Accuracy of MRI in diagnosing peripheral nerve disease: a systematic review of the literature

Diffusion tensor imaging in peroneal neuropathy: a prospective, single-centre study

Objective

Diffusion tensor imaging (DTI) showed promising results in diagnosing upper limb neuropathies, but its value in patients with foot drop due to peroneal neuropathy has not yet been investigated. We aim to establish reference values for DTI metrics of the healthy peroneal nerve and to evaluate differences in DTI metrics between patients and healthy controls.

Methods

Diffusion-weighted images (DWI) from 22 pathological nerves, 14 asymptomatic patients' nerves and 65 healthy peroneal nerves were processed for quantitative assessment of fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity and mean diffusivity. Clinical baseline and follow-up data were prospectively collected for all patients.

Results

Mean patient FA values (0.40, SD 0.08) were significantly lower compared with healthy controls (mean FA 0.44, SD 0.06). Mean patient RD values (0.98 10-3 mm2/s, SD 0.21 10-3 mm2/s) were significantly higher compared with healthy controls (mean RD 0.85 10-3 mm2/s, SD 0.16 10-3 mm2/s). FA values were significantly lower in patients with severe foot drop (mean FA 0.40, SD 0.06) compared with non-severe foot drop (mean FA 0.48, SD 0.05).

Conclusion

Based on these results, DTI appears to aid in the differential diagnostic process of patients with peroneal neuropathy. Future studies should focus on automation of DWI processing, confirm the results in larger patient groups and try to establish reliable cut-off values for DTI metrics.

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.

Diagnostic accuracy of ultrasound and MR imaging in peroneal neuropathy: A prospective, single-center study

INTRODUCTION/AIMS

Magnetic resonance imaging (MRI) findings in peroneal neuropathy are not well documented and the prognostic value of imaging remains uncertain. Upper limits of cross-sectional area (CSA) on ultrasound (US) have been established, but uncertainty regarding generalizability remains. We aimed to describe MRI findings of the peroneal nerve in patients and healthy controls and to compare these results to US findings and clinical characteristics.

METHODS

We prospectively included patients with foot drop and electrodiagnostically confirmed peroneal neuropathy, and performed clinical follow-up, US and MRI of both peroneal nerves. We compared MRI findings to healthy controls. Two radiologists evaluated MRI features in an exploratory analysis after images were anonymized and randomized.

RESULTS

Twenty-two patients and 38 healthy controls were included. Whereas significant increased MRI CSA values were documented in patients (mean CSA 20 mm2 vs. 13 mm2 in healthy controls), intra- and interobserver variability was substantial (variability of, respectively, 7 and 9 mm2 around the mean in 95% of repeated measurements). A pathological T2 hyperintense signal of the nerve was found in 52.6% of patients (50% interobserver agreement). Increased CSA measurements (MRI/US), pathological T2 hyperintensity of the nerve and muscle edema were not predictive for recovery.

DISCUSSION

Imaging is recommended in all patients with peroneal neuropathy to exclude compressive intrinsic and extrinsic masses but we do not advise routine MRI for diagnosis or prediction of outcome in patients with peroneal neuropathy due to high observer variability. Further studies should aim at reducing MRI observer variability potentially by semi-automation.

3D MR neurography with gadolinium contrast to improve the visualization of pelvic nerves and the branches

Objective

To evaluate the effectiveness of 3D NerveVIEW sequence with gadolinium contrast on the visualization of pelvic nerves and their branches compared to that without contrast.

Methods

Participants were scanned twice using 3D NerveVIEW sequence with and without gadolinium contrast to acquire pelvic nerve images. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and contrast ratio of the nerves were calculated and compared to determine the quality of images. To subjectively assess, using a 3-point scale, branch nerves critical to therapeutic decision-making, including the pelvic splanchnic nerve and pelvic plexus, the superior gluteal nerve, and the pudendal nerve.

Results

In the 32 eligible participants after using contrast, the CNRs of the images of nerve-to-bone and nerve-to-vessel significantly increased (p < 0.05). The CR of the images with contrast of all nerve-to-surrounding tissues (i.e., bone, muscle, blood vessels, and fat) were also found significantly higher (p < 0.05). The assessment of observers also shows higher scores for images with contrast compared to images without contrast.

Conclusion

The 3D NerveVIEW sequence combined with gadolinium contrast improved vascular suppression, increased the contrast between pelvic nerves and surrounding tissue, and enhanced the visualization of nerves and their branches. This study may be helpful for the technically challenging preoperative planning of pelvic diseases surgery.

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.

Magnetic resonance imaging for diagnosis of suspected neurogenic thoracic outlet syndrome-a systematic scoping review

Background: Neurogenic Thoracic Outlet Syndrome (nTOS) is a rare pathology caused by dynamic conditions or compression of neurovascular structures in the thoracic outlet region. nTOS can be difficult to diagnose due to nonspecific symptoms and magnetic resonance imaging (MRI) techniques are increasingly used to aid the diagnosis and surgical planning. This scoping systematic review explores how MRI is used for diagnosing nTOS and summarizes details of published MRI protocols. Methods: A systematic screening of PubMed, Cochrane, Web of Science, and CINAHL databases using PRISMA-IPD guidelines was conducted in September 2022 to include full-text English papers on MRI and nTOS. Inclusion criteria involved studies describing MRI protocols for the diagnosis of TOS, with a focus on the imaging sequences and protocols. Results: 6289 papers were screened to include 28 papers containing details of MRI protocols. The details of MRI protocols in the analyzed articles were incomplete in all studies. Most authors used 1.5T systems and included T1 and T2-weighted sequences. Most studies applied fat suppression, mainly with STIR. Positioning of the arm differed between studies, including neutral, hyperabducted and abducted and externally rotated positions. Conclusion: Our review highlights a prevalent lack of detailed MRI protocol documentation for brachial plexus. Authors primarily rely on conventional 1.5T systems, employing standard T1 and T2-weighted sequences. The adoption of novel MRI sequences is notably lacking, and fat suppression techniques predominantly adhere to older methods as STIR. There is a clear imperative for authors to provide more comprehensive reporting of the MRI protocols utilized in their studies, ultimately enhancing comparability and clinical applicability. Establishing clear protocol reporting guidelines is crucial to allow for comparison between studies.

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.

Non-contrast enhancement of brachial plexus magnetic resonance imaging with compressed sensing

PURPOSE

To observe the quality of brachial plexus (BP) images obtained from magnetic resonance imaging (MRI) with 3D T2 STIR SPACE sequence and compressed sensing (CS) and to compare the results with BP images from the same sequence without CS.

METHODS

In this study, compressed sensing was applied to acquire non-contrast BP images from ten healthy volunteers with 3D T2 STIR SPACE sequence to shorten acquisition time without sacrificing image quality. The acquisition time of scanning with CS was compared to that without CS. The quantitative signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared using paired t-test to determine the quality of images with and without CS. The qualitative assessment by three experienced radiologists was performed using a scoring scale from 1 (poor) to 5 (excellent) and analyzed for interobserver agreement on image quality.

RESULTS

The increasing SNR and CNR of images with CS were found in nine regions of BP images (p < 0.001) with faster acquisition time. The result of paired t-test (p < 0.001) illustrates the significant difference between images with CS compared to images without CS. The assessment of observers also shows higher scores for images with CS compared to images without CS.

CONCLUSIONS

This study demonstrates that CS can effectively increase the visibility of images and image boundaries, SNR, and CNR of BP images obtained with 3D T2 STIR SPACE sequence with the good interobserver agreement and within clinically optimal acquisition time compared to images from similar sequence without CS.

A pentavalent approach for the evaluation of traumatic brachial plexopathy on MRI: correlation of macropattern and micropattern

Macropattern analysis of traumatic brachial plexopathy (TBP) by Magnetic Resonance Imaging (MRI) encompasses localization of injured segments and determination of the severity of injury. The micropattern analysis implies the correlation of the MRI features of TBP with Sunderland's grading of the nerve injury, thereby guiding the management protocol. This review article presents a simplified novel pentavalent approach for the radiological anatomy of brachial plexus, MRI acquisition protocol for the evaluation of brachial plexus, cardinal imaging signs of TBP, and their correlation with Sunderland's microanatomical grading.

Nerve transfers for brachial plexus injuries: grading of volitional control

OBJECTIVE

After brachial plexus injuries (BPIs), nerve transfers are used to restore lost muscle function. Brain plasticity underlies the process of regaining volitional control, which encompasses disconnection of the original donor nerve-related programs and reconnection to acceptor nerve programs. To the authors' knowledge, the levels of disconnection and reconnection have never been studied systematically. In this study, the authors developed a novel 4-point plasticity grading scale (PGS) and assessed the degree of volitional control achieved, identifying clinical correlations with this score.

METHODS

Patients with BPI who underwent a phrenic, spinal accessory, median, and/or ulnar fascicle nerve transfer to restore biceps and deltoid function were asked to maximally contract their target muscle as follows: 1) by using only the donor nerve program, and 2) by activating the target muscle while consciously trying to avoid using the donor nerve, with assessment each time of the Medical Research Council (MRC) scale grade for muscle strength. The authors' PGS was used to rate the level of volitional control achieved. PGS grade 1 represented the lowest independent volitional control, with MRC grade 4 obtained in response to the donor command and MRC grade 0 in response to the acceptor command (minimum brain plasticity), whereas PGS grade 4 was no noticeable contraction in response to the donor command and MRC grade 4 in response to the acceptor command (maximum brain plasticity).

RESULTS

In total, 153 patients were studied. For biceps restoration, the phrenic nerve was used as a donor in 44 patients, the spinal accessory nerve in 40 patients, and the median and/or ulnar fascicles in 44 patients. A triceps branch was used to restore deltoid function in 25 patients. The level of volitional control achieved was PGS grade 1 in 1 patient (0.6%), grade 2 in 21 patients (13.7%), grade 3 in 103 patients (67.3%), and grade 4 in 28 patients (18.3%). The median PGS grade did not differ significantly between the four donor nerves. No correlations were observed between age, time from BPI to surgery, duration of follow-up, or compliance with rehabilitation and PGS grade.

CONCLUSIONS

Just around 20% of the authors' patients developed a complete disconnection of the donor program along with complete independent control over the reinnervated muscle. Incomplete disconnection was present in the vast majority of the patients, and the level of disconnection and control was poor in approximately 15% of patients. Brain plasticity underlies patient ability to regain volitional control after a nerve transfer, but this capacity is limited.

Neuropathy Score Reporting and Data System: A Reporting Guideline for MRI of Peripheral Neuropathy With a Multicenter Validation Study

BACKGROUND. A standardized guideline and scoring system would improve evaluation and reporting of peripheral neuropathy (PN) on MRI. OBJECTIVE. The objective of this study was to create and validate a neuropathy classification and grading system, which we named the Neuropathy Score Reporting and Data System (NS-RADS). METHODS. This retrospective study included 100 patients with nerve imaging studies and known clinical diagnoses. Experts crafted NS-RADS using mutually agreed-on qualitative criteria for the classification and grading of PN. Different classes were created to account for the spectrum of underlying pathologies: unremarkable (U), injury (I), neoplasia (N), entrapment (E), diffuse neuropathy (D), not otherwise specified (NOS), and postintervention state (PI). Subclasses were established to describe the severity or extent of the lesions. Validation testing was performed by 11 readers from 10 institutions with experience levels ranging from 3 to 18 years after residency. After initial reader training, cases were presented to readers who were blinded to the final clinical diagnoses. Interobserver agreement was assessed using correlation coefficients and the Conger kappa, and accuracy testing was performed. RESULTS. Final clinical diagnoses included normal (n = 5), nerve injury (n = 25), entrapment (n = 15), neoplasia (n = 33), diffuse neuropathy (n = 18), and persistent neuropathy after intervention (n = 4). The miscategorization rate for NS-RADS classes was 1.8%. Final diagnoses were correctly identified by readers in 71-88% of cases. Excellent inter-reader agreement was found on the NS-RADS pathology categorization (κ = 0.96; 95% CI, 0.93-0.98) as well as muscle pathology categorization (κ = 0.76; 95% CI, 0.68-0.82). The accuracy for determining milder versus more severe categories per radiologist ranged from 88% to 97% for nerve lesions and from 86% to 94% for muscle abnormalities. CONCLUSION. The proposed NS-RADS classification is accurate and reliable across different reader experience levels and a spectrum of PN conditions. CLINICAL IMPACT. NS-RADS can be used as a standardized guideline for reporting PN and improved multidisciplinary communications.

Selective MR neurography-guided anterior femoral cutaneous nerve blocks for diagnosing anterior thigh neuralgia: anatomy, technique, diagnostic performance, and patient-reported experiences

OBJECTIVE

To evaluate the clinical utility of selective magnetic resonance neurography-(MRN)-guided anterior femoral cutaneous nerve (AFCN) blocks for diagnosing anterior thigh neuralgia.

MATERIALS AND METHODS

Following institutional review board approval and informed consent, participants with intractable anterior thigh pain and clinically suspected AFCN neuralgia were included. AFCN blocks were performed under MRN guidance using an anterior groin approach along the medial sartorius muscle margin. Outcome variables included AFCN identification on MRN, technical success of perineural drug delivery, rate of AFCN anesthesia, complications, total procedure time, patient-reported procedural experiences, rate of positive diagnostic AFCN blocks, and positive subsequent treatment rate.

RESULTS

Eighteen MRN-guided AFCN blocks (six unilateral and six bilateral blocks) were performed in 12 participants (6 women; age, 49 (30-65) years). Successful MRN identified the AFCN, successful perineural drug delivery, and AFCN anesthesia was achieved in all thighs. No complications occurred. The total procedure time was 19 (10-28) min. Patient satisfaction and experience were high without adverse MRI effects. AFCN blocks identified the AFCN as the symptom generator in 16/18 (89%) cases, followed by 14/16 (88%) successful treatments.

CONCLUSION

Our results suggest that selective MR neurography-guided AFCN blocks effectively diagnose anterior femoral cutaneous neuralgia and are well-tolerated.

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.

New insights into the evaluation of peripheral nerves lesions: a survival guide for beginners

PURPOSE

To perform a review of the physical basis of DTI and DCE-MRI applied to Peripheral Nerves (PNs) evaluation with the aim of providing readers the main concepts and tools to acquire these types of sequences for PNs assessment. The potential added value of these advanced techniques for pre-and post-surgical PN assessment is also reviewed in diverse clinical scenarios. Finally, a brief introduction to the promising applications of Artificial Intelligence (AI) for PNs evaluation is presented.

METHODS

We review the existing literature and analyze the latest evidence regarding DTI, DCE-MRI and AI for PNs assessment. This review is focused on a practical approach to these advanced sequences providing tips and tricks for implementing them into real clinical practice focused on imaging postprocessing and their current clinical applicability. A summary of the potential applications of AI algorithms for PNs assessment is also included.

RESULTS

DTI, successfully used in central nervous system, can also be applied for PNs assessment. DCE-MRI can help evaluate PN's vascularization and integrity of Blood Nerve Barrier beyond the conventional gadolinium-enhanced MRI sequences approach. Both approaches have been tested for PN assessment including pre- and post-surgical evaluation of PNs and tumoral conditions. AI algorithms may help radiologists for PN detection, segmentation and characterization with promising initial results.

CONCLUSION

DTI, DCE-MRI are feasible tools for the assessment of PN lesions. This manuscript emphasizes the technical adjustments necessary to acquire and post-process these images. AI algorithms can also be considered as an alternative and promising choice for PN evaluation with promising results.

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.

Anatomy, Imaging, and Pathologic Conditions of the Brachial Plexus

The brachial plexus is an intricate anatomic structure with an important function: providing innervation to the upper extremity, shoulder, and upper chest. Owing to its complex form and longitudinal course, the brachial plexus can be challenging to conceptualize in three dimensions, which complicates evaluations in standard orthogonal imaging planes. The components of the brachial plexus can be determined by using key anatomic landmarks. Applying this anatomic knowledge, a radiologist should then be able to identify pathologic appearances of the brachial plexus by using imaging modalities such as MRI, CT, and US. Brachial plexopathies can be divided into two broad categories that are based on disease origin: traumatic and nontraumatic. In the traumatic plexopathy group, there are distinct imaging findings and management methods for pre- versus postganglionic injuries. For nontraumatic plexopathies, having access to an accurate patient history is often crucial. Knowledge of the timing of radiation therapy is critical to diagnosing post-radiation therapy brachial plexopathy. In acute brachial neuritis, antecedent stressors occur within a specific time frame. Primary and secondary tumors of the brachial plexus are not uncommon, with the most common primary tumors being peripheral nerve sheath tumors. Direct extension and metastasis from primary malignancies such as breast and lung cancer can occur. Although diagnosing a brachial plexus anomaly is potentially perplexing, it can be straightforward if it is based on foundational knowledge of anatomy, imaging findings, and pathologic features. ^©RSNA, 2020.

Performance Evaluation of High-Resolution Ultrasound versus Magnetic Resonance Imaging in Diagnosing Peripheral Nerve Pathologies

Background  High-resolution ultrasound (HRUS) and magnetic resonance neurography (MRN) are considered complementary to clinical and neurophysiological assessment for neuropathies.

Aims  The aim of our study was to compare the accuracy of HRUS and MRN for detecting various peripheral nerve pathologies, to choose the correct investigation to facilitate prompt patient management.

Materials and Methods  This prospective study was done using HRUS with 14 MHz linear-transducer and 3 or 1.5T MR in cases referred for the assessment of peripheral nerve pathologies. Image interpretation was done using a scoring system (score 0–3 confidence level) to assess for nerve continuity/discontinuity, increased nerve signal/edema, fascicular change, caliber change, and neuroma/mass lesion. We determined the accuracy, sensitivity, and specificity of these modalities compared with the diagnostic standard determined by surgical and/or histopathological, if not performed then clinical and/or electrodiagnostic evaluation.

Results  The overall accuracy of MRN was 89.3% (specificity: 66.6%, sensitivity: 92.6%, negative predictive value [NPV]: 57.1%, positive predictive value [PPV]: 95%) and that of HRUS was 82.9% (specificity: 100%, sensitivity: 80.4%, NPV: 42.8, PPV: 100). The confidence level for detecting nerve discontinuity and change in nerve caliber was found to be higher on ultrasonography than magnetic resonance imaging (MRI) (100 vs. 70% and 100 vs. 50%, respectively). Pathology of submillimeter caliber nerves was accurately detected by HRUS and these could not be well-visualized on MRI.

Conclusion  HRUS is a powerful tool that may be used as the first-line imaging modality for the evaluation of peripheral nerve pathologies, and a better means of evaluation of peripheral nerves with submillimeter caliber.

Routine knee MRI: how common are peripheral nerve abnormalities, and why does it matter?

OBJECTIVE

To evaluate the frequency, MRI appearance, and clinical significance of peripheral nerve abnormalities encountered on routine knee MRI.

MATERIALS AND METHODS

A retrospective review was performed to identify consecutive patients who underwent routine knee MRI from March 2015-2018 and had peripheral nerve abnormalities. MRIs were reviewed for the presence of tibial (TN) and common peroneal nerve (CPN) abnormalities (including hyperintensity, bulbous enlargement, discontinuity, architectural distortion, skeletal muscle denervation). The presence or absence of concomitant meniscal, cruciate, and collateral ligament tears was documented. Patient demographics and clinical outcomes were recorded. Descriptive statistics were reported.

RESULTS

The search yielded 8125 MRIs, of which 50 knee MRIs (patient age (years): 44 + 19) had peripheral nerve abnormalities (hyperintensity (TN: 30%(15/50), CPN: 80%(40/50)), bulbous enlargement (TN: 10%(5/50), CPN: 30%(15/50)), discontinuity (TN: 0, CPN: 4%(2/50)), architectural distortion (TN: 4%(2/50), CPN: 18%(9/50)), and skeletal muscle denervation (TN: 14%(7/50), CPN: 28%(14/50)). Medial meniscus (TN: 12% (6/50), CPN: 36%(18/50)), ACL (TN: 4%(2/50), CPN: 32%(16/50)), PCL (TN: 2%(1/50), CPN: 20%(10/50)), and lateral meniscus (TN: 12%(6/50), CPN: 24%(12/50)) tears were frequently present. Of these, 32% (16/50) were treated for peripheral nerve injury (PNI), characterized as high-grade (n = 7/16) or low-grade (n = 9/16). Nerve discontinuity, architectural distortion, and denervation were encountered more in high-grade PNI than low-grade PNI. Five patients were recalled for follow-up imaging and operative management was performed in 36% of cases (18/50).

CONCLUSION

Although uncommon (frequency = 0.6%), peripheral nerve abnormalities (CPN more common than TN) are encountered on routine knee MRI and affect patient management, with 36% requiring surgical treatment.

Diagnostic Accuracy of the Magnetic Resonance Imaging in Adult Post-Ganglionic Brachial Plexus Traumatic Injuries: A Systematic Review and Meta-Analysis

BACKGROUND

Traumatic brachial plexus injuries are rare but serious consequences of major traumas. Pre-ganglionic lesions are considered irreparable, while post-ganglionic injuries can be potentially treated if an early diagnosis is available. Pre-surgical diagnosis is important to distinguish low-grade from high-grade lesions and to identify their location. The aim of the review is to evaluate the diagnostic accuracy of magnetic resonance imaging (MRI) in the identification of adult post-ganglionic lesions due to traumatic brachial plexus injuries, compared to intraoperative findings.

METHODS

Research on the main scientific electronic databases was conducted. Studies of adults with traumatic post-ganglionic brachial plexus injuries were included. The index test was preoperative MRI and the reference standard was surgical exploration. Pooled sensitivity and specificity were calculated.

RESULTS

Four studies were included for the systematic review, of which three articles met the inclusion criteria for the meta-analysis. Pooled sensitivity and pooled specificity values resulted high. The sensitivity value is associated with a high heterogeneity index of the selected literature.

CONCLUSION

MRI can be considered, despite the limits, the gold standard exam in morphological evaluation of brachial plexus injuries, particularly in the diagnosis of post-ganglionic traumatic injuries.

Neurolymphomatosis of the lumbosacral plexus and its branches: case series and literature review

Background

Neurolymphomatosis (NL) is a direct process of invasion of peripheral nerves by lymphoma. It occurs in roughly 5% of patients with lymphoma and represents a particularly difficult diagnostic dilemma when it is the presenting focal manifestation of occult lymphoma.

Case presentation

We present 3 examples of invasion of the lumbosacral plexus and its branches. These cases demonstrate a protean clinical picture with regards to the time relationship to the clinical course of lymphoma and the neuroanatomical extent of lumbosacral plexus invasion. We demonstrate the complementary role of different imaging modalities. A review of the literature summarizes 23 reports where lumbosacral plexus invasion was the index manifestation, at the time of first diagnosis or recurrence of lymphoma. This series confirms the strong preponderance of B-cell type (92%). There is a marked predilection for involvement of the sciatic nerve (74%), either focally or in a longitudinally extensive fashion, from the ischium to the popliteal fossa. There can also be restricted and discrete involvement of tibial and fibular branches. In recent years, ultrasound and CT have been given a more limited role, as screening tools or as a guide for biopsy. MRI neurography and PET-CT have become leading diagnostic modalities for diagnosis, staging and assessment of treatment response.

Conclusion

The diagnosis of NL may be challenging, and it was once only reached at autopsy. Improved diagnostic imaging of focal or even asymptomatic disease offers new hope for earlier diagnosis and successful targeted therapy.

Can imaging be the new yardstick for diagnosing peripheral neuropathy?-a comparison between high resolution ultrasound and MR neurography with an approach to diagnosis

PURPOSE

Peripheral neuropathies are a group of disorders which affect the peripheral nervous system which have been conventionally diagnosed using electrodiagnostic studies. This study was carried out to assess the role of imaging in diagnosing peripheral mononeuropathy as exact anatomical localisation of the pathology is possible using high-resolution ultrasound and MR neurography, the modalities assessed in this study.

METHOD

A hospital-based prospective analytical study was carried out in a resource-limited setting on 180 peripheral nerves in 131 patients with symptoms of peripheral mononeuropathy after taking IRB approval. Each patient underwent high-resolution ultrasound examination and MR neurography, findings of which were then compared and statistically analysed assuming electrodiagnostic findings as the gold standard.

RESULTS

Overall, the diagnostic accuracy was highest for the proton density fat-saturated MR sequence (93.89%) followed by high-resolution ultrasound (80%). The sensitivity was highest for proton density fat-saturated sequence while the T1 MR sequence had the highest specificity. Combined diagnostic accuracy of both modalities was calculated to be 93.33% with a negative predictive value of 80%. High-resolution ultrasound and MRI equally detected the cases with nerve discontinuity, while neuromas were better identified on MRI.

CONCLUSION

With the advent of higher frequency probes and improved MR field strength, imaging of peripheral nerves is possible with better accuracy. Imaging assessment of nerves allows anatomical delineation with identification of exact site of involvement. This comparative study demonstrates the role of imaging in diagnosing peripheral nerve pathologies with the accuracy of MRI as high as 93.89% which may serve as an imaging gold standard. High-resolution ultrasound, being quicker, cost effective and a comparable accuracy of 80% can serve as a reliable screening tool. This study incorporates a larger study group and compares HRUS with MRI, taking NCV as gold standard, which has not been done in the preceding studies. With this study, we conclude that these two imaging modalities are not mutually exclusive. Rather, they complement each other and can be used in conjunction as an imaging yardstick for diagnosing peripheral neuropathies.

Magnetic resonance neurography of traumatic pediatric peripheral nerve injury: beyond birth-related brachial palsy

Traumatic peripheral nerve injury occurs more frequently in the pediatric population than previously recognized. High-resolution magnetic resonance (MR) imaging in the form of MR neurography can serve as a powerful noninvasive tool for detecting and characterizing peripheral nerve injury in children. In this review article we briefly discuss optimal methods of MR neurography image acquisition, highlighting core MR sequences necessary to characterize peripheral nerve injury. In addition, we illustrate the MR neurography appearance of normal and abnormal peripheral nerves in children, with emphasis on commonly used Seddon and Sunderland classification schemes to characterize peripheral nerve injury severity. The primary and secondary features associated with peripheral nerve injury including skeletal muscle denervation are reviewed in addition to key distinctive features that can impact operative versus nonoperative management of children. We include a checklist approach to interpreting MR neurography for the assessment of peripheral nerve injury.

Diffusion tensor MRI of the healthy brachial plexus

Introduction

Diffusion Tensor MRI (DT-MRI) is a promising tool for the evaluation of brachial plexus pathology. Therefore, we introduce and evaluate a fast DT-MRI protocol (8min33s scanning with 5–10 min postprocessing time) for the brachial plexus.

Materials and methods

Thirty healthy volunteers within three age-groups (18–35, 36–55, and > 56) received DT-MRI of the brachial-plexus twice. Means of fractional-anisotropy (FA), mean-diffusivity (MD), axial-diffusivity (AD), and radial-diffusivity (RD) for the individual roots and trunks were evaluated. A stepwise forward approach was applied to test for correlations with age, sex, body-mass-index (BMI), bodysurface, height, and bodyweight. Within-subject, intra-rater, and inter-rater repeatability were assessed using Bland-Altman analysis, coefficient of variation (CV), intraclass-correlation (ICC), and minimal detectable difference (MDD).

Results

No differences between sides and root levels were found. MD, AD, and RD correlated (P < 0.05) with bodyweight. Within-subject quantification proved repeatable with CVs for FA, MD, AD, and RD of 16%, 12%, 11%, and 14%, respectively.

Discussion

The DT-MRI protocol was fast and repeatable. Found correlations should be considered in future studies of brachial plexus pathology.

Fe Doped Magnetic Nanodiamonds Made by Ion Implantation as Contrast Agent for MRI

We report in this paper a new MRI contrast agent based on magnetic nanodiamonds fabricated by Fe ion implantation. The Fe atoms that are implanted into the nanodiamonds are not in direct contact with the outside world, enabling this new contrast agent to be free from cell toxicity. The image enhancement was shown clearly through T2 weighted images. The concentration dependence of the T2 relaxation time gives a relaxivity value that is about seven times that of the regular non-magnetic nanodiamonds. Cell viability study has also been performed. It was shown that they were nearly free from cytotoxicity independent of the particle concentration used. The imaging capability demonstrated here adds a new dimension to the medical application of nanodiamonds. In the future one will be able to combine this capability of magnetic nanodiamonds with other functions through surface modifications to perform drug delivery, targeted therapy, localized thermal treatment and diagnostic imaging at the same time.

Monitoring of macrophage recruitment enhanced by Toll-like receptor 4 activation with MR imaging in nerve injury

INTRODUCTION

Macrophage recruitment is critical for nerve regeneration after an injury. The aim of this study was to investigate whether ultrasmall superparamagnetic iron oxide (USPIO) nanoparticle-based MRI could be used to monitor the enhanced macrophage recruitment by Toll-like receptor 4 (TLR4) activation in nerve injury.

METHODS

Rats received intraperitoneal injections of either lipopolysaccharide (LPS) or phosphate buffered saline (PBS) or no injection (controls) after a sciatic nerve crush injury. After intravenous injection of the USPIOs (LPS and PBS groups) or PBS (control group), MRI was performed and correlated with histological findings.

RESULTS

LPS group showed more remarkable hypointense signals on T2*-weighted imaging and lower T2 values in the crushed nerves than PBS group. The hypointense signal areas were associated with an enhanced recruitment of iron-loaded macrophages to the injured nerves.

DISCUSSION

USPIO-enhanced MRI can be used to monitor the enhanced macrophage recruitment by means of TLR4 signal pathway activation in nerve injury. Muscle Nerve, 2018.

MRI biomarkers of proximal nerve injury in CIDP

Objective

To evaluate the utility of nerve diffusion tensor imaging (DTI), nerve cross‐sectional area, and muscle magnetic resonance imaging (MRI) multiecho Dixon for assessing proximal nerve injury in chronic inflammatory demyelinating polyneuropathy (CIDP).

Methods

In this prospective observational cohort study, 11 patients with CIDP and 11 healthy controls underwent a multiparametric MRI protocol with DTI of the sciatic nerve and assessment of muscle proton‐density fat fraction of the biceps femoris and the quadriceps femoris muscles by multiecho Dixon MRI. Patients were longitudinally evaluated by MRI, clinical examination, and nerve conduction studies at baseline and after 6 months.

Results

In sciatic nerves of CIDP patients, mean cross‐sectional area was significantly higher and fractional anisotropy value was significantly lower, compared to controls. In contrast, muscle proton‐density fat fraction was significantly higher in thigh muscles of patients with CIDP, compared to controls. MRI parameters showed high reproducibility at baseline and 6 months.

Interpretation

Advanced MRI parameters demonstrate subclinical proximal nerve damage and intramuscular fat accumulation in CIDP. Data suggest DTI and multiecho Dixon MRI might be useful in estimating axonal damage and neurogenic muscle changes in CIDP.

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.

High-resolution metal artifact reduction MR imaging of the lumbosacral plexus in patients with metallic implants

OBJECTIVE

To assess the quality and accuracy of metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) for the diagnosis of lumbosacral neuropathies in patients with metallic implants in the pelvis.

MATERIALS AND METHODS

Twenty-two subjects with lumbosacral neuropathy following pelvic instrumentation underwent 1.5-T MARS MRI including optimized axial intermediate-weighted and STIR turbo spin echo sequences extending from L5 to the ischial tuberosity. Two readers graded the visibility of the lumbosacral trunk, sciatic, femoral, lateral femoral cutaneous, and obturator nerves and the nerve signal intensity of nerve, architecture, caliber, course, continuity, and skeletal muscle denervation. Clinical examination and electrodiagnostic studies were used as the standard of reference. Descriptive, agreement, and diagnostic performance statistics were applied.

RESULTS

Lumbosacral plexus visibility on MARS MRI was good (4) or very good (3) in 92% of cases with 81% exact agreement and a Kendall's W coefficient of 0.811. The obturator nerve at the obturator foramen and the sciatic nerve posterior to the acetabulum had the lowest visibility, with good or very good ratings in only 61% and 77% of cases respectively. The reader agreement for nerve abnormalities on MARS MRI was excellent, ranging from 95.5 to 100%. MARS MRI achieved a sensitivity of 86%, specificity of 67%, positive predictive value of 95%, and negative predictive value of 40%, and accuracy of 83% for the detection of neuropathy.

CONCLUSION

MARS MRI yields high image quality and diagnostic accuracy for the assessment of lumbosacral neuropathies in patients with metallic implants of the pelvis and hips.

Diffusion-weighted MR neurography of median and ulnar nerves in the wrist and palm

OBJECTIVES

To investigate the feasibility of diffusion-weighted magnetic resonance neurography (DW-MRN) in the visualisation of extremity nerves in the wrist and palm.

METHODS

Thirty-two volunteers and 21 patients underwent imaging of the wrist and palm on a 3-T MR scanner. In all subjects, two radiologists evaluated the image quality on DW-MRN using a four-point grading scale. Kappa statistics were obtained for inter-observer performance. In volunteers, the chi-squared test was used to assess the differences in nerve visualisation on DW-MRN and axial fat-suppressed proton density weighted imaging (FS-PDWI).

RESULTS

In volunteers, the mean image quality scores for the median nerve (MN) and ulnar nerve (UN) were 3.71 ± 0.46 and 3.23 ± 0.67 for observer 1, and 3.70 ± 0.46 and 3.22 ± 0.71 for observer 2, respectively. The inter-observer agreement was excellent (k = 0.843) and good (k = 0.788), respectively. DW-MRN provided significantly improved visualisations of the second and the third common palmar digital nerves and three branches of UN compared with FS-PDWI (P < 0.05). In patients, the mean image quality scores for the two observers were 3.24 ± 0.62 and 3.10 ± 0.83, inter-observer performance was excellent (k = 0.842).

CONCLUSIONS

DW-MRN is feasible for improved visualisation of extremity nerves and their lesions in the wrist and palm with adequate image quality, thereby providing a supplementary method to conventional MR imaging.

KEY POINTS

• DW-MRN provides adequate image quality for wrist and palm neurography • DW-MRN performs similarly to FS-PDWI in nerve visualisation at the wrist • DW-MRN provides improved visualisation of small nerves in the palm • DW-MRN serves as a supplementary method to evaluate peripheral neuropathies.

Nerve Fascicles and Epineurium Volume Segmentation of Peripheral Nerve Using Magnetic Resonance Micro-neurography

RATIONALE AND OBJECTIVES

The aims of this study were to propose a semiautomated technique to segment and measure the volume of different nerve components of the tibial nerve, such as the nerve fascicles and the epineurium, based on magnetic resonance microneurography and a segmentation tool derived from brain imaging; and to assess the reliability of this method by measuring interobserver and intraobserver agreement.

MATERIALS AND METHODS

The tibial nerve of 20 healthy volunteers (age range = 23-69; mean = 47; standard deviation = 15) was investigated at the ankle level. High-resolution images were obtained through tailored microneurographic sequences, covering 28 mm of nerve length. Two operators manually segmented the nerve using the in-phase image. This region of interest was used to mask the nerve in the water image, and two-class segmentation was performed to measure the fascicular volume, epineurial volume, nerve volume, and fascicular to nerve volume ratio (FNR). Interobserver and intraobserver agreements were calculated.

RESULTS

The nerve structure was clearly visualized with distinction of the fascicles and the epineurium. Segmentation provided absolute volumes for nerve volume, fascicular volume, and epineurial volume. The mean FNR resulted in 0.69 with a standard deviation of 0.04 and appeared to be not correlated with age and sex. Interobserver and intraobserver agreements were excellent with alpha values >0.9 for each parameter investigated, with measurements free of systematic errors at the Bland-Altman analysis.

CONCLUSIONS

We concluded that the method is reproducible and the parameter FNR is a novel feature that may help in the diagnosis of neuropathies detecting changes in volume of the fascicles or the epineurium.

Evaluation of radiation-induced peripheral nerve injury in rabbits with MR neurography using diffusion tensor imaging and T2 measurements: Correlation with histological and functional changes

PURPOSE

To investigate the potential of diffusion tensor imaging (DTI) and T2 measurements in the evaluation of radiation-induced peripheral nerve injury (RIPNI).

MATERIALS AND METHODS

RIPNI was produced in a randomly selected side of sciatic nerve in each of 21 rabbits while the contralateral side served as the control. The limb function and MR parameters were evaluated over a 4-month period. Fractional anisotropy (FA), axial diffusivity (λ∥ ), radial diffusivity (λ⊥ ) and T2 values were obtained using 3T MR for quantitative analysis. Two animals were randomly killed for histological evaluation at each timepoint.

RESULTS

The T2 value of irradiated nerve increased at 1 day (63.95 ± 15.60, P = 0.012) and was restored at 1 month (52.34 ± 5.38, P = 0.105). It increased progressively at 2 to 4 months (60.39 ± 10.60, 66.96 ± 6.08, 75.51 ± 7.39, all P < 0.01). λ⊥ significantly increased at 1 day (0.82 ± 0.44, P = 0.046) and slightly decreased at 1 month (0.61 ± 0.17, P < 0.001). It increased gradually from 2 to 3 months (0.84 ± 0.29, 1.13 ± 0.33, both P < 0.001) followed by a decline at 4 months (0.83 ± 0.17, P < 0.001). FA was statistically lower than the contralateral sides at 1 to 4 months (0.72 ± 0.08, 0.60 ± 0.12, 0.51 ± 0.11, 0.62 ± 0.06, all P < 0.01). Changes in FA and λ⊥ correlated well with the functional and pathological changes in irradiated nerve.

CONCLUSION

DTI may be a more sensitive and accurate method to evaluate RIPNI compared with T2 measurements. FA and λ⊥ are promising quantitative indices in monitoring RIPNI. J. Magn. Reson. Imaging 2016;43:1492-1499.