White matter structural changes before and after microvascular decompression for hemifacial spasm.

Hemifacial spasm (HFS) is a syndrome characterized by involuntary contractions of the facial muscles innervated by the ipsilateral facial nerve. Currently, microvascular decompression (MVD) is an effective treatment for HFS. Diffusion weighted imaging (DWI) is a non-invasive advanced magnetic resonance technique that allows us to reconstruct white matter (WM) virtually based on water diffusion direction. This enables us to model the human brain as a complex network using graph theory. In our study, we recruited 32 patients with HFS and 32 healthy controls to analyze and compare the topological organization of whole-brain white matter networks between the groups. We also explored the potential relationships between altered topological properties and clinical outcomes. Compared to the HC group, the white matter network was disrupted in both preoperative and postoperative groups of HFS patients, mainly located in the somatomotor network, limbic network, and default network (All P < 0.05, FDR corrected). There was no significant difference between the preoperative and postoperative groups (P > 0.05, FDR corrected). There was a correlation between the altered topological properties and clinical outcomes in the postoperative group of patients (All P < 0.05, FDR corrected). Our findings indicate that in HFS, the white matter structural network was disrupted before and after MVD, and that these alterations in the postoperative group were correlated with the clinical outcomes. White matter alteration here described may subserve as potential biomarkers for HFS and may help us identify patients with HFS who can benefit from MVD and thus can help us make a proper surgical patient selection.

Alteration of White Matter Connectivity for MR-Guided Focused Ultrasound in the Treatment of Essential Tremor.

BACKGROUND: Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy has been implemented as a therapeutic alternative for the treatment of drug-refractory essential tremor (ET). However, its impact on the brain structural network is still unclear. PURPOSE: To investigate both global and local alterations of the white matter (WM) connectivity network in ET after MRgFUS thalamotomy. STUDY TYPE: Retrospective. SUBJECTS: Twenty-seven ET patients (61 ± 11 years, 19 males) with MRgFUS thalamotomy and 28 healthy controls (HC) (61 ± 11 years, 20 males) were recruited for comparison. FIELD STRENGTH/SEQUENCE: A 3 T/single shell diffusion tensor imaging by using spin-echo-based echo-planar imaging, three-dimensional T1 weighted imaging by using gradient-echo-based sequence. ASSESSMENT: Patients were undergoing MRgFUS thalamotomy and their clinical data were collected from pre-operation to 6-month post-operation. Network topological metrics, including rich-club organization, small-world, and efficiency properties were calculated. Correlation between the topological metrics and tremor scores in ET groups was also calculated to assess the role of neural remodeling in the brain. STATISTICAL TESTS: Two-sample independent t-tests, chi-squared test, ANOVA, Bonferroni test, and Spearman's correlation. Statistical significance was set at P < 0.05. RESULTS: For ET patients, the strength of rich-club connection and clustering coefficient significantly increased vs. characteristic path length decreased at 6-month post-operation compared with pre-operation. The distribution pattern of rich-club regions was different in ET groups. Specifically, the order of the rich-club regions was changed according to the network degree value after MRgFUS thalamotomy. Moreover, the altered nodal efficiency in the right temporal pole of the superior temporal gyrus (R = 0.434-0.596) and right putamen (R = 0.413-0.436) was positively correlated with different tremor improvement. DATA CONCLUSION: These findings might improve understanding of treatment-induced modulation from a network perspective and may work as an objective marker in the assessment of ET tremor control with MRgFUS thalamotomy. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 4.

An Applied Anatomic Guide to Anterior Temporal Lobectomy and Amygdalohippocampectomy: Laboratory Cranial and White Matter Dissections to Inform Surgical Practice.

BACKGROUND AND OBJECTIVES: Anterior temporal lobectomy and amygdalohippocampectomy is a challenging procedure because of the deep surgical trajectory and complex regional neurovascular anatomy. A thorough knowledge of the involved anatomic structures is crucial for a safe and effective procedure. Our objective is to explore the white matter pathways in or around the operative corridor and to illuminate the 3-dimensional relationships of the pertinent operative parenchymal and skull base anatomy, aiming to inform and simplify surgical practice. METHODS: Four normal, adult, cadaveric, formalin-fixed cerebral hemispheres (2 left and 2 right) treated with the Klinger's technique and 2 formalin-fixed and colored-latex-injected cadaveric heads (4 sides) were used. Focused white matter and cadaveric dissections were used to study the relevant anatomy implicated during an anterior temporal lobectomy. Four illustrative cases were also included. Digital photographs from every dissection step were obtained. RESULTS: Major white matter pathways that are inevitably traversed during the approach are the inferior longitudinal fasciculus, uncinate fasciculus, and inferior arm of the cingulum. Tracts that can be potentially injured, should the dissection plane tilt inadvertently superiorly or posteriorly, are the inferior fronto-occipital fasciculus, Meyer's loop, superior longitudinal fasciculus/arcuate fasciculus complex, and basal ganglia. Consistent cranial and parenchymal landmarks that can act as a roadmap during the procedure are recorded and paired with their intraoperative equivalent to provide a thorough, yet simple, stepwise guide for the surgeon. CONCLUSION: White matter dissections, cadaveric cranial dissections, and intraoperative images are put together to provide a simplified stepwise surgical manual for anterior temporal lobectomy. Laboratory investigations that focus on the intricate 3-dimensional relationships of the pertinent operative anatomy from the surgeon's eye may enrich anatomic knowledge and push surgical boundaries, to minimize complication rates and ultimately improve patient outcomes.

The arcuate fasciculus: Combining structure and function into surgical considerations.

BACKGROUND: Two Centuries from today, Karl Friedrich Burdach attributed the nomenclature "arcuate fasciculus" to a white matter (WM) pathway connecting the frontal to the temporal cortices by arching around the Sylvian fissure. Although this label remained essentially unvaried, the concepts related to it and the characterization of the structural properties of this bundle evolved along with the methodological progress of the past years. Concurrently, the functional relevance of the arcuate fasciculus (AF) classically restricted to the linguistic domain has extended to further cognitive abilities. These features make it a relevant structure to consider in a large variety of neurosurgical procedures. OBJECTIVE: Herein, we build on our previous review uncovering the connectivity provided by the Superior Longitudinal System, including the AF, and provide a handy representation of the structural organization of the AF by considering the frequency of defined reports in the literature. By adopting the same approach, we implement an account of which functions are mediated by this WM bundle. We highlight how this information can be transferred to the neurosurgical field by presenting four surgical cases of glioma resection requiring the evaluation of the relationship between the AF and the nearby structures, and the safest approaches to adopt. CONCLUSIONS: Our cumulative overview reports the most common wiring patterns and functional implications to be expected when approaching the study of the AF, while still considering seldom descriptions as an account of interindividual variability. Given its extension and the variety of cortical territories it reaches, the AF is a pivotal structure for different cognitive functions, and thorough understanding of its structural wiring and the functions it mediates is necessary for preserving the patient's cognitive abilities during glioma resection.

Atrium meningioma: Transtubular posterior intraparietal sulcus approach.

Meningiomas that arise in the atria of the lateral ventricles are relatively rare lesions, that pose a unique challenge for surgery due to their deep-seated location and proximity to critical white matter tracts. Size and anatomical variations can affect the best approach for these tumors, with several approaches described to access the atrium including the interhemispheric trans-precuneus, trans-supramarginal gyrus, distal trans-sylvian, supracerebellar trans-collateral sulcus, and finally the trans-intraparietal sulcus approach, which was the choice for this case. Minimally invasive techniques that preserve the surrounding tissue are becoming increasingly popular and are perfectly suited to deep seated lesions. The relevant subcortical anatomy surrounding the atrium is discussed. The optic radiations form the lateral wall of the atrium, whereas commissural fibers of the tapetum form the roof of the atrium, and superficial to these fibers we have the superior longitudinal fasciculus that have vertical rami that communicate with the superior parietal lobule. Utilizing the posterior half of the intraparietal sulcus can preserve these fibers. The use of neuronavigation, brain magnetic resonance imaging with diffusion tensor imaging (DTI) tractography may be helpful in the surgical planning. In this article, we present a surgical video of a trans-tubular interparietal sulcus approach for resection of an atrium meningioma. A 43-year-old right-handed female who presented with progressive headaches and a diagnosis of idiopathic intracranial hypertension was found to have an atrial meningioma that grew in follow-up and surgery was recommended. We chose the posterior intraparietal sulcus approach as it provides a good angle of attack while preserving the optic radiations and most of the superior longitudinal fasciculus, using a tubular retractor to minimize tissue damage. Gross total resection of the tumor was achieved with complete preservation of patient neurological function.

Free-water correction DTI-based tractography in brain tumor surgery: assessment with functional and electrophysiological mapping of the white matter.

Peritumoral edema prevents fiber tracking from diffusion tensor imaging (DTI). A free-water correction may overcome this drawback, as illustrated in the case of a patient undergoing awake surgery for brain metastasis. The anatomical plausibility and accuracy of tractography with and without free-water correction were assessed with functional mapping and axono-cortical evoked-potentials (ACEPs) as reference methods. The results suggest a potential synergy between corrected DTI-based tractography and ACEPs to reliably identify and preserve white matter tracts during brain tumor surgery.

Microsurgical anatomy of the isthmic cingulum: a new white matter crossroad and neurosurgical implications in the posteromedial interhemispheric approaches and the glioma invasion patterns.

ABTRACT: The dichotomy of the cingulum bundle into the dorsal supracallosal and ventral parahippocampal parts is widely accepted; however, the retrosplenial component with its multiple alternative connections has not been revealed. The aim of this study was to delineate the microsurgical anatomy of a connectionally transition zone, the isthmic cingulum, in relation to the posteromedial interhemispheric access to the atrium and discuss the relevant patterns of glioma invasion on the basis of its fiber connections. White matter (WM) fibers were dissected layer by layer in a medial-to-lateral, lateral-to-medial, and posterior-to-anterior fashion. All related tracts and their connections were generated using deterministic tractography. The magnetic resonance imaging (MRI) tractography findings were correlated with those of fiber dissection. A medial parieto-occipital approach to reach the atrium was performed with special emphasis on the cingulate isthmus and underlying WM connections. The isthmic cingulum, introduced as a retrosplenial connectional crossroad for the first time, displayed multiple connections to the splenium and the superior thalamic radiations. Another new finding was the demonstration of lateral hemispheric extension of the isthmic cingulum fibers through the base of the posterior part of the precuneus at the base of the parieto-occipital sulcus. The laterally crossing cingulum fibers were interconnected with three distinct association tracts: the middle longitudinal (MdLF), the inferior frontooccipital fasciculi (IFOF), and the claustro-cortical fibers (CCF). In the process of entry to the atrium during posterior interhemispheric approaches, the splenial and thalamic connections, as well as the laterally crossing fibers of the isthmic cingulum, were all in jeopardy. The connectional anatomy of the retrosplenial area is much more complicated than previously known. The isthmic cingulum connections may explain the concept of interhemispheric and medial to lateral cerebral hemisphere invasion patterns in medial parieto-occipital and posteromesial temporal gliomas. The isthmic cingulum is of key importance in posteromedial interhemispheric approaches to both: the atrium and the posterior mesial temporal lobe.

Examining the role of the uncinate fasciculus in proper noun naming: awake brain tumor resections and stereo EEG targeted electrical stimulation multiple case study.

While there is strong evidence from lesion and functional imaging studies implicating the left anterior temporal pole (LTP) in naming unique entities, less is known about white matter tracts in category-specific naming. We present evidence that implicates the uncinate fasciculus (UF) in proper noun naming. First, we describe two patients with left LTP gliomas who developed category specific worsening in proper noun naming in real time during awake surgery when the UF was surgically involved . We then describe a third case involving targeted electrical stimulation of the UF using stereo-electroencephalography (sEEG) that resulted in category specific naming disturbance for proper nouns..

Cortical and white matter anatomy relevant for the lateral and superior approaches to resect intraaxial lesions within the frontal lobe.

Despite being associated with high-order neurocognitive functions, the frontal lobe plays an important role in core neurological functions, such as motor and language functions. The aim of this study was to present a neurosurgical perspective of the cortical and subcortical anatomy of the frontal lobe in terms of surgical treatment of intraaxial frontal lobe lesions. We also discuss the results of direct brain mapping when awake craniotomy is performed. Ten adult cerebral hemispheres were prepared for white matter dissection according to the Klingler technique. Intraaxial frontal lobe lesions are approached with a superior or lateral trajectory during awake conditions. The highly eloquent cortex within the frontal lobe is identified within the inferior frontal gyrus (IFG) and precentral gyrus. The trajectory of the approach is mainly related to the position of the lesion in relation to the arcuate fascicle/superior longitudinal fascicle complex and ventricular system. Knowledge of the cortical and subcortical anatomy and its function within the frontal lobe is essential for preoperative planning and predicting the risk of immediate and long-term postoperative deficits. This allows surgeons to properly set the extent of the resection and type of approach during preoperative planning.

Utilizing the TractSeg Tool for Automatic Corticospinal Tract Segmentation in Patients With Brain Pathology.

Purpose: White-matter tract segmentation in patients with brain pathology can guide surgical planning and can be used for tissue integrity assessment. Recently, TractSeg was proposed for automatic tract segmentation in healthy subjects. The aim of this study was to assess the use of TractSeg for corticospinal-tract (CST) segmentation in a large cohort of patients with brain pathology and to evaluate its consistency in repeated measurements. Methods: A total of 649 diffusion-tensor-imaging scans were included, of them: 625 patients and 24 scans from 12 healthy controls (scanned twice for consistency assessment). Manual CST labeling was performed in all cases, and by 2 raters for the healthy subjects. Segmentation results were evaluated based on the Dice score. In order to evaluate consistency in repeated measurements, volume, Fractional Anisotropy (FA), and Mean Diffusivity (MD) values were extracted and correlated for the manual versus automatic methods. Results: For the automatic CST segmentation Dice scores of 0.63 and 0.64 for the training and testing datasets were obtained. Higher consistency between measurements was detected for the automatic segmentation, with between measurements correlations of volume = 0.92/0.65, MD = 0.94/0.75 for the automatic versus manual segmentation. Conclusions: The TractSeg method enables automatic CST segmentation in patients with brain pathology. Superior measurements consistency was detected for the automatic in comparison to manual fiber segmentation, which indicates an advantage when using this method for clinical and longitudinal studies.

Anatomical and Technical Preparations of the Human Brain for White Matter Fibers Dissection with Electromagnetic Neuronavigation Assistance Technical Nuances for Application.

BACKGROUND: Klinger's fiber dissection technique is widely used for studying the anatomy of white matter. Herein, we present a technical description of Klinger's proposed fiber dissection algorithm with neuronavigation assistance which allows for a more accurate determination of the projection of association fibers. METHODS: An anatomical study was conducted on 8 hemispheres of the human brain, prepared according to the Klingler fiber dissection technique. In all the cases, a frameless electromagnetic navigation system was used. For each anatomical specimen, an individualized support device was three-dimensional -printed and placed it into the magnetic resonance imaging (MRI) gantry. MRI study of each anatomical specimen was performed using a specific protocol that enabled a subsequent three-dimensional visualization of the anatomical structures as follows: FSPGR (Fast SPoiled Gradient Recalled echo) BRAVO (BRAin VOlume Imaging), T2 CUBE, FLAIR (FLuid Attenuated Inversion Recovery) CUBE, CUBE DIR (double inversion recovery) WHITE MATTER, and CUBE DIR GRAY MATTER. RESULTS: The average time required to register an anatomical specimen in the navigation system was 7 minutes 28 seconds. In all of the 8 cases, the anatomical structures were correctly identified using neuronavigation. Moreover, the choice of MRI mode depends on the purpose of the study and the region of interest in the brain. CONCLUSIONS: Electromagnetic navigation is an accurate and useful technique. It allows the researcher the ability to virtually project the association fibers and their cortico-cortical terminations to the surface of the brain, even at the final stages of dissection when the superficial structures are removed. To obtain accurate targeting, it is important to use the appropriate neuronavigation protocol.

Validation of Presurgical Simulation of White Matter Damage Using Diffusion Tensor Imaging.

BACKGROUND: The understanding of white matter (WM) was revolutionized by the emergence of tractography based on diffusion tensor imaging (DTI). Currently, DTI simulations are implemented in preoperative planning to optimize surgical approaches. The reliability of these simulations has been questioned and investigated seeking for correlation between neurological performance and anomalies in DTI parameters. However, the ability of preoperative WM simulations to predict a surgical injury has not been thoroughly evaluated. Our objective was to assess the reliability of preoperatively simulated WM injuries for conventional neurosurgical procedures. METHODS: WM surgical damage was preoperatively simulated by creating a 3-dimensional volume representing the endoscope or the surgical trajectory. This volume was used as an additional region of interest in the fascicle reconstruction to be subtracted from the original fascicle. Simulated, injured fascicles were compared in terms of the number of fibers and volume to those created from postoperative DTI studies. Reliability was assimilated into the correlation between the simulation and the postoperative reconstruction; evaluated using the intraclass correlation coefficient or Lin's Concordance correlation coefficient (CCC), and represented on Bland-Altman plots. RESULTS: The preoperative and postoperative DTI studies of 30 patients undergoing various neurosurgical approaches were processed. The correlation between simulated injuries and postoperative studies was high in terms of fibers (Concordance correlation coefficient = Rho.C = 0.989 [95% confidence interval = 0.979-0.995]) and volume (intraclass correlation coefficient = 0.95 [95% CI = 0.89-0.97]). Bland-Altman plots demonstrated that the great majority of cases fell within the mean ± 2 Standard deviations. CONCLUSIONS: Presurgical simulation of WM fascicles based on DTI is consistent with postoperative DTI studies. These findings require further validation by neurophysiological and clinical correlation.

Preservation of frontal white matter tracts in ventricular surgery: favoring an anterior interhemispheric transcallosal approach vs a transcortical transfrontal transventricular approach.

Secondary to the creation of a surgical corridor and retraction, white matter tracts degenerate, causing long-term scarring with potential neurological consequences. Third and lateral ventricle tumors require surgery that may lead to cognitive impairment. Our objective is to compare the long-term consequences of a transcortical transfrontal approach and an interhemispheric transcallosal approach on corpus callosum and frontal white matter tracts degeneration. Surgical patients with ventricular tumor accessible through both approaches were included and clinico-radiological data were retrospectively analyzed. The primary endpoint was the callosotomy length at 3-month post-operative T1 MRI, corrected by the extension of the tumor and the use of neuronavigation. Secondary outcomes included perioperative criteria such as bleeding, use of retractors and duration, FLAIR hypersignal on 3-month MRI, and re-do surgeries. To assess white matter tract interruption, 3-month FLAIR hypersignal was superposed to a tractography atlas. Seventy patients were included, 57 (81%) in the transfrontal group and 13 (19%) in the interhemispheric group. There was no difference in the mean callosotomy length on 3-month MRI (12.3 mm ± 5.60 transfrontal vs 11.7 mm ± 3.92 interhemispheric, p = 0.79) on univariate and multivariate analyses. The callosotomy length was inferior by - 3.13 mm for tumors located exclusively in the third ventricle (p = 0.016), independent of the approach. Retractors were used more often in transfrontal approaches (60% vs 33%, p < 0.001). The extent of frontal FLAIR hypersignal was higher after transfrontal approach (14.1 mm vs 0.525 mm, p < 0.001), correlated to the use of retractors (p < 0.05). After the interhemispheric approach, no tract other than corpus callosum was interrupted, whereas, after the transfrontal approach, frontal arcuate fibers and projections from the thalamus were interrupted in all patients, the cingulum in 19 (33%), the superior fronto-occipital fasciculus in 15 (26%), and the superior longitudinal fasciculus in 2 (3%). Transfrontal and interhemispheric approaches to the third and lateral ventricles both lead to the same long-term damage to the corpus callosum, but the transfrontal approach interrupts several white matter tracts essential to cognitive tasks such as attention and planning, even in the non-dominant hemisphere. These results encourage all neurosurgeons to be familiar with both approaches and favor the interhemispheric approach when both can give access to the tumor with a comparable risk. Neuropsychological studies are necessary to correlate these anatomical findings to cognitive outcomes.

Assessment of intraoperative diffusion EPI distortion and its impact on estimation of supratentorial white matter tract positions in pediatric epilepsy surgery.

The effectiveness of correcting diffusion Echo Planar Imaging (EPI) distortion and its impact on tractography reconstruction have not been adequately investigated in the intraoperative MRI setting, particularly for High Angular Resolution Diffusion Imaging (HARDI) acquisition. In this study, we evaluated the effectiveness of EPI distortion correction using 27 legacy intraoperative HARDI datasets over two consecutive surgical time points, acquired without reverse phase-encoded data, from 17 children who underwent epilepsy surgery at our institution. The data was processed with EPI distortion correction using the Synb0-Disco technique (Schilling et al., 2019) and without distortion correction. The corrected and uncorrected b0 diffusion-weighted images (DWI) were first compared visually. The mutual information indices between the original T1-weighted images and the fractional anisotropy images derived from corrected and uncorrected DWI were used to quantify the effect of distortion correction. Sixty-four white matter tracts were segmented from each dataset, using a deep-learning based automated tractography algorithm for the purpose of a standardized and unbiased evaluation. Displacement was calculated between tracts generated before and after distortion correction. The tracts were grouped based on their principal morphological orientations to investigate whether the effects of EPI distortion vary with tract orientation. Group differences in tract distortion were investigated both globally, and regionally with respect to proximity to the resecting lesion in the operative hemisphere. Qualitatively, we observed notable improvement in the corrected diffusion images, over the typically affected brain regions near skull-base air sinuses, and correction of additional distortion unique to intraoperative open cranium images, particularly over the resection site. This improvement was supported quantitatively, as mutual information indices between the FA and T1-weighted images were significantly greater after the correction, compared to before the correction. Maximum tract displacement between the corrected and uncorrected data, was in the range of 7.5 to 10.0 mm, a magnitude that would challenge the safety resection margin typically tolerated for tractography-informed surgical guidance. This was particularly relevant for tracts oriented partially or fully in-line with the acquired diffusion phase-encoded direction. Portions of these tracts passing close to the resection site demonstrated significantly greater magnitude of displacement, compared to portions of tracts remote from the resection site in the operative hemisphere. Our findings have direct clinical implication on the accuracy of intraoperative tractography-informed image guidance and emphasize the need to develop a distortion correction technique with feasible intraoperative processing time.

Disección didáctica de fibra blanca en cerebelo humano en tres pasos: entrenamiento microneuroanatómico / 3-Step didactic white matter dissection of human cerebellum: Micro-neuroanatomical training

Objetivos: Un buen conocimiento anatómico del cerebelo es fundamental para llevar a cabo abordajes al IV ventrículo (frecuentes en la neurocirugía pediátrica) de forma segura, evitando secuelas como el mutismo cerebeloso. El propósito del presente trabajo es realizar una disección didáctica del cerebelo humano centrándonos especialmente en los pedúnculos cerebelosos y en los núcleos dentados (DN); estructuras en riesgo durante estos procedimientos. Material y métodos :Se disecó el órgano, siguiendo el método de Klingler para fibras blancas, usando material de microcirugía estándar y específico, bajo un microscopio D. F. Vasconcellos M900 con aumento x6-x40. Se utilizó una cámara Canon EOS T7 con un objetivo de 18-55 mm y se editaron las imágenes con Adobe Lightroom Classic CC y Keynote. Se emplearon métodos especiales como la iluminación endoscópica con luz LED para la obtención de algunas fotografías. Resultados: Se logró disecar con éxito los DN del cerebelo y describir su relación con los pedúnculos cerebelosos, vermis inferior y velos medulares. Mediante esta guía de tres pasos (1. cara tentorial; 2. cara suboccipital; 3. estructuras del IV ventrículo) se consiguió mostrar los elementos más importantes para el estudio del órgano y caracterizar sus implicaciones en los distintos abordajes al IV ventrículo. Conclusiones: La mejor forma de completar el estudio de neuroanatomía es la disección de especímenes, ya que aporta una visión 3 D. La transiluminación con luz LED se reveló como una herramienta útil para el registro fotográfico de estructuras del IV ventrículo, lo que mejora la visión espacial. Su principal aplicación la encontramos en los velos medulares y forámenes de la fosa romboide, ya que son permeables a la luz. La guía de disección en tres fases propuesta en este trabajo puede ayudar a los neurocirujanos, en cualquier etapa de su formación, a comprender mejor el cerebelo (AU)

Objectives: A thorough understanding of cerebellum anatomy is essential in 4th ventricle approaches (more frequent in pediatric neurosurgery), avoiding relevant complications such as cerebellar mutism. The aim of the present work is to show the feasibility of a didactic dissection of human cerebellum focusing on cerebellar peduncles and dentate nucleus (DN), which are structures at high risk during these surgical procedures. Material and methods: The cerebellum was dissected according to the Klingler method for white matter, using standard and specific microsurgery tools. Surgical microscope magnification (x6-x40) provided by a D.F. Vasconcellos M900 was required. A Canon EOS T7 18-55 mm digital camera was used and Adobe Lightroom Classic CC and Keynote were selected as photo enhancing software. Special methods such as LED light endoscopic transillumination were used for photographical reasons. Results: DN dissection was successfully achieved and the relations between these nucleus and the cerebellar peduncles, inferior vermis and medullary velums were described. Through this three steps dissection guide (1. tentorial surface; 2. suboccipital surface; 3. 4th ventricle structures), the most relevant anatomical structures were shown and its implications in different 4th ventricle approaches were characterised. Conclusion: 3 D perspective provided by real specimen anatomical dissection is critical for learning neuroanatomy. ED transillumination was shown as a useful technique for the 4th ventricle structures photographic documentation which improves spatial recognition. This benefit can be applied for the study of the relations between the medullary velums and the rhomboid fossa foramina, which are permeable to light. The proposed three-steps dissection guide helps to a better understanding of human cerebellum and to gain self-confidence, allowing safer practice for neurosurgeons in all stages of their career (AU)

Structural connectivity in children after total corpus callosotomy.

OBJECTIVES: To investigate structural connectivity after total callosotomy. METHODS: Deterministic fiber tracking (tractography) of whole brain white matter was performed on 13 epilepsy patients pre- and post-callosotomy. The analysis of structural connectivity was based on graph theory and network-based analysis with a focus on the inter- and intrahemispheric networks. Clinical demographic data including seizure patterns and outcomes were scored for the identification of correlations. RESULTS: After total callosotomy, structural interhemispheric networks were significantly interrupted. Specific changes were observed in the structural intrahemispheric networks in both hemispheres: 3 edges presented with significant decreases in the left hemisphere, whereas 2 edges presented with significant decreases in the right hemisphere. No global changes were observed in the network density, average weighted strength, average characteristic path length, or global efficiency of intrahemispheric networks. The intrahemispheric hubs and nodal efficiency were minimal changed after callosotomy. CONCLUSION: While there was a significant decrease in structural interhemispheric connectivity post-callosotomy, we observed synchronously decremented changes of intrahemispheric edges in each hemisphere. This study suggests that white matter maintains the structural connectivity intrahemispherically although functional connectivity recovered after total callosotomy.

3-Step didactic white matter dissection of human cerebellum: Micro-neuroanatomical training.

OBJECTIVES: A thorough understanding of cerebellum anatomy is essential in 4th ventricle approaches (more frequent in pediatric neurosurgery), avoiding relevant complications such as cerebellar mutism. The aim of the present work is to show the feasibility of a didactic dissection of human cerebellum focusing on cerebellar peduncles and dentate nucleus (DN), which are structures at high risk during these surgical procedures. MATERIAL AND METHODS: The cerebellum was dissected according to the Klingler method for white matter, using standard and specific microsurgery tools. Surgical microscope magnification (×6-×40) provided by a D.F. Vasconcellos M900 was required. A Canon EOS T7 18-55 mm digital camera was used and Adobe Lightroom Classic CC and Keynote were selected as photo enhancing software. Special methods such as LED light endoscopic transillumination were used for photographical reasons. RESULTS: DN dissection was successfully achieved and the relations between these nucleus and the cerebellar peduncles, inferior vermis and medullary velums were described. Through this three steps dissection guide (1. tentorial surface; 2. suboccipital surface; 3. 4th ventricle structures), the most relevant anatomical structures were shown and its implications in different 4th ventricle approaches were characterised. CONCLUSION: 3 D perspective provided by real specimen anatomical dissection is critical for learning neuroanatomy. LED transillumination was shown as a useful technique for the 4th ventricle structures photographic documentation which improves spatial recognition. This benefit can be applied for the study of the relations between the medullary velums and the rhomboid fossa foramina, which are permeable to light. The proposed three-steps dissection guide helps to a better understanding of human cerebellum and to gain self-confidence, allowing safer practice for neurosurgeons in all stages of their career.