Direct Cortical Stimulation Mapping Research Articles

The Association Between Task Complexity and Cortical Language Mapping Accuracy.

Direct cortical stimulation (DCS) mapping enables the identification of functional language regions within and around gliomas before tumor resection. Intraoperative mapping is required because glioma-infiltrated cortex engages in synchronous activity during task performance in a manner similar to normal-appearing cortex but has decreased ability to encode information for complex tasks. It is unknown whether task complexity influenced DCS mapping results. We aim to understand correlations between audiovisual picture naming (PN) task complexity and DCS error rate. We also asked what functional and oncological factors might be associated with higher rates of erroneous responses. We retrospectively reviewed intraoperative PN and word reading (WR) task performance during awake DCS language mapping for resection of dominant hemisphere World Health Organization grade 2 to 4 gliomas. The complexity of word tested in PN/WR tasks, patient characteristics, and tumor characteristics were compared between correct and incorrect trials. Between 2017 and 2021, 74 patients met inclusion criteria. At median 18.6 months of follow-up, 73.0% were alive and 52.7% remained recurrence-free. A total of 2643 PN and 978 WR trials were analyzed. A greater number of syllables in PN was associated with a higher DCS error rate (P = .001). Multivariate logistic regression found that each additional syllable in PN tasks independently increased odds of error by 2.40 (P < .001). Older age was also an independent correlate of higher error rate (P < .043). World Health Organization grade did not correlate with error rate (P = .866). More severe language impairment before surgery correlated with worse performance on more complex intraoperative tasks (P < .001). A higher error rate on PN testing did not correlate with lower extent of glioma resection (P = .949). Word complexity, quantified by the number of syllables, is associated with higher error rates for intraoperative PN tasks but does not affect extent of resection.

Speech and lexico-semantic errors during direct cortical stimulation mapping of the language-dominant hemisphere: effects of object and action naming.

In this retrospective study, the authors aimed to establish the stereotactically defined probability distribution for speech (i.e., anarthria, speech arrest) and lexico-semantic errors (i.e., anomia) through direct cortical stimulation (DCS) by using two tasks: action naming and object naming. They also analyzed the patterns of interindividual variability in the localization of the language sites involved, and investigated whether any patient or lesion location factors were associated with greater variability. Eighty-one Italian-speaking patients who underwent awake surgery between 2010 and 2021 for low- and high-grade gliomas in eloquent areas of the language-dominant hemisphere were entered in the analyses. The intraoperative DCS protocol included automatic speech tasks, object naming, and action naming. The position of the tags, as depicted on the intraoperative video or photograph, was transposed into Montreal Neurological Institute space. Subsequently, a 2D scatterplot and cluster analysis were performed. Associations between various clinical and radiological characteristics and the quantity of positive stimulated sites were determined by univariate analyses using binary logistic regression. Associated variables (p < 0.2) were included in stepwise multivariate logistic regression with backward elimination (p < 0.05). A total of 1380 cortical sites were stimulated, with a positive response in 511 cases (37%). Most anarthric errors were triggered when stimulating the left precentral gyrus, and most speech arrest errors were elicited when stimulating the left posterior inferior frontal gyrus. Anomias were found in the left inferior frontal gyrus and in the posterior part of the left temporal lobe for object naming. DCS to the left dorsal premotor cortex elicited anomic errors for action naming. Anomias were also elicited during DCS to the left posterior temporal lobe, with both object and action naming. The distribution of speech and lexico-semantic errors is in line with the current literature. The action-naming results are new and mostly involve the dorsal premotor cortex. These findings stress the importance of maximizing the use of different language tasks during surgery, because even when looking for the same type of errors, different tasks may be better suited to map specific brain regions. DCS with action and object naming identifies more positive sites than object naming alone.

Real-Time Neuropsychological Testing Protocol for Left Temporal Brain Tumor Surgery: A Technical Note and Case Report.

Background: The risk of surgery in eloquent areas is related to neuropsychological dysfunctions. Maximizing the extent of resection increases the overall survival. The onco-functional balance is mandatory when surgery involves cognitive areas, and maximal information on the cognitive status of patients during awake surgery is needed. This can be achieved using direct cortical stimulation mapping and, in addition to this, a neuropsychological monitoring technique called real-time neuropsychological testing (RTNT). The RTNT includes testing protocols based on the area where the surgery is performed. We reported on tests used for left temporal lobe surgery and our RTNT decision tree.Case Report: We reported our RTNT experience with a 25-year-old right-handed man with 13 years of schooling. He reported daily partial seizures. MRI revealed the presence of a low-grade glioma involving the temporo-insular cortex. The neuropsychological status presurgery which was within the normal range was combined with functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) information. Awake surgery plus RTNT was performed. Direct electrical stimulation during object naming elicited a motor speech arrest. Resection was continuously accompanied by the RTNT. The RTNT provided enriched information to the surgeon. Performance never dropped. A slight decrement in accuracy emerged for pseudoword repetition, short-term memory and working memory, phonological processing, and verbal comprehension. Total resection was performed, and the histological examination confirmed the nature of the lesion. Immediate postsurgery performance was within the normal range as it was the fMRI and DTI assessment.Conclusion: The RTNT provides essential information that can be used online, during surgery, for clinical aims to provide the surgeon with useful feedback on the cognitive status of patients.

The Glioma-Network Interface: A Review of the Relationship Between Glioma Molecular Subtype and Intratumoral Function.

Gliomas are a major cause of morbidity. Direct cortical stimulation mapping offers the ability to identify functional areas within the broader neural network both cortically and subcortically. Since the World Health Organization (WHO) 2016 classification categorized gliomas into molecular subgroups with varied molecular signatures and clinical behavior, it is possible that gliomas may demonstrate rates of functional network integration. We therefore retrospectively reviewed a data registry of 181 patients with dominant hemisphere frontal, parietal, insular, or temporal gliomas. Our goal was to test the hypothesis that WHO glioma histopathology and molecular subtype influences functional language or motor sites identified within the tumor. Intratumoral function as determined by direct cortical and subcortical stimulation mapping was identified at the highest rate in isocitrate dehydrogenase mutant astrocytomas and oligodendrogliomas. Finally, we reviewed the emerging literature exploring the interface between functional neural networks and gliomas. These data shed light on glioma molecular and histological characteristics most commonly associated within intratumoral function.

Impact of Navigated Task-specific fMRI on Direct Cortical Stimulation.

Cortical mapping (CM) with direct cortical stimulation (DCS) in awake craniotomy is used to preserve cognitive functions such as language. Nevertheless, patient collaboration during this procedure is influenced by previous neurological symptoms and growing discomfort with DCS duration. Our study aimed to evaluate the impact of navigated task-specific functional magnetic resonance imaging (nfMRI) on the practical aspects of DCS. We recruited glioma patients scheduled for awake craniotomy for prior fMRI-based CM, acquired during motor and language tasks (i.e., verb generation, semantic and syntactic decision tasks). Language data was combined to generate a probabilistic map indicating brain regions activated with more than one paradigm. Presurgical neurophysiological language tests (i.e., verb generation, picture naming, and semantic tasks) were also performed. We considered for subsequent study only the patients with a minimum rate of correct responses of 50% in all tests. These patients were then randomized to perform intraoperative language CM either using the multimodal approach (mCM), using nfMRI and DCS combined, or electrical CM (eCM), with DCS alone. DCS was done while the patient performed picture naming and nonverbal semantic decision tasks. Methodological features such as DCS duration, number of stimuli, total delivered stimulus duration per task, and frequency of seizures were analyzed and compared between groups. The correspondence between positive responses obtained with DCS and nfMRI was also evaluated. Twenty-one surgeries were included, thirteen of which using mCM (i.e., test group). Patients with lower presurgical neuropsychological performance (correct response rate between 50 and 80% in language tests) showed a decreased DCS duration in comparison with the control group. None of the compared methodological features showed differences between groups. Correspondence between DCS and nfMRI was 100/84% in the identification of the precentral gyrus for motor function/opercular frontal inferior gyrus for language function, respectively. Navigated fMRI data did not influence DCS in practice. Presurgical language disturbances limited the applicability of DCS mapping in awake surgery.

Visualization of Brain Shift Corrected Functional Magnetic Resonance Imaging Data for Intraoperative Brain Mapping

BackgroundBrain tumor surgery requires careful balance between maximizing tumor excision and preserving eloquent cortex. In some cases, the surgeon may opt to perform an awake craniotomy including intraoperative mapping of brain function by direct cortical stimulation (DCS) to assist in surgical decision-making. Preoperatively, functional magnetic resonance imaging (fMRI) facilitates planning by identification of eloquent brain areas, helping to guide DCS and other aspects of the surgical plan. However, brain deformation (shift) limits the usefulness of preoperative fMRI during surgery. To address this, an integrated visualization method for fMRI and DCS results is developed that is intuitive for the surgeon.MethodsAn image registration pipeline was constructed to display preoperative fMRI data corrected for brain shift overlaid on images of the exposed cortical surface at the beginning and completion of DCS mapping. Preoperative fMRI and DCS data were registered for a range of misalignments, and the residual registration errors were calculated. The pipeline was validated on imaging data from five brain tumor patients who underwent awake craniotomy.ResultsRegistration errors were well under 5 mm (the approximate spatial resolution of DCS) for misalignments of up to 25 mm and approximately 10–15°. For rotational misalignments up to 20°, the success rate was 95% for an error tolerance of 5 mm. Failures were negligible for rotational misalignments up to 10°. Good quality registrations were observed for all five patients.ConclusionsA proof-of-concept image registration pipeline is presented with acceptable accuracy for intraoperative use, providing multimodality visualization with potential benefits for intraoperative brain mapping.

P32. Improved reliabilty of intraoperative language mapping through preoperative nTMS and baseline linguistic scores

Objective Repetitive navigated transcranial magnetic stimulation (rnTMS) and direct cortical stimulation (DCS) during awake surgery are complementary tools to locate speech functional areas of the brain. However, patients show inter-individual differences in their preoperative linguistic capabilities, which can impact the validity of intraoperative DSC mapping. We developed a standardized approach which utilizes preoperative aphasia scores and rnTMS to screen patients for their capability to perform reliable object naming during awake surgery. Methods We prospectively included 18 patients with language-eloquent brain tumors, scheduled for awake surgery. Aachen Aphasia Score (AAS), Demtect Score (DS) and Berlin Aphasia Score (BAS) were used to evaluate linguistic eloquence of each patient preoperatively. Moreover, all patients underwent 3 runs of naming all objects without rnTMS (baseline run), from which only promptly and correctly named objects were retained for later rnTMS mapping. These selected objects were also used for the intraoperative baseline testing and DCS mapping under level 2 of Ramsay Sedation Score. Results The degree of preoperative language impairment significantly correlated with the incidence of errors during preoperative as well as intraoperative baseline errors (AAT p = 0.01, BAS p = 0.001, DS = 0.001). Patients with significant aphasia (BAS >=2, AAT >=1) and cognitive impairment (DS >=2) committed over 50% of incorrect or delayed namings in the preoperative baseline (p = 0.001). Despite utilizing only the images retained after preoperative baseline naming, these patients still made significantly more mistakes during intraoperative baseline naming than patients with less severe aphasia. Moreover, the dosage of anaesthetic medication significantly correlated with the incidence of errors during intraoperative baseline naming (propofol p = 0.028, remifentanil p = 0.036), despite stopping all systemic analgetic and sedative medication at least 8 min before testing. Conclusion Patients with significant aphasia (BAS >=2, AAT >=2) and cognitive impairment (DS >=2) are not able to perform reliable intraoperative object naming and are therefore not suited for this procedure. In addition, dosages of analgetic and sedative medication during craniotomy should be kept as low as possible to allow for reliable intraoperative cognitive testing.

Language Mapping Using T2-Prepared BOLD Functional MRI in the Presence of Large Susceptibility Artifacts-Initial Results in Patients With Brain Tumor and Epilepsy.

At present, presurgical functional mapping is the most prevalent clinical application of functional magnetic resonance imaging (fMRI). Signal dropouts and distortions caused by susceptibility effects in the current standard echo planar imaging (EPI)-based fMRI images are well-known problems and pose a major hurdle for the application of fMRI in several brain regions, many of which are related to language mapping in presurgical planning. Such artifacts are particularly problematic in patients with previous surgical resection cavities, craniotomy hardware, hemorrhage, and vascular malformation. A recently developed T2-prepared (T2prep) fMRI approach showed negligible distortion and dropouts in the entire brain even in the presence of large susceptibility effects. Here, we present initial results comparing T2prep- and multiband EPI-fMRI scans for presurgical language mapping using a sentence completion task in patients with brain tumor and epilepsy. In all patients scanned, T2prep-fMRI showed minimal image artifacts (distortion and dropout) and greater functional sensitivity than EPI-fMRI around the lesions containing blood products and in air-filled cavities. This enhanced sensitivity in T2prep-fMRI was also evidenced by the fact that functional activation during the sentence completion task was detected with T2prep-fMRI but not with EPI-fMRI in the affected areas with the same statistical threshold, whereas cerebrovascular reactivity during a breath-hold task was preserved in these same regions, implying intact neurovascular coupling in these patients. Although further investigations are required to validate these findings with invasive methods such as direct cortical stimulation mapping as the gold standard, this approach provides an alternative method for performing fMRI in brain regions with large susceptibility effects.

Sources of Variation Influencing Concordance between Functional MRI and Direct Cortical Stimulation in Brain Tumor Surgery.

Object: Preoperative functional magnetic resonance imaging (fMRI) remains a promising method to aid in the surgical management of patients diagnosed with brain tumors. For patients that are candidates for awake craniotomies, surgical decisions can potentially be improved by fMRI but this depends on the level of concordance between preoperative brain maps and the maps provided by the gold standard intraoperative method, direct cortical stimulation (DCS). There have been numerous studies of the concordance between fMRI and DCS using sensitivity and specificity measures, however the results are variable across studies and the key factors influencing variability are not well understood. Thus, the present work addresses the influence of technical factors on fMRI and DCS concordance.Methods: Motor and language mapping data were collected for a group of glioma patients (n = 14) who underwent both preoperative fMRI and intraoperative DCS in an awake craniotomy procedure for tumor removal. Normative fMRI data were also acquired in a healthy control group (n = 12). The fMRI and DCS mapping data were co-registered; true positive (TP), true negative (TN), false positive (FP), and false negative (FN) occurrences were tabulated over the exposed brain surface. Sensitivity and specificity were measured for the total group, and for the motor and language sub-groups. The influence of grid placement, fMRI statistical thresholding, and task standardization were assessed. Correlations between proportions of agreement and error were also carefully scrutinized to evaluate concordance in more detail.Results: Concordance was significantly better for motor vs. language mapping. There was an inverse relationship between TP and TN with increasing statistical threshold, and FP dominated the total error. Sensitivity and specificity were reduced when tasks were not standardized across fMRI and DCS.Conclusions: Although the agreement between fMRI and DCS is good, variability is introduced by technical factors that can diminish the quality of patient data. Neurosurgeons should evaluate the usefulness of fMRI data while considering that (a) discordance arises primarily from FP fMRI results; (b) there is an inherent trade-off between sensitivity and specificity with fMRI statistical threshold; and (c) best results are achieved using batteries of tasks that are standardized across both mapping methods.

EP 133. Structural connectivity of eloquent speech areas defined by direct cortical stimulation mapping

The anatomical borders of eloquent speech areas, e.g. Broca’s area, have been vaguely defined and exhibit high inter-subject variability (Amunts and Zilles, 2012), mainly due to inconsistent morphology of the inferior frontal gyrus (IFG) (Ebeling et al., 1989) and small-scale incongruity of functional segregation with respect to anatomical landmarks (Garrett et al., 2012, Quiñones-Hinojosa et al., 2003). However, knowing the exact boundaries of the eloquent cortex became clinically important in preventing postoperative deficits after brain surgery (Garrett et al., 2012, Hollon et al., 2015). The awake electrical stimulation mapping (ESM) has become the preferred method to delineate the speech cortex, as the current non-invasive alternatives lack specificity and spatial resolution (Garrett et al., 2012, Hollon et al., 2015). Since the structural connectivity-based parcellation using diffusion tensor imaging (DTI) has been shown to closely relate to the cytoarchitectonics in the IFG (Klein et al., 2007), we tested whether the location of eloquent cortex could be better predicted by preoperative DTI rather than by its relation to gyrification. Seventeen patients (8 males, median age 33, range 18–63) suffering from primary brain tumor underwent pre-operative 3T MRI scanning using a high resolution T1 MPRAGE and a single shell diffusion weighted imaging (DWI) sequence (60 directions, b = 1000 s/mm2, resolution 2 × 2 × 2 mm), and intraoperative direct cortical electrical stimulation with a bipolar Ojemann electrode during awake language mapping. After standard preprocessing, probabilistic fiber tracking (PROBTRACKX in FSL (Behrens et al., 2007)) was carried out using 5 mm spheres as cortico-subcortical seeds placed at the intraoperatively defined positive stimulation sites. The resulting cortical projections were then overlaid onto the individual cortex surface (Freesurfer) and compared visually and using binary logical operations. A variety of stimulation-positive functional sites was detected, producing anomia, counting, speech and motor arrest. Anomia sites were found both in the pars triangularis and pars opercularis of the inferior frontal gyrus (also in individual patients). Even opercular anomia sites followed the connectivity pattern of triangular anomia sites and had stronger connections to the rostral parts of the mesial prefrontal cortex and pre-supplementary motor area (pre-SMA) than to the precentral gyrus and SMA proper, as opposed to opercular speech or counting arrest sites which also connected more strongly to more posterior parts of the brain, mostly posterior temporal cortex. Thus, even adjacent sites on the same gyrus that differed in function showed dissociable structural connectivity. Our results suggest that structure–function relationships are more evident between function and structural connectivity than between function and gyrification. This study was supported by the German Research Foundation, the European Union, and the German Academic Exchange Service (DAAD).

The diagnostic utility of intracranial EEG monitoring for epilepsy surgery in children.

There are limited data on the indications for the use of chronic invasive electroencephalography (EEG) monitoring (IEM) for pediatric epilepsy surgery. We retrospectively studied 102 children who underwent intracranial monitoring to map critical cortex, localize the epileptogenic region, or resolve divergent findings. We assessed IEM utility based on changes to the resection plan following analysis of noninvasive data. IEM was judged useful in 87% of cases and had greatest utility for resolving discordant data and localizing extratemporal and multilobar epileptogenic zones. IEM data were least useful for seizure onset in the temporal lobe and had little utility for direct cortical stimulation mapping unless functional magnetic resonance imaging (fMRI) revealed atypical language representation or the epileptogenic zone was in proximity to critical cortex. IEM utility was demonstrated for a majority of cases with well-defined indications. The method of assessing utility will facilitate multicentric studies toward developing future consensus and practice guidelines.

34. Structural connectivity of eloquent speech areas defined by direct cortical stimulation mapping

Background and aims The anatomical borders of eloquent speech areas, e.g. Broca's area, have been vaguely defined and exhibit high inter-subject variability (Amunts and Zilles, 2012), mainly due to inconsistent morphology of the inferior frontal gyrus (IFG) (Ebeling et al., 1989) and small-scale incongruity of functional segregation with respect to anatomical landmarks (Garrett et al., 2012; Quinones-Hinojosa et al., 2003). However, knowing the exact boundaries of the eloquent cortex became clinically important in preventing postoperative deficits after brain surgery (Garrett et al., 2012; Hollon et al., 2015). The awake electrical stimulation mapping (ESM) has become the preferred method to delineate the speech cortex, as the current non-invasive alternatives lack specificity and spatial resolution (Garrett et al., 2012; Hollon et al., 2015). Since the structural connectivity-based parcellation using diffusion tensor imaging (DTI) has been shown to closely relate to the cytoarchitectonics in the IFG (Klein et al., 2007), we tested whether the location of eloquent cortex could be better predicted by preoperative DTI rather than by its relation to gyrification. Methods Seventeen patients (8 males, median age 33, range 18–63) suffering from primary brain tumor underwent pre-operative 3T MRI scanning using a high resolution T1 MPRAGE and a single shell diffusion weighted imaging (DWI) sequence (60 directions, b =1000 s/mm 2 , resolution 2×2×2mm), and intraoperative direct cortical electrical stimulation with a bipolar Ojemann electrode during awake language mapping. After standard preprocessing, probabilistic fiber tracking (PROBTRACKX in FSL (Behrens et al., 2007)) was carried out using 5mm spheres as cortico-subcortical seeds placed at the intraoperatively defined positive stimulation sites. The resulting cortical projections were then overlaid onto the individual cortex surface (Freesurfer) and compared visually and using binary logical operations. Results A variety of stimulation-positive functional sites was detected, producing anomia, counting, speech and motor arrest. Anomia sites were found both in the pars triangularis and pars opercularis of the inferior frontal gyrus (also in individual patients). Even opercular anomia sites followed the connectivity pattern of triangular anomia sites and had stronger connections to the rostral parts of the mesial prefrontal cortex and pre-supplementary motor area (pre-SMA) than to the precentral gyrus and SMA proper, as opposed to opercular speech or counting arrest sites which also connected more strongly to more posterior parts of the brain, mostly posterior temporal cortex. Thus, even adjacent sites on the same gyrus that differed in function showed dissociable structural connectivity. Conclusions Our results suggest that structure–function relationships are more evident between function and structural connectivity than between function and gyrification. Acknowledgement This study was supported by the German Research Foundation, the European Union, and the German Academic Exchange Service (DAAD).

Repeated mapping of cortical language sites by preoperative navigated transcranial magnetic stimulation compared to repeated intraoperative DCS mapping in awake craniotomy

BackgroundRepetitive navigated transcranial magnetic stimulation (rTMS) was recently described for mapping of human language areas. However, its capability of detecting language plasticity in brain tumor patients was not proven up to now. Thus, this study was designed to evaluate such data in order to compare rTMS language mapping to language mapping during repeated awake surgery during follow-up in patients suffering from language-eloquent gliomas.MethodsThree right-handed patients with left-sided gliomas (2 opercular glioblastomas, 1 astrocytoma WHO grade III of the angular gyrus) underwent preoperative language mapping by rTMS as well as intraoperative language mapping provided via direct cortical stimulation (DCS) for initial as well as for repeated Resection 7, 10, and 15 months later.ResultsOverall, preoperative rTMS was able to elicit clear language errors in all mappings. A good correlation between initial rTMS and DCS results was observed. As a consequence of brain plasticity, initial DCS and rTMS findings only corresponded with the results obtained during the second examination in one out of three patients thus suggesting changes of language organization in two of our three patients.ConclusionsThis report points out the usefulness but also the limitations of preoperative rTMS language mapping to detect plastic changes in language function or for long-term follow-up prior to DCS even in recurrent gliomas. However, DCS still has to be regarded as gold standard.

Language mapping with navigated repetitive TMS: Proof of technique and validation

ObjectiveLesion-based mapping of speech pathways has been possible only during invasive neurosurgical procedures using direct cortical stimulation (DCS). However, navigated transcranial magnetic stimulation (nTMS) may allow for lesion-based interrogation of language pathways noninvasively. Although not lesion-based, magnetoencephalographic imaging (MEGI) is another noninvasive modality for language mapping. In this study, we compare the accuracy of nTMS and MEGI with DCS. MethodsSubjects with lesions around cortical language areas underwent preoperative nTMS and MEGI for language mapping. nTMS maps were generated using a repetitive TMS protocol to deliver trains of stimulations during a picture naming task. MEGI activation maps were derived from adaptive spatial filtering of beta-band power decreases prior to overt speech during picture naming and verb generation tasks. The subjects subsequently underwent awake language mapping via intraoperative DCS. The language maps obtained from each of the 3 modalities were recorded and compared. ResultsnTMS and MEGI were performed on 12 subjects. nTMS yielded 21 positive language disruption sites (11 speech arrest, 5 anomia, and 5 other) while DCS yielded 10 positive sites (2 speech arrest, 5 anomia, and 3 other). MEGI isolated 32 sites of peak activation with language tasks. Positive language sites were most commonly found in the pars opercularis for all three modalities. In 9 instances the positive DCS site corresponded to a positive nTMS site, while in 1 instance it did not. In 4 instances, a positive nTMS site corresponded to a negative DCS site, while 169 instances of negative nTMS and DCS were recorded. The sensitivity of nTMS was therefore 90%, specificity was 98%, the positive predictive value was 69% and the negative predictive value was 99% as compared with intraoperative DCS. MEGI language sites for verb generation and object naming correlated with nTMS sites in 5 subjects, and with DCS sites in 2 subjects. ConclusionMaps of language function generated with nTMS correlate well with those generated by DCS. Negative nTMS mapping also correlates with negative DCS mapping. In our study, MEGI lacks the same level of correlation with intraoperative mapping; nevertheless it provides useful adjunct information in some cases. nTMS may offer a lesion-based method for noninvasively interrogating language pathways and be valuable in managing patients with peri-eloquent lesions.

A Comparison of Language Mapping by Preoperative Navigated Transcranial Magnetic Stimulation and Direct Cortical Stimulation During Awake Surgery

Navigated transcranial magnetic stimulation (nTMS) is increasingly used in presurgical brain mapping. Preoperative nTMS results correlate well with direct cortical stimulation (DCS) data in the identification of the primary motor cortex. Repetitive nTMS can also be used for mapping of speech-sensitive cortical areas. The current cohort study compares the safety and effectiveness of preoperative nTMS with DCS mapping during awake surgery for the identification of language areas in patients with left-sided cerebral lesions. Twenty patients with tumors in or close to left-sided language eloquent regions were examined by repetitive nTMS before surgery. During awake surgery, language-eloquent cortex was identified by DCS. nTMS results were compared for accuracy and reliability with regard to DCS by projecting both results into the cortical parcellation system. Presurgical nTMS maps showed an overall sensitivity of 90.2%, specificity of 23.8%, positive predictive value of 35.6%, and negative predictive value of 83.9% compared with DCS. For the anatomic Broca's area, the corresponding values were a sensitivity of 100%, specificity of 13.0%, positive predictive value of 56.5%, and negative predictive value of 100%, respectively. Good overall correlation between repetitive nTMS and DCS was observed, particularly with regard to negatively mapped regions. Noninvasive inhibition mapping with nTMS is evolving as a valuable tool for preoperative mapping of language areas. Yet its low specificity in posterior language areas in the current study necessitates further research to refine the methodology.

Utility of presurgical navigated transcranial magnetic brain stimulation for the resection of tumors in eloquent motor areas

Navigated transcranial magnetic stimulation (nTMS) is a newly evolving technique. Despite its supposed purpose (for example, preoperative central region mapping), little is known about its accuracy compared with established modalities like direct cortical stimulation (DCS) and functional MR (fMR) imaging. Against this background, the authors performed the current study to compare the accuracy of nTMS with DCS and fMR imaging. Fourteen patients with tumors in or close to the precentral gyrus were examined using nTMS for motor cortex mapping, as were 12 patients with lesions in the subcortical white matter motor tract. Moreover, preoperative fMR imaging and intraoperative mapping of the motor cortex were performed via DCS, and the outlining of the motor cortex was compared. In the 14 cases of lesions affecting the precentral gyrus, the primary motor cortex as outlined by nTMS correlated well with that delineated by intraoperative DCS mapping, with a deviation of 4.4 ± 3.4 mm between the two methods. In comparing nTMS with fMR imaging, the deviation between the two methods was much larger: 9.8 ± 8.5 mm for the upper extremity and 14.7 ± 12.4 mm for the lower extremity. In 13 of 14 cases, the surgeon admitted easier identification of the central region because of nTMS. The procedure had a subjectively positive influence on the operative results in 5 cases and was responsible for a changed resection strategy in 2 cases. One of 26 patients experienced nTMS as unpleasant; none found it painful. Navigated TMS correlates well with DCS as a gold standard despite factors that are supposed to contribute to the inaccuracy of nTMS. Moreover, surgeons have found nTMS to be an additional and helpful modality during the resection of tumors affecting eloquent motor areas, as well as during preoperative planning.

CORTICAL RESECTION TAILORED TO AWAKE, INTRAOPERATIVE ICTAL RECORDINGS AND MOTOR MAPPING IN THE TREATMENT OF INTRACTABLE EPILEPSIA PARTIALIS CONTINUA

Epilepsia partialis continua (EPC) is a form of status epilepticus that is characterized by continuous simple partial seizures and can occur as a manifestation of a variety of underlying pathological processes. Because these seizures typically take onset within or close to motor cortex, the treatment of refractory EPC with resective surgery risks significant postoperative deficits. We describe our experience using ictal recordings obtained intraoperatively during awake craniotomy, in conjunction with direct cortical stimulation mapping, to tailor surgical resections in 2 patients with refractory EPC. Both patients had pan-hemispheric pathologies that made extraoperative recording difficult. Awake craniotomy takes advantage of a unique feature of refractory EPC, namely the near-continuous presence of focal seizure activity. It allows the surgeon to record seizures in the operating room and precisely define the anatomic location of epileptic activity, to resect the seizure focus, and to both visually and electrographically confirm successful cessation of EPC after resection, all within a single operation. We used standard methods of awake craniotomy to finely tailor a cortical resection to the epileptogenic cortex while sparing nearby eloquent motor areas. The precision of awake mapping made this approach safe and effective. The cases we describe demonstrate the role of focal resection in the treatment of EPC. Standard techniques of awake craniotomy have application in the treatment of this challenging problem.

When “Abegg” is read and (“A, B, E, G, G”) is not: a cortical stimulation study of musical score reading

To spare the cortical areas involved both in musical score reading and in language, the authors used a score reading task during direct cortical stimulation mapping in musicians undergoing operations for brain lesions. The organization of the cortical areas involved in language and score reading, respectively, was analyzed in relation with these surgical data. Seven patients with brain lesions were tested using three language tasks and a score-reading task. Preoperatively, none of them had exhibited significant language or musical ability deficits, and all had a special interest in music. All were involved in professional or amateur musical activities. Interference in score reading was found in small cortical areas, mainly in the dominant parietal lobe and sometimes in the frontal gyri. During direct stimulation, interference was either language-specific (15 sites), common to language and score-reading tasks (18 sites), or specific to the score-reading task (four sites). Different patterns of score-reading interferences (score-reading arrest, semantic paraphasia) were observed, probably corresponding to different stages of score reading. Postoperatively, some patients showed transitory score-reading difficulties related to the surgical procedure. The cortical areas involved in score reading can occasionally be distinct from other language areas. This could explain differential word- and score-reading impairments sometimes observed in musicians with brain lesions. Brain mapping for neurosurgical procedures in musicians should ideally be performed using a score-reading task in addition to standard language tasks, especially for mapping in the dominant parietal lobe.

Activation of language cortex with automatic speech tasks

To identify automatic speech tasks that reliably demonstrate increased regional cerebral blood flow (rCBF) in Broca's and Wernicke's areas of the cortex using PET. Localizing language with direct cortical stimulation mapping requires that patients have a stable baseline on tests that engage eloquent cortex. For dysphasic patients or younger children, automatic speech tasks such as counting are often used in lieu of more complex language tests. Evidence from both lesion and neuroimaging studies suggests that these tasks may not adequately engage language cortices. In this study, we examined rCBF during automatic oromotor and speech tasks of varying complexity to identify those eliciting increased CBF in Broca's and Wernicke's areas. Eight normal volunteers underwent PET during rest, tongue movements, and three automatic speech tasks: repeating a phoneme sequence, repeating the months of the year, and reciting a memorized prose passage. Images were averaged across subjects and compared across tasks for regional localization and laterality. Whereas all activation tasks produced increased relative CBF in brain regions that correlated with articulation and auditory processing, only the two tasks that used real words (versus phonemes) showed left-lateralized rCBF increases in posterior superior temporal lobe (Wernicke's area), and only the prose repetition task produced left lateralized activity in Broca's area. Whereas automatic speech typically does not engage language cortex, repeating a memorized prose passage showed unambiguous activation in both Broca's and Wernicke's areas. These results caution against the use of common automatic speech tasks for mapping eloquent cortex and suggest an alternative task for those with poor language abilities or acquired dysphasia who cannot perform standardized language tests reliably.

The Comparison of the Anesthetic Regimens for Functional Direct Cortical Stimulation Mapping during Craniotomy

The Comparison of the Anesthetic Regimens for Functional Direct Cortical Stimulation Mapping during Craniotomy