Clinical impact of magnetic resonance neurography in patients with brachial plexus neuropathies

A Deep Learning Approach for Nerve Injury Classification in Brachial Plexopathies Using Magnetic Resonance Neurography with Modified Hiking Optimization Algorithm

RATIONALE AND OBJECTIVES

Brachial plexopathies (BPs) encompass a complex spectrum of nerve injuries affecting motor and sensory function in the upper extremities. Diagnosis is challenging due to the intricate anatomy and symptom overlap with other neuropathies. Magnetic Resonance Neurography (MRN) provides advanced imaging but requires specialized interpretation. This study proposes an AI-based framework that combines deep learning (DL) with the modified Hiking Optimization Algorithm (MHOA) enhanced by a Comprehensive Learning (CL) technique to improve the classification of nerve injuries (neuropraxia, axonotmesis, neurotmesis) using MRN data.

MATERIALS AND METHODS

The framework utilizes MobileNetV4 for feature extraction and MHOA for optimized feature selection across different MRI sequences (STIR, T2, T1, and DWI). A dataset of 39 patients diagnosed with BP was used. The framework classifies injuries based on Seddon's criteria, distinguishing between normal and abnormal conditions as well as injury severity.

RESULTS

The model achieved excellent performance, with 1.0000 accuracy in distinguishing normal from abnormal conditions using STIR and T2 sequences. For injury severity classification, accuracy was 0.9820 in STIR, outperforming the original HOA and other metaheuristic algorithms. Additionally, high classification accuracy (0.9667) was observed in DWI. The proposed framework outperformed traditional methods and demonstrated high sensitivity and specificity.

CONCLUSION

The proposed AI-based framework significantly improves the diagnosis of BP by accurately classifying nerve injury types. By integrating DL and optimization techniques, it reduces diagnostic variability, making it a valuable tool for clinical settings with limited specialized neuroimaging expertise. This framework has the potential to enhance clinical decision-making and optimize patient outcomes through precise and timely diagnoses.

The value of MR neurography in assessing lesions of the thoracic dorsal root ganglia in patients with zoster-associated pain

OBJECTIVES

To evaluate the imaging characteristics of the thoracic dorsal root ganglia (DRG) in patients with zoster-associated pain (ZAP) using magnetic resonance neurography (MRN) and its correlation with disease stages and serological marker.

METHODS

Twenty-six consecutive ZAP patients with different disease stages (acute herpes neuralgia, subacute herpes neuralgia, and postherpetic neuralgia) and thirteen healthy subjects were scanned on a 3-T MR scanner for thoracic DRG visualization. The T1-T12 DRG for each ZAP patient were divided into three groups (prominent affected segment, rash distribution segment, and non-rash distribution segment). The volume and T2 signal intensity (SI) of thoracic DRG were measured and compared. The visual analog scale (VAS) and serological data were also recorded.

RESULTS

The volume ratio of prominent affected thoracic DRG in ZAP patients was larger than that in non-rash distribution segment of ZAP patients and that in the healthy group, respectively (both p < 0.05). The volume ratio of affected DRG in the acute herpes neuralgia and subacute herpes neuralgia group was both higher than that in the postherpetic neuralgia group (both p < 0.05). For T2 SI, no differences were found among three disease stages. The ESR index was the only parameter associated with volume ratio of prominent affected DRG segment (r = 0.48, p = 0.01).

CONCLUSION

MRN is able to visualize and identify morphological changes of thoracic DRG of ZAP patients. The imaging characteristics of affected thoracic DRG exhibit differences across different disease stages, which was associated with ESR index in ZAP patients.

KEY POINTS

Question Magnetic resonance neurography is able to detect the abnormal imaging features of dorsal root ganglia (DRG) in zoster-associated pain patients. Findings Magnetic resonance neurography (MRN) demonstrates a difference in the volume ratio of affected DRG among three disease stages in zoster-associated pain (ZAP) patients. Clinical relevance Combining serological parameter with observed thoracic DRG volume changes on MRN may serve as a viable predictor for ZAP development.

Development of an interactive ultra-high resolution magnetic resonance neurography atlas of the brachial plexus and upper extremity peripheral nerves

PURPOSE

To develop an educational, interactive, ultra-high resolution, in vivo magnetic resonance (MR) neurography atlas for direct visualization of the brachial plexus and upper extremity.

METHODS

A total of 16 adult volunteers without known peripheral neuropathy underwent magnetic resonance (MR) neurography of the brachial plexus and upper extremity. To improve vascular suppression, subjects received an intravenous infusion of ferumoxytol. To improve image quality, MR neurography datasets were reconstructed using a deep learning algorithm. The atlas was then developed using a web-based user-interface software, which allowed for labeling of peripheral nerves and muscles, and mapping of muscles to their respective innervation. The user interface was optimized to maximize interactivity and user-friendliness.

RESULTS

Fifteen subjects completed at least one scan with no reported adverse reactions from the ferumoxytol infusions. Adequate vascular suppression was observed in all MR neurography datasets. The images of the brachial plexus and upper extremity included in this atlas allowed for identification and labeling of 177 unique anatomical structures from the neck to the wrist. The atlas was made freely accessible on the internet.

CONCLUSION

A detailed and interactive MR neurography atlas of the brachial plexus and upper extremity was successfully developed to depict small nerves and fascicular detail with unprecedented spatial and contrast resolution. This freely available online resource (https://www.hss.edu/MRNatlas) can be used as an educational tool and clinical reference. The techniques utilized in this project serve as a framework for continued work in expanding the atlas to cover other peripheral nerve territories.

Use of Magnetic Resonance Neurography for Sensory Nerve Injuries of the Head and Neck

Background

Identification of peripheral nerve injuries of the head and neck can be challenging due to a broad spectrum of symptoms from neuropathic pain to headaches and migraine. This article aimed to present the clinical features and diagnostic workup of patients with acute and chronic peripheral nerve injuries of the head and neck using magnetic resonance neurography (MRN), to demonstrate potential advantages compared with conventional magnetic resonance imaging (MRI).

Methods

Patients who presented with suspected peripheral nerve injury were either referred for a conventional MRI or MRN. Patients who underwent nerve exploration for suspected nerve transection and/or neuroma formation on imaging were included in this study. Imaging findings were correlated with intraoperative observations.

Results

Four patients (3 women, 1 man, age range: 34-70 years) were included. Three subjects had a history of head and neck surgery and 1 experienced direct trauma to the medial eyebrow. Clinical symptoms included numbness, allodynia, positive Tinel sign, and pain relief following nerve blocks. Two patients underwent conventional MRI and 2 underwent MRN. MRI provided a vague indication of potential neuromas and failed to accurately depict their locations. MRN offered a comprehensive visualization of the entire nerve path, identifying nerve transection and neuromas, as well as precise location, dimensions, and relation to adjacent bones and muscles.

Conclusions

High-resolution 3-dimensional MRN provides clear visualization of acute and chronic peripheral nerve injuries of the head and neck region, facilitating early diagnosis of nerve injuries in this region and improving diagnostic accuracy, as well as surgical planning and execution.

3D printing of the brachial plexus and its osseous landmarks using magnetic resonance neurography for thoracic outlet syndrome evaluation

BACKGROUND

Patient-specific three-dimensional (3D) printed anatomic models are valuable clinical tools that facilitate enhanced visualization of pertinent anatomic structures and have demonstrated benefits of reduced surgical times, increased surgeon confidence, and improved operative results and subsequent patient outcomes. Medical image-based 3D printed anatomic models are generally created from computed tomography (CT), however magnetic resonance imaging (MRI), which offers exquisite soft tissue characterization and flexible contrast avoiding the use of ionizing radiation, is an attractive alternative. Herein, the application of 3D printing incorporating both MR neurography and zero-echo time (ZTE) MRI for visualization of the brachial plexus anatomy in a subject with thoracic outlet syndrome (TOS) is described.

METHODS

A 28-year-old man presented with chronic right upper limb discomfort and paresthesias extending from the shoulder region to the third and fourth digits. The subject underwent evaluation with a unilateral brachial plexus MR neurography protocol at 3.0 Tesla for suspicion of TOS. The protocol included T2-weighted, 3D fast spin echo short-tau inversion recovery (STIR-FSE) and 3D radial ZTE sequences for depiction of the nerves and bones, respectively. The first rib and its synostosis impinged upon the inferior aspect of the T1 nerve root (T1NR), with accompanying mild enlargement of the T1NR. A 3D printed anatomic model was created and included: (1) bone (spine, ribs, clavicle, scapula, and humerus), (2) brachial plexus, and (3) costal cartilage.

RESULTS

The 3D printed model clearly demonstrated a T1NR impingement from the synostosis, confirming the diagnosis of neurologic thoracic outlet syndrome (TOS) and guided the treatment approach in prescribing TOS-specific physical therapy, which led to significant improvements in the patient's condition.

CONCLUSION

To our knowledge, this is the first in-vivo human 3D printed case for TOS using MRI-only data. The 3D printed model allowed for improved visualization and understanding of the spatial relationships between the nerves of the brachial plexus and surrounding osseous structures responsible for the patient's symptoms.

CLINICAL TRIAL NUMBER

Not applicable.

The role of imaging in focal neuropathies

Electrodiagnostic testing (EDX) has been the diagnostic tool of choice in peripheral nerve disease for many years, but in recent years, peripheral nerve imaging has been used ever more frequently in daily clinical practice. Nerve ultrasound and magnetic resonance (MR) neurography are able to visualize nerve structures reliably. These techniques can aid in localizing nerve pathology and can reveal significant anatomical abnormalities underlying nerve pathology that may have been otherwise undetected by EDX. As such, nerve ultrasound and MR neurography can significantly improve diagnostic accuracy and can have a significant effect on treatment strategy. In this chapter, the basic principles and recent developments of these techniques will be discussed, as well as their potential application in several types of peripheral nerve disease, such as carpal tunnel syndrome (CTS), ulnar neuropathy at the elbow (UNE), radial neuropathy, brachial and lumbosacral plexopathy, neuralgic amyotrophy (NA), fibular, tibial, sciatic, femoral neuropathy, meralgia paresthetica, peripheral nerve trauma, tumors, and inflammatory neuropathies.

Diagnostic performance of deep learning-based reconstruction algorithm in 3D MR neurography

OBJECTIVE

The study aims to evaluate the diagnostic performance of deep learning-based reconstruction method (DLRecon) in 3D MR neurography for assessment of the brachial and lumbosacral plexus.

MATERIALS AND METHODS

Thirty-five exams (18 brachial and 17 lumbosacral plexus) of 34 patients undergoing routine clinical MR neurography at 1.5 T were retrospectively included (mean age: 49 ± 12 years, 15 female). Coronal 3D T2-weighted short tau inversion recovery fast spin echo with variable flip angle sequences covering plexial nerves on both sides were obtained as part of the standard protocol. In addition to standard-of-care (SOC) reconstruction, k-space was reconstructed with a 3D DLRecon algorithm. Two blinded readers evaluated images for image quality and diagnostic confidence in assessing nerves, muscles, and pathology using a 4-point scale. Additionally, signal-to-noise ratio (SNR) and contrast-to-noise ratios (CNR) between nerve, muscle, and fat were measured. For comparison of visual scoring result non-parametric paired sample Wilcoxon signed-rank testing and for quantitative analysis paired sample Student's t-testing was performed.

RESULTS

DLRecon scored significantly higher than SOC in all categories of image quality (p < 0.05) and diagnostic confidence (p < 0.05), including conspicuity of nerve branches and pathology. With regard to artifacts there was no significant difference between the reconstruction methods. Quantitatively, DLRecon achieved significantly higher CNR and SNR than SOC (p < 0.05).

CONCLUSION

DLRecon enhanced overall image quality, leading to improved conspicuity of nerve branches and pathology, and allowing for increased diagnostic confidence in evaluation of the brachial and lumbosacral plexus.

Neuropathy Score Reporting and Data System (NS-RADS): A Practical Review of MRI-Based Peripheral Neuropathy Assessment

The Neuropathy Score Reporting and Data System (NS-RADS) is a newly developed MR imaging-based classification that standardizes reporting and multidisciplinary communication for MR imaging diagnosis and follow-up of peripheral neuropathies. NS-RADS classification has shown to be accurate and reliable across different centers, readers' experience levels, and degrees of peripheral neuropathies, which include nerve injury, entrapment, neoplasm, diffuse neuropathy, post-interventional status, and temporal changes in muscle denervation. This article brings a practical review of NS-RADS classification, representative MR cases, and a step-by-step tutorial on how to approach this staging system. Readers can gain knowledge and apply it in their practice, aiming to standardize the communications between specialties and improve patient management.

MRI Advancements in Musculoskeletal Clinical and Research Practice

Over the past decades, MRI has become increasingly important for diagnosing and longitudinally monitoring musculoskeletal disorders, with ongoing hardware and software improvements aiming to optimize image quality and speed. However, surging demand for musculoskeletal MRI and increased interest to provide more personalized care will necessitate a stronger emphasis on efficiency and specificity. Ongoing hardware developments include more powerful gradients, improvements in wide-bore magnet designs to maintain field homogeneity, and high-channel phased-array coils. There is also interest in low-field-strength magnets with inherently lower magnetic footprints and operational costs to accommodate global demand in middle- and low-income countries. Previous approaches to decrease acquisition times by means of conventional acceleration techniques (eg, parallel imaging or compressed sensing) are now largely overshadowed by deep learning reconstruction algorithms. It is expected that greater emphasis will be placed on improving synthetic MRI and MR fingerprinting approaches to shorten overall acquisition times while also addressing the demand of personalized care by simultaneously capturing microstructural information to provide greater detail of disease severity. Authors also anticipate increased research emphasis on metal artifact reduction techniques, bone imaging, and MR neurography to meet clinical needs.

3D CRANI, a novel MR neurography sequence, can reliable visualise the extraforaminal cranial and occipital nerves

OBJECTIVES

We aim to validate 3D CRANI, a novel high-field STIR TSE, MR neurography sequence in the visualisation of the extraforaminal cranial and occipital nerve branches on a 3-T system. Furthermore, we wish to evaluate the role of gadolinium administration and calculate nerve benchmark values for future reference.

METHODS

Eleven consecutive patients underwent MR imaging including the 3D CRANI sequence before and immediately after intravenous gadolinium administration. Two observers rated suppression quality and nerve visualisation using Likert scales before and after contrast administration. Extraforaminal cranial and occipital nerves were assessed. Nerve calibers and signal intensities were measured at predefined anatomical landmarks, and apparent signal intensity ratios were calculated.

RESULTS

The assessed segments of the cranial and occipital nerves could be identified in most cases. The overall intrarater agreement was 79.2% and interrater agreement was 82.7% (intrarater κ = .561, p < .0001; interrater κ = .642, p < .0001). After contrast administration, this significantly improved to an intrarater agreement of 92.7% and interrater agreement of 93.6% (intrarater κ = .688, p < .0001; interrater κ = .727, p < .0001). Contrast administration improved suppression quality and significant changes in nerve caliber and signal intensity measurements. Nerve diameter and signal intensity benchmarking values were obtained.

CONCLUSION

3D CRANI is reliable for the visualization of the extraforaminal cranial and occipital nerves. Intravenous gadolinium significantly improves MR neurography when applying this sequence. Benchmarking data are published to allow future assessment of the 3D CRANI sequence in patients with pathology of the extraforaminal cranial and occipital nerves.

KEY POINTS

• MR neurography using the 3D CRANI sequence is a reliable method to evaluate the extraforaminal cranial and occipital nerves. • Gadolinium contrast administration significantly improves suppression quality and nerve visualisation. • Benchmarking values including apparent signal intensity ratios and nerve calibers depend on contrast administration and might play an important role in future studies evaluating extraforaminal cranial and occipital neuropathies.

Does the apparent diffusion coefficient from diffusion-weighted MRI imaging aid in the characterization of malignant soft tissue tumors and sarcomas

OBJECTIVE

To identify trends in apparent diffusion coefficient (ADC) measurements from diffusion-weighted imaging (DWI) with respect to tumor type classification and other tumor characteristics whether common malignant soft tissue tumors can be distinguished.

MATERIALS AND METHODS

A consecutive series of extremity malignant soft tissue tumors and soft tissue sarcomas (STS) among 78 adult patients with conventional MRI and DWI were included. Each case was evaluated with respect to T1/T2 signal alterations and heterogeneity, presence of peritumoral edema, necrosis, cystic changes, internal hemorrhage, and maximum longitudinal dimension blinded to the histology. The ADC mean and minimum were obtained using a free-hand region of interest of the whole tumor and the darkest (lowest signal area) ADC area of the tumor. Kruskal-Wallis and Wilcoxon Rank-Sum Tests were used to determine associations and significance between tumor subtypes. Intraclass correlation (ICC) and kappa calculations were utilized to assess inter-reader agreements for ADC values and reader diagnosis.

RESULTS

Liposarcomas showed more heterogenous T1W images with hyperintense T1W signal when compared to tumors not classified as liposarcoma (P = 0.046 and P = 0.010, respectively). Liposarcomas were relatively consistent in demonstrating an absence of hemorrhage (81.8%) while undifferentiated pleomorphic sarcomas consistently showed intralesional hemorrhage (90%). When comparing individual tumor classifications against the rest of the samples, lymphomas registered lower mean and minimum ADC values in the whole tumor and in the most hypointense area of the tumor for both readers (P < 0.05). The interobserver agreement between the two readers was good to excellent for all four ADC measurements (ICC = 0.65-0.98).

CONCLUSION

Diffusion-weighted imaging generated ADC measurements are reproducible but currently offer limited insight in being able to differentiate among different malignant soft tissue tumor and sarcoma histologies. T1W and T2W signal characteristics also offer limited insight in differentiating between soft tissue malignancies.

Advances in the neuroimaging of motor disorders

Neuroimaging is a valuable adjunct to the history and examination in the evaluation of motor system disorders. Conventional imaging with computed tomography or magnetic resonance imaging depicts important anatomic information and helps to identify imaging patterns which may support diagnosis of a specific motor disorder. Advanced imaging techniques can provide further detail regarding volume, functional, or metabolic changes occurring in nervous system pathology. This chapter is an overview of the advances in neuroimaging with particular emphasis on both standard and less well-known advanced imaging techniques and findings, such as diffusion tensor imaging or volumetric studies, and their application to specific motor disorders. In addition, it provides reference to emerging imaging biomarkers in motor system disorders such as Parkinson disease, amyotrophic lateral sclerosis, and Huntington disease, and briefly reviews the neuroimaging findings in different causes of myelopathy and peripheral nerve disorders.

Neuropathy Score Reporting and Data System (NS-RADS): MRI Reporting Guideline of Peripheral Neuropathy Explained and Reviewed

A standardized guideline and scoring system should be used for the MR imaging diagnosis of peripheral neuropathy. The MR imaging-based Neuropathy Score Reporting and Data System (NS-RADS) is a newly devised classification system (in press in AJR) that can be used to communicate both type and severity of peripheral neuropathy in the light of clinical history and examination findings. The spectrum of neuropathic conditions and peripheral nerve disorders covered in this system includes nerve injury, entrapment, neoplasm, diffuse neuropathy, and post-interventional states. This classification system also describes the temporal MR imaging appearances of regional muscle denervation changes. This review article is based on the multicenter validation study pre-published in American journal of Roentgenology and discusses technical considerations of optimal MR imaging for peripheral nerve evaluation and discusses the NS-RADS classification and its severity scales with illustration of conditions that fall under each classification. The readers can gain knowledge of the NS-RADS classification system and learn to apply it in their practices for improved inter-disciplinary communications and timely patient management.

Brakial Pleksopatide Klinik, EMG ve MR Nörografi Bulgularının Değerlendirilmesi

Amaç: Çalışmanın amacı brakial pleksopatide MR nörografi sonuçlarını elektrodiagnostik test ile birlikte değerlendirmek ve MR nörografinin yararlığını saptamaktır. Yöntem: Brakial pleksopati şüphesi bulunan ve elektrodiagnostik test yapılan 50 hasta çalışmaya dahil edildi. MR nörografide Brakiyal pleksusun kök, gövde ve kord seviyesinde seyri, kalibrasyonu, sinyal yoğunluğu ve devamlılığı 2 bağımsız radyolog tarafından değerlendirildi. Bulgular: Elektrodiagnostik test altın standart tanı testi kabul edilerek yapılan analizde MR nörografinin tanısal doğruluk, duyarlılık, özgüllüğü; 1. okuyucu için sırasıyla %64, %45.16, %94.73; 2. okuyucu için sırasıyla %74, %67.74, % 84.21. Okuyucular arası tutarlılık %78 idi. Sonuç: Brakial pleksopati klinik şüphesi bulunan hastalarda MR’ın duyarlılığı ve okuyucular arasındaki uyum orta derecede bulundu. MR nörografi brakial pleksopatiyi gösterebilir ancak pleksusun normal görünümü pleksopati tanısını dışlamamalıdır.

Neoplastic nerve lesions

Though metastasis and malignant infiltration of the peripheral nervous system is relatively rare, physicians should have a familiarity with their presentations to allow for prompt diagnosis and initiation of treatment. This article will review the clinical presentations, diagnostic evaluation, and treatment of neoplastic involvement of the cranial nerves, nerve roots, peripheral nerves, and muscle. Due to the proximity of the neural structure traversing the skull base, metastasis to this region results in distinctive syndromes, most often associated with breast, lung, and prostate cancer. Metastatic involvement of the nerve roots is uncommon, apart from leptomeningeal carcinomatosis and bony metastasis with resultant nerve root damage, and is characterized by significant pain, weakness, and numbness of an extremity. Neoplasms may metastasize or infiltrate the brachial and lumbosacral plexuses resulting in progressive and painful sensory and motor deficits. Differentiating neoplastic involvement from radiation-induced injury is of paramount importance as it dictates treatment and prognosis. Neurolymphomatosis, due to malignant lymphocytic infiltration of the cranial nerves, nerve roots, plexuses, and peripheral nerves, deserves special attention given its myriad presentations, often mimicking acquired demyelinating neuropathies.

Team Approach: Management of Brachial Plexus Injuries

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Traumatic brachial plexus injuries are relatively rare but potentially devastating injuries with substantial functional, psychological, and economic consequences.

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Prompt referral (ideally within 6 weeks of injury) to a center with a team of experts experienced in the diagnosis and management of these injuries is helpful to achieving optimal outcomes.

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Preoperative and intraoperative decision-making to diagnose and plan reconstructive procedures is complex and must take into account a number of factors, including the time from injury, concomitant injuries, preservation of cervical nerve roots, and the availability of intraplexal and extraplexal donor nerves for nerve transfer.

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A team approach is essential to ensure accurate localization of the pathology before surgery and to maximize rehabilitation after surgery, necessitating close contact between the surgical team, physiatrists, radiologists, and therapists.

Additive value of magnetic resonance neurography in diagnosis of brachial plexopathy: a cross-section descriptive study

Background

Management of brachial plexopathy requires proper localization of the site and nature of nerve injury. Nerve conduction studies and electrophysiological studies (ED) are crucial when diagnosing brachial neuropathy but these do not determine the actual site of the lesion. Conventional MRI has been used to evaluate the brachial plexus. Still, it carried the disadvantage of the inability to provide multi-planar images that depict the entire length of the neural plexus .It might be difficult to differentiate the brachial plexus nerves from adjacent vascular structures. Magnetic resonance neurography (MRN) is an innovative imaging technique for direct imaging of the spinal nerves. Our study aims to detect the additive role of MRN in the diagnosis of brachial plexopathy over ED. Forty cases of clinically suspected and proved by clinical examination and ED—traumatic (N = 30) and non-traumatic (N = 10)—were included in our study. We compared MRN finding with results of clinical examination and ED.

Results

MRN findings showed that the root was involved in 80% of cases, trunks in 70% of cases affecting the middle trunk in 40% of cases, the middle and posterior cord in 25%, lateral cord in 50%, and terminal branches on 10% of cases. Ten percent of cases were normal according to MRN, and 90% had abnormal findings in the form of preganglionic nerve root avulsion in 30% of cases, mild perineural edema surrounding C6/7 nerve roots in 20%, lower brachial trunk high signal in 10%, complicated with pseudo meningocele in 20%, and with increased shoulder muscle T2 signal intensity with muscle atrophy in 10%. There were minimal differences between clinical examination finding and MRN findings, with very good agreement between electromyography and nerve conduction (p value < 0.05, with sensitivity and specificity values of 94.44% and 100%, respectively).

Conclusion

MRN is important in differentiating different types of nerve injuries, nerve root avulsion, and nerve edema, playing an important role in differentiating the site of nerve injury, both preganglionic or postganglionic and planning for treatment of the cause of nerve injury, either medical or surgical.

MR Neurography of Peripheral Nerve Injury in the Presence of Orthopedic Hardware: Technical Considerations

As the frequency of orthopedic procedures performed each year in the United States continues to increase, evaluation of peripheral nerve injury (PNI) in the presence of pre-existing metallic hardware is in higher demand. Advances in metal artifact reduction techniques have substantially improved the capability to reduce the susceptibility effect at MRI, but few reports have documented the use of MR neurography in the evaluation of peripheral nerves in the presence of orthopedic hardware. This report delineates the challenges of MR neurography around metal given the high spatial resolution often required to adequately depict small peripheral nerves. It offers practical tips, including strategies for prescan assessment and protocol optimization, including use of more conventional two-dimensional proton density and T2-weighted fat-suppressed sequences and specialized three-dimensional techniques, such as reversed free-induction steady-state precession and multispectral imaging, which enable vascular suppression and metal artifact reduction, respectively. Finally, this article emphasizes the importance of real-time monitoring by radiologists to optimize the diagnostic yield of MR neurography in the presence of orthopedic hardware. © RSNA, 2021.

Magnetic Resonance Neurography for Evaluation of Peripheral Nerves

Peripheral nerve injuries (PNIs) continue to present both diagnostic and treatment challenges. While nerve transections are typically a straightforward diagnosis, other types of PNIs, such as chronic or traumatic nerve compression, may be more difficult to evaluate due to their varied presentation and limitations of current diagnostic tools. As a result, diagnosis may be delayed, and these patients may go on to develop progressive symptoms, impeding normal activity. In the past, PNIs were diagnosed by history and clinical examination alone or techniques that raised concerns regarding accuracy, invasiveness, or operator dependency. Magnetic resonance neurography (MRN) has been increasingly utilized in clinical settings due to its ability to visualize complex nerve structures along their entire pathway and distinguish nerves from surrounding vasculature and tissue in a noninvasive manner. In this review, we discuss the clinical applications of MRN in the diagnosis, as well as pre- and postsurgical assessments of patients with peripheral neuropathies.

Imaging Review of Peripheral Nerve Injuries in Patients with COVID-19

With surging numbers of patients with coronavirus disease 2019 (COVID-19) throughout the world, neuromuscular complications and rehabilitation concerns are becoming more apparent. Peripheral nerve injury can occur in patients with COVID-19 secondary to postinfectious inflammatory neuropathy, prone positioning-related stretch and/or compression injury, systemic neuropathy, or nerve entrapment from hematoma. Imaging of peripheral nerves in patients with COVID-19 may help to characterize nerve abnormality, to identify site and severity of nerve damage, and to potentially elucidate mechanisms of injury, thereby aiding the medical diagnosis and decision-making process. This review article aims to provide a first comprehensive summary of the current knowledge of COVID-19 and peripheral nerve imaging.

MR neurography of the brachial plexus in adult and pediatric age groups: evolution, recent advances, and future directions

Introduction: MR neurography (MRN) of the brachial plexus has emerged in recent years as a safe and accurate modality for the identification of brachial plexopathies in pediatric and adult populations. While clinical differentiation of brachial plexopathy from cervical spine-related radiculopathy or nerve injury has long relied upon nonspecific physical exam and electrodiagnostic testing modalities, MRN now permits detailed interrogation of peripheral nerve anatomy and pathology, as well as assessment of surrounding soft tissues and musculature, thereby facilitating accurate diagnosis. The reader will learn about the current state of brachial plexus MRN, including recent advances and future directions, and gain knowledge about the adult and pediatric brachial plexopathies that can be characterized using these techniques.Areas Covered: The review details recent developments in brachial plexus MRN, including increasing availability of 3.0-T MR scanners at both private and academic diagnostic imaging centers, as well as the advent of multiple new vascular and fat signal suppression techniques. A literature search of PubMed and SCOPUS was used as the principal source of information gathered for this review.Expert Opinion: Refinement of fat-suppression, 3D techniques and diffusion MR imaging modalities has improved the accuracy of MRN, rendering it as a useful adjunct to clinical findings during the evaluation of suspected brachial plexus lesions.

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.

Recent Advances in Pediatric Brain, Spine, and Neuromuscular Magnetic Resonance Imaging Techniques

Magnetic resonance imaging (MRI) is a powerful radiologic tool with the ability to generate a variety of proton-based signal contrast from tissues. Owing to this immense flexibility in signal generation, new MRI techniques are constantly being developed, tested, and optimized for clinical utility. In addition, the safe and nonionizing nature of MRI makes it a suitable modality for imaging in children. In this review article, we summarize a few of the most popular advances in MRI techniques in recent years. In particular, we highlight how these new developments have affected brain, spine, and neuromuscular imaging and focus on their applications in pediatric patients. In the first part of the review, we discuss new approaches such as multiphase and multidelay arterial spin labeling for quantitative perfusion and angiography of the brain, amide proton transfer MRI of the brain, MRI of brachial plexus and lumbar plexus nerves (i.e., neurography), and T2 mapping and fat characterization in neuromuscular diseases. In the second part of the review, we focus on describing new data acquisition strategies in accelerated MRI aimed collectively at reducing the scan time, including simultaneous multislice imaging, compressed sensing, synthetic MRI, and magnetic resonance fingerprinting. In discussing the aforementioned, the review also summarizes the advantages and disadvantages of each method and their current state of commercial availability from MRI vendors.

Ultrasound imaging of brachial plexus trauma in gunshot injury

INTRODUCTION

Brachial plexus trauma related to gunshot (GS) injury requires early examination and characterization to ensure appropriate treatment. Magnetic resonance imaging (MRI) may be contraindicated when there are metal fragments in a patient's body. Ultrasound (US) may present an alternative to imaging GS-related brachial plexus injury.

METHODS

Three patients with GS-related brachial plexus injury who underwent US imaging evaluation at our institution were identified. A retrospective review of the patients' medical records was performed.

RESULTS

US characterization of nerve abnormalities after GS injury to the brachial plexus was in agreement with electrodiagnostic and intraoperative findings.

DISCUSSION

Information from the US reports was useful in preparation for brachial plexus reconstruction surgery. As such, US has unique utility when MRI cannot be performed. US imaging can provide useful characterization of the brachial plexus after GS injury when performed by an experienced operator. Muscle Nerve 59:707-711, 2019.

Performance of an Interactive Upper Extremity Peripheral Nerve Training Module Among Medical Students, Radiology Residents, and Fellows: A Multi-institutional Study

BACKGROUND AND PURPOSE

Chronic pain is a common problem and imaging is becoming increasingly utilized in the characterization of peripheral neuropathy, although this topic is not emphasized during medical training. We hypothesized that an electronic module and nerve atlas would be effective in improving comprehension among trainees.

MATERIALS AND METHODS

In this IRB-approved study, a training module was created that included a side-by-side comparison of normal upper extremity nerves on magnetic resonance imaging and ultrasound (US), with embedded questions and cases, followed by a brief hands-on US scanning session. Thirty volunteers with variable training were enrolled in 1 institution, while 14 volunteers were enrolled in another. Pre- and post-test scores were collected and compared.

RESULTS

There was a response rate of 100% at both institutions. At the first institution, subjects were divided into 2 groups: group 1 (16 medical students) and group 2 (14 residents/fellows). There was a baseline deficit of knowledge among both groups, with a mean pretest score of 37.5% and 47.5% for group 1 and group 2, respectively (P = 0.017). After module completion, both groups improved with a mean post-test score of 67.2% for group 1 and 76.1% for group 2. At the second institution, there was similar improvement even if the scanning session was not done.

CONCLUSIONS

Use of an electronic module helps trainees to become more familiar with peripheral nerve imaging, regardless of level of training. Use of the module, even in the absence of hands-on US scanning, results in an improved understanding of this topic.

Conventional MR and diffusion-weighted imaging of musculoskeletal soft tissue malignancy: correlation with histologic grading

AIM

To evaluate proven soft tissue musculoskeletal malignancies blinded to their Fédération Nationale des Centres de Lutte Contre le Cancer histologic grades to identify the predictive values of conventional MR findings and best fit region of interest (ROI) apparent diffusion coefficient (ADC) measurements.

MATERIALS AND METHODS

Fifty-one consecutive patients with different histologic grades were evaluated by four readers (R1-4) of different experience levels. Quantitatively, the maximum longitudinal size, tumor to muscle signal intensity ratios, and ADC measurements and, qualitatively, the spatial location of the tumor, its signal alterations, heterogeneity, intralesional hemorrhage or fat, and types of enhancement were assessed. Intraclass correlation, weighted kappa, ANOVA, and Fisher exact tests were used.

RESULTS

There were 22/51 (43%) men (mean age ± SD = 52 ± 16 years) and 29/51 (57%) women (mean age ± SD = 54± 17 years), with the majority of tumors 38/51 (75%) in the lower extremities. Histologic grades were I in 8/51 (16%), II in 17/51 (33%), and III in 26/51 (51%), respectively. The longitudinal dimensions were different among three grades (p = 0.0015), largest with grade I. More central enhancements and deep locations were seen in grade III tumors (p = 0.0191, 0.0246). The ADC mean was significantly lower in grade III than in grade I or II (p < 0.0001 and p = 0.04). The ADC min was significantly lower in grade III than in grade I (p = 0.02). Good to excellent agreements were seen for T1/T2 tumor/muscle ratios, longitudinal dimension, and ADC (ICC = 0.60-0.98).

CONCLUSION

Longitudinal tumor dimension, central enhancement, and ADC values differentiate histology grades in musculoskeletal soft tissue malignancy with good to excellent inter-reader reliability.

KEY POINTS

• The longitudinal tumor dimension of grade III malignancy is smaller than that of grade I (p < 0.0001), and higher-grade tumors are located deeper (p = 0.0246). • The ADC mean is significantly lower in grade III than in grade I or grade II (p < 0.0001 and p = 0.04). • The ADC minimum is significantly lower in grade III than in grade I (p = 0.02).

MR imaging features of presumed retroclavicular and periscapular intermuscular vascular plexi - An observational, anatomic study

OBJECTIVE

To describe MR imaging features of presumed vascular plexi in the periscapular (PSC) and retroclavicular (RC) locations.

MATERIALS/METHODS

443 consecutive MR studies performed as "brachial plexus" protocol (axialT1-W and sagittal STIR) were reviewed for presence, size and characteristics of PSC and RC plexi.

RESULTS

Presumed PSC and RC vascular plexi were present in 10%. Both plexi more commonly occurred on the left side. Percutaneous biopsy (n = 1) yielded no vascular neoplasm.

CONCLUSION

RC and PSC vascular plexi are commonly encountered on routine brachial plexus MR imaging and may represent variant vascular networks, as they are frequently found on the contralateral asymptomatic side.

Magnetic Resonance Neurography in Chronic Lumbosacral and Pelvic Pain: Diagnostic and Management Impact-Institutional Audit

BACKGROUND/OBJECTIVE

Low back and pelvic pain are among the most prevalent conditions worldwide, with major social and economic costs. The aim of this study was to evaluate the role of magnetic resonance neurography (MRN) of lumbosacral plexus in the management and outcomes of these patients with chronic pain.

METHODS

Consecutive patients with chronic lumbosacral and pelvic pain referred for MRN over a year were included. Preimaging and postimaging clinical diagnosis and treatment, pain levels, and location were recorded. Pain-free survival was compared between treatments using a Cox proportional hazards model.

RESULTS

A total of 202 patients with mean age 53.7 ± 14.8 years and a male/female ratio of 1:1.53 were included. Of these patients, 115 presented with radiculopathy (57%), 56 with pelvic pain (28%), and 31 with groin pain (15%). Mean initial pain level was 6.9 ± 1.9. Mean symptom duration was 4.21 ± 5.86 years. Of these patients, 143 (71%) had a change in management because of MRN. After MRN, reduction in pain levels was observed in 21 of 32 patients receiving conservative treatment (66%), 42 of 67 receiving injections (63%), and 27 of 33 receiving surgery (82%). Follow-ups were available in 131 patients. Median pain-free survival was 12 months. Patients treated with surgery had significantly lower pain recurrence than patients receiving other treatments in the same time frame (hazard ratio, 3.6; 95% confidence interval, 1.4-9.2; P = 0.0061).

CONCLUSIONS

MRN use in chronic lumbosacral and pelvic pain led to a meaningful change in diagnosis and treatment. After MRN, conservative treatment and injections provided pain relief; however, patients benefited more from surgery than from any other treatment.

Plexus and peripheral nerve metastasis

Cancer in the form of solid tumors, leukemia, and lymphoma can infiltrate and metastasize to the peripheral nervous system, including the cranial nerves, nerve roots, cervical, brachial and lumbosacral plexuses, and, rarely, the peripheral nerves. This review discusses the presentation, diagnostic evaluation, and treatment options for metastatic lesions to these components of the peripheral nervous system and is organized based on the anatomic distribution. As skull base metastases (also discussed in Chapter 14) result in cranial neuropathies, these will be covered in detail, as well as cancers that directly infiltrate the cranial nerves. Particular emphasis is placed on the clinical, imaging, and electrodiagnostic features that differentiate neoplastic plexopathies from radiation-induced plexopathies. Neurolymphomatosis, in which malignant lymphocytes invade the cranial nerves, nerve roots, brachial and lumbosacral plexuses, and peripheral nerves, is a rare manifestation of lymphoma and leukemia. Diagnoses of neurolymphomatosis are often missed or delayed given its varied presentations, resulting in poorer outcomes. Thus this disease will also be discussed in depth.

MR Neurography of Greater Occipital Nerve Neuropathy: Initial Experience in Patients with Migraine

BACKGROUND AND PURPOSE

MR imaging of peripheral nerves (MR neurography) allows improved assessment of nerve anatomy and pathology. The objective of this study was to evaluate patients with unilateral occipital neuralgia using MR neurography and to assess the differences in greater occipital nerve signal and size between the symptomatic and asymptomatic sides.

MATERIALS AND METHODS

In this case-control evaluation using MR neurography, bilateral greater occipital nerve caliber, signal intensity, signal-to-noise ratios, and contrast-to-noise ratios were determined by 2 observers.

RESULTS

Among 18 subjects with unilateral occipital migraines, the average greater occipital nerve diameter for the symptomatic side was significantly greater at 1.77 ± 0.4 mm than for the asymptomatic side at 1.29 ± 0.25 mm (P = .001). The difference in nerve signal intensity between the symptomatic and asymptomatic sides was statistically significant at 269.06 ± 170.93 and 222.44 ± 170.46, respectively (P = .043). The signal-to-noise ratios on the symptomatic side were higher at 15.79 ± 4.59 compared with the asymptomatic nerve at 14.02 ± 5.23 (P = .009). Contrast-to-noise ratios were significantly higher on the symptomatic side than on the asymptomatic side at 2.57 ± 4.89 and -1.26 ± 5.02, respectively (P = .004). Intraobserver performance was good to excellent (intraclass coefficient correlation, 0.68-0.93), and interobserver performance was fair to excellent (intraclass coefficient correlation, 0.54-0.81).

CONCLUSIONS

MR neurography can be reliably used for the diagnosis of greater occipital nerve neuropathy in patients with unilateral occipital migraines with a good correlation of imaging findings to the clinical presentation.

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.

Magnetic resonance neurography: current perspectives and literature review

Magnetic resonance neurography (also called MRN or MR neurography) refers to MR imaging dedicated to the peripheral nerves. It is a technique that enhances selective multiplanar visualisation of the peripheral nerve and pathology by encompassing a combination of two-dimensional, three-dimensional and diffusion imaging pulse sequences. Referring physicians who seek imaging techniques that can depict and diagnose peripheral nerve pathologies superior to conventional MR imaging are driving the demand for MRN. This article reviews the pathophysiology of peripheral nerves in common practice scenarios, technical considerations of MRN, current indications of MRN, normal and abnormal neuromuscular appearances, and imaging pitfalls. Finally, the emerging utility of diffusion-weighted and diffusion tensor imaging is discussed and future directions are highlighted.

KEY POINTS

• Lesion relationship to neural architecture is more conspicuous on MRN than MRI. • 3D multiplanar imaging technique is essential for pre-surgical planning. • Nerve injuries can be classified on MRN using Sunderland's classification. • DTI provides quantitative information and insight into intraneural integrity and pathophysiology.