Technical principles of direct bipolar electrostimulation for cortical and subcortical mapping in awake craniotomy

Locating eloquent sites identified during brain tumor intraoperative mapping on reference MRI atlas

BACKGROUND

Correlating the human connectome with clinical responses elicited during intraoperative brain mapping helps understanding of the intrinsic organization of the human brain. Methods for locating eloquent sites on neuroimaging are not standardized. In the present study, we standardized a methodology for locating subcortical eloquent sites identified during intraoperative mapping for awake brain tumor resection on a reference brain template.

METHODS

Subcortical eloquent sites were tagged by co-registration of intraoperative photographs with early postoperative MRI ( < 48 h). Neuroimaging data were normalized into MNI152 space. To assess whether the location of subcortical eloquent sites on the MNI template was concordant with the expected brain connectivity, we compared each subcortical eloquent site with the Human Connectome Project 1065 probabilistic tractography atlas.

RESULTS

We analyze 290 subcortical eloquent sites identified during 69/90 awake surgeries. 2/290 (0.7%) subcortical eloquent sites identified intraoperatively do not intersect with a fiber tract according to the reference atlas. Among the other 288 that successfully intersect with, at least, one white matter tract, 255/288 (88.5%) have a clinical response elicited intraoperatively that is congruent with the intersected white matter tract. In the remaining 33/288 (11.5%) functional incongruent and the 2/290 (0.7%) anatomical incongruent subcortical sites, the minimal mean distance between the eloquent site and a congruent with matter tract is 3.6 ± 4.4 mm (range 1.0-23.9, median 3.6, interquartile range 2.5-5.4).

CONCLUSIONS

We propose a standardized methodology to locate with accuracy on a reference brain template subcortical eloquent sites identified intraoperatively during functional brain mapping using direct electrical stimulations under awake condition.

Pilot Trial on Awake Surgery for Low-Grade Arteriovenous Malformations in Speech Area and Systematic Review of the Literature

OBJECTIVE

One of the pressing constraints in the treatment of arteriovenous malformations (AVM) is the potential development of new neurologic deficits, mainly when the AVM is in an eloquent area. The risk of ischemia when an en passage arterial supply is present is not negligible. In this regard, awake surgery holds promise in increasing the safety of low-grade AVM resection.

METHODS

We conducted a pilot trial on 3 patients with low-grade AVMs affecting speech areas to evaluate the safety of awake craniotomy using Conscious Sedation. Each feeder was temporarily clipped before the section. Also, we performed a systematic review to analyze the existing data about the impact of awake surgery in eloquent AVM resection.

RESULTS

None of the 3 patients presented with neurologic deficits after the procedure. Awake craniotomy was useful in 1 case, as it allowed the detection of speech arrest during the temporal clipping of 1 of the feeders. This vessel was identified as an en passage vessel, closer to the nidus. The second attempt revealed the feeder of the AVM, which was sectioned. Systematic review yielded 7 studies meeting our inclusion criteria. Twenty-six of 33 patients included in these studies presented with AVM affecting speech area. Only 2 studies included the motor evoked potentials. Six studies used direct cortical and subcortical stimulation. In all studies the asleep-awake-asleep technique was used.

CONCLUSIONS

Awake craniotomies are safe procedures and may be helpful in avoiding ischemic complications in low-grade AVMs, either affecting eloquent areas and/or when en passage feeders are present.

More widespread functionality of posterior language area in patients with brain tumors

Damage to the posterior language area (PLA), or Wernicke's area causes cortical reorganization in the corresponding regions of the contralateral hemisphere. However, the details of reorganization within the ipsilateral hemisphere are not fully understood. In this context, direct electrical stimulation during awake surgery can provide valuable opportunities to investigate neuromodulation of the human brain in vivo, which is difficult through the non-invasive approaches. Thus, in this study, we aimed to investigate the characteristics of the cortical reorganization of the PLA within the ipsilateral hemisphere. Sixty-two patients with left hemispheric gliomas were divided into groups depending on whether the lesion extended to the PLA. All patients underwent direct cortical stimulation with a picture-naming task. We further performed functional connectivity analyses using resting-state functional magnetic resonance imaging (MRI) in a subset of patients and calculated betweenness centrality, an index of the network importance of brain areas. During direct cortical stimulation, the regions showing positive (impaired) responses in the non-PLA group were localized mainly in the posterior superior temporal gyrus (pSTG), whereas those in the PLA group were widely distributed from the pSTG to the posterior supramarginal gyrus (pSMG). Notably, the percentage of positive responses in the pSMG was significantly higher in the PLA group (47%) than in the non-PLA group (8%). In network analyses of functional connectivity, the pSMG was identified as a hub region with high betweenness centrality in both the groups. These findings suggest that the language area can spread beyond the PLA to the pSMG, a hub region, in patients with lesion progression to the pSTG. The change in the pattern of the language area may be a compensatory mechanism to maintain efficient brain networks.

Presentation and Management of Cerebral Venous Sinus Thrombosis After Supratentorial Craniotomy

BACKGROUND AND OBJECTIVES

Cerebral venous sinus thrombosis (CVST) after supratentorial craniotomy is a poorly studied complication, for which there are no management guidelines. This study assessed the incidence, associated risk factors, and management of postoperative CVST after awake craniotomy.

METHODS

This is an observational, retrospective, monocentric analysis of patients who underwent a supratentorial awake craniotomy. Postoperative CVST was defined as a flow defect on the postoperative contrast-enhanced 3D T1-weighted sequence and/or as a T2* hypointensity within the sinus.

RESULTS

In 401 supratentorial awake craniotomies (87.3% of diffuse glioma), the incidence of postoperative CVST was 4.0% (95% CI 2.5-6.4): 14/16 thromboses located in the superior sagittal sinus and 12/16 located in the transverse sinus. A venous sinus was exposed during craniotomy in 45.4% of cases, and no intraoperative injury to a cerebral venous sinus was reported. All thromboses were asymptomatic, and only two cases were diagnosed at the time of the first postoperative imaging (0.5%). Postoperative complications, early postoperative Karnofsky Performance Status score, and duration of hospital stay did not significantly differ between patients with and without postoperative CVST. Adjusted independent risk factors of postoperative CVST were female sex (adjusted Odds Ratio 4.00, 95% CI 1.24-12.91, P = .021) and a lesion ≤1 cm to a venous sinus (adjusted Odds Ratio 10.58, 95% CI 2.93-38.20, P < .001). All patients received standard prophylactic-dose anticoagulant therapy, and none received treatment-dose anticoagulant therapy. No thrombosis-related adverse event was reported. All thromboses presented spontaneous sinus recanalization radiologically at a mean of 89 ± 41 days (range, 7-171).

CONCLUSION

CVST after supratentorial awake craniotomy is a rare event with satisfactory clinical outcomes and spontaneous sinus recanalization under conservative management without treatment-dose anticoagulant therapy. These findings are comforting to neurosurgeons confronted with postoperative MRI reports suggesting CVST.

A priori free spectral unmixing with periodic absorbance changes: application for auto-calibrated intraoperative functional brain mapping

Spectral unmixing designates techniques that allow to decompose measured spectra into linear or non-linear combination of spectra of all targets (endmembers). This technique was initially developed for satellite applications, but it is now also widely used in biomedical applications. However, several drawbacks limit the use of these techniques with standard optical devices like RGB cameras. The devices need to be calibrated and a a priori on the observed scene is often necessary. We propose a new method for estimating endmembers and their proportion automatically and without calibration of the acquisition device based on near separable non-negative matrix factorization. This method estimates the endmembers on spectra of absorbance changes presenting periodic events. This is very common in in vivo biomedical and medical optical imaging where hemodynamics dominate the absorbance fluctuations. We applied the method for identifying functional brain areas during neurosurgery using four different RGB cameras (an industrial camera, a smartphone and two surgical microscopes). Results obtained with the auto-calibration method were consistent with the intraoperative gold standards. Endmembers estimated with the auto-calibration method were similar to the calibrated endmembers used in the modified Beer-Lambert law. The similarity was particularly strong when both cardiac and respiratory periodic events were considered. This work can allow a widespread use of spectral imaging in the industrial or medical field.

Intraoperative identification of functional brain areas with RGB imaging using statistical parametric mapping: Simulation and clinical studies

Complementary technique to preoperative fMRI and electrical brain stimulation (EBS) for glioma resection could improve dramatically the surgical procedure and patient care. Intraoperative RGB optical imaging is a technique for localizing functional areas of the human cerebral cortex that can be used during neurosurgical procedures. However, it still lacks robustness to be used with neurosurgical microscopes as a clinical standard. In particular, a robust quantification of biomarkers of brain functionality is needed to assist neurosurgeons. We propose a methodology to evaluate and optimize intraoperative identification of brain functional areas by RGB imaging. This consist in a numerical 3D brain model based on Monte Carlo simulations to evaluate intraoperative optical setups for identifying functional brain areas. We also adapted fMRI Statistical Parametric Mapping technique to identify functional brain areas in RGB videos acquired for 12 patients. Simulation and experimental results were consistent and showed that the intraoperative identification of functional brain areas is possible with RGB imaging using deoxygenated hemoglobin contrast. Optical functional identifications were consistent with those provided by EBS and preoperative fMRI. We also demonstrated that a halogen lighting may be particularity adapted for functional optical imaging. We showed that an RGB camera combined with a quantitative modeling of brain hemodynamics biomarkers can evaluate in a robust way the functional areas during neurosurgery and serve as a tool of choice to complement EBS and fMRI.

A Preoperative Scoring System to Predict Function-Based Resection Limitation Due to Insufficient Participation During Awake Surgery

BACKGROUND

Failure in achieving a function-based resection related to the insufficient patient's participation is a drawback of awake surgery.

OBJECTIVE

To assess preoperative parameters predicting the risk of patient insufficient intraoperative cooperation leading to the arrest of the awake resection.

METHODS

Observational, retrospective, multicentric cohort analysis enrolling 384 (experimental dataset) and 100 (external validation dataset) awake surgeries.

RESULTS

In the experimental data set, an insufficient intraoperative cooperation occurred in 20/384 patients (5.2%), leading to awake surgery failure in 3/384 patients (ie, no resection, 0.8%), and precluded the achievement of the function-based resection in 17/384 patients (ie, resection limitation, 4.4%). The insufficient intraoperative cooperation significantly reduced the resection rates (55.0% vs 94.0%, P < .001) and precluded a supratotal resection (0% vs 11.3%, P = .017). Seventy years or older, uncontrolled epileptic seizures, previous oncological treatment, hyperperfusion on MRI, and mass effect on midline were independent predictors of insufficient cooperation during awake surgery ( P < .05). An Awake Surgery Insufficient Cooperation score was then assessed: 96.9% of patients (n = 343/354) with a score ≤2 presented a good intraoperative cooperation, while only 70.0% of patients (n = 21/30) with a score >2 presented a good intraoperative cooperation. In the experimental data set, similar date were found: 98.9% of patients (n = 98/99) with a score ≤2 presented a good cooperation, while 0% of patients (n = 0/1) with a score >2 presented a good cooperation.

CONCLUSION

Function-based resection under awake conditions can be safely performed with a low rate of insufficient patient intraoperative cooperation. The risk can be assessed preoperatively by a careful patient selection.

Continuous subcortical language mapping in awake glioma surgery

Repetitive monopolar short-train stimulation (STS) delivered from a suction probe enables continuous mapping and distance assessment of corticospinal tracts during asleep glioma resection. In this study, we explored this stimulation technique in awake glioma surgery. Fourteen patients with glioma involving language-related tracts were prospectively included. Continuous (3-Hz) cathodal monopolar STS (five pulses, 250 Hz) was delivered via the tip of a suction probe throughout tumor resection while testing language performance. At 70 subcortical locations, surgery was paused to deliver STS in a steady suction probe position. Monopolar STS influence on language performance at different subcortical locations was separated into three groups. Group 1 represented locations where STS did not produce language disturbance. Groups 2 and 3 represented subcortical locations where STS produced language interference at different threshold intensities (≥7.5 and ≤5 mA, respectively). For validation, bipolar Penfield stimulation (PS; 60 Hz for 3 s) was used as a “gold standard” comparison method to detect close proximity to language-related tracts and classified as positive or negative regarding language interference. There was no language interference from STS in 28 locations (Group 1), and PS was negative for all sites. In Group 2 (STS threshold ≥ 7.5 mA; median, 10 mA), there was language interference at 18 locations, and PS (median, 4 mA) was positive in only one location. In Group 3 (STS threshold ≤ 5 mA; median, 5 mA), there was language interference at 24 locations, and positive PS (median 4 mA) was significantly (p < 0.01) more common (15 out of 24 locations) compared with Groups 1 and 2. Despite the continuous stimulation throughout tumor resection, there were no seizures in any of the patients. In five patients, temporary current spread to the facial nerve was observed. We conclude that continuous subcortical STS is feasibly also in awake glioma surgery and that no language interference from STS or interference at ≥7.5 mA seems to indicate safe distance to language tracts as judged by PS comparisons. STS language interference at STS ≤ 5 mA was not consistently confirmed by PS, which needs to be addressed.

Variability of Intraoperative Electrostimulation Parameters in Conscious Individuals: Language Fasciculi

OBJECTIVE

The authors analyzed the current-intensity thresholds for electrostimulation of language fasciculi and the possible consequences of threshold variability on brain mapping.

METHODS

A prospective protocol of subcortical electrostimulation was used in 50 patients undergoing brain mapping, directly stimulating presumed language fasciculi identified by diffusion tensor imaging.

RESULTS

The stimulation-intensity thresholds for identification of language fasciculi varied among patients (mean minimum current intensity of 4.4 mA, range = 1.5-10 mA, standard deviation = 1.1 mA), and 23% of fascicular interferences were detected only above 5 mA. Repeated stimulation of the same site with the same intensity led to different types of interferences in 20% of patients, and a higher current intensity led to changes in the type of response in 27%. The mean minimum stimulation intensities did not differ significantly between different fasciculi, between the different types of interference obtained, or with age, sex, or type of tumor. Positive results on cortical mapping were significantly associated with positive results on subcortical mapping (P < 0.001). Subcortical intensity thresholds were slightly lower than cortical ones (mean = 4.43 vs. 5.25 mA, P = 0.034). In 23 of 50 subcortical mappings, fascicular stimulation produced no language interference.

CONCLUSIONS

Individual variability of minimum stimulation-intensity thresholds for identification of language fasciculi is frequent. Nevertheless, even when a high current intensity was used, many stimulations on language fasciculi remained negative for various hypothetic reasons. Finding the optimal current intensity for identifying language fasciculi is of paramount importance to refine the clinical results and scientific data derived from brain mapping.

Intraoperative Resting-State Functional Connectivity Based on RGB Imaging

RGB optical imaging is a marker-free, contactless, and non-invasive technique that is able to monitor hemodynamic brain response following neuronal activation using task-based and resting-state procedures. Magnetic resonance imaging (fMRI) and functional near infra-red spectroscopy (fNIRS) resting-state procedures cannot be used intraoperatively but RGB imaging provides an ideal solution to identify resting-state networks during a neurosurgical operation. We applied resting-state methodologies to intraoperative RGB imaging and evaluated their ability to identify resting-state networks. We adapted two resting-state methodologies from fMRI for the identification of resting-state networks using intraoperative RGB imaging. Measurements were performed in 3 patients who underwent resection of lesions adjacent to motor sites. The resting-state networks were compared to the identifications provided by RGB task-based imaging and electrical brain stimulation. Intraoperative RGB resting-state networks corresponded to RGB task-based imaging (DICE:0.55±0.29). Resting state procedures showed a strong correspondence between them (DICE:0.66±0.11) and with electrical brain stimulation. RGB imaging is a relevant technique for intraoperative resting-state networks identification. Intraoperative resting-state imaging has several advantages compared to functional task-based analyses: data acquisition is shorter, less complex, and less demanding for the patients, especially for those unable to perform the tasks.

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

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

Surgery of Insular Diffuse Gliomas-Part 2: Probabilistic Cortico-Subcortical Atlas of Critical Eloquent Brain Structures and Probabilistic Resection Map During Transcortical Awake Resection

BACKGROUND

Insular diffuse glioma surgery is challenging, and tools to help surgical planning could improve the benefit-to-risk ratio.

OBJECTIVE

To provide a probabilistic resection map and frequency atlases of critical eloquent regions of insular diffuse gliomas based on our surgical experience.

METHODS

We computed cortico-subcortical "eloquent" anatomic sites identified intraoperatively by direct electrical stimulations during transcortical awake resection of insular diffuse gliomas in adults.

RESULTS

From 61 insular diffuse gliomas (39 left, 22 right; all left hemispheric dominance for language), we provided a frequency atlas of eloquence of the opercula (left/right; pars orbitalis: 0%/5.0%; pars triangularis: l5.6%/4.5%; pars opercularis: 37.8%/27.3%; precentral gyrus: 97.3%/95.4%; postcentral and supramarginal gyri: 75.0%/57.1%; temporal pole and superior temporal gyrus: 13.3%/0%), which tailored the transcortical approach (frontal operculum to reach the antero-superior insula, temporal operculum to reach the inferior insula, parietal operculum to reach the posterior insula). We provided a frequency atlas of eloquence identifying the subcortical functional boundaries (36.1% pyramidal pathways, 50.8% inferior fronto-occipital fasciculus, 13.1% arcuate and superior longitudinal fasciculi complex, 3.3% somatosensory pathways, 8.2% caudate and lentiform nuclei). Vascular boundaries and increasing errors during testing limited the resection in 8.2% and 11.5% of cases, respectively. We provided a probabilistic 3-dimensional atlas of resectability.

CONCLUSION

Functional mapping under awake conditions has to be performed intraoperatively in each patient to guide surgical approach and resection of insular diffuse gliomas in right and left hemispheres. Frequency atlases of opercula eloquence and of subcortical eloquent anatomic boundaries, and probabilistic 3-dimensional atlas of resectability could guide neurosurgeons.

Feasibility, Safety and Impact on Overall Survival of Awake Resection for Newly Diagnosed Supratentorial IDH-Wildtype Glioblastomas in Adults

Simple Summary

A few studies have suggested the benefits of awake surgery by maximizing the extent of resection while preserving neurological function and improving survival in high-grade glioma patients. However, the histomolecular heterogeneity in these series, mixing grade 3 with grade 4, and IDH-mutated with IDH-wildtype gliomas, represents a major selection bias that may influence survival analyses. For the first time, in a large homogeneous single-institution cohort of newly diagnosed supratentorial IDH-wildtype glioblastoma in adult patients, we assessed feasibility, safety and efficacy of awake surgery using univariate, multivariate and case-matched analysis. Awake surgery was associated with higher resection rates, lower residual tumor rates, and more supratotal resections than asleep resections, allowed standard radiochemotherapy to be performed systematically within a short time between surgery and radiotherapy, and was an independent predictor of progression-free survival and overall survival in the whole series, together with the extent of resection, MGMT promoter methylation status, and standard.

Abstract

Background: Although awake resection using intraoperative cortico-subcortical functional brain mapping is the benchmark technique for diffuse gliomas within eloquent brain areas, it is still rarely proposed for IDH-wildtype glioblastomas. We have assessed the feasibility, safety, and efficacy of awake resection for IDH-wildtype glioblastomas. Methods: Observational single-institution cohort (2012–2018) of 453 adult patients harboring supratentorial IDH-wildtype glioblastomas who benefited from awake resection, from asleep resection, or from a biopsy. Case matching (1:1) criteria between the awake group and asleep group: gender, age, RTOG-RPA class, tumor side, location and volume and neurosurgeon experience. Results: In patients in the awake resection subgroup (n = 42), supratotal resections were more frequent (21.4% vs. 3.1%, p < 0.0001) while partial resections were less frequent (21.4% vs. 40.1%, p < 0.0001) compared to the asleep (n = 222) resection subgroup. In multivariable analyses, postoperative standard radiochemistry (aHR = 0.04, p < 0.0001), supratotal resection (aHR = 0.27, p = 0.0021), total resection (aHR = 0.43, p < 0.0001), KPS score > 70 (HR = 0.66, p = 0.0013), MGMT promoter methylation (HR = 0.55, p = 0.0031), and awake surgery (HR = 0.54, p = 0.0156) were independent predictors of overall survival. After case matching, a longer overall survival was found for awake resection (HR = 0.47, p = 0.0103). Conclusions: Awake resection is safe, allows larger resections than asleep surgery, and positively impacts overall survival of IDH-wildtype glioblastoma in selected adult patients.

Triple motor mapping: transcranial, bipolar, and monopolar mapping for supratentorial glioma resection adjacent to motor pathways

OBJECTIVE

Maximal safe resection of gliomas near motor pathways is facilitated by intraoperative mapping. The authors and other groups have described the use of bipolar or monopolar direct stimulation to identify functional tissue, as well as transcranial or transcortical motor evoked potentials (MEPs) to monitor motor pathways. Here, the authors describe their initial experience using all 3 modalities to identify, monitor, and preserve cortical and subcortical motor systems during glioma surgery.

METHODS

Intraoperative mapping data were extracted from a prospective registry of glioma resections near motor pathways. Additional demographic, clinical, pathological, and imaging data were extracted from the electronic medical record. All patients with new or worsened postoperative motor deficits were followed for at least 6 months.

RESULTS

Between January 2018 and August 2019, 59 operations were performed in 58 patients. Overall, patients in 6 cases (10.2%) had new or worse immediate postoperative deficits. Patients with temporary deficits all had at least Medical Research Council grade 4/5 power. Only 2 patients (3.4%) had permanently worsened deficits after 6 months, both of which were associated with diffusion restriction consistent with ischemia within the corticospinal tract. One patient's deficit improved to 4/5 and the other to 4/5 proximally and 3/5 distally in the lower limb, allowing ambulation following rehabilitation. Subcortical motor pathways were identified in 51 cases (86.4%) with monopolar high-frequency stimulation, but only in 6 patients using bipolar stimulation. Transcranial or cortical MEPs were diminished in only 6 cases, 3 of which had new or worsened deficits, with 1 permanent deficit. Insula location (p = 0.001) and reduction in MEPs (p = 0.01) were the only univariate predictors of new or worsened postoperative deficits. Insula location was the only predictor of permanent deficits (p = 0.046). The median extent of resection was 98.0%.

CONCLUSIONS

Asleep triple motor mapping is safe and resulted in a low rate of deficits without compromising the extent of resection.

Use of intra-operative stimulation of brainstem lesion target sites for frameless stereotactic biopsies

INTRODUCTION

Frameless stereotactic navigation is used to direct the trajectory and biopsy site of target lesions. We report on a novel intra-operative stimulating (IOS) probe that is integrated into a commercially available stereotactic biopsy needle with the rationale that stimulation of the intended biopsy site should predict functional tissue thus preventing inadvertent biopsy of eloquent tissue.

METHODS

Patients undergoing brainstem biopsies for atypical lesions were offered the additional stimulation procedure. The IOS probe was used to deliver stimulation in an attempt to determine the proximity of eloquent tissue. Once the desired location of the biopsy needle was achieved, the IOS probe was inserted down the centre of the biopsy needle and the stimulus applied. If no action potential was recorded, biopsies from four quadrants of the lesion were taken. If however a compound action potential was recorded, a new target was selected.

RESULTS

Nine patients had the biopsy and stimulation procedure performed. The median age was 36 months. A minimum of 8 samples were obtained from each patient. Biopsy material was adequate to obtain a diagnosis in all 9 patients. In 2 cases use of the device influenced the insertion trajectory or biopsy site. No patients experienced any complications directly attributable to either the biopsy procedure or application of the stimulation.

CONCLUSIONS

Use of the IOS probe for intra-operative stimulation of the intended brainstem biopsy site was found to be safe and feasible. The addition of stimulation using the IOS probe can be done with minimal change in workflow.

Is function-based resection using intraoperative awake brain mapping feasible and safe for solitary brain metastases within eloquent areas?

To assess feasibility and safety of function-based resection under awake conditions for solitary brain metastasis patients. Retrospective, observational, single-institution case-control study (2014-2019). Inclusion criteria are adult patients, solitary brain metastasis, supratentorial location within eloquent areas, and function-based awake resection. Case matching (1:1) criteria between metastasis group and control group (high-grade gliomas) are sex, tumor location, tumor volume, preoperative Karnofsky Performance Status score, age, and educational level. Twenty patients were included. Intraoperatively, all patients were cooperative; no obstacles precluded the procedure from being performed. A positive functional mapping was achieved at both cortical and subcortical levels, allowing for a function-based resection in all patients. The case-matched analysis showed that intraoperative and postoperative events were similar, except for a shorter duration of the surgery (p<0.001) and of the awake phase (p<0.001) in the metastasis group. A total resection was performed in 18 cases (90%, including 10 supramarginal resections), and a partial resection was performed in two cases (10%). At three months postoperative months, none of the patients had worsening of their neurological condition or uncontrolled seizures, three patients had an improvement in their seizure control, and seven patients had a Karnofsky Performance Status score increase ≥10 points. Function-based resection under awake conditions preserving the brain connectivity is feasible and safe in the specific population of solitary brain metastasis patients and allows for high resection rates within eloquent brain areas while preserving the overall and neurological condition of the patients. Awake craniotomy should be considered to optimize outcomes in brain metastases in eloquent areas.

Case Report: Multimodal Functional and Structural Evaluation Combining Pre-operative nTMS Mapping and Neuroimaging With Intraoperative CT-Scan and Brain Shift Correction for Brain Tumor Surgical Resection

Background: Maximum safe resection of infiltrative brain tumors in eloquent area is the primary objective in surgical neuro-oncology. This goal can be achieved with direct electrical stimulation (DES) to perform a functional mapping of the brain in patients awake intraoperatively. When awake surgery is not possible, we propose a pipeline procedure that combines advanced techniques aiming at performing a dissection that respects the anatomo-functional connectivity of the peritumoral region. This procedure can benefit from intraoperative monitoring with computerized tomography scan (iCT-scan) and brain shift correction. Associated with this intraoperative monitoring, the additional value of preoperative investigation combining brain mapping by navigated transcranial magnetic stimulation (nTMS) with various neuroimaging modalities (tractography and resting state functional MRI) has not yet been reported. Case Report: A 42-year-old left-handed man had increased intracranial pressure (IICP), left hand muscle deficit, and dysarthria, related to an infiltrative tumor of the right frontal lobe with large mass effect and circumscribed contrast enhancement in motor and premotor cortical areas. Spectroscopy profile and intratumoral calcifications on CT-scan suggested an WHO grade III glioma, later confirmed by histology. The aforementioned surgical procedure was considered, since standard awake surgery was not appropriate for this patient. In preoperative time, nTMS mapping of motor function (deltoid, first interosseous, and tibialis anterior muscles) was performed, combined with magnetic resonance imaging (MRI)-based tractography reconstruction of 6 neural tracts (arcuate, corticospinal, inferior fronto-occipital, uncinate and superior and inferior longitudinal fasciculi) and resting-state functional MRI connectivity (rs-fMRI) of sensorimotor and language networks. In intraoperative time, DES mapping was performed with motor evoked response recording and tumor resection was optimized using non-rigid image transformation of the preoperative data (nTMS, tractography, and rs-fMRI) to iCT data. Image guidance was updated with correction for brain shift and tissue deformation using biomechanical modeling taking into account brain elastic properties. This correction was done at crucial surgical steps, i.e., when tumor bulged through the craniotomy after dura mater opening and when approaching the presumed eloquent brain regions. This procedure allowed a total resection of the tumor region with contrast enhancement as well as a complete regression of IICP and dysarthria. Hand paresis remained stable with no additional deficit. Postoperative nTMS mapping confirmed the good functional outcome. Conclusion: This case report and technical note highlights the value of preoperative functional evaluation by nTMS updated intraoperatively with correction of brain deformation by iCT. This multimodal approach may become the optimized technique of reference for patients with brain tumors in eloquent areas that are unsuitable for awake brain surgery.

What effects does awake craniotomy have on functional and survival outcomes for glioblastoma patients?

PURPOSE

Neurosurgeons adopt several different surgical approaches to deal with glioblastomas (GB) located in or near eloquent areas. Some attempt maximal safe resection by awake craniotomy (AC), but doubts persist concerning the real benefits of this type of surgery in this situation. We performed a retrospective study to evaluate the extent of resection (EOR), functional and survival outcomes after AC of patients with GB in critical locations.

METHODS

Forty-six patients with primary GB treated with the Stupp regimen between 2004 and 2019, for whom brain mapping was feasible, were included. We assessed EOR, postoperative language and/or motor deficits three months after AC, progression-free survival (PFS) and overall survival (OS).

RESULTS

Complete resection was achieved in 61% of the 46 GB patients. The median PFS was 6.8 months (CI 6.1; 9.7) and the median OS was 17.6 months (CI 14.8; 34.1). Three months after AC, more than half the patients asymptomatic before surgery remained asymptomatic, and one third of patients with symptoms before surgery experienced improvements in language, but not motor functions. The risk of postoperative deficits was higher in patients with preoperative deficits or incomplete resection. Furthermore, the presence of postoperative deficits was an independent predictive factor for shorter PFS.

CONCLUSION

AC is an option for the resection of GB in critical locations. The observed survival outcomes are typical for GB patients in the Stupp era. However, the success of AC in terms of the recovery or preservation of language and/or motor functions cannot be guaranteed, given the aggressiveness of the tumor.

How I do it: trans-cortical approach for insular diffuse glioma

BACKGROUND

The function-based resection using trans-cortical approach for removing insular diffuse glioma shares a positive benefit-to-risk ratio with a low rate of permanent morbidity.

METHOD

The technique requires intraoperative functional brain mapping to be performed under awake condition using direct electrical stimulations at both cortical and subcortical levels to identify brain connectivity supporting neurocognition.

CONCLUSION

The trans-cortical approach is a safe and efficient technique to remove insular diffuse glioma. Intraoperative functional brain mapping under awake condition allows preserving brain connectivity and tailoring the resection. Great care must be taken in preventing vascular damages, and particularly the lenticulostriate arteries.

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

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Language processing from the perspective of electrical stimulation mapping

Electrical Stimulation (ES) is a neurostimulation technique that is used to localize language functions in the brain of people with intractable epilepsy and/or brain tumors. We reviewed 25 ES articles published between 1984 and 2018 and interpreted them from a cognitive neuropsychological perspective. Our aim was to highlight ES as a tool to further our understanding of cognitive models of language. We focused on associations and dissociations between cognitive functions within the framework of two non-neuroanatomically specified models of language. Also, we discussed parallels between the ES and the stroke literatures and showed how ES data can help us to generate hypotheses regarding how language is processed. A good understanding of cognitive models of language is essential to motivate task selection and to tailor surgical procedures, for example, by avoiding testing the same cognitive functions and understanding which functions may be more or less relevant to be tested during surgery.