Spinal diffusion tensor imaging: A comprehensive review with emphasis on spinal cord anatomy and clinical applications

Improved Recovery of Complete Spinal Cord Transection by a Plasma-Modified Fibrillar Scaffold

Complete spinal cord injury causes an irreversible disruption in the central nervous system, leading to motor, sensory, and autonomic function loss, and a secondary injury that constitutes a physical barrier preventing tissue repair. Tissue engineering scaffolds are presented as a permissive platform for cell migration and the reconnection of spared tissue. Iodine-doped plasma pyrrole polymer (pPPy-I), a neuroprotective material, was applied to polylactic acid (PLA) fibers and implanted in a rat complete spinal cord transection injury model to evaluate whether the resulting composite implants provided structural and functional recovery, using magnetic resonance (MR) imaging, diffusion tensor imaging and tractography, magnetic resonance spectroscopy, locomotion analysis, histology, and immunofluorescence. In vivo, MR studies evidenced a tissue response to the implant, demonstrating that the fibrillar composite scaffold moderated the structural effects of secondary damage by providing mechanical stability to the lesion core, tissue reconstruction, and significant motor recovery. Histologic analyses demonstrated that the composite scaffold provided a permissive environment for cell attachment and neural tissue guidance over the fibers, reducing cyst formation. These results supply evidence that pPPy-I enhanced the properties of PLA fibrillar scaffolds as a promising treatment for spinal cord injury recovery.

Potential impairment of spinal cord around the apical vertebral level in hyperkyphotic patients: findings from diffusion tensor imaging

PURPOSE

To evaluate the neuronal metrics/microstructure of the spinal cord around apical region in patients with hyperkyphosis using diffusion tensor imaging (DTI).

METHODS

Thirty-seven patients with hyperkyphosis aged 45.5 ± 19.6 years old who underwent 3.0 T magnetic resonance imaging (MRI) examination with DTI sequence were prospectively enrolled from July 2022 to July 2023. Patients were divided into three groups according to spinal cord/ cerebrospinal fluid (CSF) architecture on sagittal-T2 MRI of the thoracic apex (the axial spinal cord classification): Group A-circular cord with visible CSF, Group B-circular cord without visible CSF at apical dorsal, and Group C-spinal cord deformed without intervening CSF. The fractional anisotropy (FA) values acquired from DTI were compared among different groups. Correlations between DTI parameters and global kyphosis (GK)/sagittal deformity angular ratio (sagittal DAR) were evaluated using Pearson correlation coefficients.

RESULTS

In all patients, FA values were significantly lower at apical level as compared with those at one level above or below the apex (0.548 ± 0.070 vs. 0.627 ± 0.056 versus 0.624 ± 0.039, P < 0.001). At the apical level, FA values were significantly lower in Group C than those in Group B (0.501 ± 0.052 vs. 0.598 ± 0.061, P < 0.001) and Group A (0.501 ± 0.052 vs. 0.597 ± 0.019, P < 0.001). Moreover, FA values were significantly lower in symptomatic group than those in non-symptomatic group (0.498 ± 0.049 v. 0.578 ± 0.065, P < 0.001). Pearson correlation analysis showed that GK (r2 = 0.3945, P < 0.001) and sagittal DAR (r2 = 0.3079, P < 0.001) were significantly correlation with FA values at apical level.

CONCLUSION

In patients with hyperkyphosis, the FA of spinal cord at apical level was associated with the neuronal metrics/microstructure of the spinal cord. Furthermore, the DTI parameter of FA at apical level was associated with GK and sagittal DAR.

LEVEL OF EVIDENCE: 4

The efficacy of preoperative diffusion tensor tractography on surgical planning and outcomes in patients with intramedullary spinal tumor

PURPOSE

The aim of this study was to investigate the efficacy of diffusion tensor tractography (DTT) of spinal cord on surgical planning and postoperative neurological outcomes in patients with spinal intramedullary tumors.

METHODS

The study was conducted retrospectively from the radiological and clinical data of our hospital database. Patients with intramedullary spinal cord tumors who underwent diffusion tensor imaging for spinal cord lesions were selected between 2019 and 2022. Demographic characteristics and intraoperative neurophysiological monitoring data were evaluated. The McCormick scale was used to grade the pre- and postoperative neurological status of the patients. The tumoral lesions were categorized into 3 types according to the fiber course on DTT.

RESULTS

Eleven patients were found to have radiological findings that were compatible with intramedullary tumor; eight (72.7%) of them ultimately underwent surgery following being approved as surgical candidates in the spinal diffusion tensor imaging studies. Six cases had Type 1, one case had Type 2, and 4 cases had Type 3 tumors according to the fiber course. All Type 1 tumors were classified as resectable and all of them were gross totally resected. Type 2 lesion that was rated as resectable by DTI was subtotally resected. Type 3 lesions were followed without surgery except the one with tumoral progression and neurological deficit. The postoperative neurological outcomes were compatible with intraoperative neurophysiological monitoring results.

CONCLUSION

Diffusion tensor imaging and tractography may be beneficial regarding the selection of patients suitable for surgery and in the subsequent surgical planning.

Spinal Tractography as a Potential Prognostic Tool in Spinal Cord Injury: A Systematic Review

Magnetic resonance imaging is considered the most accurate examination to study the spinal cord. Nevertheless, the use of diffusion tensor imaging (DTI) can demonstrate additional key details about spinal cord lesions. We examined the literature to investigate and discuss the role, limitations, and possible evolution as a prognostic tool of DTI in spinal cord injury (SCI). For this systematic literature review, a detailed search was performed using PubMed (2005-2021), Cochrane Database of Systematic Reviews (2016-2021), and Cochrane Central Register of Controlled Trials (2016-2021). To be included, studies had to report the use of DTI in SCIs, its clinical relevance, and its use as a prognostic tool. We identified 17 studies comprising 299 patients. The mean age of patients was 41.22 ± 10.62 years. There was a prevalence of males (70.9%) compared with females (29.1%). The main spinal cord tract involved and studied in SCIs was the cervical tract (57.5%), followed by conus terminalis (15.4%) and dorsal tract (13.7%). In all studies based on American Spine Injury Association impairment scale score for neurological assessment, a correlation was found between FA values and American Spine Injury Association impairment scale: patients with complete SCI had a statistically significative lower FA value at the injured site compared with patients with incomplete SCI. Published clinical studies showed promising results for the utility of DTI parameters as noninvasive biomarkers in SCI grade evaluation, remaining an evolving area of further investigation.

Brain Mechanisms of Pain and Dysautonomia in Diabetic Neuropathy: Connectivity Changes in Thalamus and Hypothalamus

CONTEXT

About one-third of diabetic patients suffer from neuropathic pain, which is poorly responsive to analgesic therapy and associated with greater autonomic dysfunction. Previous research on diabetic neuropathy mainly links pain and autonomic dysfunction to peripheral nerve degeneration resulting from systemic metabolic disturbances, but maladaptive plasticity in the central pain and autonomic systems following peripheral nerve injury has been relatively ignored.

OBJECTIVE

This study aimed to investigate how the brain is affected in painful diabetic neuropathy (PDN), in terms of altered structural connectivity (SC) of the thalamus and hypothalamus that are key regions modulating nociceptive and autonomic responses.

METHODS

We recruited 25 PDN and 13 painless (PLDN) diabetic neuropathy patients, and 27 healthy adults as controls. The SC of the thalamus and hypothalamus with limbic regions mediating nociceptive and autonomic responses was assessed using diffusion tractography.

RESULTS

The PDN patients had significantly lower thalamic and hypothalamic SC of the right amygdala compared with the PLDN and control groups. In addition, lower thalamic SC of the insula was associated with more severe peripheral nerve degeneration, and lower hypothalamic SC of the anterior cingulate cortex was associated with greater autonomic dysfunction manifested by decreased heart rate variability.

CONCLUSION

Our findings indicate that alterations in brain structural connectivity could be a form of maladaptive plasticity after peripheral nerve injury, and also demonstrate a pathophysiological association between disconnection of the limbic circuitry and pain and autonomic dysfunction in diabetes.

Partial Restoration of Spinal Cord Neural Continuity via Sural Nerve Transplantation Using a Technique of Spinal Cord Fusion

Background

Spinal cord injury (SCI) can cause paralysis and serious chronic morbidity, and there is no effective treatment. Based on our previous experimental results of spinal cord fusion (SCF) in mice, rats, beagles, and monkeys, we developed a surgical protocol of SCF for paraplegic human patients. We designed a novel surgical procedure of SCF, called sural nerve transplantation (SNT), for human patients with lower thoracic SCI and distal cord dysfunction.

Methods

We conducted a clinical trial (ChiCTR2000030788) and performed SNT in 12 fully paraplegic patients due to SCI between T1 and T12. We assessed pre- and postoperative central nerve pain, motor function, sensory function, and autonomic nerve function. Conduction of action potentials across the sural nerve transplant was evaluated. Neural continuity was also examined by diffusion tensor imaging (DTI).

Results

Among the 12 paraplegic patients enrolled in this clinical trial, seven patients demonstrated improved autonomic nerve functions. Seven patients had clinically significant relief of their symptoms of cord central pain. One patient, however, developed postoperative cord central pain (VAS: 4). Five patients had varying degrees of recovered sensory and/or motor functions below the single neurologic level 1 month after surgery. One patient showed recovery of electrophysiologic, motor-evoked potentials 6 months after the operation. At 6 months after surgery, DTI indicated fusion and nerve connections of white cord and sural nerves in seven patients.

Conclusion

SNT was able to fuse the axonal stumps of white cord and sural nerve and at least partially improve the cord central pain in most patients. Although SNT did not restore the spinal cord continuity in white matter in some patients, SNT could restore spinal cord continuity in the cortico-trunco-reticulo-propriospinal pathway, thereby restoring in part some motor and sensory functions. SNT may therefore be a safe, feasible, and effective method to treat paraplegic patients with SCI. Future clinical trials should be performed to optimize the type/technique of nerve transplantation, reduce surgical damage, and minimize postoperative scar formation and adhesion, to avoid postoperative cord central pain.

Clinical Trial Registration

[http://www.chictr.org.cn/showproj.aspx?proj=50526], identifier [ChiCTR2000030788].

Non-local means based Rician noise filtering for diffusion tensor and kurtosis imaging in human brain and spinal cord

BACKGROUND

To investigate the effect of using a Rician nonlocal means (NLM) filter on quantification of diffusion tensor (DT)- and diffusion kurtosis (DK)-derived metrics in various anatomical regions of the human brain and the spinal cord, when combined with a constrained linear least squares (CLLS) approach.

METHODS

Prospective brain data from 9 healthy subjects and retrospective spinal cord data from 5 healthy subjects from a 3 T MRI scanner were included in the study. Prior to tensor estimation, registered diffusion weighted images were denoised by an optimized blockwise NLM filter with CLLS. Mean kurtosis (MK), radial kurtosis (RK), axial kurtosis (AK), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) and fractional anisotropy (FA), were determined in anatomical structures of the brain and the spinal cord. DTI and DKI metrics, signal-to-noise ratio (SNR) and Chi-square values were quantified in distinct anatomical regions for all subjects, with and without Rician denoising.

RESULTS

The averaged SNR significantly increased with Rician denoising by a factor of 2 while the averaged Chi-square values significantly decreased up to 61% in the brain and up to 43% in the spinal cord after Rician NLM filtering. In the brain, the mean MK varied from 0.70 (putamen) to 1.27 (internal capsule) while AK and RK varied from 0.58 (corpus callosum) to 0.92 (cingulum) and from 0.70 (putamen) to 1.98 (corpus callosum), respectively. In the spinal cord, FA varied from 0.78 in lateral column to 0.81 in dorsal column while MD varied from 0.91 × 10^-3 mm²/s (lateral) to 0.93 × 10^-3 mm²/s (dorsal). RD varied from 0.34 × 10^-3 mm²/s (dorsal) to 0.38 × 10^-3 mm²/s (lateral) and AD varied from 1.96 × 10^-3 mm²/s (lateral) to 2.11 × 10^-3 mm²/s (dorsal).

CONCLUSIONS

Our results show a Rician denoising NLM filter incorporated with CLLS significantly increases SNR and reduces estimation errors of DT- and KT-derived metrics, providing the reliable metrics estimation with adequate SNR levels.

Effect of distortion corrections on the tractography quality in spinal cord diffusion-weighted imaging

PURPOSE

To assess the impact of a different distortion correction (DC) method and patient geometry (sagittal balance) on the quality of spinal cord tractography rendering according to different tractography approaches.

METHODS

Forty-four adults free of spinal cord diseases underwent cervical diffusion-weighted imaging. The phase-encoding direction was head→foot. Sequence with opposed polarities (foot→head) was acquired to perform DC. Eddy-current, motion effects, and susceptibility artifact correction methods were used for DC, and two deterministic and one probabilistic tractography approaches were evaluated using MRtrix and DSI Studio tractography software. Fiber length and number of fibers were extracted to evaluate the quality of the tractography rendering. For each subject, cervical lordosis was measured to assess patient geometry. The angle between the main direction of the spinal cord and the orientation of the acquisition box were computed at each spine level to assess acquisition geometry and define an angle threshold for which a tractography of good quality is no longer possible.

RESULTS

There was a significant improvement in tractography quality after performing DC with susceptibility artifact correction using a deterministic approach based on tensor. Before DC, the angle threshold was defined at C6 (15.2°) compared with C7 (21.9°) after corrections, demonstrating the importance of spinal cord angulation for DC.

CONCLUSION

The impact of DC on tractography quality is greatly impacted by acquisition geometry. To obtain a good-quality tractography, we propose as a future perspective to adapt the acquisition geometry to that of the patient by automatically adjusting the acquisition box.

Spatial correspondence of spinal cord white matter tracts using diffusion tensor imaging, fibre tractography, and atlas-based segmentation

PURPOSE

Neuroimaging provides great utility in complex spinal surgeries, particularly when anatomical geometry is distorted by pathology (tumour, degeneration, etc.). Spinal cord MRI diffusion tractography can be used to generate streamlines; however, it is unclear how well they correspond with white matter tract locations along the cord microstructure. The goal of this work was to evaluate the spatial correspondence of DTI tractography with anatomical MRI in healthy anatomy (where anatomical locations can be well defined in T1-weighted images).

METHODS

Ten healthy volunteers were scanned on a 3T system. T1-weighted (1 × 1 × 1 mm) and diffusion-weighted images (EPI readout, 2 × 2 × 2 mm, 30 gradient directions) were acquired and subsequently registered (Spinal Cord Toolbox (SCT)). Atlas-based (SCT) anatomic label maps of the left and right lateral corticospinal tracts were identified for each vertebral region (C2-C6) from T1 images. Tractography streamlines were generated with a customized approach, enabling seeding of specific spinal tract regions corresponding to individual vertebral levels. Spatial correspondence of generated fibre streamlines with anatomic tract segmentations was compared in unseeded regions of interest (ROIs).

RESULTS

Spatial correspondence of the lateral corticospinal tract streamlines was good over a single vertebral ROI (Dice's similarity coefficient (DSC) = 0.75 ± 0.08, Hausdorff distance = 1.08 ± 0.17 mm). Over larger ROI, fair agreement between tractography and anatomical labels was achieved (two levels: DSC = 0.67 ± 0.13, three levels: DSC = 0.52 ± 0.19).

CONCLUSION

DTI tractography produced good spatial correspondence with anatomic white matter tracts, superior to the agreement between multiple manual tract segmentations (DSC ~ 0.5). This supports further development of spinal cord tractography for computer-assisted neurosurgery.

Multi-shot echo-planar diffusion tensor imaging in cervical spondylotic myelopathy

AIMS

The aim of this study was to use diffusion tensor imaging (DTI) to investigate changes in diffusion metrics in patients with cervical spondylotic myelopathy (CSM) up to five years after decompressive surgery. We correlated these changes with clinical outcomes as scored by the Modified Japanese Orthopedic Association (mJOA) method, Neck Disability Index (NDI), and Visual Analogue Scale (VAS).

METHODS

We used multi-shot, high-resolution, diffusion tensor imaging (ms-DTI) in patients with cervical spondylotic myelopathy (CSM) to investigate the change in diffusion metrics and clinical outcomes up to five years after anterior cervical interbody discectomy and fusion (ACDF). High signal intensity was identified on T2-weighted imaging, along with DTI metrics such as fractional anisotropy (FA). MJOA, NDI, and VAS scores were also collected and compared at each follow-up point. Spearman correlations identified correspondence between FA and clinical outcome scores.

RESULTS

Significant differences in mJOA scores and FA values were found between preoperative and postoperative timepoints up to two years after surgery. FA at the level of maximum cord compression (MCL) preoperatively was significantly correlated with the preoperative mJOA score. FA postoperatively was also significantly correlated with the postoperative mJOA score. There was no statistical relationship between NDI and mJOA or VAS.

CONCLUSION

ms-DTI can detect microstructural changes in affected cord segments and reflect functional improvement. Both FA values and mJOA scores showed maximum recovery two years after surgery. The DTI metrics are significantly associated with pre- and postoperative mJOA scores. DTI metrics are a more sensitive, timely, and quantifiable surrogate for evaluating patients with CSM and a potential quantifiable biomarker for spinal cord dysfunction. Cite this article: Bone Joint J 2020;102-B(9):1210-1218.

Multi-parametric quantitative in vivo spinal cord MRI with unified signal readout and image denoising

Multi-parametric quantitative MRI (qMRI) of the spinal cord is a promising non-invasive tool to probe early microstructural damage in neurological disorders. It is usually performed in vivo by combining acquisitions with multiple signal readouts, which exhibit different thermal noise levels, geometrical distortions and susceptibility to physiological noise. This ultimately hinders joint multi-contrast modelling and makes the geometric correspondence of parametric maps challenging. We propose an approach to overcome these limitations, by implementing state-of-the-art microstructural MRI of the spinal cord with a unified signal readout in vivo (i.e. with matched spatial encoding parameters across a range of imaging contrasts). We base our acquisition on single-shot echo planar imaging with reduced field-of-view, and obtain data from two different vendors (vendor 1: Philips Achieva; vendor 2: Siemens Prisma). Importantly, the unified acquisition allows us to compare signal and noise across contrasts, thus enabling overall quality enhancement via multi-contrast image denoising methods. As a proof-of-concept, here we provide a demonstration with one such method, known as Marchenko-Pastur (MP) Principal Component Analysis (PCA) denoising. MP-PCA is a singular value (SV) decomposition truncation approach that relies on redundant acquisitions, i.e. such that the number of measurements is large compared to the number of components that are maintained in the truncated SV decomposition. Here we used in vivo and synthetic data to test whether a unified readout enables more efficient MP-PCA denoising of less redundant acquisitions, since these can be denoised jointly with more redundant ones. We demonstrate that a unified readout provides robust multi-parametric maps, including diffusion and kurtosis tensors from diffusion MRI, myelin metrics from two-pool magnetisation transfer, and T1 and T2 from relaxometry. Moreover, we show that MP-PCA improves the quality of our multi-contrast acquisitions, since it reduces the coefficient of variation (i.e. variability) by up to 17% for mean kurtosis, 8% for bound pool fraction (myelin-sensitive), and 13% for T1, while enabling more efficient denoising of modalities limited in redundancy (e.g. relaxometry). In conclusion, multi-parametric spinal cord qMRI with unified readout is feasible and provides robust microstructural metrics with matched resolution and distortions, whose quality benefits from multi-contrast denoising methods such as MP-PCA.

Diffusion tensor imaging with fiber tracking provides a valuable quantitative and clinical evaluation for compressed lumbosacral nerve roots: a systematic review and meta-analysis

PURPOSE

This study aimed to investigate the diagnostic value of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the diffusion tensor imaging (DTI) with fiber tracking in patients with compressed lumbosacral nerve roots.

METHODS

A systematic literature search of databases (PubMed, Embase, Cochrane Library, and Web of Science) was carried out. FA values and ADC values were compared between compressed nerve roots and healthy controls. Pooled and subgroup analyses were performed using fixed or random-effect models based on I² heterogeneity.

RESULTS

A total of 262 patients from ten studies with 285 compressed lumbosacral nerve roots and 285 contralateral normal nerve roots were included in the meta-analysis. It was showed in pooled results that FA value was significantly reduced (SMD  - 3.03, 95% CI [ - 3.75 to  - 2.31], P < 0.001) and ADC value was significantly increased (SMD 2.07, 95% CI [0.92 to 3.22], P < 0.001) in the compressed nerve roots, compared with contralateral normal nerve roots. Subgroup analysis comparing the FA values and ADC values in different nerve root ranges (L2-S1, L4-S1, L5-S1, L5, S1) revealed the different ranges of nerve roots were possible sources of heterogeneity.

CONCLUSIONS

This study showed that FA value reduction and ADC value increase were valuable indicators of compressed lumbosacral nerve roots. These changes may be related to the neurological symptoms of patients. DTI with fiber tracking can directly visualize and accurately locate the compression zone of nerve roots to help make surgical treatment plans, is more advanced than conventional MRI.

Diffusion tensor imaging shows mechanism-specific differences in injury pattern and progression in rat models of acute spinal cord injury

We investigate the ability of diffusion tensor imaging (DTI) to distinguish between three experimental rat models of spinal cord injury mechanism - contusion, dislocation, and distraction. Ex vivo DTI scans were performed on cord specimens that were preserved at different time points of the acute injury (3 hr, 24 hr, and 7 days post-injury) across all three injury mechanisms. White matter was classified as abnormal if their DTI metric was substantially different from regional values measured from a set of uninjured controls, thus allowing generation of binary "white matter damage maps" which categorizes each pixel in the DTI image as "normal" or "damaged". Damage classification was most robust using thresholds in the longitudinal diffusivity, which supports previous studies that show that longitudinal diffusivity is the most robust DTI metric in depicting damage in SCI. Furthermore, the spatial damage patterns from all subjects in the same group were consolidated into a "damage occurrence ratio map", which illustrates an average damage shape that characterizes the injury mechanism. Our analysis has yielded a dataset which highlights the differences in injury pattern due to the initial mode of mechanical injury. For example, contusion produced an initial injury that emanated radially outward from the central canal, with subsequent damage along the caudal corticospinal tract and rostral gracile fasciculus; dislocation injuries showed a high level of involvement in the lateral and ventral white matter which became less apparent by 7 days post-injury, and distraction injuries were found to be less focal and more distributed rostrocaudally. This work represents a first step in adopting the use of the primary injury mechanism as a clinical prognostic factor in SCI, which may help to inform the trialing of existing neuroprotective treatment candidates, the development of new therapies as well as personalize the management of SCI for the individual patient.

The role of diffusion tensor imaging as an objective tool for the assessment of motor function recovery after paraplegia in a naturally-occurring large animal model of spinal cord injury

Background

Traumatic spinal cord injury (SCI) results in sensory and motor function impairment and may cause a substantial social and economic burden. For the implementation of novel treatment strategies, parallel development of objective tools evaluating spinal cord (SC) integrity during motor function recovery (MFR) is needed. Diffusion tensor imaging (DTI) enables in vivo microstructural assessment of SCI.

Methods

In the current study, temporal evolvement of DTI metrics during MFR were examined; therefore, values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in a population of 17 paraplegic dogs with naturally-occurring acute SCI showing MFR within 4 weeks after surgical decompression and compared to 6 control dogs. MRI scans were performed preoperatively and 12 weeks after MFR was observed. DTI metrics were obtained at the lesion epicentre and one SC segment cranially and caudally. Variance analyses were performed to compare values between evaluated localizations in affected dogs and controls and between time points. Correlations between DTI metrics and clinical scores at follow-up examinations were assessed.

Results

Before surgery, FA values at epicentres were higher than caudally (p = 0.0014) and control values (p = 0.0097); ADC values were lower in the epicentre compared to control values (p = 0.0035) and perilesional (p = 0.0448 cranially and p = 0.0433 caudally). In follow-up examinations, no significant differences could be found between DTI values from dogs showing MFR and control dogs. Lower ADC values at epicentres correlated with neurological deficits at follow-up examinations (r = − 0.705; p = 0.0023).

Conclusions

Findings suggest that a tendency to the return of DTI values to the physiological situation after surgical decompression accompanies MFR after SCI in paraplegic dogs. DTI may represent a useful and objective clinical tool for follow-up studies examining in vivo SC recovery in treatment studies.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1630-4) contains supplementary material, which is available to authorized users.

Mechanical relationship of filum terminale externum and filum terminale internum: is it possible to detether the spinal cord extradurally?

INTRODUCTION

Intradural transection of the filum terminale (FTI) is often used to treat tethered cord syndrome. Recently, some have proposed that the extradural part of the filum terminale (FTE) can be sectioned with equal results but with fewer complications. Therefore, the present cadaveric study aimed to evaluate the anatomical foundation of such procedures.

METHODS

A posterior lumbosacral approach was performed on five fresh-frozen cadaveric specimens to expose both the FTI and FTE. Tension was then applied to the FTE and observations and measurements made of any movement of the FTI. Other morphological measurements (e.g., length, diameter) of the FTI and FTE were also made.

RESULTS

Although very minimal movement of the FTI was seen in the majority of specimens following tension on the FTE, no specimen was found to have more cranial movement of the conus medullaris or cauda equina. The mean length and diameter of the FTI was 52.2 and 0.38 mm, respectively. The mean length and diameter of the FTE was 77 and 0.60 mm, respectively. The force necessary to move the FTI with tension applied to the FTE had a mean of 0.03 N. The average distance that the FTI moved with distal FTE tension was 1.33 mm. All specimens had a thecal sac that terminated at the S2 vertebral level. And no specimen had a low-lying conus medullaris, cutaneous stigmata of occult spinal dysraphism, or grossly visible adipose tissue in either the FTI or FTE.

CONCLUSIONS

Based on our studies, tension placed on the FTE has very little effect on the FTI and no obvious effect on the conus medullaris or cauda equina. Therefore, isolated transection of the FTE for a patient with tethered cord syndrome is unlikely to have significant effect. To our knowledge, this is the first study to quantitate the distal forces needed on the FTE to move the FTI.

Ameliorating Spinal Cord Injury in an Animal Model With Mechanical Tissue Resuscitation

BACKGROUND

Traumatic spinal cord injury (SCI) is a major worldwide cause of mortality and disability with limited treatment options. Previous research applying controlled negative pressure to traumatic brain injury in rat and swine models resulted in smaller injuries and more rapid recovery.

OBJECTIVE

To examine the effects of the application of a controlled vacuum (mechanical tissue resuscitation [MTR]) to SCI in a rat model under several magnitudes of vacuum.

METHODS

Controlled contusion SCIs were created in rats. Vacuums of -50 and -75 mm Hg were compared. Analysis included open-field locomotor performance, magnetic resonance imaging (in vivo T2, ex vivo diffusion tensor imaging and fiber tractography), and histological assessments.

RESULTS

MTR treatment significantly improved the locomotor recovery from a Basso, Beattie, and Bresnahan score of 7.8 ± 1.9 to 11.4 ± 1.2 and 10.7 ± 1.9 at -50- and -75-mm Hg pressures, respectively, 4 weeks after injury. Both pressures also reduced fluid accumulations > 10% by T2-imaging in SCI sites. The mean fiber number and mean fiber length were greater across injured sites after MTR treatment, especially with treatment with -50 mm Hg. Myelin volume was increased significantly by 60% in the group treated with -50 mm Hg.

CONCLUSION

MTR of SCI in a rat model is effective in reducing edema in the injured cord, preserving myelin survival, and improving the rate and quantity of functional recovery.

ABBREVIATIONS

BBB, Basso, Beattie, and BresnahanDTI, diffusion tensor imagingFA, fractional anisotropyMTR, mechanical tissue resuscitationMTR50, mechanical tissue resuscitation with 50-mm Hg subatmospheric pressureMTR75, mechanical tissue resuscitation with 75-mm Hg subatmospheric pressureROI, region of interestSCI, spinal cord injury.

High-resolution diffusion tensor imaging in cervical spondylotic myelopathy: a preliminary follow-up study

Diffusion imaging is a promising technique as it can provide microstructural tissue information and thus potentially show viable changes in spinal cord. However, the traditional single-shot imaging method is limited as a result of various image artifacts. In order to improve measurement accuracy, we used a newly developed, multi-shot, high-resolution, diffusion tensor imaging (DTI) method to investigate diffusion metric changes and compare them with T₂ -weighted (T2W) images before and after decompressive surgery for cervical spondylotic myelopathy (CSM). T2W imaging, single-shot DTI and multi-shot DTI were employed to scan seven patients with CSM before and 3 months after decompressive surgery. High signal intensities were scored using the T2 W images. DTI metrics, including fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD), were quantified and compared pre- and post-surgery. In addition, the relationship between imaging metrics and neurological assessments was examined. The reproducibility of multi-shot DTI was also assessed in 10 healthy volunteers. Post-surgery, the mean grade of cervical canal stenosis was reduced from grade 3 to normal after 3 months. Compared with single-shot DTI, multi-shot DTI provided better images with lower artifact levels, especially following surgery, as a result of reduced artifacts from metal implants. The new method also showed acceptable reproducibility. Both FA and RD values from the new acquisition showed significant differences post-surgery (FA, p = 0.026; RD, p = 0.048). These changes were consistent with neurological assessments. In contrast, T2W images did not show significant changes before and after surgery. Multi-shot diffusion imaging showed improved image quality over single-shot DWI, and presented superior performance in diagnosis and recovery monitoring for patients with CSM compared with T2W imaging. DTI metrics can reflect the pathological conditions of spondylotic spinal cord quantitatively and may serve as a sensitive biomarker for potential CSM management.

Advances in High-Field MRI

MRI techniques and systems have evolved dramatically over recent years. These advances include higher field strengths, new techniques, faster gradients, improved coil technology, and more robust sequence protocols. This article reviews the most commonly used advanced MRI techniques, including diffusion-weighted imaging, magnetic resonance spectrography, diffusion tensor imaging, and cerebrospinal fluid flow tracking.

Comparison of Preoperative Quantitative Magnetic Resonance Imaging and Clinical Assessment of Deep Pain Perception as Prognostic Tools for Early Recovery of Motor Function in Paraplegic Dogs with Intervertebral Disk Herniations

Background

Prognostic tools to predict early postoperative motor function recovery (MFR) after thoracolumbar intervertebral disk herniation (IVDH) in paraplegic dogs represent an opportunity to timely implement novel therapies that could shorten recovery times and diminish permanent neurological dysfunctions.

Hypothesis

Fractional anisotropy (FA) values obtained using diffusion tensor imaging have a higher prognostic value than a lesion extension ratio in T2‐weighted images (T2W‐LER) and clinical assessment of deep pain perception (DPP) for MFR.

Animals

Thirty‐five paraplegic dogs with diagnosis of acute or subacute thoracolumbar IVDH.

Methods

Prospective, descriptive observational study. At admission, absence or presence of DPP, T2W‐LER, and FA values was evaluated. MFR was assessed within 4 weeks after decompressive surgery. Values of T2W‐LER and FA of dogs with and without MFR were compared using t‐tests. All 3 methods were evaluated for their sensitivity and specificity as a prognostic factor.

Results

No differences were found between groups regarding T2W‐LER. FA values differed statistically when measured caudally of lesion epicenter being higher in dogs without MFR compared to dogs with MFR (P = .023). Logistic regression analysis revealed significance in FA values measured caudally of the lesion epicenter (P = .033, area under the curve = 0.72). Using a cutoff value of FA = 0.660, the technique had a sensitivity of 80% and a specificity of 55%. Evaluation of DPP had a sensitivity of 73.3% and specificity of 75% (P = .007).

Conclusions and Clinical Importance

Evaluation of DPP showed a similar sensitivity and a better specificity predicting early MFR than quantitative magnetic resonance imaging.

Intracranial Connections of the Vertebral Venous Plexus: Anatomical Study with Application to Neurosurgical and Endovascular Procedures at the Craniocervical Junction

BACKGROUND

Descriptions of intracranial extensions of vertebral venous plexuses are lacking.

OBJECTIVE

To identify vertebral venous plexuses at the craniocervical junction in cadavers and describe them.

METHODS

The authors dissected 15 ink-injected, formalin-fixed, adult cadaveric heads and measured cranial extensions of the spinal venous plexuses.

RESULTS

All specimens had vertebral venous plexuses at the craniocervical junction composed of multiple interwoven vessels concentrated anteriorly (anterior vertebral plexuses), posteriorly (posterior vertebral venous plexuses), and laterally (lateral vertebral venous plexuses). Veins making up the plexus tended to be largest for the anterior internal vertebral venous plexus. On 33%, a previously unnamed lateral internal vertebral venous plexus was identified that connected to the lateral marginal sinus. The anterior external vertebral venous plexus connected to the basilar venous plexus via transclival emissary veins in 13%; remaining veins connected either intracranially via small perforating branches through the anterior atlanto-occipital membrane (33%) or had no direct gross connections inside the cranium (53%). The anterior internal vertebral plexus, which traveled between layers of the posterior longitudinal ligament, connected to the anterior half of the marginal sinus in 33% and anterolateral parts of the marginal sinus in 20%. The posterior internal venous plexus connected to the posterior aspect of the marginal sinus on 80% and into the occipital sinus in 13.3%. The posterior external venous plexus connected to veins of the hypoglossal canal in 20% and into the posterior aspect of the marginal sinus in 13.3%.

CONCLUSION

Knowledge of these connections is useful to neurosurgeons and interventional radiologists.

Diffusion MRI of the spinal cord: from structural studies to pathology

Diffusion MRI is extensively used to study brain microarchitecture and pathologies, and water diffusion appears highly anisotropic in the white matter (WM) of the spinal cord (SC). Despite these facts, the use of diffusion MRI to study the SC, which has increased in recent years, is much less common than that in the brain. In the present review, after a brief outline of early studies of diffusion MRI (DWI) and diffusion tensor MRI (DTI) of the SC, we provide a short survey on DTI and on diffusion MRI methods beyond the tensor that have been used to study SC microstructure and pathologies. After introducing the porous view of WM and describing the q-space approach and q-space diffusion MRI (QSI), we describe other methodologies that can be applied to study the SC. Selected applications of the use of DTI, QSI, and other more advanced diffusion MRI methods to study SC microstructure and pathologies are presented, with some emphasis on the use of less conventional diffusion methodologies. Because of length constraints, we concentrate on structural studies and on a few selected pathologies. Examples of the use of diffusion MRI to study dysmyelination, demyelination as in experimental autoimmune encephalomyelitis and multiple sclerosis, amyotrophic lateral sclerosis, and traumatic SC injury are presented. We conclude with a brief summary and a discussion of challenges and future directions for diffusion MRI of the SC. Copyright © 2016 John Wiley & Sons, Ltd.

MRI Atlas-Based Measurement of Spinal Cord Injury Predicts Outcome in Acute Flaccid Myelitis

BACKGROUND AND PURPOSE

Recent advances in spinal cord imaging analysis have led to the development of a robust anatomic template and atlas incorporated into an open-source platform referred to as the Spinal Cord Toolbox. Using the Spinal Cord Toolbox, we sought to correlate measures of GM, WM, and cross-sectional area pathology on T2 MR imaging with motor disability in patients with acute flaccid myelitis.

MATERIALS AND METHODS

Spinal cord imaging for 9 patients with acute flaccid myelitis was analyzed by using the Spinal Cord Toolbox. A semiautomated pipeline using the Spinal Cord Toolbox measured lesion involvement in GM, WM, and total spinal cord cross-sectional area. Proportions of GM, WM, and cross-sectional area affected by T2 hyperintensity were calculated across 3 ROIs: 1) center axial section of lesion; 2) full lesion segment; and 3) full cord atlas volume. Spearman rank order correlation was calculated to compare MR metrics with clinical measures of disability.

RESULTS

Proportion of GM metrics at the center axial section significantly correlated with measures of motor impairment upon admission (r [9] = -0.78; P = .014) and at 3-month follow-up (r [9] = -0.66; P = .05). Further, proportion of GM extracted across the full lesion segment significantly correlated with initial motor impairment (r [9] = -0.74, P = .024). No significant correlation was found for proportion of WM or proportion of cross-sectional area with clinical disability.

CONCLUSIONS

Atlas-based measures of proportion of GM T2 signal abnormality measured on a single axial MR imaging section and across the full lesion segment correlate with motor impairment and outcome in patients with acute flaccid myelitis. This is the first atlas-based study to correlate clinical outcomes with segmented measures of T2 signal abnormality in the spinal cord.

Microstructural changes in compressed nerve roots treated by percutaneous transforaminal endoscopic discectomy in patients with lumbar disc herniation

To investigate the microstructural changes in compressed nerves using diffusion tensor imaging (DTI) of herniated disc treated with percutaneous transforaminal endoscopic discectomy.Diffusion tensor imaging has been widely used to visualize peripheral nerves, and the microstructure of compressed nerve roots can be assessed using DTI. However, the microstructural changes after surgery are not well-understood in patients with lumbar disc herniation.Thirty-four consecutive patients with foraminal disc herniation affecting unilateral sacral 1 (S1) nerve roots were enrolled in this study. DTI with tractography was performed on S1 nerve roots before and after surgery. The mean fractional anisotropy (FA) and apparent diffusion coefficient values were calculated from tractography images.In compressed nerve roots, the FA value before surgery was significantly lower than that after surgery (P = 0.000). A significant difference in FA values was found between the compressed and normal sides before surgery (P = 0.000). However, no significant difference was found between the compressed and normal sides after surgery (P = 0.057). A significant difference in apparent diffusion coefficient values was found before and after surgery at the compressed side (P = 0.023). However, no significant difference was found between the compressed and normal sides after surgery (P = 0.203).We show that the diffusion parameters of compressed nerve roots were not significantly different before and after percutaneous transforaminal endoscopic discectomy, indicating that the microstructure of the nerve root recovered after surgery.

An Imaging-Based Approach to Spinal Cord Infection

Infections of the spinal cord, nerve roots, and surrounding meninges are uncommon, but highly significant given their potential for severe morbidity and even mortality. Prompt diagnosis can be lifesaving, as many spinal infections are treatable. Advances in imaging technology have now firmly established magnetic resonance imaging (MRI) as the gold standard for spinal cord imaging evaluation, enabling the depiction of infectious myelopathies with exquisite detail and contrast. In this article, we aim to provide an overview of MRI findings for spinal cord infections with special focus on imaging patterns of infection that are primarily confined to the spinal cord, spinal meninges, and spinal nerve roots. In this context, we describe and organize this review around 5 distinct patterns of transverse spinal abnormality that may be detected with MRI as follows: (1) extramedullary, (2) centromedullary, (3) eccentric, (4) frontal horn, and (5) irregular. We seek to classify the most common presentations for a wide variety of infectious agents within this image-based framework while realizing that significant overlap and variation exists, including some infections that remain occult with conventional imaging techniques.

Tract-specific and age-related variations of the spinal cord microstructure: a multi-parametric MRI study using diffusion tensor imaging (DTI) and inhomogeneous magnetization transfer (ihMT)

Being able to finely characterize the spinal cord (SC) microstructure and its alterations is a key point when investigating neural damage mechanisms encountered in different central nervous system (CNS) pathologies, such as multiple sclerosis, amyotrophic lateral sclerosis or myelopathy. Based on novel methods, including inhomogeneous magnetization transfer (ihMT) and dedicated SC probabilistic atlas post-processing, the present study focuses on the in vivo characterization of the healthy SC tissue in terms of regional microstructure differences between (i) upper and lower cervical vertebral levels and (ii) sensory and motor tracts, as well as differences attributed to normal aging. Forty-eight healthy volunteers aged from 20 to 70 years old were included in the study and scanned at 3 T using axial high-resolution T2 *-w imaging, diffusion tensor imaging (DTI) and ihMT, at two vertebral levels (C2 and C5). A processing pipeline with minimal user intervention, SC segmentation and spatial normalization into a reference space was implemented in order to assess quantitative morphological and structural parameters (cross-sectional areas, scalar DTI and MT/ihMT metrics) in specific white and gray matter regions of interest. The multi-parametric MRI metrics collected allowed upper and lower cervical levels to be distinguished, with higher ihMT ratio (ihMTR), higher axial diffusivity (λ∥ ) and lower radial diffusivity (λ⊥ ) at C2 compared with C5. Significant differences were also observed between white matter fascicles, with higher ihMTR and lower λ∥ in motor tracts compared with posterior sensory tracts. Finally, aging was found to be associated with significant metric alterations (decreased ihMTR and λ∥ ). The methodology proposed here, which can be easily transferred to the clinic, provides new insights for SC characterization. It bears great potential to study focal and diffuse SC damage in neurodegenerative and demyelinating diseases. Copyright © 2016 John Wiley & Sons, Ltd.

Pain and spinal cord imaging measures in children with demyelinating disease

Pain is a significant problem in diseases affecting the spinal cord, including demyelinating disease. To date, studies have examined the reliability of clinical measures for assessing and classifying the severity of spinal cord injury (SCI) and also to evaluate SCI-related pain. Most of this research has focused on adult populations and patients with traumatic injuries. Little research exists regarding pediatric spinal cord demyelinating disease. One reason for this is the lack of reliable and useful approaches to measuring spinal cord changes since currently used diagnostic imaging has limited specificity for quantitative measures of demyelination. No single imaging technique demonstrates sufficiently high sensitivity or specificity to myelin, and strong correlation with clinical measures. However, recent advances in diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) measures are considered promising in providing increasingly useful and specific information on spinal cord damage. Findings from these quantitative imaging modalities correlate with the extent of demyelination and remyelination. These techniques may be of potential use for defining the evolution of the disease state, how it may affect specific spinal cord pathways, and contribute to the management of pediatric demyelination syndromes. Since pain is a major presenting symptom in patients with transverse myelitis, the disease is an ideal model to evaluate imaging methods to define these regional changes within the spinal cord. In this review we summarize (1) pediatric demyelinating conditions affecting the spinal cord; (2) their distinguishing features; and (3) current diagnostic and classification methods with particular focus on pain pathways. We also focus on concepts that are essential in developing strategies for the detection, monitoring, treatment and repair of pediatric myelitis.

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Pain is a major presenting symptom in children with myelitis.

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Currently used imaging has limited sensitivity to myelin content.

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We provide a summary on pediatric demyelinating conditions.

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We review pain involvement and pathways affected by demyelination.

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We review imaging modalities for the diagnosis and monitoring of myelitis.

Diffusion tensor imaging in cervical syringomyelia secondary to Chiari I malformation: preliminary results

STUDY DESIGN

A prospective observational analysis.

OBJECTIVE

The aim was to perform a quantitative analysis of the neuronal status in cervical syringomyelia secondary to Chiari I malformation (CMI-S) using diffusion tensor imaging.

SUMMARY OF BACKGROUND DATA

Syringomyelia is a common finding in patients with CMI. Conventional imaging techniques frequently fail to assist clinicians in quantitatively assessing the neural damage in these patients.

METHODS

Twenty-three patients with CMI-S (aged 8-25 yr) were prospectively enrolled from April 2012 to August 2013. Sensitivity encoding single-shot echo-planar imaging was used for the sagittal diffusion tensor imaging. Fractional anisotropy (FA) values in the spinal cord were compared between the patients and normal volunteers and further evaluated with respect to syrinx severity and neurological signs/symptoms.

RESULTS

Compared with the normal controls, the FA values were significantly decreased at the level of the syrinx (0.429 ± 0.015 vs. 0.533 ± 0.007; P < 0.001), whereas no significant decreased FA value was measured in the tissue rostral and caudal to the syrinx. Concerning patients with different size of the syrinx, significantly decreased FA values at the syrinx level were observed in patients with a distended syrinx in comparison with those with a nondistended syrinx (0.397 ± 0.013 vs. 0.480 ± 0.018; P < 0.001). Moreover, the FA value at the syrinx level was found to be significantly decreased in the symptomatic group when compared with the nonsymptomatic or control groups (P < 0.05), and there was also a significant difference between the 2 latter groups (P < 0.05).

CONCLUSION

Decreased FA value at the syrinx levels may provide evidence of increased microstructural damage within the spinal cord parenchyma at this area, and changes in this diffusion tensor imaging parameter are significantly related to syrinx size and to the appearance of neurological signs/symptoms.

LEVEL OF EVIDENCE

4.