Category: Neurophysiology

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The human craniospinal venous system and its influence on postural intracranial pressure: a review

J Neurosurg 141:1484–1493, 2024

The cerebral and spinal venous systems have similar functions but unique anatomical and physiological properties. CSF occupies space in the cranial and spinal vaults, is continuously produced, and has many roles, including maintaining a favorable environment for CNS structures. The influence of the cerebrospinal venous system on CSF dynamics has been theorized since the 1940s. Newer studies suggest venous outflow pattern alterations in response to changes in body position. However, the relationship of postural cerebrospinal venous outflow shifts with and their influence on CSF homeostasis is not well understood.

METHODS The authors searched the published literature related to the anatomy and function of vertebral venous plexus (VVP), CSF, and positional cerebral venous flow characteristics. A comprehensive collection of literature was compiled and reviewed, and the relationship between cerebrospinal and venous system changes and alterations in body positions, with an emphasis on the craniocervical system, is discussed.

RESULTS The VVP is a network of valveless veins extending from the sacrum to the cranium that are interconnected with the cranial dural sinuses. The internal VVP occupies space within the extradural spinal canal and functions to return spinal venous blood to the heart, but it has additional properties, including the capability of bidirectional venous flow, an intraspinal dilatory capacity, and a role in cerebral venous outflow. When one rises to the upright position, CSF shifts toward the spinal canal and force vectors change, leading to reduced intracranial CSF pressure; simultaneously, cerebral venous outflow shifts from the jugular vein to the VVP outflow pathway. The venous outflow shift mechanism and its purpose are poorly understood. The authors review the known physiology of the system, identify gaps in knowledge to direct future research, and propose an interpretation of these data, concluding that position-dependent CSF and cerebrospinal venous shifts are part of a complementary positional craniospinal pressure regulation system that must be kept in balance for optimal CNS function.

CONCLUSIONS Current knowledge of the cerebrospinal venous anatomy, dynamic flow characteristics in response to gravity, and the venous system’s influence on CSF suggests that the VVP plays a role in influencing CSF pressure, and the authors hypothesize that it plays a role in supporting intracranial pressure in the upright body posture. Further research is needed to better characterize the functional relationship of the VVP to CSF dynamics as well as identify potentially related disease states.

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Radiofrequency thermocoagulation under neuromonitoring guidance and general anesthesia for treatment of refractory trigeminal neuralgia

Acta Neurochirurgica (2024) 166:56

Radiofrequency thermocoagulation (RFT) for refractory trigeminal neuralgia is usually performed in awake patients to localize the involved trigeminal branches. It is often a painful experience. Here, we present RFT under neuromonitoring guidance and general anesthesia.

Method Stimulation of trigeminal branches at the foramen ovale with the tip of the RFT cannula is performed under short general anesthesia. Antidromic sensory–evoked potentials (aSEP) are recorded from the 3 trigeminal branches. The cannula is repositioned until the desired branch can be stimulated and lesioned.

Conclusion aSEP enable accurate localization of involved trigeminal branches during RFT and allow performing the procedure under general anesthesia.

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Two cases of SMA syndrome after neurosurgical injury to the frontal aslant tract

Acta Neurochirurgica (2023) 165:2473–2478

Supplementarymotor area (SMA) syndrome is characterised by transient disturbance in volitional movement and speech production which classically occurs after injury to the medial premotor area.

We present two cases of SMA syndrome following isolated surgical injury to the frontal aslant tract (FAT) with the SMA intact. The first case occurred after resection of a left frontal operculum tumour. The second case occurred after a transcortical approach to a ventricular neurocytoma. The clinical picture and fMRI activation patterns during recovery were typical for SMA syndrome and support the theory that the FAT is a critical bundle in the SMA complex function.

 

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Bilateral Low-Frequency Hearing Impairment After Microvascular Decompression Surgery

Neurosurgery 93:662–669, 2023

Hearing impairment is an important complication of microvascular decompression (MVD). In patients after MVD, we have occasionally noted slight to moderate hearing deterioration at low frequencies that is difficult to detect using pure tone average.

OBJECTIVE: To assess the incidence and features of low-frequency hearing impairment (LF-HI) after MVD and evaluate its associated factors.

METHODS: This single-center, retrospective observational study assessed the audiometric outcome of 270 patients who underwent MVD between January 2015 and December 2020. Preoperative and postoperative hearing levels were compared for each frequency. LF-HI was defined as a hearing deterioration of ≥15 dB at 125, 250, or 500 Hz. The incidence, symptoms, and associated factors of LF-HI were analyzed.

RESULTS: Statistical analysis of the patients overall demonstrated slight but significant decreases in the hearing level after MVD at lower frequencies on both the operative and contralateral sides. Eighty-one patients (30.0%) had LF-HI: 49 on the operative side, 24 on the contralateral side, and 8 on both sides, while pure tone average was worsened in 5 patients (1.8%). Subjective symptoms, including hearing deterioration, ear fullness, tinnitus, and dizziness, developed in 10.4% of the patients with LF-HI but improved subsequently within several weeks. “Older age” and “operative side” were associated with LF-HI.

CONCLUSION: Decreases in lower-frequency hearing levels in both the ipsilateral and contralateral (nonoperative) ears were observed after trigeminal neuralgia and hemifacial spasm surgery. LF-HI does not cause permanent symptoms but may be a noteworthy phenomenon, possibly involved in the contralateral hearing loss encountered occasionally after other types of posterior cranial fossa surgery.

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Network-level prediction of set-shifting deterioration after lower-grade glioma resection

J Neurosurg 137:1329–1337, 2022

The aim of this study was to predict set-shifting deterioration after resection of low-grade glioma.

METHODS The authors retrospectively analyzed a bicentric series of 102 patients who underwent surgery for low-grade glioma. The difference between the completion times of the Trail Making Test parts B and A (TMT B-A) was evaluated preoperatively and 3–4 months after surgery. High dimensionality of the information related to the surgical cavity topography was reduced to a small set of predictors in four different ways: 1) overlap between surgical cavity and each of the 122 cortical parcels composing Yeo’s 17-network parcellation of the brain; 2) Tractotron: disconnection by the cavity of the major white matter bundles; 3) overlap between the surgical cavity and each of Yeo’s networks; and 4) disconets: signature of structural disconnection by the cavity of each of Yeo’s networks. A random forest algorithm was implemented to predict the postoperative change in the TMT B-A z-score.

RESULTS The last two network-based approaches yielded significant accuracies in left-out subjects (area under the receiver operating characteristic curve [AUC] approximately equal to 0.8, p approximately equal to 0.001) and outperformed the two alternatives. In single tree hierarchical models, the degree of damage to Yeo corticocortical network 12 (CC 12) was a critical node: patients with damage to CC 12 higher than 7.5% (cortical overlap) or 7.2% (disconets) had much higher risk to deteriorate, establishing for the first time a causal link between damage to this network and impaired set-shifting.

CONCLUSIONS The authors’ results give strong support to the idea that network-level approaches are a powerful way to address the lesion-symptom mapping problem, enabling machine learning–powered individual outcome predictions.

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Language hemispheric dominance analyzed with magnetic resonance DTI: correlation with the Wada test

J Neurosurg 134:1703–1710, 2021

Language lateralization is a major concern in some patients with pharmacoresistant epilepsy who will face surgery; in these patients, hemispheric dominance testing is essential to avoid further complications. The Wada test is considered the gold standard examination for language localization, but is invasive and requires many human and material resources. Functional MRI and tractography with diffusion tensor imaging (DTI) have demonstrated that they could be useful for locating language in epilepsy surgery, but there is no evidence of the correlation between the Wada test and DTI MRI in language dominance.

METHODS The authors performed a retrospective review of patients who underwent a Wada test before epilepsy surgery at their institution from 2012 to 2017. The authors retrospectively analyzed fractional anisotropy (FA), number and length of fibers, and volume of the arcuate fasciculus and uncinate fasciculus, comparing dominant and nondominant hemispheres.

RESULTS Ten patients with temporal lobe epilepsy were reviewed. Statistical analysis showed that the mean FA of the arcuate fasciculus in the dominant hemisphere was higher than in the nondominant hemisphere (0.369 vs 0.329, p = 0.049). Also, the number of fibers in the arcuate fasciculus was greater in the dominant hemisphere (881.5 vs 305.4, p = 0.003). However, no differences were found in the FA of the uncinate fasciculus or number of fibers between hemispheres. The length of fibers of the uncinate fasciculus was longer in the dominant side (74.4 vs 50.1 mm, p = 0.05). Volume in both bundles was more prominent in the dominant hemisphere (12.12 vs 6.48 cm3, p = 0.004, in the arcuate fasciculus, and 8.41 vs 4.16 cm3, p = 0.018, in the uncinate fasciculus). Finally, these parameters were compared in patients in whom the seizure focus was situated in the dominant hemisphere: FA (0.37 vs 0.30, p = 0.05), number of fibers (114.4 vs 315.6, p = 0.014), and volume (12.58 vs 5.88 cm3, p = 0.035) in the arcuate fasciculus were found to be statistically significantly higher in the dominant hemispheres. Linear discriminant analysis of FA, number of fibers, and volume of the arcuate fasciculus showed a correct discrimination in 80% of patients (p = 0.024).

CONCLUSIONS The analysis of the arcuate fasciculus and other tract bundles by DTI could be a useful tool for language location testing in the preoperative study of patients with refractory epilepsy.

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

Acta Neurochirurgica (2021) 163:1213–1226

Surgical treatment of tumors, epileptic foci or of vascular origin, requires a detailed individual pre-surgical workup and intraoperative 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 postsurgical 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.

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Electrocorticography During Deep Brain Stimulation Surgery

Neurosurgery 88:E420–E426, 2021

Intraoperative research during deep brain stimulation (DBS) surgery has enabled major advances in understanding movement disorders pathophysiology and potential mechanisms for therapeutic benefit. In particular, over the last decade, recording electrocorticography (ECoG) from the cortical surface, simultaneously with subcortical recordings, has become an important research tool for assessing basal gangliathalamocortical circuit physiology.

OBJECTIVE: To provide confirmation of the safety of performing ECoG duringDBS surgery, using data fromcenters involved in 2 BRAIN (Brain Research through Advancing Innovative Neurotechnologies) Initiative-funded basic human neuroscience projects. METHODS: Datawere collected separately at 4 centers. The primary endpoint was complication rate, defined as any intraoperative event, infection, or postoperative magnetic resonance imaging abnormality requiring clinical follow-up. Complication rates for explanatory variables were compared using point biserial correlations and Fisher exact tests.

RESULTS: A total of 367 DBS surgeries involving ECoG were reviewed. No cortical hemorrhages were observed. Seven complications occurred: 4 intraparenchymal hemorrhages and 3 infections (complication rate of 1.91%; CI=0.77%-3.89%). The placement of 2 separate ECoG research electrodes through a single burr hole (84 cases) did not result in a significantly different rate of complications, compared to placement of a single electrode (3.6% vs 1.5%; P = .4). Research data were obtained successfully in 350 surgeries (95.4%).

CONCLUSION: Combined with the single report previously available, which described no ECoG-related complications in a single-center cohort of 200 cases, these findings suggest that research ECOG during DBS surgery did not significantly alter complication rates.

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Altered corticospinal microstructure and motor cortex excitability in gliomas

J Neurosurg 134:1368–1376, 2021

This prospective case-control study was conducted to examine whether spherical deconvolution (SD) can unveil microstructural abnormalities in the corticospinal tract (CST) caused by IDH-mutant gliomas. To determine the significance of abnormal microstructure, the authors investigated the correlation between diffusion parameters and neurophysiological data collected with navigated transcranial magnetic stimulation (nTMS).

METHODS Twenty participants (10 patients and 10 healthy controls) were recruited. Diffusion-weighted images were acquired on a 3-T MRI scanner using a cardiac-gated single-shot spin echo echo-planar imaging multiband sequence (TE 80 msec, TR 4000 msec) along 90 diffusion directions with a b-value of 2500 sec/mm2 (FOV 256 × 256 mm). Diffusion tensor imaging tractography and SD tractography were performed with deterministic tracking. The anterior portion of the ipsilateral superior peduncle and the precentral gyrus were used as regions of interest to delineate the CST. Diffusion indices were extracted and analyzed for significant differences between hemispheres in patients and between patient and control groups. A navigated brain stimulation system was used to deliver TMS pulses at hotspots at which motor evoked potentials (MEPs) for the abductor pollicis brevis, first digital interosseous, and abductor digiti minimi muscles are best elicited in patients and healthy controls. Functional measurements such as resting motor threshold (rMT), amplitude of MEPs, and latency of MEPs were noted. Significant differences between hemispheres in patients and between patients and controls were statistically analyzed. The Spearman rank correlation was used to investigate correlations between diffusion indices and functional measurements.

RESULTS The hindrance modulated orientational anisotropy (HMOA), measured with SD tractography, is lower in the hemisphere ipsilateral to glioma (p = 0.028). The rMT in the hemisphere ipsilateral to a glioma is significantly greater than that in the contralateral hemisphere (p = 0.038). All measurements contralateral to the glioma, except for the mean amplitude of MEPs (p = 0.001), are similar to those of healthy controls. Mean diffusivity and axial diffusivity from SD tractography are positively correlated with rMT in the hemisphere ipsilateral to glioma (p = 0.02 and 0.006, respectively). The interhemispheric difference in HMOA and rMT is correlated in glioma patients (p = 0.007).

CONCLUSIONS SD tractography can demonstrate microstructural abnormality within the CST of patients with IDH1- mutant gliomas that correlates to the functional abnormality measured with nTMS.

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Incidence and linguistic quality of speech errors: a comparison of preoperative transcranial magnetic stimulation and intraoperative direct cortex stimulation

J Neurosurg 134:1409–1418, 2021

Given the interindividual variance of functional language anatomy, risk prediction based merely on anatomical data is insufficient in language area–related brain tumor surgery, suggesting the need for direct cortical and subcortical mapping during awake surgery. Reliable, noninvasive preoperative methods of language localization hold the potential for reducing the necessity for awake procedures and may improve patient counseling and surgical planning. Repetitive navigated transcranial magnetic stimulation (rnTMS) is an evolving tool for localizing language-eloquent areas. The aim of this study was to investigate the reliability of rnTMS in locating cortical language sites.

METHODS Twenty-five patients with brain tumors in speech-related areas were prospectively evaluated with preoperative rnTMS (5 Hz, train of five, average 105% resting motor threshold) and navigated direct cortical stimulation (DCS; bipolar, 50 Hz, 6–8 mA, 200-μsec pulse width) during awake surgeries employing a picture-naming task. Positive and negative stimulation spots within the craniotomy were documented in the same MRI data set. TMS and DCS languagepositive areas were compared with regard to their spatial overlap, their allocation in a cortical parcellation system, and their linguistic qualities.

RESULTS There were over twofold more positive language spots within the exposed area on rnTMS than on DCS. The comparison of positive rnTMS and DCS (ground truth) overlaps revealed low sensitivity (35%) and low positive predictive value (16%) but high specificity (90%) and high negative predictive value (96%). Within the overlaps, there was no correlation in error quality. On DCS, 73% of language-positive spots were located in the pars opercularis and pars triangularis of the frontal operculum and 24% within the supramarginal gyrus and dorsal portion of the superior temporal gyrus, while on rnTMS language positivity was distributed more evenly over a large number of gyri.

CONCLUSIONS The current protocol for rnTMS for language mapping identified language-negative sites with good dependability but was unable to reliably detect language-positive spots. Further refinements of the technique will be needed to establish rnTMS language mapping as a useful clinical tool.

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Mapping and anatomo-surgical techniques for SMA-cingulum-corpus callosum gliomas

Acta Neurochirurgica (2021) 163:1239–1246

Awake brain mapping paradigms are variable, particularly in SMA, and not personalised to each patient. In addition, subpial resections do not offer full protection to vascular injury, as the pia can be easily violated.

Methods Mapping paradigms developed by a multidisciplinary brain mapping team. During resection, a combined subpial/ interhemispheric approach allowed early identification and arterial skeletonization. Precise anatomo-surgical dissection of the affected cingulum and corpus callosum was achieved.

Conclusions In SMA-cingulum-CC tumours, a combined subpial/interhemispheric approach reduces risk of vascular injury allowing precise anatomo-surgical dissections. Knowledge of cognitive functions of affected parcels is likely to offer best outcomes.

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Alterations in Functional Connectomics Associated With Neurocognitive Changes Following Glioma Resection

Neurosurgery 88,(3)2021: 544–551

Decline in neurocognitive functioning (NCF) often occurs following brain tumor resection. Functional connectomics have shown how neurologic insults disrupt cerebral networks underlying NCF, though studies involving patients with brain tumors are lacking.

OBJECTIVE: To investigate the impact of brain tumor resection upon the connectome and relationships with NCF outcome in the early postoperative period.

METHODS: A total of 15 right-handed adults with left perisylvian glioma underwent resting-state functional magnetic resonance imaging (rs-fMRI) and neuropsychological assessment before and after awake tumor resection. Graph theoretical analysiswas applied to rs-fMRI connectivity matrices to calculate network properties. Network properties and NCF measures were compared across the pre- to postoperative periods with matched pairs Wilcoxon signed-rank tests.Associations between pre- to postoperative change in network and NCF measures were determined with Spearman rank-order correlations (ρ).

RESULTS: A majority of the sample showed postoperative decline on 1 or more NCF measures. Significant postoperative NCF decline was found across measures of verbal memory, processing speed, executive functioning, receptive language, and a composite index. Regarding connectomic properties, betweenness centrality and assortativity were significantly smaller postoperatively, and reductions in these measures were associated with better NCF outcomes. Significant inverse associations (ρ = −.51 to −.78, all P < .05) were observed between change in language, executive functioning, and learning and memory, and alterations in segregation, centrality, and resilience network properties.

CONCLUSION: Decline in NCF was common shortly following resection of glioma involving eloquent brain regions, most frequently in verbal learning/memory and executive functioning. Better postoperative outcomes accompanied reductions in centrality and resilience connectomic measures.

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Clinical Pearls and Methods for Intraoperative Motor Mapping

Neurosurgery 88:457–467, 2021

Resection of brain tumors involving motor areas and pathways requires the identification and preservation of various cortical and subcortical structures involved in motor control at the time of the procedure, in order to maintain the patient’s full motor capacities. The use of brain mapping techniques has now been integrated into clinical practice for many years, as they help the surgeon to identify the neural structures involved in motor functions. A common definition of motor function, as well as knowledge of its neural organization, has been continuously evolving, underlining the need for implementing intraoperative strategies at the time of the procedure. Similarly, mapping strategies have been subjected to continuous changes, enhancing the likelihood of preservation of full motor capacities. As a general rule, the motor mapping strategy should be as flexible as possible and adapted strictly to the individual patient and clinical context of the tumor.

In this work, we present an overview of current knowledge of motor organization, indications for motor mapping, available motor mapping, and monitoring strategies, as well as their advantages and limitations. The use of motor mapping improves resection and outcomes in patients harboring tumors involving motor areas and pathways, and should be considered the gold standard in the resection of this type of tumor.

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Predicting the Extent of Resection in Low-Grade Glioma by Using Intratumoral Tractography to Detect Eloquent FasciclesWithin the Tumor

Neurosurgery 88(2) 2021: E190–E202

An early maximal safe surgical resection is the current treatment paradigm for low-grade glioma (LGG). Nevertheless, there are no reliable methods to accurately predict the axonal intratumoral eloquent areas and, consequently, to predict the extent of resection.

OBJECTIVE: To describe the functional predictive value of eloquent white matter tracts within the tumor by using a pre- and postoperative intratumoral diffusion tensor imaging (DTI) tractography protocol in patients with LGG.

METHODS: A preoperative intratumoral DTI-based tractography protocol, using the tumor segmented volume as the only seed region, was used to assess the tracts within the tumor boundaries in 22 consecutive patients with LGG. The reconstructed tracts were correlated with intraoperative electrical stimulation (IES)-based language and motor subcortical mapping findings and the extent of resection was assessed by tumor volumetrics.

RESULTS: Identification of intratumoral language and motor tracts significantly predicted eloquent areas within the tumor during the IES mapping: the positive predictive value for the pyramidal tract, the inferior fronto-occipital fasciculus, the arcuate fasciculus and the inferior longitudinal fasciculus positive was 100%, 100%, 33%, and 80%, respectively, whereas negative predictive value was 100% for all of them. The reconstruction of at least one of these tracts within the tumor was significantly associated with a lower extent of resection (67%) as opposed to the extent of resection in the cases with a negative intratumoral tractography (100%) (P< .0001).

CONCLUSION: Intratumoral DTI-based tractography is a simple and reliable method, useful in assessing glioma resectability based on the analysis of intratumoral eloquent areas associated with motor and language tracts within the tumor.

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Altered Motor Excitability in Patients With Diffuse Gliomas Involving Motor Eloquent Areas: The Impact of Tumor Grading

Neurosurgery 88( 1) 2021: 183–192

Diffuse gliomas have an increased biological aggressiveness across the World Health Organization (WHO) grading system. The implications of glioma grading on the primary motor cortex (M1)-corticospinal tract (CST) excitability is unknown.

OBJECTIVE: To assess the excitability of the motor pathway with navigated transcranial magnetic stimulation (nTMS).

METHODS: Retrospective cohort study of patients admitted for surgery with diffuse gliomas within motor eloquent areas. Demographic, clinical, and nTMS-related variables were collected. The Cortical Excitability Score (CES 0 to 2 according to the number of abnormal interhemispheric resting motor threshold (RMT) ratios) was calculated for patients where bilateral upper and lower limb mapping was performed.

RESULTS: A total of 45 patients were included: 9 patients had a low-grade glioma and 36 patients had a high-grade glioma. The unadjusted analysis revealed an increase in the latency of the motor evoked potential of the lower limb with an increase of theWHOgrade (P = .038). The adjusted analysis confirmed this finding (P = .013) and showed a relation between the increase in the WHO and a decreased RMT (P = .037) of the motor evoked responses in the lower limb.When CES was calculated, an increase in the score was related with an increase in the WHO grade (unadjusted analysis—P = .0001; adjusted analysis— P = .001) and in isocitrate dehydrogenase (IDH) wild-type tumors (unadjusted analysis— P = .020).

CONCLUSION: An increase in the WHO grading system and IDH wild-type tumors are associated with an abnormal excitability of the motor eloquent areas in patients with diffuse gliomas.

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Nucleus basalis of Meynert neuronal activity in Parkinson’s disease

J Neurosurg 132:574–582, 2020

Neuronal loss within the cholinergic nucleus basalis of Meynert (nbM) correlates with cognitive decline in dementing disorders such as Alzheimer’s disease and Parkinson’s disease (PD). In nonhuman primates, the nbM firing pattern (5–40 Hz) has also been correlated with working memory and sustained attention. In this study, authors performed microelectrode recordings of the globus pallidus pars interna (GPi) and the nbM immediately prior to the implantation of bilateral deep brain stimulation (DBS) electrodes in PD patients to treat motor symptoms and cognitive impairment, respectively. Here, the authors evaluate the electrophysiological properties of the nbM in patients with PD.

METHODS Five patients (4 male, mean age 66 ± 4 years) with PD and mild cognitive impairment underwent bilateral GPi and nbM DBS lead implantation. Microelectrode recordings were performed through the GPi and nbM along a single trajectory. Firing rates and burst indices were characterized for each neuronal population with the patient at rest and performing a sustained-attention auditory oddball task. Action potential (AP) depolarization and repolarization widths were measured for each neuronal population at rest.

RESULTS In PD patients off medication, the authors identified neuronal discharge rates that were specific to each area populated by GPi cells (92.6 ± 46.1 Hz), border cells (34 ± 21 Hz), and nbM cells (13 ± 10 Hz). During the oddball task, firing rates of nbM cells decreased (2.9 ± 0.9 to 2.0 ± 1.1 Hz, p < 0.05). During baseline recordings, the burst index for nbM cells (1.7 ± 0.6) was significantly greater than those for GPi cells (1.2 ± 0.2, p < 0.05) and border cells (1.1 ± 0.1, p < 0.05). There was no significant difference in the nbM burst index during the oddball task relative to baseline (3.4 ± 1.7, p = 0.20). With the patient at rest, the width of the depolarization phase of APs did not differ among the GPi cells, border cells, and nbM cells (p = 0.60); however, during the repolarization phase, the nbM spikes were significantly longer than those for GPi high-frequency discharge cells (p < 0.05) but not the border cells (p = 0.20).

CONCLUSIONS Neurons along the trajectory through the GPi and nbM have distinct firing patterns. The profile of nbM activity is similar to that observed in nonhuman primates and is altered during a cognitive task associated with cholinergic activation. These findings will serve to identify these targets intraoperatively and form the basis for further research to characterize the role of the nbM in cognition.

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Intraoperative facial motor evoked potential monitoring for pontine cavernous malformation resection

J Neurosurg 132:265–271, 2020

The aim of this study was to predict postoperative facial nerve function during pontine cavernous malformation surgery by monitoring facial motor evoked potentials (FMEPs).

METHODS From 2008 to 2017, 10 patients with pontine cavernous malformations underwent total resection via the trans–fourth ventricle floor approach with FMEP monitoring. House-Brackmann grades and Karnofsky Performance Scale (KPS) scores were obtained pre- and postoperatively. The surgeries were performed using one of 2 safe entry zones into the brainstem: the suprafacial triangle and infrafacial triangle approaches. Six patients underwent the suprafacial triangle approach, and 4 patients underwent the infrafacial triangle approach. A cranial peg screw electrode was used to deliver electrical stimulation for FMEP by a train of 4 or 5 pulse anodal constant current stimulation. FMEP was recorded from needle electrodes on the ipsilateral facial muscles and monitored throughout surgery by using a threshold- level stimulation method.

RESULTS FMEPs were recorded and analyzed in 8 patients; they were not recorded in 2 patients who had severe preoperative facial palsy and underwent an infrafacial triangle approach. Warning signs appeared in all patients who underwent the suprafacial triangle approach. However, after temporarily stopping the procedures, FMEP findings during surgery showed recovery of the thresholds. FMEPs in patients who underwent the infrafacial triangle approach were stable during the surgery. House-Brackmann grades were unchanged postoperatively in all patients. Postoperative KPS scores improved in 3 patients, decreased in 1, and remained the same in 6 patients.

CONCLUSIONS FMEPs can be used to monitor facial nerve function during surgery for pontine cavernous malformations, especially when the suprafacial triangle approach is performed.

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Disruption of Frontal Aslant Tract Is Not Associated with Long-Term Postoperative Language Deficits

World Neurosurg. (2020) 133:192-195

The frontal aslant tract (FAT) is a white matter fiber pathway connecting the superior frontal gyrus to the Broca area. This tract in the dominant hemisphere has been shown to play a role in speech initiation and production, and direct subcortical stimulation can induce stuttering and speech arrest in a patient. However, controversy remains as to whether disruption of this pathway will lead to a permanent language deficit and if it is even necessary to map this tract during tumor resections of the dominant frontal lobe.

CASE DESCRIPTION: Here, we report a case of a patient with a lower-grade diffuse glioma invading the dominant FAT that was removed with an asleep craniotomy. In the immediate postoperative state, the patient had a transcortical motor dysphasia and was unable to initiate speech. These immediate language deficits quickly recovered, and the patient was neurologically intact at the time of discharge a few days after surgery.

CONCLUSIONS: Given the high likelihood for a complete neurologic recovery including transient aphasia, we propose that awake mapping for the purpose of identifying the dominant FAT is unnecessary during tumor resection and that disruption of this tract is not associated with any long-term language deficits.

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Neurophysiological examination combined with functional intraoperative navigation using TMS in patients with brain tumor near the central region

Acta Neurochirurgica (2019) 161:1853–1864

Feasibility and value of non-invasive transcranial magnetic brain stimulation (TMS MAGVENTURE® MagPro R30 Denmark) for preoperative diagnosis and surgical planning of brain tumor operations in everyday clinical practice.

Methods A prospective monocentric study was conducted, which included preoperative neurological and electrophysiological examination, TMS, and display of functional data in the navigation system (LOCALITE® TMS Navigator Germany). During surgery, the TMS data were correlated with the intraoperative monitoring (IOM). Twenty-four hours to 96 h and after at least 3 months, follow-ups with neurological, electrophysiological examinations and TMS stimulation were performed.

Results Twenty-five patients with tumors in or near by the primary motor cortex region were included in the study. Twenty-one patients completed preoperative and first postoperative TMS and the neurological examination. Eight of 21 patients showed slight worsening of primary motor cortex function, 8 patients had an unchanged state, and 4 patients showed an improvement early after surgery. The changes of the electrophysiological examination like significant delay of the latency and/or reduced amplitudes matched well with the postoperative neurological outcome: if patients showed a worsening of the SEP’s and MEP’s, the postoperative results revealed deterioration.

Conclusion A preoperatively performed TMS using the MAGVENTURE® MagPro R30 and the LOCALITE® TMS Navigator could be established in our clinical daily practice and allowed a safe and reliable mapping of the primary motor cortex in order to minimize the risk of postoperative neurological deficits and improve the neurological outcome of the patients.

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Inhibition of Manual Movements at Speech Arrest Sites in the Posterior Inferior Frontal Lobe

Neurosurgery 85:E496–E501, 2019

Intraoperative stimulation of the posterior inferior frontal lobe (IFL) induces speech arrest, which is often interpreted as demonstration of essential language function. However, prior reports have described “negative motor areas” in the IFL, sites where stimulation halts ongoing limb motor activity.

OBJECTIVE: To investigate the spatial and functional relationship between IFL speech arrest areas and negative motor areas (NMAs).

METHODS: In this retrospective cohort study, intraoperative stimulation mapping was performed to localize speech and motor function, as well as arrest of hand movement, hand posture, and guitar playing in a set of patients undergoing awake craniotomy for dominant hemisphere pathologies. The incidence and localization of speech arrest and motor inhibition was analyzed.

RESULTS: Eleven patients underwent intraoperative localization of speech arrest sites and inhibitory motor areas. A total of 17 speech arrest sites were identified in the dominant frontal lobe, and, of these, 5 sites (29.4%) were also identified as NMAs. Speech arrest and arrest of guitar playing was also evoked by a single IFL site in 1 subject.

CONCLUSION: Inferior frontal gyrus speech arrest sites do not function solely in speech production. These findings provide further evidence for the complexity of language organization, and suggest the need for refined mapping strategies that discern between language-specific sites and inhibitory motor areas.

 

 

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