Direct Subcortical Stimulation Research Articles

Direct Subcortical Stimulation for Intraoperative Mapping of Optic Radiations (P1-11.009)

Direct Subcortical Stimulation for Intraoperative Mapping of Optic Radiations (P1-11.009)

The quantitative evaluation of cortico-spinal tract involvement in malignant intracerebral tumors

The aim of the study was development of the method for preoperative quantitative evaluation of pyramidal tract and tumor relationship in malignant intracerebral tumors.Materials and methods. The retrospective analysis of 62 patients underwent surgery at the Department of Neurosurgery of Privolzhsky Research Medical University in 2017–2019, was performed. The patients were divide in 3 groups: metastatic brain tumor (n = 16); contrast-enhanced gliomas (grade III–IV); contrast-nonenhanced gliomas (grade II–III). The following protocol was implemented for all patients: preoperative DTI-tractography; intraoperative direct subcortical electrical stimulation with fixation of the minimum current intensity at receiving the motor response; pre- and postoperative motor function assessment using MRC-scale. Tract Involvement Index (TII) based on the ratio of the perimeter of the part of the tract involvement in pathological MRI-signal to its cross-section area was calculated using image processing of preoperative MRI and MRI-tractography data.Results. The association between TII values (from 0 to 1.75) and the severity of pre-operative paresis was demonstrated. We have discovered that the greater value of the pyramidal TII was corresponded to the greater severity of the paresis in MRC (p <0.001, n = 62). The analysis of TII values and intraoperative motor direct subcortical mapping results showed an increase in risk of contact with a tract at higher TII value (B0 = −1.6; Bi = 6.61; χ2 = 30.53; n = 62, p <0.001). The TII demonstrates better prognostic value in patients without radiation therapy in anamnesis.Conclusions. The method for preoperative quantitative evaluation of pyramidal tract and tumor relationship using TII calculation can provide additional information for planning surgical treatment in patients with intracerebral tumors without radiation treatment in the history.

Maximal surgical resection and adjuvant surgical technique to prolong the survival of adult patients with thalamic glioblastoma

The importance of maximal resection in the treatment of glioblastoma (GBM) has been reported in many studies, but maximal resection of thalamic GBM is rarely attempted due to high rate of morbidity and mortality. The purpose of this study was to investigate the role of surgical resection in adult thalamic glioblastoma (GBM) treatment and to identify the surgical technique of maximal safety resection. In case of suspected thalamic GBM, surgical resection is the treatment of choice in our hospital. Biopsy was considered when there was ventricle wall enhancement or multiple enhancement lesion in a distant location. Navigation magnetic resonance imaging, diffuse tensor tractography imaging, tailed bullets, and intraoperative computed tomography and neurophysiologic monitoring (transcranial motor evoked potential and direct subcortical stimulation) were used in all surgical resection cases. The surgical approach was selected on the basis of the location of the tumor epicenter and the adjacent corticospinal tract. Among the 42 patients, 19 and 23 patients underwent surgical resection and biopsy, respectively, according to treatment strategy criteria. As a result, the surgical resection group exhibited a good response with overall survival (OS) (median: 676 days, p < 0.001) and progression-free survival (PFS) (median: 328 days, p < 0.001) compared with each biopsy groups (doctor selecting biopsy group, median OS: 240 days and median PFS: 134 days; patient selecting biopsy group, median OS: 212 days and median PFS: 118 days). The surgical resection groups displayed a better prognosis compared to that of the biopsy groups for both the O6-methylguanine-DNA methyltransferase unmethylated (log-rank p = 0.0035) or methylated groups (log-rank p = 0.021). Surgical resection was significantly associated with better prognosis (hazard ratio: 0.214, p = 0.006). In case of thalamic GBM without ventricle wall-enhancing lesion or multiple lesions, maximal surgical resection above 80% showed good clinical outcomes with prolonged the overall survival compared to biopsy. It is helpful to use adjuvant surgical techniques of checking intraoperative changes and select the appropriate surgical approach for reducing the surgical morbidity.

The role of diffusion tensor imaging and tractography in the surgical management of brainstem gliomas.

Diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) have the ability to noninvasively visualize changes in white matter tracts, as well as their relationships with lesions and other structures. DTI/DTT has been increasingly used to improve the safety and results of surgical treatment for lesions in eloquent areas, such as brainstem cavernous malformations. This study aimed to investigate the application value of DTI/DTT in brainstem glioma surgery and to validate the spatial accuracy of reconstructed corticospinal tracts (CSTs). A retrospective analysis was performed on 54 patients with brainstem gliomas who had undergone surgery from January 2016 to December 2018 at Beijing Tiantan Hospital. All patients underwent preoperative DTI and tumor resection with the assistance of DTT-merged neuronavigation and electrophysiological monitoring. Preoperative conventional MRI and DTI data were collected, and the muscle strength and modified Rankin Scale (mRS) score before and after surgery were measured. The surgical plan was created with the assistance of DTI/DTT findings. The accuracy of DTI/DTT was validated by performing direct subcortical stimulation (DsCS) intraoperatively. Multiple linear regression was used to investigate the relationship between quantitative parameters of DTI/DTT (such as the CST score and tumor-to-CST distance [TCD]) and postoperative muscle strength and mRS scores. Among the 54 patients, 6 had normal bilateral CSTs, 12 patients had unilateral CST impairments, and 36 had bilateral CSTs involved. The most common changes in the CSTs were deformation (n = 29), followed by deviation (n = 28) and interruption (n = 27). The surgical approach was changed in 18 cases (33.3%) after accounting for the DTI/DTT results. Among 55 CSTs on which DsCS was performed, 46 (83.6%) were validated as spatially accurate by DsCS. The CST score and TCD were significantly correlated with postoperative muscle strength (r = -0.395, p < 0.001, and r = 0.275, p = 0.004, respectively) and postoperative mRS score (r = 0.430, p = 0.001, and r = -0.329, p = 0.015, respectively). The CST score was independently linearly associated with postoperative muscle strength (t = -2.461, p = 0.016) and the postoperative mRS score (t = 2.052, p = 0.046). DTI/DTT is a valuable tool in the surgical management of brainstem gliomas. With good accuracy, it can help optimize surgical planning, guide tumor resection, and predict the postoperative muscle strength and postoperative quality of life of patients.

Intraoperative MRI-based elastic fusion for anatomically accurate tractography of the corticospinal tract: correlation with intraoperative neuromonitoring and clinical status.

Tractography is a useful technique that is standardly applied to visualize subcortical pathways. However, brain shift hampers tractography use during the course of surgery. While intraoperative MRI (ioMRI) has been shown to be beneficial for use in oncology, intraoperative tractography can rarely be performed due to scanner, protocol, or head clamp limitations. Elastic fusion (EF), however, enables adjustment for brain shift of preoperative imaging and even tractography based on intraoperative images. The authors tested the hypothesis that adjustment of tractography by ioMRI-based EF (IBEF) correlates with the results of intraoperative neuromonitoring (IONM) and clinical outcome and is therefore a reliable method. In 304 consecutive patients treated between June 2018 and March 2020, 8 patients, who made up the basic study cohort, showed an intraoperative loss of motor evoked potentials (MEPs) during motor-eloquent glioma resection for a subcortical lesion within the corticospinal tract (CST) as shown by ioMRI. The authors preoperatively visualized the CST using tractography. Also, IBEFs of pre- and intraoperative images were obtained and the location of the CST was compared in relation to a subcortical lesion. In 11 patients (8 patients with intraoperative loss of MEPs, one of whom also showed loss of MEPs on IBEF evaluation, plus 3 additional patients with loss of MEPs on IBEF evaluation), the authors examined the location of the CST by direct subcortical stimulation (DSCS). The authors defined the IONM results and the functional outcome data as ground truth for analysis. The maximum mean ± SD correction was 8.8 ± 2.9 (range 3.8-12.0) mm for the whole brain and 5.3 ± 2.4 (range 1.2-8.7) mm for the CST. The CST was located within the lesion before IBEF in 3 cases and after IBEF in all cases (p = 0.0256). All patients with intraoperative loss of MEPs suffered from surgery-related permanent motor deficits. By approximation, the location of the CST after IBEF could be verified by DSCS in 4 cases. The present study shows that tractography after IBEF accurately correlates with IONM and patient outcomes and thus demonstrates reliability in this initial study.

Intraoperative direct subcortical stimulation: comparison of monopolar and bipolar stimulation

Intraoperative subcortical electrical stimulation is used to identify and preserve white matter tracts so that tumor resection can be performed while avoiding postsurgical deficits. The effects of the stimulating electrodes in identifying the white matter tracts have not been characterized; thus, different hospitals use different electrode configurations. Computational modeling can be used to conduct a systematic assessment of the effects of the stimulating electrode parameters. However, no realistic computational model of subcortical electrical stimulation has been implemented and verified. In this study, we investigated the interaction between the corticospinal tract (CST) and subcortical stimulation and compared different electrode configurations during monopolar and bipolar stimulation. For that, we computed the induced electric field in a realistic human head model coupled with a CST axon model. The implemented model was verified with available experimental data that were acquired during subcortical stimulation, and a systematic sensitivity analysis of parameters related to the stimulation was conducted. The results showed that the optimal stimulation varies according to the surgery conditions. If the CST was close to the resection border, bipolar stimulation could produce more selective activation. Monopolar stimulation was more robust and more effective for the CST far from the stimulation point.

Limitation of Intraoperative Transcranial Electrical Stimulation-Motor Evoked Potential Monitoring During Brain Tumor Resection Adjacent to the Primary Motor Cortex.

Transcranial electrical stimulation-motor evoked potential (TES-MEP) is a valuable intraoperative monitoring technique during brain tumor surgery. However, TES can stimulate deep subcortical areas located far from the motor cortex. There is a concern about false-negative results from the use of TES-MEP during resection of those tumors adjacent to the primary motor cortex. Our study reports three cases of TES-MEP monitoring with false-negative results due to deep axonal stimulation during brain tumor resection. Although no significant change in TES-MEP was observed during surgery, study subjects experienced muscle weakness after surgery. Deep axonal stimulation of TES could give false-negative results. Therefore, a combined method of TES-MEP and direct cortical stimulation-motor evoked potential (DCS-MEP) or direct subcortical stimulation should be considered to overcome the limitation of TES-MEP.

F112. Continuous monitoring with direct cortical and subcortical stimulation for perirolandic tumor resection: The experience of a Brazilian group

Introduction Tumor resection should be maximal for a longer survival and quality of life but the main concern in surgeries of the perirolandic tumors is to prevent new neurologic deficits. Neurophysiologic intraoperative techniques to continuously monitor the motor function are desired to avoid this risk. Direct cortical stimulation (DC-MEP) and subcortical (SUBC-MEP) stimulation have been successfully used for this. The aim of this paper is to present our experience with this technique. Methods We studied 36 of 45 patients with perirolandic tumors (18 female), mean age of 46.6 y (4–76 y), submitted to tumor resection under total intravenous anesthesia (TIVA) and intraoperative neuromonitoring (IONM) with our standard protocol consisting of SEP-PR, cortical motor mapping (CMM), continuous direct cortical motor evoked potential (DC-MEP) and continuous subcortical motor evoked potential (SUBC-MEP). The DC-MEP was elicited using a strip electrode placed over the hand area of the precentral gyrus (anodic stimulation) and recorded with subdermal needle electrodes placed in the contralateral hemibody muscles. SUBC-MEP was elicited through a monopolar aspirator device (cathodic stimulation) and recorded in the same muscles. A train of 4 or 5 pulses with 0,5 ms duration and inter-stimulus interval of 3 ms is applied continuously at 1 Hz alternating between cortical and subcortical. Warning criteria was 50% amplitude decrease for DC-MEP and 3–5 mA for SUBC-MEP. Results From the 45 cases, DC-MEP and SUBC-MEP were recorded in 36 patients, allowing continuous monitoring of the motor pathways. In the remaining 9 cases the surgeons decided for the use of cortical mapping only because the strip electrode positioning would disturb the tumor resection; in these patients, subcortical stimulation was performed in 5 according to the surgeon decision, but not continuously, and in two of them transitory postoperative new neurologic deficits were observed. From the 36 patients monitored with simultaneous DC-MEP and SUBC-MEP, there were no consistent amplitude decrease for DC-MEP and the threshold for SUBC-MEP was above 11 mA in 19 cases, between 6 and 10 mA in 12 and between 3 and 5 mA in 3. Only one patient with 3 mA subcortical threshold had a transitory motor deficit (less than 24 h). Our results are comparable with the previously reported in the literature. Conclusion Despite the few studied cases, it seems for us that continuous monitoring is better than cortical motor mapping alone. The DC-MEP and SUBC-MEP are precise for intraoperative diagnostic and allow a better resection with preservation of the motor pathway. In one case, SUBC-MEP showed the lowest threshold of 3 mA and was followed by a transitory deficit. Simultaneous and continuous monitoring of the cortical and subcortical MEP must be encouraged.

Intraoperative Neurophysiological Monitoring : A Review of Techniques Used for Brain Tumor Surgery in Children

Intraoperative monitoring (IOM) utilizes electrophysiological techniques as a surrogate test and evaluation of nervous function while a patient is under general anesthesia. They are increasingly used for procedures, both surgical and endovascular, to avoid injury during an operation, examine neurological tissue to guide the surgery, or to test electrophysiological function to allow for more complete resection or corrections. The application of IOM during pediatric brain tumor resections encompasses a unique set of technical issues. First, obtaining stable and reliable responses in children of different ages requires detailed understanding of normal ageadjusted brain-spine development. Neurophysiology, anatomy, and anthropometry of children are different from those of adults. Second, monitoring of the brain may include risk to eloquent functions and cranial nerve functions that are difficult with the usual neurophysiological techniques. Third, interpretation of signal change requires unique sets of normative values specific for children of that age. Fourth, tumor resection involves multiple considerations including defining tumor type, size, location, pathophysiology that might require maximal removal of lesion or minimal intervention. IOM techniques can be divided into monitoring and mapping. Mapping involves identification of specific neural structures to avoid or minimize injury. Monitoring is continuous acquisition of neural signals to determine the integrity of the full longitudinal path of the neural system of interest. Motor evoked potentials and somatosensory evoked potentials are representative methodologies for monitoring. Free-running electromyography is also used to monitor irritation or damage to the motor nerves in the lower motor neuron level : cranial nerves, roots, and peripheral nerves. For the surgery of infratentorial tumors, in addition to free-running electromyography of the bulbar muscles, brainstem auditory evoked potentials or corticobulbar motor evoked potentials could be combined to prevent injury of the cranial nerves or nucleus. IOM for cerebral tumors can adopt direct cortical stimulation or direct subcortical stimulation to map the corticospinal pathways in the vicinity of lesion. IOM is a diagnostic as well as interventional tool for neurosurgery. To prove clinical evidence of it is not simple. Randomized controlled prospective studies may not be possible due to ethical reasons. However, prospective longitudinal studies confirming prognostic value of IOM are available. Furthermore, oncological outcome has also been shown to be superior in some brain tumors, with IOM. New methodologies of IOM are being developed and clinically applied. This review establishes a composite view of techniques used today, noting differences between adult and pediatric monitoring.

Chronic spatial working memory deficit associated with the superior longitudinal fasciculus: a study using voxel-based lesion-symptom mapping and intraoperative direct stimulation in right prefrontal glioma surgery

OBJECTIVE Although the right prefrontal region is regarded as a silent area, chronic deficits of the executive function, including working memory (WM), could occur after resection of a right prefrontal glioma. This may be overlooked by postoperative standard examinations, and the disabilities could affect the patient's professional life. The right prefrontal region is a part of the frontoparietal network and is subserved by the superior longitudinal fasciculus (SLF); however, the role of the SLF in spatial WM is unclear. This study investigated a persistent spatial WM deficit in patients who underwent right prefrontal glioma resection, and evaluated the relationship between the spatial WM deficit and the SLF. METHODS Spatial WM was examined in 24 patients who underwent prefrontal glioma resection (right, n = 14; left, n = 10) and in 14 healthy volunteers using a spatial 2-back task during the long-term postoperative period. The neural correlates of spatial WM were evaluated using lesion mapping and voxel-based lesion-symptom mapping. In addition, the spatial 2-back task was performed during surgery under direct subcortical electrical stimulation in 2 patients with right prefrontal gliomas. RESULTS Patients with a right prefrontal lesion had a significant chronic spatial WM deficit. Voxel-based lesion-symptom mapping analysis revealed a significant correlation between spatial WM deficit and the region that overlapped the first and second segments of the SLF (SLF I and SLF II). Two patients underwent awake surgery and had difficulties providing the correct responses in the spatial 2-back task with direct subcortical electrical stimulation on the SLF I, which was preserved and confirmed by postoperative diffusion tensor imaging tractography. These patients exhibited no spatial WM deficits during the postoperative immediate and long-term periods. CONCLUSIONS Spatial WM deficits may persist in patients who undergo resection of the tumor located in the right prefrontal brain parenchyma. Injury to the dorsal frontoparietal subcortical white matter pathway, i.e., the SLF I or SLF I and II, could play a causal role in this chronic deficit. A persistent spatial WM deficit, without motor and language deficits, could affect the professional life of the patient. In such cases, awake surgery would be useful to detect the spatial WM network with appropriate task during tumor exploration.

P16.11 * A NEW TECHNIQUE OF "FUNCTIONAL" DTI TRACTOGRAPHY OF THE CORTICO-SPINAL TRACT BASED ON NAVIGATED BRAIN STIMULATION FOR SURGERY OF BRAIN TUMORS LOCATED NEAR THE MOTOR PATHWAY

INTRODUCTION: Surgery of brain tumors located near the motor pathway still represents a challenge because of the risk of significant post-operative morbidity. In the last few years, there have been an increasing interest for imaging techniques that could reliably define the spatial relationship between a tumor and the adjacent eloquent areas before surgery. Among these techniques, navigated brain stimulation (NBS) and DTI tractography of the cortico-spinal tract (CST) are considered the most promising. However, tractography still presents spatial inaccuracies that can be reduced by using the NBS map of the motor cortex as seeding region for the tract reconstruction. The objective of this study is to: describe a new technique of a “functional” NBS-based DTI tractography of the CST able to define its somatotopic organization; verify its accuracy by using direct subcortical stimulation (DSS); compare its reliability with the standard tractography; assess its impact on surgical strategy and motor outcome in patients operated for brain tumors located near the motor pathway. MATERIALS AND METHODS: We prospectively enrolled patients operated at the Neurosurgical Clinic of the University of Messina, Italy, between 2012 and 2014. All patients were submitted to the “functional” NBS-based DTI tractography of the CST. We reconstructed the motor pathway pre- and intra-operatively for the surgical planning as a guide for the lesion resection. In addition, after surgery, we performed the standard CST tractography. We assessed the accuracy of the CST somatotopic reconstruction using the DSS. Then, we compared the reliability of our technique with the standard tractography, analyzing the number of tract fibers obtained using the two techniques and the degree of overlapping of the CST cortical end-regions with the NBS map of the motor cortex. Lastly, we assessed the impact of our technique on surgical strategy using a multiple choice questionnaire provided to the surgeon, and assessed its efficacy in avoiding post-operative motor deficits using the Medical Research Council (MRC) scale. RESULTS: In 25 cases cases we obtained a somatotopic reconstruction of the CST, distinguishing between functionally different fiber bundles (arm, face and leg fibers) which matched with the DSS. The “functional” technique was more accurate than the standard tractography, providing useful information to the surgeon in 76% of cases. Lastly no worsening of the MRC score was recorded in all cases. CONCLUSIONS: The “functional” NBS-based DTI tractography of the CST is a reliable planning tool for surgery of brain tumors located near the motor pathway. It provides helpful anatomical and functional information about the motor pathway that can be used before and during surgery. It is also more accurate and less operator-dependent as compared to the standard tractography and is effective in avoiding post-operative motor deficits.

Clinical Application of Motor Pathway Mapping Using Diffusion Tensor Imaging Tractography and Intraoperative Direct Subcortical Stimulation in Cerebral Glioma Surgery

Glioma surgery in eloquent areas remains a challenge because of the risk of postoperative motor deficits. To prospectively evaluate the efficiency of using a combination of diffusion tensor imaging (DTI) tractography functional neuronavigation and direct subcortical stimulation (DsCS) to yield a maximally safe resection of cerebral glioma in eloquent areas. A prospective cohort study was conducted in 58 subjects with an initial diagnosis of primary cerebral glioma within or adjacent to the pyramidal tract (PT). The white matter beneath the resection cavity was stimulated along the PT, which was visualized with DTI tractography. The intercept between the PT border and DsCS site was measured. The sensitivity and specificity of DTI tractography for PT mapping were evaluated. The efficiency of the combined use of both techniques on motor function preservation was assessed. Postoperative analysis showed gross total resection in 40 patients (69.0%). Seventeen patients (29.3%) experienced postoperative worsening; 1-month motor deficit was observed in 6 subjects (10.3%). DsCS verified a high concordance rate with DTI tractography for PT mapping. The sensitivity and specificity of DTI were 92.6% and 93.2%, respectively. The intercepts between positive DsCS sites and imaged PTs were 2.0 to 14.7 mm (5.2 ± 2.2 mm). The 6-month Karnofsky performance scale scores in 50 postoperative subjects were significantly increased compared with their preoperative scores. DTI tractography is effective but not completely reliable in delineating the descending motor pathways. Integration of DTI and DsCS favors patient-specific surgery for cerebral glioma in eloquent areas.

Imagen de tractografía 3T: anatomía y aplicaciones clínicas

Tractography (TG) is the only non-invasive technique that enables the fibres of the white substance to be dissected. This technique can study the projection, association, and commissural fibres, and is an improvement and an important complement to conventional MR imaging.TG is an important tool for preoperative sub-cortical mapping, and there is a good correlation between TG and the direct sub-cortical stimulation technique. TG can have false positives in regions infiltrated by the tumour or with a mass effect. Furthermore, a negative TG does not exclude functional fibre persistence.TG is capable of demonstrating changes in other pathologies (congenital malformations, ischaemic disease and demyelinating diseases).

Surgical treatment of insular tumours with tractography, functional magnetic resonance imaging, transcranial electrical stimulation and direct subcortical stimulation support

Background and purposeSurgical treatment of insular tumours carries significant risks of limb paresis or speech disturbances due to their localization. The development of intraoperative neuromonitoring techniques that involve evoked motor potentials induced via both direct and transcranial cortical electrical stimulation as well as direct subcortical white matter stimulation, intraoperative application of preoperative tractography and functional magnetic resonanceimaging (fMRI) in conjunction with neuronavigation resulted in significant reduction of postoperative disabilities that enabled widening of indications for surgical treatment. The aim of this study was to present the authors’ own experience with surgical treatment of insular gliomas. Material and methodsOur cohort comprises 30 patients with insular gliomas treated at the Department of Neurosurgery in Sosnowiec. Clinical symptoms included sensorimotor partial seizures in 86.6%; generalized seizures in 23.3%; persistent headaches in 16.6% and hemiparesis in 6.6%. All the patients were operated on with intraoperative neuromonitoring that included transcranial cortical stimulation, direct subcortical white matter stimulation as well as tractography and fMRI concurrently with neuronavigation. The analysis included postoperative neurological evaluation along with the assessment of the radicalism of resection evaluated based on postoperative MRI. ResultsPostoperatively, four patients had permanent hemiparesis (13.3%); importantly, two out of those patients had preoperative deficits (6.6%). Persistent speech disturbances were present in four patients (13.3%). Partial sensorimotor seizures were noted in two patients (6.6%). Seizures in the other patients receded. Intraoperative transcranial electrical stimulation as well as direct subcortical white matter stimulation along with tractography (DTI) and fMRI facilitated gross total resection of insular gliomas in 53.5%, subtotal in 13.3% and partial resection in 33.1%. ConclusionsImplementation of TES, direct subcortical white master stimulation, DTI and fMRI into the management protocol of the surgical treatment of insular tumours resulted in total and subtotal resections in 66% of cases with permanent motor disability in 6.6% of patients. Poor prognosis for independent living after surgery mainly affects patients with WHO grade III or IV.

S28-3 D-wave monitoring in brain tumor surgery

through: (1) Somatosensory evoked potential phase reversal technique; (2) DCS with a short train of 5 7 monopolar stimuli (0.5ms duration, ISI 4.1, intensity up to 20mA) at 1 2Hz. To monitor motor pathways during tumor removal, MEPs are recorded from controlateral limb muscles after either DCS and/or transcranial electrical stimulation. When approaching tumor borders, MEP monitoring is combined with periodical direct subcortical stimulation (DSS) to localize the corticospinal tract (CT) and guide resection.A more than 75% drop in transcranial MEP amplitude at the end of surgery, and a DSS thresholds lower than 3 4mA are associated to post-operative neurological worsening. However these two neurophysiological warning signs are not significantly related and do not necessarily identify the same patients, suggesting that continuous MEP monitoring and periodical subcortical mapping should be combined to minimize risks. Recently, thanks to the introduction of diffusion tensor imaging and neuronavigation, there has been an increasing interest for the correlation of fiber tractography with subcortical stimulation. This work is providing some degree of reliability in the assessment of subcortical current spreading. Preliminary data suggest that 1mA = 1mm may be an acceptable practical parameter to judge on the distance from the CT, when using subcortical mapping.

Identification of the pyramidal tract by neuronavigation based on intraoperative magnetic resonance tractography: correlation with subcortical stimulation

To demonstrate the accuracy of magnetic resonance tractograpghy (MRT) in localizing the cortical spinal tract (CST) close to brain tumours by using intraoperative electric subcortical stimulation. Nine patients with intra-axial brain tumours underwent neurosurgery. Planning was based on analysis of the course of streamlines compatible with the CST. After tumour removal, intraoperative MRT was reacquired. Sites at various distance from the CST were repeatedly stimulated to assess whether registered motor evoked potential (MEP) could be elicited. All patients were assessed clinically both pre- and postoperatively. The motor function was preserved in all patients. In all patients intraoperative MRT demonstrated shift of the bundle position caused by the surgical procedure. The distance between the estimated intraoperative CST and the point of elicited MEP was 1cm or less in all nine patients. At distances greater than 2cm, no patient reported positive MEP. Intraoperative MRT is a reliable technique for localization of CST. In all patients MEP were elicited by direct subcortical electrical stimulation at a distance below 1cm from the CST as represented by MRT. Brain shifting might impact this evaluation since CST position may change during surgery in the range of 8mm.

Subcortical mapping and monitoring during insular tumor surgery

The treatment of insular tumors is controversial. Surgical treatment is associated with a higher morbidity rate than other therapies. The present work presents a new method in which the descending motor pathways are monitored during surgery for insular tumors. Intraoperative monitoring was performed in a combination of 2 techniques. The motor cortex was stimulated with a transcranial electrical stimulus. In addition, direct subcortical stimulation was performed with an electrical anodal monopolar stimulus. Compound motor action potentials (CMAPs) were recorded from target muscles. Fifteen patients were included in this preliminary study. Following transcranial stimulation, CMAPs were recorded in all cases. Subcortical stimulation was successful in 12 cases. Significant CMAP alterations were recorded in 5 patients. There were no false-negative results in the series. The technique presented here is a safe method. It allows a quantitative monitoring of motor function and functional mapping of the pyramidal tract during insular surgery.

Relationships between essential cortical language sites and subcortical pathways

Maps produced using either electrical stimulation or functional imaging have demonstrated a distributed network of cortical regions involved in expressive and receptive language tasks. The pattern of connectivity among components of this network has begun to be explored with diffusion tensor (DT) imaging, but has yet to be completely characterized. In this study the authors used DT imaging-based tractography to examine the interrelationship between cortical areas found to be essential for language by intraoperative electrical stimulation. The authors localized the arcuate fasciculus (AF), a white matter fiber system connecting frontal and parietotemporal areas in 10 patients, 9 of whom subsequently underwent left hemispheric language mapping. The authors found that 81 (79%) of 102 essential language sites (ELSs) were closely related to the AF. Of all ELSs, 59% were located within 7.5 mm of AF fiber pathway terminations, and another 20% contained pathways terminating closer to the AF than would be expected by chance (p < 0.05). Additionally, direct subcortical stimulation of the AF following focal cerebral resections produced transient language deficits. The close spatial relationship found between ELSs and the AF suggests that tractography data alone may be used for localization of ELSs. The deficits evoked by subcortical stimulation validate and demonstrate the utility of this AF localization technique, and provide further evidence that the AF is an important pathway for fluent language. Taken together, these results demonstrate that DT imaging of the AF may be used to predict the location of brain areas that will be eloquent by the standards of stimulation mapping.

Motor and language DTI Fiber Tracking combined with intraoperative subcortical mapping for surgical removal of gliomas

Preoperative DTI Fiber Tracking (DTI-FT) reconstruction of functional tracts combined with intraoperative subcortical mapping (ISM) is potentially useful to improve surgical procedures in gliomas located in eloquent areas. Aims of the study are: (1) to evaluate the modifications of fiber trajectory induced by the tumor; (2) to validate preoperative DTI-FT results with intraoperative identification of functional subcortical sites through direct subcortical stimulation; (3) to evaluate the impact of preoperative DTI-FT reconstructions in a neuronavigational setup combined with ISM technique on duration and modalities of surgical procedures, and on functional outcome of the patients. Data are available on 64 patients (52 low-grade and 12 high-grade gliomas). DTI-FT was acquired by a 3-T MR scanner with a single-shot EPI sequence (TR/TE 8986/80 ms, b = 1000 s/mm) with gradients applied along 32 non-collinear directions. 3D Fast Field Echo (FFE) T1-weighted imaging (TR/TE 8/4 ms) was performed for anatomic guidance. The corticospinal tract (CST), superior longitudinal, inferior fronto-occipital and uncinatus fasciculi were reconstructed. Data were transferred to the neuronavigational system. Functional subcortical sites identified during ISM were correlated with fiber tracts depicted by DTI-FT. In high-grade gliomas, DTI-FT depicted tracts mostly at the tumor periphery; in low-grade gliomas, fibers were frequently located inside the tumor mass. There was a high correlation between DTI-FT and ISM (sensitivity for CST = 95%, language tracts = 97%). For a proper reconstruction of the tracts, it was necessary to use a low FA threshold of fiber tracking algorithm and to position additional regions of interest (ROIs). The combination of DTI-FT and ISM decreased the duration of surgery, patient fatigue, and intraoperative seizures. Combination of DTI-FT and ISM allows accurate identification of eloquent fiber tracts and enhances surgical performance and safety maintaining a high rate of functional preservation.

運動領野周辺神経膠腫に対する手術 : 術前解剖学的および機能的マッピングの融合とニューロナビゲーションシステムおよび術中マッピング併用による運動機能温存手術

運動領野周辺神経膠腫に対する手術 : 術前解剖学的および機能的マッピングの融合とニューロナビゲーションシステムおよび術中マッピング併用による運動機能温存手術