Diagnostic Signs of Motor Neuropathy in MR Neurography: Nerve Lesions and Muscle Denervation

The Promise of Personalized Peripheral Nerve Surgery

In peripheral nerve surgery, neuropathology and neural anatomy intersect with the complexities of injury and dysfunction [...].

Magnetic resonance neurography in spinal cord injury: Imaging findings and clinical significance

BACKGROUND AND PURPOSE

It is unknown whether changes to the peripheral nervous system following spinal cord injury (SCI) are relevant for functional recovery or the development of neuropathic pain below the level of injury. Magnetic resonance neurography (MRN) at 3 T allows detection and localization of structural and functional nerve damage. This study aimed to combine MRN and clinical assessments in individuals with chronic SCI and nondisabled controls.

METHODS

Twenty participants with chronic SCI and 20 controls matched for gender, age, and body mass index underwent MRN of the L5 dorsal root ganglia (DRG) and the sciatic nerve. DRG volume, sciatic nerve mean cross-sectional area (CSA), fascicular lesion load, and fractional anisotropy (FA), a marker for functional nerve integrity, were calculated. Results were correlated with clinical assessments and nerve conduction studies.

RESULTS

Sciatic nerve CSA and lesion load were higher (21.29 ± 5.82 mm2 vs. 14.08 ± 4.62 mm2 , p < 0.001; and 8.70 ± 7.47% vs. 3.60 ± 2.45%, p < 0.001) in individuals with SCI compared to controls, whereas FA was lower (0.55 ± 0.11 vs. 0.63 ± 0.08, p = 0.022). DRG volumes were larger in individuals with SCI who suffered from neuropathic pain compared to those without neuropathic pain (223.7 ± 53.08 mm3 vs. 159.7 ± 55.66 mm3 , p = 0.043). Sciatic MRN parameters correlated with electrophysiological results but did not correlate with the extent of myelopathy or clinical severity of SCI.

CONCLUSIONS

Individuals with chronic SCI are subject to a decline of structural peripheral nerve integrity that may occur independently from the clinical severity of SCI. Larger volumes of DRG in SCI with neuropathic pain support existing evidence from animal studies on SCI-related neuropathic pain.

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.

Raman spectroscopy and sciatic functional index (SFI) after low-level laser therapy (LLLT) in a rat sciatic nerve crush injury model

Axonotmesis causes sensorimotor and neurofunctional deficits, and its regeneration can occur slowly or not occur if not treated appropriately. Low-level laser therapy (LLLT) promotes nerve regeneration with the proliferation of myelinating Schwann cells to recover the myelin sheath and the production of glycoproteins for endoneurium reconstruction. This study aimed to evaluate the effects of LLLT on sciatic nerve regeneration after compression injury by means of the sciatic functional index (SFI) and Raman spectroscopy (RS). For this, 64 Wistar rats were divided into two groups according to the length of treatment: 14 days (n = 32) and 21 days (n = 32). These two groups were subdivided into four sub-groups of eight animals each (control 1; control 2; laser 660 nm; laser 808 nm). All animals had surgical exposure to the sciatic nerve, and only control 1 did not suffer nerve damage. To cause the lesion in the sciatic nerve, compression was applied with a Kelly clamp for 6 s. The evaluation of sensory deficit was performed by the painful exteroceptive sensitivity (PES) and neuromotor tests by the SFI. Laser 660 nm and laser 808 nm sub-groups were irradiated daily (100 mW, 40 s, energy density of 133 J/cm²). The sciatic nerve segment was removed for RS analysis. The animals showed accentuated sensory and neurofunctional deficit after injury and their rehabilitation occurred more effectively in the sub-groups treated with 660 nm laser. Control 2 sub-group did not obtain functional recovery of gait. The RS identified sphingolipids (718, 1065, and 1440 cm^-1) and collagen (700, 852, 1004, 1270, and 1660 cm^-1) as biomolecular characteristics of sciatic nerves. Principal component analysis revealed important differences among sub-groups and a directly proportional correlation with SFI, mainly in the sub-group laser 660 nm treated for 21 days. In the axonotmesis-type lesion model presented herein, the 660 nm laser was more efficient in neurofunctional recovery, and the Raman spectra of lipid and protein properties were attributed to the basic biochemical composition of the sciatic nerve.

Magnetic resonance neurography: is it so complicated that it needs a touch of genius?

KEY POINTS

• Neuropathy imaging is not that complicated or illusive that it needs a touch of genius.• By gaining MR imaging expertise of peripheral nerve lesions and using knowledge of common clinical patterns and diseases, general radiology practitioners can prudently participate in the multidisciplinary care for appropriate and timely management of peripheral neuropathy patients.

MRI DTI and PDFF as Biomarkers for Lower Motor Neuron Degeneration in ALS

Objective

To evaluate the utility of nerve magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and muscle MRI multi-echo Dixon for assessing lower motor neuron (LMN) degeneration in amyotrophic lateral sclerosis (ALS).

Methods

In this prospective observational cohort study, 14 patients with ALS and 13 healthy controls underwent a multiparametric MRI protocol, including DTI of the sciatic nerve and assessment of muscle proton density fat fraction of the biceps femoris and the quadriceps femoris muscles by a multi-echo Dixon sequence.

Results

In ALS patients, mean fractional anisotropy values of the sciatic nerve were significantly lower than those of healthy controls. The quadriceps femoris, but not the biceps femoris muscle, showed significantly higher intramuscular fat fractions in ALS.

Interpretation

Our study provides evidence that multiparametric MRI protocols might help estimate structural nerve damage and neurogenic muscle changes in ALS.

Role of magnetic resonance neurography in intercostal neuralgia; diagnostic utility and efficacy

OBJECTIVE

To evaluate the utility and efficacy of MR neurography (MRN) in the diagnostic work-up for intercostal neuralgia and to assess the treatment course and outcomes in MRN-imaged clinically suspected intercostal neuropathy cases of chronic chest and abdominal wall pain syndromes.

METHODS

Following a retrospective cross-sectional study, a consecutive series of patients who underwent MRN of torso for suspected intercostal neuralgia were included. Patient demographics, pain location/level/duration, previous work-up for the same indication, MRN imaging results, and MRN cost per patient were recorded. An inter-reader reliability assessment was performed on the MRN findings using Cohen's weighted κ analysis. Post-MRN treatment choice, as well as success rates of MRN directed perineural injections and surgical management were also evaluated.

RESULTS

A total of 28 patients (mean ± SD age, 48.3 ± 18.0 years, female/male = 3.0) were included. Pain and/or numbness in the right upper quadrant were the most common complaints. The mean maximum pain level experienced was 7.4 ± 2.5 on a 1 (lowest pain level) - 10 (highest pain level) visual analog scale. The duration of pain before MRN work-up was 36.9 ± 37.9 months. The patients had seen an average of 5 ± 2.8 physicians for such syndromes. 20 (71%) patients had one or multiple other imaging studies for prior work-up. MRN identified positive intercostal nerve abnormality in 19 cases with clinical symptoms of intercostal neuralgia. From the inter-reader reliability assessment, a Cohen's weighted κ value of 0.78 was obtained. The costs of work-up was about one-third with MRN for diagnostic purposes with less financial and psychological harm. Among the MRN-positive cases, 9/19 patients received perineural injections, of which 6 reported improvement after their first round, lasting an average of 41.1 ± 83 days. Among the nine MRN-negative cases, two received perineural injections, of which none reported improvement. Surgical management was mostly successful with a positive outcome in six out of seven operated cases (85.7%).

CONCLUSION

MRN is useful in diagnostic algorithm of intercostal neuralgia and MRN-positive cases demonstrate favorable treatment response to perineural injections and subsequent surgical management.

ADVANCES IN KNOWLEDGE

The use of MRN in intercostal neuralgia is an application that has not been previously explored in the literature. This study demonstrates that MRN offers superior visualization of pathology in intercostal neuralgia and confirms that treatment directed at MRN identified neuropathy results in good outcomes while maintaining cost efficiency.

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

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

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.

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.

18 F-FDG uptake in denervated muscles of patients with peripheral nerve injury

OBJECTIVE

We aimed to investigate the clinical significance of increased uptake in ¹⁸ F-fluorodeoxyglucose positron emission tomography in patients with peripheral nerve lesions.

METHODS

We selected patients with unilateral peripheral nerve lesions confirmed with electromyography who had undergone ¹⁸ F-fluorodeoxyglucose positron emission tomography covering the lesions. In the denervated muscles and their contralateral corresponding pairs, a mean (SUVmean) and maximum standardized uptake value (SUVmax) were obtained from ¹⁸ F-fluorodeoxyglucose positron emission tomography images. We analyzed the difference in these values between the denervated and normal muscles. The lesion-to-normal ratio of the SUVmean (LNRmean) between each muscle pair was also obtained. Subgroup analysis was performed to find whether these three parameters were related to severity, abundance of abnormal spontaneous activity, and etiology.

RESULTS

Twenty-three patients with 38 denervated muscles were included. Compared to their normal counterparts, the denervated muscles showed significantly higher SUVmax (1.33 ± 0.49 vs. 1.10 ± 0.37, n = 38, P < 0.001) and SUVmean (0.91 ± 0.31 vs. 0.77 ± 0.28, n = 38, P < 0.001). The muscles with severe neuropathy showed significantly higher LNRmean than those with mild neuropathy (1.30 ± 0.36, n = 19 vs. 1.11 ± 0.24, n = 19; P = 0.046), and the muscles with traumatic neuropathy showed significantly higher LNRmean than those with nontraumatic neuropathy (1.32 ± 0.28, n = 13 vs. 1.14 ± 0.33, n = 23; P = 0.015).

INTERPRETATION

Denervated muscles with peripheral nerve injury showed higher uptake than normal muscles in ¹⁸ F-fluorodeoxyglucose positron emission tomography, and this was associated with severity and etiology.

[Neurogenic myopathies and imaging of muscle denervation]

CLINICAL ISSUE

Neurogenic myopathies are primary diseases of the nervous system, which secondarily result in denervation of the target musculature. The spectrum of potential causes is manifold ranging from acute traumatic injuries and chronic compression to neurodegenerative, inflammatory, metabolic and neoplastic processes.

STANDARD DIAGNOSTIC METHODS

The medical history, clinical neurological examination, and electrophysiological tests including electromyography and nerve conduction studies are crucial in diagnosing neuropathic myopathies. Electromyography is the gold standard for diagnosing muscle denervation.

METHODICAL INNOVATIONS

Additional imaging methods and magnetic resonance imaging (MRI) in particular, are capable of contributing valuable information. The MRI examination of denervated musculature shows edema, an increase in the apparent diffusion coefficient (ADC) and hyperperfusion. Chronic denervation results in fatty degeneration and atrophy of affected muscles, which are also detectable by MRI.

PERFORMANCE

Although the MRI findings in muscle denervation are relatively unspecific, they show a high sensitivity, comparable to electromyography. Dedicated MR neurography may often visualize the underlying lesion(s) of the innervating nerve(s).

ACHIEVEMENTS

Besides high sensitivity, comparable to electromyography, MRI is capable of evaluating muscles which are inaccessible for needle electromyography. Due to its non-invasive character, MRI is ideal for follow-up examinations.

PRACTICAL RECOMMENDATIONS

The use of MRI is often a meaningful addition to the diagnostics of neurogenic myopathies. The extent and distribution pattern of muscular alterations often provide information on the localization of the causative nerve damage. A correct diagnosis or at least a narrowing down of possible differential diagnoses can often be achieved using MRI.

Thumb Opposition Recovery Following Surgery for Severe Carpal Tunnel Syndrome: A Clinical, Radiological, and Electrophysiological Pilot Study

PURPOSE

To objectively assess recovery of thumb opposition in patients with carpal tunnel syndrome (CTS) after open carpal tunnel release and to evaluate electrophysiological and magnetic resonance (MR) neurography findings as predictors of thumb opposition recovery.

METHODS

A total of 22 patients with severe CTS and thenar atrophy were included in this study. A detailed clinical, electrophysiological, and MR neurography evaluation was done both before and after surgery at 6 months to assess thumb opposition recovery.

RESULTS

The median duration of symptoms was 12 months (interquartile range, 12-20 months). The compound muscle action potential of the abductor pollisis brevis (CMAP-APB) also showed statistically significant improvement of 0.5 + 0.2 mV after surgery. Tip-tip pulp pinch strength increased from 1.2 ± 0.4 to 2.0 ± 0.4 kg at 6-month follow-up, lateral pulp pinch strength increased from 1.9 ± 0.6 to 2.8 ± 0.9 kg at 6-month follow-up, and 3-point pulp pinch also improved from 1.9 ± 0.5 to 2.8 ± 0.9 at final follow-up. On MR neurogram, the proportion of patients with abnormal median nerve morphology decreased from 81.8% to 68.2%, abnormal thenar branch morphology decreased from 63.6% to 36.4% and denervation edema deceased from 59.1% to 13.6%.

CONCLUSIONS

Patients suffering from severe CTS with thenar atrophy and detectable CMAP-APB showed promising improvement following open carpal tunnel release.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

[Nerve injuries and traumatic lesions of the brachial plexus : Imaging diagnostics and therapeutic options]

CLINICAL/METHODICAL ISSUE

Traumatic lesions of peripheral nerves and the brachial plexus are feared complications because they frequently result in severe functional impairment. The prognosis is greatly dependent on the correct early diagnosis and the right choice of treatment regimen. It is important to distinguish between open and closed injuries.

STANDARD RADIOLOGICAL METHODS

Initial imaging must critically evaluate or prove nerve continuity and is commonly achieved by high-resolution ultrasonography. During the further course, reactive soft tissue alterations, such as constrictive scarring or neuroma formation can be detected. In the case of deep nerve and plexus injuries this can be excellently achieved by dedicated magnetic resonance neurography (MRN) sequences.

METHODICAL INNOVATIONS

The signal yield from brachial plexus imaging can be critically enhanced by the use of dedicated surface coil arrays. Furthermore, diffusion tensor imaging (DTI) may enable the regeneration potential of a nerve lesion to be recognized in the future.

PERFORMANCE

Multiple reports have shown that neurosonography enables a precise evaluation of peripheral nerve structures (up to 90% sensitivity and 95% specificity in nerve transection) and that the method can critically impact on therapeutic decision-making in 60%. Currently, there are only few quantitative data on the exact performance of MRN in traumatic nerve lesions; however, individual reports indicate a high level of agreement with intraoperative findings.

PRACTICAL RECOMMENDATIONS

In the initial work-up, especially in the case of peripheral, superficial and lesser nerve injuries, neurosonography is the preferred imaging approach to evaluate nerve integrity and the extent of nerve lesions. In the case of extensive nerve injury of proximal nerves and structures of the plexus as well as in the case of suspected root avulsion MRN is the method of choice.

Sciatic neurosteatosis: Relationship with age, gender, obesity and height

AIM

To evaluate inter-reader performance for cross-sectional area and fat quantification of bilateral sciatic nerves on MRI and assess correlations with anthropometrics.

METHODS

In this IRB-approved, HIPPA-compliant study, three readers performed a cross-sectional analysis of 3T lumbosacral plexus MRIs over an 18-month period. Image slices were evaluated at two levels (A and B). The sciatic nerve was outlined using a free hand region of interest tool on PACS. Proton-density fat fraction (FF) and cross-sectional areas were recorded. Inter-reader agreement was assessed using intra-class correlation coefficient (ICC). Spearman correlation coefficients were used for correlations with age, BMI and height and Wilcoxon rank sum test was used to assess gender differences.

RESULTS

A total of 67 patients were included in this study with male to female ratio of 1:1. Inter-reader agreement was good to excellent for FF measurements at both levels (ICC=0.71-0.90) and poor for sciatic nerve areas (ICC=0.08-0.27). Positive correlations of sciatic FF and area were seen with age (p value<0.05). Males had significantly higher sciatic intraneural fat than females (p<0.05).

CONCLUSION

Fat quantification MRI is highly reproducible with significant positive correlations of sciatic FF and area with age, which may have implications for MRI diagnosis of sciatic neuropathy.

KEY POINTS

• MR proton density fat fraction is highly reproducible at multiple levels. • Sciatic intraneural fat is positively correlated with increasing age (p < 0.05). • Positive correlations exist between bilateral sciatic nerve areas and age (p < 0.05). • Males had significantly higher sciatic intraneural fat than females (p < 0.05).

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.

Ultrasound versus MRI in common fibular neuropathy

INTRODUCTION

We prospectively compared ultrasound (US) and MRI in patients with common fibular neuropathy.

METHODS

Forty adult patients with clinical suspicion of common fibular neuropathy and 40 healthy controls underwent both US and MRI. US and MRI datasets were randomized for prospective reading.

RESULTS

The overall sensitivity of US and MRI for diagnosing fibular neuropathy was 90% (95% confidence interval [CI], 79.7%-97.3%) and 87.5% (95% CI, 71.55%-93.1%), respectively. The overall specificity of US and MRI was 92% (95% CI, 77.45%-96.1%) and 85% (95% CI, 73.3%-94.4%), respectively. The overall sensitivity and specificity of US combined with MRI were 94% (95% CI, 0.80%-0.99%) and 84% (95% CI, 0.70%-0.91%), respectively. Overall intra- and inter-observer agreements among 3 readers were 0.76% (95% CI, 0.62%-0.85%) and 0.74% (95% CI, 0.65%-0.81%).

CONCLUSIONS

US diagnostic accuracy for common fibular neuropathy was slightly higher than that of MRI. Muscle Nerve 55: 849-857, 2017.

Magnetic Resonance Neurography of the Pelvic Nerves

Chronic pelvic pain syndrome is commonly caused by nerve injury, inflammation, or entrapment. Owing to the complex anatomy and branching patterns of pelvic nerves, pelvic neuropathies are often difficult to illustrate and diagnose. High-resolution 3-T magnetic resonance neurography is a promising technique for the evaluation of peripheral neuropathy. In this article, the authors discuss the normal anatomy of major pelvic nerves, technical considerations of high-resolution imaging, and normal and abnormal imaging appearances with relevant case examples.

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

OBJECTIVE

To study the impact of brachial plexus MR neurography (MRN) in the diagnostic thinking and therapeutic management of patients with suspected plexopathy.

METHODS

MRN examinations of adult brachial plexuses over a period of 18 months were reviewed. Relevant data collection included-patient demographics, clinical history, pre-imaging diagnostic impression, pre-imaging treatment plan, post-imaging diagnosis, post-imaging treatment plan, surgical notes and electrodiagnostic (ED) results. Impact of imaging on the pre-imaging clinical diagnosis and therapeutic management were classified as no change, mild change or substantial change.

RESULTS

Final sample included 121 studies. The common aetiologies included inflammatory in 31 (25.6%) of 121 patients, trauma in 29 (23.9%) of 121 patients and neoplastic in 26 (21.5%) of 121 patients. ED tests were performed in 47 (38.8%) of 121 patients and these showed concordance with MRN findings in 31 (66.0%) of 47 patients. Following MRN, there was change in the pre-imaging clinical impression for 91 (75.2%) of 121 subjects, with a mild change in diagnosis in 57 (47.1%) of 121 patients and a substantial change in 34 (28.0%) of 121 patients. 19 (15.7%) of 121 patients proceeded to therapies that would not have been performed in the same manner without the information obtained from MRN.

CONCLUSION

MRN of the brachial plexus significantly impacts clinical decision-making and should be routinely performed in suspected brachial plexopathy. Advances in knowledge: MRN significantly impacts the diagnostic thinking and therapeutic management of patients with suspected brachial plexopathy. MRN not only provides concordant information to ED tests in majority of cases, but also supplements with additional diagnostic data in patients who are ED negative.

MR imaging of skeletal muscle signal alterations: Systematic approach to evaluation

Muscle edema or edema-like signal alterations are commonly encountered findings in musculoskeletal magnetic resonance (MR) imaging. Although such signal alterations are very sensitive for detection of the underlying muscle pathology, these are often non-specific findings. Encompassing knowledge of their typical clinical presentations, characteristic appearances and patterns of muscle signal alterations and following a systematic approach towards their assessment, a reader can effectively narrow down the differential diagnosis. This article outlines the role of conventional imaging and advanced anatomic and functional musculoskeletal MR imaging techniques in the evaluation of various muscle disorders and presents a systematic approach towards their diagnosis and management.

Magnetic resonance neurography in the management of peripheral trigeminal neuropathy: experience in a tertiary care centre

OBJECTIVE

This tertiary care experience examines the utility of magnetic resonance neurography (MRN) in the management of peripheral trigeminal neuropathies.

MATERIALS AND METHODS

Seventeen patients with clinically suspected peripheral trigeminal neuropathies (inferior alveolar nerve and lingual nerve) were imaged uniformly with 1.5-T examinations. MRN results were correlated with clinical and surgical findings in operated patients and the impact on clinical management was assessed.

RESULTS

Clinical findings included pain (14/17), sensory changes (15/17), motor changes (2/17) and palpable masses (3/17). Inciting events included prior dental surgery (12/17), trauma (1/17) and idiopathic incidents (4/17). Non-affected side nerves and trigeminal nerves in the intracranial and skull base course were normal in all cases. Final diagnoses on affected sides were nerve inflammation (4/17), neuroma in continuity (2/17), LN transection (1/17), scar entrapment (3/17), infectious granuloma (1/17), low-grade injuries (3/17) and no abnormality (3/17). Associated submandibular gland and sublingual gland oedema-like changes were seen in 3/17 cases because of parasympathetic effects. Moderate-to-excellent MRN-surgical correlation was seen in operated (8/17) patients, and neuroma and nerve transection were prospectively identified in all cases.

CONCLUSION

MRN is useful for the diagnostic work-up of suspected peripheral trigeminal neuropathy patients with significant impact on clinical management and moderate-to-excellent correlation with intra-operative findings.

KEY POINTS

• MRN substantially impacts diagnostic thinking and management in peripheral trigeminal neuropathy. • MRN has moderate-to-excellent correlation with intra-operative findings. • MRN should be considered in pre-surgical planning of peripheral trigeminal neuropathy subjects.

Accelerated magnetic resonance diffusion tensor imaging of the median nerve using simultaneous multi-slice echo planar imaging with blipped CAIPIRINHA

PURPOSE

To investigate the feasibility of MR diffusion tensor imaging (DTI) of the median nerve using simultaneous multi-slice echo planar imaging (EPI) with blipped CAIPIRINHA.

MATERIALS AND METHODS

After federal ethics board approval, MR imaging of the median nerves of eight healthy volunteers (mean age, 29.4 years; range, 25-32) was performed at 3 T using a 16-channel hand/wrist coil. An EPI sequence (b-value, 1,000 s/mm(2); 20 gradient directions) was acquired without acceleration as well as with twofold and threefold slice acceleration. Fractional anisotropy (FA), mean diffusivity (MD) and quality of nerve tractography (number of tracks, average track length, track homogeneity, anatomical accuracy) were compared between the acquisitions using multivariate ANOVA and the Kruskal-Wallis test.

RESULTS

Acquisition time was 6:08 min for standard DTI, 3:38 min for twofold and 2:31 min for threefold acceleration. No differences were found regarding FA (standard DTI: 0.620 ± 0.058; twofold acceleration: 0.642 ± 0.058; threefold acceleration: 0.644 ± 0.061; p ≥ 0.217) and MD (standard DTI: 1.076 ± 0.080 mm(2)/s; twofold acceleration: 1.016 ± 0.123 mm(2)/s; threefold acceleration: 0.979 ± 0.153 mm(2)/s; p ≥ 0.074). Twofold acceleration yielded similar tractography quality compared to standard DTI (p > 0.05). With threefold acceleration, however, average track length and track homogeneity decreased (p = 0.004-0.021).

CONCLUSION

Accelerated DTI of the median nerve is feasible. Twofold acceleration yields similar results to standard DTI.

KEY POINTS

• Standard DTI of the median nerve is limited by its long acquisition time. • Simultaneous multi-slice acquisition is a new technique for accelerated DTI. • Accelerated DTI of the median nerve yields similar results to standard DTI.