Intra-operative mapping of the subcortical visual pathways using direct electrical stimulations

Picture naming test through the prism of cognitive neuroscience and linguistics: adapting the test for cerebellar tumor survivors-or pouring new wine in old sacks?

A picture naming test (PNT) has long been regarded as an integral part of neuropsychological assessment. In current research and clinical practice, it serves a variety of purposes. PNTs are used to assess the severity of speech impairment in aphasia, monitor possible cognitive decline in aging patients with or without age-related neurodegenerative disorders, track language development in children and map eloquent brain areas to be spared during surgery. In research settings, picture naming tests provide an insight into the process of lexical retrieval in monolingual and bilingual speakers. However, while numerous advances have occurred in linguistics and neuroscience since the classic, most widespread PNTs were developed, few of them have found their way into test design. Consequently, despite the popularity of PNTs in clinical and research practice, their relevance and objectivity remain questionable. The present study provides an overview of literature where relevant criticisms and concerns have been expressed over the recent decades. It aims to determine whether there is a significant gap between conventional test design and the current understanding of the mechanisms underlying lexical retrieval by focusing on the parameters that have been experimentally proven to influence picture naming. We discuss here the implications of these findings for improving and facilitating test design within the picture naming paradigm. Subsequently, we highlight the importance of designing specialized tests with a particular target group in mind, so that test variables could be selected for cerebellar tumor survivors.

Diffusion tensor imaging versus intraoperative subcortical mapping for glioma resection: a systematic review and meta-analysis

Maintaining the integrity of crucial fiber tracts allows functional preservation and improved recovery in patients with glioma resection. Diffusion tensor imaging (DTI) and intraoperative subcortical mapping (ISM) are commonly required for pre- and intraoperative assessment of white matter fibers. This study investigated differences of clinical outcomes in glioma resection aided by DTI or ISM. A comprehensive literature retrieval of the PubMed and Embase databases identified several DTI or ISM studies in 2000-2022. Clinical data, including extent of resection (EOR) and postoperative neurological deficits, was collected and statistically analyzed. Heterogeneity was regressed by a random effect model and the Mann-Whitney U test was used to test statistical significance. Publication bias was assessed by Egger test. A total of 14 studies with a pooled cohort of 1837 patients were included. Patients undergoing DTI-navigated glioma surgery showed a higher rate of gross total resection (GTR) than ISM-assisted surgical resection (67.88%, [95% CI 0.55-0.79] vs. 45.73%, [95% CI 0.29-0.63], P = 0.032). The occurrence of early postoperative functional deficit (35.45%, [95% CI 0.13-0.61] vs. 35.60% [95% CI 0.20-0.53], P = 1.000), late postoperative functional deficit (6.00%, [95% CI 0.02-0.11] vs. 4.91% [95% CI 0.03-0.08], P = 1.000) and severe postoperative functional deficit (2.21%, [95% CI 0-0.08] vs. 5.93% [95% CI 0.01-0.16], P = 0.393) were similar between the DTI and ISM group, respectively. While DTI-navigation resulted in a higher rate of GTR, the occurrence of postoperative neurological deficits between DTI and ISM groups was comparable. Together, these data indicate that both techniques could safely facilitate glioma resection.

The role of the angular gyrus in semantic cognition: a synthesis of five functional neuroimaging studies

Semantic knowledge is central to human cognition. The angular gyrus (AG) is widely considered a key brain region for semantic cognition. However, the role of the AG in semantic processing is controversial. Key controversies concern response polarity (activation vs. deactivation) and its relation to task difficulty, lateralization (left vs. right AG), and functional-anatomical subdivision (PGa vs. PGp subregions). Here, we combined the fMRI data of five studies on semantic processing (n = 172) and analyzed the response profiles from the same anatomical regions-of-interest for left and right PGa and PGp. We found that the AG was consistently deactivated during non-semantic conditions, whereas response polarity during semantic conditions was inconsistent. However, the AG consistently showed relative response differences between semantic and non-semantic conditions, and between different semantic conditions. A combined analysis across all studies revealed that AG responses could be best explained by separable effects of task difficulty and semantic processing demand. Task difficulty effects were stronger in PGa than PGp, regardless of hemisphere. Semantic effects were stronger in left than right AG, regardless of subregion. These results suggest that the AG is engaged in both domain-general task-difficulty-related processes and domain-specific semantic processes. In semantic processing, we propose that left AG acts as a "multimodal convergence zone" that binds different semantic features associated with the same concept, enabling efficient access to task-relevant features.

Recovery of Visual Field After Awake Stimulation Mapping of the Optic Pathway in Glioma Patients

Brain mapping during awake craniotomy for gliomas can help preserve neurological functions, including maintenance of central and peripheral vision. However, the consecutive changes in the visual field remain unknown. We retrospectively assessed 14 patients who underwent awake craniotomy for gliomas infiltrating into the optic radiation. Cortico-subcortical direct electrical stimulation (DES) was intraoperatively applied until transient visual symptoms were elicited and recorded. The visual fields were examined consecutively in the preoperative period and postoperative subacute and chronic periods. To evaluate the anatomo-functional validity of the recordings, all DES-elicited points were overlaid onto a three-dimensional template that included the optic radiation, using voxel-based morphometry (VBM) mapping. All patients experienced visual symptoms that were classified as phosphenes, blurred vision, or hallucinations during DES, and surgical resection was limited to within the functional boundaries. In VBM, almost all the subcortical positive mapping points overlapped with the surface of the optic radiation, and the distribution of sites that induced visual phenomena in the upper or lower visual fields could be differentiated in the anatomical space. We observed no postoperative visual deficit in four patients (29%), time-dependent improvements in five out of eight patients that presented transient quadrantanopia or partial visual defect (36% out of 57%), and permanent hemianopsia (14%) in two patients with occipital lesions. Intraoperative DES that identifies and preserves optic radiation in awake craniotomy for gliomas is a reliable and effective technique to reduce risk of permanent deficits, but has a low success rate in patients with occipital involvement.

Visual mapping for tumor resection: A proof of concept of a new intraoperative task and a systematic review of the literature

Homonymous hemianopia has been reported after brain tumor resection with a significant impact on quality of life. Nevertheless, no standardized methods exist for intraoperative optical radiations mapping. The purpose of this article is to describe a new intraoperative task for visual mapping and to review the existing literature.

Avoidance and Improvement in Visual Field Defect After Surgery for Metastatic Brain Tumors in the Parietal and the Occipital Lobe

OBJECTIVE

Visual field defects occasionally occur secondary to tumors in the parietal and the occipital lobes. The aim of this study was to analyze the efficacy of improvement in hemianopsia after surgery for metastatic brain tumors involving or adjacent to the optic radiation (OR).

METHODS

The study included 49 patients with brain metastasis in the parietal and occipital lobes in the present study. Preoperative and postoperative neurological assessments included visual field, Mini-Mental State Examination, and Karnofsky performance scale.

RESULTS

Of 49 patients, 33 (67.3%) presented with preoperative homonymous hemianopsia. Of these 33 patients, the visual field was improved postoperatively in 17 patients (51.5%). In all patients regardless of preoperative hemianopsia, postoperative visual fields did not deteriorate. Tractography demonstrated that the OR was split by the tumor (n = 6) and fanning of fibers expanded along the lateral side of the tumor (n = 11). All tumors were removed via surgical access toward the medial side of the tumor. Gross total resection was achieved in most tumors in the group with visual improvement (n = 16/17; 94.1%). Improvement in the visual field was attributed to tumor location in the subcortical white matter, removal rate of the tumor, and higher postoperative Karnofsky performance scale score.

CONCLUSIONS

The OR tended to deviate to the lateral side of the tumor in the parieto-occipital junction. The postoperative visual field improved even in cases of an occipital tumor. Based on the present study, total resection via an appropriate surgical route should be considered to preserve the OR, leading to improvement in the postoperative visual field.

Cortical and Subcortical Anatomy of the Parietal Lobe From the Neurosurgical Perspective

Introduction: The anatomical structures of the parietal lobe at the cortical and subcortical levels are related mainly to sensory, visuospatial, visual and language function. The aim of this study was to present an intraoperative perspective of these critical structures in terms of the surgical treatment of intra-axial lesions. The study also discusses the results of the technique and the results of direct brain stimulation under awake conditions.

Materials and Methods: Five adult brains were prepared according to the Klingler technique. Cortical assessments and all measurements were performed with the naked eye, while white matter dissection was performed with microscopic magnification.

Results: Intra-axial lesions within the parietal lobe can be approached through a lateral or superior trajectory. This decision is based on the location of the lesions in relation to the arcuate fascicle/superior longitudinal fascicle (AF/SLF) complex and ventricular system. Regardless of the approach, the functional borders of the resection are defined by the postcentral gyrus anteriorly and Wernicke's speech area inferiorly. On the subcortical level, active identification of the AF/SLF complex and of the optic radiation within the sagittal stratum should be performed. The intraparietal sulcus (IPS) is a reliable landmark for the AF/SLF complex in ~60% of cases.

Conclusion: Knowledge of the cortical and subcortical anatomical and functional borders of the resection is crucial in preoperative planning, prediction of the risk of postoperative deficits, and intraoperative decision making.

Prosopagnosia following nonlanguage dominant inferior temporal lobe low-grade glioma resection in which the inferior longitudinal fasciculus was disrupted preoperatively: illustrative case

BACKGROUND

Prosopagnosia is a rare neurological condition characterized by the impairment of face perception with preserved visual processing and cognitive functioning and is associated with injury to the fusiform gyrus and inferior longitudinal fasciculus (ILF). Reports of this clinical impairment following resection of right temporal lobe diffuse gliomas in the absence of contralateral injury are exceedingly scarce and not expected as a complication of surgery.

OBSERVATIONS

The authors describe the case of a young female patient found to have an incidental diffuse glioma in the right inferior temporal lobe despite evidence of preoperative ILF disruption by the tumor. Following resection of the lesion, despite the preoperative disruption to the ILF by the tumor, the patient developed prosopagnosia. There was no evidence of contralateral, left-sided ILF injury.

LESSONS

Given the significant functional impairment associated with prosopagnosia, neurosurgeons should be aware of the exceedingly rare possibility of a visual-processing deficit following unilateral and, in this case, right-sided inferior temporal lobe glioma resections. More investigation is needed to determine whether preoperative testing can determine dominance of facial-processing networks for patients with lesions in the right inferior posterior temporooccipital lobe and whether intraoperative mapping could help prevent this complication.

New Philosophy, Clinical Pearls, and Methods for Intraoperative Cognition Mapping and Monitoring "à la carte" in Brain Tumor Patients

The purpose of surgery for brain tumors involving eloquent neural circuits is to maximize the extent of resection while preserving an optimal quality of life. To this end, especially in diffuse glioma, the goal is to remove the cerebral parenchyma invaded by the neoplasm up to the individual cortico-subcortical networks critical for brain functions. Intraoperative mapping combined with real-time cognitive monitoring throughout the resection in awake patient is thus highly recommended to resume a normal life. Indeed, beyond avoiding hemiplegia or aphasia, enjoying a familial, social, and professional life implies that motor and language mapping is not sufficient. Identifying and sparing neural networks that subserve cognition (movement control, visuospatial cognition, executive functions, multimodal semantics, metacognition) and mentalizing (theory of mind, which plays a key role for social cognition) is essential to preserve an adapted behavior. Here, the aim is to review when and how to map these critical functions, which have nonetheless been neglected for many decades by neurosurgeons. In fact, the disorders generated by surgical injuries of circuits underpinning nonmotor and nonspeech functions are usually not immediately visible on postoperative standard clinical examination, leading the physician to believe that the patient has no deficit. Yet, cognitive or emotional disturbances may subsequently prevent to resume an active life, as to work full time. Therefore, a systematic neuropsychological assessment should be performed before, during, and after mapping-guided surgery, regardless of the tumor location, to preserve the functional connectome intraoperatively and to plan a postoperative tailored cognitive rehabilitation according to the patient's needs.

Intraoperative subcortico-cortical evoked potentials of the visual pathway under general anesthesia

OBJECTIVE

To assess whether intraoperative subcortical mapping of the visual pathways during brain surgeries was feasible.

METHODS

Subcortico-cortical evoked potentials (SCEPs: 30 stimulations/site, biphasic single pulse, 1.3 Hz, 0.2 ms/phase, maximum 10 mA; bipolar probe) were measured in 12 patients for stimulation of the optic radiation, Meyer's loop or optic nerve. Recorded sites were bilateral central, parietal, parieto-occipital, occipital (subdermal scalp electrodes, 5-4000 Hz). The minimum distances from the stimulation locations, i.e. the closest border of the resection cavity to the diffusion tensor imaging based visual pathways, were evaluated postoperatively (smallest distance across coronal, sagittal and axial planes).

RESULTS

Stimulation elicited SCEPs when the visual tracts were close (≤4.5 mm). The responses consisted of a short (P1, 3.0-5.6 ms; 8/8 patients) and of a middle (P2, 15-21.6 ms; 3/8 patients) latency waveforms. In agreement with the neuroanatomy, ipsilateral occipital responses were obtained for temporal or parietal stimulations, and bi-occipital responses for optic nerve stimulations.

CONCLUSIONS

For the first time to our knowledge, intraoperative SCEPs were observed for stimulations of the optic radiation and of Meyer's loop. Short latency responses were found in agreement with fast conduction of the visual pathway's connecting myelinated fibers.

SIGNIFICANCE

The mapping of the visual pathways was found feasible for neurosurgeries under general anesthesia.

The perspectives of mapping and monitoring of the sense of self in neurosurgical patients

Surgical treatment of tumors, epileptic foci or of vascular origin, requires a detailed individual pre-surgical workup and intra-operative surveillance of brain functions to minimize the risk of post-surgical neurological deficits and decline of quality of life. Most attention is attributed to language, motor functions, and perception. However, higher cognitive functions such as social cognition, personality, and the sense of self may be affected by brain surgery. To date, the precise localization and the network patterns of brain regions involved in such functions are not yet fully understood, making the assessment of risks of related post-surgical deficits difficult. It is in the interest of neurosurgeons to understand with which neural systems related to selfhood and personality they are interfering during surgery. Recent neuroscience research using virtual reality and clinical observations suggest that the insular cortex, medial prefrontal cortex, and temporo-parietal junction are important components of a neural system dedicated to self-consciousness based on multisensory bodily processing, including exteroceptive and interoceptive cues (bodily self-consciousness (BSC)). Here, we argue that combined extra- and intra-operative approaches using targeted cognitive testing, functional imaging and EEG, virtual reality, combined with multisensory stimulations, may contribute to the assessment of the BSC and related cognitive aspects. Although the usefulness of particular biomarkers, such as cardiac and respiratory signals linked to virtual reality, and of heartbeat evoked potentials as a surrogate marker for intactness of multisensory integration for intra-operative monitoring has to be proved, systemic and automatized testing of BSC in neurosurgical patients will improve future surgical outcome.

Intraoperative Cognitive Mapping Tasks for Direct Electrical Stimulation in Clinical and Neuroscientific Contexts

Direct electrical stimulation (DES) has been widely applied in both guidance of lesion resection and scientific research; however, the design and selection of intraoperative cognitive mapping tasks have not been updated in a very long time. We introduce updated mapping tasks for language and non-language functions and provide recommendations for optimal design and selection of intraoperative mapping tasks. In addition, with DES becoming more critical in current neuroscientific research, a task design that has not been widely used in DES yet (subtraction and conjunction paradigms) was introduced for more delicate mapping of brain functions especially for research purposes. We also illustrate the importance of designing a common task series for DES and other non-invasive mapping techniques. This review gives practical updated guidelines for advanced application of DES in clinical and neuroscientific research.

New insights into the anatomo-functional architecture of the right sagittal stratum and its surrounding pathways: an axonal electrostimulation mapping study

The sagittal stratum (SS) is a large sheet-like structure where major axonal fiber tracts cross, though its anatomical delineations are still debated. Here we investigated the poorly studied anatomo-functional organization of the right SS using direct electrical stimulation (DES) in patients undergoing wide-awake surgery for a cerebral glioma. Seventeen patients were included. There were six males, the mean age was 38 years old. One patient underwent surgery twice. Fourteen patients were right-handed and one was ambidextrous. Behavior tasks were used to monitor online the patients' functions during DES, including visual and somesthetic processes, semantics, language, spatial and social cognition. Beyond the cortical DES, the mapping of axonal pathways evoked various functional responses. At the level of the core of the right SS, there were visual disturbances, visual hemi-agnosia, semantic paraphasia, left spatial neglect, confusion and comprehension difficulties, anomia, and mentalizing disturbances. At the level of the surrounding axonal pathways, there were left spatial neglect, anomia, vertigo, dysesthesia, and hearing disturbances. Our functionally defined three-dimensional map indicates that this complex region has a multilayered functional architecture, and supports an organization founded on two anatomical systems: a core system formed by the optic radiations, inferior longitudinal fasciculus, and inferior fronto-occipital fasciculus, and a peripheral one composed of surrounding or intersecting white matter tracts, including the superior longitudinal fasciculus/arcuate fasciculus, thalamocortical radiations, auditory radiations, and parieto-insular vestibular system. These results should prompt neurosurgeons to achieve awake DES mapping within the right SS because of the likelihood of causing multiple and irreversible structural disconnections.

Preserving Visual Functions During Gliomas Resection: Feasibility and Efficacy of a Novel Intraoperative Task for Awake Brain Surgery

Objective: The intraoperative identification and preservation of optic radiations (OR) during tumor resection requires the patient to be awake. Different tasks are used. However, they do not grant the maintenance of foveal vision during all testing, limiting the ability to constantly monitor the peripheral vision and to inform about the portion of the peripheral field that is encountered. Although hemianopia can be prevented, quadrantanopia cannot be properly avoided. To overcome these limitations, we developed an intra-operative Visual field Task (iVT) to monitor the foveal vision, alerting about the likelihood of injuring the OR during task administration, and to inform about the portion of the peripheral field that is explored. Data on feasibility and efficacy in preventing visual field deficits are reported, comparing the outcome with the standard available task (Double-Picture-Naming-Task, DPNT). Methods: Patients with a temporal and/or parietal lobe tumor in close morphological relationship with the OR, or where the resection can involve the OR at any extent, without pre-operative visual-field deficits (Humphrey) were enrolled. Fifty-four patients were submitted to iVT, 38 to DPNT during awake surgery with brain mapping neurophysiological techniques. Feasibility was assessed as ease of administration, training and mapping time, and ability to alert about the loss of foveal vision. Type and location of evoked interferences were registered. Functional outcome was evaluated by manual and Humphrey test; extent of resection was recorded. Tractography was performed in a sample of patients to compare patient anatomy with intraoperative stimulation site(s). Results: The test was easy to administer and detected the loss of foveal vision in all cases. Stimulation induced visual-field interferences, detected in all patients, classified as detection or discrimination errors. Detection was mostly observed in temporal tumors, discrimination in temporo-parietal ones. Immediate visual disturbances in DPNT group were registered in 84 vs. 24% of iVT group. At 1-month Humphrey evaluation, 26% of iVT vs. 63% of DPNT had quadrantanopia (32% symptomatic); 10% of DPNT had hemianopia. EOR was similar. Detection errors were induced for stimulation of OR; discrimination also for other visual processing tract (ILF). Conclusion: iVT was feasible and sensitive to preserve the functional integrity of the OR.

High Interrater Variability in Intraoperative Language Testing and Interpretation in Awake Brain Mapping Among Neurosurgeons or Neuropsychologists: An Emerging Need for Standardization

OBJECTIVE

Brain mapping with direct electric stimulation is considered the gold standard for maximum safe resection of tumors affecting eloquent regions. However, no consensus exists in selection and interpretation of intraoperative testing for language and other cognitive domains. Our aim was to capture and statistically analyze variability in practices in intraoperative language testing among neurosurgeons and neuropsychologists in the United States, Europe, and the rest of the world.

METHODS

An electronic questionnaire was developed by a multidisciplinary team at Queen Square, London, and distributed internationally through selected organized societies. The survey included 2 domains: terminology and common understanding of clinical deficits; and selection of intraoperative tests used per specific brain region. Participants were stratified by specialty, years of experience, and monthly caseload. Data were analyzed using Krippendorff α, Wilcoxon rank sum test, and Kruskal-Wallis analysis of variance.

RESULTS

A total of 137 specialists participated. A low agreement was recorded for each of the 20 questions (Krippendorff α = -0.023 to 0.312). Further subgroup analysis revealed low interrater reliability independent of specialism (neurosurgeons, α = 0.013-0.318 compared with nonneurosurgeons, α = -0.021 to 0.398; P = 0.808) and years of experience (<1 years, α = -0.003 to 0.282; 2-5 years, α = 0.009-0.327; 6-10 years, α = 0.003-0.234; and >10 years, α = -0.003 to 0.372; P = 0.200).

CONCLUSIONS

The current study documents high interrater variability, regardless of specialism and years of experience in the cohort of neurosurgeons and language specialists surveyed and may be applicable to a wider group of specialists, indicating the need to reduce interobserver, interinstitutional and interspecialty variability, reach consensus, and increase the validity, interpretation, and predictive power of intraoperative mapping.

Elaborate mapping of the posterior visual pathway in awake craniotomy

OBJECTIVE Resection of intraaxial tumors adjacent to the optic radiation (OR) may be associated with postoperative visual field (VF) deficits. Intraoperative navigation using MRI-based tractography and electrophysiological monitoring of the visual pathways may allow maximal resection while preserving visual function. In this study, the authors evaluated the value of visual pathway mapping in a series of patients undergoing awake craniotomy for tumor resection. METHODS A retrospective analysis of prospectively collected data was conducted in 18 patients who underwent an awake craniotomy for resection of intraaxial tumors involving or adjacent to the OR. Preoperative MRI-based tractography was used for intraoperative navigation, and intraoperative acquisition of 3D ultrasonography images was performed for real-time imaging and correction of brain shift. Goggles with light-emitting diodes were used as a standard visual stimulus. Direct cortical visual evoked potential (VEP) recording, subcortical recordings from the OR, and subcortical stimulation of the OR were used intraoperatively to assess visual function and proximity of the lesion to the OR. VFs were assessed pre- and postoperatively. RESULTS Baseline cortical VEP recordings were available for 14 patients (77.7%). No association was found between preoperative VF status and baseline presence of cortical VEPs (p = 0.27). Five of the 14 patients (35.7%) who underwent subcortical stimulation of the OR reported seeing phosphenes in the corresponding contralateral VF. There was a positive correlation (r = 0.899, p = 0.04) between the subcortical threshold stimulation intensity (3-11.5 mA) and the distance from the OR. Subcortical recordings from the OR demonstrated a typical VEP waveform in 10 of the 13 evaluated patients (76.9%). These waveforms were present only when recordings were obtained within 10 mm of the OR (p = 0.04). Seven patients (38.9%) had postoperative VF deterioration, and it was associated with a length of < 8 mm between the tumor and the OR (p = 0.05). CONCLUSIONS Intraoperative electrophysiological monitoring of the visual pathways is feasible but may be of limited value in preserving the functional integrity of the posterior visual pathways. Subcortical stimulation of the OR may identify the location of the OR when done in proximity to the pathways, but such proximity may be associated with increased risk of postoperative worsening of the VF deficit.

Survey on current cognitive practices within the European Low-Grade Glioma Network: towards a European assessment protocol

BACKGROUND

The European Low-Grade Glioma network indicated a need to better understand common practices regarding the managing of diffuse low-grade gliomas. This area has experienced great advances in recent years.

METHOD

A general survey on the managing of diffuse low-grade gliomas was answered by 21 centres in 11 European countries. Here we focused on specific questions regarding perioperative and intraoperative cognitive assessments.

RESULTS

More centres referred to the same speech and language therapist and/or neuropsychologist across all assessments; a core of assessment tools was routinely used across centres; fluency tasks were commonly used in the perioperative stages, and object naming during surgery; tasks that tapped on attention, executive functions, visuospatial awareness, calculation and emotions were sparsely administered; preoperative assessments were performed 1 month or 1 week before surgery; timing for postoperative assessments varied; finally, more centres recommended early rehabilitation, whenever needed.

CONCLUSIONS

There is an emerging trend towards following similar practices for the management of low-grade gliomas in Europe. Our results are descriptive and formalise current discussions in our group. Also, they contribute towards the development of a European assessment protocol.

Stimulation Mapping of Myelinated Tracts in Awake Patients

For a long time, although the functional anatomy of human cortex has extensively been studied, subcortical white matter tracts have received little consideration. Recent advances in tractography have opened the door to a non-invasive investigation of the subcortical fibers in vivo. However, this method cannot study directly the function of the bundles. Interestingly, for the first time in the history of cognitive neurosciences, direct axonal electrostimulation (DES) mapping of the neural pathways offers the unique opportunity to investigate the function of the connectomal anatomy. Indeed, this technique is able to perform real-time anatomo-functional correlations in awake patients who undergo brain surgery, especially at the level of the subcortical fibers. Here, the aim is to review original data issued from DES of myelinated tracts in adults, with regard to the functional connectivity mediating the sensorimotor, visuo-spatial, language, cognitive and emotional functions, as well as the interactions between these different sub-networks, leading ultimately to explore consciousness. Therefore, axonal stimulation is a valuable tool in the field of connectomics, that is, the map of neural connections, in order to switch from the traditional localizationist view of brain processing to a networking model in which cerebral functions are underpinned by the dynamic interactions of large-scale distributed and parallel sub-circuits. Such connectomal account should integrate the anatomic constraint represented by the subcortical fascicles. Indeed, post-lesional neuroplasticity is possible only on the condition that the white matter fibers are preserved, to allow communication and temporal synchronization among delocalized inter-connected networks.

The role of awake craniotomy in reducing intraoperative visual field deficits during tumor surgery

Objective:

Homonymous hemianopia due to damage to the optic radiations or visual cortex is a possible consequence of tumor resection involving the temporal or occipital lobes. The purpose of this review is to present and analyze a series of studies regarding the use of awake craniotomy (AC) to decrease visual field deficits following neurosurgery.

Materials and Methods:

A literature search was performed using the Medline and PubMed databases from 1970 and 2014 that compared various uses of AC other than intraoperative motor/somatosensory/language mapping with a focus on visual field mapping.

Results:

For the 17 patients analyzed in this study, 14 surgeries resulted in quadrantanopia, 1 in hemianopia, and 2 without visual deficits. Overall, patient satisfaction with AC was high, and AC was a means to reduce surgery-related complications and cost related with the procedure.

Conclusion

AC is a safe and tolerable procedure that can be used effectively to map optic radiations and the visual cortices in order to preserve visual function during resection of tumors infiltrating the temporal and occipital lobes. In the majority of cases, a homonymous hemianopia was prevented and patients were left with a quadrantanopia that did not interfere with daily function.

Impact of World War I on brain mapping

Although much tragedy was experienced during World War I (WWI), the nature of the war and the advancements of weaponry led to a change in the quality and quantity of injuries which were conducive for study. This paper discusses how trauma during WWI led to advances in brain mapping from occipital injuries. Gordon Holmes was a British neurologist who was able to create a retinotopic map of the visual cortex from studying more than 400 cases of occipital injuries; his work has contributed immensely to our understanding of visual processing. There have been many extensions from Holmes' work in regard to how we analyze other sensory modalities and in researching how the brain processes complex stimuli such as faces. Aside from the scholastic benefit, brain mapping also has functional use and can be used for neurosurgical planning to preserve important structures. With the advent of more advanced modalities for analyzing the brain, there have been initiatives in total brain mapping which has added significantly to the body of work started by Holmes during WWI. This paper reviews the history during WWI that led to advances in brain mapping, the lasting scholastic and functional impact from these advancements, and future improvements.

Stimulation mapping of white matter tracts to study brain functional connectivity

Despite advances in the new science of connectomics, which aims to comprehensively map neural connections at both structural and functional levels, techniques to directly study the function of white matter tracts in vivo in humans have proved elusive. Direct electrical stimulation (DES) mapping of the subcortical fibres offers a unique opportunity to investigate the functional connectivity of the brain. This original method permits real-time anatomo-functional correlations, especially with regard to neural pathways, in awake patients undergoing brain surgery. In this article, the goal is to review new insights, gained from axonal DES, into the functional connectivity underlying the sensorimotor, visuospatial, language and sociocognitive systems. Interactions between these neural networks and multimodal systems, such as working memory, attention, executive functions and consciousness, can also be investigated by axonal stimulation. In this networking model of conation and cognition, brain processing is not conceived as the sum of several subfunctions, but results from the integration and potentiation of parallel-though partially overlapping-subnetworks. This hodotopical account, supported by axonal DES, improves our understanding of neuroplasticity and its limitations. The clinical implications of this paradigmatic shift from localizationism to hodotopy, in the context of brain surgery, neurology, neurorehabilitation and psychiatry, are discussed.

Awake craniotomy for brain tumor: indications, technique and benefits

Increasing interest in the quality of life of patients after treatment of brain tumors has led to the exploration of methods that can improve intraoperative assessment of neurological status to avoid neurological deficits. The only method that can provide assessment of all eloquent areas of cerebral cortex and white matter is brain mapping during awake craniotomy. This method helps ensure that the quality of life and the neuro-oncological result of treatment are not compromised. Apart from the medical aspects of awake surgery, its economic issues are also favorable. Here, we review the main aspects of awake brain tumor surgery. Neurosurgical, neuropsychological, neurophysiological and anesthetic issues are briefly discussed.

The course and the anatomo-functional relationships of the optic radiation: a combined study with 'post mortem' dissections and 'in vivo' direct electrical mapping

Even if different dissection, tractographic and connectivity studies provided pure anatomical evidences about the optic radiations (ORs), descriptions of both the anatomical structure and the anatomo-functional relationships of the ORs with the adjacent bundles were not reported. We propose a detailed anatomical and functional study with 'post mortem' dissections and 'in vivo' direct electrical stimulation (DES) of the OR, demonstrating also the relationships with the adjacent eloquent bundles in a neurosurgical 'connectomic' perspective. Six human hemispheres (three left, three right) were dissected after a modified Klingler's preparation. The anatomy of the white matter was analysed according to systematic and topographical surgical perspectives. The anatomical results were correlated to the functional responses collected during three resections of tumours guided by cortico-subcortical DES during awake procedures. We identified two groups of fibres forming the OR. The superior component runs along the lateral wall of the occipital horn, the trigone and the supero-medial wall of the temporal horn. The inferior component covers inferiorly the occipital horn and the trigone, the lateral wall of the temporal horn and arches antero-medially to form the Meyer's Loop. The inferior fronto-occipital fascicle (IFOF) covers completely the superior OR along its entire course, as confirmed by the subcortical DES. The inferior longitudinal fascicle runs in a postero-anterior and inferior direction, covering the superior OR posteriorly and the inferior OR anteriorly. The IFOF identification allows the preservation of the superior OR in the anterior temporal resection, avoiding post-operative complete hemianopia. The identification of the superior OR during the posterior temporal, inferior parietal and occipital resections leads to the preservation of the IFOF and of the eloquent functions it subserves. The accurate knowledge of the OR course and the relationships with the adjacent bundles is crucial to optimize quality of resection and functional outcome.

Anatomo-functional study of the temporo-parieto-occipital region: dissection, tractographic and brain mapping evidence from a neurosurgical perspective

The temporo-parieto-occipital (TPO) junction is a complex brain territory heavily involved in several high-level neurological functions, such as language, visuo-spatial recognition, writing, reading, symbol processing, calculation, self-processing, working memory, musical memory, and face and object recognition. Recent studies indicate that this area is covered by a thick network of white matter (WM) connections, which provide efficient and multimodal integration of information between both local and distant cortical nodes. It is important for neurosurgeons to have good knowledge of the three-dimensional subcortical organisation of this highly connected region to minimise post-operative permanent deficits. The aim of this dissection study was to highlight the subcortical functional anatomy from a topographical surgical perspective. Eight human hemispheres (four left, four right) obtained from four human cadavers were dissected according to Klingler's technique. Proceeding latero-medially, the authors describe the anatomical courses of and the relationships between the main pathways crossing the TPO. The results obtained from dissection were first integrated with diffusion tensor imaging reconstructions and subsequently with functional data obtained from three surgical cases, all resection of infiltrating glial tumours using direct electrical mapping in awake patients. The subcortical limits for performing safe lesionectomies within the TPO region are as follows: within the parietal region, the anterior horizontal part of the superior longitudinal fasciculus and, more deeply, the arcuate fasciculus; dorsally, the vertical projective thalamo-cortical fibres. For lesions located within the temporal and occipital lobes, the resection should be tailored according to the orientation of the horizontal associative pathways (the inferior fronto-occipital fascicle, inferior longitudinal fascicle and optic radiation). The relationships between the WM tracts and the ventricle system were also examined. These results indicate that a detailed anatomo-functional awareness of the WM architecture within the TPO area is mandatory when approaching intrinsic brain lesions to optimise surgical results and to minimise post-operative morbidity.

A re-examination of neural basis of language processing: proposal of a dynamic hodotopical model from data provided by brain stimulation mapping during picture naming

From recent findings provided by brain stimulation mapping during picture naming, we re-examine the neural basis of language. We studied structural-functional relationships by correlating the types of language disturbances generated by stimulation in awake patients, mimicking a transient virtual lesion both at cortical and subcortical levels (white matter and deep grey nuclei), with the anatomical location of the stimulation probe. We propose a hodotopical (delocalized) and dynamic model of language processing, which challenges the traditional modular and serial view. According to this model, following the visual input, the language network is organized in parallel, segregated (even if interconnected) large-scale cortico-subcortical sub-networks underlying semantic, phonological and syntactic processing. Our model offers several advantages (i) it explains double dissociations during stimulation (comprehension versus naming disorders, semantic versus phonemic paraphasias, syntactic versus naming disturbances, plurimodal judgment versus naming disorders); (ii) it takes into account the cortical and subcortical anatomic constraints; (iii) it explains the possible recovery of aphasia following a lesion within the "classical" language areas; (iv) it establishes links with a model executive functions.

Direct electrical stimulation of the optic radiation in patients with covered eyes

Direct electrical stimulation (DES) of the optic radiation (OR) during an awake tumor resection has been repeatedly reported. In all cases, visual function monitoring was performed in patients with open eyes which were looking at a picture. We report a new modification of the standard method, OR stimulation in patient with closed and covered eyes. To the best of our knowledge, this method was not presented before. According to our first experience, this methodology may be in some cases a potentially more sensitive form of neuromonitoring than the OR stimulation in patients with open eyes, as the phosphenes elicited by DES may be more distinct in patients with covered eyes. The technique is discussed, and a literature review on intraoperative identification of the OR is presented as well. However, a future prospective study is needed to confirm the relevance of our finding.

Intraoperative cortico–subcortical stimulations in surgery of low-grade gliomas

In order to increase the impact of surgery on the natural history of low-grade glioma, resection should be of maximum importance. Nevertheless, since low-grade gliomas are frequently located in eloquent structures, function needs to be preserved. Therefore, studying the functional organization of the brain is mandatory for each patient due to the inter-individual anatomofunctional variability, increased in tumors due to cerebral plasticity. This strategy enables performance of a resection according to functional boundaries. However, preoperative neurofunctional imaging only allows the study of the gray matter. Consequently, since low-grade glioma invades cortical and subcortical structures and shows an infiltrative progression along the fibers, the goal of this review is to focus on the techniques able to map both cortical and subcortical regions. In addition to diffusion tensor imaging, which gives only anatomical information and still needs to be validated, intraoperative direct cortico-subcortical electrostimulation is the sole current method allowing a reliable study of the individual anatomofunctional connectivity, concerning sensorimotor, language and other cognitive functions. Its actual contribution is detailed, both in clinical issues, especially the improvement of the benefit/risk ratio of low-grade glioma resection, and in fundamental applications--namely, a new door to the connectionism and cerebral plasticity.

Selection of intraoperative tasks for awake mapping based on relationships between tumor location and functional networks

Intraoperative electrical brain mapping is currently the most reliable method to identify eloquent cortical and subcortical structures at the individual level and to optimize the extent of resection of intrinsic brain tumors. The technique allows the preservation of quality of life, not only allowing avoidance of severe neurological deficits but also facilitating preservation of high neurocognitive functions. To accomplish this goal, however, it is crucial to optimize the selection of appropriate intraoperative tasks, given the limited intrasurgical awake time frame. In this review, the authors' aim was to propose specific parameters that could be used to build a personalized protocol for each patient. They have focused on lesion location and relationships with functional networks to guide selection of intrasurgical tasks in an effort to increase reproducibility among neurooncological centers.

Intraoperative high-field magnetic resonance imaging combined with fiber tract neuronavigation-guided resection of cerebral lesions involving optic radiation

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) combined with optic radiation neuronavigation may be safer for resection of cerebral lesions involving the optic radiation.

OBJECTIVE

To investigate whether iMRI combined with optic radiation neuronavigation can help maximize tumor resection while protecting the patient's visual field.

METHODS

Forty-four patients with cerebral tumors adjacent to the optic radiation were enrolled in the study. The reconstructed optic radiations were observed so that a reasonable surgical plan could be developed. During the surgery, microscope-based fiber tract neuronavigation was routinely implemented. The lesion location (lateral or not to the optic radiation) and course of the optic radiation (stretched or not) were categorized, and their relationships to the visual field defect were determined.

RESULTS

Analysis of the visible relationship between the optic radiation and the lesion led to a change in surgical approach in 6 patients (14%). The mean tumor residual rate for glioma patients was 5.3% (n = 36) and 0% for patients with nonglioma lesions (n = 8). Intraoperative MRI and fiber tract neuronavigation increased the average size of resection (first and last iMRI scanning, 88.3% vs 95.7%; P < .01). Visual fields after surgery improved in 5 cases (11.4%), exhibited no change in 36 cases (81.8%), and were aggravated in 3 cases (6.8%).

CONCLUSION

Diffusion tensor imaging information was helpful in surgical planning. When iMRI was combined with fiber tract neuronavigation, the resection rate of brain lesions involving the optic radiation was increased in most patients without harming the patients' visual fields.

Intraoperative subcortical electrical mapping of optic radiations in awake surgery for glioma involving visual pathways

OBJECT

Preservation of the visual field in glioma surgery, especially avoidance of hemianopia, is crucial for patients' quality of life, particularly for driving. Recent studies used tractography or cortical occipital stimulation to try to avoid visual deficit. However, optic radiations have not been directly mapped intraoperatively. The authors present, for the first time to their knowledge, a consecutive series of awake surgeries for cerebral glioma with intrasurgical identification and preservation of visual pathways using subcortical electrical mapping.

METHODS

Fourteen patients underwent awake resection of a glioma (1 WHO Grade I, 11 WHO Grade II, 2 WHO Grade III) involving the optic radiations. The patients had no presurgical visual field deficit. Intraoperatively, a picture-naming task was used, with presentation of 2 objects situated diagonally on a screen divided into 4 quadrants. An image was presented in the quadrant to be saved and another image was presented in the opposite quadrant. Direct subcortical electrostimulation was repeatedly performed without the patient's knowledge, until optic radiations were identified (transient visual disturbances). All patients underwent an objective visual field assessment 3 months after surgery.

RESULTS

All patients experienced visual symptoms during stimulation. These disturbances led the authors to stop the tumor resection at that level. Postoperatively, only 1 patient had a permanent hemianopia, despite an expected quadrantanopia in 12 cases. The mean extent of resection was 93.6% (range 85%-100%).

CONCLUSIONS

Online identification of optic radiations by direct subcortical electrostimulation is a reliable and effective method to avoid permanent hemianopia in surgery for gliomas involving visual pathways.

Navigated three-dimensional intraoperative ultrasound-guided awake resection of low-grade glioma partially infiltrating optic radiation

We report a case of awake resection of temporal low-grade glioma infiltrating the optic radiation (OR). The OR was localized by direct electrical stimulation (DES) and the tumor was delineated by navigated intraoperative 3D ultrasound. Ultrasound artifacts were eliminated by 3D-ultrasound data acquisition with a miniature probe inserted into the resection cavity. A total of 97 % resection was achieved, and small tumor portion involving OR was intentionally left in place. Functional result was partial quadrantanopia instead of more profound visual deficit, which would follow gross-total resection. To our knowledge, DES of OR was reported once; the aforementioned method of ultrasound artifact elimination has not been reported before.

A new concept of diffuse (low-grade) glioma surgery

Preservation and even improvement of the quality of life is currently a priority in surgery for gliomas, in addition to the optimization of the extent of resection with significant increase of the overall survival. In this setting, the goal of the present review is to revisit technical aspects of glioma surgery in the lights of new concepts both in the fields of neurooncology and cognitive neurosciences, which recently emerged from translational researches - with special emphasis on diffuse low grade gliomas.Firstly, the vascularisation (arteries and veins) has to be more systematically spared, by performing subpial dissection and by limiting the use of coagulation within the brain. Secondly, individual cortical as well as subcortical mapping must be more regularly considered, with the aim of better understanding and preserving the white matter pathways underlying the functional connectivity - even in presumed "non-eloquent areas", to perform "supra-complete" resection.Therefore, brain surgeons should change their state of mind, in order to operate the nervous system involved by a chronic tumoral disease (and no more by operating a tumor mass within the brain). In other words, the neurosurgeon should see first the brain, and not the glioma, to adapt his surgical procedure to the three-dimensional anatomo-functional organization of each patient. It implies that brain surgeon must change his technique within the central nervous system, which has to be different from the surgical technique outside the brain. This perspective seems to represent the best way to build a modern and personalized "functional surgical neurooncology".

Modified trans-middle temporal gyrus approach for trigonal tumor to preserve visual field

OBJECTIVE

We evaluated a modified trans-middle temporal gyrus (MTG) approach with good postoperative visual preservation for patients with trigonal tumors.

METHODS

Three patients with a trigonal tumor were treated via the modified trans-MTG approach guided by a neuro-navigator. Modified trans-MTG approach involve the incision at the MTG within 5 mm to the superior temporal sulcus. This approach makes a proper trajectory to the trigone but also reduces the retraction injury of MTG as little as possible to prevent postoperative visual field defect. Preoperative and postoperative visual field examination using perimetry was performed to evaluate the visual field.

RESULTS

Three patients underwent surgery for lymphoma in the right trigone, meningioma in the left trigone, and focal enhancing nodule in the right paratrigonal area, respectively. In case of lymphoma, preoperative examination showed a left homonymous hemianopsia : one week later after surgery, a visual field examination was performed and revealed improvement of the visual field defect. In case of the meningioma, the preoperative examination showed no visual field defect : one month later, the visual field had no defect. In case of the enhancing nodule, preoperative visual field testing revealed a partial left homonymous hemianopsia. Visual examination within one month after surgery showed no visual field defect. All three patients treated with the modified trans-MTG approach showed no visual deterioration after surgery.

CONCLUSION

The modified trans-MTG approach provides a safe and useful technique for trigonal tumors without postoperative visual field deterioration and affords adequate exposure of the trigonal tumor with a short trajectory.

Occipital WHO grade II gliomas: oncological, surgical and functional considerations

BACKGROUND

Diffuse WHO grade II glioma (GIIG) involving the occipital lobe is a rare entity. Its surgical resection remains controversial as it implies inducing a permanent visual deficit. For the first time to our knowledge, we report a consecutive surgical series of patients who underwent an occipital lobectomy for an LGG invading visual structures.

METHOD

Six right-handed patients harboring a GIIG revealed by seizures (normal examination except a quadrantanopsia in one case) and located within the occipital lobe (4 left and 2 right tumors) were submitted to surgery. Before making this decision, the benefit-to-risk ratio of the resection was extensively discussed with the patient and his/her family, especially concerning the price to pay to remove the tumor, that is, to voluntarily generate a permanent hemianopsia. All the procedures were performed under awake condition using intraoperative electrostimulation, in order to pursue the resection until sensory-motor and/or language structures were encountered.

FINDINGS

An extensive occipital lobectomy was achieved in the six patients, with identification and preservation of sensory-motor pathways in the two cases with a right tumor and detection of language pathways in the four cases with a left tumor. The mean extent of resection was 93% (range: 91-100%). All patients experienced an expected postoperative deficit of the visual field (homonymous hemianopsia). Nonetheless, the six patients resumed a normal social and professional life (KPS at 90 in the 6 cases) with a mean follow-up of 58 months (range: 3-147 months)--with adjuvant treatment in three cases (in addition to a reoperation in two of them).

CONCLUSIONS

Our findings suggest that, despite a definitive hemianopsia, an extensive surgical resection can be considered in the rare cases of occipital GIIG involving the primary visual structures, with patients able to maintain a normal life--except regarding the medico-legal problem of driving.

Surgery for gliomas involving the left inferior parietal lobule: new insights into the functional anatomy provided by stimulation mapping in awake patients

OBJECT

Surgery in the left dominant inferior parietal lobule (IPL) is challenging because of a high density of somatosensory and language structures, both in the cortex and white matter. In the present study, on the basis of the results provided by direct cerebral stimulation in awake patients, the authors revisit the anatomofunctional aspects of surgery within the left IPL.

METHODS

Fourteen consecutive patients underwent awake craniotomy for a glioma involving the left IPL. Intraoperative motor, sensory, and language mapping was performed before and during the tumor removal, at both the cortical and subcortical levels, to optimize the extent of resection, which was determined based on functional boundaries. Anatomofunctional correlations were performed by combining the results of intraoperative mapping and those provided by pre- and postoperative MR imaging.

RESULTS

At the cortical level, the primary somatosensory area (retrocentral gyrus) limited the resection anteriorly in all cases, at least partially. Less frequently, speech arrest or articulatory problems were observed within the parietal operculum (4 cases). The lateral limit was determined by language sites that were variably distributed. Anomia was the most frequent response (9 cases) at the posterior third of the superior (and/or middle) temporal gyrus. Posteriorly, less reproducible reorganized language sites were seldom observed in the posterior portion of the angular gyrus (2 cases). At the subcortical level, in addition to somatosensory responses due to stimulation of the thalamocortical pathways, articulatory disturbances were induced by stimulation of white matter in the anterior and lateral part of the surgical cavity (11 cases). This tract anatomically corresponds to the horizontal portion of the lateral segment of the superior longitudinal fascicle (SLF III). Deeper and superiorly, phonemic paraphasia was the main language disturbance (12 cases), elicited by stimulation of the posterosuperior portion of the arcuate fascicle. All these eloquent structures were surgically preserved. Despite slight cognitive disorders (working memory, writing, or calculation) in 6 cases, no patient retained a severe or a moderate postoperative deficit (except one with right hemianopia [mean follow-up 41.8 months]). Resection was total or near total in 9 patients and partial in 3 cases.

CONCLUSIONS

To the authors' knowledge, this is the first series dedicated to the surgery of gliomas involving the left IPL. Interestingly, a certain degree of interindividual variability was observed in the distribution of the cortical maps, especially for language. Therefore, it is suggested that no rigid pattern of resection can be considered within the left IPL, and that surgery in this region should be performed in awake patients to adapt the tumor removal to individual functional limits. Nonetheless, several landmarks have been regularly identified, especially at the subcortical levels (SLF III and arcuate fascicle); a better knowledge of these functional tracts could be helpful to optimize functional outcomes.

Brain Hodotopy: From Esoteric Concept to Practical Surgical Applications

BACKGROUND:

The traditional neurosurgical approach to cerebral lesions is based on the classic view of a rigid brain organization in fixed “eloquent” areas. However, this method is brought into discussion by the conceptual and methodological advances in neurosciences that provide a more dynamic representation of the anatomo-functional distribution of the human central nervous system (CNS).

OBJECTIVE AND METHODS:

We review the relevant literature concerning the main features of the modern CNS representation and their implications in neurosurgical practice.

RESULTS:

The CNS is an integrated, wide, plastic network made up of cortical functional epicenters, “topic organization,” connected by both short-local and large-scale white matter fibers, ie, “hodological organization.” According to this model, called hodotopic, brain function results from parallel streams of information dynamically modulated within an interactive, multimodal, and widely distributed circuit. The application of this framework, which can be studied by combining preoperative, intraoperative, and postoperative mapping techniques, enables the neurosurgeon exploration of the individual anatomo-functional architecture, including neurocognitive and emotional aspects. Thus, it is possible to adapt the surgical approach specifically to each patient and to each lesion according to the individual organization. Several experiences demonstrate the possibility of removing regions traditionally considered inoperable without inducing permanent deficits and the potential use of these areas as a safe passage to deeper territories.

CONCLUSION:

We advocate the more systematic integration of a hodotopical view of the CNS to improve the surgical indications and planning for brain lesions, with the goal of optimizing both the extent of resection and functional outcome.

A method to map the visual cortex during an awake craniotomy

Much has been reported regarding the technique of performing an awake craniotomy with cortical mapping for the functional cortex responsible for sensorimotor activity and language. However, documentation for mapping the visual cortex during an awake craniotomy with a description of its technical details is rare. The authors report the case of a patient who underwent an awake craniotomy with mapping of the visual cortex to remove a glioma situated in the left medial occipital lobe. The techniques that made such a mapping procedure possible are discussed.

Surgical strategy of brain tumors adjacent to the optic radiation using diffusion tensor imaging-based tractography

The present study evaluated the efficacy of diffusion tensor imaging (DTI)-based tractography in the surgery of brain tumors adjacent to the optic radiation. Of the 14 surgical cases included, 11 had metastatic brain tumors and 3 cerebral gliomas. Additionally, 4 of the 14 patients had pre-operative visual field defects, while the remaining 10 patients experienced no visual impairment. The optic radiations on the lesion side were evident in all 14 patients. On the basis of these tractographic findings, we employed optimal surgical approaches in each patient to avoid injury to the eloquent neural structures, including optic radiation, during surgery. Successful surgical resection was performed in all 14 patients. Of the 14 patients, 2 with visual field defects during the pre-operative period showed improvement in their visual field, and the remaining 12 patients experienced no visual deterioration. DTI-based tractography thus is a feasible modality for the surgical planning of brain lesions adjacent to the optic radiation.

Awake surgery for nonlanguage mapping

OBJECTIVE

During the past decade, numerous reports have supported the contribution of awake mapping in surgical removal of brain lesions in eloquent areas, with a significant increase of the extent of resection while minimizing the risk of permanent deficit--and even improving quality of life.

METHODS

Most of these awake procedures were performed in patients with lesions in language areas, to avoid postoperative aphasia. Surprisingly, mapping of nonlanguage functions received less attention, despite the possible consequences of deficits other than aphasia on daily life. Visuospatial and cognitive deficits are reported after brain surgery, because of more objective and extensive neuropsychological assessments.

RESULTS AND CONCLUSION

This review provides new insights into the indications of awake craniotomies for nonlanguage mapping in surgery for lesions in areas not related to language processing.