Assessment of the corticospinal tract alterations before and after resection of brainstem lesions using Diffusion Tensor Imaging (DTI) and tractography at 3T

Diffusion tensor imaging with tractography in surgical resection of brainstem cavernous malformations: a systematic review and meta-analysis

Brainstem cavernous malformations are benign subset of cerebral cavernous malformations, which need a special intervention owing to being vital and complex. The diffusion tensor imaging technique, a well-recognized neuroimaging tool, can visualize the white matter tracts and their surroundings and provide promising surgical outcomes. This systematic review and meta-analysis evaluated the effect of preoperative diffusion tensor imaging in patients undergoing surgical resection of brainstem cavernous malformations. Five databases, including PubMed, Scopus, Web of Science, Cochrane Library, and Google Scholar, were searched using a comprehensive search strategy to find any article matching our inclusion criteria. We used Comprehensive Meta-Analysis (CMA) software to analyze the collected data, get the evidence, and report the results as event rate (ER), with their 95% confidence interval (CI). Twenty-eight studies involving 467 patients matched our criteria and 19 studies entered the analysis. Our analysis showed that, in patients undergoing surgical resection of brainstem cavernous malformations assisted by preoperative diffusion tensor imaging, 82.21% achieved total resection. About 12.4% of patients achieved partial resection, 65.65% improved, 8.07% worsened, 25.04% showed no change, 3.59% experienced postoperative re-bleeding, and 0.87% died. The utilization of preoperative diffusion tensor imaging significantly increased the proportion of improved patients and decreased the proportion of worsened patients. However, further controlled research is needed to draw a definite conclusion about the usefulness of its role.

Beyond conventional imaging: Advancements in MRI for glioma malignancy prediction and molecular profiling

This review examines the advancements in magnetic resonance imaging (MRI) techniques and their pivotal role in diagnosing and managing gliomas, the most prevalent primary brain tumors. The paper underscores the importance of integrating modern MRI modalities, such as diffusion-weighted imaging and perfusion MRI, which are essential for assessing glioma malignancy and predicting tumor behavior. Special attention is given to the 2021 WHO Classification of Tumors of the Central Nervous System, emphasizing the integration of molecular diagnostics in glioma classification, significantly impacting treatment decisions. The review also explores radiogenomics, which correlates imaging features with molecular markers to tailor personalized treatment strategies. Despite technological progress, MRI protocol standardization and result interpretation challenges persist, affecting diagnostic consistency across different settings. Furthermore, the review addresses MRI's capacity to distinguish between tumor recurrence and pseudoprogression, which is vital for patient management. The necessity for greater standardization and collaborative research to harness MRI's full potential in glioma diagnosis and personalized therapy is highlighted, advocating for an enhanced understanding of glioma biology and more effective treatment approaches.

In Vivo visualization of white matter fiber tracts in the brainstem using low flip angle double echo 3D gradient echo imaging at 3T

BACKGROUND

White matter (WM) fiber tracts in the brainstem communicate with various regions in the cerebrum, cerebellum, and spinal cord. Clinically, small lesions, malformations, or histopathological changes in the brainstem can cause severe neurological disorders. A direct and non-invasive assessment approach could bring valuable information about the intricate anatomical variations of the white matter fiber tracts and nuclei. Although tractography from diffusion tensor imaging has been commonly used to map the WM fiber tracts connectivity, it is difficult to differentiate the complex WM tracts anatomically. Both high field MRI methods and ultrahigh-field MRI methods at 7T and 11.7 T have been used to enhance the contrast of WM fiber tracts. Despite their promising results, it is still challenging to achieve wide clinical adoption at 3T. In this study, we explored a clinically feasible method using a proton density weighted (PDW) 3D gradient echo (GRE) sequence to directly image the WM fiber tracts in the brainstem at 3T in vivo.

METHODS

We optimized a 3D high resolution, double echo, short TR, PDW GRE sequence on 5 healthy volunteers using a clinical 3T scanner to visualize the complicated anatomy of WM fiber tracts in the brain stem. Tissue properties including T1, proton density and T2* from in vivo quantitative MRI data were used for simulations to determine the optimal flip angle for the sequence. The visualization of multiple WM fiber tracts in the brainstem was assessed qualitatively and quantitatively using relative contrast and contrast-to-noise ratio (CNR). To improve the CNR, the final images were created by averaging over all echoes from two consecutive scans at the optimal flip angle. The results were compared to anatomical atlases and histology sections to identify the major fiber tracts. All the identified major fiber tracts were labeled on axial, sagittal and coronal slices.

RESULTS

The WM fiber tracts were found to have distinct hypointense signal throughout the brainstem and most of the major WM fiber tracts, such as the corticospinal tract, medial lemniscus, medial longitudinal fasciculus, and central tegmental tract, in the brainstem up to and including the thalamus were identified in all subjects. Both qualitative and quantitative evaluations showed that the 3° scan offered the best contrast for WM fiber tracts for a TR of 20 ms. The average over the first two echo times and two consecutive 3° scans gave a CNR of 47.8 ± 6.2 for the pyramidal tracts in particular and CNRs values greater than 6.5 ± 2.4 for the rest of the fiber tracts.

CONCLUSIONS

All the major fiber tracts in the brainstem could be visualized. Given the reasonably short scan time of 10 min at 3T, double echo PDW GRE sequence is a very practical approach for clinical adoption.

Decoding the puzzle: A multidisciplinary systematic review of adult brainstem glioma

Adult brainstem gliomas (BSGs) are a group of rare central nervous system tumors with varying prognoses and controversial standard treatment strategies. To provide an overview of current trends, a systematic review using the PRISMA guidelines, Class of evidence (CE) and strength of recommendation (SR), was conducted. The review identified 27 studies. Surgery was found to have a positive impact on survival, particularly for focal lesions with CE II SR C. Stereotactic image-guided biopsy was recommended when resective surgery was not feasible with CE II and SR B. The role of systemic treatments remains unclear. Eight studies provided molecular biology data. This review gathers crucial literature on diagnosis and management of adult BSGs. It provides evidence-based guidance with updated recommendations for diagnosing and treating, taking into account recent molecular and genetic advancements. The importance of brain biopsy is emphasized to optimize treatment using emerging genetic-molecular findings and explore potential targeted therapies.

High-angular resolution diffusion imaging generation using 3d u-net

PURPOSE

To investigate the effects on tractography of artificial intelligence-based prediction of motion-probing gradients (MPGs) in diffusion-weighted imaging (DWI).

METHODS

The 251 participants in this study were patients with brain tumors or epileptic seizures who underwent MRI to depict tractography. DWI was performed with 64 MPG directions and b = 0 s/mm2 images. The dataset was divided into a training set of 191 (mean age 45.7 [± 19.1] years), a validation set of 30 (mean age 41.6 [± 19.1] years), and a test set of 30 (mean age 49.6 [± 18.3] years) patients. Supervised training of a convolutional neural network was performed using b = 0 images and the first 32 axes of MPG images as the input data and the second 32 axes as the reference data. The trained model was applied to the test data, and tractography was performed using (a) input data only; (b) input plus prediction data; and (c) b = 0 images and the 64 MPG data (as a reference).

RESULTS

In Q-ball imaging tractography, the average dice similarity coefficient (DSC) of the input plus prediction data was 0.715 (± 0.064), which was significantly higher than that of the input data alone (0.697 [± 0.070]) (p < 0.05). In generalized q-sampling imaging tractography, the average DSC of the input plus prediction data was 0.769 (± 0.091), which was also significantly higher than that of the input data alone (0.738 [± 0.118]) (p < 0.01).

CONCLUSION

Diffusion tractography is improved by adding predicted MPG images generated by an artificial intelligence model.

NTMS based tractography and segmental diffusion analysis in patients with brainstem gliomas: Risk stratification and clinical potential

Introduction

Surgery on the brainstem level is associated with a high-risk of postoperative morbidity. Recently, we have introduced the combination of navigated transcranial magnetic stimulation (nTMS) and diffusion tensor imaging (DTI) tractography to define functionally relevant motor fibers tracts on the brainstem level to support operative planning and risk stratification in brainstem cavernomas.

Research question

Evaluate this method and assess it's clinical impact for the surgery of brainstem gliomas.

Material and methods

Patients with brainstem gliomas were examined preoperatively with motor nTMS and DTI tractography. A fractional anisotropy (FA) value of 75% of the individual FA threshold (FAT) was used to track descending corticospinal (CST) and -bulbar tracts (CBT). The distance between the tumor and the somatotopic tracts (hand, leg, face) was measured and diffusion parameters were correlated to the patients' outcome.

Results

12 patients were enrolled in this study, of which 6 underwent surgical resection, 5 received a stereotactic biopsy and 1 patient received conservative treatment. In all patients nTMS mapping and somatotopic tractography were performed successfully. Low FA values correlated with clinical symptoms revealing tract alteration by the tumor (p = 0.049). A tumor-tract distance (TTD) above 2 mm was the critical limit to achieve a safe complete tumor resection.

Discussion and conclusion

nTMS based DTI tractography combined with local diffusion analysis is a valuable tool for preoperative visualization and functional assessment of relevant motor fiber tracts, improving planning of safe entry corridors and perioperative risk stratification in brainstem gliomas tumors. This technique allows for customized treatment strategy to maximize patients' safety.

A multimodal imaging-based classification for pediatric diffuse intrinsic pontine gliomas

OBJECT

Pediatric diffuse intrinsic pontine glioma (DIPG) is a radiologically heterogeneous disease entity, here we aim to establish a multimodal imaging-based radiological classification and evaluate the outcome of different treatment strategies under this classification frame.

METHODS

This retrospective study included 103 children diagnosed with DIPGs between January 2015 and August 2018 in Beijing Tiantan Hospital (Beijing, China). Multimodal radiological characteristics, including conventional magnetic resonance imaging (MRI), diffuse tensor imaging/diffuse tensor tractography (DTI/DTT), and positron emission tomography (PET) were reviewed to construct the classification. The outcome of different treatment strategies was compared in each DIPG subgroup using Kaplan-Meier method (log-rank test) to determine the optimal treatment for specific DIPGs.

RESULTS

Four radiological DIPG types were identified: Type A ("homocentric", n=13), Type B ("ventral", n=41), Type C ("eccentric", n=37), and Type D ("dorsal", n=12). Their treatment modalities were grouped as observation (43.7%), cytoreductive surgery (CRS) plus radiotherapy (RT) (24.3%), RT alone (11.7%), and CRS alone (20.4%). CRS+RT mainly fell into type C (29.7%), followed by type B1 (21.9%) and type D (50%). Overall, CRS+RT exhibited a potential survival advantage compared to RT alone, which was more pronounced in specific type, but this did not reach statistical significance, due to limited sample size and unbalanced distribution.

CONCLUSION

We proposed a multimodality imaging-based radiological classification for pediatric DIPG, which was useful for selecting optimal treatment strategies, especially for identifying candidates who may benefit from CRS plus RT. This classification opened a window into image-guided integrated treatment for pediatric DIPG.

The Assessment of White Matter Integrity Alteration Pattern in Patients with Brain Tumor Utilizing Diffusion Tensor Imaging: A Systematic Review

Alteration in the surrounding brain tissue may occur in the presence of a brain tumor. The present study aims to assess the characteristics and criteria of the pattern of white matter tract microstructure integrity alteration in brain tumor patients. The Scopus, PubMed/Medline, and Web of Science electronic databases were searched for related articles based on the guidelines established by PRISMA. Twenty-five studies were selected on the morphological changes of white matter tract integrity based on the differential classification of white matter tract (WMT) patterns in brain tumor patients through diffusion tensor imaging (DTI). The characterization was based on two criteria: the visualization of the tract-its orientation and position-and the DTI parameters, which were the fractional anisotropy and apparent diffusion coefficient. Individual evaluations revealed no absolute, mutually exclusive type of tumor in relation to morphological WMT microstructure integrity changes. In most cases, different types and grades of tumors have shown displacement or infiltration. Characterizing morphological changes in the integrity of the white matter tract microstructures is vital in the diagnostic and prognostic evaluation of the tumor's progression and could be a potential assessment for the early detection of possible neurological defects that may affect the patient, as well as aiding in surgery decision-making.

Machine learning-based prediction of motor status in glioma patients using diffusion MRI metrics along the corticospinal tract

Along tract statistics enables white matter characterization using various diffusion MRI metrics. These diffusion models reveal detailed insights into white matter microstructural changes with development, pathology and function. Here, we aim at assessing the clinical utility of diffusion MRI metrics along the corticospinal tract, investigating whether motor glioma patients can be classified with respect to their motor status. We retrospectively included 116 brain tumour patients suffering from either left or right supratentorial, unilateral World Health Organization Grades II, III and IV gliomas with a mean age of 53.51 ± 16.32 years. Around 37% of patients presented with preoperative motor function deficits according to the Medical Research Council scale. At group level comparison, the highest non-overlapping diffusion MRI differences were detected in the superior portion of the tracts’ profiles. Fractional anisotropy and fibre density decrease, apparent diffusion coefficient axial diffusivity and radial diffusivity increase. To predict motor deficits, we developed a method based on a support vector machine using histogram-based features of diffusion MRI tract profiles (e.g. mean, standard deviation, kurtosis and skewness), following a recursive feature elimination method. Our model achieved high performance (74% sensitivity, 75% specificity, 74% overall accuracy and 77% area under the curve). We found that apparent diffusion coefficient, fractional anisotropy and radial diffusivity contributed more than other features to the model. Incorporating the patient demographics and clinical features such as age, tumour World Health Organization grade, tumour location, gender and resting motor threshold did not affect the model’s performance, revealing that these features were not as effective as microstructural measures. These results shed light on the potential patterns of tumour-related microstructural white matter changes in the prediction of functional deficits.

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.

Clinical application of diffusion tensor imaging and fiber tractography in the management of brainstem cavernous malformations: a systematic review

This study aimed to systematically review the literature to determine the clinical utility and perspectives of diffusion tensor imaging (DTI) in the management of patients with brainstem cavernous malformations (BSCMs). PubMed, Embase, and Cochrane were searched for English-language articles published until May 10, 2021. Clinical studies and case series describing DTI-based evaluation of patients with BSCMs were included. Fourteen articles were included. Preoperative DTI enabled to adjust the surgical approach and choose a brainstem safe entry zone in deep-seated BSCMs. Preoperatively lower fractional anisotropy (FA) of the corticospinal tract (CST) correlated with the severity of CST injury and motor deficits. Postoperatively increased FA and decreased apparent diffusion coefficient (ADC) corresponded with the normalization of the perilesional CST, indicating motor improvement. The positive (PPV) and negative predictive value (NPV) of qualitative DTI ranged from 20 to 75% and from 66.6 to 100%, respectively. The presence of preoperative and postoperative motor deficits was associated with a higher preoperative resting motor threshold (RMT) and lower FA. A higher preoperative CST score was indicative of a lower preoperative and follow-up Medical Research Council (MRC) grade. DTI facilitated the determination of a surgical trajectory with minimized risk of WMTs' damage. Preoperative FA and RMT might indicate the severity of preoperative and postoperative motor deficits. Preoperative CST score can reliably reflect patients' preoperative and follow-up motor status. Due to high NPV, normal CST morphology might predict intact neurological outcomes. Contrarily, sparse and relatively low PPV limits the reliable prediction of neurological deficits.

Optimized Tractography Mapping and Quantitative Evaluation of Pyramidal Tracts for Surgical Resection of Insular Gliomas: a Correlative Study with Diffusion Tensor Imaging–Derived Metrics and Patient Motor Strength

We investigate the correlation between diffusion tensor imaging (DTI)-derived metric statistics and motor strength grade of insular glioma patients after optimizing the pyramidal tract (PT) delineation. Motor strength grades of 45 insular glioma patients were assessed. All the patients underwent structural and diffusion MRI examination before and after surgery. We co-registered pre- and post-op datasets, and a two-tensor unscented Kalman filter (UKF) algorithm was employed to delineate bilateral PTs after DWI pre-processing. The tractography results were voxelized, and their labelmaps were cropped according to the location of frontal and insular parts of the lesion. Both the whole and cropped labelmaps were used as regions of interest to analyze fractional anisotropy (FA) and Trace statistics; hence, their ratios were calculated (lesional side tract/contralateral normal tract). The combination of DWI pre-processing and two-tensor UKF algorithm successfully delineated bilateral PTs of all the patients. It effectively accomplished both full fiber delineation within the edema and an extensive lateral fanning that had a favorable correspondence to the bilateral motor cortices. Before surgery, correlations were found between patients' motor strength grades and ratios of PT volume and FA standard deviation (SD). Nearly 3 months after surgery, correlations were found between motor strength grades and the ratios of metric statistics as follows: whole PT volume, whole mean FA, and FA SD. We substantiated the correlation between DTI-derived metric statistics and motor strength grades of insular glioma patients. Moreover, we posed a workflow for comprehensive pre- and post-op DTI quantitative research of glioma patients.

Functional DTI tractography in brainstem cavernoma surgery

OBJECTIVE

Surgical resection of brainstem cavernomas is associated with high postoperative morbidity due to the density of local vulnerable structures. Classical mapping of pathways by diffusion tensor imaging (DTI) has proven to be unspecific and confusing in many cases. In the current study, the authors aimed to establish a more reliable, specific, and objective method for somatotopic visualization of the descending motor pathways with navigated transcranial magnetic stimulation (nTMS)–based DTI fiber tracking.

METHODS

Twenty-one patients with brainstem cavernomas were examined with nTMS prior to surgery. The resting motor threshold (RMT) and cortical representation areas of hand, leg, and facial function were determined on both hemispheres. Motor evoked potential (MEP)–positive stimulation spots were then set as seed points for tractography. Somatotopic fiber tracking was performed at a fractional anisotropy (FA) value of 75% of the individual FA threshold.

RESULTS

Mapping of the motor cortex and tract reconstruction for hand, leg, and facial function was successful in all patients. The somatotopy of corticospinal and corticonuclear tracts was also clearly depicted on the brainstem level. Higher preoperative RMT values were associated with a postoperative motor deficit (p < 0.05) and correlated with a lower FA threshold (p < 0.05), revealing structural impairment of the corticospinal tract (CST) prior to surgery. In patients with a new deficit, the distance between the lesion and CST was below 1 mm.

CONCLUSIONS

nTMS-based fiber tracking enables objective somatotopic tract visualization on the brainstem level and provides a valuable instrument for preoperative planning, intraoperative orientation, and individual risk stratification. nTMS may thus increase the safety of surgical resection of brainstem cavernomas.

Neurite orientation dispersion and density imaging in evaluation of high-grade glioma-induced corticospinal tract injury

PURPOSE

To evaluate the application of neurite orientation dispersion and density imaging (NODDI) to brain glioma-induced corticospinal tract (CST) injury.

MATERIAL AND METHODS

Twenty-four patients with high-grade glioma (HGG) in or adjacent to the CST pathway and 12 matched healthy subjects underwent structural and diffusion MRI. The CSTs were reconstructed on the both sides. The CST features including morphological features (track number, average track length and track volume) and the diffusion parameter values including fractional anisotraphy (FA), mean diffusivity (MD), intracellular volume fraction (ICVF), isotropic or free water volume fraction (ISOVF) and orientation dispersion index (ODI) along the CST were calculated. The CST features were compared between the affected and healthy side for HGG patients and between the left and right side for healthy subjects. The relative CST features were compared across the healthy subjects, patients with motor weakness and patients with normal muscle strength. Receiver operating characteristic (ROC) curve was applied to evaluate the performance of each relative CST characteristic for HGG-induced CST changes.

RESULTS

Compared with the CST features on the healthy side, the track number, track volume and FA along the CST changed significantly on the affected side for HGG patients (p < 0.05 for all), whereas MD and ICVF changed significantly on the affected side only for HGG patients with motor weakness (p = 0.012 for both). In patients with motor weakness, the relative MD was significantly higher (p < 0.001), whereas the relative FA and ICVF was significantly lower (p = 0.002 and <0.001) than those in patients with normal muscle strength. The relative ICVF had a similar area under curve (AUC) to that of MD (AUC=0.953 and 0.969). Compared with the relative CST features in the healthy subjects, only the relative ICVF was significantly lower in HGG patients with normal muscle strength (p = 0.012).

CONCLUSIONS

NODDI seems to be useful in reflecting the HGG infiltration to CST, and can evaluate the CST destruction with a performance similar to DTI by providing additional information about neurite density for HGG-induced CST injury.

The role of diffusion tensor imaging and tractography in the surgical management of brainstem gliomas

OBJECTIVE

Diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) have the ability to noninvasively visualize changes in white matter tracts, as well as their relationships with lesions and other structures. DTI/DTT has been increasingly used to improve the safety and results of surgical treatment for lesions in eloquent areas, such as brainstem cavernous malformations. This study aimed to investigate the application value of DTI/DTT in brainstem glioma surgery and to validate the spatial accuracy of reconstructed corticospinal tracts (CSTs).

METHODS

A retrospective analysis was performed on 54 patients with brainstem gliomas who had undergone surgery from January 2016 to December 2018 at Beijing Tiantan Hospital. All patients underwent preoperative DTI and tumor resection with the assistance of DTT-merged neuronavigation and electrophysiological monitoring. Preoperative conventional MRI and DTI data were collected, and the muscle strength and modified Rankin Scale (mRS) score before and after surgery were measured. The surgical plan was created with the assistance of DTI/DTT findings. The accuracy of DTI/DTT was validated by performing direct subcortical stimulation (DsCS) intraoperatively. Multiple linear regression was used to investigate the relationship between quantitative parameters of DTI/DTT (such as the CST score and tumor-to-CST distance [TCD]) and postoperative muscle strength and mRS scores.

RESULTS

Among the 54 patients, 6 had normal bilateral CSTs, 12 patients had unilateral CST impairments, and 36 had bilateral CSTs involved. The most common changes in the CSTs were deformation (n = 29), followed by deviation (n = 28) and interruption (n = 27). The surgical approach was changed in 18 cases (33.3%) after accounting for the DTI/DTT results. Among 55 CSTs on which DsCS was performed, 46 (83.6%) were validated as spatially accurate by DsCS. The CST score and TCD were significantly correlated with postoperative muscle strength (r = -0.395, p < 0.001, and r = 0.275, p = 0.004, respectively) and postoperative mRS score (r = 0.430, p = 0.001, and r = -0.329, p = 0.015, respectively). The CST score was independently linearly associated with postoperative muscle strength (t = -2.461, p = 0.016) and the postoperative mRS score (t = 2.052, p = 0.046).

CONCLUSIONS

DTI/DTT is a valuable tool in the surgical management of brainstem gliomas. With good accuracy, it can help optimize surgical planning, guide tumor resection, and predict the postoperative muscle strength and postoperative quality of life of patients.

Laplacian-Regularized Mean Apparent Propagator-MRI in Evaluating Corticospinal Tract Injury in Patients with Brain Glioma

OBJECTIVE

To evaluate the application of laplacian-regularized mean apparent propagator (MAPL)-MRI to brain glioma-induced corticospinal tract (CST) injury.

MATERIALS AND METHODS

This study included 20 patients with glioma adjacent to the CST pathway who had undergone structural and diffusion MRI. The entire CSTs of the affected and healthy sides were reconstructed, and the peritumoral CSTs were manually segmented. The morphological characteristics of the CST (track number, average length, volume, displacement of the affected CST) were examined and the diffusion parameter values, including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), mean squared displacement (MSD), q-space inverse variance (QIV), return-to-origin probability (RTOP), return-to-axis probabilities (RTAP), and return-to-plane probabilities (RTPP) along the entire and peritumoral CSTs, were calculated. The entire and peritumoral CST characteristics of the affected and healthy sides as well as those relative CST characteristics of the patients with motor weakness and normal motor function were compared.

RESULTS

The track number, volume, MD, RD, MSD, QIV, RTAP, RTOP, and RTPP of the entire and peritumoral CSTs changed significantly for the affected side, whereas the AD and FA changed significantly only in the peritumoral CST (p < 0.05). In patients with motor weakness, the relative MSD of the entire CST, QIV of the entire and peritumoral CSTs, and the AD, MD, RD of the peritumoral CST were significantly higher, whereas the RTPP of the entire and peritumoral CSTs and the RTOP of the peritumoral CST were significantly lower than those in patients with normal motor function (p < 0.05 for all). In contrast, no significant changes were found in the CST morphological characteristics, FA, or RTAP (p > 0.05 for all).

CONCLUSION

MAPL-MRI is an effective approach for evaluating microstructural changes after CST injury. Its sensitivity may improve when using the peritumoral CST features.

What do we know about pre- and postoperative plasticity in patients with glioma? A review of neuroimaging and intraoperative mapping studies

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Brain reorganization can take place before and after surgery of low- and high-grade gliomas.

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Plasticity is observed for low-grade but also for high-grade gliomas.

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The contralesional hemisphere can be vital for successful compensation.

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There is evidence of plasticity for both the language system and the sensorimotor system.

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Partial compensation can also occur at the white-matter level.

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Subcortical connectivity is crucial for brain reorganization.

Brain plasticity potential is a central theme in neuro-oncology and is currently receiving increased attention. Advances in treatment have prolonged life expectancy in neuro-oncological patients and the long-term preservation of their quality of life is, therefore, a new challenge. To this end, a better understanding of brain plasticity mechanisms is vital as it can help prevent permanent deficits following neurosurgery.

Indeed, reorganization processes can be fundamental to prevent or recover neurological and cognitive deficits by reallocating brain functions outside the lesioned areas. According to more recent studies in the literature, brain reorganization taking place following neurosurgery is associated with good neurofunctioning at follow-up. Interestingly, in the last few years, the number of reports on plasticity has notably increased.

Aim of the current review was to provide a comprehensive overview of pre- and postoperative neuroplasticity patterns. Within this framework, we aimed to shed light on some tricky issues, including i) involvement of the contralateral healthy hemisphere, ii) role and potential changes of white matter and connectivity patterns, and iii) reorganization in low- versus high-grade gliomas.

We finally discussed the practical implications of these aspects and role of additional potentially relevant factors to be explored. Final purpose was to provide a guideline helpful in promoting increase in the extent of tumor resection while preserving the patients’ neurological and cognitive functioning.

Alterations of white matter integrity associated with cognitive deficits in patients with glioma

OBJECTIVE

This study aimed to investigate the characteristic of brain structural connections in glioma patients and further evaluate the relationship between changes in the white matter tracts and cognitive decline.

METHODS

This retrospective study included a total of 35 subjects with glioma and 14 demographically matched healthy controls, who underwent diffusion tensor imaging scans and formal neuropsychological assessment tests. Fractional anisotropy (FA) values of white matter tracts were derived from atlas-based analysis to compare group differences. Furthermore, subgroup-level analysis was performed to differentiate the effects of tumor location on white matter tracts. Partial correlation analysis was used to examine the associations between neurocognitive assessments and the integrity of tracts. Region of interest-based network analysis was performed to validate the alteration of structural brain network in subjects with glioma.

RESULTS

Compared with controls, subjects with glioma exhibited reduced FA values in the right uncinate fasciculus. Besides, subjects with glioma exhibited worse performance in several cognitive assessments. Partial correlation analysis indicated that the FA value in the right superior longitudinal fasciculus temporal part was significantly positively correlated with scores of visual-spatial abilities in subjects with glioma in the right temporal lobe (r = .932, p = .002). Region of interest-based network analysis revealed that subjects with glioma exhibited reduced FA, fiber length (FL), and fiber number (FN) between specific brain regions compared with controls.

CONCLUSION

The present study demonstrated the reduced integrity of white matter tracts and altered structural connectivity in brain networks in patients with glioma. Notably, white matter tracts in the right hemisphere might be vulnerable to the effects of a frontal or temporal lesion and might be associated with deficient cognitive function.

Limited positive predictive value of diffusion tensor tractography in determining clinically relevant white matter damage in brain stem cavernous malformations: A retrospective study in a single center surgical cohort

PURPOSE

Diffusion tensor tractography (DTT) might reflect the postoperative clinical outcome of the patients with brain stem (BS) tumors correlating well with the neurological symptoms, but cavernous malformation (CM) is a hemorrhagic tumor prone to artifacts that may limit DTT. We set out to determine the correlation of DTT findings with the neurological examination before and after surgical resection in patients with BSCMs.

MATERIALS AND METHODS

DTT findings were evaluated bilaterally for fiber tract displacement or deviation, deformation and interruption in every patient before and after the surgery. Neurological examination was performed at admission, discharge and outpatient follow-up visit. The sensitivity, specificity, positive and negative predictive values of DTT were calculated both pre- and post-operatively.

RESULTS

There were 25 patients (9 men 16 women) with a mean age of 39.5±13.9 years. The mean size of the CMs was 6909±8374mm³ (range: 180-38,220mm³) The mean follow-up time was 42.7±23.2 months (range: 8 to 112 months). Preoperatively, the sensitivity, specificity, positive and negative predictive values of DTT for corticospinal tracts (CST) and medial lemnisci (ML) were 100%, 60%, 38.4%, 100% and 87.5%, 11.7%, 31.8%, 66.6%, respectively. Postoperatively, the sensitivity, specificity, positive and negative predictive values of DTT for CSTs and ML were 100%, 64.7%, 40%, 100% and 100%, 0%, 33.3%, 66.6%, respectively.

CONCLUSION

Positive findings on DTT such as fiber tract deviation, deformation, disruption or interruption should be taken cautiously before drawing conclusions of a clinically relevant damage of white matter tracts.

Recovery of consciousness after a brainstem cavernous malformation hemorrhage: A descriptive study of preserved reticular activating system with tractography

The aim of this study is to describe the imaging features, the relevant anatomy, and the fractional anisotropy (FA) values in diffusion tensor tractography (DTT) of the ascending reticular activating system (ARAS) fiber tracts in 2 patients who recovered from initial altered consciousness after presenting with a brainstem cavernous malformation (BSCM) hemorrhage. A DTT was performed in 2 patients with impaired consciousness after a brainstem cavernous malformation hemorrhage. A 1.5 T scanner was used to obtain the axial tensors. Post-processing was performed and the mean FA values were recorded. The FA maps were used to seed the following regions of interest: the ventromedial midbrain, the anterior thalamus bilaterally, and the hypothalamus bilaterally. The first case presented with posterior displacement of the dorsal raphè fiber tracts, with preservation of all the ascending reticular activating fiber tracts and spontaneous recovery of consciousness after 20 days. The second case presented with no destruction but also had posterior displacement of the inferior dorsal raphè fiber tracts, with recovery of consciousness 1 month after resection surgery. Described in this study are affected fibers of the ARAS, as well as the FA value abnormalities in 2 patients, with recovery of a transient disorder of consciousness after a BSCM hemorrhage.

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).

3D microsurgical anatomy of the cortico-spinal tract and lemniscal pathway based on fiber microdissection and demonstration with tractography

OBJECTIVE

To demonstrate tridimensionally the anatomy of the cortico-spinal tract and the medial lemniscus, based on fiber microdissection and diffusion tensor tractography (DTT).

MATERIAL AND METHODS

Ten brain hemispheres and brain-stem human specimens were dissected and studied under the operating microscope with microsurgical instruments by applying the fiber microdissection technique. Brain magnetic resonance imaging was obtained from 15 healthy subjects using diffusion-weighted images, in order to reproduce the cortico-spinal tract and the lemniscal pathway on DTT images.

RESULTS

The main bundles of the cortico-spinal tract and medial lemniscus were demonstrated and delineated throughout most of their trajectories, noticing their gross anatomical relation to one another and with other white matter tracts and gray matter nuclei the surround them, specially in the brain-stem; together with their corresponding representation on DTT images.

CONCLUSIONS

Using the fiber microdissection technique we were able to distinguish the disposition, architecture and general topography of the cortico-spinal tract and medial lemniscus. This knowledge has provided a unique and profound anatomical perspective, supporting the correct representation and interpretation of DTT images. This information should be incorporated in the clinical scenario in order to assist surgeons in the detailed and critic analysis of lesions located inside the brain-stem, and therefore, improve the surgical indications and planning, including the preoperative selection of optimal surgical strategies and possible corridors to enter the brainstem, to achieve safer and more precise microsurgical technique.

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.

Endoscopic Endonasal Transclival Approach for Resection of a Pontine Glioma: Surgical Planning, Surgical Anatomy, and Technique

BACKGROUND

The endoscopic endonasal approach (EEA) has been proposed as a potential alternative for ventral brainstem lesions. The surgical anatomy, feasibility, and limitations of the EEA for intrinsic brainstem lesions are still poorly understood.

OBJECTIVE

To describe the surgical planning, anatomy, and technique of an intrinsic pontine glioma operated via EEA.

METHODS

Six-human brainstems were prepared for white matter microdissection. Ten healthy subjects were studied with high-definition fiber tractography (HDFT). A 56-yr-old female with right-hemiparesis underwent EEA for an exophytic pontine glioma. Pre- and postoperative HDFTs were implemented.

RESULTS

The corticospinal tracts (CSTs) are the most eloquent fibers in the ventral brainstem. At the pons, CSTs run between the pontine nuclei and the middle cerebellar peduncle (MCP). At the lower medulla, the pyramidal decussation leaves no room for safe ventral access. In our illustrative case, preoperative HDFT showed left-CST displaced posteromedially and partially disrupted, right-CST posteriorly displaced, and MCP severely disrupted. A transclival exposure was performed achieving a complete resection of the exophytic component with residual intra-axial tumor. Immediately postop, patient developed new left-side abducens nerve palsy and worse right-hemiparesis. Ten days postop, her strength returned to baseline. HDFT showed preservation and trajectory restoration of the CSTs.

CONCLUSION

The EEA provides direct access to the ventral brainstem, overcoming the limitations of lateral approaches. For intrinsic pathology, HDFT helps choosing the most appropriate surgical route/boundaries for safer resection. Further experience is needed to determine the indications and limitations of this approach that should be performed by neurosurgeons with high-level expertise in EEA.

Diffusion-tensor Imaging and Tractography Application in Pre-operative Planning of Intra-axial Brain Lesions

Gliomas are the most common brain tumors that diffusely infiltrate the surrounding white matter (WM) tracts. Conventional MRI is commonly used for tumor localization and characterization. However, this does not give precise information about the WM infiltration surrounding the tumor. Diffusion-tensor imaging (DTI) is a non-invasive magnetic resonance (MR) technique that measures WM tissue integrity and tractography (fiber tracking) used to investigate the preferential directionality of diffusion. DTI allows visualization of WM tracts in the immediate vicinity of brain tumors that permit maximum tumor resection while also preserving the eloquent brain areas. The relation of tumors with the white matter tracts (deviation, infiltration, and disruption) has been one the most important initial applications of DTI. The fibers can be infiltrated in normal-appearing areas, and abnormal-appearing areas of the brain can show anatomically intact fibers. In the surgical planning of brain tumors, surgery is aided by knowing the proximity and relative position of the tumor to the adjacent WM tracts. The aim of the present study is to assess the role of DT tractography (DTT) in preoperative mapping of major WM tracts in relation to brain tumors.

Optimal Factors of Diffusion Tensor Imaging Predicting Corticospinal Tract Injury in Patients with Brain Tumors

Objective

To identify the optimal factors in diffusion tensor imaging for predicting corticospinal tract (CST) injury caused by brain tumors.

Materials and Methods

This prospective study included 33 patients with motor weakness and 64 patients with normal motor function. The movement of the CST, minimum distance between the CST and the tumor, and relative fractional anisotropy (rFA) of the CST on diffusion tensor imaging, were compared between patients with motor weakness and normal function. Logistic regression analysis was used to obtain the optimal factor predicting motor weakness.

Results

In patients with motor weakness, the displacement (8.44 ± 6.64 mm) of the CST (p = 0.009), minimum distance (3.98 ± 7.49 mm) between the CST and tumor (p < 0.001), and rFA (0.83 ± 0.11) of the CST (p < 0.001) were significantly different from those of the normal group (4.64 ± 6.65 mm, 14.87 ± 12.04 mm, and 0.98 ± 0.05, respectively) (p = 0.009, p < 0.001, and p < 0.001). The frequencies of patients with the CST passing through the tumor (6%, p = 0.002), CST close to the tumor (23%, p < 0.001), CST close to a malignant tumor (high grade glioma, metastasis, or lymphoma) (19%, p < 0.001), and CST passing through infiltrating edema (19%, p < 0.001) in the motor weakness group, were significantly different from those of the patients with normal motor function (0, 8, 1, and 10%, respectively). Logistic regression analysis showed that decreased rFA and CST close to a malignant tumor were effective variables related to motor weakness.

Conclusion

Decreased fractional anisotropy, combined with closeness of a malignant tumor to the CST, is the optimal factor in predicting CST injury caused by a brain tumor.

White matter tractography for neurosurgical planning: A topography-based review of the current state of the art

We perform a review of the literature in the field of white matter tractography for neurosurgical planning, focusing on those works where tractography was correlated with clinical information such as patient outcome, clinical functional testing, or electro-cortical stimulation. We organize the review by anatomical location in the brain and by surgical procedure, including both supratentorial and infratentorial pathologies, and excluding spinal cord applications. Where possible, we discuss implications of tractography for clinical care, as well as clinically relevant technical considerations regarding the tractography methods. We find that tractography is a valuable tool in variable situations in modern neurosurgery. Our survey of recent reports demonstrates multiple potentially successful applications of white matter tractography in neurosurgery, with progress towards overcoming clinical challenges of standardization and interpretation.

[3D anatomy of cerebellar peduncles based on fibre microdissection and a demonstration with tractography]

OBJECTIVE

To perform an anatomical and radiological study, using fibre microdissection and diffusion tensor tractography (DTT), to demonstrate the three-dimensionality of the superior, middle and inferior cerebellar peduncles.

MATERIAL AND METHODS

A total of 15 brain-stem, 15 cerebellar hemispheres, and 5 brain hemispheres were dissected in the laboratory under the operating microscope with microsurgical instruments between July 2014 and July 2015. Brain magnetic resonance imaging was obtained from 15 healthy subjects between July and December of 2015, using diffusion-weighted images, in order to reproduce the cerebellar peduncles on DTT.

RESULTS

The main bundles of the cerebellar peduncles were demonstrated and delineated along most of their trajectory in the cerebellum and brain-stem, noticing their overall anatomical relationship to one another and with other white matter tracts and the grey matter nuclei the surround them, with their corresponding representations on DTT.

CONCLUSIONS

The arrangement, architecture, and general topography of the cerebellar peduncles were able to be distinguished using the fibre microdissection technique. This knowledge has given a unique and profound anatomical perspective, supporting the correct representation and interpretation of DTT images. This information should be incorporated in the clinical scenario in order to assist surgeons in the detailed and critical analysis of lesions that may be located near these main bundles in the cerebellum and/or brain-stem, and therefore, improve the surgical planning and achieve a safer and more precise microsurgical technique.

The Medial and Lateral Lemnisci: Anatomically Adjoined But Functionally Distinct Fiber Tracts

OBJECTIVE

The dense and complex distribution of neural structures in the brainstem makes it challenging to understand their real configuration. We used the fiber microdissection technique to show the course of the medial and lateral lemnisci within the brainstem. Although these structures seem anatomically alike, they are functionally distinct.

METHODS

Fifteen human brainstems and 8 brain hemispheres (formalin-fixed and previously frozen) were dissected and studied under the operating microscope by applying the fiber microdissection technique.

RESULTS

We delineated and described the medial and lateral lemnisci, noting their gross elaborate arrangement. These structures are intimately compact and closely related to one another in their common trajectory through the tegmenta of the pons and midbrain. However, we were not able to identify the exact origin and termination of their fibers or the accurate delimitation between the medial lemniscus, spinothalamic tract, and lateral lemniscus along their course in the brainstem.

CONCLUSIONS

Using the fiber microdissection technique, we were able to define a general perspective of the topography and architecture of the medial and lateral lemnisci in the brainstem. This perspective should be incorporated into interpretations of magnetic resonance imaging techniques, recognizing both their benefits and limitations. It should also be applied to surgical planning and strategies to achieve a safer and more precise microsurgical procedure.

Preliminary Study of MR Diffusion Tensor Imaging of Pancreas for the Diagnosis of Acute Pancreatitis

OBJECTIVES

To evaluate the feasibility of differentiating between acute pancreatitis (AP) and healthy pancreas using diffusion tensor imaging (DTI) and correlate apparent diffusion coefficient (ADC) /fractional anisotropy (FA) values with the severity of AP.

MATERIAL AND METHODS

66 patients diagnosed with AP and 20 normal controls (NC) underwent DTI sequences and routine pancreatic MR sequences on a 3.0T MRI scanner. Average ADC and FA values of the pancreatic were measured. Differences of FA and ADC values between the AP group and the NC group with AP and healthy pancreas were compared by two-sample independent t-test. The severity of AP on MRI was classified into subgroups using MR severity index (MRSI), where the mean FA and ADC values were calculated. Relationship among the FA values, ADC values and MRSI were analyzed using Spearman's rank correlation coefficients.

RESULTS

The pancreatic mean ADC value in the AP group (1.68 ± 0.45×10-3mm2/s) was significantly lower than in the NC group (2.09 ± 0.55×10-3mm2/s) (P = 0.02); the same as mean FA value (0.39 ± 0.23 vs 0.54 ± 0.12, P = 0.00). In the subgroup analysis, the pancreatic ADC and FA value of edema AP patients was significantly higher than necrosis AP patients with P = 0.000 and P = 0.001respectively. In addition, as severity of pancreatitis increased according to MRSI, lower pancreatic ADC (r = -0.635) and FA value (r = -0.654) were noted.

CONCLUSION

Both FA and ADC value from DTI can be used to differentiate AP patients from NC. Both ADC and FA value of pancreas have a negative correlation with the severity of AP.

Diffusion Tractography Biomarkers of Pediatric Cerebellar Hypoplasia/Atrophy: Preliminary Results Using Constrained Spherical Deconvolution

BACKGROUND AND PURPOSE

Advances in MR imaging modeling have improved the feasibility of reconstructing crossing fibers, with increasing benefits in delineating angulated tracts such as cerebellar tracts by using tractography. We hypothesized that constrained spherical deconvolution-based probabilistic tractography could successfully reconstruct cerebellar tracts in children with cerebellar hypoplasia/atrophy and that diffusion scalars of the reconstructed tracts could differentiate pontocerebellar hypoplasia, nonprogressive cerebellar hypoplasia, and progressive cerebellar atrophy.

MATERIALS AND METHODS

Fifteen children with cerebellar ataxia and pontocerebellar hypoplasia, nonprogressive cerebellar hypoplasia or progressive cerebellar atrophy and 7 controls were included in this study. Cerebellar and corticospinal tracts were reconstructed by using constrained spherical deconvolution. Scalar measures (fractional anisotropy and mean, axial and radial diffusivity) were calculated. A general linear model was used to determine differences among groups for diffusion MR imaging scalar measures, and post hoc pair-wise comparisons were performed.

RESULTS

Cerebellar and corticospinal tracts were successfully reconstructed in all subjects. Significant differences in diffusion MR imaging scalars were found among groups, with fractional anisotropy explaining the highest variability. All groups with cerebellar pathologies showed lower fractional anisotropy compared with controls, with the exception of cerebellar hypoplasia.

CONCLUSIONS

This study shows the feasibility of constrained spherical deconvolution to reconstruct cerebellar and corticospinal tracts in children with morphologic cerebellar pathologies. In addition, the preliminary results show the potential utility of quantitative analysis of scalars of the cerebellar white matter tracts in children with cerebellar pathologies such as cerebellar hypoplasia and atrophy. Further studies with larger cohorts of patients are needed to validate the clinical significance of our preliminary results.

Preliminary Study of MR Diffusion Tensor Imaging of the Liver for the Diagnosis of Hepatocellular Carcinoma

OBJECTIVES

To evaluate the feasibility of differentiating between hepatocellular carcinomas (HCC) and healthy liver using diffusion tensor imaging (DTI).

MATERIAL AND METHODS

All subjects underwent an abdominal examination on a 3.0T MRI scanner. Two radiologists independently scored the image quality (IQ). An optimal set of DTI parameters was obtained from a group of fifteen volunteers with multiple b-values (100, 300, 500, and 800 s/mm2) and various diffusion-encoding directions (NED = 6, 9, and 12)using two way ANOVA analysis. Eighteen Patients with HCC underwent DTI scans with the optimized parameters. Fractional anisotropy(FA) and average apparent diffusion coefficient (ADC) values were measured. The differences of FA and ADC values between liver healthy region and HCC lesion were compared through paired t tests.

RESULTS

There were no significant changes in liver IQ and FA/ADC values with increased NED(P >0.05), whereas the liver IQ and FA/ADC values decreased significantly with increased b-values(P <0.05). Good IQ, acceptable scan time and reasonable FA/ADC values were acquired using NED = 9 with b-value of (0,300) s/mm2. Using the optimized DTI sequence, ADC value of the tumor lesion was significantly lower than that of the healthy liver region (1.30 ± 0.34×10-3 vs 1.52 ± 0.27×10-3 mm2/s, P = 0.013), whereas the mean FA value of the tumor lesion (0.42 ± 0.11) was significantly higher than the normal liver region (0.32 ± 0.10) (P = 0.004).

CONCLUSION

Either FA or ADC value from DTI can be used to differentiate HCC from healthy liver. HCC lead to higher FA value and lower ADC value on DTI than healthy liver.

Magnetic resonance diffusion tensor imaging-based evaluation of optic-radiation shape and position in meningioma

Employing magnetic resonance diffusion tensor imaging, three-dimensional white-matter imaging and conventional magnetic resonance imaging can demonstrate the tumor parenchyma, peritumoral edema and compression on surrounding brain tissue. A color-coded tensor map and three-dimensional tracer diagram were applied to clearly display the optic-radiation location, course and damage. Results showed that the altered anisotropy values of meningioma patients corresponded with optic-radiation shape, size and position on both sides. Experimental findings indicate that the magnetic resonance diffusion tensor imaging technique is a means of tracing and clearly visualizing the optic radiation.

Biotinylated dextran amine anterograde tracing of the canine corticospinal tract

In this study, biotinylated dextran amine (BDA) was microinjected into the left cortical motor area of the canine brain. Fluorescence microscopy results showed that a large amount of BDA-labeled pyramidal cells were visible in the left cortical motor area after injection. In the left medulla oblongata, the BDA-labeled corticospinal tract was evenly distributed, with green fluorescence that had a clear boundary with the surrounding tissue. The BDA-positive corticospinal tract entered into the right lateral funiculus of the spinal cord and descended into the posterior part of the right lateral funiculus, close to the posterior horn, from cervical to sacral segments. There was a small amount of green fluorescence in the sacral segment. The distribution of BDA labeling in the canine central nervous system was consistent with the course of the corticospinal tract. Fluorescence labeling for BDA gradually diminished with time after injection. Our findings indicate that the BDA anterograde tracing technique can be used to visualize the localization and trajectory of the corticospinal tract in the canine central nervous system.

The utility of preoperative diffusion tensor imaging in the surgical management of brainstem cavernous malformations

OBJECT

Resection of brainstem cavernous malformations (BSCMs) may reduce the risk of stepwise neurological deterioration secondary to hemorrhage, but the morbidity of surgery remains high. Diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) are neuroimaging techniques that may assist in the complex surgical planning necessary for these lesions. The authors evaluate the utility of preoperative DTI and DTT in the surgical management of BSCMs and their correlation with functional outcome.

METHODS

A retrospective review was conducted to identify patients who underwent resection of a BSCM between 2007 and 2012. All patients had preoperative DTI/DTT studies and a minimum of 6 months of clinical and radiographic follow-up. Five major fiber tracts were evaluated preoperatively using the DTI/DTT protocol: 1) corticospinal tract, 2) medial lemniscus and medial longitudinal fasciculus, 3) inferior cerebellar peduncle, 4) middle cerebellar peduncle, and 5) superior cerebellar peduncle. Scores were applied according to the degree of distortion seen, and the sum of scores was used for analysis. Functional outcomes were measured at hospital admission, discharge, and last clinic visit using modified Rankin Scale (mRS) scores.

RESULTS

Eleven patients who underwent resection of a BSCM and preoperative DTI were identified. The mean age at presentation was 49 years, with a male-to-female ratio of 1.75:1. Cranial nerve deficit was the most common presenting symptom (81.8%), followed by cerebellar signs or gait/balance difficulties (54.5%) and hemibody anesthesia (27.2%). The majority of the lesions were located within the pons (54.5%). The mean diameter and estimated volume of lesions were 1.21 cm and 1.93 cm(3), respectively. Using DTI and DTT, 9 patients (82%) were found to have involvement of 2 or more major fiber tracts; the corticospinal tract and medial lemniscus/medial longitudinal fasciculus were the most commonly affected. In 2 patients with BSCMs without pial presentation, DTI/DTT findings were important in the selection of the surgical approach. In 2 other patients, the results from preoperative DTI/DTT were important for selection of brainstem entry zones. All 11 patients underwent gross-total resection of their BSCMs. After a mean postoperative follow-up duration of 32.04 months, all 11 patients had excellent or good outcome (mRS Score 0-3) at the time of last outpatient clinic evaluation. DTI score did not correlate with long-term outcome.

CONCLUSIONS

Preoperative DTI and DTT should be considered in the resection of symptomatic BSCMs. These imaging studies may influence the selection of surgical approach or brainstem entry zones, especially in deep-seated lesions without pial or ependymal presentation. DTI/DTT findings may allow for more aggressive management of lesions previously considered surgically inaccessible. Preoperative DTI/DTT changes do not appear to correlate with functional postoperative outcome in long-term follow-up.

Alterations in fiber pathways reveal brain tumor typology: a diffusion tractography study

Conventional structural Magnetic Resonance (MR) techniques can accurately identify brain tumors but do not provide exhaustive information about the integrity of the surrounding/embedded white matter (WM). In this study, we used Diffusion-Weighted (DW) MRI tractography to explore tumor-induced alterations of WM architecture without any a priori knowledge about the fiber paths under consideration. We used deterministic multi-fiber tractography to analyze 16 cases of histologically classified brain tumors (meningioma, low-grade glioma, high-grade glioma) to evaluate the integrity of WM bundles in the tumoral region, in relation to the contralateral unaffected hemisphere. Our new tractographic approach yielded measures of WM involvement which were strongly correlated with the histopathological features of the tumor (r = 0.83, p = 0.0001). In particular, the number of affected fiber tracts were significantly (p = 0.0006) different among tumor types. Our method proposes a new application of diffusion tractography for the detection of tumor aggressiveness in those cases in which the lesion does not involve any major/known WM paths and when a priori information about the local fiber anatomy is lacking.

Diffusion tensor imaging for anatomical localization of cranial nerves and cranial nerve nuclei in pontine lesions: initial experiences with 3T-MRI

With continuous refinement of neurosurgical techniques and higher resolution in neuroimaging, the management of pontine lesions is constantly improving. Among pontine structures with vital functions that are at risk of being damaged by surgical manipulation, cranial nerves (CN) and cranial nerve nuclei (CNN) such as CN V, VI, and VII are critical. Pre-operative localization of the intrapontine course of CN and CNN should be beneficial for surgical outcomes. Our objective was to accurately localize CN and CNN in patients with intra-axial lesions in the pons using diffusion tensor imaging (DTI) and estimate its input in surgical planning for avoiding unintended loss of their function during surgery. DTI of the pons obtained pre-operatively on a 3Tesla MR scanner was analyzed prospectively for the accurate localization of CN and CNN V, VI and VII in seven patients with intra-axial lesions in the pons. Anatomical sections in the pons were used to estimate abnormalities on color-coded fractional anisotropy maps. Imaging abnormalities were correlated with CN symptoms before and after surgery. The course of CN and the area of CNN were identified using DTI pre- and post-operatively. Clinical associations between post-operative improvements and the corresponding CN area of the pons were demonstrated. Our results suggest that pre- and post-operative DTI allows identification of key anatomical structures in the pons and enables estimation of their involvement by pathology. It may predict clinical outcome and help us to better understand the involvement of the intrinsic anatomy by pathological processes.

Diffusion tensor tractography in the presurgical assessment of cerebral gliomas

Glioma is the most common intra-axial brain tumor characterized by invasion into the surrounding white matter (WM) tracts. These tumors are usually diagnosed by conventional MRI, but this method is unable to describe the relationship between tumor and neighboring WM tracts. Diffusion tensor tractography (DTT) is a new imaging modality which can solve this problem. The current study evaluated the application of DTT imaging in the presurgical assessment of gliomas, and introduces this new modality and its importance to physicians and imaging centers in Iran. Ten patients with intra-axial brain tumor and suspicion of glioma underwent conventional brain MRI pulse sequences and DTT imaging between December 2011 and February 2013 with a 1.5 Tesla system using 64 independent diffusion encoding directions. Acquired images were assessed by the neuroradiologist and neurosurgeon. The treatment strategies were recognized and compared using data before and after the tractography. On the basis of DTT data, the treatment strategy changed from radiotherapy to the craniotomy in seven patients, and in one patient, the neurosurgeon preferred to avoid surgery. In one patient, the treatment technique did not change, and in the last one radiosurgery was replaced by craniotomy. As we can infer from this study, based on the tractography results, the treatment strategy may be changed, and the treatment technique could be devised more accurately and may lead to fewer postoperative neurological deficits and better outcomes.

Quantification of primary motor pathways using diffusion MRI tractography and its application to predict postoperative motor deficits in children with focal epilepsy

As a new tool to quantify primary motor pathways and predict postoperative motor deficits in children with focal epilepsy, the present study utilized a maximum a posteriori probability (MAP) classification of diffusion weighted imaging (DWI) tractography combined with Kalman filter. DWI was performed in 31 children with intractable focal epilepsy who underwent epilepsy surgery. Three primary motor pathways associated with "finger," "leg," and "face" were classified using DWI-MAP classifier and compared with the results of invasive electrical stimulation mapping (ESM) via receiver operating characteristic (ROC) curve analysis. The Kalman filter analysis was performed to generate a model to determine the probability of postoperative motor deficits as a function of the proximity between the resection margin and the finger motor pathway. The ROC curve analysis showed that the DWI-MAP achieves high accuracy up to 89% (finger), 88% (leg), 89% (face), in detecting the three motor areas within 20 mm, compared with ESM. Moreover, postoperative reduction of the fiber count of finger pathway was associated with postoperative motor deficits involving the hand. The prediction model revealed an accuracy of 92% in avoiding postoperative deficits if the distance between the resection margin and the finger motor pathway seen on preoperative DWI tractography was 19.5 mm. This study provides evidence that the DWI-MAP combined with Kalman filter can effectively identify the locations of cortical motor areas even in patients whose motor areas are difficult to identify using ESM, and also can serve as a reliable predictor for motor deficits following epilepsy surgery.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

The paramedian supracerebellar-transtentorial approach to the entire length of the mediobasal temporal region: an anatomical and clinical study

Object

The exploration of lesions in the mediobasal temporal region (MTR) has challenged generations of neurosurgeons to achieve an appropriate approach. To address this challenge, the extensive use of the paramedian supracerebellar-transtentorial (PST) approach to expose the entire length of the MTR, as well as the fusiform gyrus, was investigated.

Methods

The authors studied the microsurgical aspects of the PST approach in 20 cadaver brains and 5 cadaver heads under the operating microscope. They evaluated the features, advantages, difficulties, and limitations of the PST approach and refined the surgical technique. They then used the PST approach in 15 patients with large intrinsic MTR tumors (6 patients), tumor in the posterior fusiform gyrus with mediobasal temporal epilepsy (MTE) (1 patient), cavernous malformations in the posterior MTR including the fusiform gyrus (2 patients), or intractable MTE with hippocampal sclerosis (6 patients) from December 2007 to May 2010. Patients ranged in age from 11 to 63 years (mean 35.2 years), and in 9 patients (60%) the lesion was located on the left side.

Results

In all patients with neuroepithelial tumors or cavernous malformations, the lesions were completely and safely resected. In all patients with intractable MTE with hippocampal sclerosis, the anterior two-thirds of the parahippocampal gyrus and hippocampus, as well as the amygdala, were removed selectively through the PST approach. There was no surgical morbidity or mortality in this series. Three patients (20%) with high-grade neuroepithelial tumors underwent postoperative radiotherapy and chemotherapy but needed a second surgery for recurrence during the follow-up period. In all patients with MTE, antiepileptic medication could be decreased to a single drug at lower doses, and no seizure activity has occurred until this point.

Conclusions

The PST approach provides the surgeon precise anatomical orientation when exposing the entire length of the MTR, as well as the fusiform gyrus, for removing any lesion. This is a novel technique especially for removing tumors involving the entire MTR in a single session without damaging neighboring neural or vascular structures. This approach can also be a viable alternative for selective removal of the parahippocampal gyrus, hippocampus, and amygdala in patients with MTE due to hippocampal sclerosis.