MR Imaging of the Brachial Plexus

Abnormal Brachial Plexus Differentiation from Routine Magnetic Resonance Imaging: An AI-based Approach

Automatic abnormality identification of brachial plexus (BP) from normal magnetic resonance imaging to localize and identify a neurologic injury in clinical practice (MRI) is still a novel topic in brachial plexopathy. This study developed and evaluated an approach to differentiate abnormal BP with artificial intelligence (AI) over three commonly used MRI sequences, i.e. T1, FLUID sensitive and post-gadolinium sequences. A BP dataset was collected by radiological experts and a semi-supervised artificial intelligence method was used to segment the BP (based on nnU-net). Hereafter, a radiomics method was utilized to extract 107 shape and texture features from these ROIs. From various machine learning methods, we selected six widely recognized classifiers for training our Brachial plexus (BP) models and assessing their efficacy. To optimize these models, we introduced a dynamic feature selection approach aimed at discarding redundant and less informative features. Our experimental findings demonstrated that, in the context of identifying abnormal BP cases, shape features displayed heightened sensitivity compared to texture features. Notably, both the Logistic classifier and Bagging classifier outperformed other methods in our study. These evaluations illuminated the exceptional performance of our model trained on FLUID-sensitive sequences, which notably exceeded the results of both T1 and post-gadolinium sequences. Crucially, our analysis highlighted that both its classification accuracies and AUC score (area under the curve of receiver operating characteristics) over FLUID-sensitive sequence exceeded 90%. This outcome served as a robust experimental validation, affirming the substantial potential and strong feasibility of integrating AI into clinical practice.

Ultrasound accuracy for brachial plexus pathology

AIM

To determine (a) the accuracy of ultrasound in detecting brachial plexus pathology and (b) outline the advantages and limitations of ultrasound compared to MRI for imaging the brachial plexus.

MATERIAL AND METHODS

cases with clinically suspected brachial plexus pathology were evaluated first by ultrasound, followed by MRI. Patients with prior brachial plexus imaging were excluded. The final diagnosis was based on a combination of ultrasound, MRI, clinical follow-up, and surgical findings. The accuracy of the ultrasound was assessed by comparing the ultrasound and the final diagnoses. The mean clinical follow-up time following ultrasound was 1.8 ± 1.4 years.

RESULTS

Ninety-two (64%) of the 143 cases had normal brachial plexus ultrasound and MRI examinations. Fifty-one (36%) of 143 cases had brachial plexus pathology on MRI, comprising post-radiation fibrosis (n=25, 49%), nerve sheath tumor (n=11, 21%), traumatic injury (n=7, 14%), inflammatory polyneuropathy (n=4, 8%), malignant infiltration (n=2, 4%), desmoid fibromatosis (n=1,2%), and neuralgic amyotrophy (n=1, 2%). Overall diagnostic accuracy of ultrasound for brachial plexus pathology was 98% (140/143), with three discordant cases (neuralgic amyotrophy n=1, inflammatory neuropathy n=1, postradiation fibrosis n=1) regarded as normal on ultrasound assessment. Sensitivity, specificity, and positive and negative predictive value of ultrasound for identifying brachial plexus pathology were 94%, 100%, 100%, and 97%, respectively.

CONCLUSION

Ultrasound identifies brachial plexus pathology with high accuracy and specificity, showing comparable diagnostic efficacy to MRI. Ultrasound can serve as an effective first-line imaging investigation for suspected brachial plexus pathology.

Accelerated 3D MR neurography of the brachial plexus using deep learning-constrained compressed sensing

OBJECTIVES

To explore the use of deep learning-constrained compressed sensing (DLCS) in improving image quality and acquisition time for 3D MRI of the brachial plexus.

METHODS

Fifty-four participants who underwent contrast-enhanced imaging and forty-one participants who underwent unenhanced imaging were included. Sensitivity encoding with an acceleration of 2 × 2 (SENSE4x), CS with an acceleration of 4 (CS4x), and DLCS with acceleration of 4 (DLCS4x) and 8 (DLCS8x) were used for MRI of the brachial plexus. Apparent signal-to-noise ratios (aSNRs), apparent contrast-to-noise ratios (aCNRs), and qualitative scores on a 4-point scale were evaluated and compared by ANOVA and the Friedman test. Interobserver agreement was evaluated by calculating the intraclass correlation coefficients.

RESULTS

DLCS4x achieved higher aSNR and aCNR than SENSE4x, CS4x, and DLCS8x (all p < 0.05). For the root segment of the brachial plexus, no statistically significant differences in the qualitative scores were found among the four sequences. For the trunk segment, DLCS4x had higher scores than SENSE4x (p = 0.04) in the contrast-enhanced group and had higher scores than SENSE4x and DLCS8x in the unenhanced group (all p < 0.05). For the divisions, cords, and branches, DLCS4x had higher scores than SENSE4x, CS4x, and DLCS8x (all p ≤ 0.01). No overt difference was found among SENSE4x, CS4x, and DLCS8x in any segment of the brachial plexus (all p > 0.05).

CONCLUSIONS

In three-dimensional MRI for the brachial plexus, DLCS4x can improve image quality compared with SENSE4x and CS4x, and DLCS8x can maintain the image quality compared to SENSE4x and CS4x.

CLINICAL RELEVANCE STATEMENT

Deep learning-constrained compressed sensing can improve the image quality or accelerate acquisition of 3D MRI of the brachial plexus, which should be benefit in evaluating the brachial plexus and its branches in clinical practice.

KEY POINTS

•Deep learning-constrained compressed sensing showed higher aSNR, aCNR, and qualitative scores for the brachial plexus than SENSE and CS at the same acceleration factor with similar scanning time. •Deep learning-constrained compressed sensing at acceleration factor of 8 had comparable aSNR, aCNR, and qualitative scores to SENSE4x and CS4x with approximately half the examination time. •Deep learning-constrained compressed sensing may be helpful in clinical practice for improving image quality and acquisition time in three-dimensional MRI of the brachial plexus.

The Application of Contrast-Enhanced 3D-STIR-VISTA MR Imaging of the Brachial Plexus

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Magnetic resonance imaging of the brachial plexus. Part 1: Anatomical considerations, magnetic resonance techniques, and non-traumatic lesions

For magnetic resonance imaging (MRI) of non-traumatic brachial plexus (BP) lesions, sequences with contrast injection should be considered in the differentiation between tumors, infection, postoperative conditions, and post-radiation changes. The most common non-traumatic inflammatory BP neuropathy is radiation neuropathy. T2-weighted images may help to distinguish neoplastic infiltration showing a high signal from radiation-induced neuropathy with fibrosis presenting a low signal.

MRI findings in inflammatory BP neuropathy are usually absent or discrete. Diffuse edema of the BP localized mainly in the supraclavicular part of BP, with side-to-side differences, and shoulder muscle denervation may be found on MRI.

BP infection is caused by direct infiltration from septic arthritis of the shoulder joint, spondylodiscitis, or lung empyema.

MRI may help to narrow down the list of differential diagnoses of tumors. The most common tumor of BP is metastasis. The most common primary tumor of BP is neurofibroma, which is visible as fusiform thickening of a nerve. In its solitary state, it may be challenging to differentiate from a schwannoma.

The most common MRI finding is a neurogenic variant of thoracic outlet syndrome with an asymmetry of signal and thickness of the BP with edema. In abduction, a loss of fat directly related to the BP may be seen.

Diffusion tensor imaging is a promising novel MRI sequences; however, the small diameter of the nerves contributing to the BP and susceptibility to artifacts may be challenging in obtaining sufficiently high-quality images.

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MRI allows narrowing the list of differential diagnoses of brachial plexus lesions.

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MRI helps to distinguish neoplastic infiltration from radiation neuropathy in T2-weighted images.

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Differentiation between tumors, infection, postoperative conditions and post-radiation changes is possible with contrast.

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MRI helps to determine the extent of the infection.

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Diffusion tensor MRI is a promising method for brachial plexus assessment.

Magnetic resonance imaging of the brachial plexus. Part 2: Traumatic injuries

The most common indications for magnetic resonance imaging (MRI) of the brachial plexus (BP) are traumatic injuries. The role of MRI of the BP has increased because of recent trends favoring earlier surgery. Determining preganglionic vs. postganglionic injury is essential, as different treatment strategies are required. Thus, MRI of the BP should be supplemented with cervical spine MRI to assess the intradural part of the spinal nerves, including highly T2-weighted techniques. Acute preganglionic injuries usually manifest as various combinations of post-traumatic pseudomeningocele, the absence of roots, deformity of nerve root sleeves, displacement of the spinal cord, hemorrhage in the spinal canal, presence of scars in the spinal canal, denervation of the back muscles, and syrinx. Spinal nerve root absence is more specific than pseudomeningocele on MRI. Acute postganglionic injuries can present as lesions in continuity or tears. The following signs indicate injury to the BP: side-to-side difference, swelling, partial, or total BP rupture. Injury patterns and localization are associated with the mechanism of trauma, which implies a significant role for MRI in the work-up of patients.

The identification and description of traumatic lesions involving the brachial plexus need to be systematic and detailed. Using an appropriate MRI protocol, obtaining details about the injury, applying a systematic anatomical approach, and correlating imaging findings to relevant clinical data to make a correct diagnosis. Information about the presence or suspicion of root avulsion should always be provided.

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Trauma is the most common indication for MRI of the brachial plexus.

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MRI of the brachial plexus should include cervical spine MRI.

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Spinal nerve root absence is seen in preganglionic injuries.

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Determining preganglionic vs. postganglionic injury is essential for treatment planning.

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Appropriate MRI rapport is crucial in communication with the clinician.

Focal chronic inflammatory demyelinating polyradiculoneuropathy: Onset, course, and distinct features

Focal chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is defined as involving the brachial or lumbosacral plexus, or one or more peripheral nerves in one upper or one lower limb (monomelic distribution). However, other auto-immune neuropathies such as Lewis-Sumner syndrome (LSS) and multifocal motor neuropathy (MMN) can also have a focal onset. From a retrospective cohort of 30 focal CIDP patients with a monomelic onset dating back at least 2 years, we distinguished patients with plexus involvement (focal demyelinating plexus neuropathy [F-PN], n = 18) from those with sensory or sensorimotor (F-SMN, n = 7), or purely motor (F-MN, n = 5) impairment located in one or several peripheral nerves. Few (39%) F-PN patients had motor nerve conduction abnormalities, but the majority showed proximal conduction abnormalities in somatosensory evoked potentials (80%), and all had focal hypertrophy and/or increased short tau inversion recovery image signal intensity on plexus MRI. Impairment remained monomelic in most (94%) F-PN patients, whereas abnormalities developed in other limbs in 57% of F-SMN, and 40% of F-MN patients (P = .015). The prognosis of F-PN patients was significantly better: none had an ONLS score > 2 at the final follow-up visit, vs 43% of F-SMN patients and 40% of F-MN patients (P = .026). Our findings from a large cohort of focal CIDP patients confirm the existence of different entities that are typically categorized under this one term: on the one hand, patients with a focal plexus neuropathy and on the other, patients with monomelic sensori-motor or motor involvement of peripheral nerves. These two last subgroups appeared to be more likely to evolve to LSS or MMN phenotype, when F-PN patients have a more distinctive long-term, focal, benign course.

The effects of three different contrast agents (Gd-BOPTA, Gd-DTPA, and Gd-DOTA) on brachial plexus magnetic resonance imaging

Background

MRI is very important for guiding the diagnosis and treatment of brachial plexus diseases. The most used type of MRI brachial plexus imaging is the 3D Short Term Inversion Recovery (STIR) sequence with contrast agent. This study aimed to investigate the effect of three contrast agents; gadobenate dimeglumine (Gd-BOPTA), gadopentetate dimeglumine (Gd-DTPA), and Gadoteric Acid Meglumine (Gd-DOTA) on brachial plexus magnetic resonance imaging (MRI).

Methods

We recruited 60 patients with suspected brachial plexus injury randomly into three groups. MRI images were obtained from each patient. Prior to scanning, the first group was injected with GD-BOPTA, the second group with Gd-DTPA, and the third with Gd-DOTA. The amount of contrast agent was 0.1 mmol/kg according to the weight of each patient, the injection rate was 1.5 mL/s, and 20 mL saline was injected at the same rate with a high-pressure injector. Immediately after the injection of contrast agent and saline, a 3D Sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) STIR sequence was used for scanning. The Signal Intensity (SI) and Standard Deviation (SD) of Maximal intensity projection (MIP) images for regions outside the anatomy (ROI background) with area of 17 mm² on both sides of the C6 peripheral nerves (ROI nerve), and tissue adjacent to the peripheral nerves (ROI tissue) were obtained. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were then calculated.

Results

The SNR was 40.66±25.27, 34.65±14.86, and 44.63±30.79 for Gd-BOPTA, Gd-DTPA, and Gd-DOTA, respectively and the CNR was 20.24±15.17, 16.07±7.50, and 20.84±15.53 for Gd-BOPTA, Gd-DTPA, and Gd-DOTA, respectively. In addition, there was no statistical difference in the SNR or CNR of brachial plexus nerves using the three contrast agents to enhance the 3D SPACE sequence χ²=1.877, P=0.391>0.05 and χ²=1.717, P=0.424, respectively.

Conclusions

There were no significant differences in the efficacy of three contrast agents in imaging the brachial plexus.

Acute Flaccid Myelitis With Neuroradiological Finding of Brachial Plexus Swelling

BACKGROUND

Acute flaccid myelitis is a recently defined clinically distinct syndrome of polio-like acute flaccid paralysis. Acute flaccid myelitis cases show characteristic neuroradiological features of longitudinal spinal cord lesions with predominant gray matter involvement. Current evidence suggests injury to the anterior horn neurons as the underlying mechanism.

METHODS

We describe three patients with acute flaccid myelitis who developed flaccid upper limb weakness with diminished deep tendon reflexes after prodromal fever. Spinal magnetic resonance imaging (MRI) (axial and sagittal T1- and T2-weighted sequences) and brachial plexus MRI (coronal short tau inversion recovery sequence) at the acute stage were performed.

RESULTS

Spinal MRI showed extensive longitudinal lesion in the spinal cord with predominant gray matter involvement. We were able to demonstrate concurrent swelling and hyperintensity in the brachial plexus in all the three patients at the acute stage.

CONCLUSION

The coexisting signal intensities suggest an extension of acute flaccid myelitis pathology to the brachial plexus, highlighting the possible peripheral nerve involvement in acute flaccid myelitis.

Novel functional imaging technique for the brachial plexus based on magnetoneurography

OBJECTIVE

To visualize neural activity in the brachial plexus using magnetoneurography (MNG).

METHODS

Using a 124- or 132-channel biomagnetometer system with a superconducting quantum interference device, neuromagnetic fields above the clavicle and neck region were recorded in response to electrical stimulation of the median and ulnar nerves in five asymptomatic volunteers (four men and one woman; age, 27-45 years old). Equivalent currents were computationally reconstructed from neuromagnetic fields and visualized as pseudocolor maps. Reconstructed currents at the depolarization site and compound nerve action potentials (CNAPs) at Erb's point were compared.

RESULTS

Neuromagnetic fields were recorded in all subjects. The reconstructed equivalent currents propagated into the vertebral foramina, and the main inflow levels differed between the median nerve (C5/C6-C7/T1 vertebral foramen) and the ulnar nerve (C7/T1-T1/T2). The inward current peaks at the depolarization site and CNAPs showed high linear correlation.

CONCLUSIONS

MNG visualizes neural activity in the brachial plexus and can differentiate the conduction pathways after median and ulnar nerve stimulations. In addition, it can visualize not only the leading and trailing components of intra-axonal currents, but also inward currents at the depolarization site.

SIGNIFICANCE

MNG is a novel and promising functional imaging modality for the brachial plexus.

Degree of Agreement between Electrodiagnostic Testing and Magnetic Resonance Imaging in the Evaluation of Brachial Plexopathy

OBJECTIVE

Electrodiagnostic study (EDX) and magnetic resonance imaging (MRI) are commonly used in the diagnosis of brachial plexopathy, but the agreement between these 2 studies is unknown. The aim of this study was to evaluate the agreement of EDX and MRI in patients with brachial plexopathy.

DESIGN

The records of 69 patients with symptoms of brachial plexopathy who underwent EDX and MRI were reviewed. Based on the degree of agreement of EDX and MRI results, patients were classified as a "complete match," "partial match," or "mismatch."

RESULTS

Both studies yielded similar results for the majority of patients (63.2%). Among the enrolled patients, 26.4% were classified as a "complete match," 36.8% as "partial match," and 36.8% as "mismatch." However, only 1 test, either EDX or MRI, revealed abnormal findings in 21.1% of patients.

CONCLUSIONS

The agreement between EDX and MRI was high in patients with brachial plexopathy. However, only one of these tests, not both, revealed abnormal findings in several cases. Although both EDX and MRI were in accord with the diagnosis of brachial plexopathy in majority of cases, these 2 studies remain complementary diagnostic modalities for evaluating brachial plexopathies.

Hourglass-Like Constriction of the Brachial Plexus in the Posterior Cord: A Case Report

BACKGROUND AND IMPORTANCE

Hourglass-like constrictions are fascicular conditions confirmed definitively by interfascicular neurolysis. Certain peripheral nerves have vulnerable areas such as around the elbow in the posterior interosseous nerve. We report the first hourglass-like constriction in the brachial plexus supplying the radial innervated forearm musculature. Preoperative magnetic resonance imaging (MRI) findings of the brachial plexus were consistent with neuralgic amyotrophy (NA).

CLINICAL PRESENTATION

A 9-yr-old boy experienced worsening left arm pain and difficulty in elevating the shoulder. Sequentially, severe palsy emerged when extending the wrist, thumb, and fingers. Based on the clinical picture, we diagnosed him with NA. The oblique coronal T2-weighted short-tau inversion recovery images showed mildly diffuse enlargement and hyperintensity of the brachial plexus. He showed few signs of improvement and interfascicular neurolysis was performed 11 mo after the onset. One of the fascicles in the posterior cord had developed an hourglass-like constriction. Electrical stimulation confirmed that the fascicle supplied forearm muscles. His wrist and finger extension had almost recovered at the 12-mo postoperative visit.

CONCLUSION

Hourglass-like constrictions can occur in the brachial plexus. Although surgical approaches for the constrictions are still controversial, several reports demonstrated their effectiveness. Meanwhile, concerning NA treatment, evidence on the surgical intervention is lacking. Brachial plexus MRI might help in discerning the lesion and planning treatment options including surgical interventions. Hourglass-like constrictions are a possible etiology for certain NA patients with residual symptoms or paresis.

Imaging of progressive weakness or numbness of central or peripheral origin

Weakness and numbness occur in a variety of patterns that reflect injury to different parts of the central and peripheral nervous system. Progressive symptoms most often signify an underlying structural or degenerative problem. Familiarity with the major descending motor and ascending sensory tracts of the central nervous system, as well as radicular (dermatome and myotome) and peripheral nerve anatomy, is essential. Damage to these tracts and nerve fibers produces characteristic clinical symptoms and signs. Imaging, when used in a hypothesis-driven way, can be a valuable adjunct to the clinical history and physical examination. One of the most useful aspects of imaging is that it allows for differentiation of edema and inflammation from gliosis and atrophy, both of which can be associated with progressive weakness or numbness. Compression of nervous system structures by nonnervous system tissue can also be easily detected. The spectrum of diseases and imaging abnormalities associated with progressive weakness and numbness is highlighted in this review via a series of illustrative cases. In each case, anatomic localization and the key imaging findings are emphasized.

Brachial metastatic plexopathy as the inaugural manifestation of lung cancer: multimodality imaging

Metastatic infiltration of a peripheral plexus, also named metastatic plexopathy (MP), often results in severe pain and muscular weakness. This rather rare event may have a dramatic impact on the quality of life of patients affected by cancer. We hereby report a rare case of painful MP of the left cervicobrachial plexus presenting as the inaugural manifestation of poorly differentiated large-cell lung carcinoma in a 53-year-old patient. This responsible lung carcinoma was fortuitously diagnosed during MRI of the brachial plexus (BP). Complementary cancer staging was completed by contrast-enhanced multidetector CT, 18-fludeoxyglucose–positron emission tomography/CT and colour Doppler ultrasound of the BP. Although MRI remains the gold standard method for imaging the BP, our reported case emphasizes the alternative diagnostic capabilities of contrast-enhanced multidetector CT and ultrasound and confirms the high specificity of 18-fludeoxyglucose–positron emission tomography/CT in distinguishing brachial MP from secondary radiation plexopathy.