Human Connectome-Based Tractographic Atlas of the Brainstem Connections and Surgical Approaches

Atlas-guided brain projection tracts: From regions of interest to tractography 3D rendering

The use of diffusion tensor imaging (DTI) has seen significant development over the last two decades, in particular with the development of the tractography of association tracts for preoperative planning of surgery. However, projection tracts are difficult to differentiate from one another and tractography studies have failed to reconstruct these ascending/descending pathways from/to the spinal cord. The present study proposes an atlas of regions of interest (ROIs) designed specifically for projection tracts tractography. Forty-nine healthy subjects were included in this prospective study. Brain DTI was acquired using the same 3 T MRI scanner, with 32 diffusion directions. Distortions were corrected using the FSL software package. ROIs were drawn using the anterior commissure (AC)-posterior commissure (PC) line on the following landmarks: the pyramid for the corticospinal tract, the medio-caudal part of the red nucleus for the rubrospinal tract, the pontine reticular nucleus for corticoreticular tract, the superior and inferior cerebellar peduncles for, respectively, the anterior and posterior spinocerebellar tract, the gracilis and cuneatus nucleus for the dorsal columns, and the ventro-posterolateral nucleus for the spinothalamic tract. Fiber tracking was performed using a deterministic algorithm using DSI Studio software. ROI coordinates, according to AC-PC line, were given for each tract. Tractography was obtained for each tract, allowing tridimensional rendering and comparison of tracking metrics between tracts. The present study reports the accurate design of specific ROIs for tractography of each projection tract. This could be a useful tool in order to differentiate projection tracts at the spinal cord level.

Local abnormal white matter microstructure in the spinothalamic tract in people with chronic neck and shoulder pain

Objective

To investigate differences in the microstructure of the spinothalamic tract (STT) white matter in people with chronic neck and shoulder pain (CNSP) using diffusion tensor imaging, and to assess its correlation with pain intensity and duration of the pain.

Materials and methods

A 3.0T MRI scanner was used to perform diffusion tensor imaging scans on 31 people with CNSP and 24 healthy controls (HCs), employing the Automatic Fiber Segmentation and Quantification (AFQ) method to extract the STT and quantitatively analyze the fractional anisotropy (FA) and mean diffusivity (MD), reflecting the microstructural integrity of nerve fibers. Correlations of these differences with duration of pain and visual analog scale (VAS) scores were analyzed.

Results

No significant differences in the mean FA or MD values of the bilateral STT were observed between people with CNSP and HCs (p > 0.05), as indicated by the two-sample t test. Further point-by-point comparison along 100 equidistant nodes within the STT pathway revealed significant reductions in FA values in the left (segments 12-18, 81-89) and right (segments 9-19, 76-80) STT in the CNSP group compared to HCs; significant increases in MD values were observed in the left (segments 1-13, 26-30, 71-91) and right (segments 8-17, 76-91) STT (p < 0.05, FWE corrected). Partial correlation analysis indicates that in people with CNSP, the FA values of the STT in regions with damaged white matter structure show a negative correlation with VAS scores and duration of pain, whereas MD values show a positive correlation with VAS scores and duration of pain.

Conclusion

This study found that people with CNSP exhibit white matter microstructural abnormalities in the specific segments of STT. These abnormalities are associated with the patient's pain intensity and disease duration. The findings offer a new neuroimaging perspective on the pathophysiological basis of chronic pain in the ascending conduction process and its potential role in developing targeted intervention strategies. However, due to the limited sample size and the lack of statistical significance when analyzing the entire spinothalamic tract, these conclusions should be interpreted with caution. Further research with larger cohorts is necessary to validate these results.

Validation of Tenths Stereotactic Coordinates Method Using Probabilistic Tractography of the Ansa Lenticularis in Parkinson's Disease Patients

OBJECTIVE

To evaluate the accuracy of stereotactic coordinates to target the ansa lenticularis (AL) using 2 surgical planning methods, the conventional millimeter method (MM) and the normalized Tenths method (TM), assessed through individualized probabilistic tractography.

METHODS

Stereotactic targeting of the AL was assessed in 2 groups: 16 patients with Parkinson's disease and 16 healthy controls from Group 1, and 39 Parkinson's disease patients from Group 2. Structural and diffusion magnetic resonance imaging probabilistic tractography identified the AL based on the Schaltenbrand-Wahren Atlas. The MM defined stereotactic coordinates in millimeters, while the TM refined the planning by dividing the intercommissural line (AC-PC) distance into 10 equal parts, normalizing the "X," "Y," and "Z" coordinates for each patient. We subsequently compared the percentage of structural connectivity (%conn) of the AL with predefined regions of interest (ROIs), including the frontopontine-corticothalamic tracts, globus pallidus internus-ventral oral anterior, and ventral oral posterior, and quantified the streamlines in 142 brain hemispheres using the MM and TM coordinates.

RESULTS

Despite anatomical variations in intercommissural (AC-PC) line lengths between both groups (22.5 ± 2.09 mm and 24.4 ± 2.56 mm, respectively; P = 0.002), as well as differences in magnetic resonance imaging acquisition parameters, we found that the TM significantly enhanced streamline identification and %conn compared to the MM. These enhancements were noted across ROIs: frontopontine-corticothalamic and globus pallidus internus-ventral oral anterior in both hemispheres, and globus pallidus internus-ventral oral posterior in the left (P < 0.001) and right hemispheres (P = 0.03).

CONCLUSIONS

TM surpasses MM in identifying the structural connectivity between the AL and predefined ROIs, underscoring the advantages of coordinate normalization. However, variations in AC-PC line lengths and Euclidean distances between methods could lead to inaccuracies in the coordinate settings, potentially affecting the precision of structural connectivity and the efficacy of therapeutic outcomes.

Bilateral hypogeusia and food aversion due to lacunar infarct in the right dorsomedial pontine tegmentum

A 70-year-old right-handed housewife suffered an acute loss of taste, an unpleasant change in the taste of foods and liquids, and a strong aversion to all kinds of food due to a small lacune in the right dorsomedial pontine tegmentum. Eating became so unpleasant that she lost 7 kg in three weeks. Olfaction and the sensibility of the tongue were spared. The right medial longitudinal fascicle, the central tegmental tract, or both, were injured by the tegmental lesion. A discrete right-sided lesion in the upper pontine tegmentum may cause a reversible syndrome consisting of bilateral hypogeusia which is more severe ipsilaterally.

The Role of Ascending Ventral-Tegmental Fibers for Recovery after Stroke

OBJECTIVES

The integrity of cortical motor networks and their descending effector pathway (the corticospinal tract [CST]) is a major determinant motor recovery after stroke. However, this view neglects the importance of ascending tracts and their modulatory effects on cortical physiology. Here, we explore the role of such a tract that connects dopaminergic ventral tegmental midbrain nuclei to the motor cortex (the VTMC tract) for post-stroke recovery.

METHODS

Lesion data and diffusivity parameters (fractional anisotropy) of the ipsi- and contralesional VTMC tract and CST were obtained from 133 patients (63.9 ± 13.4 years, 45 women) during the acute and chronic stage after the first ever ischemic stroke in the middle cerebral artery territory. Degeneration of VTMC tract and CST was quantified and related to clinical outcome parameters (National Institute of Health Stroke Scale with motor and cortical symptom subscores; modified Fugl-Meyer upper extremity score; modified Ranking Scale [mRS]).

RESULTS

A significant post-stroke degeneration occurred in both tracts, but only VTMC degeneration was associated with lesion size. Using multiple regression models, we dissected the impact of particular tracts on recovery: Changes in VTMC tract integrity were stronger associated with independence in daily activities (mRS), upper limb motor impairment (modified Fugl-Meyer upper extremity score) and cortical symptoms (aphasia, neglect) captured by National Institute of Health Stroke Scale compared to CST. Changes in CST integrity merely were associated with the degree of hemiparesis (National Institute of Health Stroke Scale motor subscale).

INTERPRETATION

Post-stroke outcome is influenced by ascending (VTMC) and descending (CST) fiber tracts. Favorable outcome regarding independence (modified Ranking Scale), upper limb motor function (modified Fugl-Meyer upper extremity score), and cortical symptoms (aphasia, neglect) was more strongly related to the ascending than descending tract. ANN NEUROL 2023.

In vivo probabilistic atlas of white matter tracts of the human subthalamic area combining track density imaging and optimized diffusion tractography

The human subthalamic area is a region of high anatomical complexity, tightly packed with tiny fiber bundles. Some of them, including the pallidothalamic, cerebello-thalamic, and mammillothalamic tracts, are relevant targets in functional neurosurgery for various brain diseases. Diffusion-weighted imaging-based tractography has been suggested as a useful tool to map white matter pathways in the human brain in vivo and non-invasively, though the reconstruction of these specific fiber bundles is challenging due to their small dimensions and complex anatomy. To the best of our knowledge, a population-based, in vivo probabilistic atlas of subthalamic white matter tracts is still missing. In the present work, we devised an optimized tractography protocol for reproducible reconstruction of the tracts of subthalamic area in a large data sample from the Human Connectome Project repository. First, we leveraged the super-resolution properties and high anatomical detail provided by short tracks track-density imaging (stTDI) to identify the white matter bundles of the subthalamic area on a group-level template. Tracts identification on the stTDI template was also aided by visualization of histological sections of human specimens. Then, we employed this anatomical information to drive tractography at the subject-level, optimizing tracking parameters to maximize between-subject and within-subject similarities as well as anatomical accuracy. Finally, we gathered subject level tracts reconstructed with optimized tractography into a large-scale, normative population atlas. We suggest that this atlas could be useful in both clinical anatomy and functional neurosurgery settings, to improve our understanding of the complex morphology of this important brain region.

Quantitative mapping of the brain's structural connectivity using diffusion MRI tractography: A review

Diffusion magnetic resonance imaging (dMRI) tractography is an advanced imaging technique that enables in vivo reconstruction of the brain's white matter connections at macro scale. It provides an important tool for quantitative mapping of the brain's structural connectivity using measures of connectivity or tissue microstructure. Over the last two decades, the study of brain connectivity using dMRI tractography has played a prominent role in the neuroimaging research landscape. In this paper, we provide a high-level overview of how tractography is used to enable quantitative analysis of the brain's structural connectivity in health and disease. We focus on two types of quantitative analyses of tractography, including: 1) tract-specific analysis that refers to research that is typically hypothesis-driven and studies particular anatomical fiber tracts, and 2) connectome-based analysis that refers to research that is more data-driven and generally studies the structural connectivity of the entire brain. We first provide a review of methodology involved in three main processing steps that are common across most approaches for quantitative analysis of tractography, including methods for tractography correction, segmentation and quantification. For each step, we aim to describe methodological choices, their popularity, and potential pros and cons. We then review studies that have used quantitative tractography approaches to study the brain's white matter, focusing on applications in neurodevelopment, aging, neurological disorders, mental disorders, and neurosurgery. We conclude that, while there have been considerable advancements in methodological technologies and breadth of applications, there nevertheless remains no consensus about the "best" methodology in quantitative analysis of tractography, and researchers should remain cautious when interpreting results in research and clinical applications.

Brainstem Diffusion Tensor Tractography and Clinical Applications in Pain

The brainstem is one of the most vulnerable brain structures in many neurological conditions, such as pain, sleep problems, autonomic dysfunctions, and neurodegenerative disorders. Diffusion tensor imaging and tractography provide structural details and quantitative measures of brainstem fiber pathways. Until recently, diffusion tensor tractographic studies have mainly focused on whole-brain MRI acquisition. Due to the brainstem's spatial localization, size, and tissue characteristics, and limits of imaging techniques, brainstem diffusion MRI poses particular challenges in tractography. We provide a brief overview on recent advances in diffusion tensor tractography in revealing human pathways connecting the brainstem to the subcortical regions (e.g., basal ganglia, mesolimbic, basal forebrain), and cortical regions. Each of these pathways contains different distributions of fiber tracts from known neurotransmitter-specific nuclei in the brainstem. We compare the brainstem tractographic approaches in literature and our in-lab developed automated brainstem tractography in terms of atlas building, technical advantages, and neuroanatomical implications on neurotransmitter systems. Lastly, we summarize recent investigations of using brainstem tractography as a promising tool in association with pain.

Predicting Functional Connectivity From Observed and Latent Structural Connectivity via Eigenvalue Mapping

Understanding how complex dynamic activity propagates over a static structural network is an overarching question in the field of neuroscience. Previous work has demonstrated that linear graph-theoretic models perform as well as non-linear neural simulations in predicting functional connectivity with the added benefits of low dimensionality and a closed-form solution which make them far less computationally expensive. Here we show a simple model relating the eigenvalues of the structural connectivity and functional networks using the Gamma function, producing a reliable prediction of functional connectivity with a single model parameter. We also investigate the impact of local activity diffusion and long-range interhemispheric connectivity on the structure-function model and show an improvement in functional connectivity prediction when accounting for such latent variables which are often excluded from traditional diffusion tensor imaging (DTI) methods.

Electrophysiological characterization of the hyperdirect pathway and its functional relevance for subthalamic deep brain stimulation

The subthalamic nucleus (STN) receives input from various cortical areas via hyperdirect pathway (HDP) which bypasses the basal-ganglia loop. Recently, the HDP has gained increasing interest, because of its relevance for STN deep brain stimulation (DBS). To understand the HDP's role cortical responses evoked by STN-DBS have been investigated. These responses have short (<2 ms), medium (2-15 ms), and long (20-70 ms) latencies. Medium-latency responses are supposed to represent antidromic cortical activations via HDP. Together with long-latency responses the medium responses can potentially be used as biomarker of DBS efficacy as well as side effects. We here propose that the activation sequence of the cortical evoked responses can be conceptualized as high frequency oscillations (HFO) for signal analysis. HFO might therefore serve as marker for antidromic activation. Using existing knowledge on HFO recordings, this approach allows data analyses and physiological modeling to advance the pathophysiological understanding of cortical DBS-evoked high-frequency activity.

There is a topographic organization in human cortico-pontine connectivity

Of the three largest outputs of the cerebral cortex, two have been extensively studied and mapped. Topographic maps of cortico-thalamic and cortico-striatal functional connectivity in humans are well established. However, for the third largest cerebral output, to the pontine nuclei, which connect the cerebrum to the cerebellum, the existence of such an organized connectivity pattern in humans is unknown. Here, using high-resolution functional MRI and a large sample size, we found a topographically organized pattern of functional connectivity between the human cerebral cortex and pons. Our results indicate a rostral-caudal topography; rostral (frontal) cerebral cortex shows connectivity to the rostral pons, and the more caudal cortical areas (i.e. the sensorimotor cortices) show functional connectivity more caudally in the pons, with the occipital lobe connectivity being most caudal. While prefrontal, sensorimotor and occipital cortices have a connectivity to the medial pontine nuclei, posterior parietal cortex and temporal lobe correlate with lateral pontine nuclei. Topography is sufficiently detailed to identify distinct connectivity for leg, trunk, hand and face areas of the motor cortex. These findings reveal the existence of a topographic organization in human cortico-pontine connectivity and provide the topographic map for future studies of cortico-ponto-cerebellum pathway in a variety of disorders.

Endoscopic Endonasal Excision of a Ventral Exophytic Brainstem Glioma: A Technical Case Report

BACKGROUND AND IMPORTANCE

Ventral midbrain glioma is an extremely rare lesion in adults. The endoscopic endonasal approach is potentially a better alternative to transcranial approach for this challenging lesion and has not been described in the literature.

CLINICAL PRESENTATION

A 22-yr-old woman previously operated through an interhemispheric approach for ventral midbrain glioma with extension in the suprasellar cistern presented with severe headache and diplopia. Imaging revealed an increase in size of the residual lesion. The tumor was resected by using an extended endonasal approach. The patient had improvement in her diplopia with no endocrine complication.

CONCLUSION

This case demonstrates the surgical technique of endoscopic endonasal resection of a ventral midbrain glioma.

Complete functional recovery in a child after endovascular treatment of basilar artery occlusion caused by spontaneous dissection: a case report

Stroke caused by dissection of arteries of the vertebrobasilar system in children is still poorly investigated in terms of etiology, means of treatment, course of disease, and prognosis. The aim of this report was to describe the unusual course of a spontaneous dissection of the basilar artery (BA) in a child treated with endovascular techniques and to point out that the plasticity of the brain stem can fully compensate for structural damage caused by stroke. We report the case of a 15-year-old boy who suffered a wake-up stroke with BA occlusion caused by spontaneous dissection. A blood clot was aspirated from the false lumen and the true lumen re-opened, but the patient deteriorated a few hours later, and repeated angiography revealed that the intimal flap was detached, occluding the BA again. The lumen of BA was then reconstructed by a stent. Despite a large pons infarction, the patient was completely recovered 11 months after the onset. The case was analyzed with angiograms and magnetic resonance imaging, macroscopic and microscopic pathological analysis, computed tomographic angiography, magnetic resonance-based angiography, and diffusion tensor imaging. This case illustrates that applied endovascular techniques and intensive care measures can alter the course of potentially fatal brain stem infarction. Our multimodal analysis gives new insight into the anatomical basis for the plasticity mechanism of the brain stem.

The trajectory of the medial longitudinal fasciculus in the human brain: A diffusion imaging-based tractography study

The aim of this study is to investigate the trajectory of medial longitudinal fasciculus (MLF) and explore its anatomical relationship with the oculomotor nerve using tractography technique. The MLF and oculomotor nerve were reconstructed at the same time with preset three region of interests (ROIs): one set at the area of rostral midbrain, one placed on the MLF area at the upper pons, and one placed at the cisternal part of the oculomotor nerve. This mapping protocol was tested in an HCP‐1065 template, 35 health subjects from Massachusetts General Hospital (MGH), 20 healthy adults and 6 brainstem cavernous malformation (BCM) patients with generalized q‐sampling imaging (GQI)‐based tractography. Finally, the 200 μm brainstem template from Center for In Vivo Microscopy, Duke University (Duke CIVM), was used to validate the trajectory of reconstructed MLF. The MLF and oculomotor nerve were reconstructed in the HCP‐1065 template, 35 MGH health subjects, 20 healthy adults and 6 BCM patients. The MLF was in conjunction with the ipsilateral mesencephalic part of the oculomotor nerve. The displacement of MLF was identified in all BCM patients. Decreased QA, RDI and FA were found in the MLF of lesion side, indicating axonal loss and/or edema of displaced MLF. The reconstructed MLF in Duke CIVM brainstem 200 μm template corresponded well with histological anatomy. The MLF and oculomotor nerve were visualized accurately with our protocol using GQI‐based fiber tracking. This GQI‐based tractography is an important tool in the reconstruction and evaluation of MLF.

A high-resolution interactive atlas of the human brainstem using magnetic resonance imaging

Conventional atlases of the human brainstem are limited by the inflexible, sparsely-sampled, two-dimensional nature of histology, or the low spatial resolution of conventional magnetic resonance imaging (MRI). Postmortem high-resolution MRI circumvents the challenges associated with both modalities. A single human brainstem specimen extending from the rostral diencephalon through the caudal medulla was prepared for imaging after the brain was removed from a 65-year-old male within 24 h of death. The specimen was formalin-fixed for two weeks, then rehydrated and placed in a custom-made MRI compatible tube and immersed in liquid fluorocarbon. MRI was performed in a 7-Tesla scanner with 120 unique diffusion directions. Acquisition time for anatomic and diffusion images were 14 h and 208 h, respectively. Segmentation was performed manually. Deterministic fiber tractography was done using strategically chosen regions of interest and avoidance, with manual editing using expert knowledge of human neuroanatomy. Anatomic and diffusion images were rendered with isotropic resolutions of 50 μm and 200 μm, respectively. Ninety different structures were segmented and labeled, and 11 different fiber bundles were rendered with tractography. The complete atlas is available online for interactive use at https://www.civmvoxport.vm.duke.edu/voxbase/login.php?return_url=%2Fvoxbase%2F. This atlas presents multiple contrasting datasets and selected tract reconstruction with unprecedented resolution for MR imaging of the human brainstem. There are immediate applications in neuroanatomical education, with the potential to serve future applications for neuroanatomical research and enhanced neurosurgical planning through "safe" zones of entry into the human brainstem.

Motor Evoked Potential Recordings During Segmented Deep Brain Stimulation-A Feasibility Study

BACKGROUND

Segmented deep brain stimulation (DBS) leads, which are capable of steering current in the direction of any 1 of 3 segments, can result in a wider therapeutic window by directing current away from unintended structures, particularly, the corticospinal tract (CST). It is unclear whether the use of motor evoked potentials (MEPs) is feasible during DBS surgery via stimulation of individual contacts/segments in order to quantify CST activation thresholds and optimal contacts/segments intraoperatively.

OBJECTIVE

To assess the feasibility of using MEP to identify CST thresholds for ring and individual segments of the DBS lead under general anesthesia.

METHODS

MEP testing was performed during pulse generator implantation under general anesthesia on subjects who underwent DBS lead implantation into the subthalamic nucleus (STN). Stimulation of each ring and segmented contacts of the directional DBS lead was performed until CST threshold was reached. Stereotactic coordinates and thresholds for each contact/segment were recorded along with the initially activated muscle group.

RESULTS

A total of 34 hemispheres were included for analysis. MEP thresholds were recorded from 268 total contacts/segments. For segmented contacts (2 and 3, respectively), the mean highest CST thresholds were 2.33 and 2.62 mA, while the mean lowest CST thresholds were 1.7 and 1.89 mA, suggesting differential thresholds in relation to CST. First dorsal interosseous and abductor pollicis brevis (34% each) were the most commonly activated muscle groups.

CONCLUSION

MEP threshold recording from segmented DBS leads is feasible. MEP recordings can identify segments with highest CST thresholds and may identify segment orientation in relation to CST.

Brainstem damage is associated with poorer sleep quality and increased pain in gulf war illness veterans

AIMS

Gulf War Illness (GWI) is manifested as multiple chronic symptoms, including chronic pain, chronic fatigue, sleep problems, neuropsychiatric disorders, respiratory, gastrointestinal, and skin problems. No single target tissue or unifying pathogenic process has been identified that accounts for this variety of symptoms. The brainstem has been suspected to contribute to this multiple symptomatology. The aim of this study was to assess the role of the brainstem in chronic sleep problems and pain in GWI veterans.

MATERIALS AND METHODS

We enrolled 90 veterans (Age = 50 ± 5, 87% Male) who were deployed to the 1990-91 Gulf War and presented with GWI symptoms. Sleep quality was evaluated using the global Pittsburgh Sleep Quality Index. Pain intensities were obtained with the Brief Pain Inventory sum score. Volumes in cortical, subcortical, brainstem, and brainstem subregions and diffusion tensor metrics in 10 bilateral brainstem tracts were tested for correlations with symptom measures.

KEY FINDINGS

Poorer sleep quality was significantly correlated with atrophy of the whole brainstem and brainstem subregions (including midbrain, pons, medulla). Poorer sleep quality also significantly correlated with lower fractional anisotropy in the nigrostriatal tract, medial forebrain tract, and the dorsal longitudinal fasciculus. There was a significant correlation between increased pain intensity and decreased fractional anisotropy in the dorsal longitudinal fasciculus. These correlations were not altered after controlling for age, sex, total intracranial volumes, or additional factors, e.g., depression and neurological conditions.

SIGNIFICANCE

These findings suggest that the brainstem plays an important role in the aberrant neuromodulation of sleep and pain symptoms in GWI.

Visualization of cerebellar peduncles using diffusion tensor imaging

The cerebellum communicates with the cerebral cortex via the superior, middle, and inferior cerebellar peduncles (CPs). To preserve the structure and function of the brainstem and cerebellum, which is compressed in various pathological conditions, it is important to delineate the spatial interrelationship of the CPs for presurgical planning and intraoperative guidance. Diffusion tensor tractography (DTT) is a technique capable of depicting the major fiber bundles in CPs. However, routine use of this technology for brainstem visualization remains challenging due to the anatomical smallness and complexity of the brainstem and susceptibility-induced image distortions. Here, we attempt to visualize CPs using high-resolution DTT in a commercial equipment for the application of this technique in normal clinical settings. DTT and fast imaging employing steady-state acquisition-cycled phases (FIESTA) of the whole brainstem were performed. We rendered the DTT fiber bundle using a region-of-interest-based fiber tracking method onto the structural image generated in FIESTA by automatic image coregistration. Fibers of the CPs were clearly visualized by DTT. The DTT-FIESTA overlaid image revealed the cross-sectional and three-dimensional anatomy of the pyramidal tract and the ascending sensory fibers, in addition to the CPs. This could indicate a geometrical relationship of these fibers in the brainstem. The CPs could be visualized clearly using DTT within clinically acceptable scanning times. This method of visualizing the exact pathway of fiber bundles and cranial nerves in the skull base helps in the planning of surgical approaches.

Deep brain stimulation for aggressiveness: long-term follow-up and tractography study of the stimulated brain areas

OBJECTIVE

Initial studies applying deep brain stimulation (DBS) of the posteromedial hypothalamus (PMH) to patients with pathological aggressiveness have yielded encouraging results. However, the anatomical structures involved in its therapeutic effect have not been precisely identified. The authors' objective was to describe the long-term outcome in their 7-patient series, and the tractography analysis of the volumes of tissue activated in 2 of the responders.

METHODS

This was a retrospective study of 7 subjects with pathological aggressiveness. The findings on MRI with diffusion tensor imaging (DTI) in 2 of the responders were analyzed. The authors generated volumes of tissue activated according to the parameters used, and selected those volumes as regions of interest to delineate the tracts affected by stimulation.

RESULTS

The series consisted of 5 men and 2 women. Of the 7 patients, 5 significantly improved with stimulation. The PMH, ventral tegmental area, dorsal longitudinal fasciculus, and medial forebrain bundle seem to be involved in the stimulation field.

CONCLUSIONS

In this series, 5 of 7 medication-resistant patients with severe aggressiveness who were treated with bilateral PMH DBS showed a significant long-lasting improvement. The PMH, ventral tegmental area, dorsal longitudinal fasciculus, and medial forebrain bundle seem to be in the stimulation field and might be responsible for the therapeutic effect of DBS.

Long-Term Outcome and Neuroimaging of Deep Brain Stimulation in Holmes Tremor: A Case Series

BACKGROUND

Different deep brain stimulation (DBS) targets have been suggested as treatment for patients with pharmacologically refractory Holmes tremor (HT). We report the clinical and quality of life (QoL) long-term (up to nine years) outcome in four patients with HT treated with DBS (in thalamic ventral intermediate nucleus-VIM or in dentato-rubro-thalamic tract-DRTT).

MATERIALS AND METHODS

The patients underwent routine clinical evaluations before and after DBS (typically annually). Tremor severity and activities of daily living (ADL) were quantified by the Fahn-Tolosa-Marin Tremor-Rating-Scale (FTMTRS). QoL was assessed using the RAND SF-36-item Health Survey (RAND SF-36). In addition, we computed, in all four patients, the VTA based on the best stimulation settings using heuristic approaches included in the open source toolbox LEAD-DBS.

RESULTS

In all patients, tremor and ADL improved significantly at one-year post-DBS follow-up (34-61% improvement in FTMTRS total score compared to baseline). In three out of four patients, the improvement of tremor was sustained no longer than two to three years and only in one patient was sustained up to nine years. In this patient, the largest intersection between VTA and DBS target has been observed. Scores for ADL deteriorated over the course of time, reaching worse levels compared to baseline already during the three-year post-DBS follow-up, in three out of four patients. Physical and mental health component scores of RAND SF-36 had very different outcome between patients and follow-ups and were not associated with tremor-related outcomes.

CONCLUSIONS

The benefits of DBS in HT might not be always long lasting. Although QoL slightly improved, this change seemed to be independent of the motor outcome following DBS. The estimation of DBS target and VTA proximity could be a useful tool for DBS clinicians in order to facilitate the DBS programming process and optimize DBS treatment.

Evolution of Human Brain Atlases in Terms of Content, Applications, Functionality, and Availability

Human brain atlases have been evolving tremendously, propelled recently by brain big projects, and driven by sophisticated imaging techniques, advanced brain mapping methods, vast data, analytical strategies, and powerful computing. We overview here this evolution in four categories: content, applications, functionality, and availability, in contrast to other works limited mostly to content. Four atlas generations are distinguished: early cortical maps, print stereotactic atlases, early digital atlases, and advanced brain atlas platforms, and 5 avenues in electronic atlases spanning the last two generations. Content-wise, new electronic atlases are categorized into eight groups considering their scope, parcellation, modality, plurality, scale, ethnicity, abnormality, and a mixture of them. Atlas content developments in these groups are heading in 23 various directions. Application-wise, we overview atlases in neuroeducation, research, and clinics, including stereotactic and functional neurosurgery, neuroradiology, neurology, and stroke. Functionality-wise, tools and functionalities are addressed for atlas creation, navigation, individualization, enabling operations, and application-specific. Availability is discussed in media and platforms, ranging from mobile solutions to leading-edge supercomputers, with three accessibility levels. The major application-wise shift has been from research to clinical practice, particularly in stereotactic and functional neurosurgery, although clinical applications are still lagging behind the atlas content progress. Atlas functionality also has been relatively neglected until recently, as the management of brain data explosion requires powerful tools. We suggest that the future human brain atlas-related research and development activities shall be founded on and benefit from a standard framework containing the core virtual brain model cum the brain atlas platform general architecture.

Deep-Brain Stimulation for Essential Tremor and Other Tremor Syndromes: A Narrative Review of Current Targets and Clinical Outcomes

Tremor is a prevalent symptom associated with multiple conditions, including essential tremor (ET), Parkinson's disease (PD), multiple sclerosis (MS), stroke and trauma. The surgical management of tremor evolved from stereotactic lesions to deep-brain stimulation (DBS), which allowed safe and reversible interference with specific neural networks. This paper reviews the current literature on DBS for tremor, starting with a detailed discussion of current tremor targets (ventral intermediate nucleus of the thalamus (Vim), prelemniscal radiations (Raprl), caudal zona incerta (Zi), thalamus (Vo) and subthalamic nucleus (STN)) and continuing with a discussion of results obtained when performing DBS in the various aforementioned tremor syndromes. Future directions for DBS research are then briefly discussed.

Red nucleus structure and function: from anatomy to clinical neurosciences

The red nucleus (RN) is a large subcortical structure located in the ventral midbrain. Although it originated as a primitive relay between the cerebellum and the spinal cord, during its phylogenesis the RN shows a progressive segregation between a magnocellular part, involved in the rubrospinal system, and a parvocellular part, involved in the olivocerebellar system. Despite exhibiting distinct evolutionary trajectories, these two regions are strictly tied together and play a prominent role in motor and non-motor behavior in different animal species. However, little is known about their function in the human brain. This lack of knowledge may have been conditioned both by the notable differences between human and non-human RN and by inherent difficulties in studying this structure directly in the human brain, leading to a general decrease of interest in the last decades. In the present review, we identify the crucial issues in the current knowledge and summarize the results of several decades of research about the RN, ranging from animal models to human diseases. Connecting the dots between morphology, experimental physiology and neuroimaging, we try to draw a comprehensive overview on RN functional anatomy and bridge the gap between basic and translational research.

Endovascular deep brain stimulation: Investigating the relationship between vascular structures and deep brain stimulation targets

BACKGROUND

Endovascular delivery of current using 'stentrodes' - electrode bearing stents - constitutes a potential alternative to conventional deep brain stimulation (DBS). The precise neuroanatomical relationships between DBS targets and the vascular system, however, are poorly characterized to date.

OBJECTIVE

To establish the relationships between cerebrovascular system and DBS targets and investigate the feasibility of endovascular stimulation as an alternative to DBS.

METHODS

Neuroanatomical targets as employed during deep brain stimulation (anterior limb of the internal capsule, dentatorubrothalamic tract, fornix, globus pallidus pars interna, medial forebrain bundle, nucleus accumbens, pedunculopontine nucleus, subcallosal cingulate cortex, subthalamic nucleus, and ventral intermediate nucleus) were superimposed onto probabilistic vascular atlases obtained from 42 healthy individuals. Euclidian distances between targets and associated vessels were measured. To determine the electrical currents necessary to encapsulate the predefined neurosurgical targets and identify potentially side-effect inducing substrates, a preliminary volume of tissue activated (VTA) analysis was performed.

RESULTS

Six out of ten DBS targets were deemed suitable for endovascular stimulation: medial forebrain bundle (vascular site: P1 segment of posterior cerebral artery), nucleus accumbens (vascular site: A1 segment of anterior cerebral artery), dentatorubrothalamic tract (vascular site: s2 segment of superior cerebellar artery), fornix (vascular site: internal cerebral vein), pedunculopontine nucleus (vascular site: lateral mesencephalic vein), and subcallosal cingulate cortex (vascular site: A2 segment of anterior cerebral artery). While VTAs effectively encapsulated mfb and NA at current thresholds of 3.5 V and 4.5 V respectively, incremental amplitude increases were required to effectively cover fornix, PPN and SCC target (mean voltage: 8.2 ± 4.8 V, range: 3.0-17.0 V). The side-effect profile associated with endovascular stimulation seems to be comparable to conventional lead implantation. Tailoring of targets towards vascular sites, however, may allow to reduce adverse effects, while maintaining the efficacy of neural entrainment within the target tissue.

CONCLUSIONS

While several challenges remain at present, endovascular stimulation of select DBS targets seems feasible offering novel and exciting opportunities in the neuromodulation armamentarium.

3D Exploration of the Brainstem in 50-Micron Resolution MRI

The brainstem, a structure of vital importance in mammals, is currently becoming a principal focus in cognitive, affective, and clinical neuroscience. Midbrain, pontine and medullary structures serve as the conduit for signals between the forebrain and spinal cord, are the epicenter of cranial nerve-circuits and systems, and subserve such integrative functions as consciousness, emotional processing, pain, and motivation. In this study, we parcellated the nuclear masses and the principal fiber pathways that were visible in a high-resolution T2-weighted MRI dataset of 50-micron isotropic voxels of a postmortem human brainstem. Based on this analysis, we generated a detailed map of the human brainstem. To assess the validity of our maps, we compared our observations with histological maps of traditional human brainstem atlases. Given the unique capability of MRI-based morphometric analysis in generating and preserving the morphology of 3D objects from individual 2D sections, we reconstructed the motor, sensory and integrative neural systems of the brainstem and rendered them in 3D representations. We anticipate the utilization of these maps by the neuroimaging community for applications in basic neuroscience as well as in neurology, psychiatry, and neurosurgery, due to their versatile computational nature in 2D and 3D representations in a publicly available capacity.

Full tractography for detecting the position of cranial nerves in preoperative planning for skull base surgery: technical note

OBJECTIVE

Diffusion imaging tractography has allowed the in vivo description of brain white matter. One of its applications is preoperative planning for brain tumor resection. Due to a limited spatial and angular resolution, it is difficult for fiber tracking to delineate fiber crossing areas and small-scale structures, in particular brainstem tracts and cranial nerves. New methods are being developed but these involve extensive multistep tractography pipelines including the patient-specific design of multiple regions of interest (ROIs). The authors propose a new practical full tractography method that could be implemented in routine presurgical planning for skull base surgery.

METHODS

A Philips MRI machine provided diffusion-weighted and anatomical sequences for 2 healthy volunteers and 2 skull base tumor patients. Tractography of the full brainstem, the cerebellum, and cranial nerves was performed using the software DSI Studio, generalized-q-sampling reconstruction, orientation distribution function (ODF) of fibers, and a quantitative anisotropy-based generalized deterministic algorithm. No ROI or extensive manual filtering of spurious fibers was used. Tractography rendering was displayed in a tridimensional space with directional color code. This approach was also tested on diffusion data from the Human Connectome Project (HCP) database.

RESULTS

The brainstem, the cerebellum, and the cisternal segments of most cranial nerves were depicted in all participants. In cases of skull base tumors, the tridimensional rendering permitted the visualization of the whole anatomical environment and cranial nerve displacement, thus helping the surgical strategy.

CONCLUSIONS

As opposed to classical ROI-based methods, this novel full tractography approach could enable routine enhanced surgical planning or brain imaging for skull base tumors.

Surgical approaches for the lateral mesencephalic sulcus

OBJECTIVE

The brainstem is a compact, delicate structure. The surgeon must have good anatomical knowledge of the safe entry points to safely resect intrinsic lesions. Lesions located at the lateral midbrain surface are better approached through the lateral mesencephalic sulcus (LMS). The goal of this study was to compare the surgical exposure to the LMS provided by the subtemporal (ST) approach and the paramedian and extreme-lateral variants of the supracerebellar infratentorial (SCIT) approach.

METHODS

These 3 approaches were used in 10 cadaveric heads. The authors performed measurements of predetermined points by using a neuronavigation system. Areas of microsurgical exposure and angles of the approaches were determined. Statistical analysis was performed to identify significant differences in the respective exposures.

RESULTS

The surgical exposure was similar for the different approaches-369.8 ± 70.1 mm2 for the ST; 341.2 ± 71.2 mm2 for the SCIT paramedian variant; and 312.0 ± 79.3 mm2 for the SCIT extreme-lateral variant (p = 0.13). However, the vertical angular exposure was 16.3° ± 3.6° for the ST, 19.4° ± 3.4° for the SCIT paramedian variant, and 25.1° ± 3.3° for the SCIT extreme-lateral variant craniotomy (p < 0.001). The horizontal angular exposure was 45.2° ± 6.3° for the ST, 35.6° ± 2.9° for the SCIT paramedian variant, and 45.5° ± 6.6° for the SCIT extreme-lateral variant opening, presenting no difference between the ST and extreme-lateral variant (p = 0.92), but both were superior to the paramedian variant (p < 0.001). Data are expressed as the mean ± SD.

CONCLUSIONS

The extreme-lateral SCIT approach had the smaller area of surgical exposure; however, these differences were not statistically significant. The extreme-lateral SCIT approach presented a wider vertical and horizontal angle to the LMS compared to the other craniotomies. Also, it provides a 90° trajectory to the sulcus that facilitates the intraoperative microsurgical technique.

The impact of modern-day neuroimaging on the field of deep brain stimulation

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is an established but growing treatment option for multiple brain disorders. Over the last decade, electrode placement and their effects were increasingly analyzed with modern-day neuroimaging methods like spatial normalization, fibertracking, or resting-state functional MRI. Similarly, specialized basal ganglia MRI sequences were introduced and imaging at high field strengths has become increasingly popular.

RECENT FINDINGS

To facilitate the process of precise electrode localizations, specialized software pipelines were introduced. By those means, DBS targets could recently be refined and significant relationships between electrode placement and clinical improvement could be shown. Furthermore, by combining electrode reconstructions with network imaging methods, relationships between electrode connectivity and clinical improvement were investigated. This led to a broad series of imaging-based insights about DBS that are reviewed in the present work.

SUMMARY

The reviewed literature makes a strong case that brain imaging plays an increasingly important role in DBS targeting and programming. Furthermore, brain imaging will likely help to better understand the mechanism of action of DBS.

Tractography in Neurosurgery: A Systematic Review of Current Applications

The ability to visualize the brain's fiber connections noninvasively in vivo is relatively young compared with other possibilities of functional magnetic resonance imaging. Although many studies showed tractography to be of promising value for neurosurgical care, the implications remain inconclusive. An overview of current applications is presented in this systematic review. A search was conducted for (("tractography" or "fiber tracking" or "fibre tracking") and "neurosurgery") that produced 751 results. We identified 260 relevant articles and added 20 more from other sources. Most publications concerned surgical planning for resection of tumors (n = 193) and vascular lesions (n = 15). Preoperative use of transcranial magnetic stimulation was discussed in 22 of these articles. Tractography in skull base surgery presents a special challenge (n = 29). Fewer publications evaluated traumatic brain injury (TBI) (n = 25) and spontaneous intracranial bleeding (n = 22). Twenty-three articles focused on tractography in pediatric neurosurgery. Most authors found tractography to be a valuable addition in neurosurgical care. The accuracy of the technique has increased over time. There are articles suggesting that tractography improves patient outcome after tumor resection. However, no reliable biomarkers have yet been described. The better rehabilitation potential after TBI and spontaneous intracranial bleeding compared with brain tumors offers an insight into the process of neurorehabilitation. Tractography and diffusion measurements in some studies showed a correlation with patient outcome that might help uncover the neuroanatomical principles of rehabilitation itself. Alternative corticofugal and cortico-cortical networks have been implicated in motor recovery after ischemic stroke, suggesting more complex mechanisms in neurorehabilitation that go beyond current models. Hence tractography may potentially be able to predict clinical deficits and rehabilitation potential, as well as finding possible explanations for neurologic disorders in retrospect. However, large variations of the results indicate a lack of data to establish robust diagnostical concepts at this point. Therefore, in vivo tractography should still be interpreted with caution and by experienced surgeons.

Surgical approaches in pediatric neuro-oncology

Tumors of the central nervous system comprise nearly a quarter of all childhood cancers and are the most frequent solid tumor in the pediatric population. The most common location is in the posterior fossa, but tumors can occur anywhere intracranially. The spectrum of lesions encountered varies, from being completely benign and requiring surveillance alone to being highly malignant and requiring aggressive treatment in the form of surgery and adjuvant therapy. The extent of resection plays a crucial role in the oncological outcome of many of these tumors. A variety of surgical approaches are available for the spectrum of lesions encountered. This review focuses on summarizing the location, types, and neurosurgical management strategies for pediatric brain intracranial brain tumors. Here, we discuss neurosurgical approaches for a variety of brain tumors and regions, including the management of tumors of the posterior fossa, brainstem, pineal region, intraventricular region, sellar and suprasellar regions, optic pathway and hypothalamus, and supratentorial hemispheres.

Diffusion tensor tractography of brainstem fibers and its application in pain

Evaluation of brainstem pathways with diffusion tensor imaging (DTI) and tractography may provide insights into pathophysiologies associated with dysfunction of key brainstem circuits. However, identification of these tracts has been elusive, with relatively few in vivo human studies to date. In this paper we proposed an automated approach for reconstructing nine brainstem fiber trajectories of pathways that might be involved in pain modulation. We first performed native-space manual tractography of these fiber tracts in a small normative cohort of participants and confirmed the anatomical precision of the results using existing anatomical literature. Second, region-of-interest pairs were manually defined at each extracted fiber's termini and nonlinearly warped to a standard anatomical brain template to create an atlas of the region-of-interest pairs. The resulting atlas was then transformed non-linearly into the native space of 17 veteran patients' brains for automated brainstem tractography. Lastly, we assessed the relationships between the integrity levels of the obtained fiber bundles and pain severity levels. Fractional anisotropy (FA) measures derived using automated tractography reflected the respective tracts' FA levels obtained via manual tractography. A significant inverse relationship between FA and pain levels was detected within the automatically derived dorsal and medial longitudinal fasciculi of the brainstem. This study demonstrates the feasibility of DTI in exploring brainstem circuitries involved in pain processing. In this context, the described automated approach is a viable alternative to the time-consuming manual tractography. The physiological and functional relevance of the measures derived from automated tractography is evidenced by their relationships with individual pain severities.

Holographic Reconstruction of Axonal Pathways in the Human Brain

Three-dimensional documentation of the axonal pathways connecting gray matter components of the human brain has wide-ranging scientific and clinical applications. Recent attempts to map human structural connectomes have concentrated on using tractography results derived from diffusion-weighted imaging data, but tractography is an indirect method with numerous limitations. Advances in holographic visualization platforms provide a new medium to integrate anatomical data, as well as a novel working environment for collaborative interaction between neuroanatomists and brain-imaging scientists. Therefore, we developed the first holographic interface for building axonal pathways, populated it with human histological and structural MRI data, and assembled world expert neuroanatomists to interactively define axonal trajectories of the cortical, basal ganglia, and cerebellar systems. This blending of advanced visualization hardware, software development, and neuroanatomy data enabled the translation of decades of amassed knowledge into a human axonal pathway atlas that can be applied to educational, scientific, or clinical investigations.

FOD-based registration for susceptibility distortion correction in brainstem connectome imaging

The high resolution, multi-shell diffusion MRI (dMRI) data from the Human Connectome Project (HCP) provides a great opportunity to map fine-grained fiber pathways in human brainstem, but the severe susceptibility-induced distortion around the brainstem poses a significant challenge. While the correction tools used in the HCP Pipeline greatly reduce the distortion artifacts in the preprocessed data, significant residual distortions are still widely present, especially in the brainstem region. One fundamental reason is that the topup tool used in the HCP Pipeline only relies on the B0 images, which lack sufficient contrast about white matter pathways, to estimate the distortion displacement between opposite phase encodings (PEs). To fully utilize the rich information of HCP data that includes dMRI data from two opposite PEs, we compute the fiber orientation distributions (FODs) from the data of each PE and propose a novel method to estimate and correct the residual distortion using FOD-based registration. Using the dMRI data of 94 HCP subjects, we show quantitatively that our method can reduce the misalignment of main fiber direction in the brainstem by 21% as compared to the topup tool used in the HCP Pipeline. Our method is fully compatible with the HCP Pipeline and thus can be readily integrated with it to enhance distortion correction in connectome imaging research.

Microstructural changes of the dentato-rubro-thalamic tract after transcranial MR guided focused ultrasound ablation of the posteroventral VIM in essential tremor

Essential tremor is the most common movement disorder in adults. In patients who are not responsive to medical treatment, functional neurosurgery and, more recently, transcranial MR-guided focused ultrasound thalamotomy are considered effective therapeutic approaches. However, the structural brain changes following a thalamotomy that mediates the clinical improvement are still unclear. In here diffusion weighted images were acquired in a cohort of 24 essential tremor patients before and 3 months after unilateral transcranial MR-guided focused ultrasound thalamotomy targeting at the posteroventral part of the VIM. Microstructural changes along the DRTT were quantified by means of probabilistic tractography, and later related to the clinical improvement of the patients at 3-months and at 1-year after the intervention. In addition the changes along two neighboring tracts, that is, the corticospinal tract and the medial lemniscus, were assessed, as well as the relation between these changes and the presence of side effects. Thalamic lesions produced local and distant alterations along the trajectory of the DRTT, and each correlated with clinical improvement. Regarding side effects, gait imbalance after thalamotomy was associated with greater impact on the DRTT, whereas the presence of paresthesias was significantly related to a higher overlap between the lesion and the medial lemniscus. This work represents the largest series describing the microstructural changes following transcranial MR-guided focused ultrasound thalamotomy in essential tremor. These results suggest that clinical benefits are specific for the impact on the cerebello-thalamo-cortical pathway, thus reaffirming the potential of tractography to aid thalamotomy targeting.

A novel radiological classification system for cerebral gliomas: The Brain-Grid

Purpose

Standard radiological/topographical classifications of gliomas often do not reflect the real extension of the tumor within the lobar-cortical anatomy. Furthermore, these systems do not provide information on the relationship between tumor growth and the subcortical white matter architecture. We propose the use of an anatomically standardized grid system (the Brain-Grid) to merge serial morphological magnetic resonance imaging (MRI) scans with a representative tractographic atlas. Two illustrative cases are presented to show the potential advantages of this classification system.

Methods

MRI scans of 39 patients (WHO grade II and III gliomas) were analyzed with a standardized grid created by intersecting longitudinal lines on the axial, sagittal, and coronal planes. The anatomical landmarks were chosen from an average brain, spatially normalized to the Montreal Neurological Institute (MNI) space and the Talairach space. Major white matter pathways were reconstructed with a deterministic tracking algorithm on a reference atlas and analyzed using the Brain-Grid system.

Results

In all, 48 brain grid voxels (areas defined by 3 coordinates, axial (A), coronal (C), sagittal (S) and numbers from 1 to 4) were delineated in each MRI sequence and on the tractographic atlas. The number of grid voxels infiltrated was consistent, also in the MNI space. The sub-cortical insula/basal ganglia (A3-C2-S2) and the fronto-insular region (A3-C2-S1) were most frequently involved. The inferior fronto-occipital fasciculus, anterior thalamic radiation, uncinate fasciculus, and external capsule were the most frequently associated pathways in both hemispheres.

Conclusions

The Brain-Grid based classification system provides an accurate observational tool in all patients with suspected gliomas, based on the comparison of grid voxels on a morphological MRI and segmented white matter atlas. Important biological information on tumor kinetics including extension, speed, and preferential direction of progression can be observed and even predicted with this system. This novel classification can easily be applied to both prospective and retrospective cohorts of patients and increase our comprehension of glioma behavior.

Surgical outcome of motor deficits and neurological status in brainstem cavernous malformations based on preoperative diffusion tensor imaging: a prospective randomized clinical trial

OBJECTIVE: Surgical management of brainstem lesions is challenging due to the highly compact, eloquent anatomy of the brainstem. This study aimed to evaluate the safety and efficacy of preoperative diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) in brainstem cavernous malformations (CMs). METHODS: A prospective randomized controlled clinical trial was performed by using stratified blocked randomization. The primary eligibility criterion of the study was being a surgical candidate for brainstem CMs (with informed consent). The study enrolled 23 patients who underwent preoperative DTI/DTT and 24 patients who did not (the control group). The pre- and postoperative muscle strength of both limbs and modified Rankin Scale (mRS) scores were evaluated. Muscle strength of any limb at 12 months after surgery at the clinic visit was the primary outcome; worsened muscle strength was considered to be a poor outcome. Outcome assessors were blinded to patient management. This study reports the preliminary results of the interim analysis. RESULTS: The cohort included 47 patients (22 women) with a mean age of 35.7 years. The clinical baselines between these 2 groups were not significantly different. In the DTI/DTT group, the corticospinal tract was affected in 17 patients (73.9%): it was displaced, deformed/partially interrupted, or completely interrupted in 6, 7, and 4 patients, respectively. The surgical approach and brainstem entry point were adjusted in 3 patients (13.0%) based on DTI/DTT data. The surgical morbidity of the DTI/DTT group (7/23, 30.4%) was significantly lower than that of the control group (19/24, 79.2%, p = 0.001). At 12 months, the mean mRS score (1.1, p = 0.034) and percentage of patients with worsened motor deficits (4.3%, p = 0.006) were significantly lower in the DTI/DTT group than in the control group (1.7% and 37.5%). Multivariate logistic regression identified the absence of preoperative DTI/DTT (OR 0.06, 95% CI 0.01-0.73, p = 0.028) and use of the 2-point method (OR 4.15, 95% CI 1.38-12.49, p = 0.011) as independent adverse factors for a worsened motor deficit. The multivariate model found a significant correlation between poor mRS score and both an increased preoperative mRS score (t = 3.559, p = 0.001) and absence of preoperative DTI/DTT (t = -2.747, p = 0.009). CONCLUSIONS: DTI/DTT noninvasively allowed for visualization of the anatomical relationship between vital tracts and pathologies as well as facilitated the brainstem surgical approach and entry-point decision making. The technique was valuable for complex neurosurgical planning to reduce morbidity. Nonetheless, DTI/DTT data should be interpreted cautiously.■ CLASSIFICATION OF EVIDENCE Type of question: therapeutic; study design: randomized controlled trial; evidence: class I. Clinical trial registration no.: NCT01758211 (ClinicalTrials.gov).

Lead-DBS v2: Towards a comprehensive pipeline for deep brain stimulation imaging

Deep brain stimulation (DBS) is a highly efficacious treatment option for movement disorders and a growing number of other indications are investigated in clinical trials. To ensure optimal treatment outcome, exact electrode placement is required. Moreover, to analyze the relationship between electrode location and clinical results, a precise reconstruction of electrode placement is required, posing specific challenges to the field of neuroimaging. Since 2014 the open source toolbox Lead-DBS is available, which aims at facilitating this process. The tool has since become a popular platform for DBS imaging. With support of a broad community of researchers worldwide, methods have been continuously updated and complemented by new tools for tasks such as multispectral nonlinear registration, structural/functional connectivity analyses, brain shift correction, reconstruction of microelectrode recordings and orientation detection of segmented DBS leads. The rapid development and emergence of these methods in DBS data analysis require us to revisit and revise the pipelines introduced in the original methods publication. Here we demonstrate the updated DBS and connectome pipelines of Lead-DBS using a single patient example with state-of-the-art high-field imaging as well as a retrospective cohort of patients scanned in a typical clinical setting at 1.5T. Imaging data of the 3T example patient is co-registered using five algorithms and nonlinearly warped into template space using ten approaches for comparative purposes. After reconstruction of DBS electrodes (which is possible using three methods and a specific refinement tool), the volume of tissue activated is calculated for two DBS settings using four distinct models and various parameters. Finally, four whole-brain tractography algorithms are applied to the patient's preoperative diffusion MRI data and structural as well as functional connectivity between the stimulation volume and other brain areas are estimated using a total of eight approaches and datasets. In addition, we demonstrate impact of selected preprocessing strategies on the retrospective sample of 51 PD patients. We compare the amount of variance in clinical improvement that can be explained by the computer model depending on the preprocessing method of choice. This work represents a multi-institutional collaborative effort to develop a comprehensive, open source pipeline for DBS imaging and connectomics, which has already empowered several studies, and may facilitate a variety of future studies in the field.

Neuroimaging in the Kleine-Levin Syndrome

PURPOSE OF REVIEW

The purpose was to review the most recent literature on neuroimaging in the Kleine-Levin syndrome (KLS). We aimed to investigate if frontotemporal and thalamic dysfunction are key KLS signatures, and if recent research indicates other brain networks of interest that elucidate KLS symptomatology and aetiology.

RECENT FINDINGS

In a comprehensive literature search, we found 12 original articles published 2013-2018. Most studies report deviations related to cerebral perfusion, glucose metabolism, or blood-oxygen-level-dependent responses in frontotemporal areas and/or the thalamus. Studies also report dysfunction in the temporoparietal junction and the oculomotor network that also were related to clinical parameters. We discuss these findings based on recent research on thalamocortical networks and brain stem white matter tracts. The hypothesis of frontotemporal and thalamic involvement in KLS was confirmed, and additional findings in the temporoparietal junction and the oculomotor system suggest a broader network involvement, which can be investigated by future high-resolution and multimodal imaging.

Connectivity-based segmentation of the brainstem by probabilistic tractography

Diffusion magnetic resonance imaging is a non-invasive tool increasingly used for the investigation of brain connectivity in vivo. In this paper we propose a method that allows segmentation of the brainstem to four subregions (frontopontine, motor, sensory and reticular) based on connections to supratentorial structures, thereby eliminating the need for using anatomical landmarks within the brainstem for the identification of these subregions. The feasibility of connectivity-based brainstem segmentation was investigated in a group of healthy subjects (n = 20). Multifiber probabilistic tractography was performed using the FMRIB Software Library, and connections between a pontomesencephalic seed mask and four supratentorial target regions (anterior and posterior limbs of the internal capsule, sensory and medial thalamus) were used to determine connectivity maps of the brainstem. Results were compared with a neuroanatomy atlas and histological sections, confirming good anatomic correspondence. The four subregions detected by the connectivity-based segmentation showed good intersubject reproducibility. The presented method may be a potential tool to investigate brainstem connectivity in diseases that distort normal anatomy, and quantitative analyses of the diffusion-related parameters may provide additional information on the involvement of brainstem pathways in certain disease states (e.g., traumatic brain injury, demyelinating disorders, brainstem tumors). The potential clinical applicability of the method is demonstrated in two cases of severe traumatic brain injury.

A Quantitative Tractography Study Into the Connectivity, Segmentation and Laterality of the Human Inferior Longitudinal Fasciculus

The human inferior longitudinal fasciculus (ILF) is a ventral, temporo-occipital association tract. Though described in early neuroanatomical works, its existence was later questioned. Application of in vivo tractography to the neuroanatomical study of the ILF has generally confirmed its existence, however, consensus is lacking regarding its subdivision, laterality and connectivity. Further, there is a paucity of detailed neuroanatomic data pertaining to the exact anatomy of the ILF. Generalized Q-Sampling imaging (GQI) is a non-tensor tractographic modality permitting high resolution imaging of white-matter structures. As it is a non-tensor modality, it permits visualization of crossing fibers and accurate delineation of close-proximity fiber-systems. We applied deterministic GQI tractography to data from 30 healthy subjects and a large-volume, averaged diffusion atlas, to delineate ILF anatomy. Post-mortem white matter dissection was also carried out in three cadaveric specimens for further validation. The ILF was found in all 60 hemispheres. At its occipital extremity, ILF fascicles demonstrated a bifurcated, ventral-dorsal morphological termination pattern, which we used to further subdivide the bundle for detailed analysis. These divisions were consistent across the subject set and within the atlas. We applied quantitative techniques to study connectivity strength of the ILF at its anterior and posterior extremities. Overall, both morphological divisions, and the un-separated ILF, demonstrated strong leftward-lateralized connectivity patterns. Leftward-lateralization was also found for ILF volumes across the subject set. Due to connective and volumetric leftward-dominance and ventral location, we postulate the ILFs role in the semantic system. Further, our results are in agreement with functional and lesion-based postulations pertaining to the ILFs role in facial recognition.

Population-averaged atlas of the macroscale human structural connectome and its network topology

A comprehensive map of the structural connectome in the human brain has been a coveted resource for understanding macroscopic brain networks. Here we report an expert-vetted, population-averaged atlas of the structural connectome derived from diffusion MRI data (N = 842). This was achieved by creating a high-resolution template of diffusion patterns averaged across individual subjects and using tractography to generate 550,000 trajectories of representative white matter fascicles annotated by 80 anatomical labels. The trajectories were subsequently clustered and labeled by a team of experienced neuroanatomists in order to conform to prior neuroanatomical knowledge. A multi-level network topology was then described using whole-brain connectograms, with subdivisions of the association pathways showing small-worldness in intra-hemisphere connections, projection pathways showing hub structures at thalamus, putamen, and brainstem, and commissural pathways showing bridges connecting cerebral hemispheres to provide global efficiency. This atlas of the structural connectome provides representative organization of human brain white matter, complementary to traditional histologically-derived and voxel-based white matter atlases, allowing for better modeling and simulation of brain connectivity for future connectome studies.

On the Origin of Individual Functional Connectivity Variability: The Role of White Matter Architecture

Fingerprint patterns derived from functional connectivity (FC) can be used to identify subjects across groups and sessions, indicating that the topology of the brain substantially differs between individuals. However, the source of FC variability inferred from resting-state functional magnetic resonance imaging remains unclear. One possibility is that these variations are related to individual differences in white matter structural connectivity (SC). However, directly comparing FC with SC is challenging given the many potential biases associated with quantifying their respective strengths. In an attempt to circumvent this, we employed a recently proposed test-retest approach that better quantifies inter-subject variability by first correcting for intra-subject nuisance variability (i.e., head motion, physiological differences in brain state, etc.) that can artificially influence FC and SC measures. Therefore, rather than directly comparing the strength of FC with SC, we asked whether brain regions with, for example, low inter-subject FC variability also exhibited low SC variability. From this, we report two main findings: First, at the whole-brain level, SC variability was significantly lower than FC variability, indicating that an individual's structural connectome is far more similar to another relative to their functional counterpart even after correcting for noise. Second, although FC and SC variability were mutually low in some brain areas (e.g., primary somatosensory cortex) and high in others (e.g., memory and language areas), the two were not significantly correlated across all cortical and sub-cortical regions. Taken together, these results indicate that even after correcting for factors that may differently affect FC and SC, the two, nonetheless, remain largely independent of one another. Further work is needed to understand the role that direct anatomical pathways play in supporting vascular-based measures of FC and to what extent these measures are dictated by anatomical connectivity.

Neuronavigation-Guided Corticospinal Tract Mapping in Brainstem Tumor Surgery: Better Preservation of Motor Function

OBJECTIVE

To evaluate a new technique in brainstem surgery, neuronavigation (NN)-guided corticospinal tract (CST) mapping, in a retrospective study of patients undergoing brainstem tumor surgery.

METHODS

We studied 40 patients with a brainstem tumor who were enrolled in this study. Patients whose worst preoperative muscle strength of the 4 limbs was greater than 3 levels from normal on the Lovett scale were divided into 2 groups: a treatment group of 21 patients who underwent NN-guided CST mapping and routine intraoperative neurophysiology monitoring (IONM) and a control group of 19 patients who underwent routine NN and IONM. Preoperative muscle strength and postoperative (day 90 postsurgery) muscle strength were assessed and compared between the 2 groups.

RESULTS

In the NN-guided CST mapping group, 3 patients (14.3%) had a decrease in muscle strength by 1 level postoperatively, and no patient experienced a decrease of >1 level. In the control group, 4 patients (21.1%) had a 1-level decrease in muscle strength, and 5 (26.3%) had a decrease of >1 level. Patients in the NN-guided CST mapping group had significantly better surgical outcomes compared with those in the control group (P = 0.018, Fisher exact test).

CONCLUSIONS

Brainstem tumor resection using NN-guided CST mapping achieved better preservation of motor function compared with routine NN and IONM. NN-guided CST mapping not only decreased the difficulty of the surgery, but also significantly improved the efficiency of surgery.

The epitrigeminal approach to the brainstem

OBJECTIVE

Surgical approaches to the ventrolateral pons pose a significant challenge. In this report, the authors describe a safe entry zone to the brainstem located just above the trigeminal entry zone which they refer to as the “epitrigeminal entry zone.”

METHODS

The approach is presented in the context of an illustrative case of a cavernous malformation and is compared with the other commonly described approaches to the ventrolateral pons. The anatomical nuances were analyzed in detail with the aid of surgical images and video, anatomical dissections, and high-definition fiber tractography (HDFT). In addition, using the HDFT maps obtained in 77 normal subjects (154 sides), the authors performed a detailed anatomical study of the surgically relevant distances between the trigeminal entry zone and the corticospinal tracts.

RESULTS

The patient treated with this approach had a complete resection of his cavernous malformation, and improvement of his symptoms. With regard to the HDFT anatomical study, the average direct distance of the corticospinal tracts from the trigeminal entry zone was 12.6 mm (range 8.7–17 mm). The average vertical distance was 3.6 mm (range −2.3 to 8.7 mm). The mean distances did not differ significantly from side to side, or across any of the groups studied (right-handed, left-handed, and ambidextrous).

CONCLUSIONS

The epitrigeminal entry zone to the brainstem appears to be safe and effective for treating intrinsic ventrolateral pontine pathological entities. A possible advantage of this approach is increased versatility in the rostrocaudal axis, providing access both above and below the trigeminal nerve. Familiarity with the subtemporal transtentorial approach, and the reliable surgical landmark of the trigeminal entry zone, should make this a straightforward approach.

A probabilistic atlas of human brainstem pathways based on connectome imaging data

The brainstem is a critical structure that regulates vital autonomic functions, houses the cranial nerves and their nuclei, relays motor and sensory information between the brain and spinal cord, and modulates cognition, mood, and emotions. As a primary relay center, the fiber pathways of the brainstem include efferent and afferent connections among the cerebral cortex, spinal cord, and cerebellum. While diffusion MRI has been successfully applied to map various brain pathways, its application for the in vivo imaging of the brainstem pathways has been limited due to inadequate resolution and large susceptibility-induced distortion artifacts. With the release of high-resolution data from the Human Connectome Project (HCP), there is increasing interest in mapping human brainstem pathways. Previous works relying on HCP data to study brainstem pathways, however, did not consider the prevalence (>80%) of large distortions in the brainstem even after the application of correction procedures from the HCP-Pipeline. They were also limited in the lack of adequate consideration of subject variability in either fiber pathways or region of interests (ROIs) used for bundle reconstruction. To overcome these limitations, we develop in this work a probabilistic atlas of 23 major brainstem bundles using high-quality HCP data passing rigorous quality control. For the large-scale data from the 500-Subject release of HCP, we conducted extensive quality controls to exclude subjects with severe distortions in the brainstem area. After that, we developed a systematic protocol to manually delineate 1300 ROIs on 20 HCP subjects (10 males; 10 females) for the reconstruction of fiber bundles using tractography techniques. Finally, we leveraged our novel connectome modeling techniques including high order fiber orientation distribution (FOD) reconstruction from multi-shell diffusion imaging and topography-preserving tract filtering algorithms to successfully reconstruct the 23 fiber bundles for each subject, which were then used to calculate the probabilistic atlases in the MNI152 space for public release. In our experimental results, we demonstrate that our method yielded anatomically faithful reconstruction of the brainstem pathways and achieved improved performance in comparison with an existing atlas of cerebellar peduncles based on HCP data. These atlases have been publicly released on NITRIC (https://www.nitrc.org/projects/brainstem_atlas/) and can be readily used by brain imaging researchers interested in studying brainstem pathways.