Awake Surgery for Left Posterior Insular Low-Grade Glioma Through the Parietorolandic Operculum: The Need to Preserve the Functional Connectivity. A Case Series

Objective: Surgical approach to low-grade glioma (LGG) involving the posterior insula is challenging, especially in the left hemisphere, with a high risk of sensorimotor, language, or visual deterioration. In this study, a case series of 5 right-handed patients harboring a left posterior insular LGG is reported, by detailing a transcorticosubcortical approach.Method: The five surgeries were achieved in awake patients using cortical and axonal electrostimulation mapping. The glioma was removed through the left rolandic and/or parietal opercula, with preservation of the subcortical connectivity.Results: The cortical mapping was positive in the five patients, enabling the selection of an optimal transcortical approach, via the anterolateral supramarginal gyrus in four patients and/or via the lateral retrocentral gyrus in three cases (plus through the left superior temporal gyrus in one case). Moreover, the white matter tracts were identified in all cases, i.e., the lateral part of the superior longitudinal fasciculus (five cases), the arcuate fasciculus (four cases), the thalamocortical somatosensory pathways (four cases), the motor pathway (one case), the semantic pathway (three cases), and the optic tract (one case). Complete resection of the LGG was achieved in two patients and near-total resection in three patients. There were no postoperative permanent sensorimotor, language, or visual deficits.Conclusion: A transcortical approach through the parietorolandic operculum in awake patients represents safe and effective access to the left posterior insular LGG. Detection and preservation of the functional connectivity using direct electrostimulation of the white matter bundles are needed in this cross-road brain region to prevent otherwise predictable postsurgical impairments.

In the back of your mind: Cortical mapping of tactile and proprioceptive paraspinal afferent inputs

Persistent pain alters brain-body representations, highlighting their potential pathological significance. In chronic low back pain (LBP), sparse evidence points towards a shift of the cortical representation of sensory afferents of the back. However, systematic investigations of the cortical representation of tactile and proprioceptive paraspinal afferents along the thoracolumbar axis are lacking. Detailed cortical maps of paraspinal afferent input might be crucial to further explore potential relationships between brain changes and the development and maintenance of chronic LBP. We therefore validated a novel and functional magnetic resonance imaging- (fMRI-)compatible method of mapping cortical representations of tactile and proprioceptive afferents of the back, using pneumatic vibrotactile stimulation ("pneuVID") at varying frequencies and paraspinal locations, in conjunction with high-resolution fMRI. We hypothesised that: (i) high (80 Hz) frequency stimulation would lead to increased postural sway compared to low (20 Hz) stimulation, due to differential evoked mechanoreceptor contributions to postural control (proprioceptive vs tactile); and (ii) that high (80 Hz) versus low (20 Hz) frequency stimulation would be associated with neuronal activity in distinct primary somatosensory (S1) and motor (M1) cortical targets of tactile and proprioceptive afferents (N=15, healthy volunteers). Additionally, we expected neural representations to vary spatially along the thoracolumbar axis. We found significant differences between neural representations of low and high frequency stimulation and between representations of thoracic and lumbar paraspinal locations, in several bilateral sensorimotor cortical regions. Proprioceptive (80 Hz) stimulation preferentially activated sub-regions S1 3a and M1 4p, while tactile (20 Hz) stimulation was more encoded in S1 3b and M1 4a. Moreover, in S1, lower back proprioceptive stimulation activated dorsal-posterior representations, compared to ventral-anterior representations activated by upper back stimulation. As per our hypotheses, we found distinct sensorimotor cortical tactile and proprioceptive representations, with the latter displaying clear topographic differences between the upper and lower back. This thus represents the first behavioural and neurobiological validation of the novel pneuVID method for stimulating muscle spindles and mapping cortical representations of paraspinal afferents. Future investigations of detailed cortical maps will be of major importance in elucidating the role of cortical reorganization in the pathophysiology of chronic LBP.

MR-safe multisegmental vibration device for cortical mapping of paraspinal afferent input

<p>The objective of this study was to develop an MR-safe stimulation device (pneumatic vibration device, pneuVID) that can apply vibrotactile stimulation to different thoracolumbar segments and to characterize stimulation parameters such as the amplitude and its stability for two relevant frequencies (20Hz/80Hz). This is the first apparatus specifically designed for paraspinal tissue vibration on different segmental levels in an MR environment. </p>

MR-safe multisegmental vibration device for cortical mapping of paraspinal afferent input

<p>The objective of this study was to develop an MR-safe stimulation device (pneumatic vibration device, pneuVID) that can apply vibrotactile stimulation to different thoracolumbar segments and to characterize stimulation parameters such as the amplitude and its stability for two relevant frequencies (20Hz/80Hz). This is the first apparatus specifically designed for paraspinal tissue vibration on different segmental levels in an MR environment. </p>

Non-invasive mapping of cortical categorization function by repetitive navigated transcranial magnetic stimulation

Over the past years navigated repetitive transcranial magnetic stimulation (nrTMS) had become increasingly important for the preoperative examination and mapping of eloquent brain areas. Among other applications it was demonstrated that the detection of neuropsychological function, such as arithmetic processing or face recognition, is feasible with nrTMS. In order to investigate the mapping of further brain functions, this study aims to investigate the cortical mapping of categorization function via nrTMS. 20 healthy volunteers purely right-handed, with German as mother tongue underwent nrTMS mapping using 5 Hz/10 pulses. 52 cortical spots spread over each hemisphere were stimulated. The task consisted of 80 pictures of living and non-living images, which the volunteers were instructed to categorize while the simulation pulses were applied. The highest error rates for all errors of all subjects were observed in the left hemisphere’s posterior middle frontal gyrus (pMFG) with an error rate of 60%, as well as in the right pMFG and posterior supra marginal gyrus (pSMG) (45%). In total the task processing of non-living objects elicited more errors in total, than the recognition of living objects. nrTMS is able to detect cortical categorization function. Moreover, the observed bihemispheric representation, as well as the higher error incidence for the recognition of non-living objects is well in accordance with current literature. Clinical applicability for preoperative mapping in brain tumor patients but also in general neuroscience has to be evaluated as the next step.

Biologically Inspired Deep Learning Model for Efficient Foveal-Peripheral Vision

While abundant in biology, foveated vision is nearly absent from computational models and especially deep learning architectures. Despite considerable hardware improvements, training deep neural networks still presents a challenge and constraints complexity of models. Here we propose an end-to-end neural model for foveal-peripheral vision, inspired by retino-cortical mapping in primates and humans. Our model has an efficient sampling technique for compressing the visual signal such that a small portion of the scene is perceived in high resolution while a large field of view is maintained in low resolution. An attention mechanism for performing “eye-movements” assists the agent in collecting detailed information incrementally from the observed scene. Our model achieves comparable results to a similar neural architecture trained on full-resolution data for image classification and outperforms it at video classification tasks. At the same time, because of the smaller size of its input, it can reduce computational effort tenfold and uses several times less memory. Moreover, we present an easy to implement bottom-up and top-down attention mechanism which relies on task-relevant features and is therefore a convenient byproduct of the main architecture. Apart from its computational efficiency, the presented work provides means for exploring active vision for agent training in simulated environments and anthropomorphic robotics.

OS10.7.A Localization patterns of language errors during direct electrical brain stimulation: a systematic review

BACKGROUND Awake craniotomy with direct electrical stimulation (DES) is the standard treatment for patients with eloquent area gliomas. Language errors (paraphasias) are detected with DES and they indicate functional boundaries that need to be maintained to preserve quality of life. However, it is not fully clear in which brain locations paraphasias at different linguistic modalities and levels (production, comprehension, reading, writing, phonology, semantics, syntax) occur. MATERIALS AND METHODS A systematic review was conducted. We included 102 studies reporting on specific paraphasias and the corresponding brain locations during awake craniotomy with DES in adult glioma patients. RESULTS First, a wide distribution of brain locations for all paraphasias (n=930) was found, but patterns were observed. Cortically, paraphasias occurred most often in the precentral gyrus (22%), while subcortically, they occurred mainly at the inferior fronto-occipital fascicle (IFOF: 10%). Localization patterns for different paraphasia types and the corresponding language functions were also found: production/articulation (n=393)-precentral gyrus (41%), inferior frontal gyrus (9%), frontal aslant/striatal tract (4%), postcentral gyrus (3%); semantics (n=128)-IFOF (57%), superior temporal gyrus (9%); phonology (n=115)-arcuate fascicle (52%), superior longitudinal fascicle (10%), uncinate fascicle (3%); reading (n=25)-temporal lobe (48%), inferior longitudinal fascicle (32%); syntax (n=15)-inferior frontal gyrus (27%); speech initiation (n=9)-supplementary motor area (33%), frontal aslant tract (22%), frontal striatal tract (22%); writing (n=7)-superior parietal gyrus (71%). Second, 59% of all paraphasias occurred cortically, 40% subcortically and 1% at both levels. CONCLUSION The localization of most paraphasias are consistent with the assumed functionality of those brain locations as presented in the Dutch Linguistic Intraoperative Protocol model. However, new locations for production/articulation, phonology, reading and writing were found. This needs to be taken into consideration for future selection of pre, intra and postoperative language tasks at different language modalities and levels. Additionally, DES should always be applied at the subcortical level as a standard addition to the routine cortical mapping during awake craniotomy. In conclusion, this is the first systematic review on the localization of specific paraphasias during awake craniotomy. Based on the identified language localization patterns, language tasks could be selected more accurately. This could guide, and perhaps improve, pre, intra and postoperative language testing and monitoring, which in turn, may pave the way to a better postoperative language outcome. The possible relation between different intraoperative paraphasias and language outcome has yet to be determined.

P07.02 Robot-assisted stereotactic brain biopsy combined with cortical mapping using navigated transcranial magnetic stimulation

BACKGROUND Frame-based stereotactic biopsy has been for decades the gold-standard method for taking samples of brain tumors for the histopathological diagnostic in cases when surgery was contraindicated. However, novel frameless techniques have been developed in order to facilitate the procedure for the neurosurgeon, and for the patient as well. Preoperative cortical mapping techniques enable the planning of the trajectory with the sparing of eloquent areas. MATERIAL AND METHODS A preoperative cortical mapping using navigated transcranial magnetic stimulation was performed in the case of a 37-year-old male that presented with headache. The MRI scan revealed multiple lesions located frontal lobe and temporal lobe on the right hemisphere and frontal and occipital lobes on the left hemisphere. The results of the preoperative cortical mapping were integrated into the neuronavigation system and used for the planning of the frameless based stereotactic brain biopsy. A biopsy procedure was performed using a robotic arm according to the planned trajectory. RESULTS The targeted lesion was the right frontal one. The planned trajectory took into account the results from the cortical mapping using nTMS, and the eloquent areas were avoided. The robotic arm guided the procedure and aligned to the entry point and trajectory. According to the histopathological result the lesion was a grade II diffuse astrocytoma. There were no perioperative complications. CONCLUSION To our knowledge, this is the first report that describes the use of a robot-guided frameless brain biopsy system combined with the preoperative mapping of the eloquent cortical areas using navigated transcranial magnetic stimulation. This approach is a safe one and carries less burden for the patient as well as for the surgeon.

Awake craniotomy for a low-grade glioma - a pilot procedure at a public hospital in Trinidad and Tobago

Awake craniotomies (AC) are proven to reduce the neurological deficit associated with tumour resection in areas of eloquent cortex. Successful performance requires not only technical skill, but the availability of neuronavigation, cortical mapping, intra-operative frozen section and the appropriate anaesthetic support. This case report describes the first fully awake craniotomy done in Trinidad, at a public hospital, for a patient with seizures secondary to a low-grade glioma. It resulted in an excellent patient outcome, with full cessation of seizures and no postoperative deficits.

Reducing the Cognitive Footprint of Brain Tumor Surgery

The surgical management of brain tumors is based on the principle that the extent of resection improves patient outcomes. Traditionally, neurosurgeons have considered that lesions in “non-eloquent” cerebrum can be more aggressively surgically managed compared to lesions in “eloquent” regions with more known functional relevance. Furthermore, advancements in multimodal imaging technologies have improved our ability to extend the rate of resection while minimizing the risk of inducing new neurologic deficits, together referred to as the “onco-functional balance.” However, despite the common utilization of invasive techniques such as cortical mapping to identify eloquent tissue responsible for language and motor functions, glioma patients continue to present post-operatively with poor cognitive morbidity in higher-order functions. Such observations are likely related to the difficulty in interpreting the highly-dimensional information these technologies present to us regarding cognition in addition to our classically poor understanding of the functional and structural neuroanatomy underlying complex higher-order cognitive functions. Furthermore, reduction of the brain into isolated cortical regions without consideration of the complex, interacting brain networks which these regions function within to subserve higher-order cognition inherently prevents our successful navigation of true eloquent and non-eloquent cerebrum. Fortunately, recent large-scale movements in the neuroscience community, such as the Human Connectome Project (HCP), have provided updated neural data detailing the many intricate macroscopic connections between cortical regions which integrate and process the information underlying complex human behavior within a brain “connectome.” Connectomic data can provide us better maps on how to understand convoluted cortical and subcortical relationships between tumor and human cerebrum such that neurosurgeons can begin to make more informed decisions during surgery to maximize the onco-functional balance. However, connectome-based neurosurgery and related applications for neurorehabilitation are relatively nascent and require further work moving forward to optimize our ability to add highly valuable connectomic data to our surgical armamentarium. In this manuscript, we review four concepts with detailed examples which will help us better understand post-operative cognitive outcomes and provide a guide for how to utilize connectomics to reduce cognitive morbidity following cerebral surgery.