Magnetic resonance neurography: current perspectives and literature review

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.

Whole-body magnetic resonance neurography in patients with chronic inflammatory demyelinating polyneuropathy

INTRODUCTION/AIMS

Whole-body magnetic resonance neurography (MRN) is an imaging modality that shows peripheral nerve signal change in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). We aimed to explore the diagnostic potential of whole-body MRN and its potential as a monitoring tool after immunotherapy in treatment-naïve CIDP patients.

METHODS

Whole-body MRN using coronal 3-dimensional short tau inversion recovery (STIR) sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE) techniques was performed in patients being investigated for CIDP and in healthy controls. Baseline clinical neuropathy scales and electrophysiologic parameters were collected, and MRN findings were compared before and after CIDP treatment.

RESULTS

We found highly concordant symmetrical thickening and increased T2 signal intensities in the brachial/lumbosacral plexus, femoral, or sciatic nerves in five of the eight patients with a final diagnosis of CIDP and none of the healthy controls. There were no treatment-related imaging changes in five patients with CIDP who completed a follow-up study. Diffuse, symmetrical thickening, and increased T2 signal in root, plexus, and peripheral nerves were found in two patients ultimately excluded due to a diagnosis of polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, skin changes (POEMS) syndrome in addition to signal changes in the muscles, bony lesions, organomegaly, and lymphadenopathy.

DISCUSSION

Whole-body MRN imaging shows promise in detecting abnormalities in proximal nerve segments in patients with CIDP. Future studies evaluating the role of MRN in assessing treatment response should consider follow-up scans after treatment durations of more than 4 months.

Assessment of traumatic mandibular nerve using MR neurography sequence: a preliminary study

BACKGROUND

Iatrogenic mandibular nerve damage resulting from oral surgeries and dental procedures is painful and a formidable challenge for patients and oral surgeons alike, mainly because the absence of objective and quantitative methods for diagnosing nerve damage renders treatment and compensation ambiguous while often leading to medico-legal disputes. The aim of this study was to examine discriminating factors of traumatic mandibular nerve within a specific magnetic resonance imaging (MRI) protocol and to suggest tangible diagnostic criteria for peripheral trigeminal nerve injury.

METHODS

Twenty-six patients with ipsilateral mandibular nerve trauma underwent T2 Flex water, 3D short tau inversion recovery (STIR), and diffusion-weighted imaging (DWI) acquired by periodically rotating overlapping parallel lines with enhanced reconstruction (PROPELLER) pulse sequences; 26 injured nerves were thus compared with contra-lateral healthy nerves at anatomically corresponding sites. T2 Flex apparent signal to noise ratio (FSNR), T2 Flex apparent nerve-muscle contrast to noise ratio (FNMCNR) 3D STIR apparent signal to noise ratio (SSNR), 3D STIR apparent nerve-muscle contrast to noise ratio (SNMCNR), apparent diffusion coefficient (ADC) and area of cross-sectional nerve (Area) were evaluated.

RESULTS

Mixed model analysis revealed FSNR and FNMCNR to be the dual discriminators for traumatized mandibular nerve (p < 0.05). Diagnostic performance of both parameters was also determined with area under the receiver operating characteristic curve (AUC for FSNR = 0.712; 95% confidence interval [CI]: 0.5660, 0.8571 / AUC for FNMCNR = 0.7056; 95% confidence interval [CI]: 1.011, 1.112).

CONCLUSIONS

An increase in FSNR and FNMCNR within our MRI sequence seems to be accurate indicators of the presence of traumatic nerve. This prospective study may serve as a foundation for sophisticated model diagnosing trigeminal nerve trauma within large patient cohorts.

Muscular MRI and magnetic resonance neurography in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease caused by the degeneration of the α-motor neurons in the anterior horn of the spinal cord. SMA is clinically characterized by progressive and symmetrical muscle weakness and muscle atrophy and ends up with systemic multisystem abnormalities. Quantitative MRI (qMRI) has the advantages of non-invasiveness, objective sensitivity, and high reproducibility, and has important clinical value in evaluating the severity of neuromuscular diseases and monitoring the efficacy of treatment. This article summarizes the clinical use of muscular MRI and magnetic resonance neurography in assessing the progress of SMA.

Updates in diagnostic tools for diagnosing nerve injury and compressions

Predicting prognosis after nerve injury and compression can be challenging, even for the experienced clinician. Although thorough clinical assessment can aid diagnosis, we cannot always be precise about long-term functional recovery of either motor or sensory nerves. To evaluate the severity of nerve injury, surgical exploration remains the gold standard, particularly after iatrogenic injury and major nerve injury from trauma, such as brachial plexus injury. Recently, advances in imaging techniques (ultrasound, magnetic resonance imaging [MRI] and MR neurography) along with multimodality assessment, including electrodiagnostic testing, have allowed us to have a better preoperative understanding of nerve continuity and prediction of nerve health and possible recovery. This article outlines the current and potential roles for clinical assessment, exploratory surgery, electrodiagnostic testing ultrasound and MRI in entrapment neuropathies, inflammatory neuritis and trauma. Emphasis is placed on those modalities that are improving in diagnostic accuracy of nerve assessment before any surgical intervention.

Neurosurgical Intervention for Nerve and Muscle Biopsies

(1) Background: Neurologic and musculoskeletal diseases represent a considerable portion of the underlying etiologies responsible for the widely prevalent symptoms of pain, weakness, numbness, and paresthesia. Because of the subjective and often nonspecific nature of these symptoms, different diagnostic modalities have been explored and utilized. (2) Methods: Literature review. (3) Results: Nerve and muscle biopsy remains the gold standard for diagnosing many of the responsible neurological and musculoskeletal conditions. However, the need for invasive tissue sampling is diminishing as more investigations explore alternative diagnostic modalities. Because of this, it is important to explore the current role of neurosurgical intervention for nerve and muscle biopsies and its current relevance in the diagnostic landscape of neurological and musculoskeletal disorders. With consideration of the role of nerve and muscle biopsy, it is also important to explore innovations and emerging techniques for conducting these procedures. This review explores the indications and emerging techniques for neurological intervention for nerve and muscle biopsies. (4) Conclusions: The role of neurosurgical intervention for nerve and muscle biopsy remains relevant in diagnosing many neurological and musculoskeletal disorders. Biopsy is especially relevant as a supportive point of evidence for diagnosis in atypical cases. Additionally, emerging techniques have been explored to guide diagnostics and biopsy, conduct less invasive biopsies, and reduce risks of worsening neurologic function and other symptoms secondary to biopsy.

One-Year Longitudinal Assessment of Patients With CMT1A Using Quantitative MRI

BACKGROUND AND OBJECTIVES

Intramuscular fat fraction (FF) assessed using quantitative MRI (qMRI) has emerged as one of the few responsive outcome measures in CMT1A suitable for future clinical trials. This study aimed to identify the relevance of multiple qMRI biomarkers for tracking longitudinal changes in CMT1A and to assess correlations between MRI metrics and clinical parameters.

METHODS

qMRI was performed in CMT1A patients at 2 time points, a year apart, and various metrics were extracted from 3-dimensional volumes of interest at thigh and leg levels. A semiautomated segmentation technique was used, enabling the analysis of central slices and a larger 3D muscle volume. Metrics included proton density (PD), magnetization transfer ratio (MTR), and intramuscular FF. The sciatic and tibial nerves were also assessed. Disease severity was gauged using Charcot Marie Tooth Neurologic Score (CMTNSv2), Charcot Marie Tooth Examination Score, Overall Neuropathy Limitation Scale scores, and Medical Research Council (MRC) muscle strength.

RESULTS

Twenty-four patients were included. FF significantly rose in the 3D volume at both thigh (+1.04% ± 2.19%, p = 0.041) and leg (+1.36% ± 1.87%, p = 0.045) levels. The 3D analyses unveiled a length-dependent gradient in FF, ranging from 22.61% ± 10.17% to 26.17% ± 10.79% at the leg level. There was noticeable variance in longitudinal changes between muscles: +3.17% ± 6.86% (p = 0.028) in the tibialis anterior compared with 0.37% ± 4.97% (p = 0.893) in the gastrocnemius medialis. MTR across the entire thigh volume showed a significant decline between the 2 time points -2.75 ± 6.58 (p = 0.049), whereas no significant differences were noted for the 3D muscle volume and PD. No longitudinal changes were observed in any nerve metric. Potent correlations were identified between FF and primary clinical measures: CMTNSv2 (ρ = 0.656; p = 0.001) and MRC in the lower limbs (ρ = -0.877; p < 0.001).

DISCUSSION

Our results further support that qMRI is a promising tool for following up longitudinal changes in CMT1A patients, FF being the paramount MRI metric for both thigh and leg regions. It is crucial to scrutinize the postimaging data extraction methods considering that annual changes are minimal (around +1.5%). Given the varied FF distribution, the existence of a length-dependent gradient, and the differential fatty involution across muscles, 3D volume analysis appeared more suitable than single slice analysis.

Fascicular Involvement of the Median Nerve Trunk in the Upper Arm: Manifestation as Anterior Interosseous Nerve Syndrome With Unique Imaging Features

Selective fascicular involvement of the median nerve trunk above the elbow leading to anterior interosseous nerve (AIN) syndrome is a rare form of peripheral neuropathy. This condition has recently garnered increased attention within the medical community owing to advancements in imaging techniques and a growing number of reported cases. In this article, we explore the topographical anatomy of the median nerve trunk and the clinical features associated with AIN palsy. Our focus extends to unique manifestations captured through MRI and ultrasonography (US) studies, highlighting noteworthy findings, such as nerve fascicle swelling, incomplete constrictions, hourglass-like constrictions, and torsions, particularly in the posterior/posteromedial region of the median nerve. Surgical observations have further enhanced the understanding of this complex neuropathic condition. High-resolution MRI not only reveals denervation changes in the AIN and median nerve territories but also illuminates these alterations without the presence of compressing structures. The pivotal roles of high-resolution MRI and US in diagnosing this condition and guiding the formulation of an optimal treatment strategy are emphasized.

3D isotropic MRI of ankle: review of literature with comparison to 2D MRI

The ankle joint has complex anatomy with different tissue structures and is commonly involved in traumatic injuries. Magnetic resonance imaging (MRI) is the primary imaging modality used to assess the soft tissue structures around the ankle joint including the ligaments, tendons, and articular cartilage. Two-dimensional (2D) fast spin echo/turbo spin echo (FSE/TSE) sequences are routinely used for ankle joint imaging. While the 2D sequences provide a good signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with high spatial resolution, there are some limitations to their use owing to the thick slices, interslice gaps leading to partial volume effects, limited fluid contrast, and the need to acquire separate images in different orthogonal planes. The 3D MR imaging can overcome these limitations and recent advances have led to technical improvements that enable its widespread clinical use in acceptable time periods. The volume imaging renders the advantage of reconstructing into thin continuous slices with isotropic voxels enabling multiplanar reconstructions that helps in visualizing complex anatomy of the structure of interest throughout their course with improved sharpness, definition of anatomic variants, and fluid conspicuity of lesions and injuries. Recent advances have also reduced the acquisition time of the 3D datasets making it more efficient than 2D sequences. This article reviews the recent technical developments in the domain 3D MRI, compares imaging with 3D versus 2D sequences, and demonstrates the use-case scenarios with interesting cases, and benefits of 3D MRI in evaluating various ankle joint components and their lesions.

Accuracy of augmented reality-guided needle placement for pulsed radiofrequency treatment of pudendal neuralgia: a pilot study on a phantom model

Background

Pudendal neuralgia (PN) is a chronic neuropathy that causes pain, numbness, and dysfunction in the pelvic region. The current state-of-the-art treatment is pulsed radiofrequency (PRF) in which a needle is supposed to be placed close to the pudendal nerve for neuromodulation. Given the effective range of PRF of 5 mm, the accuracy of needle placement is important. This study aimed to investigate the potential of augmented reality guidance for improving the accuracy of needle placement in pulsed radiofrequency treatment for pudendal neuralgia.

Methods

In this pilot study, eight subjects performed needle placements onto an in-house developed phantom model of the pelvis using AR guidance. AR guidance is provided using an in-house developed application on the HoloLens 2. The accuracy of needle placement was calculated based on the virtual 3D models of the needle and targeted phantom nerve, derived from CBCT scans.

Results

The median Euclidean distance between the tip of the needle and the target is found to be 4.37 (IQR 5.16) mm, the median lateral distance is 3.25 (IQR 4.62) mm and the median depth distance is 1.94 (IQR 7.07) mm.

Conclusion

In this study, the first method is described in which the accuracy of patient-specific needle placement using AR guidance is determined. This method could potentially improve the accuracy of PRF needle placement for pudendal neuralgia, resulting in improved treatment outcomes.

Improved visualization of median, ulnar nerves, and small branches in the wrist and palm using contrast-enhanced magnetic resonance neurography

Background

Magnetic resonance imaging of peripheral nerves in the wrist and palm is challenging due to the small size, tortuous course, complex surrounding tissues, and accompanying blood vessels. The occurrence of carpal palmar lesions leads to edema, swelling, and mass effect, which may further interfere with the display and identification of nerves.

Objective

To evaluate whether contrast-enhanced magnetic resonance neurography (ceMRN) improves the visualization of the morphology and pathology of the median, ulnar nerves, and their small branches in the wrist and palm.

Design

An observational study.

Methods

In total 57 subjects, including 36 volunteers and 21 patients with carpal palmar lesions, were enrolled and underwent ceMRN and non-contrast MRN (ncMRN) examination at 3.0 Tesla. The degree of vascular suppression, nerve visualization, diagnostic confidence, and lesion conspicuity was qualitatively assessed by two radiologists. Kappa statistics were obtained for inter-reader agreement. The signal-to-noise ratio, contrast ratio (CR), and contrast-to-noise ratio (CNR) of the median nerve were measured. The subjective ratings and quantitative measurements were compared between ncMRN and ceMRN.

Results

The inter-reader agreement was excellent (k > 0.8) for all qualitative assessments and visualization assessment of each nerve segment. Compared with ncMRN, ceMRN significantly improved vascular suppression in volunteers and patients (both p < 0.001). The ceMRN significantly enhanced nerve visualization of each segment (all p < 0.05) and diagnostic confidence in volunteers and patients (both p < 0.05). The ceMRN improved lesion conspicuity (p = 0.003) in patients. Quantitatively, ceMRN had significantly higher CRs of nerve versus subcutaneous fat, bone marrow, and vessels and CNR of nerve versus vessel than ncMRN (all p < 0.05).

Conclusion

The ceMRN significantly improves the visualization of peripheral nerves and pathology in the wrist and palm by robustly suppressing the signals of fat, bone marrow, and especially vessels in volunteers and patients.

3D SHINKEI MR neurography in evaluation of traumatic brachial plexus

3D SHINKEI neurography is a new sequence for imaging the peripheral nerves. The study aims at assessing traumatic brachial plexus injury using this sequence. Fifty-eight patients with suspected trauma induced brachial plexus injury underwent MR neurography (MRN) imaging in 3D SHINKEI sequence at 3 T. Surgery and intraoperative somatosensory evoked potentials or clinical follow-up results were used as the reference standard. MRN, surgery and electromyography (EMG) findings were recorded at four levels of the brachial plexus-roots, trunks, cords and branches. Fifty-eight patients had pre- or postganglionic injury. The C5-C6 nerve postganglionic segment was the most common (average 42%) among the postganglionic injuries detected by 3D SHINKEI MRN. The diagnostic accuracy (83.75%) and the specificity (90.30%) of MRN higher than that of EMG (p < 0.001). There was no significant difference in the diagnostic sensitivity of MRN compared with EMG (p > 0.05). Eighteen patients with brachial plexus injury underwent surgical exploration after MRN examination and the correlation between MRN and surgery was 66.7%. Due to the high diagnostic accuracy and specificity, 3D SHINKEI MRN can comprehensively display the traumatic brachial plexus injury. This sequence has great potential in the accurate diagnosis of traumatic brachial plexus injury.

Misplaced S1 screw causing L5 radiculopathy, rare and unusual presentation: a report of 2 cases

Many spine surgeons are not optimally acquainted with anatomy anterior to sacrum. Screw malposition injuring these structures can lead to unwanted lethal consequences. We report unusual cases of acute radiculopathy due to misplaced bicortical sacral screw causing L5 nerve root impingement on anterior sacrum. A 39/M patient complained of severe rest pain (VAS 9/10) post TLIF in region of L5 dermatome with sensory deficit along the right lateral leg and straight leg raise less than 30°. X-ray revealed S1 screw protruding beyond the second cortex with a straight trajectory. CT scan revealed a protrusion of 11.4mm beyond anterior cortex. The patient was taken for re-surgery and the trajectory and length of screw was revised. Sciatic pain completely disappeared immediately after surgery. A 61/M patient operated elsewhere with instrumented decompression and fusion with screws passed at L4, L5 and S1 level for lumbar canal stenosis, post-surgery patient developed new onset radicular symptoms in right lower limb. Patient was managed conservatively in the form of L5 selective nerve root block. Pain and numbness improved. Bicortical purchase of S1 screw though improves pull out strength, is associated with a risk of neurovascular complications. Surgeons should be alerted to the misplacement of S1 pedicle screws to avoid involvement not only anterior to the anteromedial neurovascular tissue, but also anterolateral to the arrangement of the L5 nerve root.

Applications of Diffusion-Weighted MRI to the Musculoskeletal System

Diffusion-weighted imaging (DWI) is an established MRI technique that can investigate tissue microstructure at the scale of a few micrometers. Musculoskeletal tissues typically have a highly ordered structure to fulfill their functions and therefore represent an optimal application of DWI. Even more since disruption of tissue organization affects its biomechanical properties and may indicate irreversible damage. The application of DWI to the musculoskeletal system faces application-specific challenges on data acquisition including susceptibility effects, the low T2 relaxation time of most musculoskeletal tissues (2-70 msec) and the need for sub-millimetric resolution. Thus, musculoskeletal applications have been an area of development of new DWI methods. In this review, we provide an overview of the technical aspects of DWI acquisition including diffusion-weighting, MRI pulse sequences and different diffusion regimes to study tissue microstructure. For each tissue type (growth plate, articular cartilage, muscle, bone marrow, intervertebral discs, ligaments, tendons, menisci, and synovium), the rationale for the use of DWI and clinical studies in support of its use as a biomarker are presented. The review describes studies showing that DTI of the growth plate has predictive value for child growth and that DTI of articular cartilage has potential to predict the radiographic progression of joint damage in early stages of osteoarthritis. DTI has been used extensively in skeletal muscle where it has shown potential to detect microstructural and functional changes in a wide range of muscle pathologies. DWI of bone marrow showed to be a valuable tool for the diagnosis of benign and malignant acute vertebral fractures and bone metastases. DTI and diffusion kurtosis have been investigated as markers of early intervertebral disc degeneration and lower back pain. Finally, promising new applications of DTI to anterior cruciate ligament grafts and synovium are presented. The review ends with an overview of the use of DWI in clinical routine. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Society of skeletal radiology position paper - recommendations for contrast use in musculoskeletal MRI: when is non-contrast imaging enough?

The following White Paper will discuss the appropriateness of gadolinium administration in MRI for musculoskeletal indications. Musculoskeletal radiologists should consider the potential risks involved and practice the judicious use of intravenous contrast, restricting administration to cases where there is demonstrable added value. Specific nuances of when contrast is or is not recommended are discussed in detail and listed in table format. Briefly, contrast is recommended for bone and soft tissue lesions. For infection, contrast is reserved for chronic or complex cases. In rheumatology, contrast is recommended for early detection but not for advanced arthritis. Contrast is not recommended for sports injuries, routine MRI neurography, implants/hardware, or spine imaging, but is helpful in complex and post-operative cases.

Musculoskeletal manifestations of COVID-19

During the COVID-19 pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected millions of people worldwide, with acute respiratory distress syndrome (ARDS) being the most common severe condition of pulmonary involvement. Despite its involvement in the lungs, SARS-CoV-2 causes multiple extrapulmonary manifestations, including manifestations in the musculoskeletal system. Several cases involving bone, joint, muscle, neurovascular and soft tissues were reported shortly after pandemic onset. Even after the acute infection has resolved, many patients experience persistent symptoms and a decrease in quality of life, a condition known as post-COVID syndrome or long COVID. COVID-19 vaccines have been widely available since December 2020, preventing millions of deaths during the pandemic. However, adverse reactions, including those involving the musculoskeletal system, have been reported in the literature. Therefore, the primary goal of this article is to review the main imaging findings of SARS-CoV-2 involvement in the musculoskeletal system, including acute, subacute, chronic and postvaccination manifestations.

Diagnostic Approach to Lower Limb Entrapment Neuropathies: A Narrative Literature Review

Entrapment neuropathies of the lower limb are a misunderstood and underdiagnosed group of disorders, characterized by pain and dysesthesia, muscular weakness, and specific provoking movements on physical examination. The most frequent of these syndromes encountered in clinical practice are fibular nerve entrapment, proximal tibial neuropathy, sural nerve neuropathy, deep gluteal syndrome or sciatic nerve entrapment, and lateral femoral cutaneous nerve entrapment, also known as meralgia paresthetica. These are commonly mistaken for lumbar plexopathies, radiculopathies, and musculotendinous diseases, which appear even more frequently and have overlapping clinical presentations. A comprehensive anamnesis, physical examination, and electrodiagnostic studies should help clarify the diagnosis. If the diagnosis is still unclear or a secondary cause of entrapment is suspected, magnetic resonance neurography, MRI, or ultrasonography should be conducted to clarify the etiology, rule out other diseases, and confirm the diagnosis. The aim of this narrative review was to help clinicians gain familiarity with this disease, with an increase in diagnostic confidence, leading to early diagnosis of nerve damage and prevention of muscle atrophy. We reviewed the epidemiology, anatomy, pathophysiology, etiology, clinical presentation, and EDX technique and interpretation of the entrapment neuropathies of the lower limb, using articles published from 1970 to 2022 included in the Pubmed, MEDLINE, Cochrane Library, Google Scholar, EMBASE, Web of Science, and Scopus databases.

An Updated Review of Magnetic Resonance Neurography for Plexus Imaging

Magnetic resonance neurography (MRN) is increasingly used to visualize peripheral nerves in vivo. However, the implementation and interpretation of MRN in the brachial and lumbosacral plexi are challenging because of the anatomical complexity and technical limitations. The purpose of this article was to review the clinical context of MRN, describe advanced magnetic resonance (MR) techniques for plexus imaging, and list the general categories of utility of MRN with pertinent imaging examples. The selection and optimization of MR sequences are centered on the homogeneous suppression of fat and blood vessels while enhancing the visibility of the plexus and its branches. Standard 2D fast spin-echo sequences are essential to assess morphology and signal intensity of nerves. Moreover, nerve-selective 3D isotropic images allow improved visualization of nerves and multiplanar reconstruction along their course. Diffusion-weighted and diffusion-tensor images offer microscopic and functional insights into peripheral nerves. The interpretation of MRN in the brachial and lumbosacral plexi should be based on a thorough understanding of their anatomy and pathophysiology. Anatomical landmarks assist in identifying brachial and lumbosacral plexus components of interest. Thus, understanding the varying patterns of nerve abnormalities facilitates the interpretation of aberrant findings.

Usefulness and Clinical Impact of Whole-Body MRI in Detecting Autoimmune Neuromuscular Disorders

Autoimmune neuromuscular diseases are a group of heterogenous pathologies secondary to the activation of the immune system that damage the structures of the peripheric nerve, the neuromuscular junction, or the skeleton muscle. The diagnosis of autoimmune neuromuscular disorders comprises a combination of data from clinical, laboratory, electromyography, imaging exam, and biopsy. Particularly, the whole-body MRI examination in the last two decades has been of great use in the assessment of neuromuscular disorders. MRI provides information about the structures involved and the status of activity of the disease. It can also be used as a biomarker, detect the pattern of specific muscle involvement, and is a useful tool for targeting the optimal muscle site for biopsy. In this work, we summarized the most used technical protocol of whole-body MRI and the role of this imaging technique in autoimmune neuromuscular disorders.

Localization and Diagnostic Evaluation of Peripheral Nerve Disorders

OBJECTIVE

This article provides a framework for the initial evaluation of patients with suspected peripheral nerve disease. The key clinical elements of peripheral nerve diseases can help the practicing neurologist differentiate among peripheral neuropathies with similar presentations.

LATEST DEVELOPMENTS

The wide range of peripheral nerve diseases with similar clinical presentations can pose a diagnostic challenge. The large array of available testing modalities (including imaging and electrodiagnostic, autonomic, laboratory, biopsy, and genetic testing) further complicates clinical decision making. Recent developments (eg, discovery of new autoantibodies, genetic variations, and histopathologic techniques) across the peripheral neuropathy spectrum have resulted in an increased need to evaluate patients logically and with a tailored diagnostic approach.

ESSENTIAL POINTS

A careful approach that focuses on key clinical elements combined with an understanding of purposeful diagnostic testing can lead to a successful diagnosis of peripheral nerve diseases.

Magnetic Resonance Neurography of the Foot and Ankle

Peripheral neuropathies of the foot and ankle can be challenging to diagnose clinically due to concomitant traumatic and nontraumatic or degenerative orthopedic conditions. Although clinical history, physical examination, and electrodiagnostic testing comprised of nerve conduction velocities and electromyography are used primarily for the identification and classification of peripheral nerve disorders, MR neurography (MRN) can be used to visualize the peripheral nerves as well as the skeletal muscles of the foot and ankle for primary neurogenic pathology and skeletal muscle denervation effect. Proper knowledge of the anatomy and pathophysiology of peripheral nerves is important for an MRN interpretation.

Spontaneous radial nerve palsy with hourglass-like constriction

Hourglass-like constriction (HLC) is an uncommon spontaneous mononeuropathy that is typically characterised by a sudden onset of pain followed by palsy, affecting branches of the radial (posterior interosseous nerve) and median nerves (anterior interosseous nerve). HLC of the radial nerve (RN) is rare, with only a few reported cases. Here, we report a case of a man who presented with acute wrist and finger drop due to the HLC of the RN. Surgery was recommended 5 months after clinical observation, when the lesion was resected and primarily repaired, resulting in satisfactory recovery. There is still much that remains unknown about HLC, especially for RN. The current understanding points out an inflammatory disease that should be treated conservatively for 3-7 months. The surgical technique depends mostly on the severity and extent of constriction; however, considering only RN constrictions, primary repair by neurorrhaphy or nerve grafts resulted in better functional outcomes.

Management of Failed Carpal and Cubital Tunnel Release: An Evidence-Based Guide to Success

Carpal tunnel and cubital tunnel syndromes are the most common compressive neuropathies of the upper extremity with surgical treatment having high success rates for both conditions. Although uncommon, persistent or recurrent carpal and cubital tunnel syndrome presents a challenge for patients and providers. Diagnosis of persistence versus recurrence of the pathology is key in establishing an appropriate treatment plan to provide the best possible patient outcomes. After an established diagnosis, a wide array of treatment options exist which varies based on previous procedures performed. This review discusses relevant anatomy, etiology, and clinical presentations of persistent and recurrent carpal and cubital tunnel syndromes. The range of treatment options is presented based on history and diagnostic findings. Treatment options span from revision of nerve decompression to the use of soft tissue rearrangement procedures. Some specific treatment options discussed include simple revision nerve decompression, external neurolysis, soft tissue rearrangement, such as the hypothenar fat flap or various transposition techniques, and the use of nerve wraps. Included is an evidence-based management guide for diagnosis and treatment of persistent versus recurrent carpal and cubital tunnel syndromes.

MR microneurography of human peripheral fascicles using a clinical 3T MR scanner

BACKGROUND AND PURPOSE

Knowledge of nerve fascicular structures is essential for managing peripheral nerve disorders. This study aimed to investigate the feasibility of z-axis high-resolution magnetic resonance (MR) microneurography (zH-MRMN) in displaying the three-dimensional structures of tibial nerve fascicles in vivo using a 3T MR scanner.

MATERIALS AND METHODS

Twelve volunteers underwent z-axis conventional-resolution MR microneurography (zC-MRMN) and zH-MRMN of tibial nerves. The visibility scores of the nerve fascicles (VSNFs) on axial zC-MRMN images and axial zH-MRMN multiplanar reformation (MPR) images were compared. The nerve fascicle appearances on the longitudinal zH-MRMN MPR images were described.

RESULTS

In the nerve segments whose long axes were perpendicular to the imaging planes of both zC-MRMN and zH-MRMN, the VSNFs were not significantly different between the axial images of the two modalities (P = 0.083). In the nerve segments whose long axes were not perpendicular to the imaging planes of zC-MRMN, the VSNFs on the axial zC-MRMN images were significantly lower than those on the axial zH-MRMN MPR images that were angled perpendicular to the long axis of the tibial nerve (P < 0.001).

CONCLUSIONS

The longitudinal zH-MRMN MPR images clearly displayed the changing features of the intraneural fascicles as well as the gross morphology of the tibial nerves. zH-MRMN can clearly delineate the topography of the tibial nerve fascicles in vivo through use of a 3T MR scanner.

Diagnostic value of diffusion-weighted MRI using apparent diffusion coefficient (ADC) in evaluation of median nerve in carpal tunnel syndrome

Background

The diagnosis of carpal tunnel syndrome is based on a combination of clinical history, clinical examination and frequent use of electrodiagnostics as nerve conduction study and electromyography which often do not provide the spatial and anatomical localizing information, especially with small nerves of the extremities. Conventional magnetic resonance imaging can reveal morphological changes in carpal tunnel syndrome patients.

Aim

The purpose of our study was to assess the efficacy of diffusion magnetic resonance imaging as a functional imaging in evaluation of median nerve in carpal tunnel syndrome.

Patients and methods

This prospective study included a group of 33 patients with carpal tunnel syndrome diagnosed by both clinical examination and electromyography; 40 writs were examined. A control group of 20 subjects of matched age group were also included. All the participants were subjected to conventional and diffusion magnetic resonance imaging studies.

Results

Median nerve apparent diffusion coefficient values of patients are lower than those of controls. The sensitivity and diagnostic accuracy of diffusion conventional magnetic resonance imaging were 95% and 97.5%, respectively, versus 25% and 62.5% of conventional magnetic resonance imaging. A cut-off apparent diffusion coefficient value ≤ 0.99 obtained at distal radio-ulnar joint level and > 1.07 at pisiform level as well as apparent diffusion coefficient ratio at a cut-off ≤ 0.2 was significantly valid for diagnosing carpal tunnel syndrome.

Conclusions

Diffusion magnetic resonance imaging provides functional evaluation of median nerve in patients with carpal tunnel syndrome.

Conjoined nerve root in a patient with lumbar disc herniation accompanied by a lumbosacral spine anomaly: a case report

BACKGROUND

A nerve root anomaly, typified by a conjoined nerve root, is a rare finding. Conjoined nerve root anomalies are easily missed even in preoperative advanced imaging modalities, which can be potentially troublesome during and after surgery. In this report, we present a case of conjoined right L5-S1 nerve root in a patient with lumbar disc herniation, accompanied by spina bifida occulta, which was undiagnosed on preoperative imaging studies.

CASE REPORT

A 55-year-old Asian (Japanese) woman presented with low back pain and right leg radiating pain due to lumbar disc herniation at the right L5/S1. Physical examination revealed a positive Lasègue sign and the range of the straight leg raising test was 20° on the right side. The right patellar tendon reflex was normal; however, the right ankle jerk reflex disappeared. Although no obvious hypoesthesia was noted, mild muscle weakness (4/5) was observed in the right leg on the manual muscle test. We planned the lumbar discectomy under a microscope. During surgery, the conjoined right L5-S1 nerve root, which was compressed by herniated nucleus pulposus, was encountered. Although it was very thick and less mobile, some pieces of herniated nucleus pulposus could be removed piece by piece from the axillary part. After sequential decompressive procedures, the tightness of the conjoined right L5-S1 nerve root decreased but its mobility did not improve much. The laterality of the thickness and exit angle of the conjoined right L5-S1 nerve root was retrospectively confirmed on T2 coronal magnetic resonance images and magnetic resonance neurography. Postoperatively, right leg pain was immediately alleviated and complete improvement of muscle weakness was achieved 1 week later (5/5).

CONCLUSIONS

Magnetic resonance neurography is extremely useful for the accurate diagnosis of anomalous nerve roots because of clear visualization of the neural tissue. Discectomy under a microscope, which enables magnified three-dimensional observation of the surgical field, must provide a valid and safe procedure to achieve not only secure resection of herniated discs but also adequate exposure of anomalous nerve roots.

Electrophysiology and Magnetic Resonance Neurography Findings of Nontraumatic Ulnar Mononeuropathy From a Tertiary Care Center

BACKGROUND

Ulnar nerve is frequently involved in mononeuropathies of the upper limb. Ulnar neuropathies have been diagnosed conventionally using clinical and electrophysiological findings. Physicians opt for nerve imaging in patients with ambiguous electrophysiological tests to gain additional information, identify etiology and plan management.

OBJECTIVES

The aim of this study was to describe the electrophysiological and the magnetic resonance neurography (MRN) findings in patients with nontraumatic ulnar neuropathy.

METHODS

All consecutive patients with suspected nontraumatic ulnar mononeuropathy were recruited; clinical assessment and electrophysiological studies (EPSs) were done in all. After EPS, patients with localization of lesion along the ulnar nerve underwent MRN.

RESULTS

All 39 patients recruited had clinical findings suggestive of ulnar neuropathy; Electrophysiological confirmation was possible in 36/39 (92.30%) patients. Localization of ulnar nerve lesion to elbow and wrist was possible in 27 (75%) and 9 (25%) patients, respectively. MRN was done in 22 patients; a lesion was identified in 19 of 22 (86.36%) ulnar nerves studied. Thickening and hyperintensity in T2 W/short TI inversion recovery images of ulnar nerve at the level of olecranon, suggesting ulnar neuropathy at elbow, was the commonest (8/22) imaging finding.

CONCLUSIONS

MRN acts as a complimentary tool to EPS for evaluating nontraumatic ulnar neuropathy. By identifying the etiology, MRN is likely to modify the management decision.

Lewis-Sumner syndrome: contribution of diffusion tensor imaging in its differential diagnosis

Lewis-Sumner syndrome (LSS) is an atypical variant of chronic inflammatory demyelinating polyneuropathy characterized by an asymmetric sensory-motor neuropathy with multifocal distribution. The diagnosis is typically clinical and electrophysiological but in some cases might be challenging causing a significant therapeutic delay. Diffusion tensor imaging (DTI) has been progressively used for the in vivo assessment of peripheral nerves integrity. In this study, we aimed to elucidate if DTI was able to detect the specific nerve damage in a patient with suspected LSS, and determine if DTI presented a specific pattern that could be useful in its differential diagnosis. A 38-year-old male with a right foot drop was studied. Physical examination, electrodiagnostic, and MRI studies were performed. MRI of the lower limb was acquired in a 3-T scanner and included T1-wi, T2-TSE-SPIR, and PD-TSE-SPAIR images in axial and coronal planes. Axial DTI was acquired using a single-shot EPI sequence with diffusion encoding in 32 directions. The electrodiagnostic tests suggested a demyelinating sensorimotor neuropathy with conduction blocks. Conventional MRI was normal. DTI showed pathological results in Tibial and Peroneal nerves consisting of thinning and discontinuities along both nerves but more significant in the Peroneal. Compared with MRI, DTI offered a significant improvement to detect the specific nerve damage and its characteristics. The observed nerve damage in DTI suggested polyneuropathy and was compatible with the electrophysiological findings, endorsing the LSS diagnosis. This is the first report in the literature presenting the DTI findings in LSS.

Prospective pre-operative 3-T MR neurography peripheral nerve mapping of upper extremity amputations implanted with FAST-LIFE electrode interfaces of robotic hands: technical report

BACKGROUND AND PURPOSE

Fascicular targeting of longitudinal intrafascicular electrode (FAST-LIFE) interface enables hand dexterity with exogenous electrical microstimulation for sensory restoration, custom neural recording hardware, and deep learning-based artificial intelligence for motor intent decoding. The purpose of this technical report from a prospective pilot study was to illustrate magnetic resonance neurography (MRN) mapping of hand and nerve anatomy in amputees and incremental value of MRN over electrophysiology findings in pre-surgical planning of FAST-LIFE interface (robotic hand) patients.

MATERIALS AND METHODS

After obtaining informed consent, patients with upper extremity amputations underwent pre-operative 3-T MRN, X-rays, and electrophysiology. MRN findings were correlated with electrophysiology reports. Descriptive statistics were performed.

RESULTS

Five patients of ages 21-59 years exhibited 3/5 partial hand amputations, and 2/5 transradial amputations on X-rays. The median and ulnar nerve end bulb neuromas measured 10.1 ± 3.04 mm (range: 5.5-14 mm, median: 10.5 mm) and 10.9 ± 7.64 mm (2-22 mm, 9.75 mm), respectively. The ADC of median and ulnar nerves were increased at 1.64 ± 0.1 × 10^-3 mm²/s (range: 1.5-1.8, median: 1.64 × 10^-3 mm²/s) and 1.70 ± 0.17 × 10^-3 mm²/s (1.49-1.98 × 10^-3 mm²/s, 1.65 × 10^-3 mm²/s), respectively. Other identified lesions were neuromas of superficial branch of the radial nerve and anterior interosseous nerve. On electrophysiology, 2/5 reports were unremarkable, 2/5 showed mixed motor-sensory neuropathies of median and ulnar nerves along with radial sensory neuropathy, and 1/5 showed sensory neuropathy of lateral cutaneous nerve of the forearm. All patients regained naturalistic sensations and motor control of digits.

CONCLUSION

3-T MRN allows excellent demonstration of forearm and hand nerve anatomy, altered diffusion characteristics, and their neuromas despite unremarkable electrophysiology for pre-surgical planning of the FAST-LIFE (robotic hand) interfaces.

Juxtaneural ganglia arising from the hip joint: focus on magnetic resonance imaging findings and clinical manifestations

OBJECTIVE

To present cases of juxtaneural ganglia arising from the hip with a discussion of the magnetic resonance imaging (MRI) findings, presenting symptoms, and possible treatment option.

MATERIALS AND METHODS

Two radiologists performed a consensus review of MRI scans obtained between January 2013 and March 2021 to identify patients with juxtaneural ganglia around the hip. A total of 11 patients with 11 juxtaneural ganglia were identified. Medical records and MRI findings were retrospectively reviewed.

RESULTS

Eight patients had lesions involving the sciatic nerve, and three patients had lesions involving the obturator nerve. Sciatic ganglia arose from a paralabral cyst in the posteroinferior quadrant and continued through a narrow channel running along the posterior acetabulum, showing increased diameter in the sciatic foramen and intrapelvic portion. Obturator ganglia showed a J- or reverse J-shape on the coronal imaging plane and extended from a paralabral cyst in the anteroinferior quadrant via the obturator canal. Nine patients (9/11, 81.8%) had symptoms resembling those of lumbosacral radiculopathy. Four patients underwent arthroscopic surgery, and one patient underwent ultrasound-guided aspiration, all of whom showed partial improvement. Spontaneous decrease in the extent of the ganglion was observed in three patients (3/11, 27.3%).

CONCLUSION

This article describes rare cases of juxtaneural ganglia arising from the hip joint and involving the sciatic and obturator nerves. The lesions share similar MRI findings, and each type of cyst (sciatic or obturator ganglia) involves a specific labral quadrant.

Diagnosing ulnar neuropathy at the elbow on MRI: importance of the longitudinal extent of the hyperintense ulnar nerve

OBJECTIVE

To evaluate the usefulness of the longitudinal extent (LE) of high ulnar nerve signal intensity (SI) for the diagnosis of ulnar neuropathy at the elbow (UNE).

MATERIALS AND METHODS

This retrospective study included 68 patients who underwent elbow MRI. Twenty-seven and 41 patients were enrolled in the UNE and control groups, respectively. Qualitative and quantitative analyses of the SI and size of the ulnar nerve at the cubital tunnel, proximal, and distal to the cubital tunnel were performed. Cross-sectional area (CSA) and nerve-to-muscle contrast ratio (NMCR) were measured at each level. The LE of the hyperintense ulnar nerve was evaluated using axial and coronal images. The presence of space-occupying lesions (SOLs), subluxation, and muscle denervation were recorded. Univariate and multivariate analyses were performed to identify independent predictive factors.

RESULTS

Ulnar nerve hyperintensity at and distal to the cubital tunnel, presence of compression, SOL, muscle denervation, LE of hyperintense ulnar nerve, NMCR, and CSA at and distal to the cubital tunnel significantly differed between the two groups. Multivariate logistic regression analysis showed that the LE of the hyperintense ulnar nerve and CSA at the cubital tunnel were independent predictive factors for UNE (p < 0.05).

CONCLUSION

LE of the hyperintense ulnar nerve could be a useful predictive factor for UNE.

Dorsal Root Ganglia Volume—Normative Values, Correlation with Demographic Determinants and Reliability of Three Different Methods of Volumetry

Background: Dorsal root ganglia (DRG) volume assessment by MR-Neurography (MRN) has evolved to an important imaging marker in the diagnostic workup of various peripheral neuropathies and pain syndromes. The aim of this study was (1) to assess normal values of DRG volume and correlations with demographic determinants and (2) to quantify the inter-reader and inter-method reliability of three different methods of DRG volumetry. Methods: Sixty healthy subjects (mean age: 59.1, range 23–79) were examined using a 3D T2-weighted MRN of the lumbosacral plexus at 3 Tesla. Normal values of DRG L3 to S2 were obtained after exact volumetry based on manual 3D segmentation and correlations with demographic variables were assessed. For the assessment of inter-reader and inter-method reliability, DRG volumes in a subset of 25 participants were measured by two independent readers, each applying (1) exact volumetry based on 3D segmentation, (2) axis-corrected, and (3) non-axis-corrected volume estimation. Intraclass correlation coefficients were reported and the Bland–Altman analysis was conducted. Results: Mean DRG volumes ranged from 124.8 mm3 for L3 to 323.3 mm3 for S1 and did not differ between right and left DRG. DRG volume (mean of L3 to S1) correlated with body height (r = 0.42; p = 0.0008) and weight (r = 0.34; p = 0.0087). DRG of men were larger than of women (p = 0.0002); however, no difference remained after correction for body height. Inter-reader reliability was high for all three methods but best for exact volumetry (ICC = 0.99). While axis-corrected estimation was not associated with a relevant bias, non-axis-corrected estimation systematically overestimated DRG volume by on average of 15.55 mm3 (reader 1) or 18.00 mm3 (reader 2) when compared with exact volumetry. Conclusion: The here presented normal values of lumbosacral DRG volume and the correlations with height and weight may be considered in future disease specific studies and possible clinical applications. Exact volumetry was most reliable and should be considered the gold standard. However, the reliability of axis-corrected and non-axis-corrected volume estimation was also high and might still be sufficient, depending on the degree of the required measurement accuracy.

Technical Update on MR Neurography

Imaging evaluation of peripheral nerves (PNs) is challenging. Magnetic resonance imaging (MRI) and ultrasonography are the modalities of choice in the imaging assessment of PNs. Both conventional MRI pulse sequences and advanced techniques have important roles. Routine MR sequences are the workhorse, with the main goal to provide superb anatomical definition and identify focal or diffuse nerve T2 signal abnormalities. Selective techniques, such as three-dimensional (3D) cranial nerve imaging (CRANI) or 3D NerveVIEW, allow for a more detailed evaluation of normal and pathologic states. These conventional pulse sequences have a limited role in the comprehensive assessment of pathophysiologic and ultrastructural abnormalities of PNs. Advanced functional MR neurography sequences, such as diffusion tensor imaging tractography or T2 mapping, provide useful and robust quantitative parameters that can be useful in the assessment of PNs on a microscopic level. This article offers an overview of various technical parameters, pulse sequences, and protocols available in the imaging of PNs and provides tips on avoiding potential pitfalls.

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.

Quantitative MR-Neurography at 3.0T: Inter-Scanner Reproducibility

Background

Quantitative MR-neurography (MRN) is increasingly applied, however, the impact of the MR-scanner on the derived parameters is unknown. Here, we used different 3.0T MR scanners and applied comparable MR-sequences in order to quantify the inter-scanner reproducibility of various MRN parameters of the sciatic nerve.

Methods

Ten healthy volunteers were prospectively examined at three different 3.0T MR scanners and underwent MRN of their sciatic nerve using comparable imaging protocols including diffusion tensor imaging (DTI) and T2 relaxometry. Subsequently, inter-scanner agreement was assessed for seven different parameters by calculating the intraclass correlation coefficients (ICCs) and the standard error of measurement (SEM).

Results

Assessment of inter-scanner reliability revealed good to excellent agreement for T2 (ICC: 0.846) and the quantitative DTI parameters, such as fractional anisotropy (FA) (ICC: 0.876), whereas moderate agreement was observed for proton spin density (PD) (ICC: 0.51). Analysis of variance identified significant inter-scanner differences for several parameters, such as FA (p < 0.001; p = 0.02), T2 (p < 0.01) and PD (p = 0.02; p < 0.01; p = 0.02). Calculated SEM values were mostly within the range of one standard deviation of the absolute mean values, for example 0.033 for FA, 4.12 ms for T2 and 27.8 for PD.

Conclusion

This study quantifies the measurement imprecision for peripheral nerve DTI and T2 relaxometry, which is associated with the use of different MR scanners. The here presented values may serve as an orientation of the possible scanner-associated fluctuations of MRN biomarkers, which can occur under similar conditions.

Accelerating Knee MRI: 3D Modulated Flip-Angle Technique in Refocused Imaging with an Extended Echo Train and Compressed Sensing

Purpose

The three-dimensional (3D) sequence of magnetic resonance imaging (MRI) plays a critical role in the imaging of musculoskeletal joints; however, its long acquisition time limits its clinical application. In such conditions, compressed sensing (CS) is introduced to accelerate MRI in clinical practice. We aimed to investigate the feasibility of an isotropic 3D variable-flip-angle fast spin echo (FSE) sequence with CS technique (CS-MATRIX) compared to conventional 2D sequences in knee imaging.

Methods

Images from different sequences of both the accelerated CS-MATRIX and the corresponding conventional acquisitions were prospectively analyzed and compared. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the structures within the knees were measured for quantitative analysis. The subjective image quality and diagnostic agreement were compared between CS-MATRIX and conventional 2D sequences. Quantitative and subjective image quality scores were statistically analyzed with the paired t-test and Wilcoxon signed-rank test, respectively. Diagnostic agreements of knee substructure were assessed using Cohen’s weighted kappa statistic.

Results

For quantitative analysis, images from the CS-MATRIX sequence showed a significantly higher SNR than T2-fs 2D sequences for visualizing cartilage, menisci, and ligaments, as well as a higher SNR than proton density (pd) 2D sequences for visualizing menisci and ligaments. There was no significant difference between CS-MATRIX and 2D T2-fs sequences in subjective image quality assessment. The diagnostic agreement was rated as moderate to very good between CS-MATRIX and 2D sequences.

Conclusion

This study demonstrates the feasibility and clinical potential of the CS-MATRIX sequence technique for detecting knee lesions The CS-MATRIX sequence allows for faster knee imaging than conventional 2D sequences, yielding similar image quality to 2D sequences.

Assessment of peripheral neuropathy in type 2 diabetes by diffusion tensor imaging

BACKGROUND

To evaluate the diagnostic accuracy of diffusion tensor imaging (DTI) in diabetic peripheral neuropathy (DPN) for patients with type 2 diabetes and detect the correlations with electrophysiology.

METHODS

A total of 27 patients with type 2 diabetes with DPN, 24 patients with type 2 diabetes without peripheral neuropathy (NDPN), as well as 32 healthy controls (HC) were enrolled in this study. Clinical examinations and neurophysiologic tests were used to determine the presence of DPN. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of peripheral nerves, including the tibial nerve (TN) and common peroneal nerve (CPN), were calculated. Receiver operating characteristic (ROC) analysis was performed for FA and ADC values. Pearson's correlation coefficient was used to assess the correlation between DTI and electrophysiology parameters in the patient group.

RESULTS

The tibial and common peroneal nerve FAs were lowest (P=0.003, 0.001, respectively) and ADC was highest (P=0.004, 0.005, respectively) in the DPN group. The FA value of the axonal injury group was lower than that in the demyelination group (P=0.035, 0.01, respectively), while the ADC value was higher (P=0.02, 0.01, respectively). In the DPN group, FA value was positively correlated with motor conduction velocity (MCV) (tibial nerve: r=0.420, P=0.007; common peroneal nerve: r=0.581, P<0.001) and motor amplitude (MA) (tibial nerve: r=0.623, P<0.001; common peroneal nerve: r=0.513; P=0.001), while ADC values was negatively correlated with MCV (tibial nerve: r=-0.320, P=0.044; common peroneal nerve: r=-0.569; P<0.001), and MA (tibial nerve: r=-0.491, P=0.001; common peroneal nerve: r=-0.524; P=0.001).

CONCLUSIONS

With a lower FA value and higher ADC value, DTI accurately discriminated DPN. The DTI multi-parameter quantitative analysis of peripheral nerves differentiated DPN axonal injury from the demyelinating lesion, and hence, could be applied in the diagnosis of DPN.

Quadrilateral space syndrome

The quadrilateral space is a confined area through which the axillary nerve and posterior circumflex humeral artery (PCHA) travel in the shoulder. Both structures are susceptible to impingement and compression as they travel though this space resulting in a constellation of symptoms known as quadrilateral space syndrome (QSS). Patients may experience paresthesias, loss of motor function, pain and vascular complications. Individuals who perform repetitive overhead arm movements such as elite athletes are at greater risk of developing QSS. The diagnosis can be difficult, but in the setting of clinical suspicion, physical exam and imaging studies can provide specific findings. On MRI, patients may have atrophy of the deltoid or teres minor muscles and angiography may show aneurysm or vascular occlusion of the PCHA. Treatment is initially conservative, with physiotherapy. Surgical decompression is effective in patients with severe or progressive symptoms. Causes of external compression such as fibrous bands, scarring, or other space occupying lesion may be addressed at that time. Neurolysis and aneurysm resection may also be performed. In some cases, emboli from the PCHA can cause ischemia in the involved upper extremity resulting in an acute presentation. Catheter directed therapy such as thrombolysis or thrombectomy may performed emergently in these cases. Though rare, in patients presenting with arm weakness, paresthesia, pain and/or arterial thrombosis in the arm, QSS is an important entity to consider.

3D MRI of the Knee

Three-dimensional (3D) magnetic resonance imaging (MRI) of the knee is widely used in musculoskeletal (MSK) imaging. Currently, 3D sequences are most commonly used for morphological imaging. Isotropic 3D MRI provides higher out-of-plane resolution than standard two-dimensional (2D) MRI, leading to reduced partial volume averaging artifacts and allowing for multiplanar reconstructions in any plane with any thickness from a single high-resolution isotropic acquisition. Specifically, isotropic 3D fast spin-echo imaging, with options for tissue weighting similar to those used in multiplanar 2D FSE imaging, is of particular interest to MSK radiologists. New applications for 3D spatially encoded sequences are also increasingly available for clinical use. These applications offer advantages over standard 2D techniques for metal artifact reduction, quantitative cartilage imaging, nerve imaging, and bone shape analysis. Emerging fast imaging techniques can be used to overcome the long acquisition times that have limited the adoption of 3D imaging in clinical protocols.

3D MR Neurography

High-resolution isotropic volumetric three-dimensional (3D) magnetic resonance neurography (MRN) techniques enable multiplanar depiction of peripheral nerves. In addition, 3D MRN provides anatomical and functional tissue characterization of different disease conditions affecting the peripheral nerves. In this review article, we summarize clinically relevant technical considerations of 3D MRN image acquisition and review clinical applications of 3D MRN to assess peripheral nerve diseases, such as entrapments, trauma, inflammatory or infectious neuropathies, and neoplasms.

Evaluation of peripheral nerve injury by magnetic resonance neurography: A systematic review

In view of the limitations of current methods for assessing peripheral nerve injury, there is a need for technical innovations to improve diagnosis, surgical approach and postoperative monitoring. The objective of this study was to conduct a systematic review to analyze the applicability of magnetic resonance neurography in peripheral nerve injuries. The present systematic review focused on the use of magnetic resonance neurography. The literature was searched in the PUBMED, Cochrane Library and Virtual Health Library databases using the PICO method. One hundred sixty-two articles were retrieved with the terms "magnetic resonance imaging" and "peripheral nerve injury", with a filter for the last 10 years (2010-2020). Nineteen were eligible for the review. Most were reviews, with few systematic reviews of randomized controlled trials. Although not included in the recommended protocol, MRI is increasingly used due to its numerous advantages: it is non-invasive, providing objective visualization of neural and perineural tissues, fascicular representation as a result of high resolution, and objective visualization of serial interval images of successful treatment. This is one of the first systematic reviews of the literature regarding the use of magnetic resonance imaging neurography to assess peripheral nerve injury, highlighting the need to implement new imaging techniques in this field of medical practice.

Hand and Wrist Neuropathies: High-resolution Ultrasonography and MR Neurography

High-resolution ultrasonography (US) and magnetic resonance neurography (MRN) have followed parallel paths for peripheral nerve imaging with little comparison of the two modalities. They seem equally effective to study a variety of neuropathies affecting large and small nerves in the wrist and hand. This article outlines the technical considerations of US and MRN and discusses normal and abnormal imaging appearances of hand and wrist nerves from etiologies such as entrapment, injury, tumor, and proximal and diffuse neuropathy, with specific case illustrations.

Evaluation of peripheral nerve acute crush injury in rabbits: comparison among diffusion kurtosis imaging, diffusion tensor imaging and electromyography

OBJECTIVE

Diffusion kurtosis imaging (DKI) has been proven to provide additional value for assessing many central nervous system diseases compared with conventional diffusion tensor imaging (DTI); however, whether it has the same value in peripheral nerve injury is unclear. This study aimed to investigate the performance of DKI, DTI, and electromyography (EMG) in evaluating peripheral nerve crush injury (PNCI) in rabbits.

MATERIALS AND METHODS

A total of 27 New Zealand white rabbits were selected to establish a PNCI model. Longitudinal DTI, DKI, and EMG were evaluated before surgery and 1 day, 3 days, 1 week, 2 weeks, 4 weeks, 6 weeks, and 8 weeks after surgery. At each time point, two rabbits were randomly selected for pathological examination.

RESULTS

The results showed that fractional anisotropy (FA) derived from both DKI and DTI demonstrated a significant difference between injured and control nerves at all time points (all P < 0.005) mean kurtosis of the injured nerve was lower than that on the control side after 2-8 weeks (all P < 0.05). No statistically significant difference was found in radial kurtosis, axial kurtosis, and apparent diffusion coefficient at almost every time point. The difference in compound muscle action potential (CMAP) of the bilateral gastrocnemius at each time point was statistically significant (all P < 0.001).

CONCLUSIONS

CMAP was a sensitive and reliable method to assess acute PNCI without being affected by perineural edema. DKI may not be superior to DTI in evaluating peripheral nerves, DTI with a shorter scanning time was preferred as an effective choice for evaluating acute peripheral nerve traumatic injury.

Neuropathies périphériques associées aux syndromes lymphoprolifératifs : spectre clinique et démarche diagnostique

Lymphoproliferative syndromes (multiple myeloma, Waldenström's disease, chronic lymphocytic leukemia, lymphomas) may be associated with peripheral neuropathies. The mechanism can be dysimmune, associated or not with monoclonal gammopathies; paraneoplastic; infiltrative; or more commonly, iatrogenic or due to vitamin deficiency. The diagnosis can be complex, especially when the neuropathy is the presenting manifestation, requiring a close cooperation between internists and neurologists. The positive diagnosis of the neuropathy is based on a systematic electro-clinical investigation, which specifies the topography and the mechanism of the nerve damage, sometimes reinforced by imaging examinations, in particular, nerve and/or plexus MRI. The imputability of the neuropathy to a lymphoproliferative syndrome is based on a set of arguments including the clinical context (B signs, tumour syndrome), first-line laboratory tests (hemogram, protein electrophoresis, viral serologies, complement), auto-antibodies discussed according to the neuropathy (anti-MAG, anti-gangliosides) and sometimes more invasive examinations (bone marrow or neuro-muscular biopsies).

"Million dollar nerve" magnetic resonance neurography: first normal and pathological findings

OBJECTIVES

To evaluate prospectively the feasibility of magnetic resonance neurography (MRN) in identifying the anatomical characteristics of thenar muscular branch (TMB) of the median nerve, also known as the "million dollar nerve," in patients and controls.

METHODS

Thirteen patients affected by carpal tunnel syndrome (CTS) and four healthy controls had their hands scanned on a 3-T MR imaging scanner for TMB visualization. Median nerve anatomical variations were classified into four groups according to Poisel's classification system modified by Lanz. TMB signal intensity and diameter were assessed for the diagnosis of neuropathy.

RESULTS

TMB was successfully identified in all patients and subjects by using MRN. The most suitable pulse sequences to identify and measure nerve diameter were 3D DW-PSIF and T2-FS-TSE. The axial oblique and sagittal oblique planes are complementary in demonstrating its entire course. TMB had mostly an extraligamentous course with radial side origin (93.8%, each). All patients experienced increased T2 signal intensity (p < 0.001) and thickened nerves. Mean TMB diameters were 1.27 ± 0.21 mm (range, 1.02-1.74 mm) and 0.87 ± 0.16 mm (0.73-1.08 mm) (p = 0.008) in the patient and control groups, respectively.

CONCLUSION

MRN is a reliable imaging technique for identification and anatomical characterization of TMB in patients affected by CTS. This innovative imaging workup may therefore be included in the preoperative evaluation of patients scheduled for carpal tunnel release, especially in CTS with TMB involvement or even in isolated TMB neuropathy.

KEY POINTS

• Magnetic resonance neurography allows precise visualization of the thenar muscular branch of the median nerve. • Thenar muscular branch anatomical variations can be correctly identified. • Preoperative scanning can contribute to reducing the risk of iatrogenic injuries during carpal tunnel release, especially in carpal tunnel syndrome with thenar muscular branch involvement or even in isolated thenar muscular branch neuropathy.

Reliability and reproducibility of sciatic nerve magnetization transfer imaging and T2 relaxometry

Objectives

To assess the interreader and test-retest reliability of magnetization transfer imaging (MTI) and T2 relaxometry in sciatic nerve MR neurography (MRN).

Materials and methods

In this prospective study, 21 healthy volunteers were examined three times on separate days by a standardized MRN protocol at 3 Tesla, consisting of an MTI sequence, a multi-echo T2 relaxometry sequence, and a high-resolution T2-weighted sequence. Magnetization transfer ratio (MTR), T2 relaxation time, and proton spin density (PSD) of the sciatic nerve were assessed by two independent observers, and both interreader and test-retest reliability for all readout parameters were reported by intraclass correlation coefficients (ICCs) and standard error of measurement (SEM).

Results

For the sciatic nerve, overall mean ± standard deviation MTR was 26.75 ± 3.5%, T2 was 64.54 ± 8.2 ms, and PSD was 340.93 ± 78.8. ICCs ranged between 0.81 (MTR) and 0.94 (PSD) for interreader reliability and between 0.75 (MTR) and 0.94 (PSD) for test-retest reliability. SEM for interreader reliability was 1.7% for MTR, 2.67 ms for T2, and 21.3 for PSD. SEM for test-retest reliability was 1.7% for MTR, 2.66 ms for T2, and 20.1 for PSD.

Conclusions

MTI and T2 relaxometry of the sciatic nerve are reliable and reproducible. The values of measurement imprecision reported here may serve as a guide for correct interpretation of quantitative MRN biomarkers in future studies.

Key Points

• Magnetization transfer imaging (MTI) and T2 relaxometry of the sciatic nerve are reliable and reproducible.

• The imprecision that is unavoidably associated with different scans or different readers can be estimated by the here presented SEM values for the biomarkers T2, PSD, and MTR.

• These values may serve as a guide for correct interpretation of quantitative MRN biomarkers in future studies and possible clinical applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-08072-9.