Magnetic resonance neurography: diffusion tensor imaging and future directions

Advances in Imaging of Compressive Neuropathies

Ultrasound and magnetic resonance neurography are useful modalities to aid in the assessment of compressive neuropathies, although they are still limited in their resolution of nerve microstructure and their capacity to monitor postoperative nerve recovery. Optical coherence tomography, a preclinical imaging modality, is promising in its ability to better identify structural and potential physiologic changes to peripheral nerves, but requires additional testing and research prior to widespread clinical implementation. Further advances in nerve imaging may elucidate the ability to visualize the zone of nerve injury intraoperatively, monitor the progression of nerve regeneration, and localize problems during nerve recovery.

Imaging Biomarkers of Peripheral Nerves: Focus on Magnetic Resonance Neurography and Ultrasonography

Peripheral neuropathy is a prevalent and debilitating condition affecting millions of individuals globally. Magnetic resonance neurography (MRN) and ultrasonography (US) are noninvasive methods offering comprehensive visualization of peripheral nerves, using anatomical and functional imaging biomarkers to ensure accurate evaluation. For optimized MRN, superior and high-resolution two-dimensional and three-dimensional imaging protocols are essential. The anatomical MRN and US imaging markers include quantitative measures of nerve and fascicular size and signal, and qualitative markers of course and morphology. Among them, quantitative markers of T2-signal intensity ratio are sensitive to nerve edema-like signal changes, and the T1-mapping technique reveals nerve and muscle tissue fatty and fibrous compositional alterations.The functional markers are derived from physiologic properties of nerves, such as diffusion characteristics or blood flow. They include apparent diffusion coefficient from diffusion-weighted imaging and fractional anisotropy and tractography from diffusion tensor imaging to delve into peripheral nerve microstructure and integrity. Peripheral nerve perfusion using dynamic contrast-enhanced magnetic resonance imaging estimates perfusion parameters, offering insights into nerve health and neuropathies involving edema, inflammation, demyelination, and microvascular alterations in conditions like type 2 diabetes, linking nerve conduction pathophysiology to vascular permeability alterations.Imaging biomarkers thus play a pivotal role in the diagnosis, prognosis, and monitoring of nerve pathologies, thereby ensuring comprehensive assessment and elevating patient care. These biomarkers provide valuable insights into nerve structure, function, and pathophysiology, contributing to the accurate diagnosis and management planning for peripheral neuropathy.

Diffusion Tensor Imaging of Peripheral Nerves: Current Status and New Developments

Diffusion tensor imaging (DTI) is an emerging technique for peripheral nerve imaging that can provide information about the microstructural organization and connectivity of these nerves and complement the information gained from anatomical magnetic resonance imaging (MRI) sequences. With DTI it is possible to reconstruct nerve pathways and visualize the three-dimensional trajectory of nerve fibers, as in nerve tractography. More importantly, DTI allows for quantitative evaluation of peripheral nerves by the calculation of several important parameters that offer insight into the functional status of a nerve. Thus DTI has a high potential to add value to the work-up of peripheral nerve pathologies, although it is more technically demanding. Peripheral nerves pose specific challenges to DTI due to their small diameter and DTI's spatial resolution, contrast, location, and inherent field inhomogeneities when imaging certain anatomical locations. Numerous efforts are underway to resolve these technical challenges and thus enable wider acceptance of DTI in peripheral nerve MRI.

Correlation between diffusion tensor indices and fascicular morphometric parameters of peripheral nerve

Introduction: Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that measures the anisotropy of water diffusion. Clinical magnetic resonance imaging scanners enable visualization of the structural integrity of larger axonal bundles in the central nervous system and smaller structures like peripheral nerves; however, their resolution for the depiction of nerve fascicular morphology is limited. Accordingly, high-field strength MRI and strong magnetic field gradients are needed to depict the fascicular pattern. The study aimed to quantify diffusion tensor indices with high-field strength MRI within different anatomical compartments of the median nerve and determine if they correlate with nerve structure at the fascicular level. Methods: Three-dimensional pulsed gradient spin-echo (PGSE) imaging sequence in 19 different gradient directions and b value 1,150 s/mm² was performed on a 9.4T wide-bore vertical superconducting magnet. Nine-millimeter-long segments of five median nerve samples were obtained from fresh cadavers and acquired in sixteen 0.625 mm thick slices. Each nerve sample had the fascicles, perineurium, and interfascicular epineurium segmented. The diffusion tensor was calculated from the region-average diffusion-weighted signals for all diffusion gradient directions. Subsequently, correlations between diffusion tensor indices of segmentations and nerve structure at the fascicular level (number of fascicles, fascicular ratio, and cross-sectional area of fascicles or nerve) were assessed. The acquired diffusion tensor imaging data was employed for display with trajectories and diffusion ellipsoids. Results: The nerve fascicles proved to be the most anisotropic nerve compartment with fractional anisotropy 0.44 ± 0.05. In the interfascicular epineurium, the diffusion was more prominent in orthogonal directions with fractional anisotropy 0.13 ± 0.02. Diffusion tensor indices within the fascicles and perineurium differed significantly between the subjects (p < 0.0001); however, there were no differences within the interfascicular epineurium (p ≥ 0.37). There were no correlations between diffusion tensor indices and nerve structure at the fascicular level (p ≥ 0.29). Conclusion: High-field strength MRI enabled the depiction of the anisotropic diffusion within the fascicles and perineurium. Diffusion tensor indices of the peripheral nerve did not correlate with nerve structure at the fascicular level. Future studies should investigate the relationship between diffusion tensor indices at the fascicular level and axon- and myelin-related parameters.

Methodologies and MR Parameters in Quantitative Magnetic Resonance Neurography: A Scoping Review Protocol

Magnetic resonance neurography (MRN), the MR imaging of peripheral nerves, is clinically used for assessing and monitoring peripheral neuropathies based on qualitative, weighted MR imaging. Recently, quantitative MRN has been increasingly reported with various MR parameters as potential biomarkers. An evidence synthesis mapping the available methodologies and normative values of quantitative MRN of human peripheral nerves, independent of the anatomical location and type of neuropathy, is currently unavailable and would likely benefit this young field of research. Therefore, the proposed scoping review will include peer-reviewed literature describing methodologies and normative values of quantitative MRN of human peripheral nerves. The literature search will include the databases MEDLINE (PubMed), EMBASE (Ovid), Web of Science, and Scopus. At least two independent reviewers will screen the titles and abstracts against the inclusion criteria. Potential studies will then be screened in full against the inclusion criteria by two or more independent reviewers. From all eligible studies, data will be extracted by two or more independent reviewers and presented in a diagrammatic or tabular form, separated by MR parameter and accompanied by a narrative summary. The reporting will follow the guidelines of the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Upon completion, the scoping review will provide a map of the available literature, identify possible gaps, and inform on possible future research. SCOPING REVIEW REGISTRATION: Open Science Framework 9P3ZM.

Assessment of peripheral neuropathy in type 2 diabetes by diffusion tensor imaging: A case-control study

OBJECTIVES

This study aimed to evaluate diabetes peripheral neuropathy (DPN) by diffusion tensor imaging (DTI) and explore the correlation between DTI parameters and electrophysiological parameters.

METHODS

We examined tibial nerve (TN) and common peroneal nerve (CPN) of 32 DPN patients and 23 healthy controls using T1-weighted magnetic resonance imaging and DTI. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) of TN and CPN were measured and compared between groups. Spearman correlation coefficient was used to explore the relationship between DTI parameters and electrophysiology parameters in the DPN group. Diagnostic value was assessed by receiver operating characteristic (ROC) analysis.

RESULTS

In the DPN group, FA was decreased (p < 0.0001) and MD and RD were increased (p < 0.05, p < 0.001) in the TN and CPN compared with the values of healthy control group. Moreover, in the DPN group, FA was positively correlated with motor nerve conduction velocity (MCV) (p < 0.0001), and both MD and RD were negatively correlated with MCV (p < 0.05, p < 0.001). However, there was no correlation between AD and any electrophysiological parameters. Among all DTI parameters, FA displayed the best diagnostic accuracy, with an area under the ROC curve of 0.882 in TN and 0.917 in CPN.

CONCLUSION

FA and RD demonstrate appreciable diagnostic accuracy. Furthermore, they both have a moderate correlation with MCV.

Review Article "Spotlight on Ultrasonography in the Diagnosis of Peripheral Nerve Disease: The Evidence to Date"

Neuromuscular ultrasound is rapidly becoming incorporated into clinical practice as a standard tool in the assessment of peripheral nerve diseases. Ultrasound complements clinical phenotyping and electrodiagnostic evaluation, providing critical structural anatomical information to enhance diagnosis and identify structural pathology. This review article examines the evidence supporting neuromuscular ultrasound in the diagnosis of compressive mononeuropathies, traumatic nerve injury, generalised peripheral neuropathy and motor neuron disease. Extending the sonographic evaluation of nerves beyond simple morphological measurements has the potential to improve diagnostics in peripheral neuropathy, as well as advancing the understanding of pathological mechanisms, which in turn will promote precise therapies and improve therapeutic outcomes.

[Peripheral nerve reconstruction - diagnostics as a basis for decision-making: report of the Consensus Workshop at the 35th Meeting of the DAM]

In the early stage of nerve lesions, the clinical differentiation between neurapraxia, axonotmesis and neurotmesis often presents a big challenge. Especially in the early stage, however, it is crucial to correctly classify the type of damage because this is what essentially determines the therapeutic concept, in particular the surgical approach and, therefore, the prognosis. A precise diagnosis not only requires detailed clinical assessment and medical history taking, but also the use of additional electrophysiological (functional) and/or imaging examinations. Electrophysiological diagnostic tests may provide information ion localization, severity, course, type of damage and incipient or past reinnervation. Preoperative functional diagnostic measures should include neurography, needle electromyography (EMG) and, if needed, evoked potentials (EP), while imaging procedures should include neural sonography and magnetic resonance imaging (MRI). As a complimentary procedure, EMG may also be performed during surgery.

Mapping the rest of the human connectome: Atlasing the spinal cord and peripheral nervous system

The emergence of diffusion, structural, and functional neuroimaging methods has enabled major multi-site efforts to map the human connectome, which has heretofore been defined as containing all neural connections in the central nervous system (CNS). However, these efforts are not structured to examine the richness and complexity of the peripheral nervous system (PNS), which arguably forms the (neglected) rest of the connectome. Despite increasing interest in an atlas of the spinal cord (SC) and PNS which is simultaneously stereotactic, interactive, electronically dissectible, scalable, population-based and deformable, little attention has thus far been devoted to this task of critical importance. Nevertheless, the atlasing of these complete neural structures is essential for neurosurgical planning, neurological localization, and for mapping those components of the human connectome located outside of the CNS. Here we recommend a modification to the definition of the human connectome to include the SC and PNS, and argue for the creation of an inclusive atlas to complement current efforts to map the brain's human connectome, to enhance clinical education, and to assist progress in neuroscience research. In addition to providing a critical overview of existing neuroimaging techniques, image processing methodologies and algorithmic advances which can be combined for the creation of a full connectome atlas, we outline a blueprint for ultimately mapping the entire human nervous system and, thereby, for filling a critical gap in our scientific knowledge of neural connectivity.

Current and future applications of ultrasound imaging in peripheral nerve disorders

Neuromuscular ultrasound (NMUS) is a rapidly evolving technique used in neuromuscular medicine to provide complimentary information to standard electrodiagnostic studies. NMUS provides a dynamic, real time assessment of anatomy which can alter both diagnostic and management pathways in peripheral nerve disorders. This review describes the current and future techniques used in NMUS and details the applications and developments in the diagnosis and monitoring of compressive, hereditary, immune-mediated and axonal peripheral nerve disorders, and motor neuron diseases. Technological advances have allowed the increased utilisation of ultrasound for management of peripheral nerve disorders; however, several practical considerations need to be taken into account to facilitate the widespread uptake of this technique.

Enhanced MR neurography of the lumbosacral plexus with robust vascular suppression and improved delineation of its small branches

PURPOSE

To evaluate whether gadolinium enhanced 3D SPACE STIR sequence technique increases the visualization of the lumbosacral plexus (LSP) and its small branches.

METHODS

A retrospective study was performed on 24 patients who had underwent 3D SPACE STIR sequences scan with and without the administration of gadolinium contrast. In this study, we focused on the healthy sides of the LSP and its branches in each patient. The contrast ratio (CR), contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were objectively calculated by two experienced radiologists. The subjective visualization scores of the branches that were vitally important to therapeutic decision-making including femoral nerves, obturator nerves, lumbosacral trunks, superior gluteal and extra-pelvic sciatic nerves, were assessed using post-processing images.

RESULTS

Of the 24 subjects, all LSP nerve roots, femoral nerves, lumbosacral trunks and sciatic nerves were illustrated on both contrast-enhanced and non-contrast images. The enhanced images were found to have higher nerve to vein CNRs compared to non-contrast images. Compared to non-contrast images, the CRs of nerves versus surrounding fat tissues, bones, veins and muscles were improved in contrast-enhanced images, while the SNRs were better but not significantly so. Targeted maximum intensity projection (MIP) nerves including femoral, obturator, superior gluteal and extra-pelvic sciatic nerves obtained significantly higher subjective scores when gadolinium was administered.

CONCLUSIONS

The gadolinium enhanced 3D SPACE STIR sequence provided superior vascular suppression, resulting in increased conspicuity of LSP and its small branches. Altogether, this shows great potential for therapeutic decision-making in traumatic LSP lesions cases.

Update in the evaluation of peripheral nerves by MRI, from morphological to functional neurography

Imaging studies of peripheral nerves have increased considerably in the last ten years. In addition to the classical and still valid study by ultrasound, new neurographic techniques developed from conventional morphological sequences (including 3D isotropic studies with fat suppression) are making it possible to assess different peripheral nerves and plexuses, including small sensory and/or motor branches, with great precision. Diffusion-weighted sequences and diffusion tensor imaging have opened a new horizon in neurographic studies. This new approach provides morphological and functional information about the internal structure and pathophysiology of the peripheral nerves and diseases that involve them. This update reviews the different MR neurography techniques available for the study of the peripheral nerves, with special emphasis on new sequences based on diffusion.

Imaging of the Peripheral Nerve: Concepts and Future Direction of Magnetic Resonance Neurography and Ultrasound

Advanced imaging is increasingly used by upper extremity surgeons in the diagnosis and evaluation of peripheral nerve pathology. Ultrasound and magnetic resonance neurography (MRN) have emerged as the most far-reaching modalities for peripheral nerve imaging and often provide complimentary information. Technology improvements allow better depiction of the peripheral nervous system, allowing for more accurate diagnoses and preoperative planning. The purpose of this review is to provide an overview of current modalities and expected advances in peripheral nerve imaging with a focus on practical applications in the clinical setting. Ultrasound is safe, inexpensive, and readily available, and allows dynamic imaging with high spatial resolution as well as immediate evaluation of the contralateral nerve for comparison. It is primarily limited by its dependency on skilled operators and soft tissue contrast. The spatial evaluation of the perineural environment, fascicular echostructure, and nerve diameter are features of particular use in the diagnosis and treatment of nerve tumors, compressive lesions, and nerve trauma. Sonoelastrography has shown promise as a useful adjunct to standard sonographic imaging. MRN refers to the optimization of magnetic resonance image sequences and technology for visualization and contrasting nerves from surrounding structures. MRN provides excellent soft tissue contrast, depicts the entire nerve in 3 dimensions, allows for early evaluation of downstream muscle injury, and functions without operator dependency limits. Images provide details of nerve anatomic relationships, congruency, size, fascicular pattern, local and intrinsic fluid status, and contrast enhancement patterns, making MRN particularly useful in the setting of trauma, tumor, compressive lesions, and evaluation of brachial plexus injuries. Advances in MR volume and cinematic rendering software, magnet and coil technology, nerve-specific contrast media, and diffusion-weighted and tensor imaging will likely continue to expand the clinical application and indications for MRN.

Comparison of Magnetic Resonance Imaging and Ultrasonography in Diagnosing and Grading Carpal Tunnel Syndrome: A Prospective Study

OBJECTIVE

To use anatomic measurements on magnetic resonance imaging (MRI) and ultrasonography (USG) in diagnosing and grading carpal tunnel syndrome (CTS) using nerve conduction studies (NCS) as the gold standard.

MATERIAL AND METHODS

In this prospective study, 26 patients with CTS (45 wrists; 22 female and 4 male patients; mean ± SD age of 49.42 + 14.47 years) and 19 age and sex matched healthy volunteers (32 wrists; 15 female and 4 male volunteers, mean ± SD age of 42.52 + 10.85 years) underwent MRI and USG. Cross-sectional area (CA) of median nerve was measured using free hand ROI at four levels: hamate hook (H0), pisiform bone (PI0), 1 cm proximal (PI1) and 2 cm proximal to PI0 (PI2). Relative median nerve signal intensity (MNSI) was calculated as ratio of median nerve signal intensity with hypothenar muscle signal intensity. Flexor retinacular bowing was calculated at hamate hook level. Echogenicity and Power Doppler vascularity of median nerve were assessed on USG. Independent t-test, chi square test and receiver operating characteristic curve analysis were used as appropriate.

RESULTS

On USG, CA measured at PI0 (95% confidence interval of 0.872-0.987) and retinacular bowing (0.816-0.912), while, on MRI, CA at PI1 (0.874-0.997) were most useful in diagnosing CTS based on the ROC and Zombie plot analysis. Area under curves for CA measurements on USG and MRI were not significantly different. CA at PI1 on MRI (0.752-0.965) was significantly different between minimal to moderate CTS and severe to extreme CTS groups (on NCS).

CONCLUSION

CA of median nerve is the most useful parameter to diagnose and grade CTS and USG and MRI are comparable for measurements. Increased retinacular bowing on USG and hypoechogenicity of median nerve increase the diagnostic confidence while MRI helps in picking up important associated conditions.

Application of diffusion tensor imaging (DTI) and MR-tractography in the evaluation of peripheral nerve tumours: state of the art and review of the literature

Peripheral nerves can be affected by a variety of benign and malignant tumour and tumour-like lesions. Besides clinical evaluation and electrophysiologic studies, MRI is the imaging modality of choice for the assessment of these soft tissue tumours. Conventional MR sequences, however, can fail to assess the histologic features of the lesions. Moreover, the precise topographical relationship between the peripheral nerve and the tumor must be delineated preoperatively for complete tumour resection minimizing nerve damage. Using Diffusion tensor imaging (DTI) and tractography, it is possible to obtain functional information on tumour and nerve structures, allowing the assess anatomy, function and biological features. In this article, we review the technical aspects and clinical application of DTI for the evaluation of peripheral nerve tumours. (www.actabiomedica.it)

Respiratory- and cardiac-triggered three-dimensional sheath inked rapid acquisition with refocused echoes imaging (SHINKEI) of the abdomen for magnetic resonance neurography of the celiac plexus

The visualisation of the celiac plexus using respiratory- and cardiac-triggered three-dimensional (3D) sheath inked rapid acquisition with refocused echoes imaging (SHINKEI) was evaluated. After ethical approval and written informed consent, eight volunteers (age 27 ± 5 years, mean ± standard deviation) were scanned at 1.5 and 3 T. Displacement of the celiac ganglia due to aortic pulsatility was studied on axial single-slice breath-hold balanced turbo field-echo cine sequences in five volunteers and found to be 3.0 ± 0.5 mm (left) and 3.1 ± 0.4 mm (right). Respiratory- and cardiac-triggered 3D SHINKEI images were compared to respiratory- and cardiac-triggered fat-suppressed 3D T2-weighted turbo spin-echo and respiratory-triggered 3D SHINKEI in all volunteers. Visibility of the celiac ganglia was rated by three radiologists as visible or non-visible. On 3D SHINKEI with double-triggering at 1.5 T, the left and right ganglia were seen by all observers in 7/8 and 8/8 volunteers, respectively. At 3 T, this was the case for 6/8 and 7/8 volunteers, respectively. The nerve-to-muscle signal ratio increased from 1.9 ± 0.5 on fat-suppressed 3D T2-weighted turbo spin-echo to 4.7 ± 0.8 with 3D SHINKEI. Anatomical validation was performed in a human cadaver. An expert in anatomy confirmed that the hyperintense structure visible on ex vivo 3D SHINKEI scans was the celiac plexus. In conclusion, double-triggering allowed visualisation of the celiac plexus using 3D SHINKEI at both 1.5 T and 3 T.

Diffusion tensor imaging of the sciatic nerve in Charcot-Marie-Tooth disease type I patients: a prospective case-control study

OBJECTIVES

This study aimed to evaluate whether diffusion tensor imaging (DTI) parameters and cross-sectional area (CSA) can differentiate between the sciatic nerve of Charcot-Marie-Tooth (CMT) disease type I (demyelinating form) patients and that of controls.

METHODS

This prospective comparison study included 18 CMT type I patients and 18 age/sex-matched volunteers. Magnetic resonance imaging including DTI and axial T2-weighted Dixon sequence was performed for each subject. Region of interest analysis was independently performed by two radiologists on each side of the sciatic nerve at four levels: hamstring tendon origin (level 1), lesser trochanter of the femur (level 2), gluteus maximus tendon insertion (level 3), and mid-femur (level 4). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated. The CSA of the sciatic nerve bundle was measured using axial water-only image at each level. Comparisons of DTI parameters between the two groups were performed using the two-sample t test and Mann-Whitney U test. Interobserver agreement analysis was also conducted.

RESULTS

Interobserver agreement was excellent for all DTI parameter analyses. FA was significantly lower at all four levels in CMT patients than controls. RD, MD, and CSA were significantly higher at all four levels in CMT patients. AD was significantly higher at level 2 in CMT patients.

CONCLUSION

DTI assessment of the sciatic nerve is reproducible and can discriminate the demyelinating nerve pathology of CMT type I patients from normal nerves. The CSA of the sciatic nerve is also a potential parameter for diagnosing nerve abnormality in CMT type I patients.

KEY POINTS

• Diffusion tensor imaging parameters of the sciatic nerve at proximal to mid-femur level revealed significant differences between the Charcot-Marie-Tooth disease patients and controls. • The cross-sectional area of the sciatic nerve was significantly larger in the Charcot-Marie-Tooth disease patients. • Interobserver agreement was excellent (intraclass coefficient > 0.8) for all diffusion tensor imaging parameter analyses.

Isotropic resolution diffusion tensor imaging of lumbosacral and sciatic nerves using a phase-corrected diffusion-prepared 3D turbo spin echo

PURPOSE

To perform in vivo isotropic-resolution diffusion tensor imaging (DTI) of lumbosacral and sciatic nerves with a phase-navigated diffusion-prepared (DP) 3D turbo spin echo (TSE) acquisition and modified reconstruction incorporating intershot phase-error correction and to investigate the improvement on image quality and diffusion quantification with the proposed phase correction.

METHODS

Phase-navigated DP 3D TSE included magnitude stabilizers to minimize motion and eddy-current effects on the signal magnitude. Phase navigation of motion-induced phase errors was introduced before readout in 3D TSE. DTI of lower back nerves was performed in vivo using 3D TSE and single-shot echo planar imaging (ss-EPI) in 13 subjects. Diffusion data were phase-corrected per kz plane with respect to T2 -weighted data. The effects of motion-induced phase errors on DTI quantification was assessed for 3D TSE and compared with ss-EPI.

RESULTS

Non-phase-corrected 3D TSE resulted in artifacts in diffusion-weighted images and overestimated DTI parameters in the sciatic nerve (mean diffusivity [MD] = 2.06 ± 0.45). Phase correction of 3D TSE DTI data resulted in reductions in all DTI parameters (MD = 1.73 ± 0.26) of statistical significance (P ≤ 0.001) and in closer agreement with ss-EPI DTI parameters (MD = 1.62 ± 0.21).

CONCLUSION

DP 3D TSE with phase correction allows distortion-free isotropic diffusion imaging of lower back nerves with robustness to motion-induced artifacts and DTI quantification errors. Magn Reson Med 80:609-618, 2018. © 2018 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Minimally Invasive Lumbar Spinal Decompression in Elderly Patients with Magnetic Resonance Imaging Morphological Analysis

Study Design

Case-control study.

Purpose

In this study, we aimed to investigate clinical outcomes and morphological features in elderly patients with lumbar spinal stenosis (LSS) who were treated by minimally invasive surgery (MIS) unilateral laminectomy for bilateral decompression (ULBD) using a tubular retractor.

Overview of Literature

Numerous methods using imaging have been attempted to describe the severity of spinal stenosis. But the relationship between clinical symptoms and radiological features remains debatable.

Objective

In this study, we aimed to investigate clinical outcomes and morphological features in elderly patients with LSS who were treated by MIS-ULBD.

Methods

We methodically assessed 85 consecutive patients aged >65 years who were treated for LSS. The patients were retrospectively analyzed in two age groups: 66-75 years (group 1) and >75 years (group 2). Clinical outcomes were assessed using the Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and the modified MacNab criteria. Outcome parameters were compared between the groups at the 1-year follow-up. Core radiologic parameters for central and lateral stenosis were analyzed and clinical findings of the groups were compared.

Results

At the 1-year follow-up, patients in both groups 1 and 2 demonstrated significant improvement in their VAS and ODI scores. All clinical outcomes, except postoperative ODI, were not significantly difference between the groups. In addition, no significant difference was noted in the preoperative radiological parameters between the groups. There was no statistically significant correlation between radiological parameters and clinical symptoms or their outcomes. Moreover, no differences were noted in perioperative adverse events and in the need for repeat surgery at follow-ups between the groups.

Conclusions

MIS-ULBD by tubular approach is a safe and effective treatment option for elderly patients with LSS. Clinical outcomes in patients with LSS and aged >75 years were comparable with those in patients with LSS and aged 66-75 years. Moreover, we did not find any correlation between radiological parameters and clinical outcomes in either of the two patient groups.

Quantitative magnetic resonance (MR) neurography for evaluation of peripheral nerves and plexus injuries

Traumatic conditions of peripheral nerves and plexus have been classically evaluated by morphological imaging techniques and electrophysiological tests. New magnetic resonance imaging (MRI) studies based on 3D fat-suppressed techniques are providing high accuracy for peripheral nerve injury evaluation from a qualitative point of view. However, these techniques do not provide quantitative information. Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are functional MRI techniques that are able to evaluate and quantify the movement of water molecules within different biological structures. These techniques have been successfully applied in other anatomical areas, especially in the assessment of central nervous system, and now are being imported, with promising results for peripheral nerve and plexus evaluation. DWI and DTI allow performing a qualitative and quantitative peripheral nerve analysis, providing valuable pathophysiological information about functional integrity of these structures. In the field of trauma and peripheral nerve or plexus injury, several derived parameters from DWI and DTI studies such as apparent diffusion coefficient (ADC) or fractional anisotropy (FA) among others, can be used as potential biomarkers of neural damage providing information about fiber organization, axonal flow or myelin integrity. A proper knowledge of physical basis of these techniques and their limitations is important for an optimal interpretation of the imaging findings and derived data. In this paper, a comprehensive review of the potential applications of DWI and DTI neurographic studies is performed with a focus on traumatic conditions, including main nerve entrapment syndromes in both peripheral nerves and brachial or lumbar plexus.

The thoracic outlet syndromes: Part 1. Overview of the thoracic outlet syndromes and review of true neurogenic thoracic outlet syndrome

The thoracic outlet syndromes (TOSs) are a group of etiologically and clinically distinct disorders with 1 feature in common: compression of 1 or more neurovascular elements as they traverse the thoracic outlet. The medical literature reflects 5 TOSs: arterial; venous; traumatic neurovascular; true neurogenic; and disputed. Of these, the first 4 demonstrate all of the features expected of a syndrome, whereas disputed TOS does not, causing many experts to doubt its existence altogether. Thus, some categorize disputed TOS as a cervicoscapular pain syndrome rather than as a type of TOS. To better understand these disorders, their distinctions, and the reasoning underlying the categorical change of disputed TOS from a form of TOS to a cervicoscapular pain syndrome, a thorough understanding of the pertinent anatomy, pathology, pathophysiology, and the electrodiagnostic manifestations of their pathophysiologies is required. This review of the TOSs is provided in 2 parts. In this first part we address information pertinent to all 5 TOSs and reviews true neurogenic TOS. In part 2 we review the other 4 TOSs. Muscle Nerve 55: 782-793, 2017.

Diagnostic Value and Surgical Implications of the 3D DW-SSFP MRI On the Management of Patients with Brachial Plexus Injuries

Three-dimensional diffusion-weighted steady-state free precession (3D DW-SSFP) of high-resolution magnetic resonance has emerged as a promising method to visualize the peripheral nerves. In this study, the application value of 3D DW-SSFP brachial plexus imaging in the diagnosis of brachial plexus injury (BPI) was investigated. 33 patients with BPI were prospectively examined using 3D DW-SSFP MR neurography (MRN) of brachial plexus. Results of 3D DW-SSFP MRN were compared with intraoperative findings and measurements of electromyogram (EMG) or somatosensory evoked potentials (SEP) for each injured nerve root. 3D DW-SSFP MRN of brachial plexus has enabled good visualization of the small components of the brachial plexus. The postganglionic section of the brachial plexus was clearly visible in 26 patients, while the preganglionic section of the brachial plexus was clearly visible in 22 patients. Pseudomeningoceles were commonly observed in 23 patients. Others finding of MRN of brachial plexus included spinal cord offset (in 16 patients) and spinal cord deformation (in 6 patients). As for the 3D DW-SSFP MRN diagnosis of preganglionic BPI, the sensitivity, the specificity and the accuracy were respectively 96.8%, 90.29%, and 94.18%. 3D DW-SSFP MRN of brachial plexus improve visualization of brachial plexus and benefit to determine the extent of injury.

Is There an Association Between Pain and Magnetic Resonance Imaging Parameters in Patients With Lumbar Spinal Stenosis?

STUDY DESIGN

A prospective multicenter cohort study.

OBJECTIVE

The aim of this study was to identify an association between pain and magnetic resonance imaging (MRI) parameters in patients with lumbar spinal stenosis (LSS).

SUMMARY OF BACKGROUND DATA

At present, the relationship between abnormal MRI findings and pain in patients with LSS is still unclear.

METHODS

First, we conducted a systematic literature search. We identified relationships of relevant MRI parameters and pain in patients with LSS. Second, we addressed the study question with a thorough descriptive and graphical analysis to establish a relationship between MRI parameters and pain using data of the LSS outcome study (LSOS).

RESULTS

In the systematic review including four papers about the associations between radiological findings in the MRI and pain, the authors of two articles reported no association and two of them did. Of the latters, only one study found a moderate correlation between leg pain measured by Visual Analog Scale (VAS) and the degree of stenosis assessed by spine surgeons. In the data of the LSOS study, we could not identify a relevant association between any of the MRI parameters and buttock, leg, and back pain, quantified by the Spinal Stenosis Measure (SSM) and the Numeric Rating Scale (NRS). Even by restricting the analysis to the level of the lumbar spine with the most prominent radiological "stenosis," no relevant association could be shown.

CONCLUSION

Despite a thorough analysis of the data, we were not able to prove any correlation between radiological findings (MRI) and the severity of pain. There is a need for innovative "methods/techniques" to learn more about the causal relationship between radiological findings and the patients' pain-related complaints.

LEVEL OF EVIDENCE

2.

Neurogenic thoracic outlet syndrome: current diagnostic criteria and advances in MRI diagnostics

Neurogenic thoracic outlet syndrome (nTOS) is caused by compression of the brachial plexus as it traverses from the thoracic outlet to the axilla. Diagnosing nTOS can be difficult because of overlap with other complex pain and entrapment syndromes. An nTOS diagnosis is made based on patient history, physical exam, electrodiagnostic studies, and, more recently, interpretation of MR neurograms with tractography. Advances in high-resolution MRI and tractography can confirm an nTOS diagnosis and identify the location of nerve compression, allowing tailored surgical decompression. In this report, the authors review the current diagnostic criteria, present an update on advances in MRI, and provide case examples demonstrating how MR neurography (MRN) can aid in diagnosing nTOS. The authors conclude that improved high-resolution MRN and tractography are valuable tools for identifying the source of nerve compression in patients with nTOS and can augment current diagnostic modalities for this syndrome.

High resolution neurography of the brachial plexus by 3 Tesla magnetic resonance imaging

The study of the structures that make up the brachial plexus has benefited particularly from the high resolution images provided by 3T magnetic resonance scanners. The brachial plexus can have mononeuropathies or polyneuropathies. The mononeuropathies include traumatic injuries and trapping, such as occurs in thoracic outlet syndrome due to cervical ribs, prominent transverse apophyses, or tumors. The polyneuropathies include inflammatory processes, in particular chronic inflammatory demyelinating polyneuropathy, Parsonage-Turner syndrome, granulomatous diseases, and radiation neuropathy. Vascular processes affecting the brachial plexus include diabetic polyneuropathy and the vasculitides. This article reviews the anatomy of the brachial plexus and describes the technique for magnetic resonance neurography and the most common pathologic conditions that can affect the brachial plexus.

Magnetic resonance neurography of the brachial plexus

Magnetic Resonance Imaging (MRI) is being increasingly recognised all over the world as the imaging modality of choice for brachial plexus and peripheral nerve lesions. Recent refinements in MRI protocols have helped in imaging nerve tissue with greater clarity thereby helping in the identification, localisation and classification of nerve lesions with greater confidence than was possible till now. This article on Magnetic Resonance Neurography (MRN) is based on the authors’ experience of imaging the brachial plexus and peripheral nerves using these protocols over the last several years.

Ultrasound in the diagnosis of peripheral neuropathy: structure meets function in the neuromuscular clinic

Peripheral nerve ultrasound (US) has emerged as a promising technique for the diagnosis of peripheral nerve disorders. While most experience with US has been reported in the context of nerve entrapment syndromes, the role of US in the diagnosis of peripheral neuropathy (PN) has recently been explored. Distinctive US findings have been reported in patients with hereditary, immune-mediated, infectious and axonal PN; US may add complementary information to neurophysiological studies in the diagnostic work-up of PN. This review describes the characteristic US findings in PN reported to date and a classification of abnormal nerve US patterns in PN is proposed. Closer scrutiny of nerve abnormalities beyond assessment of nerve calibre may allow for more accurate diagnostic classification of PN, as well as contribute to the understanding of the intersection of structure and function in PN.

Diffusion-weighted MR neurography of the brachial and lumbosacral plexus: 3.0 T versus 1.5 T imaging

PURPOSE

To compare intraindividually the nerve conspicuity of the brachial and lumbosacral plexus on diffusion-weighted (DW) MR neurography (MRN) at two different field strengths.

MATERIALS AND METHODS

16 healthy volunteers were investigated at 3.0 T and 1.5 T applying optimized variants of a DW spin-echo echo-planar imaging sequence with short TI inversion recovery fat suppression. Full-volume (FV) and curved sub-volume (CSV) maximum intensity projection (MIP) images were reconstructed and nerve conspicuity was visually assessed. Moreover, visible length and sharpness of the nerves were quantitatively analyzed.

RESULTS

On FV MIP images, nerve conspicuity at 3.0 T compared to 1.5 T was worse for brachial plexus (P=0.00228), but better for lumbosacral plexus (P=0.00666). On CSV MIP images, nerve conspicuity did not differ significantly for brachial plexus, but was better at 3.0 T for lumbosacral plexus (P=0.00091). The visible length of the analyzed nerves did not differ significantly with the exception of some lumbosacral nerves, which were significantly longer at 3.0 T. The sharpness of all investigated nerves was significantly higher at 3.0 T by about 40-60% for cervical and 97-169% for lumbosacral nerves.

CONCLUSION

DW MRN imaging at 3.0 T compared to 1.5 T is superior for lumbosacral plexus, but not for brachial plexus.