object Naming seeds for dorsal stream tracts, neither for the speech-articulatory tract nor the inter-hemispheric connections. While the two tasks appeared equally demanding for phonological-articulatory processes, ROI seeding through the task Action Naming seemed to better visualize lexico-semantic tracts in the ventral stream. This distinction was not evident in the right hemisphere. However, the distribution of tracts exposed was, overall, mirrored relative to those in the left hemisphere network. In presurgical practice, mapping and tracking of language pathways may profit from these findings and should consider inclusion of the Action Naming task, particularly for lesions in ventral subcortical regions.

Mapping of Motor Function with Neuronavigated Transcranial Magnetic Stimulation: A Review on Clinical Application in Brain Tumors and Methods for Ensuring Feasible Accuracy

Navigated transcranial magnetic stimulation (nTMS) has developed into a reliable non-invasive clinical and scientific tool over the past decade. Specifically, it has undergone several validating clinical trials that demonstrated high agreement with intraoperative direct electrical stimulation (DES), which paved the way for increasing application for the purpose of motor mapping in patients harboring motor-eloquent intracranial neoplasms. Based on this clinical use case of the technique, in this article we review the evidence for the feasibility of motor mapping and derived models (risk stratification and prediction, nTMS-based fiber tracking, improvement of clinical outcome, and assessment of functional plasticity), and provide collected sets of evidence for the applicability of quantitative mapping with nTMS. In addition, we provide evidence-based demonstrations on factors that ensure methodological feasibility and accuracy of the motor mapping procedure. We demonstrate that selection of the stimulation intensity (SI) for nTMS and spatial density of stimuli are crucial factors for applying motor mapping accurately, while also demonstrating the effect on the motor maps. We conclude that while the application of nTMS motor mapping has been impressively spread over the past decade, there are still variations in the applied protocols and parameters, which could be optimized for the purpose of reliable quantitative mapping.

Short-Interval Intracortical Facilitation Improves Efficacy in nTMS Motor Mapping of Lower Extremity Muscle Representations in Patients with Supra-Tentorial Brain Tumors

Navigated transcranial magnetic stimulation (nTMS) is increasingly used for mapping of motor function prior to surgery in patients harboring motor-eloquent brain lesions. To date, single-pulse nTMS (sp-nTMS) has been predominantly used for this purpose, but novel paired-pulse nTMS (pp-nTMS) with biphasic pulse application has been made available recently. The purpose of this study was to systematically evaluate pp-nTMS with biphasic pulses in comparison to conventionally used sp-nTMS for preoperative motor mapping of lower extremity (lE) muscle representations. Thirty-nine patients (mean age: 56.3 ± 13.5 years, 69.2% males) harboring motor-eloquent brain lesions of different entity underwent motor mapping of lE muscle representations in lesion-affected hemispheres and nTMS-based tractography of the corticospinal tract (CST) using data from sp-nTMS and pp-nTMS with biphasic pulses, respectively. Compared to sp-nTMS, pp-nTMS enabled motor mapping with lower stimulation intensities (61.8 ± 13.8% versus 50.7 ± 11.6% of maximum stimulator output, p < 0.0001), and it provided reliable motor maps even in the most demanding cases where sp-nTMS failed (pp-nTMS was able to provide a motor map in five patients in whom sp-nTMS did not provide any motor-positive points, and pp-nTMS was the only modality to provide a motor map in one patient who also did not show motor-positive points during intraoperative stimulation). Fiber volumes of the tracked CST were slightly higher when motor maps of pp-nTMS were used, and CST tracking using pp-nTMS data was also possible in the five patients in whom sp-nTMS failed. In conclusion, application of pp-nTMS with biphasic pulses enables preoperative motor mapping of lE muscle representations even in the most challenging patients in whom the motor system is at high risk due to lesion location or resection.

Paired-pulse navigated TMS is more effective than single-pulse navigated TMS for mapping upper extremity muscles in brain tumor patients

OBJECTIVE

Single-pulse navigated transcranial magnetic stimulation (sp-nTMS) is used for presurgical motor mapping in patients with motor-eloquent lesions. However, recently introduced paired-pulse nTMS (pp-nTMS) with biphasic pulses could improve motor mapping.

METHODS

Thirty-four patients (mean age: 56.0 ± 12.7 years, 53.0% high-grade glioma) with motor-eloquent lesions underwent motor mapping of upper extremity representations and nTMS-based tractography of the corticospinal tract (CST) by both sp-nTMS and pp-nTMS with biphasic pulses for the tumor-affected hemisphere before resection.

RESULTS

In three patients (8.8%), conventional sp-nTMS did not provide motor-positive points, in contrast to pp-nTMS that was capable of generating motor maps in all patients. Good concordance between pp-nTMS and sp-nTMS in the spatial location of motor hotspots and center of gravity (CoG) as well as for CST tracking was observed, with pp-nTMS leading to similar motor map volumes (585.0 ± 667.8 vs. 586.8 ± 204.2 mm³, p = 0.9889) with considerably lower resting motor thresholds (35.0 ± 8.8 vs. 32.8 ± 7.6% of stimulator output, p = 0.0004).

CONCLUSIONS

Pp-nTMS with biphasic pulses may provide motor maps even in highly demanding cases with tumor-affected motor structures or edema, using lower stimulation intensity compared to sp-nTMS.

SIGNIFICANCE

Pp-nTMS with biphasic pulses could replace standardly used sp-nTMS for motor mapping and may be safer due to lower stimulation intensity.

Function-Based Tractography of the Language Network Correlates with Aphasia in Patients with Language-Eloquent Glioblastoma

To date, the structural characteristics that distinguish language-involved from non-involved cortical areas are largely unclear. Particularly in patients suffering from language-eloquent brain tumors, reliable mapping of the cortico-subcortical language network is of high clinical importance to prepare and guide safe tumor resection. To investigate differences in structural characteristics between language-positive and language-negative areas, 20 patients (mean age: 63.2 ± 12.9 years, 16 males) diagnosed with language-eloquent left-hemispheric glioblastoma multiforme (GBM) underwent preoperative language mapping by navigated transcranial magnetic stimulation (nTMS) and nTMS-based diffusion tensor imaging fiber tracking (DTI FT). The number of language-positive and language-negative points as well as the gray matter intensity (GMI), normalized volumes of U-fibers, interhemispheric fibers, and fibers projecting to the cerebellum were assessed and compared between language-positive and language-negative nTMS mappings and set in correlation with aphasia grades. We found significantly lower GMI for language-positive nTMS points (5.7 ± 1.7 versus 7.1 ± 1.6, p = 0.0121). Furthermore, language-positive nTMS points were characterized by an enhanced connectivity profile, i.e., these points showed a significantly higher ratio in volumes for U-fibers (p ≤ 0.0056), interhemispheric fibers (p = 0.0494), and fibers projecting to the cerebellum (p = 0.0094). The number of language-positive nTMS points (R ≥ 0.4854, p ≤ 0.0300) as well as the ratio in volumes for U-fibers (R ≤ -0.4899, p ≤ 0.0283) were significantly associated with aphasia grades, as assessed pre- or postoperatively and during follow-up examinations. In conclusion, this study provides evidence for structural differences on cortical and subcortical levels between language-positive and language-negative areas, as detected by nTMS language mapping. The results may further increase confidence in the technique of nTMS language mapping and nTMS-based tractography in the direct clinical setting. Future studies may confirm our results in larger cohorts and may expand the findings to patients with other tumor entities than GBM.

Risk Assessment by Presurgical Tractography Using Navigated TMS Maps in Patients with Highly Motor- or Language-Eloquent Brain Tumors

Patients with functionally eloquent brain lesions are at risk of functional decline in the course of resection. Given tumor-related plastic reshaping and reallocation of function, individual data are needed for patient counseling and risk assessment prior to surgery. This study evaluates the utility of mapping by navigated transcranial magnetic stimulation (nTMS) and nTMS-based diffusion tensor imaging fiber tracking (DTI FT) for individual risk evaluation of surgery-related decline of motor or language function in the clinical setting. In total, 250 preoperative nTMS mappings (100 language and 150 motor mappings) derived from 216 patients (mean age: 57.0 ± 15.5 years, 58.8% males; glioma World Health Organization (WHO) grade I & II: 4.2%, glioma WHO grade III & IV: 83.4%, arteriovenous malformations: 1.9%, cavernoma: 2.3%, metastasis: 8.2%) were included. Deterministic tractography based on nTMS motor or language maps as seed regions was performed with 25%, 50%, and 75% of the individual fractional anisotropy threshold (FAT). Lesion-to-tract distances (LTDs) were measured between the tumor mass and the corticospinal tract (CST), arcuate fascicle (AF), or other closest language-related tracts. LTDs were compared between patients and correlated to the functional status (no/transient/permanent surgery-related paresis or aphasia). Significant differences were found between patients with no or transient surgery-related deficits and patients with permanent surgery-related deficits regarding LTDs in relation to the CST (p < 0.0001), AF (p ≤ 0.0491), or other closest language-related tracts (p ≤ 0.0435). The cut-off values for surgery-related paresis or aphasia were ≤12 mm (LTD—CST) and ≤16 mm (LTD—AF) or ≤25 mm (LTD—other closest language-related tract), respectively. Moreover, there were significant associations between the status of surgery-related deficits and the LTD when considering the CST (range r: −0.3994 to −0.3910, p < 0.0001) or AF (range r: −0.2918 to −0.2592, p = 0.0135 and p = 0.0473 for 25% and 50% FAT). In conclusion, this is the largest study evaluating the application of both preoperative functional mapping and function-based tractography for motor and language function for risk stratification in patients with functionally eloquent tumors. The LTD may qualify as a viable marker that can be seamlessly assessed in the clinical neurooncological setup.

Setup presentation and clinical outcome analysis of treating highly language-eloquent gliomas via preoperative navigated transcranial magnetic stimulation and tractography

OBJECTIVE Awake surgery combined with intraoperative direct electrical stimulation (DES) and intraoperative neuromonitoring (IONM) is considered the gold standard for the resection of highly language-eloquent brain tumors. Different modalities, such as functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG), are commonly added as adjuncts for preoperative language mapping but have been shown to have relevant limitations. Thus, this study presents a novel multimodal setup consisting of preoperative navigated transcranial magnetic stimulation (nTMS) and nTMS-based diffusion tensor imaging fiber tracking (DTI FT) as an adjunct to awake surgery. METHODS Sixty consecutive patients (63.3% men, mean age 47.6 ± 13.3 years) suffering from highly language-eloquent left-hemispheric low- or high-grade glioma underwent preoperative nTMS language mapping and nTMS-based DTI FT, followed by awake surgery for tumor resection. Both nTMS language mapping and DTI FT data were available for resection planning and intraoperative guidance. Clinical outcome parameters, including craniotomy size, extent of resection (EOR), language deficits at different time points, Karnofsky Performance Scale (KPS) score, duration of surgery, and inpatient stay, were assessed. RESULTS According to postoperative evaluation, 28.3% of patients showed tumor residuals, whereas new surgery-related permanent language deficits occurred in 8.3% of patients. KPS scores remained unchanged (median preoperative score 90, median follow-up score 90). CONCLUSIONS This is the first study to present a clinical outcome analysis of this very modern approach, which is increasingly applied in neurooncological centers worldwide. Although human language function is a highly complex and dynamic cortico-subcortical network, the presented approach offers excellent functional and oncological outcomes in patients undergoing surgery of lesions affecting this network.

Language-Eloquent White Matter Pathway Tractography and the Course of Language Function in Glioma Patients

Object: As various recent studies show, damage to white matter pathways leads to permanent functional deficits in a high percentage of patients. Particularly the subcortical language network is complex, and its visualization has a tremendous relevance for neurosurgeons. This pilot study aims to correlate language-eloquent white matter pathways with the course of language function after the resection of left-sided perisylvian gliomas.

Methods: We included 10 patients who underwent resection of highly language-eloquent high- (9 pts) and low-grade gliomas (1 pts). We performed navigated repetitive transcranial magnetic stimulation (nrTMS)-based tractography via diffusion tensor imaging fiber trackings (DTI FT) preoperatively (PRE-1), postoperatively (POST-1), and at long-term follow up or tumor recurrence (PRE-2). We separately tracked the inferior fronto-occipital fascicle (IFOF), the frontal aslant tract (FAT), and the superior longitudinal (SLF), and arcuate fascicle (AF), and correlated the amount of visualized fibers to the patients' language function at each date.

Results: The changes of nrTMS-based DTI FTs of single white matter pathways correlated with the according status of language function for any of the pathways in 80% of patients and in 19 of 30 (63%) single pathway comparisons between PRE-1 and POST-1. Between POST-1 and PRE-2 the nrTMS-based DTI FTs correlated with the status of language function for any of the pathways in all patients and in 24 of 30 (80%) single pathway comparisons. Single FT results correlated with the according status of language function at POST-1 in 60, 70, and 60% of cases, and with the according status of language function at PRE-2 in 60, 90, and 90% of cases for the tracking of the IFOF, FAT, and SLF/AF, respectively.

Conclusion: By the present results we were able to show that nrTMS-based DTI FT of the IFOF, FAT, and SLF/AF mainly correlates with the according status of language function preoperatively, postoperatively, and at long-term follow up after the resection of left-sided perisylvian gliomas.

Mapping of Arithmetic Processing by Navigated Repetitive Transcranial Magnetic Stimulation in Patients with Parietal Brain Tumors and Correlation with Postoperative Outcome

BACKGROUND

Preserving functionality is important during neurosurgical resection of brain tumors. Specialized centers also map further brain functions apart from motor and language functions, such as arithmetic processing (AP). The mapping of AP by navigated repetitive transcranial magnetic stimulation (nrTMS) in healthy volunteers has been reported.

OBJECTIVE

The present study aimed to correlate the results of mapping AP with functional patient outcomes.

METHODS

We included 26 patients with parietal brain tumors. Because of preoperative impairment of AP, mapping was not possible in 8 patients (31%). We stimulated 52 cortical sites by nrTMS while patients performed a calculation task. Preoperatively and postoperatively, patients underwent a standardized number-processing and calculation test (NPCT). Tumor resection was blinded to nrTMS results, and the change in NPCT performance was correlated to resected AP-positive spots as identified by nrTMS.

RESULTS

The resection of AP-positive sites correlated with a worsening of the postoperative NPCT result in 12 cases. In 3 cases, no AP-positive sites were resected and the postoperative NPCT result was similar to or better than preoperatively. Also, in 3 cases, the postoperative NPCT result was better than preoperatively, although AP-positive sites were resected.

CONCLUSIONS

Despite presenting only a few cases, nrTMS might be a useful tool for preoperative mapping of AP. However, the reliability of the present results has to be evaluated in a larger series and by intraoperative mapping data.

The impact of nTMS mapping on treatment of brain AVMs

BACKGROUND

The treatment of brain arteriovenous malformations (BAVMs) is still contrarily discussed. Despite the debatable results of the ARUBA trial, most BAVMs still require treatment depending on the Spetzler-Martin (SM) grading. Since size is measurable and venous drainage is visible, the determination of eloquence is comparably crucial but not fully objective. The present bicentric cohort study aims to examine the influence of preoperative navigated transcranial magnetic stimulation (nTMS) motor and language mapping data on decision-making for or against surgical treatment of BAVMs.

METHODS

The influence of data from nTMS on decision-making for or against treatment of BAVMs was examined by confirming/falsifying presumed motor or language eloquence.

RESULTS

The results of nTMS mappings changed the SM grading in nine cases. In six cases, the SM grading changed to a lower grade (= falsified eloquence); in three cases, the SM grading changed to a higher grade due to nTMS mappings (= unexpected eloquence). Out of all 34 cases, indication for surgery was supported by nTMS mappings in 15 cases (7 motors, 8 languages). In six cases, the decision against surgery was made based on nTMS mappings (three motors, three languages).

CONCLUSION

In 21 of 34 cases (62%), nTMS was a supportive argument. We could show that nTMS motor and language data can be used for a more objective decision-making regarding the treatment of BAVMs and for a more detailed SM grading regarding the rating of eloquence.

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.